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Enhancing Carbon Cycle Knowledge with New CO2 Measurements from Space

Explore priority science uses, reduce uncertainties, and improve biospheric process understanding using new atmospheric CO2 measurements. Discover how to leverage and prepare for missions, tackle validation strategies, and derive sources/sinks with data assimilation. Address key issues such as model improvements, observational impact, and flight testing requirements for efficient XCO2 retrieval. Aim to bridge observational gaps and enhance accuracy for better carbon flux estimations.

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Enhancing Carbon Cycle Knowledge with New CO2 Measurements from Space

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  1. Science Enabled by New Atmospheric CO2 Measurements • What are the priority science uses of the new measurements? • Reduce carbon source/sink uncertainties • Improve understanding of the underlying biospheric processes • What do we need to do scientifically to use these new measurements and/or to get ready for the mission? • Retrieving XCO2 from OCO spectra or ASCENDS differential absorption • Validation strategy and infrastructure • Deriving CO2 sources and sinks (data assimilation) • Are there any major issues to be resolved before this science is enabled, and if so, what are they and what needs to be done? • Improved atmospheric transport models • OSSEs to quantify ASCENDS measurement requirements • Flight testing of ASCENDS instruments • What is the impact of an observation gap between OCO and ASCENDS?

  2. Backup

  3. Measuring XCO2 With OCO Column Abundance Path Dependent Ratio OCO Collects Science Data in 2 Modes Nadir: Highest spatial resolution Glint: 10 to 100x SNR increase over oceans XCO2 XCO2 is the normalized CO2 mixing ratio in a column of air. Focuses on CO2 concentration variability rather than topographic variability (number of molecules) Accuracy: 1 ppm (0.3%) • OCO flies at the head of the A-Train • 705 km altitude sun synchronous, 98.2 inclination, 98.8 minute period • Global coverage with a 16-day (233 orbit) ground track repeat cycle

  4. Making Precise XCO2 Measurements from Space • High resolution spectra of reflected sunlight in near IR CO2 and O2 bands used to retrieve the column average CO2 dry air mole fraction, XCO2 • 1.61 m CO2 band: Column CO2 • 2.06 m CO2 band: Column CO2, Aerosols • 0.76 m O2 A-band: Surface pressure, clouds, aerosols • Why high spectral resolution? • Enhances sensitivity, minimizes biases O2 A-band CO2 2.06 m CO2 1.61m Column CO2 Clouds/Aerosols, H2O, Temperature Clouds/Aerosols, Surface Pressure

  5. OCO Dense, Global Sampling Will Lead to Improved Estimates of Carbon Sources and Sinks OCO Sampling 1-Day Fractional Flux Error Reduction Using OCO Data After 8 Days OCO Sampling 3-Days After 30 Days Red points show ‘mostly clear’ scenes (AOD < 0.2) where accurate XCO2 retrievals are possible Chevallier et al. 2006

  6. L2 XCO2 Preparing for OCO Data Products Validation L1 L3 Retrieval Algorithm XCO2 Maps Source/Sink Inversion Model Spectra Calibration IOC+6 Months (August 2009) L4 IOC+9 Months (November 2009) Sources/Sinks • The OCO team is focusing on: • Retrieving XCO2 from OCO spectra • Validating XCO2 retrievals from OCO • Deriving CO2 sources and sinks from OCO XCO2 data As Available

  7. Pressure Altitude (km) Latitude Active Sensing of CO2 Emissions over Nights, Days, & Seasons (ASCENDS) Mission Objectives Airborne Demonstration Day/Night Global CO2 Column Measurements • Approach • ASCENDS will deliver laser based remote sensing measurements of CO2 mixing ratios (XCO2) • Day and night • At all latitudes • During all seasons • ASCENDS includes simultaneous measurements of • CO2 number density (ND) tropospheric column • O2 ND column: surface pressure for CO2 to XCO2 • Temperature profile: improved CO2 accuracy • Altimetry: surface elevation, cloud top heights • CO profile: identify combustion sources of CO2 • ASCENDS will be a logical extension of OCO and GOSAT capabilities Airborne Test Flights • Summary • ASCENDS identified as a medium size mission in the NRC Decadal Survey • LRD 2013-2016 to overlap with OCO (OCO scheduled launch: Dec 2008) • Data have been collected from airborne instruments to verify the CO2 measurement capability of the laser based approach

