1. 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

2. MODIS calibration changes since launch band 8 412nm SD door permanently opened B side electronics A side electronics pre-launch damage to mirror coating, MS2 Terra SD – Solar Diffuser frame 979, mirror AOI 50.3 0 SV – Space View frame 23, mirror AOI 11.4 0 MS1 – Mirror Side 1 MS2 – Mirror Side 2

3. MODIS trends in ocean color products Terra/Aqua ratios normalized water-leaving radiances L wn L wn (412nm) band 8 L wn (443nm) band 9 L wn (488nm) band 10 L wn (531nm) band 11 L wn (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 L wn L wn (412nm) band 8 Mirror side 1 MS1 Mirror side 2 MS2 -10% +10% per detector

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

6. L wn (λ’) gasglint whitecap air aerosol L t (λ) = [ L r (λ) + L a (λ) + tL f (λ) + TL g (λ) + t d (λ)L w (λ) ] · t g (λ) water SeaWiFS 9-day mean from MODIS NIR assumes MCST NIR band characterization λ’ → λ fit based on bio-optical models Modeling of TOA Stokes vector over oceans LtQtUt0LtQtUt0

7. Vicarious TOA MODIS total signal L m (λ) = M 11 L t (λ) + M 12 Q t (λ) + M 13 U t (λ) = · LmQmUm0LmQmUm0 M 11 M 12 M 13 M 14 M 21 … M 24 M 31 … M 34 M 41 M 42 M 43 M 44 LtQtUt0LtQtUt0

8. TOA sensor cross-calibration L m (λ) – M 11 L t (λ) + M 12 Q t (λ) + M 13 U t (λ) minimize over global distribution of path geometries find best M 11, M 12, M 13 per band, detector, and mirror-side M 11, M 12, M 13 = f (mirror AOI) do this for one day per month over the mission lifespan MODIS measured TOA radiance, polarized m

9. Polarization of the atmosphere degree of atmospheric polarization d p air molecule (Rayleigh) and glint scattering polarization correction f p pre-launch MODIS characterization √Q t 2 + U t 2 LtLt d p = MODIS Terra swath 412nm band 8 LmLm LtLt f p =

10. Blue band temporal trends Mirror side 2 Detector 4 Mirror side 1 Space View (lunar) frame Nadir frame Solar Diffuser frame RVS = 1/M 11 412 443 488

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

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

13. MODIS-Terra vicarious characterization RVSM12M13 412 531 678 RVSM12M13 443 488 551 667 MS1, Detector 4MS2, Detector 4

14. MODIS Terra and Aqua comparison RVSM12M13 412 531 678 RVSM12M13 443 488 551 667 Terra MS2, Detector 4Aqua MS2, Detector 4

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

16. MODIS-Terra residual RVS in L wn 412443 After Vicarious Characterization 488 412443488 Before Vicarious Characterization MS1 MS2

17. MODIS-Terra temporal anomalies After Vicarious Characterization Before Vicarious Characterization L wn (488nm) band 10 chlor_a L wn (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 L wn. Results show significant improvement in agreement between MODIS- Terra and MODIS-Aqua L wn 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.