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Detection of bark beetle-attacked spruce using computer-based image analysis

University of British Columbia

The spruce beetle (Dendroctonus rufipennis Kirby) is the most destructive forest pest affecting mature spruce stands in British Columbia. A variety of responses to curtail the spread of bark beetle infestations exist. The responses, however, depend upon early detection of the infestations to minimize the cost of treatment and reduce losses of timber. It has been demonstrated that bark beetle-attacked spruce can be detected using visual interpretation of large scale colour infrared film (Churcher 1984; Churcher and McLean 1984; Murtha 1985; Murtha and Cozens 1985). These studies indicate that it is possible to distinguish attacked spruce, to some degree, by their visual colour in the photographs. The image intensities associated with trees in the photographs are profoundly influenced by factors such as the viewer's position and shape of the tree as well as the "colour" of the tree. This thesis develops a computer-based image analysis technique-projected intensity triplet space-which can be used to interpret the attack condition of a tree regardless of shading effects due to its position in the photograph or its shape. The procedure is used to classify trees in a test photo according to three beetle attack categories-unattacked, current attack and old attack. The interpretation accuracy for trees which were unattacked, fully current attacked and old attacked was high (84, 68 and 89 percent respectively). The percentages of trees from the 1983 strip attacked and 1983 pitched-out ground data classes interpreted by the computer to be attacked were very low (22 and 6 percent). The poor results for the strip attacked and pitched-out trees were attributed to the lack of evident colour differences from unattacked trees in the photographs. In cases where there were visually evident colour differences, however, the technique was able to classify the attack status reliably.

Text

2010-06-19

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http://hdl.handle.net/2429/25846

Forestry

University of British Columbia

Graduate