15 October 2012 Monitoring and assessment of the temperature fluctuation of Aqua MODIS cold focal plane assembly
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Abstract
The MODIS instruments on-board the Terra and Aqua spacecrafts have 16 thermal emissive bands (TEB), located on two cold focal plane assemblies (CFPA). The CFPAs are cryogenically cooled by a passive radiative cooler, with their temperatures further controlled at a nominal value of 83K. For Aqua MODIS, the cooler margin has gradually decreased since launch, which deteriorates the CFPA temperature stability. Since 2006, Aqua CFPA temperature fluctuates with the instrument temperature in both seasonal and orbital oscillation patterns. The magnitude of the fluctuation steadily increases on yearly basis. The gains of TEB detectors change with the CFPA temperature in a nearly linear way, as is demonstrated by both pre-launch calibration and on-orbit monitoring. As of mid 2012, the magnitude of the CFPA temperature fluctuation reaches 0.65K, causing band-dependent detector gain fluctuation of up to 6%. In this paper, the CFPA temperature and its related telemetries are monitored over both a short-term and long-term basis. The impact of the fluctuation to TEB radiometric calibration is assessed, too. Because the calibration is normally performed on a scanby- scan basis based on the observation of an onboard blackbody (BB), the detector gain change can be retrieved in nearly real time. Therefore, the impact is insignificant in general. However, for bands 33, 35 and 36, their detectors saturate when observing BB at BB temperature above certain saturation limits during quarterly held BB warmupcooldown (WUCD) activities. Since there is no valid scan-by-scan calibration during these periods, a special treatment has to be applied to calibrate these bands to reflect the detector gain fluctuation.
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Zhipeng Wang, Zhipeng Wang, Sriharsha Madhavan, Sriharsha Madhavan, Xiaoxiong Xiong, Xiaoxiong Xiong, Aisheng Wu, Aisheng Wu, Brian Wenny, Brian Wenny, } "Monitoring and assessment of the temperature fluctuation of Aqua MODIS cold focal plane assembly", Proc. SPIE 8510, Earth Observing Systems XVII, 85100K (15 October 2012); doi: 10.1117/12.930904; https://doi.org/10.1117/12.930904
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