User Manual - pancroma

53. Haze Reduction – DEM Method________________________________________________________________A third method for reducing image haze uses a digital elevation model (DEM)plus a RGB color image. The method uses the DEM to determine how muchatmosphere is between the earth’s surface and the satellite sensor. The higherthe ground elevation, the less atmosphere there is to scatter light. The algorithmthen corrects each pixel in the RGB color image in order to compensate for theatmospheric effects. This algorithm is not suitable for multispectral analysis butmay be useful for improving RGB color composites for other purposes.You will need a matched image/DEM pair in order to use the image. A goodcombination is an RGB color image prepared from Landsat bands 1, 2 and 3 andASTER DEM data. Both have pixel resolutions of 30m. ASTER DEMs can beobtained free of charge for most of the world from the USGS/NASA LP DAACGlobal Data Explorer website at http://gdex.cr.usgs.gov/gdex/. Select your areaof interest by coordinates. It is important to download your ASTER DEM first,and then subset the Landsat data to the corner coordinates of the ASTER DEM.This is because the Global Data Explorer selection tool rounds the coordinates,making it more difficult to get a match. Use UTM coordinates to make yourselection, and make sure the datums match (should be WGS 84). Your selectioncriteria should look something like those in the image below.149