Multiscale Local Map-Drift-Driven Multilateration SAR Autofocus Using Fast Polar Format Image Synthesis

摘要

This new autofocus method is based on multilateration by ranging to small target areas at independent directions on the ground. Range-clipped Doppler low-filtered profiles around target points are used to compute local images using frequency-domain polar format algorithm. Images obtained from adjacent subapertures are registered, and the displacements yield elevation, trajectory, or clock drift (bistatic case) errors. To alleviate the insensitivity of map drift to error fluctuation faster than subaperture duration, the algorithm is reiterated with coarse-to-fine resolution, yielding high to low frequency errors. This allowed true bistatic synthetic aperture radar (SAR) autofocus (without monostatic image), autofocus in circular SAR on remote areas, and, as a side product, our first successful air-to-air inverse SAR high-resolution imaging.