Backscattering over bare soils: measurements and simulations using SIRC/XSAR and ERASME 1994 data over Orgeval

During the 1994 SIRC/XSAR mission (Shuttle Imaging Radar C/X-Synthetic Aperture Radar), a part of the scientific activities was devoted to hydrology applications. In April 94, as the ground condition stayed very wet over the Orgeval watershed, France, the SAR imagery was used to assess the sensitivity of radar on the single problem of soil roughness over bare soils. To complement the Shuttle Radar data the helicopter-borne scatterometer ERASME was used. As a result, incidence angles ranging from 25 to 50 degrees are available in C- and X-bands. Principal results are the following. The difference in backscatter response due to direction angles (perpendicular and parallel to the row direction) remain large over fields with moderate periodicity and height root mean square. The comparison between radar data and numerical simulations from a theoretical model (IEM) and a semiempirical algorithm (Oh et al., 1994) shows adequacies and limits. The IEM model reproduces well radar scatter over smooth surfaces. The Oh algorithm agrees with the backscatter response over rough surfaces at medium incidence angle.