Synthetic aperture radar (SAR) is emerging as a promising technique for high resolution monitoring of region of interest regardless of cloud cover or time of day. This paper describes the design and the development of a X-band SAR system comprised of a newly developed electric unit with full radar functionality and an active phased array antenna (APAA). The electric unit is capable of generation, transmission, and reception of radar signals, and the APAA enables flexible beam management. Test flight was performed using the developed X-band SAR system and the effectiveness of the SAR system was verified by the results of the flight test.

This paper describes the Fast Factorized Back-Projection (FFBP) algorithm developed for processing SAR data. Parallelization method is applied to split intermediate data into small data sizes which allows the use of small memory units and to accelerate the FFBP process. Intermediate results of airborne SAR data processed by the FFBP algorithm is presented.

This paper proposes a web-based visualization tool called 3DSPOPP for visualizing the relationship between sets of attributes as two data points put on separate planes and connected by a line in a 3D scatter plot. The motivation for creating this tool is to visualize darknet traffic data to find communication anomalies. Although 3D scatter plots can visualize network packet data by assigning time, source IP address and destination IP address to each axis, users can not easily understand the relationship between one set of source IP addresses and source ports and another set of destination IP addresses and destination ports. For anomaly detection, these four attributes are all significant. Therefore, the authors elongate each axis to create multiple plot zones of up to eight separate areas in 3D space, usually called octants. This tool is called 3D Scatter Plots of Octants, abbreviated as 3DSPO. Furthermore, projection planes of two octants are combined with 3DSPO to visualize the relationship between two attribute pairs of two octants such as source IP/port pair and destination IP/port pair. This combined tool is called 3DSPOPP.

Phased-Array L-band Synthetic Aperture Radar-3 (PALSAR-3) onboard Advanced Land Observing Satellite-4 (ALOS-4) is a spaceborne L-band Synthetic Aperture Radar (SAR) system, capable of high resolution and wide swath observation. ALOS-4 utilizes digital beamforming (DBF) and multiple transmit channel (MTC) techniques to overcome swath width and azimuth resolution trade-off relationship. In addition, ALOS-4 signal data requires signal processing, such as azimuth multi-beamforming and sub-band phase correction, before conventional SAR image processing can be implemented. In this paper, newly developed signal pro-cessing algorithm for ALOS-4 and results of the validation of the algorithm using flight model data will be discussed.

Phased Array type L-band Synthetic Aperture Ra-dar-3 (PALSAR-3) onboard Advanced Land Observing Satellite-4 (ALOS-4) is a spaceborne L-band Synthetic Aperture Radar (SAR) system. ALOS-4 is capable of achieving high resolution (3m) with 4 times wider swath width compared to ALOS-2. Hardware design and implementation of SAR techniques, namely digital beamforming (DBF) in the elevation direction and multiple transmit channel (MTC), enables high-resolution wide-swath observation. Data acquired by ALOS-4 requires specific signal processing techniques such as azimuth multi-beamforming and sub-band phase correction for high resolution wide swath image production. The flight model of PALSAR-3 system has been integrated and final test evaluation is expected to finish by the middle of 2021.

Range ambiguity level is one of the most important metrics of the spaceborne synthetic aperture radar (SAR) image quality. Alternating transmission of up- and down-chirp signals is an effective method to suppress the range ambiguity. However, this modulation method brings new unwanted azimuth ambiguity, since an intra-pulse Doppler effect causes opposite range shift for up- and down- chirp. In this paper, we propose a signal processing strategy for multi-channel sliding spotlight SAR with alternate up- and down-chirp modulation. The proposed algorithm is based on the sub-aperture method with azimuth digital beamforming, and a special care is taken for the correction of the intra-pulse Doppler effect to suppress the azimuth ambiguity. The performance of the intra-pulse Doppler effect correction process is evaluated through a point target simulation, and it is shown that the ambiguity-to-signal ratio (AASR) has been improved by 4.4dB.

Maritime surveillance is one of the useful application of spaceborne Synthetic Aperture Radar (SAR) because of its ability to operate in all weather conditions during day and night. In this application, wide swath width is favorable. The swath width depends on Pulse Repetition Frequency (PRF). Generally, high PRF is selected to avoid range/azimuth ambiguity signals in receiving beams, however low PRF must be applied to obtain wide images [1]. Thus, ambiguity appears in wide swath width images taken with low PRF. Ambiguities presents challenges for high detection rate and low false alarm rate, which are both necessary for efficient maritime surveillance.Generally, Constant False Alarm Rate (CFAR) algorithm is applied for ship detection in SAR images. However, CFAR algorithm does not work well with high ambiguity images due to an increase in false alarms. In order to discriminate real images from ambiguities, a discrimination algorithm, which utilizes the Doppler spectrum, was created. The Doppler spectrum of the real images in the range direction is different from that of ambiguities. This paper describe the detail of the discrimination algorithm and the evaluation applied to the SAR image.

