SCANSAR PROCESSING AND SIMULATION FOR ASAR USING ERS-1 RAW DATA

This paper presents results from a study on scanSAR processing and simulation. ERS-1 raw data in both normal mode and roll tilt mode are used for Doppler centroid estimation, processing and simulation. Azimuth gain variations and azimuth ambiguity ratios are evaluated for different scanning strategies and as a function of Doppler centroid errors. A scanning strategy with two scan cycles in each imaging cycle has been selected and a processing scheme with three range looks and two azimuth looks has been implemented. SPECAN is considered very favourable for azimuth processing because of its efficiency. The degradation in image quality is investigated by imposing individual (differential) beam pointing errors on real ERS-1 data. It is demonstrated in this work that the individual azimuth beam pointing errors should be less than 0.004 degrees to avoid visible degradations in homogeneous regions in the scanSAR image. Using many bursts and all subswaths for Doppler centroid estimation, it is assumed that Doppler centroid estimates will be so accurate that no image degradation is visible when azimuth intensity compensation is performed.