The baisc principle of operation of the radar sounder MARSIS is based on the electromagnetic wave transmission by the antenna impinging on the top of the Mars surface producing a first reflection echo which propagates backward to the radar. However, thanks to the long wavelengths employed, a significant fraction of the e.m. energy is transmitted into the crust and propagates downward. Additional reflections, due to subsurface dielectric discontinuitites (due to water or ice), would occur and the relevant echoes would propagate backward through the first layer medium and then to the radar generating further echo signals, much weaker than the front surface signal. A consequent time domain analysis of the strong surface return, eventually after multi-look non-coherent integration, will allow estiamtion of surface roughness, reflectivity and mean distance, just like in classical pulse limited surface radar altimeters. The presence of weaker signals after the first strong surface return will enable the detection of subsurface interfaces, while the estimation of their time delay from the first surface signal will allow the measurement of the depth of the detected interfaces. Moreover, the detection performance will be limited by two main factors, namely the surface clutter echoes and the noise floor entering the receiver. The Mars surface geometric structure has been defined in terms of a large-scale morphology on which a small-scale geometric structure is superimposed. The first one results from gentle geometric undulations of the surface on a scale of many hundreds to thousands of meters and the second one from fast slight variations of the surface height, due to rocks, over a horizontal scale of some tenths of meters. From the statistical point of view, the surface height has been modeled as a Gaussian random process. Recently, attempts have been made to describe the structure of the planet surfaces by means of fractals, and this appears to be fruitful both as a means of describing the surface, and for tying the radar results to physical models of the surface. In this paper, MARSIS performance is analysed in terms of sounding depth vs. layer composition and surface structure, taking into account new parameters obtained from processing data from MOLA (Mars orbiter laser altimeter) from the current Mars global surveyor mission. The surface clutter and consequently the depth of subsurface interface detection are analysed by considering the new model and new parameters as input, in order to predict the strength of the clutter signal. Moreover, differences between results obtained with fractal model and with the two-scale model are evaluated.


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    Title :

    Subsurface investigations in 'Mars advanced radar for subsurface and ionospheric sounding' (MARSIS) (Mars express mission)


    Contributors:
    Biccari, D. (author) / Picardi, G. (author) / Seu, R. (author)

    Published in:

    Publication date :

    2002


    Size :

    10 Seiten, 5 Bilder, 7 Tabellen, 8 Quellen


    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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