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Profiling Tropospheric CO2 using the Aura TES and TCCON instruments
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Le Kuai1, John Worden1, Susan Kulawik1, Kevin Bowman1, Sebastien C. Biraud2, James B. Abshire3,
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Abstract
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Monitoring the global distribution and long-term variations of CO2 sources and sinks
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is required for characterizing the global carbon budget. Although total column
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measurements will be useful for estimating large regional fluxes, model transport
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remains a significant error source, particularly for local sources and sinks. To
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improve the capability of estimating regional fluxes, we estimate near-surface CO2
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values from ground-based near infrared (NIR) measurements with space-based
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thermal infrared (TIR) measurements. The NIR measurements are obtained from
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the Total Carbon Column Observing Network (TCCON) of solar measurements,
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which provide an estimate of the total CO2 atmospheric column amount. Estimates
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of tropospheric CO2 that are co-located with TCCON are obtained by assimilating
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Tropospheric Emission Spectrometer (TES) free-tropospheric CO2 estimates into
Steven C. Wofsy4, Vijay Natraj1, Christian Frankenberg1, Debra Wunch5, Brian Connor6, Charles
Miller1, Coleen Roehl5, Run-Lie Shia5, and Yuk Yung5
1.
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail
stop: 233-200, Pasadena, CA 91109, USA
2.
Lawrence Berkeley National Laboratories, Berkeley, CA, 94720, USA
3.
NASA Goddard Space Flight Center, Greenbelt, MD, USA
4.
Harvard University, Cambridge, MA, USA
5.
California Institute of Technology, 1200 E. California Blvd., Pasadena, CA, 91125, USA
6.
BC Consulting Ltd., 6 Fairway Dr., Alexandra 9320, New Zealand
Correspondence to: Le Kuai (lkuai@jpl.nasa.gov)
Submitted to Atmos. Meas. Tech.
© Author(s) 2012.
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the GEOS-Chem model. We find that quantifying lower tropospheric CO2 by
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subtracting free tropospheric CO2 estimates from total column estimates is a linear
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problem.
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We find that the calculated random uncertainties in total column and lower
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tropospheric estimates are consistent with actual uncertainties as compared to
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aircraft data. For the total column estimates, the random uncertainty is about 0.55
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ppm with a bias of -5.66 ppm, consistent with previously published results. After
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accounting for the total column bias, the bias in the lower tropospheric CO2
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estimates is 0.26 ppm with a precision (one standard deviation) of 1.02 ppm. This
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precision is sufficient for capturing the winter to summer variability of
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approximately 12 ppm in the lower troposphere; double the variability of the total
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column. This work shows that a combination of NIR and IR measurements can
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profile CO2 with the precision and accuracy needed to quantify near-surface CO2
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variability.
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I. Introduction
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Our ability to infer surface carbon fluxes depends critically on interpreting spatial
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and temporal variations of atmospheric CO2 and relating them back to surface
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fluxes. For example, surface CO2 fluxes are typically calculated using surface or near
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surface CO2 measurements along with aircraft data (Law and Rayner,
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1999;Bousquet et al., 2000;Rayner and O'Brien, 2001;Gurney et al., 2002;Rayner et
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al., 2008;Baker et al., 2010a;Chevallier et al., 2010;Chevallier et al., 2011;Rayner et
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al., 2011;Keppel-Aleks et al., 2012). More recently it has been shown that total
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column CO2 measurements derived from ground-based or satellite observations can
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be used to place constraints on continental-scale flux estimates (O'Brien and
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Rayner, 2002;Chevallier, 2007;Chevallier et al., 2011;Keppel-Aleks et al., 2012).
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However, because CO2 is a long-lived greenhouse gas, measurements of the total
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column CO2 is primarily sensitive to synoptic scale fluxes as discussed in (Baker et
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al., 2010b;Keppel-Aleks et al., 2011); it is shown that variations in the total column
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are only partly driven by local surface fluxes because the total column also varies
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related to the transport of CO2 from remote locations. Furthermore, the variations
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caused by the surface source and sinks are largest in the lower tropospheric (LT)
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CO2 (Sarrat et al., 2007;Keppel-Aleks et al., 2011;Keppel-Aleks et al., 2012). In
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addition, Stephen et al., (2007) concludes that most of the current models
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overpredict the annual-mean midday vertical gradients and consequently lead to an
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overestimated carbon uptake in northern lands and underestimated carbon uptake
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over tropical forests. For these reasons we could expect that vertical profile
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estimates of CO2 will improve constraints on the distributions of carbon flux.
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Therefore, we are motivated to derive a method to estimate the LT CO2 (surface to
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600 hPa) from current available column and free tropospheric observations.
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Total column CO2 data are calculated from solar near infrared (NIR) measurements
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from the Total Carbon Column Observatory Network (TCCON) (Wunch et al.,
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2010;Wunch et al., 2011a), as well as space-borne instruments, starting from
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SCIAMACHY (Schneising et al., 2011;Schneising et al., 2012) and GOSAT (Yoshida et
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al., 2009;Wunch et al., 2011b;Yoshida et al., 2011;Crisp et al., 2012;O'Dell et al.,
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2012). Similar space-borne instruments include OCO-2, which is expected to be
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launched in 2014 (Crisp et al., 2004), and GOSAT-2, which are also expected to be
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launched later this decade. In addition, CarbonSat (Bovensmann et al., 2010;Velazco
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et al., 2011) is a proposed instrument that could also be launched in the next decade.
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The ground-based FTS measurements have high precision and accuracy compared
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to satellite instruments but limited spatial coverage. TCCON provides a validation
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resource for SCIIAMACHY, GOSAT and OCO-2 and is a useful link between the
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ground-based in situ and satellite-based remote sensing observations. Satellite
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observations have lower precision and accuracy relative to the ground-based data,
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but obtain global measurements of atmospheric CO2. In addition to the column CO2
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from NIR measurements, there are also free tropospheric CO2 measurements from
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passive thermal infrared satellite instruments such as TES (Kulawik et al.,
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2010;Kulawik et al., 2012) and AIRS (Chahine et al., 2005). All these measurements
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by different techniques play important roles in the carbon flux inversion problem
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and provide complementary information of the atmospheric CO2 distribution.
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However, none of these instruments measure the lower tropospheric CO2.
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In this paper, we present a method to estimate the LT CO2 by combining column and
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free tropospheric CO2 from two data sources: total column estimates from TCCON
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and free tropospheric estimates from TES data, assimilated into the GEOS-Chem
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model. We do not use the direct profiling approach discussed in Christi and
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Stephens (2004) because we found that spectroscopic errors and sampling error
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due to poor co-location of the NIR and IR data currently result in unphysical
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retrieved CO2 profiles. Instead we simply subtract free tropospheric column
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estimates from total column estimates in order to quantify lower tropospheric CO2
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column amounts. As long as the retrievals converge and the estimated states are
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close to the true states, the problem of subtracting free tropospheric column amount
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from total column amount is a linear problem with well-characterized uncertainties.
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2. Measurements
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The averaging kernel indicates the sensitivity of the retrieved estimates to the true
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states. Figure 1 shows that TCCON averaging kernel can retrieve the total column
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CO2. The TES averaging kernels for an estimate of CO2, averaged from surface to
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top–of-atmosphere, is also shown in Fig. 1. Both averaging kernels show sensitivity
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of these estimates to the free tropospheric CO2 whereas the TCCON total column
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estimate also has sensitivity to the lower tropospheric CO2.
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2.1 Ground-Based Total Column CO2 Measurements from TCCON:
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The column data used to derive LT CO2 in this study are from TCCON observations.
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These observations are obtained by a Fourier Transform Spectrometer instrument,
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with a precise solar tracking system, which measures incoming sunlight with high
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spectral resolution (0.02 cm-1) and high signal to noise ratio (SNR) between 500 and
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885, depending on the spectral region observed (Washenfelder et al., 2006). The
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recorded spectra range from 4000 to 15,000 cm-1. It provides a long-term
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observation of column-averaged abundance of greenhouse gases, such as CO2, CH4,
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N2O and other trace gases (e.g. CO) over twenty TCCON sites around the world
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including both operational and future sites (Yang et al., 2002;Washenfelder et al.,
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2006;Deutscher et al., 2010;Wunch et al., 2010;Messerschmidt et al., 2011). Figure 2
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shows a measurement in the 1.6 μm CO2 absorption band, which is used for analysis
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here.
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As discussed in Wunch et al., (2010;2011a), total column-averaged abundances
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using TCCON data can be estimated using a non-linear least squares approach that
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compares a forward model spectrum that depends on CO2, temperature, H2O, and
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instrument parameters against the observed spectrum. The retrieval approach
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adjusts atmospheric CO2 concentrations by scaling an a priori CO2 profile until the
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observed and modeled spectra agree within the noise levels. The precision in the
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column-averaged CO2 dry air mole fraction from the scaling retrievals is better than
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0.25% (Wunch et al., 2010;Wunch et al., 2011a). The absolute accuracy is ~1% and
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after calibration by aircraft data, it can reach 0.25% (Wunch et al., 2010;Wunch et
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al., 2011a).
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In this paper, we use a profile retrieval algorithm that scales multiple levels of the
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CO2 profile instead of the whole profile (Kuai et al., 2012). We find that the precision
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of retrieved column averages of the profile using this approach (0.55 ppm) is
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consistent with the scaling retrievals described by Wunch et al. (2010). The profile
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retrieval algorithm is described in section 4.
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2.2 Satellite-Based free tropospheric CO2 measurements from TES:
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Free tropospheric CO2 estimates are derived from thermal IR radiances measured
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by the Aura Tropospheric Emission Spectrometer (TES) (Beer et al., 2001). The TES
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instrument measures the infrared radiance emitted by Earth’s surface and
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atmospheric gases and particles from space. These measurements have peak
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sensitivity to the mid-tropospheric CO2 at ~500 hPa (Kulawik et al., 2012). Because
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the sampling for the TES CO2 measurements is sparse (e.g., 1 measurement every
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100 km approximately) and passing over the Lamont TCCON site ~ every 16 days
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(Beer et al., 2001), we assimilated the CO2 measurements into the GEOS-Chem
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model, a global 3-D chemical transport model (CTM) (Nassar et al., 2010;Kulawik et
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al., 2010;Kulawik et al., 2012).
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GEOS-Chem (V8.2.1) is a global 3-D chemical transport model (CTM) for
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atmospheric composition, with sources and additional modifications specific to the
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carbon cycle as described in (Nassar et al., 2010) and (Kulawik et al., 2011). It has
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2°×2.5° resolution and 47 hybrid-sigma vertical levels. Surface fluxes are described
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in Table 1.
