Digital Image Processing -Image Restoration Atmospheric Corrections Objectives To understand: ➢ Radiometric Errors ➢ Atmospheric correction ➢ Sun Illumination correction Introduction 3 ➢ Radiometric errors can be sensor driven or due to atmospheric attenuation Radiometric Errors- Sensor driven ➢ Occurs due to improper functioning of the sensor system a. Line Banding b. Line Dropout ➢ Line Banding: noise generated- Multiple detectors ➢ Life of individual detectors Line Banding in Landsat-5 TM Image 5 Line Banding Correction 6 ➢A histogram for each detector in each band is produced. ➢For a four detector system, histogram 1 is formed from data in lines 1, 5, 9 ... etc., histogram 2 from lines 2, 6, 10 ..., histogram 3 from lines 3,7, 11 ... and histogram 4 from lines 4, 8, 12 ...etc. ➢ Assuming each detector has sensed a representative sample of all the surface classes within the scene, each of the histograms will be similar (i.e. have the same mean and standard deviation) if the detectors are matched and Histogram for each detector of Band 1 calibrated (say) Line Banding Correction 7 ➢However, if one detector is no longer producing data readings consistent with the other detectors, its histogram will be different. Detector 4 in the figure is producing higher digital numbers than the other detectors. ➢ An average histogram is produced by using the digital number from all the detectors (excepting the defective detector) ➢The DNs produ ...
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