Modeling the spectral signature of forests: Application of remote sensing models to coniferous canopies

The vertical and horizontal structure of forest canopies is one of the most important driving factors of various ecosystem processes and has received increasing attention during the past 20 years and served as an impetus for earth observation missions. In the remote sensing community, the variables which describe canopy structure are called biophysical variables, and are directly coupled with the fundamental physical problem behind remote sensing: radiative transfer in vegetation. There are basically three different approaches to interpreting biophysical variables from remotely sensed data: (1) empirical, (2) physically based, and (3) various combinations of them. The physical approach builds upon an understanding of the physical laws governing the transfer of solar radiation in vegetative canopies, and formulates it mathematically by canopy reflectance models which relate the spectral signal to biophysical properties of the vegetation. In this chapter, we will first outline the basic principles and existing physically based model types for simulating the spectral signature of forests. After this, the focus is on the specific issues related to applying these models to the complex 3D structure of coniferous canopies.