ALOS-4 succeeds the concept of ALOS-2 and hence the system design of ALOS-4 satellite basically follows on that of ALOS-2, except for improvements in mission performance. The swath width is drastically improved in ALOS-4 by applying DBF (Digital Beam Forming) technique. DBFU (DBF Unit) is newly designed for ALOS-4 SAR sensor. In ALOS-4 system, receiving channels are divided into 6 sub-arrays in elevation, and received signals are converted into digital data independently by ADCs for DBF processing. In conventional radar systems, high frequency signals, such as L-band signals, are down-converted by local and COHO (COHerent Oscillator) signals by mixers in RF front-end to make sampling frequency lower. In DBF systems composed of multiple receiving channels, the number of local and COHO signals must be increased to match the number of channels. To overcome this issue, under sampling technique is applied. This technique allows band-pass filtered signals to be sampled at a rate below the Nyquist frequency of the target signal. With under sampling, COHO signals can be eliminated, so downsizing of H/W scale of DBFU can be achieved. This paper describes the under sampling system design result for ALOS-4.

ALOS-4 succeeds the concepts of ALOS-2[1] except for improvements in mission performance. ALOS-4 utilizes digital beam forming on receive to improve observation swathwidth [2]. PALSAR-3 on-board ALOS-4 has an onboard digital beam forming processor in order to increase the swathwidth of the 3m resolution Stripmap mode to 200 km. Transmit signal with a wide beam-width in the elevation direction is generated in order to cover the wider swathwidth. The reflected signal from the ground is received by several independent receive channels, which are processed in order to form several antenna patterns. There is an inverse relationship between the beam-width and the antenna length. It is necessary that the antenna length should be short in order to obtain the wide beam-width.One way of downsizing the antenna length is to turn off the Transmit/Receive Modules (TRMs), which are connected to each antenna element of Active Phased Array Antenna (APAA). However, this will cause the NESZ to get worse due to the reduction of transmit power.The phase spoiling technique is utilized to solve this problem. Even with a long antenna, wide beam-width can be obtained with this technique. In this paper, the principle of the phase spoiling technique with various phase distributions and the simulation results applied to APAA installed on ALOS-4 are presented.

Conventional synthetic aperture radar (SAR) systems suffer from the contradictory requirements of high resolution and wide swath observation. SAR systems with multiple receive channels in azimuth and/or elevation have been studied and shown to overcome this trade-off. When the system with multiple receive channels in elevation employs variable pulse repetition frequency (PRF) in order to eliminate the blind ranges, it requires azimuth resampling process at some point in the image formation. If the system also has multiple channels in azimuth, then there will be an additional difficulty in the resampling process, because the average PRF is set to be lower than the Doppler bandwidth of the signal received by each receive channel.In this paper, we propose a processing strategy for combining the variable PRF SAR observation with multiple channels both in elevation and azimuth. In the proposed method, multiple azimuth beams are formed at first for each pulse, and azimuth resampling is applied to the signals of each beam. In order to reduce the resampling error, overlapped beams are formed, and only a fraction in the vicinity of the center of the beams are used to reconstruct the full Doppler spectrum.

ALOS-4 succeeds the concepts of ALOS-2 and hence system design of ALOS-4 satellite basically follows that of ALOS-2, except for improvements in mission performance. In order to use data sets of both ALOS-2 and ALOS-4 for monitoring long term (more than 10 years) changes, the orbit of ALOS-4 is identical to that of ALOS-2. Even though ALOS-4 and ALOS-2 share the same orbit, revisit time of ALOS-4 can be shortened by increasing the swath width. Therefore ALOS-4 utilizes digital beam forming on receive to improve observation swath width. PALSAR-3, the successor of PALSAR-2 onboard ALOS-2, is now designed as an active phased array antenna with on-board digital beam forming processor in order to increase the swath width of the 3m resolution Stripmap mode to 200 km. Transmit signal with a broad beam-width in the elevation direction is generated in order to cover the wider swath. The reflected signal from the ground is received by several independent receive channels and processed to form several antenna patterns. To achieve approximately equivalent NESZ as ALOS-2, the size of PALSAR-3 antenna is designed to be 1.2 times larger than that of PALSAR-2/ALOS-2.ALOS-4 has successfully passed its Preliminary Design Review and engineering model is currently under development. This paper describes the radar instrument design of ALOS-4.

