Radar Sounding Waveform Fitting for Roughness parameters estimation

SHARAD (Shallow Radar) and MARSIS (Mars advanced Radar for subsurface and ionosphere sounding) are two low frequency sounder radars in orbit around Mars whose aim is to assess the distribution of on-ground and buried water, to provide the material composing its crust and to study its topography at global scale. The estimation of dielectric properties using radar data, can be pursued by means of different methods, including a parametric data inversion approach. Our method provides for the estimation of surface permittivity and loss tangent by exploiting the ratio between the return powers from the surface and the subsurface at different frequencies. As the roughness of the surface as well as the subsurface, affects  the returned power, inversion techniques are often applied  on moderately flat surfaces, where the power loss due to roughness can be considered negligible.

In this work we present an approach for the estimation of surface roughness properties and power loss compensation via waveform fitting, whose shape is modified in relation to the  characteristics of the surface impinged by the emitted electromagnetic wave. Such fitting procedure exploits a large-scale roughness model for the power return obtained under the Kirchhoff approximation hypotheses and comprising both the coherent and the non-coherent components of the scattered field. Our method allows to estimate the roughness regime of the selected area in terms of height standard deviation and root mean squared slope and therefore to compensate for  power losses in relation with the estimated parameters.

The performances of the fitting procedure are tested using a ray-tracing simulator of the range-compressed SHARAD and MARSIS received signal. As a fist step we applied the analysis on isotropic gaussian surfaces with different roughness characteristics showing the possibility to recover the power lost due to roughness effects. Moreover, the analysis will be performed on MOLA simulated products to represent MARS surface and finally, will be applied to SHARAD real data acquired over the volcanic region of Elysium Planitia.