Multiple Scattering Within the FLAIR Model Incorporating the Photon Recollision Probability Approach

In this paper, a combined approach based on the adding method is incorporated into the four-scale linear model for anisotropic reflectance (FLAIR) to enhance the description of the spectrally dependent multiple-scattered radiation field of a forest canopy. The proposed scheme is based on the decomposition of the multiple-scattered radiation field into two parts. The first part deals with multiple scattering within the canopy, considering a competently black soil, and the second part deals with multiple scattering between the canopy and the background. Such advances to radiative transfer modeling are required to better exploit the potential of hyperspectral remote sensing for monitoring canopy biochemical indicators such as chlorophyll concentration and equivalent water content. The validation was performed using the multiangular data sets obtained by the airborne sensor POLarization and Directionality of the Earth´s Reflectances (POLDER) during the BOReal Ecosystem-Atmosphere Study (BOREAS) campaign of 1994. The results indicate that this approach is well suited to the FLAIR model. It is also demonstrated that the multiple-scattering problem can be parameterized by a limited number of architectural parameters and the leaf scattering coefficient.