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TES at all pressure levels between 40° S and 40° N, along with the predicted
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sensitivity and errors, was assimilated for the year 2009 using 3d-var assimilation.
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We compare model output with and without assimilation to surface based in situ
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aircraft measurements from the US DOE Atmospheric Radiation Measurement
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(ARM) Southern Great Plains site during the ARM-ACME (Biraud et al., 2012,
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http://www.arm.gov/campaigns/aaf2008acme) and HIPPO-2 (hippo.ucar.edu/)
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mission (Kulawik et al., 2012). We find improvement in the seasonal cycle amplitude
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in the mid-troposphere at the SGP site, but also discrepancies with HIPPO at remote
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oceanic sites, particularly outside of the latitude range of assimilation (Kulawik et
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al., 2012).
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We use the results from the assimilation as our free-tropospheric estimates of CO2.
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The uncertainties in the assimilation fields are calculated by comparison to aircraft
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data as discussed in Sect. 5.2.
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2.3 Flight measurements:
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Aircraft data are used as our standard to assess the quality of the different CO2
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estimates. The aircraft measure CO2 profiles typically up to 6 km and sometimes to
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10 km or higher. For comparison with the TCCON CO2 estimates, we collected profile
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observations from different aircraft campaigns, such as HIPPO (Wofsy et al., 2011)
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and Learjet (Abshire et al., 2010) (http://www.esrl.noaa.gov/gmd/ccgg/aircraft/qc.
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html), at the Southern Great Plains (SGP) ARM site (Biraud et al., 2012)
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(http://www.arm.gov/campaigns/aaf2008acme) over the year 2009. These data
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are compared to the TCCON CO2 observations at the Lamont site, Oklahoma (36.6°N,
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97.5°W).
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3. Calculation of column and LT CO2
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The approach discussed in this paper is to estimate LT CO2 by subtracting estimates
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of free tropospheric CO2 partial column amount from the total column amount. The
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total column amount is usually obtained by integrating the gas concentration profile
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from the surface to the top of atmosphere.
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∝(𝑝=0)
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𝐶g = ∫
dry
𝒇g (𝒛) ∙ 𝝆(𝒛) ∙ 𝑑𝑧
(1)
0
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where Cg is total vertical column amount for gas ‘g’ and 𝝆(𝒛) represents the number
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dry
density vertical profile and 𝒇g (𝒛) is dry-air gas concentration profile as a function
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of altitude (z).
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dry
𝒇g (𝒛) =
𝒇g (𝒛)
1 − 𝒇H2 O (𝒛)
(2)
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The ratio of the total column between gas and air will give the dry-air column-
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averaged abundance, e.g. for CO2:
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XCO2 =
𝐶CO2
𝐶air
(3)
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Here we use XCO2 to refer to dry-air column-averaged mole fraction of CO2.
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Since TCCON also provides precise measurements of O2, dividing by the retrieved O2
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using spectral measurements from the same instrument improves the precision of
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XCO2 by significantly reducing the effects of instrumental or measurement errors
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that are common in both gases (e.g. solar tracker pointing errors, zero level offsets,
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instrument line shape errors, etc.) (Wunch et al., 2010). Therefore, we also remove
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the water fraction by normalizing simultaneously retrieved O2. Because we retrieve
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the CO2 profile, we can remove the water component layer by layer.
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dry
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𝒇CO2 (𝒛) =
𝒇CO2 (𝒛)
× 0.2095
𝒇O2 (𝒛)
(4)
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Then the column amount (𝐶CO2 ) and the column average (XCO2) can be computed
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using Eq. (1) and (3) respectively.
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Consistent with the discussions in Wunch et al., (2010), the precision of column
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estimates using O2 as the dry air standard will be improved but the bias specific
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from the use of the O2 band will be transferred to XCO2. For example, Fig. 3 shows
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total column XCO2 estimates, retrieved from our algorithm, corresponding to
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aircraft in which data was taken from the surface past 10 km. The bias is found to
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negligibly vary over time and over different sites as discussed in Wunch et al.,
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(2010).
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Because O2 normalized estimates of XCO2 have higher precision but about 1%
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negative bias (Wunch et al., 2010;Wunch et al., 2011a) (Fig. 3), we need to remove
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the mean bias in TCCON XCO2 when estimating the total column amount:
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𝐶CO2
XCO2TCCON
= 𝐶air (
)
𝛼
(5)
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1
where 𝛼 is an empirical correction factor to remove the bias in TCCON column
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retrievals.
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4
TROP
The partial vertical column amount of CO2 in free troposphere and above (𝐶CO
) is
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estimated by integrating TES GEOS-Chem assimilated profile (𝒇TES
CO2 ) above 600 hPa.
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∝(𝑝=0)
TROP
𝐶CO
2
7
𝒇TES
CO2 (𝒛) ∙ 𝝆(𝒛) ∙ 𝑑𝑧
=∫
(6)
𝑧(𝑝=600)
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The partial vertical column amount of CO2 in the LT can then be computed as the
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difference between the total column amount (Eq. 6) and partial free tropospheric
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column amount (Eq. 7):
LT
𝐶CO
= 𝐶air (
2
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∝(𝑝=0)
XCO2TCCON
)−∫
𝒇TES
CO2 (𝒛) ∙ 𝝆(𝒛) ∙ 𝑑𝒛
𝛼
𝑧(𝑝=600)
(7)
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Applying Eq. (3) within the lower troposphere gives the estimate of the LT CO2 mole
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LT
fraction (XCO2LT ), the ratio of partial vertical column between CO2 (𝐶CO
) and air
2
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LT
(𝐶air
= ∫0
𝑧(𝑝=600)
1 ∙ 𝝆(𝒛) ∙ 𝑑𝒛) is
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LT
𝑋CO
2
∝(𝑝=0)
XCO2TCCON ∝(𝑝=0)
1
∙
𝝆(𝒛)
∙
𝑑𝑧
−
𝒇TES (𝒛) ∙ 𝝆(𝒛) ∙ 𝑑𝑧
∫
∫
0
𝑧(𝑝=600) CO2
𝛼
=
600
∫𝑝 1 ∙ 𝝆(𝒛) ∙ 𝑑𝑧
(8)
𝑠
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where XCO2LT is defined as the TCCON/TES LT CO2. These estimates can be
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compared to the integrated partial column-averaged CO2 measured by aircraft
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within the lower troposphere (surface to 600 hPa for Lamont).
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4. CO2 Profile Retrieval Approach
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In this section, we describe a profile retrieval algorithm that is based on the scaling
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retrieval discussed in Wunch et al., (2010;2011a). Characterization of the errors,
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based on this retrieval approach, is discussed in the Appendix. The profile of
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atmospheric CO2 is obtained by optimal estimation (Rodgers, 2000) using the same
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line-by-line radiative transfer model discussed in Wunch et al. (2010) (or GFIT). It
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computes simulated spectra using 71 vertical levels with 1 km intervals for the
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input atmospheric state (e.g. CO2, H2O, HDO, CH4, O2, P, T and etc.). The details about
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the TCCON instrument setup and GFIT are also described in Yang et al., (2002);
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Washenfelder et al., (2006); Deutscher et al., (2010); Geibel et al., (2010); Wunch et
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al., (2010;2011a). The retrievals in this study use one of TCCON-measured CO2
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absorption bands, centered at 6220.00 cm-1 with a window width of 80.00 cm-1 (Fig.
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2). Note that ultimately we do not use the full profiles for this study as we find that
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spectroscopic or other errors introduce vertical oscillations into the estimated
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profiles with larger values than expected in the upper troposphere that are
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compensated by lower values than expected in the lower troposphere. The same
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effect is found in the GOSAT CO2 retrievals as discussed in O’Dell et al. (2012). This
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vertical oscillation is one of the potential issues in joint retrievals by combining NIR
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and TIR radiance in additional to the limitation of the coincident measurements
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from two different instruments. However, the total columns of these profile are still
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good estimates with well-characterized errors as discussed in section 5.1.
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Therefore, the profiles are mapped into column amounts and are shown to be
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consistent with the results of Wunch et al. (2011a). We use the profile retrieval
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instead of the Wunch et al. (2010) column scaling retrieval in order to understand
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the error characteristics of the CO2 retrieval.
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In the scaling retrieval discussed by Wunch et al. (2010;2011a), the retrieved state
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vector (𝜸) includes the eight constant scaling factors for four absorption gases (CO2,
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H2O, HDO, and CH4) and four instrument parameters (continuum level: ‘cl’,
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continuum tilt: ‘ct’, frequency shift: ‘fs’, and zero level offset: ‘zo’).
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𝛾[CO2]
𝛾[H2 O]
𝛾[HDO]
𝜸 = 𝛾[CH4]
𝛾cl
𝛾ct
𝛾fs
[ 𝛾zo ]
1
(9)
2
3
Each element of 𝜸 is a ratio between the state vector (𝒙) and its a priori (𝒙𝒂 ). In the
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profile retrieval, for the target gas CO2, we estimate the altitude dependent scaling
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factors instead. For other interfering gases, a single scaling factor is retrieved. Ten
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levels are chosen for CO2 (see Fig. 4 a) to capture its vertical variation:
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𝛾1[CO2]
⋮
𝛾10[CO2 ]
𝛾[H2O]
𝜸 = 𝛾[HDO]
𝛾[CH4]
𝛾cl
𝛾ct
𝛾fs
[ 𝛾zo ]
8
(10)
9
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To obtain a concentration profile, the retrieved scaling factors need to be mapped
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from retrieval grid (i.e. 10 levels for CO2 and 1 level for other three gases) to the 71
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forward model levels.
13
14
𝜷 = 𝐌𝜸
(11)
15
𝝏𝜷
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where 𝐌 =
17
model altitude grid. Multiplying the scaling factor (𝜷) on the forward model level to
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𝐌𝒙 = 𝝏𝜷, a diagonal matrix of the concentration a priori (𝒙𝒂 ), gives the true state of
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gas profile:
𝝏𝜸
is a linear mapping matrix relating retrieval level to the forward
𝝏𝒙
20
11
1
(12)
𝒙 = 𝐌𝒙 𝜷
2
3
According
to
the
above
definition,
4
̂.
