SAR Exploitation of GPS

Lawrence E. Brad, William H. Dunlevy, and Robert F. Rawson

Abstract:	The P-3/SAR system is a three wavelength fully pola- rimetric Synthetic Aperture Radar (SAR) system that has stripmap and spotlight modes. The P-3/SAR is equipped with a non-military P-code GPS receiver (Ashtech P-12); identical units are used as base reference stations to sup- port post-collection differential GPS (DGPS) processing. The accuracy of the GPS system is needed when collecting radar data of ocean scenes where no hard targets are avail- able to assist with image geometric registration. The P-3&@& system exploits both non-differential and differential GPS data. Real time non-differential GPS data is used to update the Inertial Navigation System (INS) which guides the auto-pilot as well as control radar antenna pointing, control pulse repetition frequency (PRF), and phase correct the radar signal. Post mission DGPS processing supports precise motion compensation of the radar data which allows for the production of focused and geometrically registered SAR images. Results show that real time GPS is accurate enough to point the 10 degree radar beam at the desired target, to generate a variable PRF which fixes the along track spac- ing to better than 0.1%. and to phase correct the data to keep it within the recording bandwidth of the sensor. Results also show that DGPS data is allowing radar data collected over a 10 km flight segment to produce images geometrically co-registered to within 1 meter. Additionally, a comparison of radar range with DGPS position data over a flight segment was made using a sta- tionary radar reflector. These two independent systems agreed to less than 20 cm.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	1173 - 1182
Cite this article:	Brad, Lawrence E., Dunlevy, William H., Rawson, Robert F., "SAR Exploitation of GPS," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 1173-1182.
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