Robert E. Eplee, Gerhard Meister, Frederick S. Patt, Robert A. Barnes, Sean W. Bailey, Bryan A. Franz, and Charles R. McClain, "On-orbit calibration of SeaWiFS," Appl. Opt. 51, 8702-8730 (2012)
Ocean color climate data records (CDRs) require water-leaving radiances with 5% absolute and 1% relative accuracies as input. Because of the amplification of any sensor calibration errors by the atmospheric correction, the 1% relative accuracy requirement translates into a 0.1% long-term radiometric stability requirement for top-of-the-atmosphere (TOA) radiances. The rigorous prelaunch and on-orbit calibration program developed and implemented for Sea-viewing Wide Field-of-view Sensor (SeaWiFS) by the NASA Ocean Biology Processing Group (OBPG) has led to the incorporation of significant changes into the on-orbit calibration methodology over the 13-year lifetime of the instrument. Evolving instrument performance and ongoing algorithm refinement have resulted in updates to approaches for the lunar, solar, and vicarious calibration of SeaWiFS. The uncertainties in the calibrated TOA radiances are addressed in terms of accuracy (biases in the measurements), precision (scatter in the measurements), and stability (repeatability of the measurements). The biases are 2%–3% from lunar calibration and 1%–2% from vicarious calibration. The precision is 0.16% from solar signal-to-noise ratios, 0.13% from lunar residuals, and 0.10% from vicarious gains. The long-term stability of the TOA radiances, derived from the lunar time series, is 0.13%. The stability of the vicariously calibrated TOA radiances, incorporating the uncertainties of the in situ measurements and the atmospheric correction, is 0.30%. This stability of the radiometric calibration of SeaWiFS over its 13-year on-orbit lifetime has allowed the OBPG to produce CDRs from the ocean color data set.
Robert E. Eplee, Wayne D. Robinson, Sean W. Bailey, Dennis K. Clark, P. Jeremy Werdell, Menghua Wang, Robert A. Barnes, and Charles R. McClain Appl. Opt. 40(36) 6701-6718 (2001)
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204 lunar observations have been made by SeaWiFS over the period of November 1997—November 2010. 145 observations were obtained at the nominal phase angle of and have been used for long-term radiometric trending. 59 observations were obtained over a range of phase angles and have been used for investigating phase effects in the lunar time series.
Cals between and .
Changes to the instrument calibration that were implemented at each reprocessing are shown. For more information on ocean color data reprocessings, see the NASA Ocean Color website: oceancolor.gsfc.naa.gov/WIKI/OCReproc.html.
Gain 1 is the standard gain for ocean observations. Gain 2 is the secondary gain () for ocean observations. Gain 3 and Gain 4 are the commanded gains designed to give full-scale output for lunar and solar observations.
The first on-orbit coefficients were introduced with Reprocessing R2002.0, the second on-orbit coefficients were introduced with Reprocessing 2007.0, and the current on-orbit coefficients were introduced with Reprocessing R2009.0. The units are .
The prelaunch SNRs are measured at , while the on-orbit SNRs are measured at . The radiance units are . The table also shows the SNR specification for each band.
The gain ratios for lunar calibrations are given for each band. The calibration pulse counts from which the ratios were derived are provided for the start and end of the missions. The long-term stability of the gain ratios are provided.
The Band 7 stability is also provided after the Gain 3 drift correction.
The NIST-based vicarious gains were derived using the NIST-measured counts-to-radiance conversion coefficients, while the SBRS-based vicarious gains were derived using the SBRS-measured counts-to-radiances conversion coefficients.
Gains derived from MOBY radiances propagated to the TOA.
Gains derived from aerosol retrievals.
No vicarious calibration. The MOBY uncertainties are for the water-leaving radiances.
The third column shows the SeaWiFS bias relative to the ROLO model. The fourth column shows the SeaWiFS bias relative to MOBY. The uncertainty in the NIST prelaunch calibration is 4% [15].
Table 15.
Long-Term Stability of the Radiometric Calibrationa
The RMS errors before and after the coherent noise correction.
Bands used to compute the coherent noise correction.
Error including the Gain 3 drift uncertainty.
The solar-derived and lunar-derived precision are instrumental properties. The vicarious gain precision is a property of the atmospheric correction algorithm.
The accuracy is relative to the ROLO model or to MOBY. The stability is given for TOA radiances and vicariously calibrated (VC) TOA radiances. The precision estimates have the indicated sources. Band 8 does not have a vicarious calibration.
Including the Band 7 Gain 3 drift correction.
204 lunar observations have been made by SeaWiFS over the period of November 1997—November 2010. 145 observations were obtained at the nominal phase angle of and have been used for long-term radiometric trending. 59 observations were obtained over a range of phase angles and have been used for investigating phase effects in the lunar time series.
Cals between and .
Changes to the instrument calibration that were implemented at each reprocessing are shown. For more information on ocean color data reprocessings, see the NASA Ocean Color website: oceancolor.gsfc.naa.gov/WIKI/OCReproc.html.
Gain 1 is the standard gain for ocean observations. Gain 2 is the secondary gain () for ocean observations. Gain 3 and Gain 4 are the commanded gains designed to give full-scale output for lunar and solar observations.
The first on-orbit coefficients were introduced with Reprocessing R2002.0, the second on-orbit coefficients were introduced with Reprocessing 2007.0, and the current on-orbit coefficients were introduced with Reprocessing R2009.0. The units are .
The prelaunch SNRs are measured at , while the on-orbit SNRs are measured at . The radiance units are . The table also shows the SNR specification for each band.
The gain ratios for lunar calibrations are given for each band. The calibration pulse counts from which the ratios were derived are provided for the start and end of the missions. The long-term stability of the gain ratios are provided.
The Band 7 stability is also provided after the Gain 3 drift correction.
The NIST-based vicarious gains were derived using the NIST-measured counts-to-radiance conversion coefficients, while the SBRS-based vicarious gains were derived using the SBRS-measured counts-to-radiances conversion coefficients.
Gains derived from MOBY radiances propagated to the TOA.
Gains derived from aerosol retrievals.
No vicarious calibration. The MOBY uncertainties are for the water-leaving radiances.
The third column shows the SeaWiFS bias relative to the ROLO model. The fourth column shows the SeaWiFS bias relative to MOBY. The uncertainty in the NIST prelaunch calibration is 4% [15].
Table 15.
Long-Term Stability of the Radiometric Calibrationa
The RMS errors before and after the coherent noise correction.
Bands used to compute the coherent noise correction.
Error including the Gain 3 drift uncertainty.
The solar-derived and lunar-derived precision are instrumental properties. The vicarious gain precision is a property of the atmospheric correction algorithm.
The accuracy is relative to the ROLO model or to MOBY. The stability is given for TOA radiances and vicariously calibrated (VC) TOA radiances. The precision estimates have the indicated sources. Band 8 does not have a vicarious calibration.
Including the Band 7 Gain 3 drift correction.
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