User Manual - pancroma

example ‘outputfile1.tif’, outputfile2.tif, etc. When you accept the file name,PANCROMA TM will decode the bundle file and write individual band files to thedirectory that you designated. The numbering convention will be consistent withthat for Landsat band data, to an extent practical. That is, band1 will be theshortest wavelength (blue) band, band2 the next longer, band 3 the next longer,etc. Make sure to consult the Digital Globe web site for band file specificationsas the 8 band WorldView2 files do not match the 8 Landsat bands at all. Theblue, green and red bands are band2, band3 and band5, respectively.Another difference is the dynamic range. Some products are offered with adynamic range of 11 bits-per-pixel. Since the GeoTiff file format only allowsnumerical data types that are multiples of 8-bit bytes, 11 bit files are actuallyrecorded as SHORT (16-bit) integers. PANCROMA TM will resolve the 11 bits intothe 8-bit color channels by scaling by 255/maxValue, where maxValue is thelargest magnitude 11-bit integer in the data file. Quite often most of the pixelvalues in an 11-bit file are less than 255.This has the effect of producing a dark image when scaled. As an alternative,PANCROMA TM allows you to bit-shift the pixel data. (Each bit shift is equivalentto dividing the pixel value by 2). This allows more flexibility in creating imageswith reasonable overall brightness. To bit shift, check the ‘Activate ImageProcessing Routines’ check box on the Main Window. When the imageprocessing data entry window becomes visible, select the ‘Bit Shift Enable’ checkbox in the ‘Input Channel Adjust Group’ and select either 1, 2 or 3 pixels from theCombo Box. Another alternative is to Histogram Stretch the band files afterdecoding using the ‘Pre Process’|’HistogramStretch’ menu selection.IMPORTANT NOTE: WorldView 2 files must be individually converted from 16-bit to 8-bit format before subsequent processing. It is not possible to openmultiple WorldView2 11-bit files and directly create a RGB color composite, forexample.Calibrating WorldView2 Imageryin contrast to Landsat WorldView2, QuickBird and other very high-resolutionsatellites can acquire images at high off nadir angles. This presents a muchlonger atmospheric path to the satellite sensors, and can produce a blue-greencoloring when RGB images are produced from the band files. Calibrating theimages often produces better color results.The calibration procedure is described in the Digital Globe publication entitledRadiometric Use of WorldView-2 Imagery available at the Digital Globe website.Quoting from this publication: "WorldView-2 products are delivered to thecustomer as radiometrically corrected image pixels. Their values are a function ofhow much spectral radiance enters the telescope aperture and the instrumentconversion of that radiation into a digital signal. That signal depends on the105