
Modeling Tools
Microwave Radiative Transfer Model
The microwave model used at NSSTC is a coherent radiative transfer (CRT) model developed for a stratified medium characterized by potentially complex moisture and temperature profiles (Njoku and Kong, 1977). The model is used to convert measured or modeled soil moisture and temperature conditions to microwave brightness temperatures for purposes of validating remote sensing observations. The model is based on the vertical profiles of temperature and emissivity, the latter of which is strongly controlled by the soil moisture content. Required input variables to the CRT are surface temperature, vegetation water content, and profiles of soil moisture, temperature and porosity . The brightness temperature, neglecting the effects of surface roughness and vegetation, is calculated by integrating over depth an expression involving the wavelength, observation angle from nadir, and the vertical profiles of temperature (T) and complex dielectric constant (e). Although soil moisture does not appear explicitly in the integral, it strongly influences e. For uniform profiles of T and e, the solution is equivalent to that of the Fresnel reflectance function. The dielectric constant is estimated by either the mixing model of Dobson et al. (1985) or Wang and Schmugge (1980). The following link gives a detailed description of the CRT and a comparison of the mixing models:
Crosson, W.L. , C.A. Laymon, R. Inguva and C. Bowman, 2002. Comparison of two microwave radiobrightness models and validation with field measurements. IEEE Trans. on Geosci. and Rem. Sens., 40, 143152.