  8. ASCENDS Payload CO2 column measurement CO2Laser Absorption Spectrometer to resolve (or weight) the CO2 altitude distribution, particularly across the mid to lower troposphere. Baseline: 1.6 µm LAS Option: Integrated 1.6 µm + 2.0 µm Surface pressure measurement O2 Laser Absorption Spectrometer to convert CO2 number density to mixing ratio. Surface/cloud top altimeter Laser altimeter to measure CO2 column length. Temperature sounder Six channel passive radiometer to provide temperature corrections. CO sensor Gas Filter Correlation Radiometers (at 2.3 & 4.6 µm) to separate biogenetic fluxes from biomass burning and fossil fuel combustion. Imager To provide cloud clearing for soundings. CO2 column mixing ratio (XCO2) measurement with Laser Absorption Spectrometer (LAS) technique requires the simultaneous measurement of the CO2 column number density (CND); the O2 column number density to converting the CND to XCO2; and the path length of the measurement. A temperature profile measurement is also required to constrain the XCO2 measurement. A column CO measurement over the same XCO2 path is also recommended for interpreting sources and sinks of CO2.

  9. Pre-Phase A: Present – April 2010 Start Phase A: April 2010 Confirmation: April 2012 Payload Delivery: April 2014 Satellite Ship: September 2015 Launch: October 2015 End of Primary Mission (3 years): October 2018 Note: Earlier launch (August 2014) is technically feasible if prior year implementation funding is provided. ASCENDS Key Mission Milestones

  10. Transmittances & Weighting Functions from Orbit 1.57 mm 2.05 mm RTM April 2008

  11. Advanced CO2 and Climate LAser International Mission (ACCLAIM)(Active Laser System for ASCENDS) ITT Engineering Development Unit used to validate end-end system performance model; technology readiness for ACCLAIM Mission; and capability for high precision CO2 measurements. ACCLAIM Flight Test Campaigns May 21-25, 2005 Ponca City, Oklahoma (DOE ARM Site) (5 Science Flights: Land, Day & Night, ) June 20-26, 2006 Alpena, Michigan (6 Science Flights: Land & Water, Day & Night) October 20-24, 2006 Portsmouth, New Hampshire (4 Science Flights: Land (inc. mountains) & Water, Day & Night) May 20-24, 2007 Newport News, Virginia (8 Science Flights: Land & Water, Day & Night) October 17-22, 2007 Newport News, Virginia (9 Science Flights: Land & Water, Day & Night, Clear & Cloudy)

  12. ACCLAIM & JPL LAS Flight Test CampaignNewport News/ Williamsburg Airport, 17-23 October 2007 JPL LAS-Twin Otter ACCLAIM-Lear 25

  13. Water-Land Transition Between Tracks 2 & 1 on 22 Oct. 2007 Trk-2 Trk-1 Center On-Line Signals Off-Line-2 Signals (-50 pm) CO2 Optical Depths Land-Leg: SNR (1 s) = 263 (~1.4 ppm) Water-Leg: SNR (10 s) = 291 (~1.3 ppm)

  14. Example of Data from Oct. 21 Virginia Flight • Online and Offline return signal powers are highly correlated along Track 4, as expected when primary fluctuation source is due to surface reflectance variability • We achieved a differential absorption precision of ~2%. This is consistent with speckle-limited fluctuation amplitudes for the data averaging time (~ 1 s). Faster data transfer electronics will reduce speckle effect for a given data averaging time. RTM April 2008

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