TCCON > TCCON Data and Network Policies > Data Use Policy > Data Description GGG2012

Data Description GGG2012

TCCON Dry Column-Averaged Mixing Ratios of CO2, CO, N2O, CH4, H2O, HDO and HF. The data can be found on the TCCON database. A MATLAB script to read the database output is provided at the bottom of this page.

Version: GGG2012. For the GGG2009 data description, please see the Data Description GGG2009 page. For up-to-date information, please sign up to the TCCON Users mailing list at https://lists.gps.caltech.edu/mailma...fo/tccon_users.

Common questions about the usage of the data not answered below may be in our FAQ page.

CONTENTS

INTRODUCTION

Column-average Dry Mole Fractions (DMF) reported in this database were acquired using a Fourier Transform Spectrometer (FTS). Direct solar spectra
were acquired in the near-infrared spectral region. These spectra were used to retrieve column abundances of CO2, O2, CH4, N2O, H2O, HDO and HF.

GENERAL COMMENTS ON THE DATA

Dry column-average Gas G DMF has been calculated according to

Where there are several bands from which a gas is retrieved, the average is used for the final XG value. The standard windows used by TCCON retrievals are in the table below. Warning: Some TCCON stations can not measure all of the windows (e.g., CH4, H2O, HDO for Tsukuba120, H2O, HDO for Karlsruhe and Izana, see below for details), and so their data are not on the same scale as the other TCCON data.

Gas Central Wavenumber
(cm-1)
Window Width
(cm-1)
  Gas Central Wavenumber
(cm-1)
Window Width
(cm-1)
CO2 6220.00
6339.50
80.00
85.00
  CO 4233.00
4290.40
48.60
56.80
CH4 5938.00
6002.00
6076.00
116.00
11.10
138.00
  HF 4038.95 0.32
N2O 4395.20
4430.10
43.40
23.10
  O2 7885.00 240.00
H2O 4565.20
4571.75
4576.85
4611.05
4622.00
4699.55
6076.90
6099.35
6125.85
6177.30
6255.95
6301.35
6392.45
6401.15
6469.60
2.50
2.50
1.90
2.20
2.30
4.00
3.85
0.95
1.45
0.83
3.60
7.90
3.10
1.15
3.50
  HDO 4054.60
4116.10
4212.45
4232.50
6330.05
6377.40
3.30
8.00
1.90
11.00
45.50
50.20

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Sources of Uncertainty

The dry column-averaged DMF () is affected by three main sources of uncertainty:

Measurement precision (repeatability)

The TCCON measurement precision is <0.25% (1-sigma) under clear or partly cloudy skies (up to 5% fractional variation in solar intensity), and solar zenith angles <82 degrees.

Spectroscopic uncertainties

The retrieved O2 columns were NOT reduced to bring them into agreement with the dry surface pressure, as described in Washenfelder et al. (2006). The absolute accuracy of the retrievals was calibrated by comparison to integrated aircraft profiles, resulting in the corrections listed below. The aircraft profiles were performed with the sun at lower airmasses, and the column-average DMF are now well-calibrated for these values. However, additional systematic uncertainties may be present at higher airmass due to uncertainties in the spectroscopy of the gas of interest and/or O2.

Systematic instrumental changes over time

There are known drifts in these instruments, and care is taken to minimize and correct for these uncertainties.

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Data Comparisons

TCCON data should be compared with other data using the Rodgers and Connor (2003) approach. Column averaging kernels and a priori profiles are available either on the Auxiliary Data page or from the individual principal investigators.

Changes from GGG2009 Version

The differences between GGG2009 and GGG2012 are summarized in the TCCON Update presentation attached at the bottom of this page. Briefly, the following changes have occurred between GGG2009 and GGG2012:

  • A Priori ProfilesEdit section

    • The a priori profiles have been modified to have a more realistic interhemispheric gradient and seasonal cycle, based on aircraft, balloon and satellite profiles. This especially improves the CH4 and CO.
    • The CH4 and N2O a priori profiles correlate better with HF and compare better with ACE-FTS and MkIV slopes.
  • Spectroscopy

    • Included the June 2009 HITRAN update + tweaks for H2O
    • O2 line positions shifted in the 7600-8200 cm-1 range
    • Assigned reasonable E” to CH4 line list in the N2O windows and added missing lines from the line list
    • Assigned 422/722 missing H2O lines that had been identified in TCCON spectra
  • Solar Line List

