The emissivity Spatial, Spectral and Angular Variations
The land AMSU emissivities have been analysed and their angular and their frequency dependencies examined. The emissivity varies smoothly in frequency (at least for snow free areas). This makes it possible to extrapolate, at a specific location, the emissivity at sounding frequencies from the window channel estimates. The temporal and spatial variations of AMSU emissivities have also been studied. In addition, good agreement has been found between AMSU, SSM/I, AMSR-E and TMI emissivities. AMSU emissivities varies with the frequency, with the surface type and also with the observation scan angle. For instance, there is a strong angular dependence of the AMSU emissivity over bare soils whereas it is negligible over forested land. Additional resulats are presented in Karbou et al. 2005.