MODIS ChlorophyllFluorescence

Ricardo Letelier, Mark Abbott,Jasmine NahorniakOregon State University

OutlinePhotosynthesis and fluorescenceMeasurement and validation of chlorophyll natural fluorescence from spaceFluorescence and the estimation of sea surface chlorophyll concentrationUsing fluorescence to estimate variability in phytoplankton quantum yield

Weekly FLH

Weekly chl_MODIS

Use of FLHImprove 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

Light Harvesting, Fluorescence and PhotosynthesisLHC2 e-u Fluorescence ffheat fhADP+P ATPNADP + 2H+

NADPH2Fp + Ff + Fh = 1Light energy not used for photosynthesis is lost as heat and fluorescence

letelier - Light absorbed by the algal photosystem may follow three major dissipation paths:1) Used in the split of water and the flow of resulting electrons from photosystem II to photosystem I, generating ATP and NADPH used for the fixation of inorganic carbon. From a fluorescence measurement perspective this is termed "photochemical quenching" 2) Energy in the exited state of chlorophyll is released as fluorescence.3) Energy is dissipated as heat by photoprotective pigments "non-photochemical quenching"The summ of these three probabilities is equal to 1

Fp + Ff + Fh = 1

FLH = Lu683 Baseline

Baseline = Lu1 - [(Lu1-Lu2)/(lLu2-lLu1)]*(683-lLu1)

Absorption spectra for water, CDOM, and phytoplankton

MODIS FLH bands: avoid oxygen absorbance at 687 nmWeighting factor used to compensate for off-center FLH

letelier - MODIS Fluorescence wavebands (!#, 14, and 15) superimposed to the upwelling light spectrum of the ocean for surface waters containing 0.01 and 10 mg chl/m3

Note that band 14 is not centered around 683 nm. This is due to the fact that at 683 nm it would be affected by the absorption of oxygen at 685 nm in the atmosphere.

1.4%Wavelength, nmRadiance, W m-2 m-1 sr-110 mg0.01 mgD TOA spectra(10 - 0.01 mg)Normalized band transmittance anddifference between TOA Spectra, W m-2 m-1 sr-1Band #146606706806907007107.47.98.48.99.49.90.20.30.40.50.6

Radiance, W m-2 m-1 sr-1Wavelength, nm% Difference between FASECODE FLHand LOWTRAN FLHLOWTRAN FLHFASE FLH% differenceMODIS Specified Band 14 CWActual Band 14 CW

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

(From Frank Hoge and Paul Lyon)

FLH vs. chlorophyllFLH vs. CDOM

GLOBEC NEP AUGUST 2002

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

Day 217Day 218Day 211Day 212Day 212Day 213

In situ chlorophyll, mg m-3FLH, W m-2 m-1 sr-1 GLOBEC NEP AUGUST 2002[chl] = .021 + 43.4 FLH1.866

chlFLH empirical(this study)chlFLH semi-analytical(Huot & Cullen assuming ff = 0.006)In situ chlGLOBEC NEP AUGUST 2002Both 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)

Natural (passive) Fluorescence where F = fluorescence[chl] = chlorophyll concentrationPAR = photosynthetically available radiationa* = chlorophyll specific absorptionF = fluorescence quantum yield

Absorbed Radiation by PhytoplanktonARP = a* x [chl] x PAR (calculated independently from [chl])

F/ARP = Chl Fluor. Efficiency (CFE) F ARP / ([chl] x PAR) = a*

Huot & Cullens approachFLH = EPAR(0) [chl] aj*(512) Qa* j Cf Kfabs + af

Where Qa* = aj*(678) / asol*(678)

We have to assume j constant

MODIS_Chl MODIS_FLH MODIS_CFE MODIS_ARPOSU Direct Broadcast October 04, 2001MODIS data shows chl not always in spatial correspondence with fluorescencePhysiological parameters also vary spatially

, W m-2 mm-1 sr-1, mg m-2 offshoreinshoreFisher and Kronfeld(1990) AssumingCFE = 0.003

In Situ Observations of F/[chl] suggest it can be a proxy for ffInitial slope proportional to F

letelier - Field observations of the quantum yield of fluorescence suggest that it is high in waters with low nutrient levels and low in coastal areas.

MODIS ARPHuot & Cullen ARPusing in situ chl toDerive an average ff chlFLH empirical(this study)

Thalassiosira weissflogii Chemostat results 2001-2002After 3 days of constant cell counts

After 14 days

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 naturalenvironments?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.

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.

AcknowledgmentsWayne Esaias (NASA/GSFC)Bob Evans, Kay Kilpatrick & Howard Gordon (Univ. Miami)

Fluorescence Product FlagsBit 6 FLH/chloro_MODIS > 1Bit 7 FLH/chloro_MODIS > 0.5Bit 8 FLH > 2Bit 9 FLH > 1Bit 10 chloro = -1

Bit 11 ARP quality 2Bit 12 ARP quality = 1Bit 13 CFE > 0.1

FlagsFor 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 setFor 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

End of talk

LatitudeLongitudePP/PSPhotoprotective:Photosynthetic pigment ratioPP/PSOther alternatives : - Changes in ARP (We just finished analyzing the filter pad particulate absorption samples)- Heat dissipation processes not accounted for

FLH/chl vs. Fv/Fm as Function of SSTMODIS FLH / chl, W m-2 m-1 sr-1 (mg m-3)-1 (proxy for Ff)