MODELING MULTIFREQUENCY DIURNAL BACKSCATTER FROM A WALNUT ORCHARD

The Michigan Microwave Canopy Scattering Model (MIMICS) is used to model scatterometer data that were obtained during the August 1987 EOS synergism study. During this experiment, truck-based scatterometers were used to measure radar backscatter from a walnut orchard in Fresno County, CA. Multi-polarized L- and X-band data were recorded for orchard plots for which dielectric and evapotranspiration characteristics were carefully monitored. MIMICS, a scattering model based on radiative transfer theory, is applied to model two data sets that were recorded during this experiment. These consist of a multi-angle data set in which a single orchard plot was observed at varying incidence angles and a series of diurnal measurements in which backscatter from this same plot was measured continuously over several 24-h periods. Ancillary ground measurements are used as inputs to MIMICS and the resulting modeled data are compared to the measured backscatter. Results of the modeling analysis demonstrate extraordinarily good agreement with the measured data. MIMICS is shown to account for variations in canopy backscatter driven by changes in canopy state that occur diurnally as well as on longer time scales. L-band backscatter is found to be dependent not only on properties of the vegetation but also on properties of the underlying soil surface. Behavior of the X-band backscatter is found to be dominated by properties of the tree crowns.