Estimation of kidney bean crop variables using ground-based scatterometer data at 9.89 GHz

Abstract

Crop variables were estimated using ground-based multi-temporal, multi-angle and co-polarized scatterometer X-band data at 9.89 GHz. An outdoor crop-bed was prepared to observe the scatterometer response at VV and HH polarizations in the incidence angle range from 20° to 70°. Soil moisture (SM) and crop variables, including leaf area index (LAI), leaf water area index (LWAI) and plant height (PH), of a kidney bean crop at different stages of growth were measured. The aim of this study was to estimate the crop variables and to determine how the variables interact with microwaves. We found that LAI correlated better than LWAI with the microwave backscattering coefficient σ⁰ (at 9.89 GHz) and the correlation with PH was lower, at the most suitable incidence angle of 40°. The value of σ⁰ increased with an increase in LAI at both polarizations. The crop variables retrieved by inversion of the cloud model and a polarization-based model were compared with another model based on least squares optimization. The results are promising for the estimation of crop variables, particularly LAI.