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 13-14 2005
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
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
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
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
Top of the Atmosphere Radiances (Lsat)
Image: NASA
Radiative Transfer Models
Normalized Water Leaving Radiances (nLw)
Photosynthetic
Available Radiation
(PAR)
 = 400-700 nm
Ocean Chlorophyll Algorithms
(empirical or semi-analytical)
Sea surface Chl a
concentrations
Photosynthetic
efficiency (P)
(derived empirically
from SST)
Primary Production model
Higher level model (e.g.
export production, carbon
sequestration, fisheries)
Image: OPP IMCS Rutgers
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
Chl fluorescence, photosynthesis, & production:
PriProd = PAR  ([chl]  a*)  P
0.016
0.014
Phytoplankton absorption
= [chl]  a*
0.012
Phytoplankton
fluorescence
by chl
0.01
Lu/Es
So, P - F are
inversely related:
0.008
PAR (sunlight)
0.006
Absorbed Radiation
by Phytoplankton
(ARP  PAR  chl  a*)
0.004
0.002
0
400
450
500
550
600
Wavelength, nm
650
700
F = PAR  ([chl]  a*)  F
Photosynthesis
P
Fluorescence
F
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
Chl fluorescence can be measured by modern
remote sensors, e.g. MODIS or MERIS
Fluorescence Line Height
Sea surface upwelling irradiance (calculated @ 10 mg Chl m-3 )
0.8
Lu683
0.7
0.6
Lu1
0.5
FLH
Exitance, W m-2 µm-1
(FLH)
0.4
0.3
0.2
0.1
Lu2
FLH = Lu683 – Baseline683
Baseline683 = Lu1 - [(Lu1-Lu2)/(lLu2-lLu1)]*(683-lLu1)
0
600
620
640
660
680
700
720
740
760
Wavelength, nm
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
FLH validation:
Coastal:
- GLOBEC
- COAST
Open ocean:
- HOT cruises
- Southern Ocean
- MOBY mooring
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
In situ vs. remotely sensed FLH:
Oregon coastal region
MODIS Terra FLH, W m-2 mm-1 sr-1
0.18
1:1
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0
0.05
0.1
0.15
0.2
0.25
Oregon Drifters FLH, W m-2 mm-1 sr-1
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
Validating MODIS Fluorescence:
Line ‘A’
Frontal regions
Line ‘B’
From Hoge et al.
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
FLH
Images: ocean at mesoscales, a
decoupling between FLH & chl
chl
Differences in?
• species composition
• environmental forcing
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
Observe changes in FLH/chl during the day:
nearshore, frontal, and pelagic regions
A
B
C
B = frontal regions
C = nearshore
A = offshore
Chl FLH
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
Can associate variability in FLH/PAR
with photosynthetic differences
resulting from nutrient availability
Nitrate-limited
Nitrate-starved
FLH
FLH / PAR
PAR irradiance (mmol quanta m-2 s-1)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
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
Ocean color  other important rates :
Silicate flux
Rate of N2 fixation
e.g. Subramaniam group, Westberry
Rate of calcification
e.g. Platt group
e.g. Balch group
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
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
Variability in patterns of chl and FLH
MODIS Terra L2 1 km resolution scene (October 3rd 2001) – COAS/OSU Direct Broadcast
Sea Surface Temperature
(°C)
Chl a
(mg m-3)
Chl Fluorescence Line Height
(W m-2 mm-1 sr-1)
Laney-Letelier-Abbott 2005 CoRP CalVal Symposium, CIOSS COAS OSU
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
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