Abstract

The NASA Ocean Biology Processing Group's Calibration and Validation Team has analyzed the mission-long Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) on-orbit gain and detector calibration time series to verify that lunar calibrations, obtained at nonstandard gains and radiance ranges, are valid for Earth data collected at standard gains and typical ocean, cloud, and land radiances. For gain calibrations, a constant voltage injected into the postdetector electronics allows gain ratios to be computed for all four detectors in each band. The on-orbit lunar gain ratio time series show small drifts for the near infrared bands. These drifts are propagated into the ocean color data through the atmospheric correction parameter ϵ, which uses the 765/865  nm band ratio. An anomaly analysis of global mean normalized water-leaving radiances at 510  nm shows a small decrease over the mission, while an analysis of ϵ shows a corresponding increase. The drifts in the lunar time series for the 765 and 865   nm bands were corrected. An analysis of the revised water-leaving radiances at 510   nm shows the drift has been eliminated, while an analysis of ϵ shows a reduced drift. For detector calibrations, solar diffuser observations made by the individual detectors in each band allows the response of the detectors to be monitored separately. The mission-long time series of detector calibration data show that the variations in the response of the individual detectors are less than 0.5% over the mission for all bands except the 865  nm band, where the variations are less than 1%.

© 2007 Optical Society of America

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