    • Disk-integrated (DI) and disk-centred (DC) line lists have been merged
      • This allows each solar spectrum to be analyzed for the fraction of the solar disk that it actually saw
    • The entire solar spectrum has subsequently been refitted over all spectral regions used by TCCON, with 2700 new solar lines added
    • A more realistic model of the Doppler broadening caused by the solar spin has been included into the solar model
  • Correction Factors

    • An inconsistency in the line lists used to calculate the calibration factors for the TCCON DMFs has been eliminated. This results in a ~0.5 ppm increase in Xco2 in the current version of the TCCON data.
    • The "in situ" (airmass independent) and airmass dependent correction factors were recalculated as listed in the CORRECTIONS AND CALIBRATIONS section below. The GGG2009 values can be found, for comparison, on the GGG2009 CORRECTIONS_AND_CALIBRATIONS page.
  • Overall Differences

    • As a result of these effects, there are some changes in the retrieved values. E.g. Xco2 changes by ~+0.5ppm. There is some seasonality to this, especially at higher latitude NH sites - the difference is relatively constant with season at Wollongong, Lauder, Darwin and Lamont. The +0.5 ppm shift is due to the elimination of a spectroscopic line list inconsistency. The seasonality is likely due to the improvement in the seasonality of the a priori profiles.
    • For other species, the changes are minor:
      • Xch4 changes by a few ppb (generally < 2ppb); with a small seasonal cycle difference
      • Xco is now generally lower by ~4 ppb and has a ~2.5 ppb seasonal cycle difference; in the tropics the difference is larger - from 5 to 11ppb, with a seasonal cycle difference of around 6 ppb
      • Xn2o is now generally higher by 0-4ppb in the northern hemisphere, -2 to 2 ppb different in Wollongong and ~2ppb lower in Darwin, with a significant seasonal cycle difference (~3 ppb) in Lamont
      • Xh2o and Xhdo now have ~no bias but some differences in the wettest months
      • Xhf is now generally higher by ~2ppt in Park Falls and Lamont, lower in Darwin by ~1 ppb, with a small seasonal cycle difference

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CORRECTIONS AND CALIBRATIONS

The data are corrected for known airmass-dependent and airmass-independent (calibration) biases. These correction factors are applied to the column-averaged mole fractions.

The airmass-dependent correction factor (ADCF) is determined offline from the symmetric component of the diurnal variation. The airmass-independent correction factor (AICF) is determined offline by comparisons with in situ profiles measured over TCCON sites with aircraft equipped with WMO-standard instrumentation.

Gas ADCF ADCF Error (σ) AICF AICF Error (σ)
xco2 -0.0065 0.0050 0.989 0.001
xch4 0.0055 0.0080 0.978 0.002
xn2o 0.0172 0.0100 0.958 0.005
xco - - 0.98 0.02
xh2o - - 1.031 0.010

No airmass dependent correction is applied to XCO, XH2O, XHDO or XHF at the present time.

The airmass-dependent calibration is described in the supplementary material to:

Wunch, D., G. C. Toon, J.-F. L. Blavier, R. A. Washenfelder, J. Notholt, B. J. Connor, D. W. T. Griffith, V. Sherlock, P. O. Wennberg. The Total Carbon Column Observing Network, doi: 10.1098/rsta.2010.0240 Phil. Trans. R. Soc. A 28 May 2011 vol. 369 no. 1943 2087-2112. Available from: http://rsta.royalsocietypublishing.o.../2087.full.pdf

The in situ calibration factors were developed and described in:

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., Keppel-Aleks, 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, doi:10.5194/amt-3-1351-2010, 2010. Available from: http://www.atmos-meas-tech.net/3/1351/2010/

Note that XHF and XHDO are not calibrated. These are preliminary data sets that should be used with caution.

XHF

TCCON retrievals of XHF are uncalibrated because there have been no WMO-standard profiles of HF measured over our TCCON stations. The XHF asbsorption line used for TCCON retrievals is narrow and on the wing of a strong H2O line. This line can black out when it's wet, especially at high airmass. If you wish to use these data, please ensure that you carefully inspect the data and use low airmasses only. It would be appropriate for you to consult with a TCCON PI about the use of the XHF data. These XHF retrievals are useful if you wish to compute tropospheric columns of CH4, and perhaps N2O:

Washenfelder, R. A., P. O. Wennberg, and G. C. Toon (2003), Tropospheric methane retrieved from ground-based near-IR solar absorption spectra, Geophysical Research Letters, 30(23), 1-5, doi:10.1029/2003GL017969. Available from: http://www.agu.org/pubs/crossref/200...GL017969.shtml

XHDO

TCCON retrievals of XHDO are uncalibrated because there have been no WMO-standard profiles of HDO measured over our TCCON stations. These data, however, have been used successfully in several papers when the absolute HDO value is not critical. We would recommend that you use caution when using these data. Below are several references that successfully use TCCON HDO. See the HDO FAQ for details.

Risi, C., D. Noone, J. Worden, C. Frankenberg, G. Stiller, M. Kiefer, B. Funke, K. Walker, P. Bernath, M. Schneider, D. Wunch, V. Sherlock, N. Deutscher, D. Griffith, P. O. Wennberg, K. Strong, D. Smale, E. Mahieu, S. Barthlott, F. Hase, O. García, J. Notholt, T. Warneke, G. Toon, D. Sayres, S. Bony, J. Lee, D. Brown, R. Uemura, and C. Sturm (2012), Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopologues : 1 . Comparison between models and observations, Journal of Geophysical Research, 117, 1-26, doi:10.1029/2011JD016621. Available from: http://www.agu.org/pubs/crossref/201...JD016621.shtml

Risi, C., D. Noone, J. Worden, C. Frankenberg, G. Stiller, M. Kiefer, B. Funke, K. Walker, P. Bernath, M. Schneider, S. Bony, J. Lee, D. Brown, and C. Sturm (2012), Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopic observations: 2 . Using isotopic diagnostics to understand the mid and upper tropospheric moist bias in the tropics and subtropics, Journal of Geophysical Research, 117(D05304), 1-25, doi:10.1029/2011JD016623. Available from: http://www.agu.org/pubs/crossref/201...JD016623.shtml

Frankenberg, C., Wunch, D., Toon, G., Risi, C., Scheepmaker, R., Lee, J.-E., Wennberg, P., and Worden, J.: Water vapor isotopologues retrievals from high resolution GOSAT short-wave infrared spectra, Atmos. Meas. Tech. Discuss., 5, 6357-6386, doi:10.5194/amtd-5-6357-2012, 2012. Available from: http://www.atmos-meas-tech-discuss.n...6357-2012.html

Boesch, H., Deutscher, N. M., Warneke, T., Byckling, K., Cogan, A. J., Griffith, D. W. T., Notholt, J., Parker, R. J., and Wang, Z.: HDO/H2O ratio retrievals from GOSAT, Atmos. Meas. Tech. Discuss., 5, 6643-6677, doi:10.5194/amtd-5-6643-2012, 2012. Available from: http://www.atmos-meas-tech-discuss.n...6643-2012.html  

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Laser Sampling Errors

The laser sampling boards in the Bruker 125HR instruments were faulty, causing zero-level offsets (or ghosts) in the spectra (Messerschmidt et al., 2010). The boards were replaced by Bruker Optics at various times at each TCCON station (usually in 2011). When the boards were changed, the ghost problem was eliminated, but historical data are still affected by the laser sampling errors. Data recorded before the board exchange are biased relative to the data recorded after. A resampling algorithm has been developed (Dohe et al., 2013) and will be applied to all our data in the next TCCON data release. However, in the interim, we recommend the following corrections to our data. Please note that after these corrections are applied, the site-to-site biases should be reduced, but there may be an overall TCCON bias (on the order of a few tenths of a ppm) compared with the WMO scale.

Estimated Laser Sampling Errors in XCO2. These are the recommended corrections to the data published up to Jan 2014. Please note that after these corrections are applied, the site-to-site biases should be reduced, but there may be an overall TCCON bias (on the order of a few tenths of a ppm) compared with the WMO scale. All sites with N/A in the "Dates Affected" column have publicly released data only using the newer laser sampling boards, or are thought to have a laser sampling board that is unaffected by this type of error. The Revised Recommendations (Jan 2014) reflect our ongoing efforts in resampling the interferograms and the estimated biases, resulting from a comparison of the resampled and original (GGG2012) results. The next version of GGG will include resampled interferograms, and no correction will be required.
Site Dates Affected Estimated Bias Correction Already Applied? Recommended Correction for Dates Affected
Revised Recommendations (January 2014)
Lamont Start - April 14, 2011 -0.5 ppm (>-1 ppm) NO +0.5 ppm

Start - April 16, 2009: -0.4±0.2 ppm
April 17, 2009 - April 14, 2011: -0.2±0.1 ppm
April 15, 2011 - Present: 0±0.1 ppm

Park Falls Start - June 23, 2011 +0.8 ± 0.4 ppm NO -0.8 ppm Start - June 23, 2011: -0.55±0.1 ppm
June 24, 2011 - Present: 0.08±0.1 ppm
Bialystok Start - September 27, 2009 -0.96 ppm YES 0 The recommendations are to apply the following corrections to the current public release data:

