ESTIMATING THE CHARACTERISTICS OF VEGETATION CANOPIES WITH AIRBORNE RADAR MEASUREMENTS

Possible use of synthetic aperture radars (SAR) for monitoring agricul tural canopies is investigated in this paper. Data have been acquired on the Orgeval watershed during the AGRISCATT'88 campaign. Four radar experiments were carried out with the airborne scatterometer ERASME (C and X bands, HH and VV polarizations, multi-incidence angles). Simult aneous ground measurements (soil moisture, leaf area index, water cont ent of the canopy,...) were conducted on 11 wheat fields. Backscatteri ng coefficients of the canopies are interpreted in the framework of se mi-empirical 'water-cloud' models. A simple parametrization of the ang ular effect of soil roughness is introduced, allowing the simultaneous use of multi-incidence angle radar data. With a unique set of paramet ers for each radar configuration (frequency and polarization) the wate rcloud model appears to describe adequately the backscattering of all the fields, over the range of incidence angles. It is shown that in th is case, attenuation is the dominant effect of the vegetation and an i nversion algorithm is proposed for estimating the water content of veg etation. This algorithm requires measurements at two different inciden ce angles and various combinations of radar configurations are then te sted.