Backscattering simulations from the Martian surface and subsurface in the case of the MARSIS radar sounder.

Details Backscattering simulations from the Martian surface and subsurface in the case of the MARSIS radar sounder. Backscattering simulations from the Martian surface and subsurface in the case of the MARSIS radar sounder.

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p31b1061g&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #P31B-1061

Statistics

Computation

0659 Random Media And Rough Surfaces, 0689 Wave Propagation (4275), 3947 Surfaces And Interfaces, 6225 Mars, 6297 Instruments And Techniques

Scientific paper

In December 2003, the Mars Express spacecraft will be inserted into orbit around Mars. One of the scientific instruments is a radar sounder named MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding). Its main objective is to detect the presence of water, liquid or solid, in the upper crust of Mars down a depth of 5 km. MARSIS is a nadir looking radar with four operative modes of bandwidth 1 MHz and central frequency 1.8 MHz, 3 MHz, 4 MHz and 5 MHz. The maximum penetration depth is obtained for the lowest altitude (250 km) and with the lowest frequency. Unfortunately the clutter from the off-nadir direction may dwarf the subsurface echo return. To characterize the clutter and the subsurface return level according to the surface roughness and the subsurface geology (layering and composition), we simulate the backscattering of a pulse from the surface and the subsurface to the antenna. The Martian surface consists of a random rough surface described statistically by 3 parameters: the RMS height, the correlation length and the Hurst exponent. Each parameter may be adjusted according to the requirements of the simulations.
The subsurface is composed of different geological layers with a complex permittivity which is function of the composition and the depth of the material (Maxwell Garnet model). Each layer is divided in sub-layers with constant permitivities. Different subsurface models (2 layers, 3 layers) with different compositions (porous basalt, andesite, basalt + water.) were used. The interface between two layers is not flat. The backscattered field from the surface is analytically computed using the scalar Kirchhoff approximation whereas the subsurface return consists of simple transmission and reflection through the different sub-layers along the nadir direction (i.e. we did not consider the 3D volume scattering because it is too expensive in term of computation) . The signal reaching the radar is then compressed by the matched filter and we also investigate the clutter reduction by Doppler filtering. We present map of power returns in function of the nadir point position of the radar through the surface and the time delay for the signal to reach the antenna.

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