MEASURING WATER AND CHLOROPHYLL CONTENT ON THE LEAF AND CANOPY SCALE

Abstract

ABSTRACT Interpreting hyperspectral images of forests can be challenging because reference measurements are difficult to obtain. Forest stands are too high for field spectroscopy, and up-scaling leaf reflec-tance to canopy reflectance is not straightforward. We took reflectance, transmittance and water and chlorophyll content measurements of forest leaves collected by tree climbers. On the leaf level good agreement between the measured chemical properties and reflectance model inversion re-sults was achieved. The measured spectra were up-scaled into canopy spectra using a GORT model. The up-scaled spectra agreed well with a HyMap image showing pronounced BRDF effects but worse with a “corrected” HyMap image pretending nadir viewing. INTRODUCTION Hyperspectral, also known as Imaging Spectroscopy, data have been used for deriving biochemi-cal variables like water and chlorophyll content in forests for some time ( 1 ), but current methods have not delivered unambiguous results and operational methods (