The paper describes hardware performances of PALSAR-3 onboard ALOS-4, which is a follow-on mission of ALOS-2. To implement land deformation and subsidence monitoring with SAR interferometry and to improve performance of disaster monitoring (more frequent, wider coverage), ALOS-4 observe wider swath while keeping as higher spatial resolution as that of ALOS-2. PALSAR-3, which is successor of PALSAR-2 onbaard ALOS-2, is now designed as an active phased array antenna with onboard digital beam forming processor in order to improve swath width of 3 m resolution Stripmap mode to 200 km.

For SAR (Synthetic Aperture Radar) system, the high resolution (range/azimuth) and wide swath are required constantly. It is challenge to achieve both high azimuth resolution and wide swath imaging for spaceborne SAR system because it poses contradicting requirements for pulse repetition frequency. The technique of the multiple receive apertures and digital beam forming is utilized to overcome the difficulty. The reconstruction process for the independent receive channels has been developed to process the multiple received data [4]. The PRF should be selected carefully on this processing in order to keep S/N (Signal to Noise ratio), though it is difficult to control the PRF flexibly in orbit. The digital beam forming processing for azimuth direction (Azimuth DBF) is proposed instead of the reconstruction processing, which PRF can be selected flexibly in this processing. Azimuth DBF was applied to the experimental data required by airborne SAR system and it seems to be successfully processed. In this paper, the concept of Azimuth DBF and the evaluation result are described.

In order to enhance the performance of spaceborne synthetic aperture radar-ground moving target indication (SAR-GMTI) systems, multichannel systems with large and preferably nonuniform baselines are required. In this paper, SAR-GMTI algorithms for multichannel SAR systems, which we call multichannel displaced phase center antenna (DPCA), multichannel along track interferometry (ATI), and multichannel DPCA-ATI, are presented. Multichannel DPCA is a deterministic algorithm for clutter and azimuth ambiguity suppression. It successfully suppresses not only uniform azimuth ambiguities but also nonuniform isolated ones, since it does not require uniform clutter covariance assumption as adaptive algorithms do. Multichannel ATI and multichannel DPCA-ATI are the algorithms for target radial velocity estimation. Both of them reduce the target radial velocity ambiguities, which arise with the long baseline systems, by exploiting the multiple receive channel signals. And multichannel DPCA-ATI further achieves robust performance to clutter influence by suppressing the clutter and the azimuth ambiguity in advance. The performances of the proposed algorithms are shown through airborne Ku-band three-channel SAR experiments. It is shown that the multichannel DPCA suppresses strong azimuth ambiguity up to more than 20 dB, and the accuracy of the radial velocity estimation of the multichannel DPCA-ATI is on the order of 0.1 m/s. Furthermore, statistical performance analysis is presented to discuss the potential performance on the spaceborne system.

This paper presents 3D model generation of cattle by shape-from-silhouette method for ICT agriculture. The use of advanced ICT has any possibility to improve various agricultural activities. The authors have such a project whose targets are beef cattle. The goal of the project is to capture 3D shape information of cattle for the estimation of their body condition scores (BCS). Cattle do not stop moving because they are animals. Therefore, it is very difficult to capture their body shape information even using a commercial 3D scanner. Another reason is that the color of beef cattle is almost black and then a commercial 3D scanner like a laser range finder cannot be used. The authors use multiple RGB cameras to capture silhouette images of a cow and employ shape-from-silhouette method to generate its 3D model. Actually, the authors have taken multiple RGB camera images of cows and generated their 3D models. And then, it can be found that the generated 3D models' volumes of cows have positive correlation with their weights. This result says that the estimation of cows' weights is possible from multiple RGB camera images of them.

Advanced Land Observing Satellite-2 (ALOS-2) is a spaceborne Synthetic Aperture Radar (SAR) system, developed by Mitsubishi Electric Corporation under contract to Japan Aerospace Exploration Agency (JAXA). The SAR system named Phased Array type L-band Synthetic Aperture Radar-2(PALSAR-2) is installed to ALOS-2. Its unique frequency of L-band is expected continuous investigation such as forest, volcanoes, and earthquake activities. Compact polarimetry mode and Along track interferometry (ATI) mode are available in PALSAR-2 as experimental mode. The evaluation of each experimental mode has been completed and reported in this paper. Compact polarimetry mode is that H and V polarization are transmitted at the same time, therefore the swath can be maintained. Each polarization status of compact polarimetry is calculated from the covariance matrix using some assumption. The full polarimetry-like image can be obtained as first evaluation. Along track interferometry is the technique to detect the moving target. ALOS-2 has two receiver channels. The moving target and its velocity are obtained from the interferometric image of each channel. The velocity can be calculated from the phase difference between two images. This result compared with another method using Doppler shift to validate it.

