The hotspot effect in heterogeneous vegetation canopies and performances of various hotspot models

In an earlier paper (Qin and Goel, 1995), we reviewed various analytical hotspot models and evaluated them for homogeneous vegetation canopies by comparing them against Diana—a computer graphics, radiosity based, model. In this paper, we complete their evaluation by studying the hotspot effect of heterogeneous canopies (trees and crops). For this purpose, we first describe a computer graphics based method with which the cross‐correlation (or overlap) function that drives the hotspot effect can be accurately evaluated. We find that all the analytical hotspot models, more or less, overestimate the cross‐correlation function for tree canopies. Except the hybrid model, they perform worse in the principal cone (PC) than in the principal plane (PP); for big leaves or at low LAI or small spacing than for small leaves or at high LAI or large spacing. We investigate in detail various elements of heterogeneity (spacing distance between trees/plants, mutual shadowing between leaves and between tree crowns, crown por...

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