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MODIS Chlorophyll Fluorescence

MODIS Chlorophyll Fluorescence. Ricardo Letelier, Mark Abbott, Jasmine Nahorniak Oregon State University. Outline. Photosynthesis and fluorescence Measurement and validation of chlorophyll natural fluorescence from space

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MODIS Chlorophyll Fluorescence

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  1. MODIS ChlorophyllFluorescence Ricardo Letelier, Mark Abbott, Jasmine Nahorniak Oregon State University

  2. Outline • Photosynthesis and fluorescence • Measurement and validation of chlorophyll natural fluorescence from space • Fluorescence and the estimation of sea surface chlorophyll concentration • Using fluorescence to estimate variability in phytoplankton quantum yield

  3. Weekly FLH

  4. Weekly chl_MODIS

  5. Use of FLH • Improve estimates of ocean Primary Production through: - Improving [chl] estimates in case II waters - Improving our capability to monitor the variability in the mean physiological state of algal assemblages in surface waters

  6. Light Harvesting, Fluorescence and Photosynthesis Light energy not used for photosynthesis is lost as heat and fluorescence Fp + Ff + Fh = 1 u NADP + 2H+ NADPH2 2 e- LHC ADP+P ATP Fluorescence ff heat fh

  7. Blue light induced chlorophyll fluorescence in Tobacco leaf. A. photographed in white light. B. taken in the low steady state of fluorescence, 5 min after the onset of illumination. The bright red fluorescing upper part of the leaf is where photosynthesis has been blocked by the herbicide duiron (DCMU). (From Krause and Weis, 1988) u e- PSI LHC (ATP & NADPH2) L683 heat u DCMU PSI LHC (ATP & NADPH2) L683 heat Fp + Ff + Fh = 1

  8. 0.8 Lu683 0.7 0.6 Exitance, W m-2 µm-1 Lu1 FLH 0.5 0.4 0.3 0.2 Lu2 0.1 0 600 620 640 660 680 700 720 740 760 Wavelength, nm FLH = Lu683 – Baseline Baseline = Lu1 - [(Lu1-Lu2)/(lLu2-lLu1)]*(683-lLu1)

  9. MODIS FLH bands: avoid oxygen absorbance at 687 nm Weighting factor used to compensate for off-center FLH

  10. 0.6 10 mg 9.9 D TOA spectra (10 - 0.01 mg) 0.5 9.4 0.01 mg 8.9 Radiance, W m-2 µm-1 sr-1 Normalized band transmittance and difference between TOA Spectra, W m-2 m-1 sr-1 0.4 8.4 Band #14 0.3 7.9 1.4% 0.2 7.4 660 670 680 690 700 710 Wavelength, nm

  11. LOWTRAN FLH FASE FLH Radiance, W m-2 µm-1 sr-1 % Difference between FASECODE FLH and LOWTRAN FLH Actual Band 14 CW % difference Wavelength, nm MODIS Specified Band 14 CW

  12. SNR sensitivity = 0.012 W m-2mm-1 sr-1 Requires correction at low chl concentrations due to the convex behavior of the TOA signal between 667 and 683 nm

  13. (From Frank Hoge and Paul Lyon)

  14. FLH vs. chlorophyll FLH vs. CDOM

  15. GLOBEC NEP AUGUST 2002

  16. GLOBEC NEP AUGUST 2002 (July 31st – August 19th) In situ chl a, mg m-3 MODIS chl a, mg m-3

  17. Day x MODIS_FLH day x+1 MODIS_FLH day x Day 218 Day 217 Day 212 Day 213 Day 211 Day 212

  18. All cruise data Only pixels of passes within 5 hrs of sampling time GLOBEC NEP AUGUST 2002 FLH, W m-2 µm-1 sr-1 [chl] = .021 + 43.4 FLH1.866 In situ chlorophyll, mg m-3

  19. GLOBEC NEP AUGUST 2002 chlFLH semi-analytical (Huot & Cullen assuming ff = 0.006) chlFLH empirical (this study) In situ chl • Both FLH derived chl algorithms appear to slightly overestimate chl a fields. • They do not seem to reproduce the low values observed in situ. • Some of the differences between in situ and FLH derived could be due to time differences and sampling depth (in situ = 5 m depth)

