User Manual - pancroma

76. Tutorial - Pan Sharpening Landsat with SPOT________________________________________________________________One of the main advantages of the SPOT1 through SPOT4 over Landsat data isits slightly higher resolution. Landsat band files are approximately 30m resolutionwith a 15m panchromatic band. SPOT ® on the other hand has 20m band filesand a 10m panchromatic band. The disadvantage of SPOT ® is that it does nothave a visible blue band. As a result, if you want to create pan sharpened naturalcolor RGB images from SPOT ® , you have to first synthesize the natural colorbands from the three false color bands using a utility such as the one offered byPANCROMA. This can work reasonably well but even after a fair amount of effortthe results will never be perfect. So one is left with either a true color pansharpened RGB image at the lower 15m resolution or else a synthetic RGBimage at the higher 10m resolution.A third possibility is to use the SPOT ® panchromatic band to pan sharpen theLandsat band files. PANCROMA TM has the necessary utilities to do this, and theresults can be quite satisfactory.The first step is to locate your Landsat and SPOT ® files. You will need threeLandsat band files and a corresponding SPOT ® panchromatic band. Thisprocedure works best if the following conditions are met:• Use ortho images if available.• Both images should share the same projection and if possible the samedatum.• Both images should be relatively cloud free.• It is OK if there is some mountain snow but it is better if there is none. Ifsnow coverage exists, it should be similar in both images.Select your SPOT ® scene first. Select the Landsat scene so that it completelysurrounds the SPOT scene. That is, the SPOT scene should be locatedcompletely within the bounds of the Landsat scene. This is not too hard to dobecause Landsat scenes cover an area approximately 185 km by 185 km whileSPOT scenes cover an area of 60 km by 60 km.Download the SPOT ® panchromatic band. Record the latitude and longitudes ofits upper left and lower right corner coordinates. Now select and download thethree Landsat band files, i.e. band1, band2 and band3 (blue, green and red)according to the rules above. Subset the Landsat bands by opening the files asusual. In my case I subsetted the Landsat image to the SPOT ® set of cornercoordinates. Select 'Band Combination'|'Subset Images'|'Subset Three Bands'.When the Subset Input Box appears select the 'Select by Coordinates' radiobutton. Now enter the upper left and lower right corner coordinates that yourecorded previously. These are the corner coordinates of the SPOT ® scene. If354