Surface temperature and soil moisture retrieval in the Sahel from airborne multifrequency microwave radiometry

Bipolarized microwave brightness temperatures of Sahel semiarid landscapes are analysed at two frequencies: 5.05, and 36.5 GHz. These measurements were performed in Niger, West Africa, by the radiometer PORTOS in the framework of the Hydrologic Atmospheric Pilot Experiment in the Sahel (HAPEX-Sahel), during the end of the rainy season (August-September) 1992. The airborne microwave data were collected simultaneously with radiosoundings of the atmosphere, and ground measurements of surface temperature, soil moisture, and biomass of several vegetation types. After estimating the soil roughness parameters it is shown that two kinds of vegetation canopies must be considered: sparse canopies and patchy canopies including bare soil strips. The mixed soil-vegetation microwave emission is analysed using a random continuous approach. The sparse canopies emission is efficiently described by considering the vegetation layer as homogeneous. Conversely, a simple soil-vegetation mixing equation must be used for the patchy canopies. The problem with retrieving the canopy temperature and the near-surface soil moisture is addressed. For every canopy, soil moisture retrieval can be achieved. Soil moisture maps are proposed. The canopy temperature can also be retrieved with good accuracy provided both vertical (v) and horizontal (h) polarizations are available