The propagation of foliar biochemical absorption features in forest canopyreflectance: A theoretical analysis

Remotely sensed estimates of the foliar biochemical content of vegetation c anopies could be used to derive indicators of ecosystem functioning at regi onal to global scales. In the past decade, the number of studies have repor ted strong correlations between the reflectance spectra of vegetation canop ies and their foliar biochemical content. However, these studies have commo nly employed multiple regression techniques or spectral indices to determin e biochemical content, which have been found to be highly sensitive to vari ation in canopy architecture [such as leaf area index (LAI) and canopy clos ure] and understory. To date, these effects combined with the low signal-to -noise ratios of airborne spectrometers have inhibited the development of r obust and portable spectral techniques for the estimation of canopy biochem ical content. This paper reports on a theoretical study in which a leaf mod el, LIBERTY (leaf incorporating biochemicals exhibiting reflectance and tra nsmittance yields), characterized specifically for conifer needles, was cou pled with a hybrid geometric/radiative transfer bidirectional reflectance d istribution function FLIGHT (forest light) model. By varying leaf biochemic al content, LAI, canopy closure and understory, we analyzed the simulated c anopy reflectance spectra to determine if the biochemical adsorption featur es in leaf spectra were preserved at the canopy scale. Absorption features or wavelength regions that were both related to a specific biochemical of i nterest (water, lignin-cellulose) and persistent at the scale of both the l eaf and the canopy were identified at a number of wavelengths or wavelength regions. (C)Elsevier Science Inc. 1999.