ASSESSMENT OF FOREST DAMAGE WITH LANDSAT TM - CORRECTION FOR VARYING FOREST STAND CHARACTERISTICS

The utility of satellite data in forest decline assessment is influenced by effects associated with variations in stand characteristics such as species composition, age, and density. In this study, the spectral effects of stand variations were determined for forest dominated by Norway spruce. The usefulness of digitized stand data for potentially reducing these effects were investigated. It is suggested that a damage estimation algorithm based solely on Landsat TM Band 4 is more appropriate than earlier proposed ratio algorithms in areas with moderate defoliation symptoms but no chlorosis. The two factors with the strongest negative effect on the defoliation assessment were varying hardwood and pine component, A hardwood component of 20% completely neutralized a defoliation of 20%. Age had a clear spectral effect up to 70 years, but above that the response was stable. There was no confusion between defoliation classes in stands with moderate to high density. A spruce defoliation model that used stand data from digitized forest maps to modify the intensity values of TM Band 4 prior to estimation of defoliation was developed. The resulting assessment of moderate defoliation in forest areas on level ground was of adequate accuracy when the spruce component was larger than 75%.