User Manual - pancroma

27. XIONG Algorithm – Manual Method________________________________________________________________The XIONG algorithm offers another alternative to correct the blue spectraldistortion inherent in Landsat panchromatic bands 4 . This algorithm oftenproduces better results than the ENHG algorithm described above.Like the ENHG, both manual and automatic processing is available. If computedas a pre-processing step, the output file is saved for subsequent processing. Inthis case the pan sharpening process is conducted as usual, this timesubstituting XIONG file for the panchromatic band. This example will againassume that a Landsat image is being processed although it can be applied toany image set.The first step is to download five band files as before: bands 1, 2, 3 andpanchromatic as usual for pan sharpening plus the extra (NIR) band: band 5.The easiest way to proceed is to subset the band files first. This allows you toexperiment with the XIONG scale factor in order to iteratively produce the optimalcolor tones without taking up a lot of computing time. PANCROMA TM provides aspecial five-file subset utility for this purpose. After loading your five files in theorder: band1; band2; band3; panchromatic; and NIR band select ‘BandCombination’ | ‘Subset Images’ | ‘Subset Five Bands’.The subsetting procedure is exactly as described for subsetting four bands asdescribed previously except that an additional subsetted file will be producedcorresponding to the NIR band. The usual subsetting techniques can be usedand of course the subset files will be the same size and co-registered.IMPORTANT NOTE: You must open the files in the specified order or an errormessage will result.4The XIONG algorithm is particularly useful when pan sharpening using the Landsatpanchromatic band. The reason is that the Landsat panchromatic band spans wavelengths of0.52 to 0.90 microns. This covers the green, red and NIR bands. This means that a Landsatpanchromatic band contains no blue color information. Pan sharpening using this band can leadto spectral distortion. You can easily notice this when pan sharpening scenes with a high bluespectral component, i.e. forested scenes. Desert scenes in contrast that lack a lot of blue are notso much affected. The PANCROMA TM XIONG and AJISANE algorithms are designed to helpcorrectthis.On the other hand the SPOT panchromatic band spans a spectrum of 0.48 to 0.71 microns. Thisalmost exactly covers the blue, green and red spectral bands. Pan sharpening with the SPOTpanchromatic band does not produce the kind of spectral distortions common with Landsat, andthe XIONG algorithm may actually produce poorer results than the four-file HSI algorithm. It isgenerally helpful to check the specifications of the panchromatic band in whatever data set youare using in order to select the most appropriate pan sharpening algorithm.70