̂ = 𝐌𝒙 𝜷
𝐌𝒙 𝜷𝒂 and estimated state is 𝒙
the
a
priori
profile
is 𝒙𝒂 =
5
6
The non-linear least squares retrieval is a standard optimal estimation retrieval that
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employs an a priori constraint matrix to regularize the problem (Rodgers,
8
2000;Bowman et al., 2006). The non-diagonal CO2 covariance matrix used to
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generate the constraint matrix has larger variance in the lower troposphere and
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decreases with altitude. This covariance is generated using the GEOS-Chem model as
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guidance. However, we scale the diagonals of the covariance matrix in order to
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match the variability observed at the TCCON sites. The square root of the diagonal of
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this covariance is approximately 2% (8 ppm) in the lower troposphere, 1% (4 ppm)
14
in the free troposphere, and less than 1% (4 ppm) in the stratosphere (Fig. 4a). The
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off-diagonal correlations are shown in Fig. 4b. All the other prior covariance is set to
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be 100% uncertainty.
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The measurement noise, or signal-to-noise (SNR) is used to weight the
19
measurement relative to the a priori in the non-linear least squares retrieval.
20
Although the SNR of the TCCON instrument is better than 500, we use a SNR of
21
approximately 200 because spectroscopic uncertainties degrade the comparison
22
(O'Dell et al., 2011;Wunch et al., 2011a); use of this SNR results in a chi-square in our
23
retrievals of about 1.
24
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To obtain the best estimate of the state vector that minimize the difference between
26
the observed spectral radiances (𝒚𝒐 ) and the forward model spectral radiances (𝒚𝒎 )
27
we perform Bayesian optimization by minimizing the cost function, 𝜒(𝜸):
28
29
𝜒(𝜸) = (𝒚𝒎 − 𝒚𝒐 )T 𝐒𝑒−1 (𝒚𝒎 − 𝒚𝒐 ) + (𝜸 − 𝜸𝒂 )T 𝐒𝐚−1 (𝜸 − 𝜸𝒂 )
(13)
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12
1
where 𝐒𝐚 is chosen to be the covariance shown in Fig. 4 and 𝐒𝐞 is the measurement
2
noise covariance, a diagonal matrix with values of noise squared.
3
4
5
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5. Results
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8
5.1 Quality of the column-averaged CO2 estimates:
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10
To characterize the quality of the CO2 estimates, we compare the TCCON column-
11
averaged estimates with the aircraft column-integrated data. Calculated errors (as
12
derived in the Appendix) are compared to actual errors as derived empirically from
13
comparison of the estimates to the aircraft data and are shown to be consistent.
14
15
There are forty-one SGP aircraft measured CO2 profiles in 2009 (Fig. 5). Most
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aircraft measurements are from the surface to 6 km; however, three profiles have
17
measurements from the surface to 10 km or higher (July 31, August 2nd and 3rd). To
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estimate the total column, the CO2 values for altitudes above the top of the aircraft
19
measurements are replaced by the TCCON CO2 a priori, shifted to match the mean
20
aircraft value at the top of the aircraft profile. As discussed in the Appendix (A1.2.1),
21
this approximation to the upper tropospheric CO2 values negligibly contributes to
22
uncertainty in the comparison between TCCON XCO2 estimates and the aircraft +
23
shifted upper troposphere a priori profiles. The comparisons between TCCON
24
column averages and the derived aircraft column averages are summarized in Fig. 6
25
and Table 2.
26
27
TCOON XCO2 estimates are calculated within a 4-hour time window, centered about
28
the time corresponding to each aircraft profile. A 4-hour time window is chosen to
29
ensure that comparisons are statistically meaningful and also to ensure that
30
variations in CO2 and temperature are small relative to calculated uncertainties.
31
Comparisons between TCCON and aircraft 𝑋CO2 are shown in Table 2. Results listed
13
1
in Table 2 are only for clear-sky scenes because it is difficult to quantify the effect of
2
clouds on the TCCON retrievals and errors. We find that the calculated precision for
3
the collection of measurements within each 4-hour time window encompassing the
4
aircraft is, on average, approximately 0.32 ppm. This precision is, on average,
5
consistent with the variability of the TCCON 𝑋CO2 estimates within this 4-hour time
6
window of 0.35 ppm. The error on the mean will be arbitrarily small because of the
7
large number of measurements within this 4-hour time window. Consequently, we
8
expect that the 𝑋CO2 variability within each 4-hour time window is driven by noise
9
and not by variations in temperature and CO2. However, we calculate that errors in
10
temperature lead to an error in 𝑋CO2 of approximately 0.69 ppm on average (last
11
column, Table 2). We find that the TCCON 𝑋CO2 estimates are biased on average by
12
−5.66 ± 0.55 ppm. The magnitude of this bias estimate is consistent with that
13
described in Wunch et al. (2010) and is attributed to errors in the O2 spectroscopy.
14
The error in the bias (0.55 ppm) is consistent with the calculated error due to
15
temperature (0.69 ppm) and is a result of temperature variations between aircraft
16
measurements.
17
18
5.2 Quality of the LT CO2 estimates:
19
20
In this section we examine the robustness of estimates of 𝑋CO2 in the LT (surface to
21
600 hPa) by comparison of the TCCON/TES 𝑋CO2 estimates to aircraft data. We
22
separate the lower troposphere from the free-troposphere at the 600 hPa pressure
23
level because the aircraft profiles indicate that the variability in the free
24
troposphere becomes “small” above this pressure (Fig. 5). However, knowledge of
25
the boundary layer height will affect use of these LT estimates for quantifying
26
surface fluxes because boundary layer heights are typically at higher pressures than
27
600 hPa (von Engeln et al., 2005). Figure 7a shows comparisons of the LT XCO2 as
28
calculated from integrating a priori profiles used with GFIT from surface to 600 hPa.
29
Figure 7b shows comparisons of the LT XCO2 as calculated from TCCON and TES
30
data. The −5.66 ppm bias (or factor  in Eq. 9) is removed from the TCCON total
14
1
column before computing XCO2in the LT using TCCON data and TES data. As shown
2
in Table 3, the average difference between aircraft and TCCON/TES LT XCO2 values
3
is 0.26 ± 1.02 ppm. This uncertainty (1.02 ppm) in the surface-to-600 hPa estimates
4
is improved compared to the uncertainty of the similar estimates by the TCCON
5
prior (2.0 ppm). The average difference between TES (assimilated into GEOS-Chem)
6
free tropospheric CO2 (above 600 hPa) and aircraft free tropospheric CO2 is 0.38 ±
7
0.71. According to Appendix A.2 (Eq. A2.1), the estimated uncertainty in LT XCO2 by
8
TCCON/TES is 0.90 ppm, consistent with actual uncertainty of 1.02 ppm. The
9
improvement in this lower tropospheric XCO2 comparison (1.02 ppm), relative to
10
the a priori (2.0 ppm), is mainly during summer time when surface CO2 is low,
11
relative to wintertime, because the biosphere is more active in the summer (Fig. 7).
12
With these uncertainties, the LT XCO2 estimates are able to capture the seasonal
13
variability of the lower troposphere as discussed next.
14
15
5.3 Seasonal variability of LT CO2 compared to column CO2.
16
17
The aircraft, TCCON, and TES assimilated estimates of atmospheric CO2 have
18
sufficient temporal density to provide an estimate of CO2 variability over most of the
19
year. In Fig. 8 we show the monthly averaged total column averages and the partial
20
column averages (surface to 600 hPa) calculated from the aircraft data and the same
21
quantities derived from the TCCON data and the TCCON minus TES assimilated data
22
respectively. The TCCON column averages (black dots) and TCCON/TES derived LT
23
data (red dots) are consistent with the aircraft measurement (black diamonds and
24
red diamonds) within the expected uncertainties indicating that the estimates are
25
robust. Based on these forty-one flight profiles, during most of each month, there
26
are about 3 to 5 measured profiles can be averaged except September and October,
27
both of which only have one available aircraft profile and are unfortunately under
28
unclear sky scenes. Therefore, the comparisons for these two months are not shown.
29
In Fig. 8, both TCCON column averages and TCCON/TES LT CO2 capture the seasonal
30
variability.
31
15
1
The response of the seasonal variability in LT CO2 is more than twice that in the
2
column averages. It is 14 ppm peak-to-peak in LT CO2 and 5 ppm in the column-
3
averaged CO2 because there is a rapid drawdown in LT CO2 at the growing season
4
onset over mid latitude due to the biosphere uptake. The difference between the LT
5
CO2 and column CO2 changes from positive (about 3 ppm) to negative (lower than -4
6
ppm) over the year (Fig. 8b) suggest that the processes driving the surface fluxes at
7
Lamont are different than the processes driving the total column. Consequently,
8
these results empirically indicate that these estimated LT CO2 will provide improved
9
sensitivity to local fluxes than the total column (Keppel-Aleks et al., 2011).
10
11
6. Summary
12
13
Total column estimates of atmospheric CO2 and partial column estimates of CO2 in
14
the lower troposphere (surface to 600 hPa) are calculated using TCCON and Aura
15
TES data. In order to determine if the retrieval approach, forward model, and
16
understanding of uncertainties are robust, it is crucial to determine if the calculated
17
uncertainties are consistent with the actual uncertainties. In addition, we need to
18
assess any biases in the estimates and ideally attribute these bias errors in the
19
measurement system. The bias and its uncertainties in TCCON column-averaged CO2
20
are explained at two different time scales: 4-hour time windows centered about
21
individual aircraft measurement and day-to-day time scales from comparison to the
22
collection of forty-one aircraft profiles. We find that for multiple retrievals of the
23
same air parcel within a 4-hour time window, the mean bias is from the
24
uncertainties of atmospheric states (i.e. temperature or interference gases) or
25
spectroscopy parameters. The variability of the collection of total column estimates
26
within the 4-hour time window of 0.35 ppm is consistent with the calculated
27
random error of about 0.32 ppm, which is associated with the measurement error.
28
When comparing the TCCON total column estimates to aircraft data over several
29
days, we can assume that the daily systematic errors due to temperature or other
30
interference error is pseudo-random. For example, the estimated mean bias across
31
multiple days is −5.66 (±0.55) ppm. The standard deviation of the bias error of
16
1
approximately 0.55 ppm is consistent with the expected error of 0.69 ppm, which is
2
primarily driven by temperature error; measurement error for these comparisons is
3
arbitrarily small because of the large number of measurements used to calculate the
4
mean CO2 estimate.