  20. Natural (passive) Fluorescence where F = fluorescence [chl] = chlorophyll concentration PAR = photosynthetically available radiation a* = chlorophyll specific absorption F = fluorescence quantum yield • Absorbed Radiation by Phytoplankton ARP = a* x [chl] x PAR (calculated independently from [chl]) • F/ARP = Chl Fluor. Efficiency (CFE)  F • ARP / ([chl] x PAR) = a*

  21. Huot & Cullen’s approach • FLH = EPAR(0) [chl] aj*(512) Qa*j Cf Kfabs + af Where Qa* = aj*(678) / asol*(678) We have to assume j constant

  22. OSU Direct Broadcast October 04, 2001 MODIS_Chl MODIS_FLH MODIS_CFE MODIS_ARP MODIS data shows chl not always in spatial correspondence with fluorescence Physiological parameters also vary spatially

  23. offshore , W m-2mm-1 sr-1 Fisher and Kronfeld (1990) Assuming CFE = 0.003 inshore , mgm-2

  24. 5.0E-02 4.5E-02 4.0E-02 3.5E-02 3.0E-02 (Lu683-backscatter) / Chlest, (µW cm-2 nm-1) / mg m-3 2.5E-02 2.0E-02 1.5E-02 1.0E-02 5.0E-03 0.0E+00 30 40 50 60 0 10 20 Ed490, µW cm-2 nm-1 sr-1

  25. In Situ Observations of F/[chl] suggest it can be a proxy for ff Initial slope proportional to F

  26. Qnp Ek

  27. chlFLH empirical (this study) Huot & Cullen ARP using in situ chl to Derive an average ff MODIS ARP

  28. Fv/Fm, n.d. 9 AM CFE, r.u. m/mmax , n.d. Thalassiosira weissflogii Chemostat results 2001-2002 After 3 days of constant cell counts After 14 days

  29. Where do we stand? • Field observations suggest that MODIS FLH is a robust product. • Preliminary comparison of [chl]field vs FLHMODIS suggest that FLH may prove of use to derive [chl] in turbid waters. However: - CFE was almost constant in the set of samples used in this study. Is this the range of values we should expect to see in natural environments? • CFE validation requires that of FLH and ARP. • In order to interpret CFE we need field and laboratory based work that explores the effect of environmental variability and phytoplankton specific composition.

  30. In other words: • FLH and CFE are very different MODIS products in terms of validation. • - FLH is based on nLw at 678 nm after baseline correction • - CFE is a proxy for Ff (a physiological • parameter) that requires the previous • validation of ARP ([chl] x a*). • - Further use of Ff to infer Fp requires • the characterization of the variability • in energy distribution within the • photosystem.

  31. Acknowledgments • Wayne Esaias (NASA/GSFC) • Bob Evans, Kay Kilpatrick & Howard Gordon (Univ. Miami)

  32. Fluorescence Product Flags • Bit 6 FLH/chloro_MODIS > 1 • Bit 7 FLH/chloro_MODIS > 0.5 • Bit 8 FLH > 2 • Bit 9 FLH > 1 • Bit 10 chloro = -1 • Bit 11 ARP quality ≥ 2 • Bit 12 ARP quality = 1 • Bit 13 CFE > 0.1

  33. Flags • For FLH - 0 if 6-10 are clear - 1 if 7 and 9 are set but 6, 6, and 10 are clear - 2 if 6, 8, or 10 are set - 3 if any common flags are set • For CFE - 0 if common flags are clear and bits 11 and 12 are clear - 1 if bit 12 is set or FLH quality is 1 - 2 if bit 11 or bit 13 is set or FLH quality is 2 - 3 if any common flags are set or if CFE > 0.15 or if FLH quality is 3

  34. End of talk

  35. Photoprotective:Photosynthetic pigment ratio PP/PS Latitude Longitude PP/PS Other alternatives : - Changes in ARP (We just finished analyzing the filter pad particulate absorption samples) - Heat dissipation processes not accounted for

  36. SST, °C 0.55 17.30 Fp + Ff + Fh= 1 0.50 16.34 0.45 15.39 In situ Fv / Fm (proxy for Fp) 0.40 14.43 0.35 13.47 0.30 12.51 0.25 0.20 11.55 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 FLH/chl vs. Fv/Fm as Function of SST MODIS FLH / chl,W m-2 µm-1 sr-1 (mg m-3)-1 (proxy for Ff)

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