Sun-Climate Symposium
Early Results from the First Year of
Operations of the OCO-2 Mission
David Crisp
for the OCO-2 Science Team
Jet Propulsion Laboratory,
California Institute of Technology
November 13, 2015
Copyright 2015 California Institute of Technology.
Government sponsorship acknowledged.
1
The Natural Carbon Cycle
330 Gt CO2
Ocean
340 Gt CO2
440 Gt CO2
450 Gt CO2
Land
2
Human Activities and the Carbon Cycle
3
Measuring Atmospheric Carbon Dioxide
4
What Processes Regulate CO2?
Atmospheric
growth rate
5
Why is it so hard to find 10 billion tons of
carbon dioxide?
Ott et al. GEOS-5 GMAO, GSFC
6
Using the Space Based Vantage Point
7
Measuring CO2 from Space
• Record spectra
of CO2 and O2
absorption in
reflected sunlight
Retrieve variations in
the column averaged
CO2 dry air mole
fraction, XCO2 over the
Validate measurements
to ensure XCO2 accuracy
of 1 ppm (0.25%)
sunlit hemisphere
Initial
Surf/Atm
State
New
State
(inc.
XCO2)
Generate
Synthetic
Spectrum
GOSAT and OCO-2
Instrument
Model
Difference
Spectra
Tower
Inverse
Model
XCO2
Aircraft
Flask
FTS
8
The OCO Instrument – Optimized for
Sensitivity
0.765µm O2 A-Band
CO2 1.61µm Band
CO2 2.06 µm Band
Each 1/3 sec frame includes 8 footprints with 1,016 wavelengths
in 3 channels, yielding almost 1 million soundings each day
9
A Perfect Launch
Credit: NASA
Credit: Bill Ingalls, NASA
Credit: Jeff Sullivan
Lift-off at 2:56 am
PDT, 02 July 2014
Credit: Jeff Sullivan
Separation!
Joining the A-Train
3 August 2014
10
The OCO-2 XCO2 Retrieval Algorithm
Altitude
State Vector First Guess
CO2
T
Gas Cross Sections
Cloud & Aerosol
Optical Properties
Solar Spectra
Viewing
geometry
δτaer
Full-res Spectrum
Mixing Ratio Temp.
Aerosol
Forward Radiative
Transfer Model
Jacobians
Spectra + Jacobians
Calibration
Simulated Spectrum
Spectral + Polarization
Inverse Model
Apriori +
Covariance
• Compare obs. &
simulated spectra
• Update State
Vector
Retrieved State Vector
Final State &
Diagnostics
converged
Altitude
Observed
Spectra
XCO2
not converged
Instrument Model
δτaer
CO
2
T
Mixing Ratio Temp.Aerosol
11
A Quick Look at the First 11 Months of Operations
12
Detection example : Spatial Coincidence
- Alberta Tar Sands, Canada
B7000
NEW !
B4300
13
Validation: Targeting Total Carbon Column
Observing Network (TCCON) Stations
14
Comparison of TCCON and OCO-2 XCO2
Comparisons with
Total Carbon Column
Observing Network
(TCCON) stations are
being used to identify
and correct biases in
target observations.
Debra Wunch – July 17, 2015
After applying a
preliminary bias
correction,
differences are
approaching 1 ppm.
15
The OCO-2 Solar Spectrum
• An accurate solar spectrum is essential
to retrieve XCO2 from OCO-2
observations
– Missing or poorly-modeled solar lines
introduce spectral residuals that prevent
convergence
– Errors in the absolute radiometry
introduce biases in the surface albedo
and cloud/aerosol retrievals
• The OCO-2 retrieval algorithm uses a
“full-disk” solar spectrum consisting of:
– A high-resolution solar line spectrum
derived from a solar line list compiled
from KPNO & balloon spectra (G. Toon)
– A slowly-varying solar continuum derived
from SOLSPEC+ATLAS 3 measurements
765 nm O2 A-Band
1610 nm CO2 Band
2060 nm CO2 Band
16
Impacts of Solar Spectrum Uncertainties
on XCO2 retrievals
• Uncertainties in the solar spectrum
introduce small (< 1%), persistent residuals
in the fits to observed spectra
– These residuals limit the algorithm’s ability to
converge to yield high quality XCO2 fits
• We also see residuals when fitting solar
calibration observations
• To reduce this source of error, we have
modified the solar spectrum, using the
residuals derived in full-orbit “Solar
Doppler” calibration measurements
– The Solar Doppler measurements provide a
very well sampled solar spectrum at the
resolution of the OCO-2 instrument
17
Identifying Contributions to Persistent
Spectral Residuals
Here, the solar Doppler residuals have been scaled, inverted,
and then superimposed on the atmospheric spectral residuals.
18
Summary
• OCO-2 was successfully launched on 2 July 2014, and began
routine operations on 6 September 2014
– Now returning about 1 million measurements each day over
the sunlit hemisphere
– Over 10% of these measurements are sufficiently cloud free
to yield full-column estimates of XCO2
• Over one year of data has been delivered to the Goddard
Earth Sciences Data and Information Services Center (GESDISC) for distribution to the science community
– All data back to September 6 2014 have been reprocessed
http://disc.sci.gsfc.nasa.gov/OCO-2
• This product is now being used by the world’s carbon cycle
science community to identify and quantify the CO2 sources
and sinks on regional scales over the globe
19