Moisture in a grass canopy from SSM/I radiobrightness

Abstract

Soil-Vegetation-Atmosphere Transfer (SVAT) schemes are used to estimate land-atmosphere moisture, energy, and momentum fluxes and provide boundary forcing to atmospheric models (AMs). Model studies of continental climate have shown that predictions of AMs are highly dependent upon soil moisture and latent energy flux between the land and the atmosphere. There are several popular SVAT schemes. Among these are the Biosphere-Atmosphere Transfer Scheme (BATS) and the Simple Biosphere model (SiB). These models have been validated to some extent through field experiments, but the validations have not extended over many terrains or through several seasons. The Michigan Cold Region Radiobrightness (MCRR) model is a first generation SVAT model that links land-atmosphere hydrologic processes in northern prairie grasses to satellite radiobrightness for the purposes of validation and correction of the SVAT state. The model has two modules, a thermal module that tracks isotherms in the soil as forced by the energy balance at the land-atmosphere interface, and a radiobrightness module that employs a halfspace soil model to predict radiobrightness at the SSM/I frequencies of 19.35, 37.0, and 85.5 GHz. The MCRR model was tested with data from our first Radiobrightness Energy Balance Experiment, REBEX-l near Sioux Falls, South Dakota, during October, 1992, through April, 1993. One cause for the poor performance of the radiobrightness module was moisture and temperature dependent absorption, emission, and scattering within the grass canopy. A refractive model for grass is to make predictions. It is then compared to REBEX-1 data for a 21 day, snow-free period in October, 1992.<>