M. Iorio 1, F. Fois 2, R. Mecozzi 1; R. Seu 1, E. Flamini 3 1 INFOCOM Dept., Università “La Sapienza”, Rome, Italy, 2 Thales Alenia Space Italy, Rome, Italy, 3 A.S.I. Agenzia Spaziale Italiana, Rome Italy. Mars North Polar Cup Subsurface Materials Property Estimation Using GPR SHallow RADar Data INTRODUCTION SHARAD is a low frequency (20MHz center frequency) Ground Penetrating Radar (GPR) in altimeter configuration actually operating on Mars which uses the synthetic aperture technique. The instrument has a vertical resolution of 15m and an along track resolution of 300x500m spatial with a penetrating capability of about 2Km. Data acquired from the Martian surface are processed in range and azimuth dimension to produce the scientific final image that generally shows the surface echo line in along track dimension, the surface clutter in ground range dimension and eventually the subsurface echo presence. In order to evaluate the Mars subsurface material property the first step is the subsurface detection. To discriminate the subsurface echo from the surface echo will be used a recently coherent clutter estimation procedure that, using the available Mars topography by the optical altimeter MOLA instrument, generates a simulated surface radar gram to compare with the experimental data. The subsurface loss materials estimation is possible using an appropriate Split-Band Processor (SBP) that split the total band in two different sub-bands, the first one is 15-20MHz centered in 17.5MHz and the other one is 20-25MHz centred in 22.5MHz. Clearly, the geometrical surface and subsurface propriety as roughness and slope, causes a power reduction due the decomposition of the surface and subsurface backscattering in the coherent and incoherent component; in this work, using the radar power distribution, a robust procedure to remove this contribution is developed to obtain a significant data set. Finally, through a multilayer model, will be estimated a mixed reflection coefficient between the surface and the generic subsurface layer for a Mars north polar cup region, and presented an overview of possible dielectric material nature. Subsurface Detection As above mentioned the principal problem is represented by the synchronous overlap between the off-nadir surface clutter and the subsurface time echo. In order to detect the subsurface presence a solution is represented by the estimation of the surface clutter using a coherent model, in this case the surface power clutter is generated as coherent sum of the surface contributes using the surface topography in according with the facets model. Remanding for the details to specific literature here will be presented an application of this technique to Mars north polar cup region. 1-a) 1-b) 2-a) 2-b) 3) Orbit : (1-a and 1-b) MOLA map of the partial zone covered by the radar during the observation. The line at zero kilometers is the ground-track of the radar; (2-a and 2-b) Experimental and estimated data with coherent model, (3) Experimental data of Mars north polar cup region. Power Statistical Distribution Model Referring to an active sensor as SHARAD typically the received power can be modeled as a sum of different power contributes: where: P c RX, P nc RX are respectively the coherent and incoherent received power and P n is the noise system power. Considering the nature of the power returns the probability distribution of the received power can be expressed by a Gamma probability density function: By the mean and standard deviation results: Surface Dielectric Material Estimation Signal to noise ratio (SNR) is connected to surface reflectivity by the radar equation: where: SNR is the signal to noise ratio; P n is the noise power; P t is the transmitted power (10W); G is the antenna gain (-4.7dB); λ is the wavelength (15m); r az is the along track resolution (500); DC is the system duty cycle (6%); K= J/K; T e is the system equivalent V T is the tangential velocity (3.397 Km/s). temperature ( K); L-band H-band first layer second layer not relevant for the H-band Subsurface Material Loss Tangent Estimation The inversion procedure is based on the received power measure by a multilayer subsurface interface Here: r i,i+1 is the reflection coefficient between the i-th and i+1-th subsurface interface; g s,…sn is the overall surface and subsurface geometric contribution depending on coherent and incoherent subsurface scattering, f is the carrier frequency, i is the i-th time delay between the arrival of both returns, Tan( ) is the i-th material loss tangent defined as ratio between the image and real part of material dielectric constant. Subsurface Results Subsurface material composition in the Mars north polar cup region CONCLUSIONS The first layer of north polar cups Mars planet appears compatible (using the Maxwell-Garnett model) of indurated sediment material ( =2.1/2.3, =-13.5/-14.5) with CO 2 ICE host material ( =~10). 2 r  Ratio (2-way) 2 r 