Chavez (1986), Chavez and Bowell (1988), and Chavez et al, (1991) merged both digitized National High Altitude Program photography and SPOT panchromatic data with Landsat TM data using a high-pass spatial filter applied to high-spatial-resolution imagery. The resultant high-pass image contains high-frequency information that is related mostly to spatial characteristics of the scene. The spatial filter removes most of the spectral information. The high-pass filter results were added, pixel by pixel, to the lower-spatial-resolution TM data. This process merged the spatial information of the higher-spatial-resolution data set with the higher spectral resolution inherent in the TM datasets.