Comparison of ERS wind-scatterometer and SSM/I data for sahelian vegetation monitoring

ERS wind scatterometer (WSC) and SSM/I data are compared for monitoring the seasonal variation of herbaceous vegetation over a sahelian region. Tempor al evolution of polarization difference brightness temperatures derived fro m SSM/I data and WSC backscattering coefficient acquired at 45 degrees of i ncidence angle over four different sites during the period 1992-1993, exhib its a marked seasonality with opposite and symmetrical trends, Observed dif ferences between both signals are mainly attributed to atmospheric effects affecting SSM/I data. The use of a semi-empirical model during the 1992 rai ny season shows that Delta T temporal evolution is mainly due to the variat ion of integrated water vapor content of the atmosphere, surface, and air t emperature, soil moisture content, and bare soil fraction area. In order to retrieve biomass from SSM/I data, an inversion procedure is performed and compared to previous results obtained with ERS WSC data. The absence of acc urate atmospheric data over the Sahel, combined with the sensitivity of the passive model to soil moisture leads to poor results with regard to biomas s retrieval from SSM/I data.