Functional Block Diagram

1
The Orbital Carbon Observatory (OCO)
Mission David Crisp (OCO PI) and the OCO
Team COSPAR 2002 Thursday, 17 October 2002
2
Why Measure CO2?

• ISSUES Carbon dioxide (CO2) is the
• Principal atmospheric component of the global
  carbon cycle
• Primary anthropogenic driver of climate change
• Only half of CO2 produced by human activities
  over the past 30 years has remained in the
  atmosphere.
• Where are the sinks?
• Will this continue?

3
The Global Carbon Cycle
Natural carbon fluxes account for 300 GtC/yr and
exist in near equilibrium.
6 GtC/yr
The 6 GtC/yr produced by human activity
represents only 2 of the carbon flux, but it may
tip the balance
4
An Uncertain FutureWhere are the Missing Carbon
Sinks?

• What are the relative roles of the oceans and
  land ecosystems in absorbing CO2?
• Is there a northern hemisphere land sink?
• What are the relative roles of North America/
  Eurasia
• What controls carbon sinks?
• Why does the atmospheric buildup vary with
  uniform emission rates?
• How will the sinks respond to climate change?
• Climate prediction requires an improved
  understanding of natural CO2 sinks
• Future atmospheric CO2 increases
• Their contributions to global change

Cox et al. Nature, 408, 184, 2000.
5
Why Measure CO2 from Space?Improved CO2 Flux
Inversion Capabilities

• Current State of Knowledge
• Global maps of carbon flux errors for 26
  continent/ocean-basin-sized zones retrieved from
  inversion studies
• Studies using data from the 56 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 lt0.5 GtC/yr/zone for all
  zones
• Global flux error reduced by a factor of 3.

1.0 0.5 0.0
Flux Retrieval Error GtC/yr/zone
1.0 0.5 0.0
Rayner OBrien, Geophys. Res. Lett. 28, 175
(2001)
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The Orbiting Carbon Observatory (OCO) Mission

• OCO will use mature technologies to
• Make the first, global, space-based observations
  of the column integrated dry air mole fraction,
  XCO2
• Provide independent data validation approaches to
  ensure high accuracy (1 ppm, 0.3)
• Combine satellite data with ground-based
  measurements to characterize CO2 sources and
  sinks on regional scales on monthly to
  interannual time scales
• Fly in formation with the A-Train to facilitate
  coordinated observations and validation plans

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OCO Science Team
David Crisp, PI Charles Miller, Deputy PI
Education Gil Yanow
Retrieval Algorithms D. OBrien G. Stephens G.
Toon Y. Yung
Cal/Val F. Bréon L. Brown J. Burrows P. Ciais B.
Connor C. Miller R. Salawitch S. Sander P.
Tans P. Wennberg S. Wofsy
Source/Sink Modeling R. Atlas S. Doney I. Fung D.
Jacob S. Pawson J. Randerson P. Rayner
Ground Data System Interface B. Sen
8
XCO2 Retrieved from Bore-Sited CO2 and O2 Spectra
Taken Simultaneously

• High resolution spectroscopic measurements of
  reflected sunlight in near IR CO2 and O2 bands
  provide the data needed to retrieve XCO2
• Column-integrated CO2 abundance
• Maximum contribution from surface
• Other data needed (provided by OCO)
• Surface pressure, albedo, atmospheric
  temperature, water vapor, clouds, aerosols
• Why high spectral resolution?
• Lines must be resolved from the continuum to
  minimize systematic errors

Clouds/Aerosols, Surface Pressure
Clouds/Aerosols, H2O, Temperature
Column CO2
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Spatial Sampling Strategy

• OCO is designed provide an accurate description
  of XCO2 on regional scales
• Atmospheric motions mix CO2 over large areas as
  it is distributed through the column
• Source/Sink model resolution limited to 1o x 1o
• High spatial resolution
• 1 km x 1.5 km footprints
• Isolates cloud-free scenes
• Provides thousands of samples on regional scales

Spatial sampling along ground track
Ground tracks over the tip of South America
10
Operational Strategy

