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Estimating Chlorophyll Concentrations using MODIS Fluorescence: Preliminary Evaluation in Coastal Waters

This study evaluates the use of MODIS fluorescence to estimate chlorophyll concentrations in coastal waters. The relationship between fluorescence and chlorophyll is examined, and the challenges and potential solutions are discussed.

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Estimating Chlorophyll Concentrations using MODIS Fluorescence: Preliminary Evaluation in Coastal Waters

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  1. Estimating Chlorophyll Concentrations using MODIS Fluorescence: A Preliminary Evaluation in Coastal Waters Ricardo Letelier, Mark Abbott, Jasmine Nahorniak College of Oceanic and Atmospheric Sciences Oregon State University Acknowledgment: Robert Evans et al. University of Miami

  2. 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*

  3. IfFp + Ff + Fh = 1 &Fh = const. thenFp = const. – Ff  PP = [chl] x (PAR x a*) x (const. – Ff) or PP  ARP x (const. - FLH/ARP)  (const./ARP) - FLH

  4. Can we use FLH to tell us about chlorophyll? • Absorption-based algorithms fail in waters where there are other materials that absorb and scatter and are not correlated with chlorophyll • Sediment • Dissolved organic matter • Chlorophyll fluorescence is specific to chlorophyll • But it also depends on physiology

  5. Goddard DACC weekly declouded 36 km starting 12/02/2000 (Quality=0 L2 V 4.2.2) MODIS ARP MODIS FLH

  6. Goddard DACC weekly declouded 36 km starting 12/02/2000 (Quality=0 L2 V 4.2.2) MODIS CHL MODIS CFE

  7. Chlorophyll December 4, 2000

  8. FLH December 4, 2000

  9. Chlorophyll June 25, 2002

  10. FLH June 25, 2002

  11. A B C (From Frank Hoge)

  12. MODIS_Chl MODIS_FLH MODIS_CFE MODIS_ARP OSU Direct Broadcast October 04, 2001

  13. Field Approach • Mesoscale Surveys (Cowles/Barth)

  14. Some Survey Measurements -Continuous from Flow-through system -Temperature/ Salinity - Active Fluorometry - Fast Repetition Rate Fluorometry - Total and dissolved absorption and attenuation -Discrete - Pigments (Fluor/HPLC) - Nutrients (autoanalyzer) - Particulate absorption - Other Platforms - Optical Drifters, tethered buoys - Moorings - Satlantic MicroSAS underway reflectance - Satellites (SeaWiFS, MODIS, AVHRR,…)

  15. Comparison between field measurements and Remote Sensing data (Mesoscale Survey August 2000 And MODIS Image from August 2nd) MODIS chl_2 (mg m-3) MODIS FLH, W m-2 um-1 sr-1 In situ chl (mg m-3) In situ chl (mg m-3) (In situ chl derived from the calibration of the flow through fluorometer with HPLC chlorophyll determinations ) -Blue = all mesoscale survey data (July 31st – August 7th) -Red = Within 0.5 days of the MODIS Image Time stamp

  16. Oregon Coast DB Image 2001150 East Coast Image 2001095.1605 Range covering most oceanic regions (Gordon, 1979; Carder & Steward, 1985; and others) # occurences # occurences CFE CFE , mg m-2 , mg m-2

  17. , W m-2mm-1 sr-1 , W m-2mm-1 sr-1 Fischer and Kronfeld (1990) Assuming CFE = 0.003 , mg m-2 , mg m-2 Oregon Coast DB Image 2001150 East Coast Image 2001095.1605

  18. Chlorophyll biomass proxy Optimum photosynthesis max yield (From Rachel Sander’s work)

  19. August 2000 (Nighttime) Optimum Absorption Quantum Yield Latitude Fv/Fm Longitude Absorption Cross-section of Photosystem II Latitude sPSII Longitude

  20. 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

  21. However: • 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.

  22. 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

  23. Summary • Fluorescence and chlorophyll • Generally a linear relationship between absorption-based estimates and fluorescence-based estimates of chlorophyll • Exceptions are apparent, for example near the coast • Slope of line relating FLH to chl is related to CFE • Can we estimate chlorophyll from FLH? • Challenge is that many processes affect F • Photoprotective pigments, absorption cross-section • Appears, though, that CFE appears to fall into 2 clusters so problem may be tractable • High values of CFE appear to be associated with communities far from equilibrium • Time history of CFE may be key

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