Vital information wireless sensing is an interesting alternative to conventional techniques based on contact sensors. The evolution of radar technologies enables the proposal of cost-effective and compact radar sensors designed for diverse health monitoring, diagnostics, and Internet of Medical Things (IoMT) applications. It is possible to observe respiratory rate (RR), heart rate (HR), cardiac rhythm, blood pressure waveform (BPW), and emerging biometrics from the phase of radar echo signals. However, recognition and separation of the signals of interest from other interfering motion is a challenge, taking into account the diversity of signal patterns depending on subjects, health and observation conditions. In this context, we propose a novel wireless vital sensing system with a self-designed 120 GHz Frequency-Modulated Continuous Wave (FMCW) Radar. The developed sensor, based on a Radar System-on-Chip (RSoC), uses a real-time Repetitive Waveform Adaptive Matched Filter (RWAMF) maximizing Signal-to-Interference-plus-Noise Ratio (SINR) for reliable cardiac rhythm and BPW observations. The radar design has been optimized for vital sensing with a very short wavelength providing excellent sensitivity to micro-motion and a centimetric range and transversal resolutions to reject clutter and unwanted motions. The superior performance of our solution has been validated and evaluated experimentally on different subjects and measurement conditions with our own acquired vital signal database.

Data obtained during a ground-based SAR experiment and an associated field campaign have been exploited to study the rate and sources of decorrelation in an agricultural test site in the conditions of observation of a geosynchronous SAR. It was found that the scene is less affected by temporal decorrelation when the primary image is acquired during night time or early morning. Additionally, a periodic oscillation on a sub-daily scale was observed when creating coherence time series with increasing temporal baseline. Two factors which strongly contribute to these oscillations are the daily cycles of soil moisture and evapotranspiration.

Low Earth Orbit (LEO) remote sensing missions present a main limitation regarding their revisit time of several days or weeks. They cannot provide continuous monitoring over the same area of the planet. The on-going studies on Geosynchronous Synthetic Aperture Radar (GEOSAR), which have a revisit time of less than 24 h, aim to mitigate this limitation [1] . Since high altitude GEO missions are beyond MEO navigation satellites coverage, a ground based interferometric system (GEODE) has been developed for GEO Precise Orbit Determination, a requirement to form focused GEOSAR synthetic apertures [2] . Since no operational GEOSAR missions are available yet, present Geostationary telecommunications satellites can be used as transmitters of opportunity for GEODE experimental testing and validation. Recent results show the convenience of using ground reflectors to extend interferometric baselines lengths up to kilometers to achieve the required GEOSAR orbit precision. Locating stable reflectors of opportunity for interferometric orbit determination in urban areas is possible by complementing the ground interferometer with a multistatic SAR imaging processor capable to map the surrounding scattering centers.

HydroSoil is a measurement campaign, funded by the European Space Agency (ESA), where the temporal evolutions of two crops, barley and corn, have been continuously monitored during the whole crop period by means of a C-band Fully Polarimetric C-band Ground-Based Synthetic Aperture Radar (GB-SAR). SAR data has been collected together with ancillary data, and both are being processed to demonstrate the retrieval of soil moisture and vegetation parameters in an agricultural field under controlled conditions, to simulate the frequent acquisitions of GeoSAR missions.

The advent of geosynchronous remote sensing missions requires the development of precise orbit determination techniques at high orbits. Geosynchronous satellites require station-keeping manoeuvres to be performed periodically. Dynamical models do not consider artificial forces. Therefore, the tracking system must be able to detect them in order to keep track of the spacecraft autonomously. A compact baseline interferometer is deployed in order to track the signals of opportunity from the ASTRA 19.2°E geostationary constellation. The system is capable of autonomously estimate the trajectory of the satellite for a period of 22 days. Even after artificial orbital manoeuvres are performed. These results show that interferometry is a valid alternative for future geosynchronous remote sensing missions which require precise orbit determination.

