L-MEB: A simple model at L-band for the continental areas - Application to the simulation of a half-degree resolution and global scale data set.

摘要

L-band (1-2 GHz) microwave radiometry is the most relevant remote sensing technique to monitor soil moisture over land surfaces at the global scale. A synthetic multi-angular brightness temperature data set over land surfaces was simulated at 1.4 GHz, at a half-degree resolution and at the global scale (Pellarin et al., 2003a). This data set was built in order to develop and validate methods to retrieve soil moisture for near-future 1.4 GHz space missions. Brightness temperatures were computed using a simple model (L-MEB, L-band Microwave Emission of the Biosphere) based on radiative transfer equations. The L-MEB model is the result of an extensive review of the current knowledge of the microwave emission of various land covers (herbaceous and woody vegetation, frozen and unfrozen bare soil, snow, etc.) at L-Band considering that the model should be simple enough to be compatible with the simulation of a half-degree resolution and global scale data set. This model was parameterized for simulating L-band observations (in the 1-2 GHz range) but the model equations remain valid in a low frequency range (about 1 to 10 GHz) and thus including the L-, C- and X-bands. The soil and vegetation characteristics needed to initialize the L-MEB model were derived from existing land cover maps. Continuous simulations from a land-surface scheme for 1987 and 1988 provided time series of the main variables driving the L-MEB model: soil temperature at the surface and at depth, surface soil moisture, proportion of frozen surface soil moisture, and snow cover characteristics (depth, density, grain size, liquid water content). The different components of the emission model are described in the following sections. These sections present the general formulation of TB for a composite pixel and the microwave emission modules for soil, vegetation-covered surfaces, open water, snow-covered surfaces and atmospheric effects.