Preliminaly Evaluation of the SIR-B Response to Soil Moisture, Surface Roughness, and Crop Canopy Cover

Abstract

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 (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 30°) but with opposite azimuth viewing directions (Δα = 180°). The digitally recorded and processed SIR-B imagery is externallyi-calibrated with respect to the radar backscattering coefficient σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> 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 × 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, σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SIR-B</sub> is found to vary over a 16-to 20-dB dynamic range for a given observation date. The magnitude of σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SIR-B</sub> is found to be proportional to soil moisture, surface roughness, and canopy biomass. Although the SIR-B sensor parameters es ( L-band, HH polarization, θnd 0 ° 300) were not expected to be optimum for estimation of near-surface soil moisture, significant linear correlations are observed between σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SIR-B</sub> (in decibels) and 0-5-cm volumetric moisture m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v. For a given target class as broadly defined by surface roughness and canopy cover, linear regression of σ⁰_SIR-B (dB) to m&#x01d52f; generally yields correlation coefficients of &#x01d52f;² ≃ 0.8.</sub>