Failure of the retaining wall of a residential building resulted in the collapse of the structure and raised the risk of additional damage to the surrounding area. This study demonstrates the monitoring of residential area affected by retaining wall failure using ground-based synthetic aperture radar (GB-SAR) to provide early warnings for potential secondary failure events. A Ku-band GB-SAR system operating at 17.2 GHz was installed on the rooftop of the building. This installed SAR system continuously monitors the displacement of the target area in near-real time. The estimated results depict a noticeable displacement pattern, reaching a maximum of 15mm during the five-month monitoring period.

This letter proposes a new atmospheric phase screen (APS) compensation method for ground-based synthetic aperture radar interferometry (InSAR). Conventionally, the APS trend is retrieved employing the assumption that the displacement component is a high spatial frequency component, thus making it separable from the APS trend and easy to be identified as outliers during the trend estimation whether using least squares or spectral analysis. However, landslides generally occur over a wide area forming a low spatial frequency component similar to the atmospheric component, which could give significant bias during the parameter estimation. This led to the suppression of the observed displacement from its true since it was partly misidentified as the APS. This specific APS misidentification issue is rarely mentioned in previous literature regarding APS compensation. A robust method to address this issue is proposed in this letter, dubbed best subsample consensus (BeSSaC). This method employs a robust estimation technique using the least median absolute residual criteria, it is shown that a wide-displacement component can be effectively separated from the APS using this technique.

This study evaluates and quantifies the atmospheric phase screen (APS) effects in a 79 GHz multi-input multi-output (MIMO) radar system. In addition to the 79 GHz radar measurement, the 17 GHz ground-based synthetic aperture radar (GB-SAR) measurement was performed simultaneously for comparison. We conducted a 24-hours continuous experiment in an outdoor environment with a maximum range distance of 130m. We deployed nine stationary corner reflectors (CR) to investigate the sensitivity to atmospheric disturbance. Our analysis revealed that the effect of APS in 79 GHz radar was more pronounced than in 17 GHz GB-SAR. Nonetheless, appropriate APS compensation led to smaller residual APS than 17 GHz radar. The feasibility of using a 79 GHz low-cost small radar system for long-range environmental displacement monitoring would partly be shown in the presented study.

This letter proposes a multiple signal classification (MUSIC)-based algorithm to generate a super-resolution velocity-depth spectrum for precise subsurface multilayer analysis, which cannot be achieved by conventional Common MidPoint (CMP) velocity-depth analysis. A self-adaptive peak detection process and a MUSIC algorithm with a modified steering matrix are the key components of the proposed method. Both numerical simulation and experimentation are used to verify the feasibility of this study. Regarding both accuracy and resolution, the results show that the suggested method outperforms the conventional SAR-based method, as the layer information on the spectra is correctly located and strongly focused. Moreover, the proposed approach can distinguish between the layers that cause weak reflections and those that cause strong reflections. Compared to previous studies, the proposed method enables self-adaptive super-resolution imaging in ground penetrating radar (GPR) CMP subsurface layer analysis, and it has a great potential for usage in other GPR subsurface applications.

We present a practical examination of a 79 GHz multiple-input multiple-output ground-based interferometric synthetic aperture radar (MIMO GB-InSAR) system and evaluate its abilities for deformation monitoring. Experiments with fixed setups were carried out indoor-environment and under more challenging climatic conditions featuring sunshine, sand, dry, and wind in Egypt. The aptitudes and limitations of the radar are emphasized. We prove that an accurate and focused displacement of less than 0.6 mm is detectable on a 20 cm2area, thus allowing prompt interventions for maintenance or safety. Moreover, the climate impact is explored by monitoring the phase and amplitude variation over time, showing reliable results with only 0.05 mm displacement drift which is relatively small.

We developed a full-polarimetric MIMO Ground Penetrating Radar (MIMO-GPR) “X-Yakumo” and evaluated its radar performance. X-Yakumo is equipped with 4 pairs of orthogonal antennas and polarization can be switched. To construct Cross Bow-tie antenna array system more simply, we redesigned the antenna feeding structure. The polarimetric antenna array is combined with RTK-GNSS positioning system, X-Yakumo can acquire full-polarimetric GPR data. We performed first full-polarimetric MIMO GPR measurement in the laboratory and actual site by X-Yakumo, and we have observed the buried target on the GPR profiles processed from the polarized dataset.

MIMO Radar operating at 79GHz was used for visualization of vibration of bridges. A FM-CW MIMO radar consists from 12 Transmitting and 16 receiving antennas was used. 2D SAR images reconstruction with PRF higher than 20Hz was achieved, and we demonstrated that vibration of any points in the 2D SAR image can be obtained. We measured vibration of brides, which have different structures, namely steel, and RC concrete. We showed that the vibration mode is very different between these two bridges, and demonstrated that this system can be used for practical safety observation of social infra structures,

We used an array GPR system YAKUMO developed at Tohoku University with RTK GNSS positioning system for archeological survey in Chiba, Japan. Combining with a GNSS positioning system, the GPR system could cover over a large area within a short period of time, acquiring a large amount of data. We processed the acquired data and interpreted the 3D data, using its multi-static antenna configurations. By applying signal processing, including 3D migration, we could find subsurface unknown structures that can be related to the historical building. In this paper, we introduced applicability of an array GPR system equipped with an RTK GNSS system and showed the result of field measurement.

In landmine detection by a hand-held ground penetrating radar (GPR) sensor, GPR signal is suffered from the unstable stand-off distance between the antenna and the rough ground surface. We propose in this letter a method to compensate the irregularity in the arrival time of the ground reflection in GPR and applied it to data sets acquired in minefields in Cambodia. Selecting the frequency with the highest power of the ground surface reflection, the phase of the received signal at the frequency is equalized to compensate the irregular reflection. We demonstrate that the ground reflection signal became uniform and confirmed the quality of the shape of the target can be improved.

In multitemporal interferometric synthetic aperture radar (InSAR) applications, propagation delay in the troposphere introduces a major source of disturbance known as atmospheric phase screen (APS). This study proposes a novel framework to compensate for the APS from multitemporal ground-based InSAR data. The proposed framework first performs time-series clustering in accordance with the temporal APS behavior realized by the$k$-means clustering approach. In the second step, joint estimation of the APS and displacement velocity is performed. For this purpose, a novel interferometric signal model, including the APS modeled by the median profiles defined in each cluster, is proposed. The proposed framework is validated with the Ku-band ground-based synthetic aperture radar data sets measured over a mountainous area in Kumamoto, Japan. Tests on these data sets reveal that compared with the conventional approach, the presented approach improves displacement estimation accuracy under severe atmospheric conditions.

In the above paper[1], there are errors in the following twoequations (7) and (8):

A monostatic/bistatic ground-based synthetic aperture radar (GB-SAR) system using an optical electric field sensor (OEFS) as the bistatic receiving unit has been designed for target imaging and 2-D displacement estimation purposes. The designed system has the capability of acquiring the monostatic and bistatic SAR images simultaneously from different looking angles, enabling the displacement vector estimation of the illuminated area. The spatial baseline between the monostatic and bistatic receivers is selected according to the estimation precision analysis. Experimental results are presented to evaluate the performance of the designed system and the proposed method. The displacement estimation accuracies in x- and y-directions can reach up to millimeter level.

The full-polarimetric ground-penetrating radar (FP-GPR) can obtain the polarimetric attributes of targets and achieve more accurate identification compared with traditional GPRs. However, in most cases, the polarimetric signals collected by GPRs are not only from the targets but also from the ground surface. According to the classical Fresnel formulas, the polarized directions of the waves will change after transmissions due to the difference in the transmission coefficients between horizontally and vertically polarized waves. This effect, called induced field rotation (IFR), will interfere with the acquisition of polarimetric attributes and also exists in the field measurements on a rough surface. In this study, we have derived the association between the measured FP-GPR data and transmission coefficients of the rough surface provided by the small perturbation method (SPM). The effects of IFRs from the rough surface on H-Alpha decomposition are analyzed later. The results show that the parameters of the rough surface will affect the values of components in the scattering matrix, but will not change the matrix and H-Alpha decomposition result; the incident angle and relative permittivity play main roles; for the H-Alpha decomposition results of three typical targets, the flat and dihedral are little influenced by IFRs, but the cylinder is seriously affected; simultaneously, a template for discriminating whether the calibration for H-Alpha decomposition is necessary is established. Both numerical and experimental tests validate the conclusions. Finally, a novel application strategy of H-Alpha decomposition is proposed, which has taken IFR from the rough surface into considerations.

Propagation delay in the atmosphere is the most important artifact that has to be mitigated in the interferometric SAR applications for displacement estimates. In the case of 3D spatial heterogeneous refractivity distribution, propagation delay in the atmosphere known as atmospheric phase screen (APS) is difficult to be corrected without a priori knowledge of displacement location. Especially for ground-based radar interferometric (GRI) measurement in the mountainous area suffers from a significant effect of APS which is difficult to fully be compensated by conventional compensation methods. This paper presents a novel approach to compensate for the APS, especially for the GRI application. In this framework, the time-series clustering approach is proposed to identify the local APS pattern due to the heterogeneity of refractivity. The correlation of each couple of temporal profiles is employed to cluster phase profiles by the rational of the k-means clustering approach. The proposed method further compensates the residual APS by estimating the temporal behavior of each cluster. Synthetic displacements are generated to assess the performances of the method in disentangling terrain displacements and propagation delay in the atmosphere.

Stepped frequency continuous wave (SFCW)-based radar with passive cooperative target is a promising nondestructive method to monitor the concrete temperature change. By burying a surface acoustic wave (SAW) sensor in the concrete to act as the cooperative target, the physical properties of the concrete can be measured by analyzing the reflections of the probing SFCW signal. Because the SAW sensor should be connected to an antenna to convert the electromagnetic wave into the acoustic wave, a half-cut compact monopole antenna is designed and fabricated in this letter. Taking the advantages of corrugated edge and half-structure technologies, the size of the monopole antenna decreases significantly without sacrificing the performance, which makes the SAW sensor together with antenna suitable to be inserted into the concrete. The experimental results show that the proposed antenna can work well with the SAW sensor in the concrete and the proposed method can measure the temperature change in concrete continuously.

In this article, an atmospheric phase screen (APS) compensation algorithm for a near real-time ground-based interferometry synthetic aperture radar (GB-InSAR) over a mountainous area is investigated. A novel APS compensation scheme is proposed to compensate the fluctuated APS caused by a spatial 3-D inhomogeneous refractivity index distribution without any a priori knowledge of moving location. The proposed method simultaneously addresses to identify moving pixels by a criterion of absolute velocity estimated by the coherent pixels technique (CPT). The proposed method consists mainly of three steps: 1) the stratified APS compensation; 2) identification of moving pixel candidate; and 3) the residual APS [remained APS after 1)] compensation by Kriging interpolation. The steps mentioned above are iteratively applied in order to increase the accuracy of the whole process. In this framework, we develop the 2-D quadratic polynomial model of the refractivity index with respect to slant range and topographic height for modeling the stratified APS. Furthermore, a prediction of the residual APS is achieved by applying the intrinsic random function of order k (IRF-k) Kriging interpolation, taking into account the nonstationarity of the residual APS. We evaluate the proposed method using zero-baseline GB-differential InSAR (GB-DInSAR) data over a mountainous area located in Minami-Aso, Kumamoto, Japan, through the near real-time post-landslide measurement campaign.

In this article, we focus on the detection of the interlayer debonding of the asphalt airport pavement by the ground-penetrating radar (GPR) system. Since the interlayer debonding usually occurs in the shallow region of the asphalt airport pavement (several centimeters), it is difficult to interpret the anomalies or the defects from the GPR signals composed of many waves under the boundary conditions. Moreover, the wavelength of the ordinary GPR system is over several centimeters. Therefore, the spatial resolution of the system is not accurate enough to consider the millimeter thickness of the debonding layer. To overcome these problems, we propose a new method based on evaluating the lateral wave behavior of common midpoint (CMP) gathers collected by a multiple static GPR system. The multistatic GPR system is a stepped frequency continuous wave (SFCW) radar system, which consists of eight transmitting and eight receiving bowtie antennas. The system operates in the frequency range from 50 MHz to 1.5 GHz. After the validation of the simulation, the results of the interlayer debonding detection were evaluated by a field experiment obtained at Tokyo International Airport. The proposed method can detect the debonding layers which are less than 1 mm. Also, it is shown that our proposed method has a high consistency with the conventional acoustic finding method in the field measurement. It provides an innovative and effective method for the interlayer debonding detection of a partially damaged airport asphalt pavement, which is difficult to be observed by the ordinary GPR signals.

