FEASIBILITY OF LAND SURFACE-TEMPERATURE AND EMISSIVITY DETERMINATION FROM AVHRR DATA

The surface temperature and emissivity of natural media are very useful to know for many applications. in this article, we show that the scheme proposed in our previous work to retrieve both the spectral emissivities and land surface temperature from AVHRR data is feasible. From the concept of the temperature independent spectral index (TISI) in thermal infrared bands, we recall how the emissivities in Channels 3, 4, and 5 are obtained by combining day and night data, assuming that the TISI for Channels 3, 4, and 5 of AVHRR does not vary substantially between day and night, which has been checked for a particular data acquired in situ over the La Crau test site in Southeastern France. Once the emissivities in Channels 4 and 5 are known, the surface temperature can be determined using the local split-window method proposed in our previous work. In order to test the applicability of the method when atmospheric radiosoundings are not available, we discuss the effects of the errors generated by an approximate knowledge of the atmosphere on the retrieval of both emissivity and surface temperature. It is shown that if a radiosounding or a satellite sounding (from TOVS for instance) of the atmosphere is not available, the use of a climatic atmosphere leads to satisfactory results because the retrieval of emissivity is less sensitive to atmospheric uncertainties than the temperature itself, The method is applied to one AVHRR image over La Crau and results fit with in situ measurements. The problems raised by this method and errors are then discussed, and further work to improve the method is suggested.