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MODIS-Terra cross-calibration for ocean color bands

MODIS-Terra cross-calibration for ocean color bands. Ewa Kwiatkowska Bryan Franz, Gerhard Meister Ocean Biology Processing Group 13 May 2008 MODIS Science Team Meeting. MODIS calibration changes since launch band 8 412nm . SD – Solar Diffuser frame 979, mirror AOI 50.3 0

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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 Ocean Biology Processing Group 13 May 2008 MODIS Science Team Meeting

  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 SD door permanently opened

  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% per detector

  5. Issues and limitations with MODIS-Terra • Temporal and scan-dependent trend in Lwn of MODIS-Terra suggests • instrument RVS may be in error • polarization sensitivity may be changing • on-board calibration capabilities may be degrading (SD, SDSM) • On-board calibration (lunar or solar) CANNOT assess • changes in RVS “shape” • changes in polarization sensitivities • OBPG developed a vicarious approach for on-orbit Terra characterization • RVS • polarization sensitivity

  6. Lt Qt Ut 0 Modeling of TOA Stokes vector over oceans air whitecap glint gas aerosol water Lt(λ) = [ Lr(λ) + La(λ) + tLf(λ) + TLg(λ) + td(λ)Lw(λ) ] · tg(λ) from MODIS NIR assumes MCST NIR band characterization λ’ → λ fit based on bio-optical models SeaWiFS 9-day mean Lwn(λ’)

  7. Lm Qm Um 0 Lt Qt Ut 0 M11 M12 M13 M14 M21 … M24 M31 … M34 M41 M42 M43 M44 = · Vicarious TOA MODIS total signal Lm(λ) = M11Lt(λ) + M12Qt(λ) + M13Ut(λ)

  8. TOA sensor cross-calibration MODIS measured TOA radiance, polarized m Lm(λ) – M11Lt(λ) + M12Qt(λ) + M13Ut(λ) • minimize over global distribution of path geometries • find best M11, M12, M13 per band, detector, and mirror-side • M11, M12, M13 = f (mirror AOI) • do this for one day per month over the mission lifespan

  9. Polarization of the atmosphere √Qt2 + Ut2 dp = Lt degree of atmospheric polarization dp air molecule (Rayleigh) and glint scattering polarization correction fp pre-launch MODIS characterization MODIS Terra swath 412nm band 8 Lm fp = Lt

  10. Blue band temporal trends Mirror side 1 Mirror side 2 RVS = 1/M11 412 Detector 4 443 Space View (lunar) frame Nadir frame Solar Diffuser frame 488

  11. Blue band RVS & polarization sensitivity MS1 M13 fixed to pre-launch 412 443 488 Detector 4

  12. Blue band RVS & polarization sensitivity MS2 M13 fixed to pre-launch 412 443 488 Detector 4

  13. MODIS-Terra vicarious characterization MS1, Detector 4 MS2, Detector 4 RVS M12 M13 RVS M12 M13 412 443 488 531 551 667 678

  14. MODIS Terra and Aqua comparison Terra MS2, Detector 4 Aqua MS2, Detector 4 RVS M12 M13 RVS M12 M13 412 443 488 531 551 667 678

  15. Comparison of MODIS-Terra and MODIS-Aqua Lwn Before Vicarious Characterization Lwn(412nm) band 8 Lwn(443nm) band 9 Lwn(488nm) band 10 Lwn(531nm) band 11 Lwn(551nm) band 12 After Vicarious Characterization

  16. MODIS-Terra residual RVS in Lwn Before Vicarious Characterization 412 443 488 MS1 MS2 After Vicarious Characterization 412 443 488

  17. MODIS-Terra temporal anomalies Before Vicarious Characterization Lwn(488nm) band 10 chlor_a After Vicarious Characterization Lwn(488nm) band 10 chlor_a

  18. Summary • MODIS-Terra shows evidence of residual error in instrument response versus scan-angle and/or changes in polarization sensitivity. • The MODIS on-board calibration system can not assess changes in RVS “shape” or changes in polarization; these characteristics are restricted to our pre-launch knowledge, which itself may be in error. • The OBPG developed a vicarious on-orbit characterization for visible band polarization and RVS changes over time, using SeaWiFS Lwn. • Results show significant improvement in agreement between MODIS-Terra and MODIS-Aqua Lwn over the combined mission lifetime. • Future work will focus on vicarious characterization of the NIR. Franz, B.A., E.J. Kwiatkowska, G. Meister, and C.R. McClain (2008). Moderate Resolution Imaging Spectroradiometer on Terra: limitations for ocean color applications. J. Appl. Rem. Sens., in press.

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