Vertical profiling of chlorophyll within wheat canopies using multi-angular remote sensing data

CHRIS-PROBA data were acquired at a test site near Munich, Germany, during the vegetation periods of 2004 and 2005. CHRIS provides angular monitoring of land surfaces at up to five different angles, which were used to investigate the possibility of deriving chlorophyll content of wheat (Triticum aestivum L. cv. Achat) at the tops of the canopies and in the lower, less illuminated parts of the canopies. The differentiation of sun and shade chlorophyll content enables a better estimation of the overall photosynthetic capacity of a canopy and may prove to be a useful tool for the monitoring of plant diseases. Ground measurements were carried out on the test fields to validate the hyperspectral data. The chlorophyll absorption integral (CAI) was used to estimate leaf chlorophyll contents per unit surface area (in mg·m-2) of sun and shade parts of the wheat canopies. Slight forward view angles turned out to be the most promising for estimating chlorophyll contents: near-nadir forward view angles enable the estimation of chlorophyll contents of both the sun layer and the shade layer. The backward-pointing 36° and 55° view angles exhibit moderate correlations with sun chlorophyll a and chlorophyll b, and the forward-pointing 36° view angle is highly correlated with shade chlorophyll a and chlorophyll b.