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MODIS Chlorophyll Fluorescence Ricardo Letelier, Mark Abbott, Jasmine Nahorniak Oregon State University Slide 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 Slide 3 Weekly FLH Slide 4 Weekly chl_MODIS Slide 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 Slide 6 Light Harvesting, Fluorescence and Photosynthesis LHC 2 e - Fluorescence f heat h ADP+P ATP NADP + 2H + NADPH 2 p + f + h = 1 Light energy not used for photosynthesis is lost as heat and fluorescence Slide 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) LHC PSI e-e- L 683 heat (ATP & NADPH 2 ) LHC PSI L 683 heat (ATP & NADPH 2 ) DCMU p + f + h = 1 Slide 8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 600620640660680700720740760 FLH Lu 1 Lu 2 Lu 683 Wavelength, nm Exitance, W m -2 m -1 FLH = Lu 683 Baseline Baseline = Lu 1 - [(Lu 1 -Lu 2 )/( Lu 2 - Lu 1 )]*(683- Lu 1 ) Slide 9 Slide 10 MODIS FLH bands: avoid oxygen absorbance at 687 nm Weighting factor used to compensate for off- center FLH Slide 11 1.4% Wavelength, nm Radiance, W m -2 m -1 sr -1 10 mg 0.01 mg TOA spectra (10 - 0.01 mg) Normalized band transmittance and difference between TOA Spectra, W m -2 m -1 sr -1 Band #14 660670680690700710 7.4 7.9 8.4 8.9 9.4 9.9 0.2 0.3 0.4 0.5 0.6 Slide 12 Radiance, W m -2 m -1 sr -1 Wavelength, nm % Difference between FASECODE FLH and LOWTRAN FLH LOWTRAN FLH FASE FLH % difference MODIS Specified Band 14 CW Actual Band 14 CW Slide 13 Requires correction at low chl concentrations due to the convex behavior of the TOA signal between 667 and 683 nm SNR sensitivity = 0.012 W m -2 m -1 sr -1 Slide 14 (From Frank Hoge and Paul Lyon) Slide 15 FLH vs. chlorophyll FLH vs. CDOM Slide 16 GLOBEC NEP AUGUST 2002 Slide 17 GLOBEC NEP AUGUST 2002 (July 31 st August 19 th ) In situ chl a, mg m -3 MODIS chl a, mg m -3 Slide 18 Slide 19 MODIS_FLH day x MODIS_FLH day x+1 Day x Day 217 Day 218 Day 211 Day 212 Day 213 Slide 20 In situ chlorophyll, mg m -3 FLH, W m -2 m -1 sr -1 GLOBEC NEP AUGUST 2002 [chl] =.021 + 43.4 FLH 1.866 All cruise data Only pixels of passes within 5 hrs of sampling time Slide 21 chl FLH empirical (this study) chl FLH semi-analytical (Huot & Cullen assuming f = 0.006) In situ chl GLOBEC NEP AUGUST 2002 -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) Slide 22 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* Slide 23 FLH = E PAR (0) [chl] a * (512) Q a * C f K f abs + a f Where Q a * = a * (678) / a sol * (678) We have to assume constant Huot & Cullens approach Slide 24 MODIS_Chl MODIS_FLH MODIS_CFE MODIS_ARP OSU Direct Broadcast October 04, 2001 MODIS data shows chl not always in spatial correspondence with fluorescence Physiological parameters also vary spatially Slide 25 , W m -2 m -1 sr -1, mg m-2 offshore inshore Fisher and Kronfeld (1990) Assuming CFE = 0.003 Slide 26 Slide 27 In Situ Observations of F/[chl] suggest it can be a proxy for f Initial slope proportional to F Slide 28 EkEk Q np Slide 29 MODIS ARP Huot & Cullen ARP using in situ chl to Derive an average f chl FLH empirical (this study) Slide 30 Fv/Fm, n.d. 9 AM CFE, r.u. / max, n.d. Thalassiosira weissflogii Chemostat results 2001-2002 After 3 days of constant cell counts After 14 days Slide 31 Where do we stand? Field observations suggest that MODIS FLH is a robust product. Preliminary comparison of [chl] field vs FLH MODIS 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. Slide 32 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 f (a physiological parameter) that requires the previous validation of ARP ([chl] x a*). - Further use of f to infer p requires the characterization of the variability in energy distribution within the photosystem. Slide 33 Acknowledgments Wayne Esaias (NASA/GSFC) Bob Evans, Kay Kilpatrick & Howard Gordon (Univ. Miami) Slide 34 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 Slide 35 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 Slide 36 End of talk Slide 37 Latitude Longitude PP/PS Photoprotective:Photosynthetic pigment ratio PP/PS Other alternatives : - Changes in ARP (We just finished analyzing the filter pad particulate absorption samples) - Heat dissipation processes not accounted for Slide 38 FLH/chl vs. F v /F m as Function of SST MODIS FLH / chl, W m -2 m -1 sr -1 (mg m -3 ) -1 (proxy for f )