Synthetic Aperture Radar (SAR) Processing Application

Abstract

Scietice Applications Iiiteriiatioiial corporation (SAIC) has deveilopcd a software application for processing raw synthetic aperture radar (SAK) phase liistories. Tlic software allows efficicnt workstation processitig of satellite and aircraft data. The processor was origiiially ititelided as an aiialysis tool for testing SAR processing algorithms atid for iinproviiig image quality . These iiiiages have occaiiograpliic applications such as wave or ship wake enhaiicelncnt atid environmental monitoring. I. INTKOIILJCTION Synthetic Aperture Radar (SAII) is an all-weather remote sensing technique which achievcs high resolution and large swath widths (l). SAR uses a short chirped pulse and matched-filter processing to obtain fine range resolution. Fine azimuth resolution which is range-indepcndent is obtained by using the platform motion and coherent processing of (lie Doppler-shifted radx pulses to synlliesize a large antelma. The range and aziinulli resolution of the processed phase history data is a few incters for aircraft SAll's atid about 10 meters for satellite SAR's. Image swath widths of 100 kin square are obtained from satellites aiid 5-10 kin froin aircraft SAR's. During the 1990's four coininercial intcriiational satellite- based synthetic aperture radar systems - the European Space Agency's ERS-I, the Japanese JERS-1, the Canadian RADARSAT and Uie Soviet ALMA% satellites - will be operating. In addition, aircraft systems which include the Canadian CV-580, the NASA JPL DC-8, and the US Navy P3 SAR collect interfcroinetric, inulti-ch:inncl or multi- polarization data uscful for yuantitative remote scnsiiig analyses. Data from these systems have many applications such as moriitoring ice motions ;md oil slicks, rncasuring ocean wavcs and fronts, aiitl evaluating natural rcsot~rces. One disadvantage of SAli is a significant increase in thc amount of data and processing requirements for image formation. In the past, processed S AI< images have bcen provided by large data facilities with hardware dedicated to producing catalogued scenes. For example , the satellite scenes of the IJS imaged by EIiS-1 and JGRS-1 will be processed by the Alaska SAR Facility. I Iowever, even with dedicated hardware this facility is able to process only a fraction of the phase histories of hundreds of images received each day. SAR processing at these facilities is performed using automated standard processing. The fundamental assumption inade in the azimuth Doppler processing is that the scatterers in the scene are stationary. For oceanographic applications this assumption is not satisfied because the short-scale surface waves which are imaged by the radar are moving. Since this motion significantly degrades a conventionally processed S Ali image, specialized processing is required to obtain better resolution images for oceanographic applications.