In the framework of a feasibility study in support of the Hydroterra mission, a high resolution radar has been setup to monitor continuously a crop field with high resolution synthetic aperture radar images. In parallel, ground-truth data is acquired such as soil roughness, soil moisture and crop biological parameters. From this experimental data set the possibility to monitor soil moisture and crop biological parameters from back-scattering radar measurements will be assessed. To use the phase information of SAR images it is interesting to compensate the atmospheric phase screen induced by tropospheric refractive index. The paper presents a study of the atmosphetric phase drift prediction and compensation based on the local measurement of meteorological parameters.

The orbit accuracy requirements for a Geosynchronous Synthetic Aperture Radar (GEOSAR) are studied. Compared to telecommunication GEO satellites' station keeping needs, focusing the GEOSAR synthetic aperture demands a more accurate orbital determination. For this reason, the most suitable Precise Orbit Observation (POB) techniques are considered.Several radar tracking techniques fulfil the accuracy requirements while presenting a trade-off problem in terms of cost an operation. GNSS allow for precise autonomous navigation even at high orbits like GEO. Optical observation techniques perform well in order to calibrate other tracking systems.Interferometry stands out since it can be used taking advantage of present illuminators of opportunity. A ground interferometer is being designed and built in order to provide experimental measurements which will serve as proof of concept.

Technological developments in low-power mmW radar allow the measurement of deformations in the order of few micrometers and monitoring dynamic processes like structural vibration. This paper presents a fast acquisition FMCW radar operating at 94 GHz and recent experimental results of remote observation of micrometric vibration motion for bridge structural health monitoring. The presented approach offers cost reduction and applicability advantages compared to conventional techniques.

The application of differential synthetic aperture radar interferometry (DInSAR) techniques has been traditionally limited to the single-polarimetric case. The launch of satellites with polarimetric capabilities has triggered the synergy between polarimetric and interferometric algorithms, leading to a significant improvement in final DInSAR products. During the last years, the different polarimetric optimization techniques available have been successfully applied to the so-called classical phase quality estimators, i.e., the coherence and the amplitude dispersion estimators. In this context, a new estimator to evaluate the pixels' phase quality, referred to as temporal sublook coherence (TSC), has recently demonstrated to provide promising results in DInSAR applications. The nature of this estimator, which is based on exploiting the spectral properties of pointlike scatterers through the coherence evaluation of different sublooks of the image spectrum, allows its adaptation to the existing polarimetric optimization methods. This letter presents the benefits of extending the TSC estimator to work with fully polarimetric data. For this purpose, a fully polarimetric data set consisting of ten X-band ground-based SAR (GB-SAR) images is employed. The final DInSAR results obtained by means of TSC polarimetric optimization are compared with the ones obtained with its classical single-polarimetric approach, achieving up to more than a twofold increase in the pixels' density.

Hyperspectral indices from the Compact Airborne Spectrographic Imager (CASI 550), together with land surface temperatures from the Thermal Airborne Spectrographic Imager (TASI 600) and brightness temperatures from a L-band radiometer were combined in a semi-empirical model to obtain soil moisture at very high spatial resolution (3.5 m). The airborne imagery was acquired in an experiment performed over the Soil Moisture Measurement Stations Network of the University of Salamanca (REMEDHUS) in 2012, including intensive field measurements. The feasibility of the hyperspectral optical bands from CASI acting as soil moisture proxy is tested through the cross-correlation between every possible two-CASI bands combination and in situ soil moisture. Next, the potential of combining the selected hyperspectral indices with thermal and microwave observations for soil moisture mapping is explored, synergistically with thermal and microwave observations, for obtaining soil moisture.

