The imaging algorithm for steadily flying and maneuvering big targets

摘要

Usually inverse synthetic aperture radar (ISAR) imaging is for small aircraft, with long range, moreover the coherent integration angle is small, that is the target's wavenumber spectrum support region can be regard as a rectangle, Range-Doppler(RD) algorithm or Range-Instantaneous-Doppler (RID) algorithm are employed for image reconstruction after translational motion compensation (TMC), which includes envelope alignment (such as envelope correlation algorithm, minimum entropy algorithm) and autofocus (such as single PPP algorithm, multiple PPP algorithm, PGA, weighted least square algorithm). But migration through resolution cell (MTRC) is not considered after TMC, in fact, the scatterers around the target usually take place MTRC if the size of target is large. In the paper, we first align and focus the high resolution radar target echoes according target center, then we do time scale transform in target's wavenumber domain, that is Soumekh proposed 'keystone' interpolation to compensate MTRC (which can also be realized rapidly by DFT-IFFT or SFT-IFFT in azimuth direction), after range compression (range IFFT), for steadily flying target, target image can be obtained only after azimuth compression (that is FFT in azimuth direction), for maneuvering target, time-frequency analysis must be taken for every range cell, and the existing instantaneous imaging algorithms (such as joint time-frequency distribution algorithm, Radon-Wigner algorithm) are also effective to obtain RID images. This paper gives the ISAR imaging algorithm flow diagram to obtain images from raw data of steadily flying and maneuvering big targets, and simulate data and real data prove that algorithm flow is effective.