Measurements of atmospheric CO2 columns using ground-based FTIR spectra

The investigation of CO2 sources and sinks within the carbon cycle is important in order to understand global climate change. In this work high resolution ground-based FTIR measurements were used to retrieve total column amounts of CO2. Required measures for the reduction of error sources and the improvement of total column accuracies are presented. In addition, a novel analysis procedure to retrieve vertical CO2 profiles from TCCON measurements is shown and validated with in situ measurements

CO2 total column amounts at the TCCON sites Izaña (28.3 N, 16.5 W) and Karlsruhe (49.1 N, 8.5 E)

Póster presentado en: International Radiation Symposium, celebrado del 6 al 10 de agosto de 2012 en Berlín, Alemania

CO2 total column amounts at TCCON sites Izana (28.3 N, 16.5 W) and Karlsruhe (49.1 N, 8.5 E)

The Total Carbon Observing Network (TCCON) is a global network of ground-based Fourier Transform Spectrometers recording direct solar spectra in the near-infrared (NIR) spectral region. Accurate and precise columnaveraged abundances of different greenhouse gases (GHGs) are retrieved, which are used for carbon cycle research [1] and for satellite validation (e.g. SCIAMACHY, GOSAT, OCOII). Official TCCON data are generated using the GFIT code compared FTIR retrieval results with in-situ measurements developed at NASA/JPL [2]. In this study, we compare FTIR retrieval results with in-situ measurements as well as the GFIT code with the radiative transfer and retrieval algorithm PROFFIT [3]

A compact and low resolution spectrometer for the inversion of water vapor total column amounts

Observations of atmospheric water vapor (H2O) amounts are required for the investigation of important and current atmospheric studies, such as the hydrological cycle, energy balance, climate change, etc. In this context, we present a portable, very compact, commercial and very low resolution Fourier transform spectrometer for the remote sensing of total column amounts of H2O at a high measurement frequency (one measurement about every 2 minutes). The methodology applied to carry out this work is explained. Moreover, first results are compared with high quality H2O total column amounts obtained by a collocated non-mobile high resolution Fourier transform spectrometer. This inter-comparison documents that the very low resolution instrument is well suited for capturing the variability of H2O total column amounts (with precision better than 4%), but that suffers from a significant wet bias (about 30%).E. Sepúlveda enjoys a pre-doctoral fellowship from the Spanish Ministry of Education. M. Schneider is supported by the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007- 2013)/ERC Grant agreement number 256961. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) within the NORS project (grant agreement no. 284421)

Total Carbon Column Observing Network (TCCON) activities at Izana Atmospheric Research Center, Tenerife Island (28.3 N, 16.5 W) and KIT Campus North, Karlsruhe, Germany (49.1 N, 8.5 E)

Comunicación presentada en: EGU General Assembly 2011 celebrada del 3 al 8 de abril en Viena, Austria

Simultaneous retrieval of atmospheric CO_2 and light path modification from space-based spectroscopic observations of greenhouse gases: methodology and application to GOSAT measurements over TCCON sites

This paper presents an improved photon path length probability density function method that permits simultaneous retrievals of column-average greenhouse gas mole fractions and light path modifications through the atmosphere when processing high-resolution radiance spectra acquired from space. We primarily describe the methodology and retrieval setup and then apply them to the processing of spectra measured by the Greenhouse gases Observing SATellite (GOSAT). We have demonstrated substantial improvements of the data processing with simultaneous carbon dioxide and light path retrievals and reasonable agreement of the satellite-based retrievals against ground-based Fourier transform spectrometer measurements provided by the Total Carbon Column Observing Network (TCCON)

Global CO2 fluxes inferred from surface air-sample measurements and from TCCON retrievals of the CO2 total column

We present the first estimate of the global distribution of CO2surface fluxes from 14 stations of the Total Carbon Column Observing Network (TCCON). The evaluation of this inversion is based on 1) comparison with the fluxes from a classical inversion of surface air-sample-measurements, and 2) comparison of CO2mixing ratios calculated from the inverted fluxes with independent aircraft measurements made during the two years analyzed here, 2009 and 2010. The former test shows similar seasonal cycles in the northern hemisphere and consistent regional carbon budgets between inversions from the two datasets, even though the TCCON inversion appears to be less precise than the classical inversion. The latter test confirms that the TCCON inversion has improved the quality (i.e., reduced the uncertainty) of the surface fluxes compared to the assumed or prior fluxes. The consistency between the surface-air-sample-based and the TCCON-based inversions despite remaining flaws in transport models opens the possibility of increased accuracy and robustness of flux inversions based on the combination of both data sources and confirms the usefulness of space-borne monitoring of the CO2 column.It was co-funded by the European Commission under the EU Seventh Research Framework Programme (grants agreements 218793, MACC, and 212196, COCOS

