A new fourth order SAR processing algorithm for very high resolution

Abstract

Summary form only given. A new fourth-order SAR processing algorithm has been developed for a general satellite-Earth relative motion. The Earth is modelled as an ellipsoid and the relative motion between a satellite in a Kepler orbit and a rotating Earth is approximated with fourth order Taylor polynomials over the time of integration. The two-dimensional exact transfer function (ETF) is calculated and range variant phase corrections have been calculated in order to process many azimuth lines per block. ETF together with the phase corrections has been called the fourth-order EETF or EETF4 (Extended Exact Transfer Function). It is shown that a fourth order algorithm is necessary to process high quality images from spaceborne SAR with long integration times with spatial resolution around 1 m. New formulas for the fourth-order ETF is calculated, The ETF performs the bulk of the SAR compression and would be exact if the Doppler parameters were range invariant. To cope with varying Doppler parameters in the cross-track direction and to increase the speed of the ETF, new formulas for range variant phase corrections are developed. In this way many azimuth lines can be processed with the same ETF. The EETF4 algorithm has been implemented and tested on simulated point target raw data. There is no assumption that the phase in the emitted pulse is quadratic, hence, the down link chirp replica can be used. A detailed description of the algorithm and analysis of its performance will appear in K. Eldhuset (1998). It is shown in the present paper that accurate processing can be performed with 5 looks for a yaw steered X-band SAR with 1 m resolution.