In this study, we used the digital television signal broadcasted by geostationary satellite for passive bistatic synthetic aperture radar (SAR) imaging and interferometry applications. A prototype system was designed and fabricated with commercial-off-the-shelf (COTS) components. Specifically, three COTS low noise block downconverters (LNBs) were synchronized for a longtime coherent measurement. Multiple TV channels were combined to achieve a wider bandwidth to improve the range resolution. The potential applications of this ground-based radar system are SAR imaging, displacement estimation, and digital elevation model generation. Hardware design and data processing algorithms are described. Experimental results are presented to validate the performance of the designed system and the proposed methods.

In this study, a ground-based radar system with two multiple input multiple output (MIMO) arrays is developed for 2D displacement estimation applications. To reduce the influences of antenna position error, channel delay, and phase/gain difference on the imaging quality, calibration methods and phase coherence factor (PCF) based filtering methods are applied. For each MIMO array, target displacement can be measured along its line of sight direction. Co-registration is conducted to help to derive the 2D displacement vector estimations of the targets.

In this study, we investigated the potential use of polarimetric information to detect the land morphological changes without APS compensation. We proposed to use the APS independent descriptor and the covariance matrix likelihood ratio for APS. We validated the proposed technique by selecting the soil accumulated zone for a land elevation as a part of the restoration work at the landslide affected slope. The 24-hour processed time-series result reveals that both the APS independent descriptor and the likelihood-ratio are in agreement with the APS-compensated DInSAR result. The proposed idea shows the reasonable capability of detecting the land morphological change without APS compensation.

In this study, an anomalous atmospheric phase screen (APS) compensation in the frame of a ground-based differential synthetic aperture radar interferometry (GB-DInSAR) is investigated. The two improved methods are proposed and verified with GB-SAR data acquired at the mountain cliff exposed by a landslide. The first method adopts the piecewise multiple regression approach by assuming the inhomogeneity of the refractivity index distribution along the range direction. As for the second method, we apply nth order of two-dimensional (2D) polynomial with respect to slant range and topography height which enables the flexible fitting for the anomalous APS. In the second method, the cross-validation is employed to avoid both underfitting and overfitting problem. The applicability of both methods is validated with GB-DInSAR data which presents the anomalous APS. As a result, both methods yield significant reduction of the residual error compared to the conventional method.

To detect pavement damage of airport taxiway caused by cracks inside layer, we applied a novel method to common midpoint (CMP) dataset obtained by multistatic ground penetrating radar (GPR) system YAKUMO. Thin cracks within asphalt layers cause slight variation to the electromagnetic (EM) signal propagation velocity. The proposed method can show higher-resolution images of velocity changes of two different time set data with a small number of CMP traces. YAKUMO can acquire several parallel distributed CMP datasets at each position while moving the system linearly in real time, which makes it possible to apply this method to large-scale inspections. In this research, we acquired datasets at an airport taxi-way model with artificial damages at several times over a year. The datasets are analyzed with the proposed method to find out how the conditions of pavement changes by pressurization and time course. The results show that the method can detect not only overall change but also local area changes.

Debris estimation is one of the most important initial challenges after a disaster like the Great East Japan Earthquake and Tsunami. Reasonable estimates of the debris must be made available to decision makers as quickly as possible. Classical approaches to obtain this information are far from being optimal, usually relying on manual interpretation of optical imagery. We have developed a novel approach for the estimation of tsunami debris pile heights and volumes for improved emergency response. The method is based on a stereo-synthetic aperture radar (stereo-SAR) approach for very high-resolution airborne polarimetric SAR. An advanced gradient-based optical-flow estimation technique is applied for optimal image coregistration of the low-coherence non-interferometric data. Its suitability to combine multiresolution data allows generating stereo SAR data by combining two different sensors. Based on model-based decomposition of the PolSAR data, only the odd bounce scattering contributions are used to optimize echo time computation. In this paper, we propose the further development of the method by combining multiresolution data from i) air-/spaceborne SAR and spaceborne/spaceborne SAR with various illumination geometries. The proposed technique is validated using in situ data of real tsunami debris taken on a temporary debris management site in the tsunami affected area near Sendai city, Japan. The estimated height error is in the order of 0.7 m RMSE. The good quality of derived pile heights allows estimating debris volume with an RMSE of 2500 m3corresponding to <; 10% of the total debris volume. Advantages of the proposed method are fast computation time, and robust height and volume estimation of debris piles without the need for pre-event data or auxiliary information like DEM, topographic maps or GCPs

This is the introduction to the organized session entitled "The 2011 Eastern Japan Great Earthquake Disaster -How remote sensing was used, and what we have to do now-". We introduce in this session, how remote sensing methodologies including SAR, GB-SAR and GPR have been used for quick observation of Disaster, just after the event occurred, and how they have contributed to the society in the rehabilitation stage. In this paper, we show some examples of GB-SAR observation of landslide, and GPR used for Tsunami victim survey, and for safety in local community, after the 2011 Eastern Japan Great Earthquake Disaster.

A novel ground-based bistatic polarimetric synthetic aperture radar (SAR) system using an Optical Electric Field Sensor (OEFS) as the receiver was developed for environmental studies. Fundamental experiments were carried out with a trihedral corner reflector (CR) as a target, showing the polarimetric capability of the system. Different polarization signatures from the monostatic SAR images were found by analyzing the bistatic polarimetric SAR images. Meanwhile, this system has the capability to estimate the two-dimensional (2D) displacement of the targets in the field of view. The simulation shows the feasibility and effectiveness of the 2D displacement estimation. The experimental results demonstrate that the accuracy along the x and y direction to the line of sight (LOS) based on the designed bistatic synthetic aperture radar system can reach millimeter level for the displaceable corner reflector.

We designed a ground-based radar system with a C-band 2-D cross multiple input multiple output (MIMO) array for 3-D imaging and displacement estimation purposes. For this system, we developed a far-field pseudo-polar image format algorithm using pseudo-polar spherical coordinate. The use of a tensor compressive sensing technique allows to focus under-sampled raw data and to optimize the data acquisition time and memory usage. A novel algorithm, named as tensor-based iterative adaptive approach, is proposed for the effective and efficient reconstruction of sparse targets with a reduced level of sidelobes. Experimental results validate the designed radar system and the proposed algorithms.

To reduce the data acquisition time and the high-level sidelobes produced by conventional focusing methods for ground-based synthetic aperture radar interferometry, we present a new method to provide accurate displacement maps based on the dimension-reduced compressive sensing (CS) method combined with the multiple measurement vectors (MMVs) model. The proposed CS method consists in selecting the supported area of targets, estimated by the fast conventional method with undersampled data. The following sparse reconstruction is applied only to the selected areas. The MMV-based approach allows increasing the coherence and the precision of displacement estimates. Two experiments are carried out to assess the performance of the proposed method.

In this paper, an efficient and accurate imaging algorithm is presented for Ground-Based Synthetic Aperture Radar (GB-SAR) or other radar systems that could be formed by a physical or synthetic linear aperture. The imaging algorithm is based on the fractional Fourier transform (FrFT) for the azimuth compression. A mathematical framework is derived according to the projection of a sample reflectivity image onto the pseudopolar coordinate, and its implementation was presented. With the data acquisition geometry and the pseudopolar imaging coordinate, the phase of a point target can be expressed as a quadratic phase exponential. It makes that only 1-D FrFT is needed for the azimuth compression of the time-domain backscatter data for the GB-SAR imaging problem. By further research, the optimal transformation order that represents the spatial frequency changes by the FrFT was given subsequently. Taking advantage of this optimal representation, the proposed approach avoids the large calculation that occurs in the time-domain back projection (TDBP). Comparing to the far-field pseudopolar format algorithm (FPFA), the accuracy of the proposed algorithm is much improved. Meanwhile, the proposed approach holds almost the same computational cost and complexity as the FPFA. The proposed approach keeps the advantages of the imaging quality of the TDBP and the computational cost of the FPFA that are two important aspects of the GB-SAR applications. Both the numerical simulation and the field GB-SAR experiment show that the algorithm is more suitable for the high-precision GB-SAR imaging, especially for the near field.

We have studied passive radar with digital broadcasting terrestrial signals for imaging moving and stationary targets. We combined multiple TV channels to improve the range resolution. In order to reduce the high-level sidelobes caused by the frequency gaps among multiple channels, a low rank matrix completion based method is proposed. We present the experiment results of range- Doppler mapping of moving targets, high-resolution time delay estimation, and passive synthetic aperture radar (SAR) imaging of stationary targets. It is shown that, by the designed system, a landing airplane can be detected and tracked. By combining multiple TV channels, high resolution time delay estimation can be achieved. Buildings located within 55 meters can be effectively imaged by the proposed method.

We study the imaging and interferometric performances of a MIMO radar on board of an airship as alternative to airborne and spaceborne SAR remote sensing techniques. Four different MIMO radar arrays are designed working in L, C, X and Ku frequency bands. A frequency bandwidth of 250 MHz has been considered for the MIMO radars. The spatial resolution is 0.6 m in range and 0.3 degree in azimuth. The imaging and interferometric performances of the MIMO radar are analyzed in terms of the airship stability. A synthetic raw data set is generated assuming a target deployed on a flat area at different azimuth angle. This MIMO imaging solution is intended for continuous imaging over an area of interest.

In this paper, we attempt to develop the soil moisture retrieval method taking into account a wide variety of vegetation variations for the sparsely vegetated area. The method is constructed by introducing generalized volume scattering model into the polarimetric two-scale two-component model (PTSTCM). The proposed method was applied to L-band fully polarimetric ALOS-2 SAR datasets obtained over tropical peatland, Indonesia. The retrieved results were validated by simultaneously measured in-situ soil moisture. The proposed method yields more improved results than original PTSTCM with specific types of volume model (i.e., randomly, horizontally, and vertically oriented volume models) regarding the root-mean-square-error (RMSE) as well as inversion rate.

We introduce the development and deployment of ALIS for Humanitarian Demining. ALIS is a dual sensor, which combines EMI (Electromagnetic Induction) sensor and GPR (Ground Penetrating Radar). This is a hand held sensor, equipped with position tracking system, then ALIS can acquire the EMI and GPR signal together with its position information, while it is scanned on the ground surface by an operator by hand manually. Therefore, the data can be processed using Synthetic Aperture Radar (SAR) processing (migration) and can reconstruct 3-D subsurface image. GPR of ALIS operates at 1-3GHz, and the penetration depth of the GPR is 20- 50cm. By deploying the ALIS in Cambodia since 2009, we found that ALIS is capable for imaging buried mines, and can reduce the false alarm ratio drastically. We have detected more than 80 buried land mines in Cambodia mine fields. In 2017 we completed the advanced ALIS system, which is compact and light weight which is less than 3.1 kg.

We proposed a methodology to apply inverse boundary scattering transform to process complex radar data with minimum imaging artifacts. Unlike other boundary extraction-based methods, such as shape estimation algorithm based on boundary scattering transform and extraction of directly scattered waves, the developed approach does not rely on peaks of signals, does not require to connect points to quasi wavefronts, and it is numerically stable and robust. Instead of quasi wavefronts extraction, the method process huge amount of the wave-tracking lines, match the weight values to them, and apply multistage filtration based on the first and second derivatives. It makes the developed method to be able to be used for processing cluttered data like GPR. Using the experimentally obtained GPR profile, we demonstrated that the method allows separating the buried objects from clutter, noise, and imaging artifacts. Compared to conventional diffraction stacking method, weighted envelopes transformation results show good clearness of the targets, which makes the profiles easy to interpret. A number of filtration parameters over huge number of extracted features provide good flexibility and wide applicability of our approach.

We developed a SFCW sparse array radar system for 3D imaging, which consists from 16 transmitters and 16 receivers and operates at the frequency range from 270MHz to 8GHz. The 2D antenna array layout was optimized using the middle point approximation. Several image reconstruction methods, which include the least square, Compressive Sampling Matching Pursuit and Regularized Orthogonal Matching Pursuit were developed and applied to the data acquired by the system to improve the resolution and suppress the artifacts caused by the antenna sparsity. The developed methods showed better performance compared to the conventional ones while they have the equivalent robustness. In addition, we propose to include the antenna radiation pattern into the image reconstruction algorithm, and we demonstrated that it gives better convergence and reduces artifacts on the results for the near range measurements. The proposed methods was successfully validated by the laboratory experiments.

