CHARACTERIZATION OF LAND-SURFACE THERMAL STRUCTURE FROM NOAA-AVHRR DATA OVER A NORTHERN ECOSYSTEM

This paper focuses on the estimation and analysis of surface thermal p arameters (emissivities and surface temperatures) in a nordic environm ent (Quebec, Canada). The land cover in this region varies from boreal forest in the south to tundra in the north. The thermal parameters ar e estimated from two variants of a new model that combines the radianc es of the short wave infrared (SWIR) spectral band [advanced very high resolution radiometer (AVHRR) channel 3: 3.55-3.93 mu m] and the ther mal bands (AVHRR channel 4: 10.5-11.5 mu m; and AVHRR channel 5: 11.5- 12.5 mu m). The study, carried out for images acquired on different da tes, reveals that, in most situations, the two approaches allow the se paration of emissivities and surface temperatures. Analysis of the var iations of the estimated emissivities in relation to surface patterns shows that they are slightly variable in spectral bands 4, and 5, with values generally greater than 0.95. Variations are more important in the SWIR channel, where values less than 0.90 appear, especially in ur ban areas. In general, surface emissivities increase with the density of the vegetation cover. Moreover, for densely vegetated areas, SWIR s urface reflectivities, which can be derived from emissivities, appear to be well correlated with the reflectivities of the AVHRR visible cha nnel. As with emissivities, variations of the estimated land surface t emperatures (LST) in relation to vegetation density, characterized by the normalized difference vegetation index (NDVI), were considered. Th e relations between the two parameters (LST and NDVI) show essentially two opposite directions of linear variations (positive and negative c orrelations). In the light of the main results obtained the synergisti c use of the different spectral regions (visible, near mid-, and therm al infrareds) could be very useful in the parameterization of boreal e cosystems. (C) Elsevier Science Inc., 1997.