Measuring Carbon Dioxidefrom the A-Train:
The OCO-2 Mission
David Crisp, OCO-2 Science Team Leader
for the OCO-2 Science Team
Jet Propulsion Laboratory, California Institute of Technology
March 2013
Copyright
Copyright 20122013 California
California Institute
Institute ofof Technology.
Technology.
Government
Government sponsorshipsponsorship acknowledged.
acknowledged.

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1

Fossil Fuel CO2 Emissions: Top Emitters
Global Carbon Project, 2011

In recent years, thelargest increases infossil fuel emissions
have occurred indeveloping countries.
Emissions by somedeveloped countries
declined due to theglobal economiccrisis.
China is now thelargest single emitter,but its per capita
emissions are still
well below those inthe U.S.
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Global Measurements from Space are
Essential for Monitoring Atmospheric CO2
To limit the rate of atmospheric carbon dioxide buildup, we must
– Control emissions associated with human activities– Understand & exploit natural processes that absorb carbon dioxide
We can only manage what we can measure

Ground-based measurements
describe the global CO2 trends.

High resolution, space-based
measurements are needed todiscriminate its sources and sinks.
Page 33CO2 is a Component of the Carbon Cycle

Page 44

What Processes Regulate CO2 Absorption?
What naturalprocesses are
currently
absorbing almost
half of the CO2
emitted by humanactivities?
Why does theamount of CO2that stays in theatmospherechange so muchfrom year toyear?
We don’t know.
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Measuring CO2 from Space• Record spectraof CO2 and O2
absorption inreflected sunlight• Retrieve variations in
the column averaged
CO2 dry air mole
fraction, XCO2 overthe sunlit hemisphere
InitialSurf/AtmState• Validate measurementsto ensure XCO2 accuracyof 1 - 2 ppm (0.3 - 0.5%)

Generate
Synthetic
Spectrum

OCO/GOSAT
NewState(inc.
XCO2)

Instrument
ModelDifference
SpectraInverse
Model

XCO2

AircraftTower

FTS
Flask
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Driving Requirements for Space-based CO2
Measurements
390• Precision and accuracy
388
XCO2

– High precision required to resolve small (0.2-0.3%)
variations in CO2 associated with sources and sinks– High accuracy essential to avoid regional-scale biases

386
384-60 -40 -20 0 20 40 60 80
Latitude• Spatial coverage– Nadir and glint observations are needed to yield usefulobservations over both continents and ocean• Spatial resolution and sampling– Sensitivity to point sources scales with area of footprint– Small measurement footprints reduce data losses due
to clouds• Temporal sampling– Monthly measurements required over > 1 year toresolve seasonal and inter-annual variability in CO2
The OCO-2 Mission

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The Pioneers: GOSAT and OCO
24 Feb 2009GOSAT launched successfully
on 23 January 2009

OCO was lost a month later
when its launch system failed
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The ACOS/GOSAT Collaboration
After the loss of OCO, NASA reformulated the OCO
Team under the Atmospheric CO2 Observations fromSpace (ACOS) task to continue the collaboration withthe GOSAT Project Team at JAXA and NIES to:• Conduct vicarious calibration campaigns in Railroad
Valley, Nevada, U.S.A. and analyze results of thosecampaigns•

Retrieve XCO2 from GOSAT spectra– Model development, and testing– Data production and delivery• Validate GOSAT retrievals by comparing– GOSAT retrievals with TCCON measurements– 0ther validation standards (surface pressure, aircraft
and ground-based CO2 measurements)
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ACOS GOSAT B2.10 XCO2 Retrievals

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TCCON Comparisons Show Improvements in
ACOS GOSAT XCO2 Bias and Random Error

B2.7

B2.8

B2.9

B2.10

Zonal profiles of ACOS/GOSAT XCO2 estimates (green and grey triangles) are compared to themonthly mean XCO2 estimates from TCCON stations (red diamonds) for July 2009. The precision(scatter), bias, and yield of the ACOS/GOSAT products have improved over time (Crisp et al. 2011).
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The NASA Orbiting Carbon Observatory-2(OCO-2) Mission