A novel compressive sensing (CS) based imaging method for SFCW radar near range targets is proposed. Different from existing CS based methods, the azimuth-dependency of the target reflection coefficient is considered. Based on the block sparsity property of the received signal in the proposed sparsifying dictionary, the 2D image of targets can be obtained at each spatial sampling point. Cross-correlation method is then employed to fuse these 2D images to get the final result. Compared to the classical back projection (BP) method, the proposed method can obtain higher resolution with fewer artifacts via fewer frequencies. Compared to the conventional CS based method, artifacts can be significantly reduced. Experiment results of a SFCW linear sparse array radar system demonstrate that, with only 1/8 data, the proposed method can achieve accurate high-resolution 2D image of targets in the near range. In 30dB dynamic range, no artifact was produced on the imaging result.

Ground Penetrating Radar (GPR) has been practically deployed since 1980's. Nowadays GPR is a standard methodology in detection of buried pipes, inspection of inner structure of concrete, monitoring of concrete pavement and detection of void. The improvement of the capability of personal computers in data storage and processing drastically developed the GPR signal processing on site and advanced data analysis afterwards. Recently, accurate 3 dimensional GPR imaging is introduced by using the simultaneous data acquisition of GPR and high-precision GPS, and array GPR systems. GPR is ultra wide band (UWB) radar system, and interferences to other wireless instruments have always to be paid attention. We started preparation of establishing general regulation of the effective use for GPR in the community in Japan.

A quick response to a large-scale natural disaster such as earthquake and tsunami is vital to mitigate further loss. Remote sensing, especially the spaceborne sensors, provides the possibility to monitor a very large scale area in a short time and with regular revisit circle. Damage ranges and damage levels of the destructed urban areas are extremely important information for rescue planning after an event. Rapid mapping of the urban damage levels with synthetic aperture radar (SAR) is still challenging. Compared with single-polarization SAR, fully polarimetric SAR (PolSAR) has a better potential to understand the urban damage from the viewpoint of scattering mechanism investigation. In radar polarimetry, the dominant double-bounce scattering mechanism in an urban area is primarily induced by the ground-wall structures and can reflect the changes of these structures. In this sense, urban damage level in terms of destroyed ground-wall structures can be indicated by the reduction of the dominant double-bounce scattering mechanism, which is the basis of this study. This work first establishes and validates the linear relationship between the urban damage level and the proposed polarimetric damage index using polarimetric model-based decomposition. Then, efforts are focused on the development of a rapid urban damage level mapping technique which mainly includes two steps of urban area extraction and polarimetric damage level estimation. The 3.11 East Japan earthquake and tsunami inducing great-scale destruction are adopted for study using L-band multitemporal spaceborne PolSAR data. Experimental studies demonstrate that the estimated damage levels are closely consistent to the ground-truth. The final urban damage level map for the full scene is generated thereafter. Results achieved in this study further validate the necessity of exploring fully polarimetric technique for damage assessment.

Mapping of the urban damage levels with synthetic aperture radar (SAR) is still challenging. Fully polarimetric SAR (PolSAR) has the potential to identify the type of scattering mechanism changes induced by urban damage. In radar polarimetry, dominant double-bounce scattering mechanism in urban areas is primarily induced by the ground-wall structures. Thereby, within an urban patch, the reduction of the dominant double-bounce scattering mechanism reflects the urban damage level in terms of destroyed ground-wall structures, which is the basis of this study. Based on our previous study, the proposed polarimetric index is further investigated. A rapid urban damage mapping technique including mainly two steps of urban area extraction and damage level index estimation is proposed. The 3.11 East Japan Earthquake and Tsunami is adopted as the study case using multi-temporal ALOS/PALSAR PolSAR data. Experimental studies demonstrate that the estimated damage levels are closely consistent to the ground-truth.

A full polarimetric ground-based SAR system for subsurface damage assessment of wooden building structures has been developed. The system is based on a 4-channel VNA connected to a polarimetric antenna array. The array elements consist of 4 newly developed circular polarization cavity-backed spiral antennas, which have very good wideband characteristics and excellent polarimetric performance. By 2 dimensional scanning the system can achieve polarimetric 3D imaging with super high-resolution of 1 cm in x-/y-direction and 2 cm in z-direction. Using the polarimetric phase information, deformations of internal wooden structures like beams and bars with inclination angles <;1 deg. can be detected, which is not possible with any other non-destructive testing technique.

An empirical soil moisture retrieval model for dual-polarimetric L-band SAR imaging, the ALOS-2 standard observation, is being developed. The model, based on empirical relations between ALOS/PALSAR and Pi-SAR-L2 observations and ground measurements, can correct for the disturbing effects caused by surface roughness or vegetation cover. In this paper we focus on airborne campaigns carried out over the Sendai area, Japan, in 2013 and 2014. In situ surface parameters (soil moisture and surface roughness) were measured on bare soil and under rice canopy. Using roughness and biomass corrections the SAR derived soil moisture estimates yield an accuracy of 5.9 Vol.-% RMSE. The results indicate that the proposed approach, which was mainly parameterized in test sites in Germany, can also work in different geographic regions.

We investigated a velocity analysis algorithm for the new array Ground Penetrating Radar (GPR) system “Yakumo”. The common mid-point (CMP) data, which is used to estimate the vertical profile of subsurface velocity can be acquired easily with this system. However, each CMP data set acquired by Yakumo includes only 8 GPR traces with more than 20 cm trace interval. In order to estimate the velocity with this sparse GPR data, we proposed a reversible normal move-out (NMO) processing to remove aliasing and to interpolate the data with a new iterative f-k domain interpolation method to reconstruct the dense data before the velocity analysis. The proposed processing algorithm is applied to both the simulated and the measured data. With the CMP data acquired by 100 MHz antennas, the re-sampled data with more than 0.5 m gaps can still be well interpolated. And the artifacts in the velocity spectrum caused by the noise were well suppressed. We also applied the process to Yakumo CMP data and the estimated the velocity profile in a sandpit. Comparing to the velocity measured by Time Domain reflectometer (TDR), the error was less than 10%. With Yakumo system, we can obtain the CMP data together with the three dimensional GPR data, which greatly benefit the data acquisition.

This paper focuses on earthquake/tsunami damage investigation over urban areas by exploring the multitemporal spaceborne ALOS/PALSAR PolSAR data. The polarimetric scattering mechanism changes before- and after-tsunami, at the city block scale, have been examined using model-based decomposition and PO angle techniques. These analyzes are used to establish the relationships between the polarimetric scattering mechanism changes and damage levels. The basic scattering structures such as ground-wall dihedral structures from the built-up areas were found to be stable even over a long temporal baseline. Two polarimetric indexes have been proposed for damage level indication. Experimental results validate the efficiency of these two indicators, since the built-up areas with different damage levels can be well discriminated. These results demonstrate the importance and efficiency of full polarimetric information for natural disaster assessment.

Full polarimetric airborne SAR data acquired over the Tsunami affected coastal area in Northeastern Japan is used to estimate soil moisture and debris volumes. Using empirical surface roughness calibration of the I2EM soil moisture is estimated with a RMSE of 5.2 Vol.-%. The heights of Tsunami debris piles are estimated with a RMSE of 0.71 m by using a reference point aided stereo-SAR approach. Debris pile volumes are estimated with an overall RMSE of 2478 m3. The accuracy increases with increasing size of the piles. While the error ranges from 50% to 90% for the smallest piles, it is in the order of 20% to 30% for the large piles.

We are developing radar technology to inspect the inner structure of wooden buildings suffered from strong quake by earthquake. GB-SAR (Ground Based Synthetic Aperture Radar) for inspection of wooden and concrete walls and structures has been developed and the system was evaluated by test measurements. The GB-SAR system uses frequency bandwidth 1-20GHz, and it can acquire full polarimetric radar signal. We found that frequency up to 20GHz can be usefully used for inspection, and show that the radar could achieve the resolution about 1.5cm, and found that t can be used for detection of crack inside concrete structure. Then Synthetic Aperture (SAR) Radar signal processing is used to reconstruct 3-dimenatioal images of inner structure of the targets. We found that the radar polarimetry gives us very precise information of the damaged structures, and demonstrated that radar polarimetry is a useful tool for detecting fractures inside a concrete structures, and detection of small deformation of wooden structures.

This letter proposes a constraint for a volume scattering power employing the principal minors, which can be used for polarimetric synthetic aperture radar (POLSAR) model-based decomposition. This constraint effectively allows for avoiding unreasonable results which yield negative eigenvalues. The proposed constraint is derived so that all the principal minors of the coherency matrix after volume scattering subtraction are nonnegative. Mathematically, the constraint is exactly the same as that based on the nonnegative eigenvalues. Thus, it is guaranteed that the result is physically reasonable and that the volume scattering power is not overestimated. A significant advantage of the proposed method compared to the constraint based on the nonnegative eigenvalues is the high computation efficiency, since the maximal volume scattering power can be derived analytically, while the nonnegative eigenvalue constraint requires a numerical calculation. In our experiment, the computation of the maximal power is six times faster using the approach based on the principal minors than that based on the nonnegative eigenvalues.

The overestimation of volume scattering power and the scattering mechanism ambiguity are still present in model-based decompositions even with the implementation of the deorientation processing. These effects are demonstrated and investigated. One possible reason is because of the limited dynamic range of the models themselves that are not fully satisfied for the mixed scene cases. An empirical volume scattering model is proposed, using the repeat-pass polarimetric synthetic aperture radar interferometry (PolInSAR) coherence, to extend the model dynamic range to be more adaptive. PolInSAR coherence is sensitive to different types of forests and terrains. The proposed model inherits these characteristics. In addition, it considers the cross-polarization power induced by oriented man-made structures. Thereby, a model-based polarimetric decomposition scheme is developed. The efficiency of the proposed method is demonstrated using E-SAR airborne and ALOS/PALSAR spaceborne repeat-pass PolInSAR datasets. Comparative experiments are carried out and show that the proposed decomposition overcomes the scattering mechanism ambiguity between forests and oriented built-up areas, since it successfully identifies the oriented buildings as double- or odd-bounce man-made structures while keeping the volume scattering dominant for the forests. Besides, the stable decomposition performance over the oriented built-up patches with quite different orientation angles also validates the improvement of the proposed decomposition. In addition, the demonstrations with short and long temporal baselines validate the generality of the proposed method.

This paper presents the development of a uniform polarimetric matrix rotation theory in the rotation domain along the radar line of sight for polarimetric synthetic aperture radar (PolSAR) data interpretation. The uniform representation of each coherency matrix element is a sinusoidal function in the rotation domain. A set of oscillation parameters, including oscillation amplitude, oscillation center, angular frequency, and initial angle, is proposed to fully characterize the scattering behavior in the rotation domain. A set of rotation angle parameters, including stationary angle, null angle, and minimization/maximization angles, is derived to indicate specific states of the rotation property. The rotation relationships between the coherency and covariance matrices with linear and circular polarization bases are established. A look-up table for these parameters is provided, and their physical meanings are interpreted. These derived parameters directly link to the Huynen parameters. Therefore, the proposed theory has the ability to achieve a desired state of one Huynen parameter by rotating the polarimetric matrix at a designated rotation angle. This theory also generalizes both the classic polarization orientation angle originally derived from the covariance matrix in a circular polarization basis and the deorientation theory developed from the minimization of the cross-polarization term. The roll-invariant terms have also been summarized. Finally, multifrequency Pi-SAR and AIRSAR PolSAR data sets are used to demonstrate the derived parameters. One oscillation amplitude parameter has been verified to be especially suitable for characterization of oriented man-made targets. Two angle parameters are sensitive to the reflection symmetry condition and crop types. Therefore, a simple unsupervised classification scheme has been developed and demonstrated. Further utilization perspectives of the proposed theory have been discussed.

