Wavelength diversity PRF-ambiguity resolver: calibration and test for ERS-1 SAR

A novel PRF-ambiguity resolver for SAR processing has been recently developed. It takes advantage of the linear relationship between Doppler centroid and radar frequency. The slope of this dependence and, hence, the unambiguous Doppler centroid can be estimated by Fourier transforming the SAR raw data in the range direction and measuring the Doppler centroid for every range frequency. Because of the small relative bandwidth of SAR systems the estimation of that slope is a delicate issue and a large number of data samples is required for save resolution of the PRF-ambiguity. A computationally efficient algorithm has been proposed for that task. The method was originally developed for processing of X-SAR data where classical methods like look-correlation are subject to fail. For test purposes the new algorithm has been operationally applied for ERS-1 SAR processing at the German Processing and Archiving Facility (D-PAF). The paper summarizes the results of that tests. The estimation accuracy is reported based on 300 different scenes, including also roll-tilt mode data. The Doppler centroid values covered the range from the -4th to the +4th PRF band