Post on 01-Jan-2016
Page 1 1 of 14, Vijay, Ge152
The Orbiting Carbon ObservatoryThe Orbiting Carbon Observatory (OCO) Mission(OCO) Mission http://oco.jpl.nasa.gov
Vijay Natraj (Caltech)Vijay Natraj (Caltech)
Ge152Ge152
May 28 2008
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Introduction: Carbon Sinks?
• Atmospheric Carbon dioxide (CO2)
– Primary man-made greenhouse gas
– Mixing ratios increased by ~25% since 1860
– Only half of the CO2 from fossil fuel emissions in atmosphere
• Outstanding Issues– Where are the CO2 sinks?
– Why does atmospheric buildup vary with uniform emission rates?
– How will CO2 sinks respond to climate change?
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Why Measure CO2 from Space?
• Studies from GV-CO2 stations – Flux residuals exceed 1 GtC/yr in
some zones – Network is too sparse
• Inversion tests– Global XCO2 pseudo-data with 1
ppm accuracy – Flux errors reduced to < 0.5
GtC/yr/zone for all zones– Global flux error reduced by a
factor of ~3
Courtesy: Rayner and O’Brien, 2001
1.2
0.6
0.0
Flu
x Re
sidu
als (G
t/yr/zon
e)
1.2
0.6
0.0
Flu
x Re
sidu
als (G
t/yr/zon
e)
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Precise CO2 Measurements Needed
• Space-based XCO2 estimates will improve constraints on CO2 fluxes
– Near global coverage on monthly intervals
– Precisions of 1–2 ppm (0.3–0.5%) on regional scales
– No spatially coherent biases > 1–2 ppm (0.3 to 0.5%) on regional scales
CO
2 M
ixin
g R
atio
(p
pm
)
356
360
364
Lat
itu
de
90
-90
0
356
360
364
Lat
itu
de
90
-90
0
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The Orbiting Carbon Observatory (OCO)
• Spectra of CO2 and O2 absorption in reflected sunlight used to estimate XCO2
• Random errors and biases no larger than 1 - 2 ppm (0.3 - 0.5%) on regional scales at monthly intervals
OCO will make the first space-based measurements with the precision and resolutions needed to quantify CO2 sources and sinks and monitor their variability.
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OCO Fills a Critical Measurement Gap
OCO will make precise global measurements of XCO2 needed to monitor CO2 fluxes on regional to continental scales.
Spatial Scale (km)
1
2
3
4
5
6
CO
2 E
rror
(pp
m)
1 10 100 1000 10000
OCO
FlaskSite
AquaAIRS
Aircraft
0
FluxTower
Globalview Network
NOAATOVS
ENVISATSCIAMACHY
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Spectroscopy
Clouds/Aerosols, Surface Pressure Clouds/Aerosols, H2O, TemperatureColumn CO2
• Column-integrated CO2 abundance– Maximum contribution from surface
• Why high spectral resolution?– Enhances sensitivity, minimizes biases
O2 A-band
CO2 1.61m
CO2 2.06 m
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OCO Will Fly in the A-Train
OCO files at the head of the A-Train, 4 minutes ahead of the Aqua platform
1:26
Coordinated Observations
GLORY1:34
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Nadir Observations
• Observatory points instrument at local nadir– Collects science data over sunlit hemisphere at
solar zenith angles < 85
• Advantages+ Small footprint (< 3 km2) isolates cloud-free
scenes and reduces biases from spatial inhomogeneities over land
+ Simplifies operations
• Liabilities Low Signal/Noise over dark ocean
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Glint Observations
• Glint Observations: views “glint” spot– Angle of reflection equals angle of
incidence of sunlight at surface: R = I
• Advantages + Improves Signal/Noise over oceans
• Disadvantages More interference from clouds
Operations more complicated
Local Nadir
Glint Spot
Ground Track
R I
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Target Observations
• Tracks a stationary surface target (calibration site) to collect large numbers of soundings
• Uplooking ground-based FTS data acquired simultaneously through same slant column
• Acquire Target data over 1 surface validation site each day
447-
m W
LE
F T
ow
er
Geolocation Accuracy
Scan Direction Spa
tial D
irect
ion
Alo
ng S
lit
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Validation Program
• Ground-based in-situ measurements• NOAA CMDL Flask Network + Tower Data
• TAO/Taurus Buoy Array
• Uplooking FTS measurements of XCO2
• 3 funded by OCO
• 4 upgraded NDSC
• Aircraft measurements of CO2 profile
Buoy Network CMDL
Page 14 14 of 14, Vijay, Ge152
Acknowledgments
• Yuk Yung
• David Crisp, Charles Miller
• Retrieval Algorithm: Denis O’Brien, Geoff Toon, Bhaswar Sen, Hartmut Boesch, Rob Spurr, Hari Nair, James McDuffie, Mick Christi
• Validation: Paul Wennberg, Ross Salawitch, Brian Connor
• Calibration: Carol Bruegge
• OCO Science Team