Orientation angle compensation was incorporated into model-based decomposition to cure overestimation of the volume scattering contribution for interpretation of polarimetric synthetic aperture radar (PolSAR) data. The compensation is based on rotating the coherency matrix to minimize the cross-polarization term. However, this processing cannot always guarantee that the double- and odd-bounce scattering components will be rotated back to zero orientation angle and left with zero cross-polarization power. As a result, built-up patches with large orientation angles may still suffer from the scattering mechanism ambiguity. In this paper, double- and odd-bounce scattering models were generalized to fit the cross-polarization and off-diagonal terms, by separating their independent orientation angles. A general decomposition framework is proposed that utilizes all elements of a coherency matrix. The residual minimization criterion is used for model inversion. All the model parameters are simultaneously obtained using a nonlinear least squares optimization technique. The manual intervention, branch conditions, and negative power issues are avoided. The performance and advantages of this approach are demonstrated and evaluated with spaceborne L-band ALOS/PALSAR and airborne X-band Pi-SAR PolSAR data sets. Comparison studies are also carried out and demonstrate that further improved decomposition performance is achieved by the proposed method, especially in oriented built-up areas.

Ground-penetrating radar (GPR) has been studied for landmine detection and identification. Since this application employs higher frequencies as compared to conventional largescale GPR measurements, the GPR performance is greatly influenced by soil properties and their spatial heterogeneity. In order to study the influence of soil heterogeneity on GPR performance, three types of soil were investigated. From the soil heterogeneity, GPR clutter was modeled with the aim of assessing the difficulty encountered in successful GPR performance. A handheld dual-sensor system that combines a metal detector and GPR was tested in these three test soils, and its performance for identifying buried objects was evaluated. The GPR performance obtained from the test showed a clear correlation with the modeled GPR clutter. Hence, the present study illustrates that clutter plays a major role in the detection of small objects in heterogeneous soil by GPR.

This paper presents the development of a uniform polarimetric matrix rotation theory in the rotation domain along the radar line of sight for polarimetric SAR (PolSAR) data interpretation. The uniform representation of each coherency matrix element is a sinusoidal function in the rotation domain. A set of oscillation parameters, including oscillation amplitude, oscillation center, angular frequency and initial angle, is proposed to fully characterize the scattering behavior in the rotation domain. A set of rotation angle parameters, including stationary angle, null angle, and minimization/maximization angles, is derived from the angular frequency and initial angle to indicate the specific states of the rotation property. A look-up table for these parameters is provided and their physical meanings are interpreted. The proposed theory generalizes both the classic polarization orientation (PO) angle originally derived from the covariance matrix in a circular polarization basis and the deorientation theory developed from the minimization of the cross-polarization term. The roll-invariant terms have also been summarized. Finally, multi-frequency AIRSAR and Pi-SAR PolSAR data sets are used to demonstrate the derived parameters.

SAR Interferometry is a common methodology for detection of Natural disaster affected area. However, we applied radar polarimetric analysis to ALOS/PALSRA data sets to investigate the possibility of detection of Tsunami affected area only from the SAR data acquired after the event. The resolution of the SAR image is 30m by 30m and cannot identify each house or buildings in the area. However, we have demonstrated that single-bonce and double-bounce scattering mechanism clearly shows the Tsunami affected area in Ishinomaki city, Japan, after the Great East Japan Earthquake and Tsunami. We could also showed that the standard deviation of the polarimetric orientation angle increases by the damage, and can be used for the measure of the damage.

An array GPR system equipped with 8 transmitting and 8 receiving antennas has been developed at Tohoku University, Japan. It is a Stepped Frequency Continuous Wave system and operates at 50MHz-1.5GHz. The maximum speed of data acquisition is 7km/h, when the data is acquired every 1cm density. The system was tested in a few archaeological areas near Sendai, Japan. We could demonstrate objects buried at 1m can be clearly imaged by the system, and the data acquisition of 100m by 50m area can be carried out within 2 hours. The system will be used for rehabilitation of the area from the Great East Japan Earthquake and Tsunami that attacked this region in March 2011.

Ground-based synthetic aperture radar (GB-SAR) interferometry is a technique suitable for monitoring the movement and/or deformation of widespread targets remotely. The technique is capable of detecting a few tenths of millimeters. However, since the measurement is commonly carried out with a long-range distance, the influence of atmospheric condition can be a serious issue. A common and a practical way of correcting the influence on interferometric phase is based on coherent scatteres (CSs). In the present paper, a newly proposed method to detect CSs from measured data is discussed. The method detects CSs by taking the complex coherence of two SAR sub-images, which are formed from a data set. In order to form sub-images, the measured data are interleaved and SAR processing is applied respectively. An experimental demonstration showed that the method can successfully detect deployed corner reflectors as CSs. Furthermore, the movement of a target can accurately be measured when atmospheric correction based on CSs, which are detected by the proposed method. Since the method requires only data sets in the analyzing time period to detect CSs, the proposed method has an advantage in the real-time detection of target movements over a conventional method based on dispersion index, which requires number of data sets.

Circular cylinders are important classes of environmental and engineering targets which act as depolarizing features, such as pipes, cables, rebar and tree roots. Two-dimensional plan survey using the linearly polarized Ground Penetrating Radar (GPR) is verified as an effective method to obtain the full-resolution image of subsurface objects and architecture. Compared to the regular measurement, a circular measurement using bow-tie antenna is proposed and shown its obvious advantage to map subsurface crossing cylinders with unknown orientations. The configuration of circular measurement is also an important index for obtaining a high-quality image; meanwhile, the proper spatial sampling interval can reduce the data acquisition time which is very important factor in field survey. A field measurement using 500MHz bow-tie antenna was carried out in the sandpit and validated the effectiveness and feasibility of the proposed circular measurement.

Deorientation processing has been incorporated into model-based decomposition to cure the overestimation of volume scattering contribution, by rotating the coherency matrix to minimize the cross-polarization term. First, the derivation of the rotation angle is clarified for avoiding the ambiguity. Moreover, even with the implementation of deorientation processing, oriented built-up areas with large orientation angles are still misjudged as volume scattering dominant. Further to the investigation of the deorientation effect, we focus on oriented built-up patches. A parameter, named dominant polarization orientation angle (DPOA), is introduced to label each patch. The behavior of the deorientation on coherency matrix and model-based decomposition over purely oriented built-up areas with respect toDPOAis disclosed. Experimental studies from the Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar (ALOS/PALSAR) polarimetric SAR data set demonstrate that model-based decompositions with deorientation work well for oriented built-up areas when |DPOA| ≤ 22.5°. However, for large |DPOA| (e.g., |DPOA| >; 22.5°), even with the deorientation processing, for the conventional decompositions which assume that only the volume scattering contributes to the cross-polarization term, the decomposed volume scattering power may also be dominant even for purely oriented built-up areas. Thereby, misinterpretation still occurs, motivating further advancements.

This paper explores the use of full polarimetric synthetic aperture radar (PolSAR) images for tsunami damage investigation from the polarimetric viewpoint. The great tsunami induced by the earthquake of March 11th, 2011, which occurred beneath the Pacific off the northeastern coast of Japan, is adopted as the study case using the Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar multitemporal PolSAR images. The polarimetric scattering mechanism changes were quantitatively examined with model-based decomposition. It is clear that the observed reduction in the double-bounce scattering was due to a change into odd-bounce scattering, since a number of buildings were completely washed away, leaving relatively a rough surface. Polarization orientation (PO) angles in built-up areas are also investigated. After the tsunami, PO angle distributions from damaged areas spread to a wider range and fluctuated more strongly than those from the before-tsunami period. Two polarimetric indicators are proposed for damage level discrimination at the city block scale. One is the ratio of the dominant double-bounce scattering mechanism observed after-tsunami to that observed before-tsunami, which can directly reflect the amount of destroyed ground-wall structures in built-up areas. The second indicator is the standard deviation of the PO angle differences, which is used to interpret the homogeneity reduction of PO angles. Experimental results from after- and before-tsunami comparisons validate the efficiency of these indexes, since the built-up areas with different damage levels can be well discriminated. In addition, comparisons between before-tsunami pairs further confirm the stability of the two polarimetric indexes over a long temporal duration. These interesting results also demonstrate the importance of full polarimetric information for natural disaster assessment.

Orientation angle compensation has been incorporated into model-based decomposition to cure the overestimation of volume scattering contribution, by rotating the coherency matrix to minimize the cross-polarization term. However, this processing cannot always guarantee to rotate the double-and odd-bounce scattering components back to zero orientation angle cases and with zero cross-polarization power. Therefore, built-up patches with large orientation angles still suffer from the scattering mechanism ambiguity. General double- and odd-bounce scattering models are proposed to fit for the cross-polarization and off-diagonal terms, by separating their independent orientation angles. The general decomposition framework is proposed. Its efficiency and advantage is demonstrated and evaluated.

A validation method for polarimetric SAR model-based decompositions is proposed based on correlation coefficients between polarizations. The correlation coefficient is examined if it ranges from 0 to 1 for covariance matrices after the subtraction of volumetric scattering components. The three combinations of the polarizations seen in covariance matrices are examined. It is confirmed that, in general, the condition above is not held, which clarifies the overestimate of volume scattering, even though conventional procedures take negative powers into account. Furthermore, the possible maximal power of volume scattering is estimated by employing the condition as a constraint. The constraint by correlation coefficients is a part of the one by nonnegative eigenvalues. In order to equalize them, the third-order principal minor, that is the determinant in the case of 3*3 matrices, must be considered. Finally, the possible maximal power, equal to the one derived from the constraint by nonnegative eigenvalues, can be derived analytically, while that is estimated numerically for the case of nonnegative eigenvalues.

In order to accurately monitor the dynamic groundwater level change caused by the well pumping in a non-destructive way, we developed Common Mid-Point (CMP) method using Ground Penetrating Radar (GPR). The envelope velocity spectrum and an automatic velocity picking scheme were proposed for the accurate velocity analysis of CMP dataset. We applied the algorithm to the GPR data acquired near Tuul river in Mongolia. The obtained vertical velocity profile was converted to the vertical water content profile, in which the groundwater level could be easily identified. In this measurement, a groundwater level rise of 0.21 m was observed after the pumping was stopped. The dynamic groundwater level change estimated by GPR was used to estimate the hydraulic conductivity of the unconfined groundwater aquifer. The result agreed well with a previous study.

GPR (Ground Penetrating Radar) technology has been widely accepted as shallow geophysical exploration method. We have developed 3DGPR system, which uses high-accuracy positing information together with GPR data actuation, and have demonstrated that it can obtain subsurface 3-dimensional GPR images much clear than conventional GPR surveys. We have applied this method to some archaeological sites in Japan, including Sitobaru, Sakitama and Zuiganji. We could demonstrate that it is not only detection, but also can image subsurface structures. After the 3.11 Great East Japan Earthquake and Tsunami, we have used this method for understanding the geological anomalies caused by the earthquakes.

A ground-based synthetic aperture radar (GB-SAR) system was installed for the observation and monitoring of post-landslide slope in Kurihara-city, Miyagi, Japan. The system is operated at 17 GHz (Ku-band) with a frequency bandwidth of 150 MHz. Horn antennas scan about 2 m horizontally to cover a large observation area and SAR processing is applied to achieve higher azimuth and range resolutions. In addition, the interferometric technique is used to detect very small changes on the target, resulting in the expected interferometer resolution of 0.1 mm. In 2011, the system operated from November to December to acquire preliminary results and to study the feasibility of the technique for monitoring landslide surface. During the period, major events on the landslide surface did not happen and, thus, no significant changes were detected by the GB-SAR system. However, it detected small movements at some locations approaching to the system that is likely caused by a snowfall. It demonstrates the capability of the GB-SAR technique in detecting very small changes on a target.

Although many electronic safety-related systems require very high reliability, it is becoming harder and harder to achieve it because of delay-related failures, which are caused by decreased noise margin. This paper describes a technology named DART and its implementation. The DART repeatedly measures the maximum delay of a circuit and the amount of degradation in field, in consequence, confirms the marginality of the circuit. The system employing the DART will be informed the significant reduction of delay margin in advance of a failure and be able to repair it at an appropriate time. The DART also equips a technique to improve the test coverage using the rotating test and a technique to consider the test environment such as temperature or voltage using novel ring-oscillator-based monitors. The authors applied the proposed technology to an industrial design and confirmed its effectiveness and availability with reasonable resources.

