Jesus Sanz-Marcos

SABRINA: A SAR Bistatic Receiver for Interferometric Applications

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

Phase Synchronization and Doppler Centroid Estimation in Fixed Receiver Bistatic SAR Systems

This paper discusses temporal and phase synchronization in bistatic synthetic aperture radar (SAR) systems that use orbital sensors as coherent sources of opportunity and receivers at a fixed location. The discussion is particularized to SAR Bistatic Receiver for INterferometric Applications (SABRINA), a ground-based bistatic receiver that uses ENVISAT and ERS-2 as transmitters. Transmitter-receiver synchronization is hindered by the presence of independent reference oscillators at the transmit and receive end and by the lack of a common time frame. Phase synchronization and pulse alignment are achieved using a dedicated channel that receives a clean signal directly from the satellite. How to align the acquired data with the satellite orbit and how to estimate the Doppler centroid (DC) are studied. It is shown that in the bistatic configuration considered, the receiver provides an implicit control point which limits the negative impact of a DC misestimation on the resulting images. An algorithm to achieve this temporal alignment using the apparent phase history of the received pulses is proposed. Finally, this algorithm is validated through Monte Carlo simulations and experimental data acquired by SABRINA.

On the Usage of GRECOSAR, an Orbital Polarimetric SAR Simulator of Complex Targets, to Vessel Classification Studies

This paper presents a synthetic aperture radar (SAR) simulator that is able to generate polarimetric SAR (POLSAR) and polarimetric inverse SAR data of complex targets. It solves the electromagnetic problem via high-frequency approximations, such as physical optics and the physical theory of diffraction, with notable computational efficiency. In principle, any orbital monostatic sensor working at any band, resolution, and operating mode can be modeled. To make simulations more realistic, the targets bearing and speed are considered, and for the particular case of vessels, even the translational and rotational movements induced by the sea state. All these capabilities make the simulator a powerful tool for supplying large amounts of data with precise scenario information and for testing future sensor configurations. In this paper, the usefulness of the simulator on vessel classification studies is assessed. Several simulated polarimetric images are presented to analyze the potentialities of coherent target decompositions for classifying complex geometries, thus basing an operational algorithm. The limitations highlighted by the results suggest that other approaches, like POLSAR interferometry, should be explored

First ENVISAT and ERS-2 Parasitic Bistatic Fixed Receiver SAR Images Processed with the Subaperture Range-Doppler Algorithm

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 ESAs 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.

Bistatic parasitic SAR processor evaluation

Bistatic radar systems will pay a great role in the coming decade since a large number of radar missions are being foreseen. Using existing transmitters, formations of small passive receivers will enhance our capability to gather backscatter information from Earth. A bistatic SAR system operates with separated transmitting and receiving antenna and both antennas can follow independent trajectories. In this paper, the recently developed imaging algorithm for the case where the transmitting antenna follows a rectilinear trajectory while the receiver remains in a fixed position and orientation will be evaluated. This new imaging algorithm is based on a projecting the bistatic geometry onto the chirp scaling algorithm which results on a scaling factor in the azimuth compression function. This scaling factor is derived from the bistatic configurations and assumes a flat topography. The main purpose of this paper is to determine the accuracy of the algorithm when used with real case simulated scenarios such as the airborne case where the transmitter is onboard an airplane while the receiver will be installed in the top of a high tower

A SAR processing algorithm for TOPS imaging mode based on extended chirp scaling

This paper presents an efficient phase preserving processor for TOPS (Terrain Observation by Progressive Scans) imaging mode. TOPS has been proposed as a new wide swath imaging mode, which solves the problems of scalloping and azimuth-varying ambiguities introduced by the conventional ScanSAR mode by means of steering the antenna along the azimuth direction. An algorithm based on ECS (Extended Chirp Scaling) is proposed, which uses sub-apertures and a new azimuth scaling step. The proposed solution is also efficient in the sense that it allows selecting the final azimuth image spacing by means of azimuth scaling, hence easing the forthcoming mosaicking of the different sub swaths. Simulations with point targets are used to validate the processor.

Bistatic fixed-receiver parasitic SAR processor based on the back-propagation algorithm

In bistatic SAR systems the transmitter and the receiver are not in the same platform and therefore can follow different trajectories. Parasitic receivers record the backscattered echo of the signal transmitted from existing monostatic SARs, such as satellites or airplanes, and represent a challenging opportunity to start to understand the complexities of bistatic systems before constellations of SAR satellites are deployed on space. The case under study is based on a transmitting antenna following a rectilinear trajectory, while the receiver remains on the ground in the top of a high tower looking down to the illuminated scene. In this case, efficient SAR monostatic algorithms (Chirp scaling, Range Doppler, Omega-K, etc) are not suitable to accurately focus bistatic SAR data with fixed receiver due to the topography dependence of the impulse response. In this paper we will demonstrate the problems that arise when using already mentioned standard processing algorithms and we will propose a way to use the backpropagation technique adapted to the bistatic fixed-receiver case. The major problem regarding focusing raw data from these systems is that the target impulse response not only depends on the distance from the target to the transmitter but also on the distance to the receiver which is constant and adds a delay which depends on the target complete position (azimuth, range and height). First the algorithm will be suited to a flat ground model and later to a real case where the Digital Elevation Model is known. The implemented algorithms will be evaluated and verified with simulated scenes formed by ideal targets. Keywords-component; bistatic; processor; SAR; backpropagation; fixed receiver

Phase and temporal synchronization in bistatic SAR systems using sources of opportunity

This paper discusses temporal and phase synchronization in SABRINA, a bistatic system that uses ENVISAT and ERS-2 as transmitters of opportunity. Phase synchronization and pulse alignment is achieved using a dedicated channel that receives a clean signal directly from the satellite. It is studied how to temporally align the acquired data with the satellite orbit using the apparent range migration history.

Bistatic SAR interferometry using ENVISAT and a ground based receiver: Experimental results

The Universitat Politecnica de Catalunya is developing a ground based bistatic system using ESAs 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.

Multimode SAR data processor for satellite and airborne systems

The most recent and advanced synthetic aperture sensors are able to work in different operating modes and are currently being installed in an increasing variety of platforms. In order to be ready to process data generated not only by these new sensors but by the incoming ones, it is important to identify the common processing blocks. For instance, different chirp scaling algorithm implementations have been analyzed to derive an approach of the same algorithm being able to process raw data in StripMap, ScanSAR and SpotLight operating modes. Next to the Radar imaging techniques, the processing software has been developed to be able to dynamically adapt its performance to the memory and CPU resources. Maximum portability has also been one of the major tasks and the same code runs under IBM and SUN UNIX, Linux and Windows 32 bits platforms. Finally, Extended Markup Language (XML) standard has been adopted for parameter, setup and report files to improve the user experience. The processing kernel and the specific modules for each operating mode and platform have been validated using raw data from ERS-1, RADARSAT and DLR while to validate SpotLight mode, simulated data has been used for both air- and space borne platforms.