An evaluation of hotspot models for vegetation canopies

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Abstract
Hotspot effect is a typical angular reflectance signature of vegetation canopies. In this paper, the basic principles for various physical models for the hotspot effect of vegetation canopies are reviewed. The performance of several analytical models for homogeneous canopies are evaluated by comparing with a computer‐graphics based model—Diana. Almost all of these models perform better for a canopy with smaller leaves, higher LAI or when the solar zenith angle is high. Among these models, the mixed model, which quantitatively takes into account of the leaf size, shape and orientation by adding a geometrical‐optical kernel to modeling of the hotspot for the continuous canopies, performs best in most cases. The influences of both canopy structure and sun geometry on hotspot effect, especially hotspot width, are examined and the topics for further study are suggested.

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