Validity Regions of Soil Moisture Retrieval on the LAI-theta Plane for Agricultural Fields at L-, C-, and X-Bands

Abstract

To quantitatively examine the sensitivity of the soil moisture retrieval over agricultural fields, first, we generated a database of radar backscattering coefficients using the first-order vector radiative transfer model for various leaf area indices (LAIs), incidence angles, frequencies, and polarizations. Then, soil moisture contents were retrieved from the backscattering coefficients of the database using the water-cloud model (WCM) and Oh et al.'s scattering model. Based on the sensitivity examination for LAI and. (incidence angle) on soil moisture retrieval, we propose validity regions of soil moisture retrieval over agricultural fields on the LAI-theta plane at L-, C-, and X-bands for vv- and hh-polarizations in the form of theta(Fpp) < -A(Fpp) LAI + theta(0, Fpp), where the constants A(Fpp) and theta(0, Fpp) are determined in this letter for F-frequency band and pp-polarization. The validity regions were verified with inversion results from synthetic aperture radar (SAR) data of bean and wheat fields.