Spatial variability of land surface emissivity in the thermal infrared band: Spectral signature and effective surface temperature

Abstract

Experimental access to effective surface parameters, surface temperature, and emissivity, relevant to satellite investigations in the thermal infrared band (TIR), is addressed and discussed. The spatial variability of the broad (8–14μ) emissivity was measured over an overall homogeneous area with a movable measuring system. Spectral ground radiances were also measured at many places, the spatial average of which is assumed to represent the effective spectral ground radiance. The effective surface temperature is obtained through renormalization of the effective emissivity signature over the RMS broad band emissivity previously measured. The method is shown to produce the effective surface temperature with an accuracy better than 1 K, without any direct temperature measurement. From the effective signature, the channel emissivities pertaining to a given instrument can be calculated. This has been done for NOAA-11/AVHRR Channels 4 and 5. A preliminary test was made to try and validate nighttime satellite-derived surface temperature by comparison with field effective temperature. The image was acquired during the field experiment. The first result of this attempt is encouraging, although only qualitative because of standard atmospheric corrections. Orientation of future work for better accuracy and reliability is discussed as well.