User Manual - pancroma

48. Gap Filling a Landsat 7 ETM+ Image______________________________________________________________It is possible to use PANCROMA TM utilities to fill the gaps in Landsat ETM+ SLCoff(post 2003) imagery. The gap filling procedure requires a Target image (theone you are trying to correct, i.e. with gaps) and at least one Adjust image (theone you will extract data from to fill the gaps in the Reference image. The Adjustimage is often gap-free, but it does not have to be. Because the gaps in twoimages may not coincide exactly, at least some useful data may be transferredfrom the Adjust image to the Target image despite possible gaps in both. Youwill need three Reference bands and three Adjust bands (blue green and red) foreach image.IMPORTANT NOTE: If you decide to use two gapped images rather than onegapped and one gap-free, there are two ways you can fuse the images. It isoften useful to experiment to see which substitution direction gives better results.PANCROMA TM currently provides three methods for gap filling a Landsat image.The Transfer method conducts a histogram match between the Adjust andReference images and then transfers the missing pixels of pixels from the Adjustimage to the Reference image. The Hayes method uses an approximationalgorithm to reconstruct each missing pixel in the Reference using a comparisonbetween a sliding window sample of Adjust image pixels. The TERAS methoduses a local optimization algorithm and a proprietary sliding window algorithmthat results in fast processing times.The Hayes method is a sliding-window method, meaning a small but significantnumber of computations is required for each pixel in the image. As a result, theHayes method can be time consuming. In order to help with this, a batchprocessingmode is available for Hayes processing. Select ‘Gap Fill’ | ‘Gap FillHayes Interpolation Method’ | ‘Six File Set’ to use this utility. When you do so abatch processing data input screen will become available. Add six files in theorder: band1 gap, band1 no gap; band2 gap, band2 no gap; band3 gap, band3no gap by successively clicking on the ‘Add File’ button and selecting your filesfrom the dialog box.When all six band files are entered, select ‘Save Path’. Select the save fileformat and the base file name. Then select ‘Run’. Processing will take place asin the two file Hayes processing method. As PANCROMA processes each file, itwill save the result, appending the band number to the base file name. See theTutorial section for more information on this utility.The TERAS method is also a sliding-window routine that uses a proprietary localoptimization algorithm. Processing times are similar to the Hayes algorithm andshould produce similar results.127