<title>Remote measurement of dark-green canopy chlorophyll concentration by directional reflectance spectra</title>

Abstract

We present a simple algorithm to predict canopy chlorophyll content from directional reflectance spectra. The purpose is the compensation of the branches, soil and multiple reflection effect in the reflectance in order to obtain the single leaf spectra that are more closely correlated with chlorophyll content, as already assessed in literature. The analysis is limited to leaves with a chlorophyll content higher than 25-30 µg/cm2 since we verified that their spectra are little affected by multiple leaf reflection in the green spectral region, where the leaf reflectance is mostly dependent on chlorophyll concentration. In order to understand better the nature of the canopy reflectance, we measured the reflectance spectrum of both single and multiple leaves of two kinds of plants (Pittosporum tobira and Nerium oleander), of some branches and of some brown soil. Finally, we developed an algorithm able to translate the canopy reflectance to the single leaf level. We tried the algorithm on a canopy of Pittosporum. We found that it was able to retrieve the true chlorophyll content with an error ~ 10%.