Doppler centroid estimation for azimuth-offset SARS

Abstract

Successful processing of Synthetic Aperture Radar (SAR) data requires that the Doppler centroid frequency be accurately estimated. A method for estimating the Doppler centroid for azimuth-offset SAR signals in the presence of noise and speckle is presented. For azimuth-offset SAR systems, changes in the Doppler centroid will cause distortions in the shape of the azimuth spectrum. As a result, the traditional correlation-based estimators will not provide accurate estimates. Doppler centroid estimation based on edge detection provides a practical alternative. The edge detector is tuned to detect a fairly wide, smooth, roof-like type of edge in the signal power spectrum. This method of estimation is evaluated with real data to measure its performance. The results are compared to those obtained by other estimation techniques based on spectrum fitting and energy balance. The accuracy of the edge detection technique over a 2048 azimuth cells by 16 range cells area is found to be 0.02 PRF rms. The edge detection principles can offer a convenient solution for Doppler estimation of range-offset and non-offset SAR signals as well.