A theoretical assessment of the relation between woody canopy cover and red reflectance

Several studies have demonstrated the potential of brightness indices, especially red band reflectance, from Earth resources satellite sensors to estimate vegetation canopy cover and biomass in semiarid savannas as well as in boreal forests. These studies showed that the relation between woody canopy cover and red reflectance varies with geographical location, season, and other factors. This paper models the relation between woody canopy cover and red reflectance, using two simple geometric canopy models developed by Li-Strahler and Jasinski, respectively. Model simulations show that the relation between woody canopy cover and red band reflectance is sensitive to changes in background reflectance, canopy reflectance, solar zenith angle, and topography, which together determine the intercept, slope, and linearity of the relation. The nwdel results provide a theoretical framework that serves as a guide for the most effective conditions for the use of reflectance measurements to estimate canopy cover to be selected a priori. It is predicted that woody canopy cover is best estimated with the use of red band measurements acquired at a solar zenith angle less than 30° in a season when the contrast between background reflectance and canopy reflectance is the largest during the year.