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The OCO-2 Mission Overview
3-Channel Grating
Spectrometer (JPL)

NASA NEN (GSFC)
and SN (TDRSS)

Dedicated Spacecraft
Bus (OSC)

Formation Flying as Partof the A-Train
Constellation

Delta-II Launch
VehicleMission Operations(OSC)

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The OCO Instrument – Optimized for Sensitivity• 3 co-bore-sighted, high resolution,
imaging grating spectrometers• Resolving Power ~20,000• High Signal-to-Noise Ratio• Collects 4 to 8 cross-trackfootprints at 3 Hz

Relay
Optics
Detector

TelescopeSlit
O2 A-Band
Collimator
CO2 1.61µm BandCamera

CO2 2.06 µm Band

CryocoolerGrating

key components of each channel.
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Pre-Flight Instrument
Calibration and Characterization• Pre-flight testing quantifies keyInstrument performance and knowledge
parameters– Geometric• Field of view, Bore-sight alignment– Radiometric• Zero-level offset (bias)• Gain, Gain non-linearity– Spectroscopic• Spectral range, resolution, sampling• Instrument Line Shape (ILS)– Polarization– Instrument stability

Heliostat
TCCON Station• Pre-flight instrument characterizationand calibration completed in April 2012
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Observatory I&T Activities OngoingThe instrument has now been integrated with the spacecraft bus to produce theObservatory. The first Observatory thermo-vacuum test was completed in 2012.
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Launch Date Driven by Launch ServiceAvailability

Credit: Steve Greenberg, JPL• OCO-2 will fly on a United Launch
Alliance (ULA) Delta II 7320
• Selected by NASA in July 2012,(along with launch vehicles forSMAP, JPSS-1, and Jason-3)• The OCO-2 Team is currently working
closely with ULA to accommodate
OCO-2 on the Delta-II vehicle• Substantially different interface andlaunch environment• New plans are being made forascent navigation and A-Train entry• The nominal OCO-2 launch date is “noearlier than 1 July 2014”
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Flying in Formation in the A-Train

OCO-2 will fly at the head of A-Train (now called the 705-km Constellation),but has changed it flight path to share the ground track with CloudSat andCALIPSO, which is 217 km East of the AQUA (WRS-2 Standard) track.
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Observation Modes Optimize Sensitivity
and Accuracy
Glint Observations:+ Small footprint (< 3 km2)
+ Improves Signal/Noise− Low Signal/Noise over dark over oceans− More cloud interference
surfaces (ocean, ice)

Glint Spot

Target Observations:• Validation over groundbased FTS sites, field
campaigns, othertargets

447-m WLEF Tower

Nadir Observations:

Local Nadir
Park Falls, WI
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Glint vs. Nadir Coverage• OCO-2 will obtain Nadir and Glint observations of the sunlit hemisphereon alternate 16-day ground track repeat cycles.
• The mission plan has been modified to return all 8 cross-track footprints,
yielding ~380 Soundings/degree of latitude or 106 soundings/day.

Nadir observations provide better
coverage over continents

Glint observations provide better
coverage over oceans
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Conclusions• Space-based remote sensing observations hold substantial promise for
future long-term monitoring of CO2 and other greenhouse gases– These measurements will complement those from the existing
ground-based greenhouse gas monitoring network with increased:spatial coverage and sampling density• The principal challenge is the need for high precision (~0.3% or 1 ppm)
• The Japanese GOSAT mission (Nicknamed “Ibuki”) has provided avaluable pathfinder for analysis techniques• Once it is launched in 2014, the NASA OCO-2 mission will demonstrate
the measurement precision, coverage, and resolution needed to:– Quantify CO2 sources on the scale of an average-sized nation– Find the natural “sinks” that are absorbing over half of the CO2
emitted by human activities
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