Performance of the PROSPECT leaf radiative transfer model version 4 for Norway spruce needles

Abstract

Leaf optical properties (LOPs) are a key input parameter for vegetation canopy radiative transfer models. The uncertainty introduced in the measurement and/or the simulation of this spectral information determines a final reliability of the modelled canopy reflectance. The broad-leaf radiative transfer model PROSPECT version 3.01 has been previously applied for some needle-leaf type species (e.g. pine trees) to estimate biochemical parameters through its inversion. Nevertheless, in a particular case of Norway spruce (Picea abies (L.) Karst.) PROSPECT 3.01 showed a poor performance in near infrared wavelengths and had to be recalibrated. Therefore, the applicability of PROSPECT version 4, which has been recently released, is verified for this type of leaves in this experiment. Forward simulations of an optimized version of the original PROSPECT 4 suggest that it is possible to reduce the average RMSE of reflectance and transmittance from 8% to 3.5- 4 % in the near infrared domain. For this achievement, the absorption coefficients for chlorophyll and dry matter together with the refractive index had to be simultaneously optimized via model inversion using measured LOPs of Norway spruce needles.