Highly-squinted MEO SAR focusing based on joint time and doppler scaling

The squinted observation geometry along with long integration time significantly increases the space variance of the medium-Earth-orbit SAR signal. Firstly, in order to solve the range walk of the signal, a variable pulse repetition frequency (PRF) technology was used to receive the echos. Variable pulse repetition frequency is recommended to handle the severe range walk. The existing wavenumber algorithms cannot handle the nonlinear and range-azimuth-coupled space variance over a large scene. We propose a modified Stolt mapping method along with a modified joint time and Doppler scaling for imaging. An azimuth time scale transformation is used to deal with the quadratic space variance of the azimuth frequency modulation rate. A modified Stolt mapping is used to correct range cell migration. To address the range-azimuth-coupled space variance, the Doppler linearization is done in the range-Doppler domain using range-dependent Doppler scale transformation. Simulation results are shown to verify the effectiveness of the developed focusing approaches. © 2020, Editorial Office of Systems Engineering and Electronics. All right reserved.