PALSAR-2 (Phased Array type L-band Synthetic Aperture Radar-2) is a spaceborne L-band SAR (Synthetic Aperture Radar) system installed on Japanese Advanced Land Observing Satellite-2 (ALOS-2). PALSAR-2 is expected to provide valuable data for global monitoring and disaster monitoring. To meet the variety of demands, PALSAR-2 provides various operational modes. This paper describes the overview of the calibration plan of PALSAR-2. Since PALSAR-2 have more than 1,000 operational modes, effective and efficient procedure is crucial. The process is divided in three different phases; pre-launch calibration, check-out phase (C/O phase) after the launch, and image calibration phase. The overview of each phase is described.

This paper describes SAR system design of the Advanced Land Observing Satellite-2 (ALOS-2), which is a next-generation Japanese L-band SAR satellite. Since one of an important mission of ALOS-2 is a global monitoring using its unique frequency of L-band, a capability of wider coverage is required. On the contrary, in the point of disaster monitoring especially for urban area, relatively higher spatial resolution is essential. To comply with such a contradictive requirement of wide swath and high resolution, ALOS-2 utilizes a dual-receive channel (DRC) technique, and achieved a coverage area of up to 50km with a spatial resolution of down to 3m. In the paper, the H/W design of ALOS-2 DRC mode is explained. For a wider coverage of polarimetric observation, ALOS-2 installs the fully redundant and “quad-receive channel” system to full-polarimetric mode, achieving a maximum coverage of 50km at 6m resolution. As an experimental mode, new polarimetric mode called “compact polarimetry” is installed for a wide coverage of polarimetric observation.

This paper presents new algorithms for moving target detection and velocity estimation for multi-channel SAR (Synthetic Aperture Radar) system. The algorithms are derived as the extensions of conventional DPCA (Displaced Phase Center Antenna) and ATI (Along Track Interferometry) to the multichannel case. The proposed multi-channel DPCA based on orthogonal projection completely suppresses the static clutter even with the presence of the azimuth ambiguity. The multi-channel ATI utilizes the phase differences of all the pairs of the channels to estimate the target radial velocity. The combination of the two, which we call multi-channel DPCA-ATI, is also proposed as the more robust velocity estimation method.

Passive bistatic radars (PBRs) exploit existing transmitters such as TV broadcasts, radio broadcasts, Global Navigation Satellite System (GNSS), etc., as the source of illumination. PBR consists of two receivers, with one antenna pointed at the source and the other at the target, and the target range is determined by correlating the signal scattered by the target with the signal directly arrived at the receiver. Since PBR dode not transmit any wave form, it consumes lower power, and no frequency allocation is required. We are investigating the target imaging capability of PBR. In This paper an experimental study on obtaining In verse Synthetic Aperture Radar (ISAR) image with cross range resolution of a few meters, using terrestrial digital TV based PBR. In this study, we conducted a field experiment to observe some aircraft targets. Due to the relatively low frequency band employed by the digital TV broadcast system, a very wide synthetic aperture angle is required to obtain a few meters cross-range resolution. Using the data acquired in the experiment, we show the limit of the range Doppler processing approach and we investigate the advantage of the Polar Format Algorithm (PFA). We also discuss the issue on autofocus and show results of initial study on autofocus algorithms.

Passive bistatic radars (PBRs) exploit existing transmitters such as TV broadcasts as the source of illumination. PBR is consisted of two receivers, with one antenna pointed at the source and the other at the target, and the target range is determined by correlating the signal scattered by the target with the signal directly arrived at the receiver. Since PBR does not transmit any waveform, it consumes lower power, and no frequency allocation is required. We have conducted a field experiment exploiting terrestrial digital TV broadcast to assess the feasibility of ISAR (Inverse Synthetic Aperture Radar) observation based on PBR. The wide and flat spectrum of the OFDM signal and the small gap between the channels enables us to obtain high range resolution of up to several meters by exploiting multiple physical channels. Therefore, moderate resolution ISAR imaging is expected to be possible. In this paper, PBR based ISAR algorithm is briefly explained, and the first example of observed PBR based ISAR image of an aircraft target is shown.