AN EFFICIENT AND ACCURATE METHOD FOR MAPPING FOREST CLEARCUTS IN THE PACIFIC-NORTHWEST USING LANDSAT IMAGERY

Two variations of image differencing were compared. The first was base d on unsupervised classification, repeated five times, using five sequ ential date-pairs of difference images between 1972 and 1993. Referred to as merged image differencing, this method required merging the res ults from five separate time intervals into a single map of forest har vest activity. The other method involved a single unsupervised classif ication of the full sequential difference image data set, and was refe rred to as simultaneous image differencing. A thorough harvest map err or assessment using an independent reference database was compared to two methods of assessment based on visual interpretation of the Landsa t data used to develop the difference images. Results indicate that ha rvest activity was mapped using merged image differencing with greater than 90 percent accuracy, and that visual methods of error assessment using the Landsat images gave nearly identical results with those of the independent reference data. Simultaneous image differencing result ed in a map that was consistent with merged image differencing and mor e considerably more cost-effective to implement.