Detection Of Moderate Damage On Norway Spruce Using Landsat TM And Digital Stand Data

During the summer of 1985 three Landsat TM scenes covering an area in southwestern Sweden suffering from moderate defoliation on Norway spruce (Picea abies) were obtained. Defoliation assessment from color infrared (CIR) aerial photography was used as a reference to study the capability of Landsat TM data to detect this defoliation, which ranged from 15 to 46% mean needle loss. No chlorosis was evident. The TM imagery from September were more strongly correlated to defoliation level than were the July scenes. This may be explained by an expanded defoliation range and by a sun elevation decline from 47° in late July to 20° in late September, resulting in shadowed understorey vegetation. The reflectance decreased in all TM bands as spruce needle loss increased from 10 to 40%. The results implied that increased bark spectral contribution does not dominate the spectral effects of low and moderate defoliation on Norway spruce. Symptoms in living needles such as tissue damages and pigment alterations other than chlorosis are likely to be predominant. If the variation in hardwood composition was kept under 5% and the variation in pine composition under 15% there was a statistically strong relationship between the most powerful image transformations and the defoliation level.