A multisensor system could offer an effective solution to land-mine detection. A handheld dual-sensor system with a position tracking system is developed, which can acquire ground-penetrating radar (GPR) and metal detector (MD) data with 2-D space coordinates. However, as the measurement points are random and data are irregular for the human operator, it is difficult to display subsurface visualization imaging. We develop a set of techniques to achieve visualization imaging of both GPR and MD. A modified migration algorithm with continuous-root-mean-square velocity is proposed to process irregular GPR data, and an interpolation algorithm is recommended to process irregular MD data. In an application to field experiment data, clear subsurface targets imaging was achieved in both GPR slice and MD image.

The earthquake and tsunami of March 11, 2011 killed more than 15 000 people in Eastern Japan. The importance of remote sensing in understanding the damage caused by natural disasters is quite significant, and many data sets were acquired after the events. In this paper, we demonstrate the importance and the potential of full polarimetric synthetic aperture radar (SAR) images for damage assessment. Full polarimetric SAR images acquired by the spaceborne ALOS/PALSAR system from the Japan Aerospace Exploration Agency (JAXA) on November 21, 2010 and April 8, 2011 and acquired by the airborne Pi-SAR2 system from the National Institute of Information and Communications Technology (NICT) on March 12 and 18, 2011 are used for this analysis. Model-based decomposition is applied and clearly shows the scattering mechanism changes at the seriously damaged downtown of Ishinomaki city and the flooded areas near the main stream of the Kitakami River. Polarization orientation angle is estimated to provide additional information to understand the damage effect in the built-up areas. Eigenvalue-eigenvector-based decomposition analysis is also employed to further confirm the scattering mechanism changes of the flooded areas. ALOS/PALSAR does not have fine enough resolution; however, the difference of the scattering mechanisms is sufficient to identify the damaged and flooded areas. In addition, the Pi-SAR2 data sets are used to analyze the flooded paddy fields in Natori city. The relative backscattering values are compared with the multitemporal images and the cross-polarization component (HV) is observed to be more sensitive to the flooded boundary. The automatically detected flooding maps using the cross-polarization component were found to provide relatively accurate results.

Most polarimetric synthetic aperture radar interferometry (PolInSAR) data processing procedures and their applications are based on the polarimetric complex coherence descriptor. The reliable estimation of the complex coherence requires selecting sufficient homogeneous pixels for generating an unbiased estimator. In this paper, two indicators using only polarimetric and both polarimetric and interferometric information are derived as the similarity measures for complex Wishart distributed PolInSAR covariance matrix, respectively. Using these indicators, a double similarity test scheme, which shows high sensitivity to both polarimetric and interferometric properties, is proposed for similar pixel selection. The full information utilization could characterize the homogeneous pixels more accurately. Furthermore, since the similarity test has the potential to reject the pixels with different populations, it is suitable to be applied in a large searching area (e.g., 15 × 15 window) to accept sufficient homogeneous pixels. Thereby, combining with unbiased estimator, reliable estimation is achieved. The efficiency and advantage of the proposed estimation scheme are demonstrated with the aid of simulated and real PolInSAR data sets.

Simultaneous field data collections and Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar (PALSAR) full polarimetry observations were performed in Ulaanbaatar (Mongolia) and Alaska (USA). Permafrost is present at the Alaska test sites. Backscattering copolarization ( σco-pol0) values derived from the PALSAR data were compared with those calculated using the integrated equation method (IEM) model, a popular theoretical model describing surface scattering. PALSAR data taken in Ulaanbaatar matched the IEM model results to within a few decibels, whereas data taken in Alaska were 5 to 7 dB lower than those calculated using the IEM model. On the other hand, the σcross-pol0(σVH0) components estimated from the Oh model were well matched to the PALSAR data in both Ulaanbaatar and Alaska. Moisture levels of the sphagnum moss layer in Alaska were estimated to be about 10% while moisture levels of the underlying organic and mineral layers were 25% to 79%; the moisture values of the organic and mineral layers were factored into the IEM and Oh models. When surface moisture levels of 10% were assumed for Alaska ground conditions, the σco-pol0values calculated using the IEM model and those derived from the PALSAR data were well matched. From these observations, we conclude that the sphagnum moss layer, which is a seasonally unfrozen layer that occurs above permafrost, plays an important role in radar backscattering processes in permafrost regions and is a main contributor to the σco-pol0backscattering component; the underlying organic and mineral layers contribute mainly to the σcross-pol0backscattering component. A two-layer model was applied to the data from a test site in Alaska; the model described the co- and cross-polarization backscatter (σ0) derived from PALSAR data with off-nadir angles of 21.5° and 34.3°.

A volume scattering model utilizing polarimetric SAR interferometry (PolInSAR) coherence is proposed. The new model is more adaptive and better fit for both forest and skew-oriented built-up areas. Thereby, a new model-based polarimetric decomposition scheme is developed. The advantage of the proposed method is demonstrated by E-SAR PolInSAR data. And comparison experiments show that better decomposition results are achieved by the proposed method, since all the oriented built-up areas are well discriminated as double or odd bounce structures.

The un-correlation assumption between like- and cross-polarizations as well as the standard trihedral target is widely used in many calibration methods. However, it is inconvenient to deploy standard calibrators in any scene, and the utilization of un-correlation assumption should also be carefully examined. In this study, we propose a practical polarimetric calibration method which uses neither the standard trihedral nor the assumption that like- and cross-polarizations are uncorrelated. Alternatively, the statistical property of odd-bounce target is extracted to substitute the standard trihedral. By applying the proposed method on the ALOS/PALSAR uncalibrated data, it is shown that the polarization signature of the trihedral reflector agrees excellently with the theoretical value. Comparing to the standard ALOS/PALSAR calibration result, the non-reciprocal effect including the Faraday rotation has been removed by the proposed method.

The hydrological setting of the area west of Aswan city. Egypt that is mainly covered by dry sand is still not well understood, and its groundwater potential remains largely unknown. The ALOS/PALSAR L-band sensor has been used to detect and delineate the subsurface structures along the study area. The circular polarization transformation has been applied on the ALOS/PALSAR full polanmetric data by changing the orientation angle (ψ=0°) and elliptical angle (χ = 45°) and revealed many buried faults in various strike directions, which were not reported on the last version of the official geologic map. Such derived circular polarization images were further enhanced by applying the Optimal Polarization Contrast Enhancement (O.P.C.E) method. Thus the proper stocks vectors of the transmitter and receiver have been calculated from the PALSAR full polanmetric data and plotted on the Poincare sphere to determine the best polarization states for imaging these buried faults. The moisture content of the study sites was generally low, with an average of roughly 0.3% during the field campaign. Therefore, the average Root Mean Square Height (hRMs) of the surface roughness was 0.01 cm across all sites. On the other hand, 21 conventional 2D-GPR profiles have been acquired using 270 MHz antenna to validate the radar remote sensing results. These GPR profiles reveal obvious offset in the subsurface stratigraphy.

Ground-Based Synthetic Aperture Radar (GB-SAR) has been used to show the difference in polarimetric behavior of a metal sphere object located in different azimuth positions. However, this study has a problem with long data collection in experiment and the probability of measurement error due to antenna vibration during the movement in antenna rail. In this paper, Compressive Sensing (CS) is used in simulation by doing the sampling process to the measurement data from experiment. Full GB-SAR images are produced by solving 11 minimization problem using the sampled data. The result shows that CS can reduce measurement to around 1%, while giving better quality images and give the same conclusions to the conventional system.

The stepped-frequency continuous wave (SFCW) ground penetrating radar (GPR) combined with wideband bow tie antennas and a handheld VNA is successfully demonstrated and compared with three types of commercial pulse GPRs for the detection and identification of the buried targets at depths of 20 cm and 80 cm. It has the performance of the better signal to clutter ratio than all of the tested commercial pulse GPRs for the metal pipe at a depth of 20 cm and also the better range and azimuth resolutions than the pulse GPR having a center frequency of 250 MHz. It is strongly expected to be simultaneously satisfied with the conflicting needs of both deeper penetration and higher resolutions and to be finally replaced all of the tested pulse GPRs.

GPR is a geophysical method which uses electromagnetic pulse radiation to make the image of subsurface and objects in it. The main advantage of the method is that it is nondestructive method. In this paper we proposed to use transformation of coordinates from iGPS system to GPS format for synchronization measurement traces and it coordinates in the RAMAC system. The experimental data was processed by diffraction summation algorithm, because it is universal method. It can takes into account variable velocity case and topographical properties of surface. The experiment result demonstrates the possibility of performing the migration on uneven ground surface.

In this paper, we introduce interpolation for a detailed observation of synthetic aperture radar (SAR) data. The interpolation is done by zero-padding in the frequency domain. By comparing the raw SAR data and the interpolated data, for example, it is observed that the raw span at a corner reflector we deployed is 0.75 times smaller than its real values. Also, we propose a resampling method applied to the interpolated data to keep data amount same as raw data. The proposed method resamples points where peaks of the span due to coherent targets exist. As for pixels where the peak does not exist, points with the smallest polarimetric entropy are selected. The proposed method is compared to raw data and the resampled data by the maximum filter. It is confirmed that the proposed data emphasizes the characteristics of the raw data. Also, its blurring effect is not as much as that in the resampled data by the maximum filter. This technique is quite basic, however, the effect is not negligible.

In this paper, we proposed a new cross-correlation sum making use of the complex analytic signal to calculate the coherency of the signals for velocity spectrum analysis. It can estimate dielectric constant from multi-channel dataset robustly even the signal with low SNR. On the other hand, a vector network analyzer based GPR system with an antenna array was developed. The antenna array consisted of one transmit antenna and five receive antennas and it can detect the refection signals at different antenna offset with a high signal-to-clutter ratio. Air layer, gypsum wall and concrete wall of different thickness from 10 cm to 30 cm were tested and four field datasets on asphalt pavement of highway road were collected. The estimation results of dielectric constant and layer thickness validated the accuracy. The maximum errors of the thickness estimation results were less than 1.3 cm and the relative errors were smaller than 11%.

We have conducted GPR survey at a site which was partly excavated and filled with highly contaminated soils. The electrical properties and TPH concentration of the core samples were measured in the laboratory. It is verified that an inverse relation between TPH concentration and relative dielectric constant, and a direct proportional correlation between TPH concentration and electrical resistivity. LNAPL contamination area is illustrated by GPR data which shows the decreased radar signal amplitude.

The electromagnetic wave scattering from a dielectric dihedral structure is discussed in this paper. In order to measure the scattering mechanism, we measured a scattering from a brick by using a polarimetric GB-SAR system. And we found three scattering characteristics of the dielectric dihedral structure. Especially, separated scattering at the center of the target in HV component and penetration of electromagnetic wave in VV component may be used to extract information of a target. Then, we validated a scattering from a concrete block at different azimuth angles and detected the dependency of the azimuth angles by evaluating the polarization orientation angle based on circular polarization basis. Therefore, the polarimetric GB SAR can validate the scattering mechanism of buildings by using dielectric dihedral object like a concrete block.

On behalf of the IEEE Geoscience and Remote Sensing Society, and the IGARSS 2011 Organizing Committee, we are pleased to welcome you to Vancouver, Canada for IGARSS 2011.

We propose an algorithm to estimate surface roughness and moisture level of active layer of permafrost over permafrost area. This algorithm is based on the Oh's semi-empirical model, and PALSAR data observed both in winter and summer seasons with vh polarization. PALSAR vh polarization data observed in winter is used to estimate surface roughness of permafrost. Then, the estimated surface roughness and PALSAR vh polarization data observed in summer is used to estimate the moisture level of the active layer of the permafrost. The moisture levels estimated from PALSAR data moderately matched with those of validation data taken in the field, while the surface roughness value shows some difference. The possible cause of this difference is that the surface roughness derived from the field data collection represents the roughness of the top of the sphagnum moss layer covered on the active layer of the permafrost, while the one estimated from PALSAR represents the roughness of the underlying active layer of the permafrost.

A new approach for estimation of the tree root biomass is proposed by using GPR system with high accuracy positioning system. The 3D images of subsurface can be obtained clearly with this system, which we refer as "3DGPR". We try to estimate the biomass of tree roots quantitatively by measuring the volume of the tree roots. We tested this system for tree roots measurement, and the broadening of the tree root with horizontal direction could be detected with 500 MHz and 800 MHz antenna. We excavated this tree every 10 cm from 0 cm to 50 cm to validate the accuracy of the result. Compared with the measurement result and the excavated one, the tree root whose diameter is more than 5 cm could be detected correctly. Some tree roots whose diameter is 3 cm also could be detected. The diameter in most of the tree roots is more than 2cm. In this result, we expect that the volume is supposed to be estimated within 30 percent error by using the excavated result for calibration data.

