Inversion of the PROSPECT + SAIL canopy reflectance model from AVIRIS equivalent spectra: Theoretical study

Abstract

The potentials and limits of estimating canopy parameters are investigated using only a reflectance spectrum in the optical domain, and the PROSPECT + SAIL model. Simulations are performed on AVIRIS (Airborne Visible / Infrared Imaging Spectrometer) equivalent spectra, corrected for the atmospheric effects. It is established that this model is numerically invertible. The sensitivity analysis of reflectance spectral features to changes in the values of canopy parameters (leaf mesophyll structure N, chlorophyll a + b concentration Cab, water depth Cw, leaf area index, LAI, and average leaf inclination angle θ1) suggests that the accuracy of the inversion procedure needs some constraints. The Cab and Cw parameters, which describe the leaf physiological status, can be generally retrieved with a reasonable accuracy; it is somewhat difficult to estimate the canopy geometrical parameters (LAI and θ1) separately. Determining the fraction of absorbed photosynthetic active radiation (APAR) with parameters derived from the inversion procedure is discussed.