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Thermal canopy photography in forestry - an alternative to optical cover photography

Nils Nölke   , Philip Beckschäfer, Christoph Kleinn

iForest - Biogeosciences and Forestry, Volume 8, Issue 1, Pages 1-5 (2015)
doi: https://doi.org/10.3832/ifor1129-007
Published: May 07, 2014 - Copyright © 2015 SISEF

Technical Advances


Hemispherical canopy photography is a widely used technique to observe crown-related forest variables. However, standardization of this technique remains challenging, as exposure and threshold settings continue to constitute the main sources of variation of such photographs. This paper, therefore, presents a new method to overcome standardization issues by using thermal canopy photography. With a thermal camera, images are produced which are not critically limited in their dynamic range so that photographic exposure becomes irrelevant. Moreover, the high temperature contrast between “sky” and “non-sky”, resulting from extreme low sky temperatures, facilitates the unambiguous selection of a threshold which separates “sky” from “non-sky” pixels. For our comparison, we have taken canopy images with a high-resolution thermal camera (VarioCam hr head [Infratec, Dresden, Germany]) and an optical camera (Nikon D70s). The correlation of canopy closure values derived from the image pairs was r = 0.98. Our findings thus show that thermal canopy photography is a promising and simple to use alternative to optical canopy photography, because it limits possible sources of variability, since exposure settings and threshold definition cease to be an issue.

  Keywords


Hemispherical Photographs, Exposure, Thresholding, Thermal Images, Canopy Structure

Authors’ address

(1)
Nils Nölke
Philip Beckschäfer
Christoph Kleinn
Chair of Forest Inventory and Remote Sensing, Georg-August-Universität Göttingen, Büsgenweg 5, D-37077 Göttingen (Germany)

Corresponding author

 
Nils Nölke
nnoelke@gwdg.de

Citation

Nölke N, Beckschäfer P, Kleinn C (2015). Thermal canopy photography in forestry - an alternative to optical cover photography. iForest 8: 1-5. - doi: 10.3832/ifor1129-007

Academic Editor

Francesco Ripullone

Paper history

Received: Sep 17, 2013
Accepted: Mar 13, 2014

First online: May 07, 2014
Publication Date: Feb 02, 2015
Publication Time: 1.83 months

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