5
6
Comparisons of the aircraft data to free tropospheric CO2, calculated by assimilating
7
Aura TES CO2 estimates into the GEOS-Chem model (Nassar et al., 2011) suggest
8
that the TES assimilated data has a bias error of 0.38(±0.71) ppm in the free
9
troposphere. We calculated a lower tropospheric estimate (surface to 600 hPa) of
10
the CO2 amount by subtracting the TES assimilated free tropospheric estimate from
11
the TCCON total column amount estimates. Comparisons of these lower
12
tropospheric estimates from TCCON/TES data to those from aircraft data are
13
consistent after the bias in the TCCON is removed. The precision in the derived LT
14
CO2 is 1.02 ppm, which is consistent with the calculated precision of 0.90 ppm. The
15
dominant sources of the error in the LT estimates are due to uncertainties in the
16
free troposphere data from TES assimilation and the temperature driven error in
17
column averages from TCCON. We show that this precision is sufficient to
18
characterize the seasonal variability of lower tropospheric CO2 over TCCON Lamont
19
site.
20
21
The approach describe in this paper shows that the problem of using independent
22
total column and free tropospheric estimates to estimate lower tropospheric CO2 is
23
a linear problem. This linear problem is in contrast to using a similar approach for
24
quantifying lower tropospheric ozone (Worden et al., 2007) or CO (Worden et al.,
25
2010) by using total column and profile estimates.
26
27
The study shown here indicates that assimilating total column and free tropospheric
28
CO2 will increase sensitivity to surface fluxes by placing improved constraints on
29
lower tropospheric CO2. Furthermore, quantifying lower tropospheric CO2 using
30
total column and free tropospheric estimates is useful for evaluating model
31
estimates of lower troposphere.
17
1
2
This study also highlights the potential of combining simultaneous measurements
3
from near IR and IR sounding instruments to obtain vertical information of the CO2
4
profile (Christi and Stephens, 2004). The present TCCON network is relatively
5
sparse but has a good latitudinal coverage and long-term accurate observations of
6
column abundance of CO2. Column estimates of CO2 by space measurement are
7
currently available from GOSAT and SCIAMACHY data (Schneising et al.,
8
2011;Schneising et al., 2012) and are expected from OCO-2. Column CO2 estimates
9
from these satellite data together with the free tropospheric CO2 estimates are
10
anticipated to provide complementary constraints to infer CO2 fluxes and advance
11
the ability to study the carbon cycle problem by providing constraints on near-
12
surface CO2 variations and atmospheric mixing. Our future work will apply this
13
method to combine GOSAT and TES data to expand the spatial coverage of these
14
lower tropospheric CO2 estimates.
15
16
17
18
19
20
Appendix A
21
One of the reasons we used our own retrieval algorithm to estimates the total
22
column CO2 instead of standard TCCON product is that the optimal estimation allow
23
us to characterize the error budget. This appendix discusses the expected errors and
24
shows how these terms represent the actual errors. With the characterized errors,
25
the derived CO2 estimates in this study would be useful for evaluating model
26
estimates.
27
28
29
30
Error Characterization
A1 Errors in TCCON column-averaged CO2
In this section, we develop the error characterization for (1) the estimates of TCCON
31
CO2 column averages from the profile retrievals for a 4-hour time window around
32
each aircraft CO2 profile measurement and (2) comparisons of TCCON estimates
33
against forty-one aircraft profiles.
18
1
2
First of all, we need derive an equation for the estimated state vector by single
3
retrieval. As discussed in the text (Section 4), the retrieval vector is defined by:
4
𝛾1[CO2]
⋮
𝛾10[CO2 ]
𝛾[H2O]
𝜸 = 𝛾[HDO]
𝛾[CH4 ]
𝛾cl
𝛾ct
𝛾fs
[ 𝛾zo ]
5
(𝐴1)
6
7
Each element of 𝜸 is a ratio between the state vector (𝒙) and its a priori (𝒙𝒂 ). For the
8
target gas CO2, altitude dependent scaling factors are retrieved. For other
9
interferential gases, a constant scaling factor for the whole profile is retrieved. The
10
last four are for the instrument parameters (continuum level: ‘cl’, continuum title:
11
‘ct’, frequency shift: ‘fs’, and zero level offset: ‘zo’). To obtain a concentration profile,
12
the retrieved scaling factors are mapped from the retrieval grid (i.e. 10 levels for
13
CO2 and 1 level for other three gases) to the 71 forward model levels.
14
15
𝜷 = 𝐌𝜸
(𝐴2)
16
𝝏𝜷
17
where 𝐌 =
18
model altitude grid. Multiplying the scaling factor (𝜷) on the forward model level to
19
the concentration a priori (𝒙𝒂 ) gives the estimates of the gas profile. We define 𝐌𝒙 =
20
𝝏𝒙
𝝏𝜷
𝝏𝜸
is a linear mapping matrix relating retrieval levels to the forward
where 𝐌𝒙 is a diagonal matrix filled by the concentration a priori (𝒙𝒂 ):
21
22
̂
̂ = 𝐌𝒙 𝜷
𝒙
(𝐴3)
23
19
1
From Eq. (A1.3), it follows that 𝒙𝒂 = 𝐌𝒙 𝜷𝒂 and 𝒙 = 𝐌𝒙 𝜷. The Jacobian matrix of
2
retrieved parameter with respect to the radiance is
3
4
𝐊𝛄 =
𝜕𝑳(𝐌𝜸)
𝜕𝜸
(𝐴4)
5
6
Using the chain rule, we can obtain the equation relating the retrieval Jacobians to
7
the full-state Jacobian
8
9
𝝏𝑳 𝝏𝑳 𝝏𝒙 𝝏𝜷
=
𝝏𝜸 𝝏𝒙 𝝏𝜷 𝝏𝜸
(𝐴5)
𝐊 𝜸 = 𝐊 𝒙 𝐌𝒙 𝐌 = 𝐊 𝜷 𝐌
(𝐴6)
10
11
or
12
13
14
15
If the estimated state is “close” to the true state, then the estimated state for a single
16
measurement can be expressed as a linear retrieval equation (Rodgers, 2000):
17
̂ = 𝜷𝒂 + 𝐀 𝜷 (𝜷 − 𝜷𝒂 ) + 𝐌𝐆𝜸 𝜺𝒏 + ∑ 𝐌𝐆𝜸 𝐊 𝒍𝒃 ∆𝒃𝒍
𝜷
18
(𝐴7)
𝒍
19
20
where 𝜺𝒏 is a zero-mean noise vector with covariance 𝐒𝐞 and the vector ∆𝒃𝒍 is the
21
error in true state of parameters (l) that also affect the modeled radiance, e.g.
22
temperature, interfering gases, spectroscopy. The 𝐊 𝒍𝒃 is the Jacobian of parameter
23
(l). In this study, we found the systematic error is primarily due to the temperature
24
uncertainty (𝜺𝑻 ) and spectroscopic error (𝜺𝑳 ). 𝐆𝜸 is the gain matrix, which is
25
defined by
26
27
𝐆𝜸 =
𝝏𝜸
= (𝐊 𝐓𝜸 𝐒𝐞−𝟏 𝐊 𝜸 + 𝐒𝐚−𝟏 )−𝟏 𝐊 𝐓𝜸 𝐒𝐞−𝟏 (𝐴8)
𝝏𝑳
20
1
2
The averaging kernel for 𝜷 in forward model dimension is
3
4
𝐀 𝜷 = 𝐌𝐆𝜸 𝐊 𝜷
(𝐴9)
5
6
We can define 𝐀 𝑥 = 𝐌𝒙 𝐀 𝜷 𝐌𝒙−𝟏 as the averaging kernel for 𝒙. In order to convert Eq.
7
̂), we apply Eq. (A1.7) into Eq. (A1. 3)
(A1. 7) to the state vector of concentration (𝒙
8
and obtain:
9
10
̂ = 𝒙𝒂 + 𝐀 𝑥 (𝒙 − 𝒙𝒂 ) + 𝐌𝒙 𝐌𝐆𝜸 𝜺𝒏
𝒙
11
+𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑻 𝜺𝑻 + 𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑳 𝜺𝑳
(𝐴10)
12
13
The temperature uncertainty (𝜺𝑻 ) and spectroscopic error (𝜺𝑳 ) represent the
14
systematic errors (∆𝒃𝒍 ).
15
16
A2 Total error budget
17
The total error for a single retrieval is the difference between the estimated state
18
vector (Eq. A10) to the true state vector (𝒙):
19
20
21
̂=𝒙
̂ − 𝒙 = (𝐈 − 𝐀 𝒙 )(𝒙𝒂 − 𝒙) + 𝐌𝒙 𝐌𝐆𝜸 𝜺𝒏
𝜹𝒙
+𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑻 𝜺𝑻 + 𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑳 𝜺𝑳
(𝐴11)
22
23
The second order statistics for the error is
24
25
𝐒𝜹𝒙̂ = 𝐒̂𝐬𝐦 + 𝐒̂𝐦 + 𝐒̂𝑻 + 𝐒̂𝑳 ,
(𝐴12)
26
27
where the smoothing error covariance is
28
29
𝐒̂𝐬𝐦 = (𝐈 − 𝐀 𝒙 )𝐒𝒂 (𝐈 − 𝐀 𝒙 )𝐓
(𝐴13);
30
21
1
a measurement error covariance is
2
𝐒̂𝐦 = 𝐌𝒙 𝐌𝐆𝐒𝐞 (𝐌𝒙 𝐌𝐆)𝐓
3
(𝐴14);
4
5
and two systematic error covariance matrices are
6
7
𝐒̂𝑻 = 𝐌𝒙 𝐌𝐆𝐊 𝑻 𝐒𝑻 (𝐌𝒙 𝐌𝐆𝐊 𝑻 )𝐓
(𝐴15);
𝐒̂𝑳 = 𝐌𝒙 𝐌𝐆𝐊 𝑳 𝐒𝑳 (𝐌𝒙 𝐌𝐆𝐊 𝑳 )𝐓
(𝐴16)
8
9
10
11
Sa is the a priori covariance for CO2, Se is the covariance describing the TCCON
12
measurement noise (see section4), ST is the a priori covariance for temperature and
13
is based on the a priori covariance used for the Aura TES temperature retrievals
14
(Worden et al., 2004); this temperature covariance is based on the expected
15
uncertainty in the re-analysis fields that are inputs to the TES retrievals. 𝐒𝑳 is the
16
covariance associated with spectroscopic error. It has been found that spectroscopic
17
inadequacies are common to all retrievals from TCCON radiances (e.g. line widths,
18
neglect of line-mixing, inconsistencies in the relative strengths of weak and strong
19
lines) (Wunch et al., 2010).
20
21
A3 Individual error budget terms
22
Considering different time scales, the uncertainties of the estimates would be
23
attributed to different error terms. In this section, we will discuss the error terms
24
one by one.
