Canopy water stress detection in conifers using the airborne imaging spectrometer

Imagery acquired by the Airborne Imaging Spectrometer (AIS-2) over adjacent plots of control and water stressed canopies of Norway spruce and white pine was analyzed for differences in near-infrared reflectance features. Water stress had been induced by severing the sapwood and was assessed with shoot potential and relative water content measurements. Stressed Norway spruce was found to have greater relative reflectance in the 1.0-1.3-μm region as compared to the control in the midmorning image 13 days after stress induction. However, the difference in reflectance decreased to an insignificant amount in the image take 3 h later that day. In white pine, no significant differences in reflectance between stressed and control canopies were found in images obtained 14 and 20 days after stress induction. Detection of these small differences in reflectance between stressed and control canopies was possible only because sites were known and ground measurements were collected at times of overflights.