  The paper deals with the investigation of the Mars subsurface by means of
data collected by the Mars Advanced Radar for Subsurface and Ionosphere
Sounding working at few MHz frequencies. A data processing strategy, which
combines a simple inversion model and an accurate procedure for data selection
is presented. This strategy permits to mitigate the theoretical and practical
difficulties of the inverse problem arising because of the inaccurate knowledge
of the parameters regarding both the scenario under investigation and the
radiated electromagnetic field impinging on the Mars surface. The results
presented in this paper show that, it is possible to reliably retrieve the
electromagnetic properties of deeper structures, if such strategy is accurately
applied. An example is given here, where the analysis of the data collected on
Gemina Lingula, a region of the North Polar layer deposits, allowed us to
retrieve permittivity values for the basal unit in agreement with those usually
associated to the Earth basaltic rocks.
