Assessment of moderate damages on spruce using Landsat TM
During the summer 1985 three cloudless Landsat TM scenes covering an area in southwestern Sweden suffering from moderate damages on Norway Spruce we re obtained. Damage assessment from CIR aerial photography was used as a reference to study the capability of Landsat TM data to detect those damages, ranging from 10 to 46% mean needle loss. The data studied indicated that the TM registrations from September were more strongly correlated to damage level than were the July scenes. This may be explained by a sun elevation decline from 480 in late July to 280 in late September, resulting in shadowed understorey vegetation, and by an expanded damage range. The reflectance decreased in all TM bands as spruce needle loss increased from 10% to 40%. The results suggest that Landsat TM based assessment of damages on Norway spruce might be feasible if digital ancillary forest data in a GIS environment is used as support in the survey. When the hardwood component was not varying more than 5% the correlation between TM data and damages was strong enough to implicate a possible division into two damage classes with the class border preferably at 30% needle loss. The image transformations yielding the most promising results were TM 4/2+4+7, TM 4/1+2+4 and TM 4/2+3+4. Inclusion of a limited number of sites situated on ground sloping with 5-150 gave a small correlation decrease due to different illumination conditions. The chromaticity indices and ratios did not clearly reduce this effect.