Soil moisture (SM) is a key parameter in the climate studies at a global scale and a very important parameter in applications such as precision agriculture at a local scale. The Global Navigation Satellite Systems Interference Pattern Technique (IPT) has proven to be a useful technique for the determination of SM, based on observations at vertical polarization (V-Pol) due to the Brewster angle. The IPT can be applied at both V-Pol and horizontal polarization (H-Pol) at the same time, observing the Brewster angle only at V-Pol. This letter presents a measurement technique based on tracking the phase difference between V-Pol and H-Pol interference patterns to improve the accuracy of the Brewster angle determination and, consequently, that of the SM retrievals. This technique benefits from the different phase behavior of the reflection coefficients between H-Pol and V-Pol in the angular observation range. To be sensitive to the phase difference, the Rayleigh criterion for smooth surfaces must be accomplished. This technique is not sensitive to topography as it is intrinsically corrected. Experimental results are presented to validate the proposed algorithm.

In this paper, a new model-based technique for the compensation of severe height-dependent atmospheric artifacts, using ground-based synthetic aperture radar (SAR) data over mountainous regions, is proposed. The method presented represents an extension of already existing techniques, but now taking into account the effect of steep topography in the atmospheric phase screen compensation process. In addition, the technique is adapted to work with polarimetric SAR data, showing, in that case, a noticeable improvement in the compensation process. The method is validated in the mountainous environment of El Forn de Canillo, located in the Andorran Pyrenees, where there is a slow-moving landslide that nowadays is being reactivated coinciding with strong rain episodes. In this framework, ten zero-baseline fully polarimetric data sets have been acquired at X-band during a one-year measurement campaign (October 2010-October 2011) with the GB-SAR sensor developed at the Universitat Politècnica de Catalunya. First, the impact of the severe atmospheric fluctuations among multitemporal GB-SAR measurements is carefully studied and analyzed. Hence, the need to correctly estimate and compensate the resulting phase differences when retrieving interferometric information is put forward in the frame of differential-SAR-interferometry applications.

In this paper, a study of polarimetric optimization techniques in the frame of differential synthetic aperture radar (SAR) interferometry (DInSAR) is considered. Historically, DInSAR techniques have been limited to the single-polarimetric case, mainly due to the unavailability of fully polarimetric data. Lately, the launch of satellites with polarimetric capabilities, such as the Advanced Land Observing Satellite (ALOS), RADARSAT-2, or TerraSAR-X, allowed merging polarimetric and interferometric techniques to improve the pixels' phase quality and, thus, the density and the reliability of the final DInSAR results. The relationship between the polarimetrically optimized coherence or amplitude dispersion maps and the final DInSAR results is carefully analyzed, using both orbital and ground-based SAR fully polarimetric data. DInSAR processing using polarimetric optimization techniques in the pixel selection process is compared with the classical single-polarimetric approach, achieving up to a threefold increase of the number of pixel candidates in the coherence case and up to a factor of seven in the amplitude dispersion case.

Revisiting time constitutes a key constraint for continuous monitoring activities based on space- and airborne synthetic aperture radar (SAR) acquisitions. Conversely, the employment of terrestrial platforms overcomes this limitation and makes it possible to perform time-continuous observations of small space-scale phenomena. New research lines of SAR dealing with the backscattering evolution of different types of scenarios become hence possible through the analysis of ground-based SAR (gbSAR) data collections. The Remote Sensing Laboratory of the Universitat Politècnica de Catalunya drove a one-year measurements campaign in the village of Sallent, northeastern Spain, using its X-Band gbSAR sensor. The field experiment aimed at studying the subsidence phenomenon induced by the salt mining activity carried out in this area during the past decades. In this paper, the polarimetric behavior of an urban environment is investigated at different time scales. After a brief description of the test site and the measurement campaign, the analysis is focused on the stability on man-made structures at different time scales. PolSAR data monthly acquired from June 2006 to July 2007 are employed to stress the presence of nonstationary backscattering processes within the urban scene and the effect they have on differential phase information. Then, a filtering procedure aiming at reducing backscattering randomness in one-day and long-term data collections is then put forward. The improvements provided by the proposed technique are assessed using a new polarimetric descriptor, the time entropy. In the end, the importance of preserving the interferometric phase information from nonstationary backscattering contaminations using fully polarimetric data is discussed.

