ALOS Data Users Handbook

Section 7 Overview of Processing Algorithms7.2.2.2 AVNIR-2(1) Basic Concept of the Radiometric Distortion CorrectionFigure 7.2-3 shows the output component of AVNIR-2 at the observation.PD SignalPD Dark CurrentOutputLevelCCD DarkCurrrentElectricalOffsetSignalOutput ODarkOutput BDummyPixel CFigure 7.2-3 Output Component of each PixelIt is only the PD signal component of the effective pixel signal output O that correlates with the radiance L ofthe object. Therefore, it needs to deduct the offset component (PD dark current, CCD dark current andelectrical offset) from the signal output O when the radiometric correction is performed. Since this offsetcomponent is the same as the output B at the dark, the PD signal output can be determined by deducting theoutput B at the dark from the signal output O in theory.However, since the signal output O and the output B at the dark time are not the data obtained simultaneously,the temperature condition of each equipment is different. According to this temperature difference, the offsetcomponent varies. Therefore, if only finding the differences between O and B, its difference is still largedepending on the above reason. Then the dummy pixel output C obtained simultaneously along with theeffective pixels is used in the offset correction. Since there is a possibility that offset of the exposurecoefficient is added to the signal output O, it also should be given a consideration.(2) Equation of the Radiometric CorrectionA basic Equation of the radiometric distortion correction which calculates the incidence radiance from thedigital output of AVNIR-2 is shown as follows.7-14