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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

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Flu

x Re

sidu

als (G

t/yr/zon

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1.2

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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

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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

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Geolocation Accuracy

Scan Direction Spa

tial D

irect

ion

Alo

ng S

lit

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Retrieval Algorithm

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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

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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