In this paper, the study of polarimetric optimization techniques for Differential SAR Interferometry (DInSAR) applications is analyzed. This work has been carried out in the framework of deformation map retrieval on landslides. A large number of landslides occur on vegetated areas with a poor density of temporal coherent scatterers, which are characterized by a fast decorrelation at X-band. The objective of the techniques proposed in this paper is to increase the number of temporal coherent scatterers to improve the robustness of the DInSAR algorithms exploiting the polarimetric capabilities of data. The relationship between optimum coherences and its corresponding phase quality in terms of DInSAR application is analyzed using Ground-Based SAR zero-baseline fully-polarimetric data.

This paper aims to demonstrate that radar-based remote sensing techniques can be as effective as the conventional geotechnical ones for the detection and monitoring of well suited areas. Many of the high mountain landslides are vegetated areas that decorrelate faster at X-band. As in these scenarios the number of coherent scatterers is low and, in addition, the area of interest is usually small, the processing can be benefited of the usage of high-resolution data. This will maximize the chances of detecting persistent scatters coming from both natural targets and man-made structures. The high resolution Spotlight mode of TerraSAR-X is thus the perfect choice as it offers a fine resolution. On the other hand, its 11 days of revisit time and X-band carrier allows the monitoring of small variations in the landslide trend and deal with its variable dynamics.

Global navigation satellite system reflectometry has already shown its potential to perform retrievals of a number of geophysical parameters, including soil moisture, vegetation height, etc. This letter focuses on the study of snow-covered soils using the interference pattern technique (IPT) with the Soil Moisture Interference-pattern GNSS Observations at L-band (SMIGOL) reflectometer, a ground-based instrument. Snow effects are analyzed, and an algorithm has been developed for this type of surfaces. From November 2010 to May 2011, a long-term field experiment was carried out at the Pyrenees (Val d'Aran, Lleida, Spain) to test the IPT and the retrieval algorithms on snow-covered soils.

HUMID is a regional level airborne soil moisture mission. The envisioned product combines two key characteristics. On one hand, it provides robustness in presence of surface roughness and vegetation. On the other hand, it improves the current spatial resolution offered by L-band radiometers using a data fusion approach, where the data from an L-band radiometer developed by the Remote Sensing Lab at the Universitat Politecnica de Catalunya will be combined with data from a thermal and a VNIR hyperspectral sensors from the Institut Cartografic de Catalunya.

GNSS-R techniques are currently being studied to remotely sense a number of geophysical parameters over different types of surfaces [1-6]. The Interference Pattern Technique (IPT) is based on the measurement of the interference pattern of the GPS direct and reflected signals, after reflecting over the surface, as the GPS satellites move. This paper extends previous studies [7-11], in which water level was monitored [7] and land areas were observed retrieving soil moisture, topography and vegetation height for different kinds of crops (wheat, barley and maize) [8-10], to a snow- covered soils studies.

The use of a low-profile, lightweight, and easy-to-fabricate transpolarizing surface placed on one side of a trihedral corner reflector (TCR) as a polarimetric calibrator is presented in this letter. The transpolarizing TCR presents a high backscattered cross-polar response contrary to standard TCRs. The performance of this device has been tested at the X-band using the Universitat Politecnica de Catalunya ground-based synthetic aperture radar.

The paper presents the development of a ground based bistatic receiver using TerraSAR-X as a transmitter. The receiver subsystems like antennas, low-noise amplifiers, mixers, filters, synthesizers, etc. have been developed using low-cost monolithic devices in order to allow affordable deployment and at the same time offer final year students a challenging SAR engineering project. First raw data have been acquired on the Barcelona harbor area that has been focused producing geocoded images well matched with existing maps. A preliminary interferogram have been also produced.

The Global Navigation Satellite Signals Reflections (GNSS-R) techniques have been widely used for remote sensing purposes retrieving geophysical parameters over different types of surfaces. Over the ocean, altimetry or sea state can be retrieved. Over land, soil moisture can be inferred and over ice, altimetry, and ice age are also retrieved. This paper presents the results of using GNSS-R techniques to retrieve altimetry from the measurements of an airborne GNSS-Reflectometer.

