Remote sensing of solar radiation absorbed and reflected by vegetated land surfaces

The problem of remotely sensing the amount of solar radiation absorbed and reflected by vegetated land surfaces was investigated with the aid of one- and three-dimensional radiative transfer models. Desert vegetation was modeled as clumps of leaves randomly distributed on a bright dry soil with a ground cover of generally less than 100%. Surface albedo (ALB), fraction of photosynthetically active radiation absorbed by the canopy (FAPAR), fractions of solar radiation absorbed by the canopy (FASOLAR) and soil (FASOIL), and normalized difference vegetation index (NDVI) were calculated for various illumination conditions. The magnitude of errors involved in the estimation of surface albedo from broadband monodirectional measurements was assessed. The nature of the relationships between NDVI vs. FASOLAR, FAPAR, FASOIL, and ALB and their sensitivity to all problem parameters were investigated in order to develop simple predictive models. The relationship between NDVI measured above the atmosphere and that sensed above the canopy at the ground surface was studied to characterize atmospheric effects