Total Zero Doppler Steering - A New Method for Minimizing the Doppler Centroid

Abstract

This paper presents a new method, called Total Zero Doppler Steering, to perform yaw and pitch steering for space-borne synthetic aperture radar (SAR) systems. The new method reduces the Doppler centroid to theoretically zero Hertz, independent of the range position of interest. Residual errors are only due to pointing in-accuracy or due to approximations in the implementation of the Total Zero Doppler Steering law. This paper compares the new method with currently applied methods. The attitude angles and the residual Doppler centroid frequencies are calculated and depicted exemplarily for the parameters of TerraSAR-X, for which the new method will be implemented and used. The new method provides a number of advantages. The low residual Doppler centroid as well as the reduced variation of the Doppler centroid over range allow a more accurate Doppler centroid estimation. Due to the low residual Doppler centroid, the SAR processing can be alleviated since the range cell migration is reduced and the Doppler frequencies are low. This facilitates the use of very efficient processing algorithms, which are based on approximations whose quality is better for low Doppler frequencies. The new method will furthermore optimize the overlap of the azimuth spectra of SAR image pairs for cross-track interferometry. Low Doppler centroids will also reduce the impact of co-registration errors on the interferometric phase. Furthermore, scalloping corrections in the ScanSAR processing are alleviated due to the low variation of the Doppler centroid over range.