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stract-Two pre-dawn ascending data-akes (dt. 49.2 and 97.2) by the Shuttle Imaging Radar (SIR-B) are used to evaluate the effects of soil moisture, surface roughness, and crop canopy cover on radar backscattering. The two images are separated in acquisition date by three days and were obtained at the same local angle of incidence (Â¿1 = 30Â°) but with opposite azimuth viewing directions (Â¿Â¿ = 180Â°). The digitally recorded and processed SIR-B imagery is externallyi-calibrated with respect to the radar backscattering coefficient Â¿Â° via response to arrays of point and area-extended targets of known radar cross section. Extensive ancillary data pertaining to scene physical and biophysical al conditions were collected from approximately 400 agricultural fields within a 20 km Ã 20 km test site in west-central Illinois. The test site was largely agricultural and consisted primarily of corn and soybeans at harvest-ready conditions. For the agricultural portions of the scene, Â¿Â°SIR-B is found to vary over a 16-to 20-dB dynamic range for a given observation date. The magnitude of Â¿Â°SIR-B is found to be proportional to soil moisture, surface roughness, and canopy biomass. Although the SIR-B sensor parameters es ( L-band, HH polarization, Â¿nd 0 Â° 300) were not expected to be optimum for estimation of near-surface soil moisture, significant linear correlations are observed between Â¿Â°SIR-B (in decibels) and 0-5-cm volumetric moisture mÂ¿. For a given target class as broadly defined by surface roughness and canopy cover, linear regression of Â¿Â°SIR-B (dB) to mÂ¿ generally yields correlation coefficients of r2 0.8.