Multiscale local Map Drift driven Multilateration SAR Autofocus using fast Polar Format Image Synthesis

This new autofocus 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 yields elevation, trajectory or clock drifts (bistatic case) errors. To alleviate the insensitivity of map-drift to error fluctuation faster than sub-aperture duration, algorithm is reiterated with coarse-to-fine resolution yielding high to low frequency errors. This allowed true bistatic SAR autofocus (without monostatic image) and our first successful air-to-air ISAR high resolution imaging.