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MODIS-Terra cross-calibration for ocean color bands

This study examines calibration changes in MODIS-Terra ocean color bands since launch, focusing on band 8 (412nm). It analyzes solar diffuser frame data, mirror angles, electronic damages, and detects trends in ocean color products. Cross-calibration methods are used to optimize the RVS for all ocean-color bands per mirror side and detector. The paper also explores polarization sensitivity and temporal calibration changes. SeaWiFS data is utilized for vicarious calibration, ensuring stable spatial and temporal accuracy. Global optimization is conducted to derive M11, M12, and M13 parameters for each day of the Terra mission, enhancing the accuracy of ocean color measurements.

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MODIS-Terra cross-calibration for ocean color bands

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  1. MODIS-Terra cross-calibrationfor ocean color bands Ewa Kwiatkowska Bryan Franz, Gerhard Meister, Gene Eplee OBPG 30 January 2008

  2. MODIS calibration changes since launch band 8 412nm SD – Solar Diffuser frame 979, mirror AOI 50.30 SV – Space View frame 23, mirror AOI 11.40 MS1 – Mirror Side 1 MS2 – Mirror Side 2 B side electronics pre-launch damage to mirror coating, MS2 Terra SD door permanently opened A side electronics

  3. MODIS trends in ocean color products Terra/Aqua ratios normalized water-leaving radiances Lwn Lwn(412nm) band 8 Lwn(443nm) band 9 Lwn(488nm) band 10 Lwn(531nm) band 11 Lwn(551nm) band 12

  4. MODIS-Terra ocean color RVS band 8 412nm Terra response versus scan angle (RVS) in terms of normalized water-leaving radiances Lwn Lwn(412nm) band 8 Mirror side 1 MS1 Mirror side 2 MS2 +10% -10%

  5. TOA sensor cross-calibration • Goal • Extract MODIS-Terra • RVS, and • polarization sensitivity • For all ocean-color bands, per mirror side and detector • Through the entire Terra mission • Optionally, derive temporal calibration change • Approach • Vicarious calibration / cross-calibration using SeaWiFS • SeaWiFS – stable spatially and temporally • SeaWiFS – insensitive to polarization

  6. TOA sensor cross-calibration TOA air aerosol whitecap glint gas polariz water L’t() = [ Lr() + La() + tLf() + TLg() + td()Lw() ] · tg() ·fp() MODIS – measured TOA radiance Lt() MODIS – vicarious ’   (fit in the ln-ln space) ’   (fit based on bio-optical models) SeaWiFS AOT(’) nLw(’)

  7. Current implementation TOA air aerosol whitecap glint gas polariz water L’t() = [ Lr() + La() + tLf() + TLg() + td()Lw() ] · tg() ·fp() MODIS – vicarious MODIS operational assuming accuracy of MODIS NIR band calibration ’   (fit based on bio-optical models) SeaWiFS nLw(’)

  8. Polarization fp M11 … M14 M21 … M24 M31 … M34 M41 … M44 1 0 0 0 0 cos2 -sin2 0 0 sin2 cos2 0 0 0 0 1 It Qt Ut 0 Im = • Polarization correction • fp = Im / It • Im = M11It + M12(Qtcos2 – Utsin2) + M13(Qtsin2 + Utcos2) • It – Stokes vector exiting the TOA • Mueller matrix M – instrument characterization, including polarization • - rotation angle • Im – Stokes vector measured by a sensor • Im = MR() It

  9. Polarization of the atmosphere  Q2 + U2 I dp = degree of atmospheric polarization dp air molecule (Rayleigh) and glint scattering polarization correction fp pre-launch MODIS characterization MODIS Terra swath 412nm band 8

  10. Time series and global optimization Lt = M11L’t + M12(Qtcos2 – Utsin2) + M13(Qtsin2 + Utcos2) • Known: • Lt – MODIS-measured • L’t – MODIS-vicarious • Qt and Ut – atmospheric molecular and glint polarization, Rayleigh tables, glint derivation •  – theoretical calculation • Unknown: • M11 – RVS and absolute calibration • M12 and M13 – polarization sensitivity • Global time series throughout the entire Terra mission • MODIS Terra – one day a month global set of granules (90 days) • SeaWiFS – 9-day global L3s centered on each month’s day from MODIS • Strict screening criteria for SeaWiFS L3 bins and MODIS L2 pixels • Global optimization for each day to derive M11, M12, and M13 • M11, M12, M13 = fn(mirror AOI)

  11. 412nm 6 March 2000 1.0 1-1.5% 0.99 0.98 443nm 1.01 1-2% 1.0 polynomial across scan RVS M12 M13 3-rd degree linear linear 0.99 488nm 1.01 2% 1.0 0.99 531nm 1.02 2% 1.01 1.0 551nm 1.02 1.5% 1.01 667nm 1.014 1% Detector 4 Mirror side 1 Mirror side 2 1.01 1.006 678nm 1.015 1% 1.005

  12. 412nm 16 October 2007 1.05 0.95 15% 0.85 443nm 1.02 0.98 7% polynomial across scan RVS M12 M13 3-rd degree linear linear 0.94 488nm 6% 1.02 0.98 531nm 1.04 3% 1.02 1.0 551nm 1.02 2% 1.0 667nm 1.02 1.3% Detector 4 Mirror side 1 Mirror side 2 1.01 678nm 1.025 1.4% 1.015 1.005

  13. Blue band temporal trends Mirror side 1 Mirror side 2 RVS Detector 4 Space View (lunar) frame Nadir frame Solar Diffuser frame

  14. Blue band temporal trends Mirror side 1 Mirror side 2 M12 Detector 4 Space View (lunar) frame Nadir frame Solar Diffuser frame

  15. 412nm Temporal trends 1.08 1.08 1.08 1.08 1.08 1.08 1.08 1.04 1.04 1.04 1.04 1.04 1.04 1.04 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.96 0.96 0.96 0.96 0.96 0.96 0.96 443nm RVS M12 M13 488nm 531nm Mirror side 2 Detector 4 551nm 667nm Space View (lunar) frame Nadir frame Solar Diffuser frame 678nm

  16. Pre-launch M13 RVS M12 M13 RVS M12 M13

  17. Temporal smoothing Polynomial fit through time into derived RVS and M12 per individual frame

  18. Smoothed results 412nm 443nm Mirror side 1 Detector 4 488nm RVS M12 531nm October 2007 Daily RVS and M12 use temporally smoothed values for all frames 551nm 667nm 678nm March 2000

  19. Smoothed results 412nm 443nm Mirror side 1 Detector 4 488nm RVS M12 531nm October 2007 Daily RVS and M12 use temporally smoothed values for all frames 551nm 667nm 678nm March 2000

  20. Verification of the vicarious cross-calibration with lunar measurements band 8 412nm Terra detector ratios detector 10 / detector 1 • lunar measurements — vicarious cross-cal 412nm band 8 Mirror side 1 MS1 Mirror side 2 MS2

  21. Future plans • Why seasonality in M13? • Is extracted polarization sensitivity too large? RVS? • Global time-series testing for water-leaving radiances • Validation of RVS and detector calibration • Application of the cross-calibration to Aqua

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