MISR: In-Flight Radiometric Calibration and Characterization Plan

5.2.1 High-altitude sensor-based calibrationThe VC which utilizes high-altitude sensors is the most accurate. The utilization of asensor such as AirMISR 13 would be ideal, and is probably the only methodology which will meetour accuracy requirements for all MISR sensor view angles. The method relies on a sunlit,optically stable target being imaged simultaneously by the aircraft sensor and MISR. Cloud-freeconditions are required. The airborne sensor views the target at the same geometry as the camerato be calibrated. As several AirMISR passes would be necessary to cover a range of MISR viewangles, it is important to understand the deviations in upwelling radiance due to changes in solarillumination angle during the overpass. Small corrections must also be applied to account for theeffects of the atmospheric path between the aircraft and the satellite, and to account for thedifference between the footprints of the two instruments on the target. Although this techniquehas the disadvantages of a higher cost and difficulty in scheduling and implementing, it is thepreferred vicarious methodology. A semi-annual overpass is planned.In order to weight radiance-based calibration coefficients against other methodologies, theaccuracy of this product must be understood. Additionally, the uncertainty estimates provide inputto the MISR radiance retrieval uncertainty estimates. Table 5.2 details the error budget for thecalibration of MISR, using the high-altitude radiance-based methodology. The actualuncertainties will be determined prior to VC implementation in the post-launch era.Table 5.2. High-altitude sensor uncertainty sources (worst case over MISR view angles).SourceUncertainty(%)at ρ eq =0.05Uncertainty(%) atρ eq =1.0Budget Actual Budget ActualAirMISR calibration accuracy 5.0 2.5AirMISR in-flight sensor stability 0.5 0.5Scene Registration 3.0 1.3Atmospheric Correction 0.5 0.5Observation Geometry 1.0 0.5AirMISR/ MISR differences in spectralprofile0.5 0.5Total Uncertainty (Root Sum of Squares) 6.0 3.05.2.2 Surface radiance-based calibrationIt is proposed that a surface-based radiometer, such as PARABOLA, be used to measuresurface upwelling radiance. This technique, while not as accurate as the high-altitude sensormethodology, has cost and implementation advantages. For this reason these data will always betaken, as a backup should there be difficulties in the previous data set. Use of in-situIn-flight Radiometric Calibration and Characterization Plan, JPL D-1331547