The use of Global Navigation Satellite Signals Reflections (GNSS-R) techniques to retrieve geophysical parameters from surfaces has been increased in the recent years. These techniques have resulted in suitable tools to obtain information about the sea state of oceans, which is very useful to improve the ocean salinity retrieval, and also, information about the soil moisture of lands. The present work focuses on the use of the Interference Pattern Technique (IPT), a particular type of GNSS-R technique, to study vegetation-covered soils. The IPT consists mainly of the measurement of the interference pattern between the GPS direct and reflected signals (the interference power), after they impinge over the ensemble soil surface and vegetation layer. The measured interference signal provides information on the soil moisture of the surface and also, on the vegetation height.

A light-weight L-band radiometer has been designed and implemented at the RS Lab of the Universitat Politecnica de Catalunya (UPC) to gather radiometric airborne data sets. The design of the compact L-band Dicke radiometer (ARIEL) and a general overview of the self-designed aircraft were described in. Preliminary results of the avionics and the radiometer have proven the system performance and capabilities for soil moisture and sea surface salinity retrieval applications. Among other activities, ARIEL will be involved in the SMOS CAL/VAL activities that will take place in the REMEDHUS site (Salamanca, Spain) during the second half of 2009.

In this paper a compact, lightweight, low power consumption airborne SAR sensor able to be fitted in an UAV is presented. The Air-Based Remote Sensing (ARBRES) system is based on the previous experience acquired in developing GB-SAR sensors for subsidence and landslide monitoring. Prior to the in-flight evaluation of the developed SAR, different tests were performed boarding the hardware on a car to evaluate its performance. After this debugging step, tests of the system in an airborne platform were carried out and the results are presented. GPS and INS systems are used to record the aircraft position, velocity, and attitude for future Motion Compensation (MoCo) Techniques.

The use of a transpolarizing surface placed on one side of a trihedral corner reflector (TCR) as polarimetric calibrator is presented in this paper. The transpolarizing-TCR presents a high back-scattered cross-polar response. This structure has been tested at 9.65 GHz (X-band) with the help of the UPC GB-SAR system.

GRAJO (GPS and RAdiometric Joint Observations) is a longterm field experiment over land which is being conducted since November 2008 at the REMEDHUS site, Zamora, Spain. REMEDHUS has been identified as a cal/val site for ESA's SMOS mission. The objectives of GRAJO are multiple: (i) validate and calibrate SMOS-derived soil moisture, (ii) study the variability of soil moisture within the SMOS footprint, (iii) test pixel disaggregation techniques to improve the spatial resolution of SMOS observations, (iv) determine the optical depth and vegetation water content of barley and grass and assess their influence on soil moisture estimates from radiometric and GNSS-R measurements, and (v) characterise the soil roughness factor. This paper presents an overview of the GRAJO experiment, describing the setup and measurements strategy.

In this paper, the potentials of polarimetric coherence-optimization techniques for differential interferometric SAR (DInSAR) applications are examined. For this purpose, the cutting-edge approaches available in the literature are considered. First, synthetic PolSAR data simulating homogeneous distributed scatterers are employed to demonstrate the convergence of the optimized differential phase to the deformation phase information. Then, real X-band ground-based PolSAR acquisitions concerning an urban environment are analyzed. The relation between optimum coherences and corresponding optimum phase in terms of deformation on retrieval is carefully analyzed using two zero-baseline fully-polarimetric data sets. In the end, general conclusions about the advantages and drawbacks of the alternative maximization approaches are drawn.

The Remote Sensing Laboratory of the Universitat Politecnica de Catalunya carried out a one-year measuring campaign in the village of Sallent, northeastern Spain, using a polarimetric ground-based synthetic aperture radar (SAR) sensor. The objective was to study the subsidence phenomenon induced by the salt mining activity conducted in this area up to the middle of the last century. Zero-Baseline polarimetric SAR (PolSAR) data were gathered at X-band in nine different days, from June 2006 to March 2007. In this letter, the problem of extracting subsidence information from fully PolSAR acquisitions for the retrieval of high-quality deformation maps is addressed. After compensating for the atmospheric artifacts caused by troposphere changes, the linear component of the deformation process is estimated separately for each polarization channel with the Coherent Pixels Technique (CPT). Afterward, a novel polarimetric approach mixing the differential-phase information of each polarization channel is proposed. The results obtained in the two cases are quantitatively compared, and the advantages provided by the polarimetric acquisitions are finally stressed.