Migration is an important signal processing method that can improve signal-clutter ratio and reconstruct subsurface image. Diffraction stacking migration and Kirchhoff migration sum amplitudes along the migration trajectory, which generally is hyperbolic. But when the ground surface varies acutely, the migration trajectory is not hyperbolic. To computer the migration trajectory need the technique of ray tracing. We introduce a method of ray tracing based on 3D velocity model. Firstly, we build the 3D velocity model depending on the estimation of both ground surface topography and velocities. Then we compute the travel time between transmitter, receiver and each subsurface scattering point, and search the propagation ray depending on the Fermat's principle. The method is tested by an experiment data acquired by the stepped-frequency (SF) CMP antenna GPR system. The target is a metal ball that is buried under a sand mound. A nice result of ray tracing is shown in the case.

A ground reflection and a direct wave which propagates directory from a transmitting antenna to a receiving antenna are often arisen as issues especially for a ground penetrating radar (GPR) to monitor a near-surface region. In this paper, a 3D subsurface radar image by suppressing those components with a bistatic GPR system is presented. A relative permittivity of a ground surface is measured at the beginning, and a Brewster angle is estimated from that value. Then, the transmitting antenna is located to match an incident angle with the Brewster angle. In this case, the ground reflection does not occur, and all the energy penetrates into the ground. The direct wave is suppressed with an f-k filter which works automatically from position information of the antennas. An experimental result gives the 3D subsurface image without the ground reflection and the direct wave under a condition that a landmine model is buried at a depth of 10cm in a dry sand.

In this paper, the first detection result of coherent scatterers (CSs) in forest environment is addressed. As a scatterer associated with CS, the dihedral structure consists of the tree-trunk like a vertical cylinder and the ground surface is assumed. The potential of CSs as being the phase stable scatterers as permanent scatterers will be also demonstrated with P-&L-band Pol-InSAR datasets acquired in repeat-pass InSAR mode over boreal forest test site by German Aerospace Center's E-SAR airborne system.

ALIS is a dual sensor for humanitarian demining, which is a combination of electromagnetic Induction sensor (EMI) and Ground Penetrating Radar (GPR), developed by Tohoku University, Japan. ALIS is equipped with a sensor tracking system using a CCD camera with image processing, which enables signal processing for subsurface imaging. Two sets of ALSI have been deployed in mine fields in Cambodia since 2009 and more than 50 buried landmines have been detected. We found that the Synthetic Aperture Radar processing (SAR processing) is effective not only imaging the buried objects, but also for reduction of clutter of soil.

A fully polarimetric borehole radar system with four combinations of dipole and cylindrical slot antennas was developed to acquire fully polarimetric data sets in drilled boreholes. To better under the fully polarimetric response to subsurface fractures with different roughness, in this study, synthetic fractures with different roughness are generated on a computer via fractal theory based simulation techniques. Quantitative assessment for the roughness of synthetic fractures is possible by use of three main parameters: the fractal dimension, the rms roughness at a reference length, and a length scale describing the degree of mismatch between the two fracture surfaces, allowing future detailed study of mechanical and transport properties of fractures and fully polarimetric radar response on them. Next, a 3D sub-grid FDTD numerical simulation is used to synthesize fully polarimetric data sets with synthetic fractures as primary reflectors. Based on the synthetic data sets, it is possible to evaluate the applicability of different radar polarimetry analysis approaches to physical characterization of subsurface fractures in future.

High-resolution Ground Penetrating Radar (GPR) images of the ground surface and shallow subsurface are needed in order to detect and identify small buried explosive materials such as Anti-Personnel (AP) landmines. A key requirement to produce sharp visualizations is centimetre-precise sensor positioning with real-time imaging results. We are pursuing two complementary approaches to accomplish this task: 1) Sensor tracking with a CCD camera, 2) and large work volume Indoor GPS. In outdoor field tests both methods have successfully imaged small landmine targets, which has a plastic body of less than 10cm diameter.

Two design methods of a filter in a frequency-spatial frequency (f-k) domain have been developed for bistatic ground penetrating radar. The proposed methods suppress the direct wave, which causes significant artifacts in radar images, and are evaluated by laboratory measurements. Because the geometric positions of a transmitting antenna and a receiving antenna are not fixed, the suppression of a direct wave is an important issue. Then, we propose anf-kfiltering approach for the solution, and present two methods to design thef-kfilter. Both methods use a difference of an apparent horizontal velocity between a direct wave and a reflection from a target, and work automatically from position information of a transmitting antenna and a receiving antenna. One method is to mask anf-kspectrum in a region where a spectrum of the direct wave is distributed. The region is defined from the maximum and the minimum apparent horizontal velocity of the direct wave, which are calculated from the location of the transmitting antenna and the scanning area of the receiver. As for the other method, the most essential point is applying a time shift to eliminate a difference of an arrival time of a direct wave, where the time shift is calculated beforehand from the location of the transmitting antenna and the receiving antenna. Then, an apparent horizontal velocity of the direct wave becomes infinitely large due to the time shift. Thus, thef-kspectrum of the direct wave concentrates around a frequency axis because its slope is infinitely large. Then, a filter to reject the dc component in the spatial frequency direction is applied. Both methods are applied to an experimental data set which is acquired by a bistatic radar measurement to detect a buried landmine model with a depth of 10 cm. In addition, it is confirmed that they can suppress the undesired fluctuation of the images nearly one-tenth and help the reliable detection of a buried object.

Polarimetric ground-based synthetic aperture radar (GB-SAR) measurements in a paddy field and its analysis results are presented. The measurements were carried out three times before and after an ear emergence of rice, and SAR images of full polarimetric components are reconstructed from the acquired dataset. By using those images, a sensitivity of a polarimetric component and a frequency range due to the ear emergence is discussed. Then, we could confirm that HH component of C-band is the most sensitive parameter although HV and VV components do not give significant changes. Especially, HH component of 5-6 GHz and 6-7 GHz show 10 dB increases after the ear emergence. Moreover, Freemen decomposition is applied to the SAR images. And, increases of a surface scattering component and a double bounce component in a same frequency range with the increase of HH component can be observed.

Directional borehole radar was developed for detection of three-dimensional (3-D) target localization in single-hole radar measurement. Phase differences among four dipole elements of receiving circular array uniquely determine an azimuth direction of a reflected wave. Receiving voltages of dipole elements are measured by optical electric field sensors whose high electrical isolation feature enables data acquisition of highly correlated signal between the channels. Besides, a switching unit to control resonant frequency of dipole elements was newly developed to reduce mutual coupling between the dipole elements. Laboratory experiments have demonstrated that approximately 30% frequency bandwidth enlargement is achieved by the switching operation without been affected by the mutual coupling in air. The directional borehole radar system was tested in a field test site in Kamaishi-Mine in Japan. All the boreholes available in this test site is filled with water and past borehole radar surveys conducted in this test site revealed presence of complex fracture system. Cross-hole and single-hole borehole radar measurement were conducted to clarify the performance of the resonant switching control and also to detect 3-D geometrical structure of fractures in this test site. 3-D analysis of data acquired by the directional borehole radar in a single-hole measurement clarified azimuth orientation fractures up to a range distance of 15 m with a range resolution less than 1 m. High reliability of the result was inferred from the fact that individual fracture pattern in a reflection profile showed a consistent color along the depth and also high repeatability of the result was obtained by repeating measurements.

It is often advantageous to estimate the ground surface topography from radar returns. However, the popular method, searching for the brightest pixel in the ground-penetrating radar profile, cannot achieve accurate surface topography in the sharp variable surface case because of the effects of diffraction waves. In this letter, we propose a method to solve the problem and improve the accuracy of surface topography. A migration technique is introduced to refocus the diffraction waves before searching for the brightest pixel. Experimental data have been used to display the effects of diffraction waves and test the method. The result shows that the method can dramatically estimate accurate surface topography even in the sharp variable surface area.

Ground-penetrating radar (GPR) is recognized as a promising sensor for detecting buried landmines. In this case, the GPR antenna(s) must be elevated above the ground. However, this requirement results in heavy surface clutter. It is therefore necessary to overcome the effect. A commonly used procedure of time gating and background averaging cannot suit to small shallow nonmetallic landmine beneath a rough ground surface. In this letter, we proposed techniques to enhance the target signal through common midpoint (CMP) antenna array and data processing techniques, including velocity spectrum and CMP multifold stacking. The method has been tested using experiment data over a rough ground under which small plastic antipersonnel landmines is shallowly buried. The result shows the signal-to-clutter ratio was dramatically improved.

More than 60 courtiers are still suffered from land mines. ALIS is a hand-held dual-sensor developed for humanitarian demining, which has been developed at Tohoku University, Japan since 2002. The dual-sensor ALIS is equipped with a metal detector and a GPR (Ground Penetrating Radar). A unique and novel sensor tracking system, which can record the GPR and Metal detector signal with their acquired locations, is equipped in ALIS. Due to its sensor location information, we can reconstruct buried land mine images in 3D space after data acquisition. IN addition, we found that the image reconstruction or migration processing drastically increases the quality of the image of the buried objects. ALIS evaluation test was conducted in Croatia in October 2007. Then a half-year evaluation test of ALIS in QC test in Croatia was held during December 2007 and April 2008. In this test, we could obtain fruitful experience in various soil and environmental conditions in Croatia.

We performed three field experiments with PALSAR/polarimetry observations in Ulaanbaatar/Mongolia, Arctic National Wildlife Region (ANWR/ Alaska)/US, and Sendai/Japan, to evaluate soil moisture models. The PALSAR polarimetry observations with off-nadir angle of 21.5deg were done in May 4, 2007, Jul. 29, 2007, and Apr. 14, 2007 in each place. On the other hand, the field experiments were done for May 2-7, 2007, Jul. 28-Aug 4, 2007, and Apr. 14, 2007. The surface parameters derived from field measurements show large dynamic ranges, which are from 4% to 80% for soil moisture value, from 0.16 to 2.22 for surface roughness, and from 1.97 to 8.09 for correlation length. We applied SPM model, X-bragg model, and Oh model in this time. While some discrepancies are appeared, the SPM and Oh models show agreements with absolute/relative sigma0value in some degree. The X-bragg model shows moderate agreement in anisotropy-ks relation.

We performed a Ground Based SAR (GB-SAR) and PiSAR simultaneous experiment over a flood test site. In this site, one prefab was constructed in a baseball field of a Nihon University in Chiba, Japan. The PiSAR observations were done for three days with different soil moisture condition of ~25%, ~50%, and 100%. Some GB-SAR experiments have been also done in two of three days and the scattering process are examined. Preliminary experiment with GB-SAR showed that L-band sigma0from a double scattering of ground-wall is increased for a few dB, when a reflectivity of the ground is assumed to be 1. These increase are also confirmed in the test site for both PiSAR and GB-SAR. Furthermore, high resolution GB-SAR images show double and single bounce scattering from a metal bar behind the wooden board of the prefab. We conclude that L-band SAR has a enough ability to detect a flooding area in urban site.

Polarimetric synthetic aperture radar (SAR) images describe objects via polarization synthesis and present much richer information than monopolarized SAR images. Furthermore, multidirectional flights of polarimetric SAR can see 3-D stereo objects in different angles. The height and the location of the 3-D objects can be retrieved from the polarimetric SAR images in multidirectional flights. This letter presents a tractable approach for the reconstruction of 3-D stereo buildings from two airborne PI-SAR images taken from opposite directions (at X-band with a spatial resolution of 1.5 m).

We acquired several data sets of Polarimetrc SAR data in Sendai, Japan by airborne Pi-SAR system for fundamental research of radar polarimetry and interfereometry. Among these data acquisitions, two data sets were acquired in multiple flight paths in a short time period, and polarimetric SAR image acquired from different angles are available. We found very clear azimuth incident angle dependency of the polarimetric SAR images. In addition, a square-loop fight was carried out in the same location in January 2004. The incident angle dependency of the SAR image in polarimetry in X-band is very clear in these SAR images. We found that the phase difference in orthogonal circular polarization has significant dependency on the azimuth incident angle. The data sets also has a very good potential for SAR radargrammetry. We discussed the possibility of application of polarimetric SAR data acquired from multiple directions.

