TITLE:
New Methods to Quantify Canopy Structure of Leafless Boreal Birch Forest from Hemispherical Photographs
AUTHORS:
T. D. Reid, R. L. H. Essery
KEYWORDS:
Hemispherical Photography; Image Processing; Leafless Canopies; Boreal Forest; Snow; Abisko
JOURNAL NAME:
Open Journal of Forestry,
Vol.3 No.2,
April
30,
2013
ABSTRACT:
Hemispherical photography has been used for many years to measure the physical characteristics of forests, but most related image processing work has focused on leafy canopies or conifers. The boreal forest contains large areas of deciduous trees that remain leafless for over half the year, influencing surface albedo and snow dynamics. Hemispherical photographs of these sparse, twiggy canopies are difficult to acquire and analyze due to bright bark and reflections from snow. This Note presents new methods for producing binary images from hemispherical photographs of a leafless boreal birch forest. Firstly, a thresholding method based on differences between colour panes provides a quick way to remove bright sunlit patches on vegetation. Secondly, an algorithm for joining up fragmented pieces of tree after thresholding ensures a continuous canopy. These methods reduce the estimated hemispherical sky view fraction by up to 6% and 3%, respectively. Although the processing remains subjective to some degree, these tools help to standardize analysis and allow the use of some photographs that might have previously been considered unsuitable for scientific purposes.