Current maps and bathymetry from P-band SAR images: preliminary results

Microwave remote sensing at very long wavelength is already used and validated for coastal zone regions and regions covered by ice (Antarctica) using airborne systems. For many other applications, a high potential exists and the PYLA 2001 experiment allowed the acquisition of data for fields still under preliminary tests. The experiment was carried on a Transall aircraft (French army/DGA) and used the SAR sensor RAMSES (multifrequency/multipolarization) from ONERA by P. Paillou et al. (2001). For the experiment, the acquisition was performed in P band (435 MHz). The aim was to explore potentials of the low frequency domain for sub-surface moisture detection (Pyla sand dune), biomass evaluation (Nezer forest), mapping of the ocean bathymetry and salinity (Arcachon inlet, estuary of the river Gironde), and archaeology (St Germain d´Esteuil, Dignac, Moulin du Fa). A dedicated P-band calibration site was set up in order to fully exploit the polarimetric information. This part of the study consists of analyzing SAR images from RAMSES (P band) in order to be able to take into account the effect of longer surface waves, winds and currents on the surface roughness in the Arcachon inlet. Tidal currents associated with long oceanic waves recorded at the mouth of the inlet, including the northern channel and sand banks of the ebb tidal delta. The analysis provides tools allowing the production of current maps, which are in turn compared to in-situ measurements by GPS on surface drifting buoys and to current velocity fields provided by a 2DH numerical model, MARS-2D. The evaluation of the ability of a 1D hydrodynamical model applied to SAR images in order to reproduce currents in the area presented. Multipolarization images can be used in order to separate the information associated with the ocean surface (tilt) modulation, which is different for each polarimetric image, from the hydrodynamic modulation, similar for each image. The tilt modulation is representative of a Real Aperture Radar-like (RAR) image. The data being available quite late, we just performed correlations between each set of data by using polarimetric coefficient. We obtain good answers on the information associated with the motion of the scatterers.