Azimuth-variant compensation in subaperture processing of curved trajectory SAR

Curved trajectory SAR has the variant velocity and attitude. The acceleration and vertical velocity increase the azimuth variation of Doppler rate when the supaperture processing is taken. The assumption of identical Doppler rate for targets of the same slant range no longer holds. As a result of that, the conventional SPECAN algorithm will defocus the targets far away from the centre of illumination region. In order to solve the problem, this paper proposes an azimuth-variant compensation method used in the subaperture processing of curved trajectory SAR. The method uses Fourier transform of short block in azimuth to divide the illumination region into several parts and to apply respective compensation. Two practical considerations of the compensation, the block size and the over-lapping rate of blocks, are analysed in detail. Simulation results verify the effectiveness of the compensation method.