A one-year subsidence monitoring activity has been carried out by the Remote Sensing Laboratory (RSLab) of the Universitat Politecnica de Catalunya (UPC) using an X-band ground-based SAR sensor. The project aimed at studying the subsidence phenomenon induced by salt mining extraction of the past years in the village of Sallent (Spain). The polarimetric capability of the system allowed to gather zero-baseline POL-SAR data in the single-pass mode in 9 different days, from June 2006 to April 2007. The estimation of the linear component of deformation process obtained using each polarization channel separately is here compared with the result of a new approach exploiting the full knowledge of the scattering matrix at once. For this purpose, a coherence-based approach is employed. The higher amount information carried by polarimetric data is finally pointed out both in terms of number of reliable pixels selected within the scene and higher quality of the retrieved subsidence map.

This paper presents the description and first results on the performance of a light-weight airborne L-band radiometer. This radiometer will be used in the SMOS CAL/VAL activities in the REMEDHUS site (Salamanca, Spain). First, a brief description of the overall system is presented. The first results obtained during a field experiment over the Ebro river mouth are then presented. These include flights over the sea shore (fresh and sea water) and land (dry and irrigated rice fields). This field experiment has also served to test the aircraft and the data processing algorithms that will be used in future campaigns with PAU-ORA, a reduced airborne demonstrator version of the PAU instrument.

In this letter, a coherence-based technique for atmospheric artifact removal in ground-based (GB) zero-baseline synthetic aperture radar (SAR) acquisitions is proposed. For this purpose, polarimetric measurements acquired using the GB-SAR sensor developed at the Universitat Politecnica de Catalunya are employed. The heterogeneous environment of Collserola Park in the outskirts of Barcelona, Spain, was selected as the test area. Data sets were acquired at X-band during one week in June 2005. The effects of the atmosphere variations between successive zero-baseline SAR polarimetric acquisitions are treated here in detail. The need to compensate for the resulting phase-difference errors when retrieving interferometric information is put forward. A compensation technique is then proposed and evaluated using the control points placed inside the observed scene.

The development of new concepts in remote sensing may improve the retrieval of geophysical parameters, an particularly the sea surface salinity. PAU (passive advanced unit for ocean monitoring), a new hybrid, L-band radiometer, GNSS- reflectometer and IR radiometer. This instrument will include a receiving antenna array of 4times4 elements, each one with its corresponding dual-polarization receiver. Since the calibration procedure for the whole ensemble needs to be thoroughly verified, the implementation of single-receiver PAU sensors has been undertaken to obtaining the first experimental data and to allow to compare them with simulation results. Since both ground-based and airborne measurements will be obtained with the full version of PAU, ground-based and airborne one-receiver demonstrators have being implemented. These sensors do not incorporate the IR radiometer included in the full PAU instrument, but are representative of the hybrid radiometer- reflectometer concept. This paper describes both instruments and its future applications.

A novel transpolarizing or crosspolarizing surface has been proposed to be applied in polarimetric SAR calibrating systems, like trihedrals, since they can not provide initially a crosspolar response. So the trans-surface has been designed and measured in an anechoic chamber, providing good results for normal incidence.

The Universitat Politecnica de Catalunya is developing a ground based bistatic system using ESA's ENVISAT and ERS-2 as transmitters. The spatial resolution of this configuration is similar to that of their monostatic counterpart, although foreshortening effects have a lesser impact. First single-pass interferometric images corresponding to a local test-site are presented and compared to a synthetic interferogram.

