INVERSION OF THE PROSPECT + SAIL CANOPY REFLECTANCE MODEL FROM AVIRIS EQUIVALENT SPECTRA - THEORETICAL-STUDY

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 C(ab), water depth C(w), leaf area index, LAI, and average leaf inclination angle theta(1)) suggests that the accuracy of the inversion procedure needs some constraints. The C(ab) and C(w) 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 theta(1)) separately. Determining the fraction of absorbed photosynthetic active radiation (APAR) with parameters derived from the inversion procedure is discussed.