Low frequency SAR (P-band) represents a promising tool for remote sensing, since it allows us to investigate the subsurface down to several meters under certain circumstances as well as the vegetation cover. On the other hand, polarimetric capabilities of such system bring also new contributions in SAR measurements. ONERA developed a multi-frequency, full polarimetric, high resolution airborne SAR facility named RAMSES which now operates at Pband (435 MHz). An experiment was performed over the Pyla region near Bordeaux, in France during April and May 2001, in order to assess the benefit of low frequency, multi-polarization and polarimetric in interpreting SAR measurements over natural sites. This area was chosen as a suitable laboratory site for fieldwork validation : (1) subsurface soil moisture detection (Pyla sand dune), (2) biomass evaluation (Nezer forest), (3) mapping of the ocean bathymetry and salinity (basin of Arcachon), and (4) archeology. In addition, a dedicated P-band calibration site was set up in order to fully exploit the polarimetric information as well as ground measurements in order to derive the biophysical and geophysical characteristics of the terrain. During this workshop, firt results of this experiment obtained over the Nezer test site (a forested area located in les Landes) will be investigated. Amplitude and phase distributions of the radar signal derived from several images will be considered in terms of the geometrical tree parameters and the biomass.