Multistation intercomparison of column-averaged methane from NDACC and TCCON: impact of dynamical variability

Dry-air column-averaged mole fractions of methane (XCH4) retrieved from ground-based solar Fourier transform infrared (FTIR) measurements provide valuable information for satellite validation, evaluation of chemical-transport models, and source-sink-inversions. In this context, Sussmann et al. (2013) have shown that midinfrared (MIR) soundings from the Network for the Detection of Atmospheric Composition Change (NDACC) can be combined with near-infrared (NIR) soundings from the Total Carbon Column Observing Network (TCCON) without the need to apply an overall intercalibration factor. However, in spite of efforts to reduce a priori impact, some residual seasonal biases were identified, and the reasons behind remained unclear. In extension to this previous work, which was based on multiannual quasi-coincident MIR and NIR measurements from the stations Garmisch (47.48° N, 11.06° E, 743 m a.s.l.) and Wollongong (34.41° S, 150.88° E, 30 m a.s.l.), we now investigate upgraded retrievals with longer temporal coverage and include three additional stations (Ny-Ålesund, 78.92° N, 11.93° E, 20 m a.s.l.; Karlsruhe, 49.08° N, 8.43° E, 110 m a.s.l.; Izaña, 28.31° N, 16.45° W, 2.370 m a.s.l.). Our intercomparison results (except for Ny-Ålesund) confirm that there is no overall bias between MIR and NIR XCH4 retrievals, and all MIR and NIR time series reveal a quasi-periodic seasonal bias for all stations, except for Izaña. We find that dynamical variability causes MIR-NIR differences of up to ~ 30 ppb (parts per billion) for Ny-Ålesund, ~ 20 ppb for Wollongong, ~ 18 ppb for Garmisch, and ~ 12 ppb for Karlsruhe. The mechanisms behind this variability are elaborated via two case studies, one dealing with stratospheric subsidence induced by the polar vortex at Ny-Ålesund and the other with a deep stratospheric intrusion event at Garmisch. Smoothing effects caused by the dynamical variability during these events are different for MIR and NIR retrievals depending on the altitude of the perturbation area. MIR retrievals appear to be more realistic in the case of stratospheric subsidence, while NIR retrievals are more accurate in the case of stratosphere-troposphere exchange (STE) in the upper troposphere/lower stratosphere (UTLS) region. About 35% of the FTIR measurement days at Garmisch are impacted by STE, and about 23% of the measurement days at Ny-Ålesund are influenced by polar vortex subsidence. The exclusion of data affected by these dynamical situations resulted in improved agreement of MIR and NIR seasonal cycles for Ny-Ålesund and Garmisch. We found that dynamical variability is a key factor in constraining the accuracy of MIR and NIR seasonal cycles. To mitigate this impact it is necessary to use more realistic a priori profiles that take these dynamical events into account (e.g., via improved models), and/or to improve the FTIR retrievals to achieve a more uniform sensitivity at all altitudes (possibly including profile retrievals for the TCCON data)

A method to correct sampling ghosts in historic near-infrared Fourier transform spectrometer (FTS) measurements [Discussion paper]

The Total Carbon Column Observing Network (TCCON) has been established to provide ground-based remote sensing measurements of the column-averaged dry air mole fractions (DMF) of key greenhouse gases. To ensure network-wide consistency, biases between Fourier transform spectrometers at different sites have to be well controlled. Errors in interferogram sampling can introduce significant biases in retrievals.From 2004 to 2011 the Lauder TCCON programme was funded by the New Zealand Foundation of Research Science and Technology contracts CO1X0204, CO1X0703 and CO1X0406

Simultaneous retrieval of atmospheric CO2 and light path modification from space-based spectroscopic observations of greenhouse gases: Methodology and application to GOSAT measurements over TCCON sites

This paper presents an improved photon path length probability density function method that permits simultaneous retrievals of column-average greenhouse gas mole fractions and light path modifications through the atmosphere when processing high-resolution radiance spectra acquired from space. We primarily describe the methodology and retrieval setup and then apply them to the processing of spectra measured by the Greenhouse gases Observing SATellite (GOSAT). We have demonstrated substantial improvements of the data processing with simultaneous carbon dioxide and light path retrievals and reasonable agreement of the satellite-based retrievals against ground-based Fourier transform spectrometer measurements provided by the Total Carbon Column Observing Network (TCCON)