25
26
For comparisons of TCCON retrievals to each aircraft profile we choose the TCCON
27
measurements taken within a 4-hour time window centered about the aircraft
28
measurement.
29
atmospheric state hasn’t changed but it is also long enough that there are enough
30
samples of retrievals for good statistics (e.g. ~100 samples).
This time window is short enough so that we can assume the
22
1
2
There are forty-one aircraft measurements that measured CO2 profiles over Lamont
3
in 2009. On any given day (or ith day), we have 𝑛𝑖 TCCON retrievals within a 4-hour
4
time window around aircraft measurement where 𝑛𝑖 varies by day (or aircraft
5
profile comparison). The difference of the mean of these retrievals to the aircraft
6
measurement is the error on that day. The average of the errors from these forty-
7
one comparison estimates the mean bias error. Which term contributes to the
8
uncertainties will be discussed in follow.
9
10
A3.1 Error due to extrapolation of CO2 above aircraft profile
11
In reality, the true state (𝒙) is unknown and can only be estimated by our best
12
measurements, such as by aircraft, which have a precision of 0.02 ppm. With the
13
̂) can be estimated by the
validation standard, the error in the retrieval (𝜹𝒙
14
̂) to the validation standard (𝒙
̂𝒔𝒕𝒅 ). In
comparison of the retrieved state vector (𝒙
15
order to do an inter-comparison of the measurements from two different
16
instruments, we apply a smoothing operator described in Rodgers and Connor
17
(2003) to the complete profile (𝒙𝑭𝑳𝑻 ) based on aircraft measurement so that it is
18
smoothed by the averaging kernel and a priori constraint from the TCCON profile
19
retrieval:
20
21
̂𝒔𝒕𝒅 = 𝒙𝒂 + 𝐀 𝒙 (𝒙𝑭𝑳𝑻 − 𝒙𝒂 )
𝒙
(𝐴17)
22
23
̂𝒔𝒕𝒅 is the profile that would be retrieved from TCCON measurements for the same
𝒙
24
air sampled by the aircraft without the presence of other errors. 𝒙𝑭𝑳𝑻 is the
25
complete CO2 profile based on aircraft measurement.
26
27
Several aircraft only measure CO2 up to approximately 6 km, but three of them go up
28
to 10 km or higher, which are measured by Learjet on July 31, August 2 and 3 (Fig.
29
5). These three profiles show that the free troposphere is well mixed and the
30
vertical gradient is small (Wofsy et al., 2011), less than 1 ppm/km on average
31
between 600 hPa and tropopause. Therefore, the lower part of 𝒙𝑭𝑳𝑻 is from the
23
1
direct aircraft measurements. Above that, the TCCON a priori is scaled to the
2
measured CO2 values at the top of the aircraft measurement so that the profile is
3
continuously extended up to 71 km. Then the complete profile based on the aircraft
4
measurement is
5
6
𝒙𝑭𝑳𝑻
𝒙𝒎𝒆𝒂𝒔
𝜹𝒙𝒎𝒆𝒂𝒔
𝑭𝑳𝑻
𝑭𝑳𝑻
=[
]
𝑭 ] = 𝒙 − 𝜹𝒙𝑭𝑳𝑻 = 𝒙 − [ 𝑭
𝝀𝒙𝒂
𝒙 − 𝝀𝒙𝑭𝒂
(𝐴18)
7
8
where 𝒙𝒎𝒆𝒂𝒔
𝑭𝑳𝑻 is the direct aircraft measurements in the lower atmosphere, which has
9
been mapped to forward model grid. 𝜹𝒙𝒎𝒆𝒂𝒔
𝑭𝑳𝑻 is its unknown error relative to the
10
‘truth’ and is order of 0.02 ppm. 𝝀 is the ratio between the CO2 at the top of aircraft
11
measurement to the a priori CO2 on that level. 𝒙𝑭𝒂 and 𝒙𝑭 represent the a priori and
12
‘true’ state above direct aircraft measurement in the free troposphere and above.
13
𝝀𝒙𝑭𝒂 is the shifted a priori to smoothly extend the profile up to stratosphere. 𝒙𝑭𝑳𝑻
14
represents the complete profile based combining a priori. 𝜹𝒙𝑭𝑳𝑻 is the unknown
15
error in the 𝒙𝑭𝑳𝑻 to the true state.
16
17
Subtracting Eq. (A1.27) from Eq. (A1.10) results in the following expression:
18
19
̂=𝒙
̂−𝒙
̂𝒔𝒕𝒅 = 𝐀 𝒙 𝜹𝒙𝑭𝑳𝑻 + 𝐌𝒙 𝐌𝐆𝜸 𝜺𝒏
𝜹𝒙
20
+𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑻 𝜺𝑻 + 𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑳 𝜺𝑳
(𝐴19)
21
22
23
The second order statistics for the error in the complete aircraft based profile,
24
𝜹𝒙𝑭𝑳𝑻 , is:
25
26
27
𝐒𝜹𝒙𝑭𝑳𝑻 = 𝑬[𝜹𝒙𝑭𝑳𝑻 − 𝑬(𝜹𝒙𝑭𝑳𝑻 )][𝒙𝑭𝑳𝑻 − 𝑬(𝜹𝒙𝑭𝑳𝑻 )]𝑻
=[
𝒎𝒆𝒂𝒔
𝐒𝑭𝑳𝑻
𝟎
𝟎
]
𝐒𝐚𝐅
(𝐴20)
28
24
1
𝒎𝒆𝒂𝒔
𝐒𝑭𝑳𝑻
is the error covariance for direct aircraft measurements, which is a diagonal
2
matrix with a constant value of the square of 0.02 ppm (the precision of aircraft
3
instruments) (Wunch et al., 2010). 𝐒𝐚𝐅 is the sub matrix of TCCON a priori covariance
4
matrix above the aircraft measurements. Since we scale the a priori to the aircraft
5
data, the actual error covariance in the upper atmosphere should be much smaller
6
than 𝐒𝐚𝐅 .
7
8
The uncertainty in retrieved column averages driven by the smoothing error can be
9
estimated by
10
11
𝝈𝒔𝒎 (𝜹𝑿CO2 ) = √𝒉𝐓 𝐀 𝒙 𝐒𝜹𝒙𝑭𝑳𝑻 𝐀𝐓𝒙 𝒉
(𝐴21)
12
13
The upper limit of this uncertainty is approximately 0.5 ppm when using the a priori
14
covariance in the upper atmosphere where the aircraft measurement is missing (e.g.
15
above 6 km). Since the free troposphere is well mixed and the upper atmosphere is
16
constrained by the aircraft measurement, the actual uncertainty for the validation
17
standard should be much smaller than above estimates. For example, if we assume
18
conservatively that the term, 𝐒𝜹𝒙𝑭𝑳𝑻 , is half the size of the Sa used to describe our CO2
19
covariance, then this term becomes negligible relative to the temperature error.
20
21
A3.2 measurement error
22
The measurement noise vector 𝜺𝒏 is a zero-mean random variable. In a 4-hour time
23
window, the measurement error covariance will drive the variability of the
24
retrieved column averages. The uncertainty in retrieved column averages driven by
25
the measurement error can be estimated by
26
27
𝝈𝒎 (𝜹𝑿CO2 ) = √𝒉𝐓 𝐒̂𝐦 𝒉
(𝐴22)
28
25
1
𝐒̂𝐦 is defined in Eq. (A14). We calculate that this term is approximately 0.32 ppm.
2
The error on the mean is related to the number of samples in 4-hour time window:
3
𝒉𝐓 𝐒̂𝐦 𝒉
𝝈𝒎 (𝜹𝑿CO2 ) = √
𝑛𝑖
4
(𝐴23)
5
6
where 𝑛𝑖 is number of retrieval samples within 4-hour on ith day (listed in table 2).
7
8
A3.3 Temperature error
9
Within a 4-hour time window, we assume that variations in temperature do not
10
result in variations in the CO2 estimate; however, the uncertainty in the temperature
11
profiles will result in a bias:
12
𝐓
̅̅̅̅̅̅̅̅̅̅̅̅̅
(𝜹𝑿
CO𝟐 )𝑻𝒊 = 𝒉 𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑻 𝜺𝑻𝑖
13
(𝐴24)
14
15
16
However, 𝜺𝑻𝑖 varies from day to day. The mean bias error from temperature
17
uncertainties over days becomes
18
𝒎
1
̅̅̅̅̅̅̅̅̅̅̅̅
(𝜹𝑿CO2 )𝑻 = 𝒉𝑻 𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑻 ( ∑ 𝜺𝑻𝑖 )
𝑚
19
(𝐴25)
𝒊=𝟏
20
21
with a covariance of
22
𝝈𝑻 (𝜹𝑿CO2 ) = √𝒉𝐓 𝐒̂𝐓 𝒉
23
(𝐴26)
24
25
where 𝐒̂𝐓 is from Eq. (A1.25). The estimate of this term is, on average, approximately
26
0.69 ppm.
27
26
1
A3.4 Spectroscopic error
2
The spectroscopic error is another significant source of systematic error. Different
3
from temperature error, it does not vary significantly on any time scales and even
4
over different sites (Wunch et al., 2010). Therefore, its covariance is always
5
negligible. However, it is found to be the primary source of the bias error.
6
𝐓
̅̅̅̅̅̅̅̅̅̅̅̅
(𝜹𝑿
CO2 )𝑳 = 𝒉 𝐌𝒙 𝐌𝐆𝜸 𝐊 𝑳 𝜺𝑳 (𝐴27)
7
8
9
10
The estimate of this term is about -5 ppm. It is mainly due to the error in O2 cross
section.
11
12
13
14
15
16
17
A4 Errors in LT column-averaged CO2
We estimate the LT CO2 by subtracting the TES assimilated free tropospheric CO2
18
from the TCCON total column CO2. The TCCON dry-air total column estimated by
19
weighted to the retrieved O2 column has a bias of approximately -5.66 ppm.
20
Therefore, we remove the bias using Eq. (9) before subtracting the free tropospheric
21
partial column amount. Because the TCCON estimates and TES/GEOS-Chem
22
estimates are independent estimates of CO2, the uncertainties in the lower
23
tropospheric estimates are simply the uncertainties summed in quadrature:
24
25
TES
TCCON
2
2
𝜎(𝜹𝑿LT
)
CO2 ) = √𝜎 (𝜹𝑿CO2 ) + 𝜎 (𝜹𝑿CO2
(𝐴28)
26
27
The estimate of this term is 0.90 ppm. The TES assimilated free tropospheric bias
28
error and uncertainty (0.38 ± 0.71 ppm) is estimated by the comparison to the free
29
tropospheric estimates from the aircraft-based profile (𝒙𝑭𝑳𝑻 ). The TCCON total
30
column mean bias error and uncertainty (-5.66 ± 0.55 ppm) has been discussed in
31
previous section.
