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The detection of mountain pine beetle green attacked lodgepole pine using compact airborne spectrographic imager (CASI) data Heath, Jamie

Abstract

The mountain pine beetle (Dendroctonus ponderosae Hopkins) is the major pest of mature lodgepole pine (Pinus contorta var. ladfolia) in western North America. The present method of surveying bark beetle attack is by sketch mapping or photographing the location of last year's damaged trees (red attack) from an aircraft. The area around the red attack is then ground probed to find currently infested trees that have not changed colour (green attack). If there was a way to locate both the "red and green attack" pine trees without the need to ground probe, it would greatly assist bark beetle management and reduce costs. Previous studies have indicated that there is a reflectance change in the near infrared and the visible wavelength regions (particularly the red rise and red edge regions). This study analyses the use of a compact airborne spectrographic imager (CASI) for its ability to detect subtle reflectance changes that are believed to occur following a mountain pine beetle attack. Imagery was acquired in 36 discrete narrow bands with a ground resolution of 60 cm. Differences between the (24) green and (25) non-attack populations could not be visually detected on the imagery, therefore the digital numbers (DN) from the central crown portion of the sample trees were examined statistically. A stepwise inclusive discriminant analysis indicated that two spectral bands, the shoulder of the green rise (539.5 +/-7.7 nm) and the toe portion of the red edge (706.4 +/-7.8 nm) exhibited a difference between the populations. A jackknifed classification matrix displayed that 79 percent of the green attack and 68 percent of the non-attack trees were properly classified. A graph showing the central frequencies from the results of the canonical scores of the populations indicate that the populations are quite close together and overlap considerably. The subtle spectral differences between the populations may complicate future attempts at classifying the populations. The difficulty may be due, in part, to the complex ecological diversity of the lodgepole pine sites, insufficient needle desiccation (from cool / moist environmental conditions following initial beetle attack) and from the low sun angle at the time of the imagery acquisition. The low sun angle adds complexity to the analysis from poorly lit tree crowns, long shadows, and from having only the southern side of the tree crown illuminated.

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