Science Enabled by New Atmospheric CO2 Measurements

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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?

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Backup
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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

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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
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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 lt 0.2)
where accurate XCO2 retrievals are possible
Chevallier et al. 2006
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Preparing for OCO Data Products
Validation
L1
L3
Retrieval Algorithm
XCO2 Maps
Source/Sink Inversion Model
Spectra
Calibration
IOC6 Months (August 2009)
L4
IOC9 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
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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

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ASCENDS Payload
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.

• CO2 column measurement
• CO2 Laser 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.

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ASCENDS Key Mission Milestones

• 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.

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Transmittances Weighting Functions from Orbit
2.05 mm
1.57 mm
RTM April 2008
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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)
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ACCLAIM JPL LAS Flight Test CampaignNewport
News/ Williamsburg Airport, 17-23 October 2007
JPL LAS-Twin Otter
ACCLAIM-Lear 25
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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)
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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