Using complex independent component analysis to extract weak returns in MARSIS radar data and their possible relation to a subsurface reflector on Mars

Abstract

Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar signals returned from the surface and subsurface of the northern lowlands of Mars are mostly characterized as a prominent surface pulse followed by a tail of weak signals. We applied the method of blind source separation (BSS) using complex independent component analysis (CICA) to examine if there is any subsurface information hidden in the apparent clutter and noise in the tails. In this paper we describe the application of the method with a case study in a selected region in the western part of Utopia Planitia (88°E–91°E, 45°N–51°N) where an unnamed large (∼160 km in diameter), semifilled crater is located. Applying CICA, we find a particularly significant signal from one of the blind sources. This signal is interpreted as representing a subsurface reflection interface, based on analysis of characteristics of the separated sources and their relation to surface roughness inside and outside the crater. A numerical simulation is conducted to examine the conditions under which the method tends to be effective. We conclude that CICA is helpful for recognizing subsurface signals above the noise level but obscured by clutter and thermal noise, provided the surface is relatively smooth.