The University of Michigan's Land Surface Process/Radiobrightness model, originally developed for bare and grass-covered prairie soils in the northern great plains, was adapted to winter wheat-stubble found within the region of the Southern Great Plains Hydrology Experiment (SGP'97). The model consists of two modules, a 1-d Thermal and Hydrology (1-dTH) module and a Radiobrightness (R) module. The 1-dTH module captures diurnal and seasonal changes in soil temperature and moisture profiles when forced by weather. In this module, soil has eleven layers with distinct physical, thermal and hydraulic properties. The layers are discretized with sixty nodes, the thicknesses of which increase with depth. The canopy has two layers, a vertical layer made up of wheat-stubble, weeds and grass, and a horizontal layer made up of wheat-straw. The R module is a microwave emission model for vegetation canopies that predicts brightness temperatures of terrain using the estimated profiles from the 1-dTH module. Because the brightness is sensitive to surface soil moisture, differences between predicted (model) and observed (ground-, aircraft- or satellite-based) brightnesses are indicators of errors in surface soil moisture prediction and, through LSP/R models, of errors in stored water estimates.
The LSP/R model was driven by micro-meteorological and sky radiance data collected during SGP'97. SGP'97 was an interdisciplinary investigation conducted from June 18 through July 19, 1997 at selected sites in Oklahoma and Kansas. The main objective of this experiment was to extend point-scale surface soil moisture retrieval algorithms using ground or aircraft-based sensors to regional scales using satellite sensors. The model was validated by comparing its predictions with the data from our fifth Radiobrightness Energy Balance Experiment (REBEX-5) and other experiments conducted during SGP'97. As a contribution to SGP'97, REBEX-5 was conducted at the Atmospheric Radiation Measurement-Cloud and Radiation Testbed (ARM-CART) Central Facility near Lamont, Oklahoma. During REBEX-5, microwave brightness of senescent winter wheat and, after harvest, wheat-stubble was observed with the Tower Mounted Radiometer System (TMRS). TMRS consists of a 10 m tower which houses three radiometers at SSM/I frequencies of 19.35, 37.0 and 85.5 GHz, a Thermal Infrared (TIR) sensor, and a video camera. Mean difference between the predicted and observed canopy temperatures was 0.45 K with the variance of 2.6 K2 , and the mean differences for soil temperatures at 3, 10, 20, 40 and 60 cm depths were 0.04, -0.16, 0.18, 0.92 and -0.23 K, respectively, with variances of 1.01, 0.62, 0.35, 0.08 and 0.22 K2, respectively. Results from the validation will be presented in de