Spectral reflectance characteristics and digital imagery of a pine needle blight in the southeastern United States

Abstract

A field study determined an optimal approach for the remote sensing of a pine needle blight of unknown cause that occurs frequently in the southeastern United States. Needle spectral reflectance was measured in five pairs of slash pines (Pinuselliottii Engelm. var. elliottii), each comprising a blighted and a nonblighted tree. Reflectance of blighted needles generally was greater within the 400–700 nm wavelength range and less in the 720–850 nm range compared with nonblighted needles (p ≤ 0.050). The relative change in reflectance, or reflectance sensitivity to the blight, was greatest near 680 nm. As predicted by the reflectance sensitivity, a black and white digital image at 680 ± 5 nm revealed strong contrast of a blighted compared with a nonblighted tree; the blighted canopy was nearly white in the image, while the nonblighted canopy was dark grey. Contrasts were much less at 560 ± 5, 694 ± 3, and 700 ± 5 nm, in the panchromatic visible spectrum (410–740 nm), and at 760 ± 5 nm. Remote sensing of southeastern pine forests at 680 ± 5 nm ultimately could provide regional estimates of blight occurrence and distribution, and thus contribute to determining its cause.