Since 2002, we have developed a new hand-held land mine detection dual-sensor ALIS. ALIS is equipped with a metal detector and a GPR, and it has a sensor tracking system, which can record the GPR and Metal detector signal with its location. It makes possible to process the data afterwards, including migration. The migration processing drastically increases the quality of the image of the buried objects. ALIS uses two different GPR systems, namely VNA (Vector Network Analyzer) based GPR and an Impulse GPR. VNA based GPR can provide better quality GPR images, although the impulse GPR is faster and light weight. ALIS evaluation tests were held in mine affected courtiers including Afghanistan, Croatia, Egypt and Cambodia. In the two-month evaluation test in Cambodia, ALIS worked without any problem. After some demonstrations and evaluation, we got many useful suggestions. Using these advises, we have modified the ALIS and it is now more easy to use. ALIS will be commercialized in 2007.

JERS-1/SAR images taken in 1990’s and ALOS/PALSAR images taken in 2000’s are used and examined the deforestation status during ∼14 years. Many trees had been fallen by a typhoon hit in 2004 in a test site, Tomakomai. There is also a plantation area and the site show active change during the term. The forest stands could be roughly classified for four types, forest stands, vacant, where almost all trees were carried out, and two types of transitional stands from a forest to a vacant. Many deforested areas are easily detected by using the difference of backscattering coefficients between two images, if fallen trees have been carried out from the stands. The change from the normal forest to the vacant stands causes 3.1dB decrease in the σ0HH. On the other hands, transitional stands show almost same backscattering as the normal forest stands, although. Threecomponent scattering model shows surface scattering component accounts for 50% over the vacant stands, while volume scattering component accounts for ∼60% over the forest stands. But the model doesn’t show the clear difference between transitional forest site and normal forest. The temporal changes of the forest during 14 years are also examined for the plantation area. One stand show gradual increase of σ0and the values seem to be saturated around 17.4 tons/ha (∼5m in average height).

We present a fully polarimetric borehole radar in conjunction with radar polarimetry, Pauli decomposition, and H-alpha decomposition techniques to carry out physical characterization of subsurface fractures. Further tests are needed to validate the applicability of radar polarimetry analysis for physical characterization of subsurface targets. Toward this goal, we present the implementation of two other decomposition techniques, namely: (1) the Durden-Freeman decomposition and (2) polarimetric anisotropy parameter methods, in the context of previous research and examine the consistency of results using various polarimetric decomposition techniques. While results from the radar polarimetry decomposition were found to depend greatly upon the kind of physical or mathematical models, these techniques seem to provide comparable performances in terms of fracture characterization and classification.

The 17 papers in this special issue focus on subsurface sensing using ground-penetrating radar (GPR). These papers describe new approaches to subsurface sensing, including developments in electromagnetic wave propagation imaging/inversion of GPR data and antenna/radar technologies. Associated applications range from glaciology to pavement evaluation to landmine detection.

In this paper, the polarization orientation angle shifts induced by artificial structures were analyzed and attempted to combine target orientation information which characterizes an urban area with the polarization orientation angle information extracted by the circular-polarization method. In order to illustrate the characteristic of the polarization orientation angle shifts represented in an urban area, the X-band polarimetric synthetic aperture radar (SAR) datasets of Sendai City acquired by Pi-SAR were used. This paper is based on Kimura's idea that the variation of the polarization orientation angle shifts depends on the artificial structures, particularly for the target rotation angle. We found that the polarization orientation angle shift is also affected by the relative relationship between the target rotation angle and the flight direction. From these results, it is possible to estimate the target rotation angle via computation of the polarization orientation angle shift from polarimetric SAR data.

A directional borehole radar system using an array antenna connected to passive optical electric field sensors was developed and evaluated by laboratory and field experiments. This system uses a single dipole antenna for a transmitter and a four-dipole element circular array for a receiver. The received signals are transmitted through optical fibers from optical electric field sensors. The receiver array measures the phase differences between four dipole antennas and estimates the azimuth direction of the incoming reflection wave. The accuracy of the phase measurement was first evaluated in a laboratory test and then tested in a field experiment. To compensate for the sensitivity differences among the sensors, we propose anin situcalibration technique. The dominant operating frequency of the system is 70 MHz. Subsequently, we used borehole radar for subsurface measurements in a vertical borehole in granite. Estimation of the azimuth orientations of subsurface fractures was successfully demonstrated.

Ground-penetrating radar (GPR) is capable to detect plastic antipersonnel landmines as well as other subsurface targets. In order to reduce false alarms, an option of automatic landmine discrimination from neutral minelike targets would be very useful. This paper presents a possibility for such discrimination and analyzes it experimentally. The authors investigate time-frequency features of an ultrawideband (UWB) target response for the discrimination between buried landmines and other objects. The discrimination method includes the extraction of an early-time target impulse response, its time-frequency transformation, and the extraction of time-frequency features based on a singular value decomposition of the transformed image. In order to take into account the changes in the UWB target signals, the experimental conditions are completely controlled to focus on the behavior of the target's response with respect to its depth and the horizontal position of the GPR above it. The dependence of the features on the GPR bandwidth is analyzed as well. The Mahalanobis distance is used as a criterion for optimal discrimination. The obtained results define the best features and conditions when the landmine discrimination is successful. For comparison, the discriminant power of the proposed features has been tested on a dataset, acquired during a field campaign in Angola

A directional borehole radar system has been developed for the purpose of 3-D imaging of subsurface targets in a single-hole measurement. The radar system is equipped with a uniform circular array consisting of four dipole antennas as a receiver in order to realize azimuth bearing sensitivity. We propose a new direction-finding (DF) algorithm that is suitable for directional borehole radar measurement, and we apply this algorithm to actual field measurement data. This algorithm is based on the Adcock DF antenna principle where the complex time series (analytic signal) expression, the optimization, and the filtering procedure are incorporated to provide more accurate estimation. The algorithm was first verified in a transmission measurement in boreholes with a cross-hole configuration (15 m apart from each other) by estimating a direction of the incident wave from a transmitter to the receiver. Finally, the algorithm was applied to single-hole measurement data to demonstrate the ability to detect the 3-D location of a subsurface tunnel which was located 5.5 m from the borehole. The result showed fairly good agreement with the actual location of the tunnel, i.e., to an azimuth estimation error of within 10$^{\circ}$.

This paper discusses the reconstruction of the subsurface from radar data using a time-domain reconstruction method. Before the reconstruction is conducted, data preprocessing is carried out. The preprocessing transforms measured data transmitted and received by 3-D dipole antennas into equivalent data excited and received by 3-D ideal electric dipoles and, then, into equivalent data excited and received by 2-D ideal electric dipoles. Distributions of permittivity, conductivity, and permeability are reconstructed from the preprocessed data by a 2-D forward-backward time-stepping waveform inverse scattering technique. Two 2-D examples of permittivity and conductivity reconstruction from synthetic noisy and field borehole radar data are demonstrated to show the effectiveness of the proposed method

A new parametric inversion technique to locate cylindrical structures has been developed for borehole radar cross-hole measurements. The technique calculates prediction errors, focusing on curve shapes of first-arrival times, and explicitly uses known parameters on a target. Two schemes to compare the measured first-arrival time curves with the calculated ones are proposed. One is by taking the errors between curve gradients of measured and calculated first-arrival times, and the other is by taking the cross correlation between calculated first-arrival times and measured data. The schemes do not need to select the true first-arrival times, which makes this inversion technique robust and easy to use. This technique is validated with synthetic data sets modeling a metallic pipe in homogeneous and heterogeneous medium models. By both models, the inversion technique is able to retrieve the exact location of the pipe, though it employs a rather simple forward model, which can be solved by only geometrical calculations. The technique is applied to measured data sets, and it successfully estimates a pipe location in good agreement with known information. The inversion is also used for an air-filled subsurface cavity with a very simplified forward model, which considers only Snell's law at the cavity-subsurface media interface. It is also able to locate the cavity at a similar location estimated by other conventional techniques

A fully polarimetric borehole radar system using four combinations of dipole and slot antennas was developed to acquire fully polarimetric data sets in drilled boreholes. First, to implement radar polarimetry analysis, a processing scheme suitable for analyzing a single-hole reflection data set acquired by the system is presented. This processing consists of antenna-characteristic compensation, migration for image reconstruction, and time-frequency analysis for single-frequency data set construction. Two polarimetric target decomposition methods, namely: 1) Pauli decomposition and 2) eigenvector-based decomposition, are applied to characterize the scattering problem of the subsurface fractures. The Pauli decomposition method provided important radar polarimetry information of fractures, and the eigenvector-based decomposition method made a significant contribution to understanding the scattering mechanisms from different fractures with different properties. Furthermore, information about fracture classification can be obtained by analysis of the H-alpha distribution provided by eigenvector-based decomposition of local radar image regions. The potential of polarimetric target decomposition techniques to fracture characterization is shown, which, in turn, provides valuable information about water permeabilities of fractures in hydrogeological studies

In order to apply to land mine detection effectively, bistatic GPR using an optical electric field sensor as a receiver has been developed. The optical electric field sensor is very small and uses optical fiber instead of metallic coaxial cable. With the combination of these advantages and the bistatic radar system, it can be possible for an operator to measure quite flexible and safely. The sensor has been tested in stepped frequency radar system with frequency which consists of a vector network analyzer, a fixed double ridged horn antenna as transmitter and computer controlled receiver-positioner for 2D scanning. For considering effectiveness in real field, we applied impulse radar system, which consist of a digital oscilloscope and an impulse generator to produce the impulse with 250 psec pulse width and the diffraction stacking has been adopted for 3D image reconstruction. Detection of a PMN2 mine model was carried out by the impulse radar system at a sand pit with two modes of data acquisition: the stepped data acquisition and the continuous data acquisition. The PMN2 were detected clearly with sufficiently high resolution in TM mode measurement in both modes, the target contrast was almost the same while the scanning time decreased down to 1/18, 9 min/m2 in case of continuous data acquisition mode which satisfies the requirement for practical use.

We are developing a new landmine detection system, namely advanced landmine imaging system (ALIS), which is equipped with metal detector (MD) and ground penetrating radar (GPR). Despite it is a hand-held system, we can record the MD and GPR signals together with the sensor position information acquired by CCD camera. Therefore, MD image and GPR image can be obtained after signal processing. Since ALIS is a hand-held system, the sensor position is random when it is operated in the field. So interpolation processing is needed to provide a gridded data set for both MD and GPR. A good MD image can be achieved after interpolation. Also, interpolation can prepare the gridded data set for migration. 3D Kirchhoff migration is used to enhance the signal-clutter ratio for effective image reconstruction. The ALIS was tested in Afghanistan in December 2004 and showed a good performance. In particular, the GPR could obtain a good image of anti-personnel (AP) mine buried at more than 20 cm depth. Also images from both sensors could be combined to distinguish a mine from a metal fragment.

This paper shows first results of polarimetric SAR stereo applied to urban areas. SAR stereo is known as a useful technique for three-dimensional mapping. Until now many approaches and results have been reported, based on single polarization measurements. But stereogrammetry has not been used with polarimetric information. In this paper, we use polarimetric SAR measurements acquired during a square loop flight. It is shown that typical objects, like a TV tower can be reconstructed and its polarimetric properties analysed using this method.

In order to evaluate the SAR signal processing algorithm for stereographic SAR, indoor experiment using Ground-based SAR system was conducted. We used two SAR processing algorithms, namely diffraction stacking (back projection) and F-K (ω-k) migration. The both algorithms can re- construct 3-D images of targets, but showed differences. F-K migration is much faster and reconstructs better images, but needs larger memory space. Pi-SAR is an airborne polarimetric SAR system developed by NiCT (formerly Communication Research Laboratory: CRL) and JAXA (formerly NASDA), Japan. This system has two independent radar systems of L-band and X-band. The X- band radar has interferometry and polarimetry functions and the L-band radar has polarimetric function. We obtained Pi- SAR data in Sendai, Japan several times since 2001. In each data acquisition, we set a few corner reflectors for polarimetric calibration.