In this work, a preliminary study on the use of polarimetric persistent scatterers for differential interferometric applications within an urban environmental is presented. The PolSAR measurements campaign that the RSLab of UPC is carrying on in the village of Salient using an X-Band ground- based SAR sensor is first described. The work is then focused on the additional information the knowledge of full scattering matrix [S] may provide with respect to the single polarization approach. The problem of instability of the polarimetric signature of urban targets is also analyzed. Finally, a solution based on the search of repeated patterns in the long-temporal profile of pixels' polarimetric signature is briefly introduced.

This letter discusses the implementation of SABRINA, Synthetic Aperture radar Bistatic Receiver for Interferometric Applications. The ground resolution of a fixed-receiver bistatic system is studied, showing that it is comparable to that of a monostatic system. Due to the short distance from target to receiver, large sensitivity is obtained. The noncooperative nature of the bistatic system forces a conservative data-acquisition strategy based on continuously sampling the scattered signal during a temporal window around the predicted satellite overpass time. Also, to be able to synchronize the system in time and in frequency, sampling of a direct signal obtained through an antenna pointed at the satellite is required. Besides the signal processing required to phase-lock the received signal, the bistatic synthetic aperture radar processing needs to take into account the azimuth-dependent phase history. First focused images obtained with the SABRINA-ENVISAT combination are discussed

This work summarizes the main findings of the activities carried out in the past years by the Microwave Radiometry Team at the Technical University of Catalonia (UPC) in the field of sea surface salinity retrieval within the frame of the SMOS mission in collaboration with the Institute of Marine Sciences (ICM/CMIMA-CSIC). They cover the measurement of the dielectric permittivity of the sea water at L- band, the impact on the sea emissivity of the surface roughness (waves, swell, currents, rain ...) and oil spills, and its comparison with numerical models, as well as the development of sea surface salinity retrieval algorithms for SMOS.

In this paper, a study of the temporal evolution of the elements of 3 x 3 covariance matrix using an X-band polarimetric ground-based SAR sensor is proposed. Although the heterogeneity of the scenario allows to select different target typologies, the study is mainly focused on the analysis of azimuthally symmetric distributed targets. The fluctuations of the most representative elements of [C] as a function of time and the decorrelation among the polarimetric channels are investigated. A relation with atmospheric parameters like temperature, humidity and wind is considered in order to make out the weight these parameters can influence the polarimetric signature of the observed area.

Past and current SAR missions, such as SIR-C, ERS- 1/2, ENVISAT, SRTM, E-SAR, etc. had in common that the signal transmitter and the receiver were located at the same moving platform. New missions are being planned [1] based on the bistatic concept, where transmitter and receiver subsystems are located at different locations and thus may follow different trajectories. But before these missions become a reality, there are several experiments to be considered. One of them is the Parasitic Bistatic Fixed Receiver case, a novel and challenging configuration regarding hardware development and SAR processing techniques. This configuration will improve our experience in the bistatic field with cost effective measurements. In this paper, we will present the first images of the ongoing satellite bistatic campaign in our department. The images have been acquired with the specific hardware SABRINA (SAR bistatic fixed receiver for interferometric applications, fully developed at UPC) and processed with the Subaperture Range- Doppler Algorithm which will be explained in detail. We have been using ESA's ENVISAT and ERS-2 C-band SAR satellites as opportunity transmitters and we have located the hardware prototype receiver at the roof of our department looking to the illuminated scene, a hill in front of the Campus. The mean bistatic angle is about 75deg, the capture window is only two seconds long and experiments have a period of 35 days due to the satellite revisiting time.

In this paper, the first results of the Polarimetric Ground-Based SAR system developed at the Technical University of Catalonia (UPC) are presented. A heterogeneous scenario containing different kinds of targets such as low vegetation, forest and urban areas has been chosen for performing a measurement campaign. The monitoring activity has dealt with the observation of the test-site at X-Band for a whole day with a revisiting time of approximately one hour: a temporal sequence of PolDInSAR dataset has been gathered. A first study of temporal decorrelation effects on multi-polarization differential coherence concerning different kinds of targets is here shown. Preliminary results are commented and future activities are proposed.

