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.
Cite this paper
Reid, T. & Essery, R. (2013). New Methods to Quantify Canopy Structure of Leafless Boreal Birch Forest from Hemispherical Photographs. Open Journal of Forestry, 3, 70-74. doi: 10.4236/ojf.2013.32012.
 Antonarakis, A. S., Richards, K. S., Brasington, J., & Muller, E. (2010). Determining leaf area index and leafy tree roughness using terrestrial laser scanning. Water Resources Research, 46, W06510.
 Chapman, L. (2007). Potential applications of near infrared hemispherical imagery in forest environments. Agricultural and Forest Meteorology, 143, 151-156. doi:10.1016/j.agrformet.2006.12.006
 Coté, J.-F., Widlowski, J.-L., Fournier, R. A., & Verstraete, M. M. (2009). The structural and radiative consistency of three-dimensional tree reconstructions from terrestrial lidar. Remote Sensing of Environment, 113, 1067-1081. doi:10.1016/j.rse.2009.01.017
 Dozier, J., & Frew, J. (1990). Rapid calculation of terrain parameters for radiation modeling from digital elevation data. IEEE Transactions on Geoscience and Remote Sensing, 28, 963-969.
 Essery, R., Pomeroy, J., Ellis, C., & Link, T. (2008). Modelling longwave radiation to snow beneath forest canopies using hemispherical photography or linear regression. Hydrological Processes, 22, 27882800. doi:10.1002/hyp.6930
 Frazer, G., Canham, C., & Lertzman, K. (1999). Gap light analyzer (GLA): Imaging software to extract canopy structure and gap light transmission indices from true-colour sheye photographs, users manual and program documentation. Burnaby: Simon Fraser University.
 Ishida, M. (2004). Automatic thresholding for digital hemispherical photography. Canadian Journal of Forest Reseach, 34, 2208-2216.
 Kriegler, F., Malila, W., Nalepka, R., & Richardson, W. (1969). Preprocessing transformations and their effect on multispectral recognition. Proceedings of the 6th International Symposium on Remote Sensing of Environment. Ann Arbor, MI: University of Michigan, 97-131.
 Lang, M., Kuusk, A., Mttus, M., Rautiainen, M., & Nilson, T. (2010). Canopy gap fraction estimation from digital hemispherical images using sky radiance models and a linear conversion method. Agricultural and Forest Meteorology, 150, 20-29.
 Link, T., Marks, D., & Hardy, J. (2004). A deterministic method to characterize canopy radiative transfer properties. Hydrological Processes, 18, 3583-3594.
 Nobis, M., & Hunziker, U. (2005). Automatic thresholding for hemisphericalcanopy photographs based on edge detection. Agricultural and Forest Meteorology, 128, 243-250.
 Ovhed, M., & Holmgren, B. (1995). Spectral quality and absorption of solar radiation in a mountain birch forest, Abisko, Sweden. Arctic and Alpine Research, 27, 380-388. doi:10.2307/1552031
 Pueschel, P., Buddenbaum, H., & Hill, J. (2012). An efficient approach to standardizing the processing of hemispherical images for the estimation of forest structural attributes. Agricultural and Forest Meteorology, 160, 1-13.
 van Gardingen, P., Jackson, G., Hernandez-Daumas, S., Russell, G., & Sharp, L. (1999). Leaf area index estimates obtained for clumped canopies using hemispherical photography. Agricultural and Forest Meteorology, 94, 243-257.
 Zhang, Y., Chen, J. M., & Miller, J. R. (2005). Determining digital hemispherical photograph exposure for leaf area index estimation. Agricultural and Forest Meteorology, 133, 166-181.