The objective of our work is to quantify the radar system capabilities to penetrate the soils for retrieving their structure and physical properties, especially in arid areas where no vegetation is observed. Data acquisition systems considered are ground-penetrating radar (GPR) and airborne radar, for frequencies ranging from 100 MHz la 900 MHz. First fieldwork results presented here concern the area of the Dune du Pyla. Ta quanlify the performance of GPR on this site. measurements are compared to 2D synthetics radar section. High penetration reached with GPR can he explained by the very low imaginary part of the sand dielectric constant. Backscattering models taking into account both surface and volumic terms show the capability of airborne radar to detect subsurface structures up to several metres depth.