AIRBORNE MICROWAVE RADIOMETRY ON A SEMIARID AREA DURING HAPEX-SAHEL

Airborne microwave radiometric measurements in the framework of the HA PEX-Sahel Experiment were performed by the Push Broom Microwave Radiom eter (PBMR) and the PORTOS radiometer. The flights of both radiometers produced an original set of data covering the 1.4-90 GHz range of fre quency. The East and West Central Super Sites were the areas most inte nsively observed by the microwave radiometers. Over those sites, sever al brightness temperature (T-B) maps are available at seven dates dist ributed over a 1 month period in the middle of the rainy season. A com parison of the two radiometers demonstrates their radiometric quality and the precision of the localization of the microwave observations. A t 1.4 GHz, the vegetation had very little effect on the soil microwave emission. Maps of soil moisture were developed using a single linear relationship between T-B and the surface soil moisture. There is an im portant spatial heterogeneity in the soil moisture distribution, which is explained by both the soil moisture hydrodynamic properties and th e localization of the precipitation fields. At 5.05 GHz, the vegetatio n must be accounted for to infer soil moisture from the microwave obse rvations. A method based on a simple radiative transfer model and on m icrowave data has shown encouraging results. (C) 1997 Elsevier Science B.V. All rights reserved.