1. Ocean Color Products: The challenge of going from stocks to rates
Sam Laney
Ricardo Letelier
Mark Abbott
NOAA/NESDIS CoRP Satellite Calibration & Validation Symposium
July
Cooperative Institute for Oceanographic Satellite Studies
College of Oceanic & Atmospheric Sciences
Oregon State University, Corvallis OR
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

2. Overview:
How ocean phytoplankton standing stocks relate to primary productivity in the ocean
Current remote sensing approach for estimating marine primary productivity, & some concerns with it
How remote sensing of chlorophyll fluorescence is providing insight into photosynthetic variability that affects estimates of primary production
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

3. Good at measuring stocks of phytoplankton with remote sensors:
Stocks (or pools):
Biomass, abundance
“standing stock”
Good at measuring stocks of phytoplankton with remote sensors:
SeaWiFS “chlorophyll”
#1 scientific use of ocean color remote sensing data: phytoplankton chl
Rates (or flux):
Flow of energy or matter through a stock
“primary production”
“sustainable yield”
“carbon sequestration”
Important issues in marine ecology, but…
Not nearly so easy to assess using remote sensing
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

4. Challenges of aquatic photosynthesis:
Challenges of aquatic photosynthesis: (compared to remote sensing terrestrial production)
Optical:
Need large dynamic range from a weak signal
Physiological:
C uptake rates ~ 10x standing stock (0.2x for land)
Considerable spatiotemporal variability in stocks
Phytoplankton very different photosynthetically
Chl not major absorbing pigment in some phytoplankton
Wide physiological range of carbon:chl (factor of 10)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

5. Top of the Atmosphere Radiances (Lsat)
Radiative Transfer Models
Image: NASA
Normalized Water Leaving Radiances (nLw)
Photosynthetic Available Radiation (PAR)  = nm
Ocean Chlorophyll Algorithms (empirical or semi-analytical)
Photosynthetic efficiency (P) (derived empirically from SST)
Sea surface Chl a concentrations
Primary Production model
Image: OPP IMCS Rutgers
Higher level model (e.g. export production, carbon sequestration, fisheries)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

6. Chl fluorescence, photosynthesis, & production:
PriProd = PAR  ([chl]  a*)  FP
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
400
450
500
550
600
650
700
Wavelength, nm
Lu/Es
Phytoplankton absorption
= [chl]  a*
Phytoplankton
fluorescence by chl
So, P - F are inversely related:
PAR (sunlight)
Absorbed Radiation by Phytoplankton (ARP  PAR  chl  a*)
Photosynthesis P
Fluorescence F
F = PAR  ([chl]  a*)  FF
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

7. Chl fluorescence can be measured by modern remote sensors, e. g
Chl fluorescence can be measured by modern remote sensors, e.g. MODIS or MERIS
Fluorescence Line Height (FLH)
Sea surface upwelling irradiance 10 mg Chl m-3 )
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
600
620
640
660
680
700
720
740
760
FLH
Lu1
Lu2
Lu683
Wavelength, nm
Exitance, W m-2 µm-1
FLH = Lu683 – Baseline683
Baseline683 = Lu1 - [(Lu1-Lu2)/(lLu2-lLu1)]*(683-lLu1)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

8. FLH validation: Coastal: - GLOBEC - COAST Open ocean: - HOT cruises
- Southern Ocean
- MOBY mooring
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

9. In situ vs. remotely sensed FLH:
Oregon coastal region
Oregon Drifters FLH, W m-2 mm-1 sr-1
MODIS Terra FLH, W m-2 mm-1 sr-1
1:1
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

10. Validating MODIS Fluorescence:
Line ‘A’
Frontal regions
Line ‘B’
From Hoge et al.
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

11. Images: ocean at mesoscales, a decoupling between FLH & chl
Differences in?
species composition
environmental forcing
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

12. Observe changes in FLH/chl during the day:
nearshore, frontal, and pelagic regions
A = offshore
B = frontal regions
C = nearshore A B C
Chl FLH
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

13. Can associate variability in FLH/PAR with photosynthetic differences resulting from nutrient availability
Nitrate-limited Nitrate-starved
FLH
FLH / PAR
PAR irradiance (mol quanta m-2 s-1)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

14. FLH: status & future directions
Field validation efforts suggest that FLH is a robust remote sensing product
Lab validation shows that FLH helps to identify & quantify key physiological aspects of photosynthesis & production
To improve remote sensing PP with FLH, need to know its diurnal dynamics. Chl fluorescence from geosynchronous sensor (HES-CW on GOES-R)?
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

15. Ocean color  other important rates :
Silicate flux
Rate of N2 fixation
e.g. Platt group
e.g. Subramaniam group, Westberry
Rate of calcification
e.g. Balch group
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

16. Acknowledgments:
Jasmine Nahorniak & Curt Vandetta (OSU MODIS Direct Broadcast Station)
NOAA/NESDIS funding through CIOSS
Dennis Clark (NOAA)
Wayne Esaias, Frank Hoge (NASA)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

17. Variability in patterns of chl and FLH
MODIS Terra L2 1 km resolution scene (October 3rd 2001) – COAS/OSU Direct Broadcast
Sea Surface Temperature Chl a Chl Fluorescence Line Height
(°C) (mg m-3) (W m-2 mm-1 sr-1)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

18. chlFLH semi-analytical
GLOBEC NEP AUGUST 2002
In situ chl
chlFLH empirical
(this study)
chlFLH semi-analytical
(Huot & Cullen
assuming ff = 0.006)
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)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU

19. Relevance:
Aquatic photosynthesis affects global fluxes of C, N, O, & other bioelements
Response to climate change, ecosystem carrying capacities (e.g. fisheries), depend both on stocks & rates
Phytoplankton standing stocks and primary production correlate only on very large time & space scales
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU