Satellite observations using microwave radiometers operating near the window regions are strongly affected by surface emissivity. Presently, the measurements obtained over land are not directly utilized in numerical weather prediction models because of uncertainties in estimating the emissivity. A model was developed to simulate the microwave emissivity over various land conditions (Weng et al. 2001). However, the discrepancy between simulated and observed emissivity on the snow conditions is quite significant especially for higher microwave frequencies due to inaccurate snow optical parameters based on the small perturbation theory which is valid only for lower frequencies. This study will develop a new method to compute the snow optical parameters using generalized Mie theory. The coherent scattering due to closely spaced particles within a snow layer is explicitly taken into account without neglecting the near-field effects on the phase function or asymmetry factor. The snow emissivity model is derived as a function of the effective particle size, particle volume fraction and the snow depth. It is shown that the discrepancy between simulated and observed emissivity on the snow conditions is greatly reduced.

Weng, F., B. Yan, and N. Grody, 2001: A microwave land emissivity model, JGR, in press.