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Title: Assessment of automatic gap fraction estimation of forests from digital hemispherical photography
Authors: Jonckheere, Inge
Nackaerts, K
Muys, Bart
Coppin, Pol #
Issue Date: Sep-2005
Publisher: Elsevier science bv
Series Title: Agricultural and forest meteorology vol:132 issue:1-2 pages:96-114
Abstract: Thresholding is a central part of the analysis of hemispherical images in terms of gap fraction and leaf area index (LAI), and the selection of optimal thresholds has remained a challenge over decades. The need for an objective, automatic, operator-independent thresholding method has long been of interest to scientists using hemispherical photography. This manuscript deals with the comparison of a wide variety of different well-known automatic thresholding techniques against the subjective manual method, using high-dynamic range digital hemispherical photographs. The performance of the different thresholding methods was evaluated based on: (1) visual inspection by means of a multi-criteria decision system and (2) quantitative analysis of the methods' sensitivity to an overall performance criterium. The automatic Ridler clustering method proved to be the most robust thresholding method for various canopy structure conditions. This automatic method might be the best solution for a fast, reliable and objective use of hemispherical photographs for gap fraction and LAI estimation in forest stands, given that the threshold setting is no longer manually performed. The fine-tuning potential of local thresholding methods to better address particular photographic limitations (e.g. over-exposure in a certain image region) is also presented. (c) 2005 Elsevier B.V. All rights reserved.
ISSN: 0168-1923
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Division Forest, Nature and Landscape Research
Division M3-BIORES: Measure, Model & Manage Bioresponses (-)
# (joint) last author

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