Abstract
Correspondences of the relationship between normalized difference vegetation index (NDVI) and surface radiative temperature (Ts) to surface conditions were analyzed at vegetated areas in the tropical monsoon zone in Thailand using NOAA/AVHRR image data. As a result, NDVI-Ts relationship showed clear seasonal variations responding to variations of surface conditions of dry and wet seasons. And it was suggested that each pixel of NOAA/AVHRR image data over study sites can be treated as a mixed pixel composed of relatively characteristic surfaces such as vegetated surfaces, wet soil surfaces, and dry soil surfaces. A model describing NDVI-Ts relationship based on surface energy balance depending on this concept was proposed. Theoretical analysis using this model suggested that NDVI-Ts relationship reflects surface moisture condition. A regional scale latent heat flux map was produced as an example of expansion of observed flux data to regional scale depending on the mixed pixel concept. And it was suggested that to estimate regional flux by this method, the flux data are needed that are observed at the surfaces extremely different from each other such as dense vegetated surface and non-vegetated bare soil surface.
