Institute of Astrophysics and Atmospheric Physics, Estonian Academy of Sciences, EE2444 Tõravere, Tartu, Estonia
Two analytical models of vegetation canopy reflectance are combined. The new model considers the diffuse and specular reflection of optical radiation on leaves, the canopy hot spot and nonlambertian soil. Diffuse fluxes are treated in a four-stream approximation. An elliptical distribution has been used for leaf inclination. Comparisons of the models demonstrate a good agreement.
The Fortran-77 code of the model can be used in MS-DOS and UNIX environment. A complete set of algorithms of the new model is appended.
In the well-known SAIL model the treatment of multiple scattering of radiation and diffuse sky radiation is very rational. At the same time there are some difficulties representing the specific features of canopy reflectance angular distribution with the SAIL model, caused by single scattering of direct solar radiation. These difficulties have been successfully overcome in the Nilson-Kuusk model. Using the advantages of each model, a new computationally efficient model has been developed. The new model has the precision of the Nilson-Kuusk model and the speed of the SAIL model, it works about 50 times faster than the Nilson-Kuusk model. The last property is especially important in real-time calculations and in solving of inverse problems when numerous calculations with the model are necessary.