• 115 PM near polar (98.2o) orbit
• 15 minutes ahead of EOS A-Train
• Same ground track as AQUA
• Global coverage every 16 days
• Science data taken on day side
• Nadir mode
• Highest spatial resolution
• Glint mode
• Highest SNR over ocean
• Target mode
• Validation
• airmass dependence
• Comparison with surface FTS stations
• Calibration data taken on night side
• Solar, limb, dark, lamp

11
Will it Work?

• Accuracies of 1ppm needed to identify CO2 sources
  and sinks.
• Realistic, end-to-end, Observational System
  Simulation Experiments
• Reflected radiances for a range of
  atmospheric/surface conditions
• line-by-line multiple scattering models
• Comprehensive description of
• mission scenario
• instrument characteristics
• Results The OCO payload will
• meet or exceed the requirements for measuring CO2
• provide rigorous constraints on the distribution
  and optical properties of clouds and aerosols

End-to-end retrievals of XCO2 from individual
simulated nadir soundings at SZAs of 35o and 75o.
The model atmospheres include sub-visual cirrus
clouds (0.02??c? 0.05), light to moderate aerosol
loadings (0.05??a? 0.15), over ocean and land
surfaces. INSET Distribution of XCO2 errors
(ppm) for each case
12
Validation Program Ensures Accuracy and Minimizes
Spatially Coherent Biases

• 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
• Complemented by Laboratory and on-orbit
  calibration

Buoy Network
CMDL
13
The OCO Implementation Team
ESSP PMO
14
OCO Mission Concept
Simple, Mature 3-channel Spectrometer
Ground Validation Sites
Dedicated Spacecraft
Data Processing Center
2007 Launch
Mission Ops
Ground Stations
Data Products
15
OCO Instruments

• Three bore-sighted, high resolution, grating
  spectrometers
• CO2 1.6 ?m band
• CO2 2.0 ?m band
• O2 0.76 ?m A-band
• Similar optics and electronics
• 200 mm F/2 refractive optics
• Spectral Resolution 20,000
• RSC Hawaii HgCdTe FPAs for CO2 channels
• RSC HyViSI FPA for O2 channel
• Existing Designs For Critical Components
• Hubble WFC-3 detectors
• Build-to-Print Aura HIRDLS cooler
• Provided by Hamilton Sundstrand Sensor
  Systems(Pomona Ca)

16
OCO Spacecraft

• 4th build of Orbital LEOStar-2 Bus
• Orbview 4, GALEX, SORCE
• Now in NASAs RSDO Catalog
• Satisfies all OCO Requirements with large margins

17
OCO Data Product Pipeline
AIRS T, P, H2O

• The OCO data flow from space through an automated
  pipeline which yields Level 1 and 2 data
  products.
• Level 3 and Level 4 products are produced by
  individual Science Team members.
• Preliminary tests of the retrieval algorithm
  demonstrate the OCO mission concept
• (Kuang et al., Geophys. Res. Lett., 29 (15)
  2001GL014298, 2002).

Space-borne Data Acquisition
Level 2
Calibration Validation Data
Spectral Radiances
Level 3
Ancillary Data FTIR XCO2 GVCO2 CO2 MODIS
Aerosol NCEP Fields
Global 1ppm XCO2 Maps
Data Assimilation Models
Inversion Models
Level 4
Temporally Varying CO2 Source/Sink Maps
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Summary

• Climate Forcing/Response
• T/H2O/O3 AIRS/TES/MLS
• Clouds CloudSat
• Aerosols CALIPSO
• CO2 OCO

• OCO will provide critical data for
• Understanding the carbon cycle
• Essential for developing carbon management
  strategies
• Predicting weather and climate
• Understanding sources/sinks essential for
  predicting CO2 buildup
• O2 A-Band will provide global surface pressure
  measurements
• OCO validates technologies critically needed for
  future operational CO2 monitoring missions
• Satisfies an unaccommodated measurement need
  identified by NPOESS

XCO2 (ppm)