27
1
2
3
Supplementary material related to this article is available online at :
4
5
6
http://www.atmos-meas-tech-discuss.net/5/1/2012/amtd-5-1-2012supplement.pdf.
7
Acknowledgement. Part of this research was carried out at the Jet Propulsion
8
Laboratory, California Institute of Technology, under a contract with the National
9
Aeronautics and Space Administration. The GEOS-Chem model results with
10
assimilated TES data was funded by proposal No. 09-ACOS09-0010. US funding for
11
TCCON comes from NASA’s Terrestrial Ecology Program, grant number
12
NNX11AG01G, the Orbiting Carbon Observatory Program, the Atmospheric CO2
13
Observations from Space (ACOS) Program and the DOE/ARM Program. SGP data
14
was supported by the Office of Biological and Environmental Research of the US
15
Department of Energy under contract No. DE-AC02-05CH11231 as part of the
16
Atmospheric Radiation Measurement Program. The authors wish to thank G. Toon
17
and P. Wennberg for making available their GFIT code and TCCON data.
18
19
20
21
22
23
24
25
26
27
28
29
30
31
28
1
2
3
4
5
6
7
8
9
10
11
12
Biosphere
Biomass burning
Bio fuel
Fossil fuel
Ocean
Ship
Chemical source
Plane emission
Chemical surface
CASA-GFED3-v2 (3hr)
GFED3-Fire-v2 (daily)
GFED3-fuel-v2 (monthly)
CDIAC (monthly)
ECCO2-Darwin (daily) (Brix et al., in prep.)
ICOADS (monthly)
GEOS-Chem-V8.2.1 (Nassar et al. 2010) (monthly)
GEOS-Chem-V8.2.1 (Nassar et al. 2010) (monthly)
GEOS-Chem-V8.2.1 (Nassar et al. 2010) (monthly)
13
14
15
Table 1. Surface fluxes used in GEOS-Chem model
16
17
18
19
20
21
22
23
24
25
29
1
2
3
4
5
6
7
8
9
10
Unit (ppm)
Day (yyyymmdd)
20090108
20090116
20090129
20090204
20090211
20090219
20090221
20090308
20090314
20090316
20090318
20090329
20090407
20090408
20090420
20090421
20090423
20090517
20090518
20090520
20090526
20090528
20090530
20090604
With cloud filter
Actual (1 ×
Bias+5.66 (ppm)
𝜎)
0.66
0.30
0.45
0.30
0.36
0.30
0.58
0.26
0.69
0.49
0.39
0.38
0.67
0.42
0.25
0.39
0.98
0.42
0.00
0.27
0.26
0.44
-0.08
0.28
0.13
0.26
-0.03
0.40
-0.59
0.44
-0.32
0.29
-0.21
0.30
-0.19
0.32
0.82
0.32
0.60
0.50
-0.12
0.36
0.11
0.30
0.30
0.34
0.01
0.38
Expected
𝑛
161
171
169
169
90
96
130
132
102
154
112
76
98
121
69
130
122
130
131
75
86
130
130
128
𝒅𝒂𝒚
𝒉𝒓
𝜎(𝛿𝑋𝑪𝑶
) 𝜎(𝛿𝑋𝑪𝑶
)
𝟐
𝟐
0.27
0.33
0.34
0.33
0.33
0.33
0.34
0.32
0.33
0.32
0.32
0.33
0.33
0.32
0.32
0.32
0.32
0.32
0.32
0.32
0.32
0.32
0.32
0.32
0.74
0.74
0.77
0.74
0.75
0.76
0.77
0.71
0.73
0.69
0.69
0.72
0.72
0.69
0.70
0.70
0.66
0.70
0.68
0.67
0.67
0.68
0.66
0.68
30
20090612
20090616
20090621
20090623
20090629
20090701
20090706
20090731
20090802
20090803
20090823
20091101
20091102
20091103
20091122
20091218
20091220
Mean
1×𝜎
-0.96
-1.31
-0.85
-0.56
0.16
-0.24
0.85
0.31
0.26
-0.37
-0.74
-0.47
-0.68
-0.94
-0.38
-0.23
0.33
0.00
0.55
0.35
0.34
0.28
0.32
0.32
0.46
0.33
0.34
0.29
0.33
0.38
0.36
0.33
0.35
0.39
0.47
0.38
0.35
72
128
95
129
118
119
43
125
131
130
130
130
131
131
68
127
101
118
0.32
0.31
0.31
0.31
0.31
0.31
0.32
0.32
0.31
0.31
0.31
0.32
0.32
0.32
0.32
0.33
0.33
0.32
0.66
0.64
0.63
0.63
0.64
0.65
0.66
0.66
0.65
0.63
0.65
0.68
0.69
0.70
0.71
0.75
0.72
0.69
1
2
Table 2. Lists of bias error and its standard deviation (1 × 𝜎) of TCCON profile
3
retrieved column averages within 4-hr time window of each flight measurement.
4
The expected uncertainties from measurement error covariance and the
5
temperature error covariance are also listed in the last two columns. To remove the
6
unclear sky spectra measurements, we dismiss the retrievals when the parameter
7
‘fvis’ (fractional variation in solar intensity) is greater than 0.05, which suggests the
8
cloud coverage during the spectra measurement. By applying the cloud filter, the
9
consistency between the empirical error estimates and expected error estimates is
10
improved. The columns for ‘𝑛’ are the total numbers of retrievals within 4-hr time
11
window.
12
13
14
15
16
17
18
31
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Unit (ppm)
21
22
23
24
25
26
Total column averages
TCCON
TCCON prior
Estimated Precision
Bias
-5.66
0.55
1.04
1.50
LT column averages;
Combining two data set;
[Total column amount – free
troposphere column amount
(above 600 hPa)]
TCCON – TES/GEOS-Chem
0.26
1.02
TCCON – TCCON prior
-0.96
2.26
Table 3. Bias and Precision
27
28
29
30
31
32
32
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Fig. 1. Averaging kernel for TES retrieval (blue) and TCCON retrieval (red).
15
16
17
18
19
20
21
33
1
2
3
4
Fig. 2. CO2 band at 1.6 m observed on June 17, 2008 by TCCON at Park Falls
5
(Wisconsin) with solar zenith angle of 22.5.
6
7
8
34
1
2
Fig. 3. Comparison of column-averaged CO2 estimates to derived aircraft column
3
averages. Red points indicate that H2O is used as dry air standard. Black points
4
indicate that O2 is used as dry air standard. Dots for Parkfalls site and diamonds for
5
Lamont site. Error bars are not shown in this figure.
6
7
8
35
1
2
3
Fig. 4 (a) The square root of the diagonal in CO2 covariance matrix. (b) The 2-D plot
4
of the CO2 covariance matrix.
5
36
1
2
3
Fig. 5. Samples of CO2 profiles measured by aircraft (black) and TES Geos-Chem
4
assimilation (red) at SGP.
5
6
7
8
9
10
11
12
13
37
1
2
3
4
Fig. 6. Comparison of total column-averaged CO2 from TCCON profile retrievals to
5
that derived from aircraft. Black dots indicate comparison of TCCON estimates to
6
aircraft that measure up to 6 km. Green dots are comparison of TCCON estimates to
7
the three aircraft profiles that measure up to 12 km.
8
9
10
11
38
1
2
3
Fig. 7. (a) (Left Panel) Comparison of LT CO2 estimates derived from integrating
4
from surface to 600 hPa by TCCON a priori and aircraft. (b) (Right Panel)
5
Comparison of LT CO2 estimates derived from TCCON and TES with aircraft.
6
39
1
2
3
Fig. 8 (a) Monthly mean XCO2 for total column and LT CO2 in 2009 at Lamont.
4
Aircraft data (FLT) are indicated by diamonds (black for total XCO2; red for LT XCO2)
5
and TCCON or TCCON/TES estimates are indicated by black or red dots + error bars.
6
(b) The difference of LT CO2 and total column-averaged CO2 by flight (diamonds)
7
and by TCCON/TES (dots). Error bars are the standard deviation of the monthly
8
estimates.
9
10
11
40
1
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9
10
11
12
13
14
15
16
17
18
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23
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25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
References:
Abshire, J. B., Riris, H., Allan, G. R., Weaver, C. J., Mao, J. P., Sun, X. L., Hasselbrack, W.
E., Kawa, S. R., and Biraud, S.: Pulsed airborne lidar measurements of atmospheric
CO2 column absorption, Tellus Series B-Chemical and Physical Meteorology, 62,
770-783, 10.1111/j.1600-0889.2010.00502.x, 2010.
Baker, D. F., Boesch, H., Doney, S. C., O'Brien, D., and Schimel, D. S.: Carbon
source/sink information provided by column CO(2) measurements from the
Orbiting Carbon Observatory, Atmospheric Chemistry and Physics, 10, 4145-4165,
10.5194/acp-10-4145-2010, 2010a.
Baker, D. F., Bosch, H., Doney, S. C., O'Brien, D., and Schimel, D. S.: Carbon
source/sink information provided by column CO2 measurements from the Orbiting
Carbon Observatory, Atmospheric Chemistry and Physics, 10, 4145-4165,
10.5194/acp-10-4145-2010, 2010b.
Beer, R., Glavich, T. A., and Rider, D. M.: Tropospheric emission spectrometer for the
Earth Observing System's Aura Satellite, Applied Optics, 40, 2356-2367,
10.1364/ao.40.002356, 2001.
Biraud, S. C., Torn, M. S., Smith, J. R., Sweeney, C., Riley, W. J., and Tans, P. P.: A MultiYear Record of Airborne CO2 observations in the U.S. Southern Great Plains., AMTD,
5, 7187-7222, doi: 10.5194/amtd-5-7187-2012, 2012.
Bousquet, P., Peylin, P., Ciais, P., Le Quere, C., Friedlingstein, P., and Tans, P. P.:
Regional changes in carbon dioxide fluxes of land and oceans since 1980, Science,
290, 1342-1346, 2000.
Bovensmann, H., Buchwitz, M., Burrows, J. P., Reuter, M., Krings, T., Gerilowski, K.,
Schneising, O., Heymann, J., Tretner, A., and Erzinger, J.: A remote sensing technique
for global monitoring of power plant CO2 emissions from space and related
applications, Atmospheric Measurement Techniques, 3, 781-811, 10.5194/amt-3781-2010, 2010.
