Estimation of regional surface resistance to evapotranspiration from NDVI and thermal-IR AVHRR data

We tested a hypothesis that the relationship between surface temperature and canopy density is sensitive to seasonal changes in canopy resistance of conifer forests. Surface temperature (T_s) and canopy density were computed for a 20×25 km forested region in Montana, from the NOAA/AVHRR for 8 days during the summer of 1985. A forest ecosystem model, FOREST-BGC, simulated canopy resistance (R_c) for the same period. For all eight days, surface temperatures had high association with canopy density, measured as Normalized Difference Vegetation Index (NDVI) (R²=0.73-0.91), implying that latent heat exchange is the major cause of spatial variations in surface radiant temperatures. -from Authors