Ku-band SAR data for bare soil moisture retrieval over agricultural fields

This study focused on the analyses of multiangle, Ku-band (14.85 GHz), synthetic aperture radar (SAR) data for bare soil moisture retrieval over agricultural fields. The radar data were acquired at three incidence angles (35 degrees, 55 degrees, and 75 degrees), VV polarization, and 2-m nominal spatial resolution. The fields presented either a small-scale or an intermediate-scale periodic soil roughness components, associated with level-basin and furrow irrigation systems, respectively. Both of these periodic structures were randomly perturbed by the presence of soil clods. Radar backscatter and soil surface moisture data were obtained from 39 ''borders'' (within-field level basins). The results showed that the bare soil moisture retrieval over agricultural fields with periodic roughness components from Ku-band SAR data is dependent upon the incidence angle and the soil roughness condition. For fields with level-basin irrigation system, a good linear relationship between radar backscattering coefficients and volumetric soil moisture contents was found, especially at 35 degrees incidence angle (r(2) = 0.90; for 55 degrees and 75 degrees incidence angles, r(2) = 0.74 and 0.41, respectively). However, for fields with the furrow irrigation system, the radar backscattering data were nearly insensitive to soil moisture due to the stronger influence of soil roughness.