MARSIS Radar Echo Ionospheric Correction and The Estimation of Mars Ionosphere's Total Electron Content
Résumé
On June 19th, 2005, Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) recorded its first radar echoes from the surface of Mars. MARSIS is capable of radiating between 0.1 and 5.5 MHz. The subsurface mode of MARSIS consists of four one-MHz bands with center frequencies at 1.8, 3.0, 4.0, and 5.5 MHz. The primary objectives of the subsurface sounding mode are to detect subsurface structures and search for water reservoirs. The amplitude and phase of MARSIS echoes are distorted by the Mars ionosphere by amounts depending on the number of free electrons and their distribution profile in the ionosphere. The compensation for the ionospheric distortion is one of major steps in MARSIS subsurface mode data processing. In this paper, we present the first results of the de-dispersion processing which yields very detailed information about the total electron content (TEC) between the radar and the Mars surface and to some degree how it is distributed in the ionosphere. For a given orbit, the TEC can be measured at high spatial resolution of approximately 5-10 km. We will also discuss issues related to variability of the TEC in Mars ionosphere and how it impacts MARSIS subsurface echo interpretation. The research described in this paper was carried out by the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautical and Space Administration.