Phase: RAMI IV
A directional multispectral forest reflectance model has been developed in the group of vegetation remote sensing at Tartu Observatory. The first version of the model was published in Nilson, T. and Peterson, U. A forest canopy reflectance model and a test case, Remote Sens. Environment, 37:131-142 (1991). More recent publications use a newer version of the model. More informationon on Forest Reflectance and Transmittance Model (FRT) can be found here.
The FRT model may be classified as a hybrid-type model, including the properties both geometrical and radiative transfer equation-based models. Tree crown envelopes are modeled as ellipsoids of rotation or cones in the upper and cylinders in the lower part (Fig.1). Leaves and branches are uniformly distributed in the crown and spherically oriented.
Several tree classes of different size and/or species are possible (Fig.1). Within each class, trees are considered identical.
A homogeneous layer of vegetation is present on the ground surface. A forested scene is divided into four components: sunlit tree crowns, sunlit ground vegetation, shaded crowns, and shaded ground vegetation. The radiances of these components are estimated with the help of geometrical and radiative transfer concepts. Special attention is paid to the adequate modeling of single scattering reflectance components, whereas reflectance caused by multiple scattering of radiation in the canopy is more roughly modeled. The model works in the optical domain of radiation, 400-2400 nm, spectral resolution is 1 nm.
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