Canadian Forest Service Publications
A method for estimating canopy openness, effective leaf area index, and photosynthetically active photon flux density using hemispherical photography and computerized image analysis techniques. 1997. Frazer, G.W.; Trofymow, J.A.; Lertzman, K.P. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Information Report BC-X-373. 73 p.
Issued by: Pacific Forestry Centre
Catalog ID: 4867
Indirect optical techniques have been used increasingly in place of more laborious and often-destructive direct methods to derive stand-level estimates of gap fraction distribution, canopy openness, and effective leaf area index. Hemispherical canopy photography, combined with digital image analysis, is one indirect technique that has proven to be a fast and efficient way to measure various attributes of canopy structure and to predict seasonal patterns of forest canopy light transmission.
The Canadian Forestry Service, Pacific Forestry Centre, utilized hemispherical photography and paired LAI-2000 Plant Canopy Analyzers to measure gap fraction distribution, canopy openness, effective leaf area index, and seasonally-integrated understory light levels in several age sequences of Coastal Western Hemlock and Douglas-fir forests on southern Vancouver Island, British Columbia, Canada. The main purpose of the research was to document some of the structural changes caused by the conversion of old-growth temperate forests to second growth. This report describes the general theory, practical application, and technical shortcomings associated with the hemispherical photography and image-processing component of this project. The field and analytical methodologies used in this research are presented as a case study for those interested in similar ecological applications.
Current hemispherical image analysis systems have not kept pace with evolving digital technologies, computer hardware and software, or scientific models. A number of improvements must therefore be made to realize the full potential of this technique. Hemispherical models do not take into account the effects of local weather conditions, nor do they compensate for the effects of regional landform geometry and site orientation on the distribution of direct and diffuse solar radiation. Post-processing techniques that would correct for some of these deficiencies are possible, but only if intermediate summary data are made accessible to the end-user.