Bowman, K. W., Rodgers, C. D., Kulawik, S. S., Worden, J., Sarkissian, E., Osterman, G.,
Steck, T., Lou, M., Eldering, A., Shephard, M., Worden, H., Lampel, M., Clough, S.,
Brown, P., Rinsland, C., Gunson, M., and Beer, R.: Tropospheric emission
spectrometer: Retrieval method and error analysis, Ieee T Geosci Remote, 44, 12971307, 10.1109/tgrs.2006871234, 2006.
Chahine, M., Barnet, C., Olsen, E. T., Chen, L., and Maddy, E.: On the determination of
atmospheric minor gases by the method of vanishing partial derivatives with
application
to
CO2,
Geophysical
Research
Letters,
32,
L22803,
doi:22810.21029/22005gl024165, L22803
10.1029/2005gl024165, 2005.
Chevallier, F.: Impact of correlated observation errors on inverted CO(2) surface
fluxes from OCO measurements, Geophysical Research Letters, 34, L24804
10.1029/2007gl030463, 2007.
Chevallier, F., Ciais, P., Conway, T. J., Aalto, T., Anderson, B. E., Bousquet, P., Brunke,
E. G., Ciattaglia, L., Esaki, Y., Frohlich, M., Gomez, A., Gomez-Pelaez, A. J., Haszpra, L.,
Krummel, P. B., Langenfelds, R. L., Leuenberger, M., Machida, T., Maignan, F.,
41
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
Matsueda, H., Morgui, J. A., Mukai, H., Nakazawa, T., Peylin, P., Ramonet, M., Rivier, L.,
Sawa, Y., Schmidt, M., Steele, L. P., Vay, S. A., Vermeulen, A. T., Wofsy, S., and Worthy,
D.: CO(2) surface fluxes at grid point scale estimated from a global 21 year
reanalysis of atmospheric measurements, Journal of Geophysical ResearchAtmospheres, 115, D21307
10.1029/2010jd013887, 2010.
Chevallier, F., Deutscher, N. M., Conway, T. J., Ciais, P., Ciattaglia, L., Dohe, S., Frohlich,
M., Gomez-Pelaez, A. J., Griffith, D., Hase, F., Haszpra, L., Krummel, P., Kyro, E.,
Labuschagne, C., Langenfelds, R., Machida, T., Maignan, F., Matsueda, H., Morino, I.,
Notholt, J., Ramonet, M., Sawa, Y., Schmidt, M., Sherlock, V., Steele, P., Strong, K.,
Sussmann, R., Wennberg, P., Wofsy, S., Worthy, D., Wunch, D., and Zimnoch, M.:
Global CO(2) fluxes inferred from surface air-sample measurements and from
TCCON retrievals of the CO(2) total column, Geophysical Research Letters, 38,
L24810
10.1029/2011gl049899, 2011.
Christi, M. J., and Stephens, G. L.: Retrieving profiles of atmospheric CO2 in clear sky
and in the presence of thin cloud using spectroscopy from the near and thermal
infrared: A preliminary case study, Journal of Geophysical Research-Atmospheres,
109, art. no.-D04316, 2004.
Crisp, D., Atlas, R. M., Breon, F. M., Brown, L. R., Burrows, J. P., Ciais, P., Connor, B. J.,
Doney, S. C., Fung, I. Y., Jacob, D. J., Miller, C. E., O'Brien, D., Pawson, S., Randerson, J.
T., Rayner, P., Salawitch, R. J., Sander, S. P., Sen, B., Stephens, G. L., Tans, P. P., Toon, G.
C., Wennberg, P. O., Wofsy, S. C., Yung, Y. L., Kuang, Z. M., Chudasama, B., Sprague, G.,
Weiss, B., Pollock, R., Kenyon, D., and Schroll, S.: The orbiting carbon observatory
(OCO) mission, Trace Constituents in the Troposphere and Lower Stratosphere, 34,
700-709, 10.1016/j.asr.2003.08.062, 2004.
Crisp, D., Fisher, B. M., O'Dell, C., Frankenberg, C., Basilio, R., Bosch, H., Brown, L. R.,
Castano, R., Connor, B., Deutscher, N. M., Eldering, A., Griffith, D., Gunson, M., Kuze,
A., Mandrake, L., McDuffie, J., Messerschmidt, J., Miller, C. E., Morino, I., Natraj, V.,
Notholt, J., O'Brien, D. M., Oyafuso, F., Polonsky, I., Robinson, J., Salawitch, R.,
Sherlock, V., Smyth, M., Suto, H., Taylor, T. E., Thompson, D. R., Wennberg, P. O.,
Wunch, D., and Yung, Y. L.: The ACOS CO2 retrieval algorithm - Part II: Global X-CO2
data characterization, Atmospheric Measurement Techniques, 5, 687-707, Doi
10.5194/Amt-5-687-2012, 2012.
Deutscher, N. M., Griffith, D. W. T., Bryant, G. W., Wennberg, P. O., Toon, G. C.,
Washenfelder, R. A., Keppel-Aleks, G., Wunch, D., Yavin, Y., Allen, N. T., Blavier, J. F.,
Jimenez, R., Daube, B. C., Bright, A. V., Matross, D. M., Wofsy, S. C., and Park, S.: Total
column CO2 measurements at Darwin, Australia - site description and calibration
against in situ aircraft profiles, Atmos. Meas. Tech., 3, 947-958, 10.5194/amt-3-9472010, 2010.
Geibel, M. C., Gerbig, C., and Feist, D. G.: A new fully automated FTIR system for total
column measurements of greenhouse gases, Atmos. Meas. Tech., 3, 1363-1375,
10.5194/amt-3-1363-2010, 2010.
Gurney, K. R., Law, R. M., Denning, A. S., Rayner, P. J., Baker, D., Bousquet, P.,
Bruhwiler, L., Chen, Y. H., Ciais, P., Fan, S., Fung, I. Y., Gloor, M., Heimann, M., Higuchi,
K., John, J., Maki, T., Maksyutov, S., Masarie, K., Peylin, P., Prather, M., Pak, B. C.,
42
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
Randerson, J., Sarmiento, J., Taguchi, S., Takahashi, T., and Yuen, C. W.: Towards
robust regional estimates of CO2 sources and sinks using atmospheric transport
models, Nature, 415, 626-630, 10.1038/415626a, 2002.
Keppel-Aleks, G., Wennberg, P. O., and Schneider, T.: Sources of variations in total
column carbon dioxide, Atmospheric Chemistry and Physics, 11, 3581-3593,
10.5194/acp-11-3581-2011, 2011.
Keppel-Aleks, G., Wennberg, P. O., Washenfelder, R. A., Wunch, D., Schneider, T.,
Toon, G. C., Andres, R. J., Blavier, J. F., Connor, B., Davis, K. J., Desai, A. R.,
Messerschmidt, J., Notholt, J., Roehl, C. M., Sherlock, V., Stephens, B. B., Vay, S. A., and
Wofsy, S. C.: The imprint of surface fluxes and transport on variations in total
column carbon dioxide, Biogeosciences, 9, 875-891, 10.5194/bg-9-875-2012, 2012.
Kuai, L., Wunch, D., Shia, R. L., Connor, B., Miller, C., and Yung, Y.: Vertically
constrained CO2 retrievals from TCCON measurements, J Quant Spectrosc Ra, 113,
1753-1761, Doi 10.1016/J.Jqsrt.2012.04.024, 2012.
Kulawik, S. S., Jones, D. B. A., Nassar, R., Irion, F. W., Worden, J. R., Bowman, K. W.,
Machida, T., Matsueda, H., Sawa, Y., Biraud, S. C., Fischer, M. L., and Jacobson, A. R.:
Characterization of Tropospheric Emission Spectrometer (TES) CO(2) for carbon
cycle science, Atmospheric Chemistry and Physics, 10, 5601-5623, 10.5194/acp-105601-2010, 2010.
Kulawik, S. S., Bowman, K. W., M. Lee, R. N., Jones, D. B. A., Biraud, S. C., Wofsy, S.,
Wunch, D., Gregg, W., Worden, J. R., and Frankenberg, C.: Constraints on near surface
and free Troposphere CO2 concentrations using TES and ACOS-GOSAT CO2 data and
the GEOS-Chem model, AGU presentation, 2011.
Kulawik, S. S., Worden, J. R., Wofsy, S., Biraud, S. C., Nassar, R., Jones, D. B. A., Olsen, E.
T., and Osterman, G. B.: Comparison of improved Aura Tropospheric Emission
Spectrometer (TES) CO2 with HIPPO and SGP aircraft profile measurements, Atmos.
Chem. Phys., 2012.
Law, R. M., and Rayner, P. J.: Impacts of seasonal covariance on CO2 inversions,
Global Biogeochemical Cycles, 13, 845-856, 10.1029/1999gb900073, 1999.
Messerschmidt, J., Geibel, M. C., Blumenstock, T., Chen, H., Deutscher, N. M., Engel, A.,
Feist, D. G., Gerbig, C., Gisi, M., Hase, F., Katrynski, K., Kolle, O., Lavric, J. V., Notholt, J.,
Palm, M., Ramonet, M., Rettinger, M., Schmidt, M., Sussmann, R., Toon, G. C., Truong,
F., Warneke, T., Wennberg, P. O., Wunch, D., and Xueref-Remy, I.: Calibration of
TCCON column-averaged CO(2): the first aircraft campaign over European TCCON
sites, Atmospheric Chemistry and Physics, 11, 10765-10777, 10.5194/acp-1110765-2011, 2011.
Nassar, R., Jones, D., Suntharalingam, P., Chen, J., Andres, R., Wecht, K., Yantosca, R.,
Kulawik, S., Bowman, K., Worden, J., Machida, T., and Matsueda, H.: Modeling global
atmospheric CO2 with improved emission inventories and CO2 production from the
oxidation of other carbon species, Geoscientific Model Development, 3, 689-716, DOI
10.5194/gmd-3-689-2010, 2010.
Nassar, R., Jones, D., Kulawik, S., Worden, J., Bowman, K., Andres, R., Suntharalingam,
P., Chen, J., Brenninkmeijer, C., Schuck, T., Conway, T., and Worthy, D.: Inverse
modeling of CO2 sources and sinks using satellite observations of CO2 from TES and
surface flask measurements, Atmospheric Chemistry and Physics, 11, 6029-6047,
DOI 10.5194/acp-11-6029-2011, 2011.
