Sensor band selection for detecting current defoliation caused by the spruce budworm

Ground-based spectral data were obtained for single crowns of balsam fir trees with varying degrees of current defoliation caused by feeding of the spruce budworm [ Choristoneura fumiferana (Clem.)]. These data were acquired with a Spectrascan spectrometer mounted on a 21-m boom truck, which provided spectral reflectances in 117 wavelength bands from 380 to 2400 nm. The spectra were related to measures of defoliation symptoms: needle loss, quantity of red needles and other feeding debris, and exposure of bare twigs. Wavelength bands suitable for discriminating different levels of these damage symptoms were defined and compared with wavelength bands available with various airborne and satellite sensors. The most effective bands, in order of importance, were 2030–2210, 660–670, 1560–1620, and 770–790 nm. Well-placed, narrow wavelength bands are important for discriminating levels of current defoliation caused by spruce budworm feeding.