Landsat TM data has a spatial resolution of 30m x 30m and a spectral resolution of 8 bits. The use of a supervised classification algorithm requires apriori knowledge of the location for specific land-cover types that represent typical forest and wetland areas. In lieu of ground verification, existing USGS Anderson Land Cover Classification vector data was overlaid on the existing image and used to delineate training sites. Overlaying vector data onto image data requires both the image and land-cover data to be referenced to identical coordinate systems. Therefore, the Landsat TM data was rectified to the existing land-cover projection UTM zone 17, NAD 83.
Image rectification involves both geometric and radiometric correction.
Geometric correction is the alignment of image pixel values to a known coordinate system thereby removing image distortion. RMSE is an indication of how well the first order affine transformation equation predicts the new coordinates of the rectified GCP pixels. The large RMSE may be due to excessive distortion of the image as a result of the irregularities associated with the optical-mechanical scanning sensor system of the Landsat TM system. However, a more likely explanation is the extent of the area being rectified. The Edisto watershed is approximately 500 square miles and the area rectified was well beyond watershed boundaries as to include proper rectification of watershed edges.