Continuous terrain fast changes monitoring is difficult to implement via airborne/satellite SAR systems, mainly due to the lack of flexibility and low revisiting times. Other SAR approaches based on small and simple ground-based systems, easy to deploy wherever are needed, must be considered. Transportability, low cost, and ruggedized structure are the main constrains, but the required resolution and performances have to be preserved. An experimental, short to medium range, ground-based, with optional polarimetric capability, Synthetic Aperture Radar (SAR) will be presented. First results of an experimental X-band SAR with a 100 MHz bandwidth, with 20 dBm of radiated power in differential interferometry operation will be shown

The knowledge of the seawater dielectric properties is very important in the areas of remote sensing. The models mainly used today seems not to be enough accurate for the actual applications. A new model has been derived from measurements at L Band.

Carrying out an effective control of fishing activities is essential to guarantee a sustainable exploitation of sea resources. As the regulated areas are extended, satellite-based synthetic aperture radar (SAR) provides a powerful surveillance capability allowing the observation of broad expanses, independently from weather effects and from the day/night cycle. This paper proposes a novel approach for ship detection based on the analysis of oceanic SAR images by means of the wavelet transform. The analysis of the detection performance over both simulated and real RADARSAT SAR images confirms the robustness of the proposed method: ships, undetectable with other conventional techniques are noticeably sharpened, whereas background noise is drastically reduced

Soil Moisture and Ocean Salinity (SMOS) is an Earth Explorer Opportunity Mission from the European Space Agency with a launch date in 2007. Its goal is to produce global maps of soil moisture and ocean salinity variables for climatic studies using a new dual-polarization L-band (1400-1427 MHz) radiometer Microwave Imaging Radiometer by Aperture Synthesis (MIRAS). SMOS will have multiangular observation capability and can be optionally operated in full-polarimetric mode. At this frequency the sensitivity of the brightness temperature (T/sub B/) to the sea surface salinity (SSS) is low: 0.5 K/psu for a sea surface temperature (SST) of 20/spl deg/C, decreasing to 0.25 K/psu for a SST of 0/spl deg/C. Since other variables than SSS influence the T/sub B/ signal (sea surface temperature, surface roughness and foam), the accuracy of the SSS measurement will degrade unless these effects are properly accounted for. The main objective of the ESA-sponsored Wind and Salinity Experiment (WISE) field experiments has been the improvement of our understanding of the sea state effects on T/sub B/ at different incidence angles and polarizations. This understanding will help to develop and improve sea surface emissivity models to be used in the SMOS SSS retrieval algorithms. This paper summarizes the main results of the WISE field experiments on sea surface emissivity at L-band and its application to a performance study of multiangular sea surface salinity retrieval algorithms. The processing of the data reveals a sensitivity of T/sub B/ to wind speed extrapolated at nadir of /spl sim/0.23-0.25 K/(m/s), increasing at horizontal (H) polarization up to /spl sim/0.5 K/(m/s), and decreasing at vertical (V) polarization down to /spl sim/-0.2 K/(m/s) at 65/spl deg/ incidence angle. The sensitivity of T/sub B/ to significant wave height extrapolated to nadir is /spl sim/1 K/m, increasing at H-polarization up to /spl sim/1.5 K/m, and decreasing at V-polarization down to -0.5 K/m at 65/spl deg/. A modulation of the instantaneous brightness temperature T/sub B/(t) is found to be correlated with the measured sea surface slope spectra. Peaks in T/sub B/(t) are due to foam, which has allowed estimates of the foam brightness temperature and, taking into account the fractional foam coverage, the foam impact on the sea surface brightness temperature. It is suspected that a small azimuthal modulation /spl sim/0.2-0.3 K exists for low to moderate wind speeds. However, much larger values (4-5 K peak-to-peak) were registered during a strong storm, which could be due to increased foam. These sensitivities are satisfactorily compared to numerical models, and multiangular T/sub B/ data have been successfully used to retrieve sea surface salinity.