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Microwave emissivities of land surfaces are estimated from special sensor microwave/imager (SSM/I) observations by removing the contributions from the atmosphere, clouds, and rain using ancillary satellite data (International Satellite Cloud Climatology Project (ISCCP) and TIROS Operational Vertical Sounder (TOVS) products). In the first step, cloud-free SSM/I observations are isolated with the help of collocated visible/infrared satellite observations (ISCCP data). The cloud-free atmospheric contribution is then calculated, from an estimate of the local atmospheric temperature-humidity profile (TOVS retrieval). Finally, with the surface skin temperature derived from IR observations (ISCCP estimate), the surface emissivity is calculated for all the SSM/I channels. As an exploration the method is applied to the SSM/I data for four months in 1991 within the Meteosat observation area. The magnitude and fluctuations of the atmospheric contributions are estimated along with the effect of surface temperature variations. Correspondences between geographical and seasonal patterns of the emissivities and topography, vegetation, flooding, and snow cover are analyzed. The potential for using microwave emissivities to monitor vegetation phenology and surface properties at regional and continental scale is investigated, and the possibility of retrieving atmospheric parameters (water vapor content, cloud liquid water path, and precipitation) over land is discussed.