Thomas Espeter

Processing the Azimuth-Variant Bistatic SAR Data by Using Monostatic Imaging Algorithms Based on Two-Dimensional Principle of Stationary Phase

This paper presents a new bistatic point target reference spectrum. It is derived by using the 2-D principle of stationary phase which is first applied in the synthetic aperture radar (SAR) community. The spectrum contains two hyperbolic range-azimuth coupling terms and thus is very similar to the monostatic spectrum. It shows the characteristic of the conventional monostatic SAR besides an additional azimuth scaling term. Therefore, it makes the common Doppler-based monostatic processing algorithms readily suitable to handle the Bistatic SAR (BiSAR) data in the moderate-squint azimuth-variant configurations with two moving platforms. Based on the spectrum, two Doppler-based monostatic imaging algorithms [i.e., range-Doppler algorithm (RDA) and chirp-scaling algorithm (CSA)] are readily implemented to deal with the moderate-squint azimuth-variant BiSAR data. Compared to the processing procedure for the monostatic SAR, the RDA and CSA for the BiSAR need only the adjustment of Doppler parameters. Finally, the potential and limitation of the spectrum are analyzed, and the real raw data in the spaceborne/airborne configurations are used to validate the proposed spectrum and processing methods.

Focusing Bistatic SAR Data in Airborne/Stationary Configuration

This paper presents a frequency-domain-based focusing algorithm for the bistatic synthetic aperture radar (BiSAR) data in airborne/stationary configuration. In this bistatic configuration, only the moving platform contributes to the azimuth modulation, whereas the stationary platform introduces a range offset (RO) to the range migration trajectories of targets at the same range. The offset is determined by the azimuth position of different targets with respect to the stationary platform. Since the RO is position dependent, monostatic SAR imaging algorithms are not able to focus the bistatic data collected in this configuration. In this paper, an analytical bistatic point-target reference spectrum is derived, and then, a frequency-domain-based algorithm is developed to focus the bistatic data. It uses an interpolation-free wavenumber-domain algorithm as a basis and performs a range-variant interpolation to correct the position-dependent RO in the image domain after coarse focusing. The proposed algorithm is validated by the simulated data and the real BiSAR data acquired by the Forschungsgesellschaft fu¿r Angewandte Naturwissenschaftens airborne SAR system, PAMIR, in December 2007. In this BiSAR experiment, an X-band transmitter was stationary operated on a hill with PAMIR as the receiver mounted on a Transall C-160.

Performance analysis of a hybrid bistatic SAR system operating in the double sliding spotlight mode

A bistatic synthetic aperture radar uses a separated transmitter and receiver flying on different platforms to achieve benefits like exploitation of additional information contained in the bistatic reflectivity of targets, reduced vulnerability for military applications, forward looking SAR imaging or increased RCS. A particular constellation, where the transmitter is in space and the receiver near or on the earth surface (e.g. aircraft, tower) is called a hybrid bistatic SAR system. Besides technical challenges, like the synchronization of transmitter and receiver, the overlap of the two antenna footprints is of vital importance. Due to the extreme platform velocity differences, SAR modes with flexible steering of the antenna beams are necessary. The sliding spotlight mode offers such a beam steering, where the antenna footprint velocity can be chosen slower or faster than the platform velocity. If both transmitter and receiver use this mode it is called double sliding spotlight mode, which will be investigated in this paper using the example of the satellite TerraSAR-X and the airborne SAR system PAMIR. Several aspects like the ground resolution, Doppler frequency and Doppler-bandwidth will be analyzed.

Results and analysis of hybrid bistatic SAR experiments with spaceborne, airborne and stationary sensors

Bistatic SAR is a promising and useful supplement to a classical monostatic SAR system. Since transmitter and receiver are spatially separated, additional information of a scene may be provided. Further, as shadowing, layover, and foreshortening depend on the bistatic geometry, which can be quite different to the monostatic case, they can contribute to image analysis and classification. The transmitter and receiver are located on different platforms, which may either be close together or hundreds of kilometers apart. Typical platforms are satellites, UAVs, aircrafts, and towers. This paper presents recent bistatic SAR experiments with spaceborne, airborne, and stationary sensors, which have been conducted at FHR or in cooperation with Defence Research & Development Canada. Image results are presented and analyzed with respect to scattering behavior and resolution and compared to monostatic images.

Synchronization techniques for the bistatic spaceborne/airborne SAR experiment with TerraSAR-X and PAMIR

The separation of transmitter and receiver makes bistatic SAR (synthetic aperture radar) systems preferable to conventional monostatic systems in several applications. However, this separation also leads to difficulties in image processing and in synchronization of the involved systems. For the upcoming hybrid bistatic SAR experiment with the TerraSAR-X satellite as transmitter and the airborne SAR/GMTI system PAMIR as receiver the synchronization issues are discussed in this paper and possible solutions are presented.