User Manual - pancroma

spectral transmission of the telescope and MS filters, the throughput of thetelescope, the spectral quantum efficiency of the detectors, and the analog todigital conversion. Therefore, image pixel data are unique to WorldView-2 andshould not be directly compared to imagery from other sensors in aradiometric/spectral sense. Instead, image pixels should be converted to top-ofatmospherespectral radiance at a minimum."Calibration requires multiplication of each grayscale image digital number (DN)by the Absolute Calibration Factor and then dividing it by the EffectiveBandwidth. After calibration, each of the grayscale bands must be rescaled toreasonable brightness levels using the same scale factor for each image. Thecode required for the calibration and scaling and incorporated it into the latestversion of PANCROMA TM . To calibrate an image you must first obtain theAbsolute Calibration Factor (absCalFactor) and Effective Bandwidth(effectiveBandwidth) from the .IMI file that accompanies each WorldView2 dataset. Note that each of the eight bands has its own calibration coefficients. Eachband must be calibrated using its own calibration coefficients but scaled using acommon scale factor.To calibrate, open a single grayscale image using the 'File|Open' menu selection.After opening the file, select 'Pre Process'|'Calibrate WorldView2 Band'. A datainput form will be displayed. Insert the calibration coefficients for the band youare calibrating into the text boxes on the data input form. You can use the defaultscale factor, or input one of your own. The optimum scale factor can becomputed as:Scale Factor = SUM(absScaleFactor)/SUM(effectiveBandwidth)WhereSUM(absScaleFactor)= (absCalFactor1 + absCalFactor2 + absCalFactor3)AndSUM(effectiveBandwidth = (effectiveBandwidth1 + effectiveBandwidth2 +effectiveBandwidth3)After calibrating the band and panchromatic images it is often beneficial to applya histogram stretch to each of the bands for better contrast. (Note: it is notnecessary to stretch the panchromatic band as it will be automatically histogrammatched during the pan sharpening operation.)106