24 September 2002 SeaWiFS Detector and Gain Calibrations: Four Years of On-Orbit Stability
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Abstract
The SeaWiFS Project uses daily on-orbit detector and gain calibrations to address issues which arise from the bilinear gain in the SeaWiFS radiometric response function. The bilinear gains provide high sensitivity over the ocean while preventing saturation over clouds or land. The bilinear gains are implemented by averaging the output from three high-sensitivity ocean detectors and one low-sensitivity cloud detector for each band. The calibration issues are: 1) the applicability of time corrections computed from lunar data obtained at one set of instrument gains to ocean data obtained at a different set of gains; and 2) the applicability of time corrections computed from data obtained with all four detectors in each band to the cloud detector alone. The Project uses the gain calibration to monitor the SeaWiFS gain ratios over time. The gain ratios for each detector are computed from measurements at each gain of a constant voltage injected into the post-detector electronics. The gain ratios are stable to within 0.1% over the course of the mission. The Project uses the detector calibrations to compare the response of individual detectors within each band to the response of the four detectors in that band. The detector response is monitored during a modified solar calibration where measurements are obtained from each detector. The departure of the cloud detectors from the four detectors is less than 0.5% for all eight bands. These analyses show that, for SeaWiFS, the time corrections derived from lunar calibrations are applicable to both ocean and land data.
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Robert E. Eplee, Robert A. Barnes, Charles R. McClain, "SeaWiFS Detector and Gain Calibrations: Four Years of On-Orbit Stability", Proc. SPIE 4814, Earth Observing Systems VII, (24 September 2002); doi: 10.1117/12.450565; https://doi.org/10.1117/12.450565
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