| Abstract | Geometric optical (GO) models have been widely used in remote sensing applications because of their simplicity and ability to simulate the angular variation of remote sensing signals from the earth's
surface. GO models are generally accurate for the visible part of the solar spectrum, but less accurate at near-infrared wavelengths at which multiple scattering in plant canopies is the strongest within the solar spectrum. Although turbid-media
radiative transfer (RT) methods have been introduced to GO models to cope with the second and higher order scattering, the problem of canopy geometrical effects on multiple scattering still remains and becomes the main obstacle in GO model
applications. In this paper, we propose and test a multiple scattering scheme to simulate angular variation in multiply scattered radiation in plant canopies. This scheme is based on the various view factors between sunlit and shaded foliage and
background and allows the geometrical effects to propagate to the second and higher order scattering simulations. As the view factors depend on the canopy geometry, the scheme is particularly useful in GO models. This new scheme is implemented in the
4-Scale model (Chen and Leblanc, 1997, IEEE Transactions on Geoscience & Remote Sensing 35:1316-1337), which previously used band-specific multiple scattering factors. With the use of the scheme, these factors are no longer needed and the multiple
scatttering at a given wavelength and angle of observation can be automatically computed. Improvements made with this scheme are shown through comparison of modelled results with the top-of-canopy (i.e., PARABOLA) and airborne (i.e., POLDER)
measurements. Examples of canopy-level hyperspectral signatures simulated using the scheme are also shown. |