Borehole radar is a special mode of ground penetrating radar. It has several distinguished features from surface radar. For examples, by means of borehole access to deep regions below the surface, the radar sonde can be located relatively close to the anomalies or targets to be measured, this results in more precise targets response than surface measurement. The experimental site is located on the top of a granite hill west of Beijing, China. There are a group of boreholes intersected by many fractures. The measured single-hole reflection data are processed and interpreted. The radial detecting range is more than 30 meters at this site. The subsurface fracture distribution can be imaged very clearly. Many fractures can be "seen", and their distance from borehole and their dip angle can be determined. The azimuth determinations for these fractures are possible in some situations. It is concluded that the borehole radar is an effective tool for subsurface imaging.

A new parametric inversion technique to estimate a buried pipe location was developed for borehole radar cross-hole measurements. This technique evaluates the shapes of the approximated and measured arrival time curves instead of the first arrival time itself or wavefield in conventional inversion or tomographic techniques. In this study, we propose an algorithm of the technique and demonstrate its performance for synthetic and measured datasets.

An array type directional borehole radar system employing passive sensors, optical electric field sensors was developed. The system uses a dipole antenna for transmission and four optical electric field sensors for reception. Four sensors are evenly arranged in the circumferential direction to constitute an antenna array. Although an optical electric field sensor itself does not have directivity, azimuth angle of a target can be known from phase differences among the four sensors. Difficulty of this approach lies in the fact that, due to the size of a borehole, the spacing between sensors is limited to a few centimeters that is significantly smaller than the wavelength. As a result, phase difference to be extracted is small and easily subject to noise. In addition, mutual coupling between the antenna elements may causes distortion of target signal. In this paper, we discuss feasibility of target azimuth detection. A laboratory experiment was carried out to examine capability of extracting a small phase difference and to evaluate the mutual coupling between antenna elements.

The accuracy of a migration image of ground-penetrating radar (GPR) depends strongly on the accuracy of permittivity distribution determined from multioffset data. This paper proposes a migration velocity analysis method using a genetic algorithm (GA). The objective function is defined as the summation of normalized zero-delay cross correlation of all common-image point gathers. Under the assumptions that the media are blockwise and that the permittivity of each block can be expressed as a polynomial with limited terms, all coefficients of the permittivity function of each block, which maximize the objective function, are determined by migration velocity analysis method with GA. Prestack migration is performed by a reverse-time migration method based on Maxwell's equations solved by the finite-difference time-domain method with a perfectly matched layer absorbing boundary conditions. The migration velocity analysis method is applied to synthetic common-transmitter datasets to test the method. Then, the velocity analysis and prestack migration method are applied to field data. From the distribution of dielectric constant obtained from the field data, water content is derived, and the depth of a water aquifer is deduced from the water content distribution and a migration stack profile.

SAR is usually used for airborne or space borne remote sensing. It can also advantageously be exploited in a ground-based radar imaging system named Ground-based SAR (GB-SAR). We extended earlier approaches and developed an ultrawideband, ground-based, fully polarimetric SAR (Pol-GB-SAR) system for the monitoring of vegetation growth variations. Measurements on three type trees in different conditions were carried out by the developed SAR system. We proposed effective 3D broadband Pol-GB-SAR data processing algorithms in the paper. In situ polarimetric calibration obviously improved the features of the system. 3D images were reconstructed from the acquired data by a series of signal processing procedures based on a variety of wave equation migration methods. By implementing methods of radar polarimetry, the broadband GB-SAR system has possibility for monitoring changes in tree structure characteristics due to seasonal variations. Interpreted results demonstrated the target scattering characteristics in different vegetation growth situations showed good agreement with the ground truth

We have developed a ground-based polarimetric broadband synthetic aperture radar (SAR) system for noninvasive ground-truth validation in polarimetric SAR remote sensing of terrestrial vegetation cover. This system consists of a vector network analyzer, one dual-polarized antenna, and an antenna positioner. It can be operated in a frequency range from 50 MHz to 20 GHz, with a scanning aperture of 20 m in the horizontal and 1.5 m in the vertical direction. Tests carried out with standard reflectors showed that the polarimetric measurement capabilities of this system are satisfactory. Using the polarimetric ground-based SAR (GB-SAR) system, we carried out measurements on a specific vegetation cover pertinent to the remote sensing of forested regions within Sendai City, consisting of three different kinds of trees common within the Kawauchi Campus of Tohoku University. Measurements were collected in spring, summer, and autumn. Three-dimensional (3-D) polarization-sensitive images were reconstructed from the acquired data. Analysis of the 3-D polarimetric images of each measurement found differences (at times strong differences) among the polarization signatures. There were stronger reflections in all of the HH, VH, VV images in the second (summer) measurement, especially in the VH image, due to the substantial growth of branches and leaves in summer. This ground-truth validation system provided valuable information about the scattering mechanisms of the three trees selected for analysis in different seasons, which can be detected by broadband polarimetric ground-based SAR measurements. The experimental results demonstrate the excellent polarimetric performance of the newly developed SAR imaging system, which should find many useful and immediate applications in noninvasive ground-truth validation of diverse terrestrial vegetation covers.

Travel time tomography uses direct waves of crosshole radar data. A great deal of information concerning the media is contained in later arrivals, such as reflections and diffractions. More reliable results can be obtained by incorporating both direct waves and later arrivals. In this paper, the combination of travel time tomography and migration is introduced. A smoothed velocity model obtained by travel time tomography is used as the basis of migration. Then, a reverse-time migration technique is applied to direct-wave-suppressed crosshole data. The result of tomography indicates that there is an abnormal area, and the result of migration gives a more accurate position of the abnormal area, which is a cavity. The real example shows that the cooperation of tomography and migration is an effective technique for subsurface-cavity imaging. The synthesis of all information, including parallel crosshole measurement and forward simulation, assists in the interpretation of the results of tomography and migration.

Logic BIST is well known as an effective method for low cost testing. However, it is difficult to realize at-speed testing, as it requires a deliberate timing design in regard to logic design and layout of the chip. This paper presents a timing design methodology for at-speed BIST, using a multiple-clock domain scheme. Some experimental test results of large industrial designs using our custom fool "Singen", will also be shown.

In this overview, reasons are provided on why we do need to place multi-modal, multi-band single and multiple pass POLinSAR monitoring platforms into air and space. The questions "on what POLinSAR monitoring can provide that POL-SAR and IN-SAR by themselves cannot accomplish" is assessed; whereupon facts and justifications on placing POL-IN-BISAR satellite clusters into space are presented. Reasons for this technology becoming a basic requirement for current, near-future and much more so for future all day & night year-round monitoring of the terrestrial covers are analyzed in view of the un-abating and uncontrollable terrestrial population explosion, which has, does and for ever will result in unavoidable conflicts deteriorating unfortunately at times into terrorism. The pertinent questions on how to reduce the exorbitant cost for initiating this "home-globe security protection" technology are therefore also broached, and the expected benefits are laid out. The pertinent National and International airborne and space borne multi-modal, multi-band SAR remote sensing and security conflict surveillance support agencies are herewith invited for co-sponsoring our proposal, which is timely and fleets of orbiting multi-band POLinSAR platforms are urgently required to be placed into space.

Most of the landmine detection techniques by GPR use a monostatic type radar system, which is suitable for detecting landmines buried in shallow soil, which is normally less than 10 cm. The shallow target is difficult to detect by conventional GPR due to its low range resolution. We developed a broadband Vivaldi type antenna, which operates at 1GHz-10GHz. Using this antenna, we made a prototype of a GPR system, which operates at 2GHz-5GHz. By scanning the antenna on a 2D plane, we could obtain clear 3-D images of mine-like targets buried in dry sand. We proposed an array signal processing technique using CMP method, and found it is effective for rejection of the ground surface clutter, even if the ground surface has roughness.

In order to classify tree types, we introduce a new technique, which detects the change of Polarimetric Entropy parameters. We define the difference of the two-dimensional polarimetric entropy parameters, and applied the proposed technique to Pi-SAR airborne polarimetric SAR data. The result in an urban area shows that the seasonal change is very random and we could not find significant changes between two scenes. Then, we applied the technique in a forested region. The change in coniferous trees and broadleaf trees is statistically different. Using the change in polarimetric entropy properties, we find this technique can be used for tree type classification.

We introduce applications of radar polarimetry in borehole radar. One example is classification of subsurface fractures, where we estimate the water permeability of each fracture by radar polarimetry. Then polarimetric borehole radar was then used for cross-hole radar measurement. Transmitted signal between boreholes having a 20 m separation was measured, and we could show that the polarization information can be used for estimation of the orientation of a subsurface cavity.

In order to understand the capability of monitoring ground water movement by ground penetrating radar (GPR), we carried out a field survey in Mongolia. We controlled water production at a ground water source area and the change of ground water level at about 5 m in depth could be detected by GPR. The change of the ground water level was observed more than 15 m in the radial distance from the pumping well. The change of the vertical water content was also evaluated by GPR.

An electromagnetic logging technique based on borehole radar is introduced in this paper. The tool consists of one transmitter and two receivers, which can be used to cancel the effect of the antenna characteristics by taking the ratio of two receiver signals. Since receiver signals measured in the time domain can be converted into the frequency domain by Fourier transformation, the amplitude ratio and the phase difference between two receiver signals in a wide-frequency band are obtainable. The response of the tool to different formations is investigated, and the algorithm that converts the amplitude and the phase information to the conductivity and the relative permittivity of the surrounding medium is given by a three-dimensional finite-difference time domain. The effect of the borehole on measurement and the response of the tool to a formation interface are simulated and analyzed numerically. The validity of this technique is confirmed by experiment. This technique can be applied to detect physical properties, including the conductivity and the relative permittivity, of the surrounding medium and the locations of the fractures intersecting the borehole.

Increasing number of pins or gates in the latest LSIs requires a lot of testing resources. The conventional scan-based testing requires a costly tester (ATE) equipped with a lot of pin electronics. Since reducing the testing cost is a crucial issue in industry, we have introduced an approach using scan-based logic BIST to solve this problem. The logic BIST has been applied to many ASIC design chips, which have up to several million gates.

An analytical method based on the multiple signal classification (MUSIC) algorithm is applied to three-dimensional (3D) estimation of target positions using a directional borehole radar. A cylindrical conformal array on a conducting cylinder in a borehole was used for experimental measurements estimating the position of targets. It is also shown that the algorithm provides much better resolution than the Fourier-based algorithm in both a computer simulation and real tests. Soil at the experimental site is not necessarily uniform, and there can be many clutter sources such as small stones in the subsurface. For this situation, it is difficult for the super-resolution technique to work properly. Results of the experiments show that the super-resolution technique for locating targets, despite being seriously limited by both the space available for the array and the bandwidth, is promising for directional borehole radar. In the developed algorithm, it is assumed that the distribution of electromagnetic constants inside a borehole is known before estimation of target positions.

A full-polarimetric borehole radar system is presented with combinations of dipole antennas and axial slot antennas and is applied to subsurface fracture measurement. First, to determine a scattering matrix from measurements with antennas having different antenna transfer functions between orthogonal polarizations, the authors present an antenna compensation algorithm that is achieved by an inverse filtering method with the antenna transfer functions experimentally determined by crosshole measurements. The results of crosshole and single-hole measurements carried out in granite at the Kamaishi Mine are shown to verify the proposed method. In the crosshole measurement, the authors find that the used dipole and slot antennas have almost the same radiation pattern and frequency dependency from 50 to 120 MHz. The transmission matrices through the host rock are the unit matrix for most paths, while depolarization is observed in some sections. Reflections from subsurface fractures show significant depolarization in the polarimetric single-hole reflection measurements. Using the scattering matrix, it is evaluated that subsurface fractures have a randomly isotropic rough surface for wavelengths between 1 and 2 m on the rotation of polarization basis.

A theoretical approach to cross-hole radar measurements is presented. An approximate analytical form for the current distribution on an antenna in a borehole is derived, and the theoretical receiving signal of the borehole radar in the cross-hole measurement is calculated. Theory is compared in the time-domain with the measured borehole radar signal obtained in a salt deposit. The radiation pattern of a borehole radar excited by a pulse is discussed. The accuracy of tomographic analysis, which is often applied to cross-hole radar measurements, is strongly governed by this radiation pattern. It is found that, in practice, most borehole radars have a pattern of a lambda /2 dipole antenna. However, the radiation pattern can be deformed by short pulse excitation, loading by the surrounding media, and coupling to the logging cable.>