Improved Contrast Optimization Autofocus Algorithm for Compensating Ionospheric Phase Dispersion Effect on Spaceborne P-Band Ultrawideband SAR

Ionospheric dispersion will introduce quadratic and cubic phase error into spaceborne P-band ultra-wideband synthetic aperture radar (SAR) signals, causing range defocusing. We propose an improved contrast optimization (CO) autofocus algorithm for compensating for this error. By analysis of the effect of quadratic and cubic phase error on image contrast we give the rationale for the improved algorithm. The procedures of the improved algorithm are presented. Its superiority to traditional algorithm is demonstrated using simulations based on point target in clutter background and PALSAR2 data.