SURFACE-TEMPERATURE AND SOIL-MOISTURE RETRIEVAL IN THE SAHEL FROM AIRBORNE MULTIFREQUENCY MICROWAVE RADIOMETRY

Bipolarize microwave brightness temperatures of Sahel semiarid landsca pes are analyzed at two frequencies: 5.05 and 36.5 GHz, These measurem ents were performed in Niger, West Africa, by the radiometer PORTOS in the framework of the Hydrologic Atmospheric Pilot Experiment in the S ahel (HAPEX-Sahel), during the end of the rainy season (August-Septemb er 1992), The airborne microwave data were collected simultaneously wi th radiosoundings of the atmosphere, and ground measurements of surfac e 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 p atchy canopies including bare soil strips, The mixed soil vegetation m icrowave emission is analyzed using a random continuous approach. The sparse canopy emission is efficiently described by considering the veg etation layer as homogeneous. Conversely, a simple soil-vegetation mix ing equation must be used for the patchy canopies, The problem with re trieving the canopy temperature and the near-surface soil moisture is addressed, For every canopy, soil moisture retrieval is possible. Soil moisture maps are proposed. The canopy temperature can also be retrie ved with good accuracy provided both vertical (v) and horizontal (h) p olarizations are available. It is shown that the retrieved variables c an be used to separate landscape units through a classification proced ure.