Marsis Radar: the Contrast Method Algorithm

Abstract

It is well known that Mars does not possess an appreciable global magnetic field, by contrast to Earth, which has a strong geomagnetic field of core origin. In these conditions, the solar wind can directly interact with the Martian ionosphere and induce modifications of its local properties, producing a clear distinction between the day side and the night side ionosphere behaviors . This is mainly due to the fact that the day side is directly hit by solar EUV photons which ionize atmospheric neutrals. As a consequence, the use of a radar sounder to analyse the surface and subsurface of Mars, through the ionosphere, must deal with serious constraints, depending on the operative frequencies adopted. In this document, we describe the Contrast Method algorithm used for the on-board and the on- ground processing of the MARSIS radar, in order to compensate the distortions introduced by the Mars ionosphere on the data collected by MARSIS in its subsurface operation mode. We show the effects obtained with the Contrast Method in different environmental. The result is that, the presence of the Contrast Method in the processing pipeline has allowed the collection of relevant scientific data not only during the night side, but also during the day side, producing a substantial improvement of the data quality and the Mars coverage.