Estimating Chlorophyll Concentrations using MODIS Fluorescence: A

Preliminary Evaluation in Coastal Waters

Ricardo Letelier, Mark Abbott, Jasmine Nahorniak

College of Oceanic and Atmospheric SciencesOregon State University

Acknowledgment: Robert Evans et al. University of Miami

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*

*[ ] ( )F

F chl PAR a

If p + f + h = 1 & h = const.

then p = const. – f

PP = [chl] x (PAR x a*) x (const. – f)

or PP ARP x (const. - FLH/ARP)

(const./ARP) - FLH

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

Goddard DACC weekly declouded 36 km starting 12/02/2000 (Quality=0 L2 V 4.2.2)

MODIS ARP

MODIS FLH

Goddard DACC weekly declouded 36 km starting 12/02/2000 (Quality=0 L2 V 4.2.2)

MODIS CHL

MODIS CFE

Chlorophyll December 4, 2000

FLH December 4, 2000

Chlorophyll June 25, 2002

FLH June 25, 2002

A

B

C

(From Frank Hoge)

MODIS_Chl MODIS_FLH MODIS_CFE MODIS_ARP

OSU Direct Broadcast October 04, 2001

Field Approach

• Mesoscale Surveys (Cowles/Barth)

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,…)

Comparison between field measurements and Remote Sensing data

(Mesoscale Survey August 2000And MODIS Image from August 2nd)

(In situ chl derived from the calibration of the flow through fluorometer withHPLC chlorophyll determinations )

-Blue = all mesoscale survey data (July 31st – August 7th)-Red = Within 0.5 days of the MODIS Image Time stamp

In situ chl (mg m-3) In situ chl (mg m-3)

MO

DIS

chl

_2 (

mg

m-3)

MO

DIS

FLH

, W

m-2 u

m-1 s

r-1

0 0.005 0.01 0.015 0.02 0.025 0.030

500

1000

1500

2000

2500

3000

Range covering mostoceanic regions(Gordon, 1979;Carder & Steward,1985; and others)

East Coast Image 2001095.1605Oregon Coast DB Image 2001150#

occu

renc

es

# oc

cure

nces

CFE CFE

, m

g m

-2

, m

g m

-2

East Coast Image 2001095.1605Oregon Coast DB Image 2001150

Fischer and Kronfeld(1990) AssumingCFE = 0.003,

W m

-2

m-1 s

r-1

, W

m-2

m-1 s

r-1, mg m-2 , mg m-2

Chlorophyll biomass proxy Optimum photosynthesis max yield

(From Rachel Sander’s work)

25.8

24.8

23.8

22.7

21.723.3

24.3

25.3 PS

II

Longitude

Lat

itud

e

2625

24

23

22

23

24

25

Fv/

Fm

Longitude

Lat

itud

e

Optimum Absorption Quantum Yield August 2000(Nighttime)

Absorption Cross-section of Photosystem II

0.2

0.4

0.6

0.8

1

1.2

45° N

44° N

43° N

42° N

41° N

123° W 124

° W 125

° W 126

° W 127

° W

Coos Bay

New port

Cape Blanco

Heceta Head

Lat

itud

e

Longitude

PP/PS

Photoprotective:Photosynthetic pigment ratio

0.0903226

0.298387

0.506452

0.714516

0.922581

1.13065

1.33871

30 30.5 31 31.5 32 32.5 33 33.5 349

10

11

12

13

14

15

16

17

18

19

2625

24

23

2223

24

25

Salinity (ppt)Te

mpe

ratu

re (C

)PP/PS

Other alternatives : - Changes in ARP (We just finished analyzing the filter pad particulate absorption samples)- Heat dissipation processes not accounted for

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 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.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Fv/

Fm

, n.d

.9

AM

CF

E, r

.u.

/max , n.d.

Thalassiosira weissflogii Chemostat results 2001-2002

After 3 days of constant cell counts

After 14 days

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