Radiative Transfer in the IAGL Land Surface Model

Abstract

The radiation subscheme of a land surface model is presented. It is based on the two-stream approximation and includes explicit calculations for the scattering coefficients of direct and diffuse radiation. It applies to horizontally homogenous vegetation canopies, for both solar and thermal infrared radiation. Leaf orientation is accounted for by a leaf inclination index. An intercomparison with field data indicates that, when using general vegetation type?dependent parameters, the radiation scheme has an absolute accuracy on the order of a few percent for the amount of radiation absorbed by the surface and up to 10% as far as the partitioning between soil and vegetation is concerned. Finally, the radiation scheme is used in order to derive a method to calculate an effective leaf area index for transpiration that is physically based and consistent with observations.