SHARAD (SHAllow RADar) is the sub-surface sounding radar provided by the Italian Space Agency (ASI) as a facility instrument to NASA's 2005 Mars Reconnaissance Orbiter (MRO). SHARAD has been launched on August '05 and has started its nominal observation phase since November '06. Primary objective of its investigation is to map, in selected regions, dielectric interfaces to depths of up to one kilometer in the Martian subsurface and to interpret these interfaces in terms of the occurrence and distribution of expected materials, including rock, regolith, water, and ice. SHARAD which is a wideband low-frequency nadir-looking pulse limited radar sounder is expected to map Mars surface with a theoretical range resolution of 15 m in free space propagation, an along-track horizontal resolution of 300-1000 m and an across-track horizontal resolution of 1500-8000 m, depending on spacecraft altitude and terrain roughness. These performances can be reached by means of a focused synthetic aperture processing. The processing chain has been specifically designed and developed by CORISTA within SHARAD Ground Data System development activities with the aim of generating Level 1B products. This paper will be focused on of Level 1B SHARAD data processing description. Some results will be presented using SHARAD first data.