文献类型：期刊文献

英文题名：A Universal Canopy Gap Fraction Model for Forests with Various Tree Distributions Based on Nilson's Models Considering Directional Overlaps Among Crowns

作者：Geng, Jun[1,2] Roujean, Jean-Louis[2] Kuusk, Andres[3] Pang, Yong[4] Tu, Lili[2,5] Zhang, Teng[1] Chen, Jing M.[6,7]

第一作者：Geng, Jun

机构：[1] Hefei University of Technology, Hefei, 230009, China; [2] Centre d’Etudes Spatiales de la BIOsphère [CESBIO], Toulouse III University, Toulouse, 31400, France; [3] Department of Economics, Estonia; [4] Institute of Forest Resource Information Technique, Chinese Academy of Forestry, Beijing, 100091, China; [5] College of Resources and Environment, Anhui Agricultural University, Hefei, 23000, China; [6] School of Geographical Sciences, Fujian Normal University, Fuzhou, 350108, China; [7] Department of Geography and Program in Planning, University of Toronto, Toronto, ON, M5S 3G3, Canada

年份：2023

外文期刊名：SSRN

收录：EI(收录号：20230317870)

语种：英文

外文关键词：Forestry - Plants (botany) - Poisson distribution - Space optics

摘要：An accurate estimation of forest canopy gap fraction (GF) is a prerequisite for remote sensing retrievals of several associated canopy parameters e.g. leaf area index, fAPAR (fraction of photosynthetically active radiation absorbed by the canopy), clumping index, etc. A universal canopy GF model for forests is required for various tree distribution patterns on flat and slopping terrains, yet existing models so far do not possess all these abilities simultaneously. For example, the Neyman type-A model, the Poisson model, and the hypergeometric model are suitable only to forests with clumped, random, and regular tree distributions, respectively. In this regard, the suite of Nilson’s canopy GF models developed for forests with various tree distributions have the potential to become universal models. For this purpose, this study attempts to overcome the following limitations of these models to make them be true universally applicable: (1) canopy GF calculated by the Nilson’s models is mostly accurate for various tree distributions at nadir whereas at off-nadir, it is either underestimated for clumped tree distributions or overestimated for regular tree distributions at off-nadir. And (2) Nilson’s models were developed for flat terrains and untested for sloping terrains. Herein, two Nilson’s models are modified by expanding the calculation of overlap among crowns (OAC) at nadir to the whole hemispherical space. The results show that all canopy GF simulations in the new models (New91 and New99) show higher consistency with ray-tracing results than those in original Nilson’s models in all directions, highlighting the need to consider directional OAC. The modified models (especially for New99) are suitable for various tree distributions on flat and slopping terrains and therefore increased the universality of the original Nilson’s models suitable for a wide-range of remote sensing applications. New99 can be deemed as a universal canopy GF model for forests with various tree distributions. ? 2023, The Authors. All rights reserved.