MISR: In-Flight Radiometric Calibration and Characterization Plan

coefficients. These pathways utilize OBC, vicarious calibration (VC), histogram equalization(HE), and trending data sets, as depicted in Figure 5.1.It is anticipated that these multiple data sets will not all provide the same radiometriccalibration, and that discrepancy conflicts will need to be resolved. Figure 5.2 depicts post launchsensor degradation, as might be measured for the OBC (PIN and HQE detector standards),vicarious, and trend determinations. Histogram equalization is not shown in this figure, as itprovides relative-pixel response, rather than long-term degradation information. The trend dataare the retrospective coefficients, including the preflight data. For each of these methodologies anuncertainty analysis, the frequency of data collection, and overall data quality metrics will beutilized to define a weighing coefficient. These weighting coefficients may be reassigned withtime. Following the weighting of the various methodologies, a single coefficient set is computed,and delivered to the DAAC for subsequent processing of MISR data. This coefficient set is useduntil updated by subsequent calibrations. That is, the most recently measured (as distinct from thepredicted) calibration parameters are used in radiance retrieval. Note that if only the preflightcalibration parameters were used, the radiance error would grow with time, as no compensationfor sensor degradation would be made. MISR specifications allow for a 10% mission lifedegradation in sensor response [ISR]. It is believed that signal-to-noise and dynamic rangerequirements will be maintained, provided the sensor maintains this budget.0Sensor Degradation(%)10HQEPINPreflightTrend data(reportedARP values)VCVC*(OBC=PIN, HQE)o+ = Current coef.to reconcile* = Weightedo = Smoothedresult (to ARP)+ + 6 Year EOSStable responseassumed, untilnext updateLaunchTIMEPresentFigure 5.2. MISR degradation, as measured by multiple methodologies.The preflight coefficients have more of an impact on the ARP in the early months of themission, when on-orbit data are scarce. They are folded in via the calibration trend history. Withtime they have diminishing influence on the sensor in-flight calibration. Radiance, as determinedusing the HQE photodiode standards are also weighted less with time. Their stability has beenmeasured preflight, and used to develop an uncertainty model which grows with time. Currentlythe plan is to weight HQE and PIN photodiode data equally for the first six months of flight, afterwhich the HQE may degrade in known quantum efficiency. The HQE and PIN flight photodiode5. In-flight calibration40