A Phase-Gradient-Autofocus Algorithm for the Recovery of MARSIS Subsurface Data

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is currently operating, providing information of the subsurface structure of the planet Mars. The transmitted chirp signals pass through the ionosphere, resulting delayed, attenuated, and, in the phase, distorted. MARSIS signals are routinely phase corrected during ground processing by adopting a predefined model based on the Chapman theory. In this letter, phase distortions are compensated by using a phase-gradient-autofocus algorithm, which is capable of correcting distortions of different nature by exploiting their redundancy along the orbit. For the first time, images presenting saturated regions have been recovered.