In the frame of the NETLANDER project, we have developed a ground penetrating radar (GFR) aimed at initial observations of the geological features in the deep Martian subsurface and the detection of potential liquid water reservoirs. Initial ground tests at 2, 3 and 4 MHz were recently performed on the Pyla Dune, which is a sand dune nearly 100 meter high along the south-west Atlantic coast in France. The horizontal reflecting layer located at the base of the dune together with the known permittivity value of the sand offer the opportunity to test the performance of the device in a rather well-documented and simple environment. These first experimental results are reported in the paper. We will focus on the precise measurement of the electric antenna characteristics and the analysis of the backscattered signals using both electric and magnetic components of the received field. Comparisons with numerical simulations taking into account the actual environment of the GPR are also presented for comparisons.