43
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
O'Brien, D. M., and Rayner, P. J.: Global observations of the carbon budget - 2. CO2
column from differential absorption of reflected sunlight in the 1.61 mu m band of
CO2, Journal of Geophysical Research-Atmospheres, 107, art. no.-4354, 2002.
O'Dell, C. W., Day, J. O., Pollock, R., Bruegge, C. J., O'Brien, D. M., Castano, R.,
Tkatcheva, I., Miller, C. E., and Crisp, D.: Preflight Radiometric Calibration of the
Orbiting Carbon Observatory, Ieee T Geosci Remote, 49, 2438-2447,
10.1109/Tgrs.2010.2090887, 2011.
O'Dell, C. W., Connor, B., Bosch, H., O'Brien, D., Frankenberg, C., Castano, R., Christi,
M., Eldering, D., Fisher, B., Gunson, M., McDuffie, J., Miller, C. E., Natraj, V., Oyafuso, F.,
Polonsky, I., Smyth, M., Taylor, T., Toon, G. C., Wennberg, P. O., and Wunch, D.: The
ACOS CO2 retrieval algorithm - Part 1: Description and validation against synthetic
observations, Atmospheric Measurement Techniques, 5, 99-121, 10.5194/amt-5-992012, 2012.
Rayner, P. J., and O'Brien, D. M.: The utility of remotely sensed CO2 concentration
data in surface source inversions (vol 28, pg 175, 2001), Geophys. Res. Lett., 28,
2429-2429, 2001.
Rayner, P. J., Law, R. M., Allison, C. E., Francey, R. J., Trudinger, C. M., and PickettHeaps, C.: Interannual variability of the global carbon cycle (1992-2005) inferred by
inversion of atmospheric CO(2) and delta(13)CO(2) measurements, Global
Biogeochemical Cycles, 22, Gb3008
10.1029/2007gb003068, 2008.
Rayner, P. J., Koffi, E., Scholze, M., Kaminski, T., and Dufresne, J. L.: Constraining
predictions of the carbon cycle using data, Philosophical Transactions of the Royal
Society a-Mathematical Physical and Engineering Sciences, 369, 1955-1966,
10.1098/rsta.2010.0378, 2011.
Rodgers, C. D.: Inverse Methods for Atmospheric Sounding: Theory and Practice,
World Scientific, London, 256 pp., 2000.
Sarrat, C., Noilhan, J., Lacarrere, P., Donier, S., Lac, C., Calvet, J. C., Dolman, A. J.,
Gerbig, C., Neininger, B., Ciais, P., Paris, J. D., Boumard, F., Ramonet, M., and Butet, A.:
Atmospheric CO2 modeling at the regional scale: Application to the CarboEurope
Regional Experiment, Journal of Geophysical Research-Atmospheres, 112, D12105
10.1029/2006jd008107, 2007.
Schneising, O., Buchwitz, M., Reuter, M., Heymann, J., Bovensmann, H., and Burrows,
J. P.: Long-term analysis of carbon dioxide and methane column-averaged mole
fractions retrieved from SCIAMACHY, Atmospheric Chemistry and Physics, 11,
2863-2880, 10.5194/acp-11-2863-2011, 2011.
Schneising, O., Bergamaschi, P., Bovensmann, H., Buchwitz, M., Burrows, J. P.,
Deutscher, N. M., Griffith, D. W. T., Heymann, J., Macatangay, R., Messerschmidt, J.,
Notholt, J., Rettinger, M., Reuter, M., Sussmann, R., Velazco, V. A., Warneke, T.,
Wennberg, P. O., and Wunch, D.: Atmospheric greenhouse gases retrieved from
SCIAMACHY: comparison to ground-based FTS measurements and model results,
Atmospheric Chemistry and Physics, 12, 1527-1540, 10.5194/acp-12-1527-2012,
2012.
Stephens, B. B., Gurney, K. R., Tans, P. P., Sweeney, C., Peters, W., Bruhwiler, L., Ciais,
P., Ramonet, M., Bousquet, P., Nakazawa, T., Aoki, S., Machida, T., Inoue, G.,
Vinnichenko, N., Lloyd, J., Jordan, A., Heimann, M., Shibistova, O., Langenfelds, R. L.,
44
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
Steele, L. P., Francey, R. J., and Denning, A. S.: Weak northern and strong tropical land
carbon uptake from vertical profiles of atmospheric CO(2), Science, 316, 1732-1735,
10.1126/science.1137004, 2007.
Velazco, V. A., Buchwitz, M., Bovensmann, H., Reuter, M., Schneising, O., Heymann, J.,
Krings, T., Gerilowski, K., and Burrows, J. P.: Towards space based verification of CO2
emissions from strong localized sources: fossil fuel power plant emissions as seen
by a CarbonSat constellation, Atmospheric Measurement Techniques, 4, 2809-2822,
Doi 10.5194/Amt-4-2809-2011, 2011.
von Engeln, A., Teixeira, J., Wickert, J., and Buehler, S. A.: Using CHAMP radio
occultation data to determine the top altitude of the Planetary Boundary Layer,
Geophysical Research Letters, 32, 10.1029/2004gl022168, 2005.
Washenfelder, R. A., Toon, G. C., Blavier, J. F., Yang, Z., Allen, N. T., Wennberg, P. O.,
Vay, S. A., Matross, D. M., and Daube, B. C.: Carbon dioxide column abundances at the
Wisconsin Tall Tower site, J. Geophys. Res.-Atmos., 111, 11 PP, D22305
10.1029/2006jd007154, 2006.
Wofsy, S. C., Team, H. S., Cooperating Modellers, T., and Satellite, T.: HIAPER Pole-toPole Observations (HIPPO): fine-grained, global-scale measurements of climatically
important atmospheric gases and aerosols, Philosophical Transactions of the Royal
Society a-Mathematical Physical and Engineering Sciences, 369, 2073-2086,
10.1098/rsta.2010.0313, 2011.
Worden, H. M., Deeter, M. N., Edwards, D. P., Gille, J. C., Drummond, J. R., and Nedelec,
P.: Observations of near-surface carbon monoxide from space using MOPITT
multispectral retrievals, Journal of Geophysical Research-Atmospheres, 115,
10.1029/2010jd014242, 2010.
Worden, J., Kulawik, S. S., Shephard, M. W., Clough, S. A., Worden, H., Bowman, K., and
Goldman, A.: Predicted errors of tropospheric emission spectrometer nadir
retrievals from spectral window selection, J. Geophys. Res.-Atmos., 109, D09308,
doi:09310.01029/02004jd004522, D09308
10.1029/2004jd004522, 2004.
Worden, J., Liu, X., Bowman, K., Chance, K., Beer, R., Eldering, A., Gunson, M., and
Worden, H.: Improved tropospheric ozone profile retrievals using OMI and TES
radiances, Geophysical Research Letters, 34, 10.1029/2006gl027806, 2007.
Wunch, D., Toon, G. C., Wennberg, P. O., Wofsy, S. C., Stephens, B. B., Fischer, M. L.,
Uchino, O., Abshire, J. B., Bernath, P., Biraud, S. C., Blavier, J. F. L., Boone, C., Bowman,
K. P., Browell, E. V., Campos, T., Connor, B. J., Daube, B. C., Deutscher, N. M., Diao, M.,
Elkins, J. W., Gerbig, C., Gottlieb, E., Griffith, D. W. T., Hurst, D. F., Jimenez, R., KeppelAleks, G., Kort, E. A., Macatangay, R., Machida, T., Matsueda, H., Moore, F., Morino, I.,
Park, S., Robinson, J., Roehl, C. M., Sawa, Y., Sherlock, V., Sweeney, C., Tanaka, T., and
Zondlo, M. A.: Calibration of the Total Carbon Column Observing Network using
aircraft profile data, Atmos. Meas. Tech., 3, 1351-1362, 10.5194/amt-3-1351-2010,
2010.
Wunch, D., Toon, G. C., Blavier, J. F. L., Washenfelder, R. A., Notholt, J., Connor, B. J.,
Griffith, D. W. T., Sherlock, V., and Wennberg, P. O.: The Total Carbon Column
Observing Network (TCCON), Philosophical Transactions of the Royal Society aMathematical
Physical
and
Engineering
Sciences,
369,
2087-2112,
10.1098/rsta.2010.0240, 2011a.
45
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
Wunch, D., Wennberg, P. O., Toon, G. C., Connor, B. J., Fisher, B., Osterman, G. B.,
Frankenberg, C., Mandrake, L., O'Dell, C., Ahonen, P., Biraud, S. C., Castano, R., Cressie,
N., Crisp, D., Deutscher, N. M., Eldering, A., Fisher, M. L., Griffith, D. W. T., Gunson, M.,
Heikkinen, P., Keppel-Aleks, G., Kyro, E., Lindenmaier, R., Macatangay, R., Mendonca,
J., Messerschmidt, J., Miller, C. E., Morino, I., Notholt, J., Oyafuso, F. A., Rettinger, M.,
Robinson, J., Roehl, C. M., Salawitch, R. J., Sherlock, V., Strong, K., Sussmann, R.,
Tanaka, T., Thompson, D. R., Uchino, O., Warneke, T., and Wofsy, S. C.: A method for
evaluating bias in global measurements of CO2 total columns from space,
Atmospheric Chemistry and Physics, 11, 12317-12337, 10.5194/acp-11-123172011, 2011b.
Yang, Z. H., Toon, G. C., Margolis, J. S., and Wennberg, P. O.: Atmospheric CO 2
retrieved from ground-based near IR solar spectra, Geophys. Res. Lett., 29, 1339,
10.1029/2001GL014537, 2002.
Yokota, T., Yoshida, Y., Eguchi, N., Ota, Y., Tanaka, T., Watanabe, H., and Maksyutov,
S.: Global Concentrations of CO2 and CH4 Retrieved from GOSAT: First Preliminary
Results, Sola, 5, 160-163, 10.2151/sola.2009-041, 2009.
Yoshida, Y., Yokota, T., Eguchi, N., Ota, Y., Tanaka, T., Watanabe, H., and Maksyutov,
S.: Global Concentrations of CO(2) and CH(4) Retrieved from GOSAT: First
Preliminary Results, Sola, 5, 160-163, 10.2151/sola.2009-041, 2009.
Yoshida, Y., Ota, Y., Eguchi, N., Kikuchi, N., Nobuta, K., Tran, H., Morino, I., and Yokota,
T.: Retrieval algorithm for CO2 and CH4 column abundances from short-wavelength
infrared spectral observations by the Greenhouse gases observing satellite,
Atmospheric Measurement Techniques, 4, 717-734, Doi 10.5194/Amt-4-717-2011,
2011.
46