Start - Sep 27, 2009: -0.5 ± 0.2 ppm
Sep 27, 2009 - April 2010: 0 ± 0.1 ppm
April 2010 - Sep 2010: 0.1 ± 0.3 ppm
Sep 2010 - present: 0 ± 0.1 ppm

Orleans Start - October 12, 2011 -0.42 ppm YES 0

The recommendations are to apply the following corrections to the current public release data:

Start - October 3, 2009: -0.2 ± 0.2 ppm
Oct 3, 2009 - May, 2010: 0 ± 0.1 ppm
May 2010 - Oct 2010: -0.2 ± 0.2 ppm
Oct 2010 - Oct 12, 2011: -0.4 ± 0.1 ppm
Oct 12, 2011 - present: 0 ± 0.1ppm

Izana Start - November 30, 2010 0.14 - 2 ppm ± 0.5 ppm YES 0  
Bremen Start - June 17, 2009 +1.2 ppm NO -1.2 ppm  
June 18, 2009 - July 5, 2011 Unknown but small NO 0
July 6, 2011 - May, 2012 small NO 0
JPL2007 All dates negative, with a magnitude no greater than 1 ppm NO +0.5 ppm All dates:
+0.1±0.15 ppm
Garmisch Start - July 20, 2009 +/- 1 ppm NO  0  
July 21, 2009 - August 9, 2010 Small (< +/- 0.2 ppm) NO  0
Saga Start - July 27, 2011 Unknown NO    
Wollongong Start - July 22, 2011 <+1 +/- 1 ppm NO -1.0 +/- 1 ppm

Start -13 Mar 2009: 0 ± 0.1 ppm
10 Jun 2009 - 30 Jun 2009: -0.2 ± 0.1 ppm
1 Jul 2009 - 26 Jul 2009: +0.7 ± 0.2 ppm
27 Jul 2009 - 3 Nov 2009: -0.1 ± 0.1 ppm
4 Nov 2009 - 21 Jul 2011: +0.4 ± 0.1 ppm
22 Jul 2011 - 03 Aug 2013: 0 ± 0.1 ppm
04 Aug 2013 - 29 sep 2013: +0.1 ± 0.1 ppm
30 Sep 2013 - present: 0 ± 0.1 ppm

Darwin

Start - Jan 23, 2012
(laser board change)

0 +/- 1 ppm NO  0 +/- 1 ppm Start - Dec 1, 2006: -0.1±0.1 ppm
Dec 2, 2006 - Sep 9, 2008:  0.3±0.08 ppm
Sep 10, 2008 - Jan 16, 2009: 0.8±0.14 ppm
Jan 17, 2009 - Sept 10, 2010: -0.54±0.12 ppm
Sept 11, 2010 - Jan 27, 2012: 0.08±0.07 ppm 
Jan 28, 2012 - May 13, 2012: -1.1±0.2 ppm
May 14, 2012 - Oct 25, 2012: -0.06±0.25 ppm
Oct 26, 2012 - present:  0.15±0.14 ppm
Jan 24, 2012 - May 13, 2012 (adjustment) 0 +/- 1 ppm NO 0 +/- 1 ppm
May 14, 2012 - Oct 22, 2012 (adjustment) 0 +/- 1 ppm NO 0 +/- 1 ppm
Oct 23, 2012 - present 0 NO 0
Sodankyla Start - March 6, 2010 2.5 ppm YES 0  
Lauder 120HR All dates "small" NO 0  
Lauder 125HR N/A     0  
Tsukuba 120HR All dates -1.48 ± 0.5 ppm YES 0  
Tsukuba 125HR N/A     0  
Eureka N/A     0  
JPL2011/Dryden/Indianapolis N/A     0  
Ny Alesund N/A     0  
Ascension Island N/A     0  
Reunion Island N/A     0  
Karlsruhe N/A     0  
Four Corners N/A     0  

 

Estimated Laser Sampling Errors in other gases. Other gases are also impacted by the Laser Sampling Errors but these have not yet been quantified.  The error will likely be approximately proportional to those of CO2 (e.g. of order 1 part in 400 or less).

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SITE-SPECIFIC NOTES

Lamont

The wind speed and direction sensor was faulty until March 26, 2009. It is possible that the wind speed values prior to March 26, 2009 are valid but noisy, but the wind direction values are not. All values since March 26, 2009 are valid.

New laser detector boards and laser were installed on April 14, 2011 to eliminate the effect of mis-sampling ('ghosts'). The magnitude of the change has not yet been quantified, but the data before April 14, 2011 are likely too low by <1 ppm in XCO2 (0.5 ppm is the current best estimate).

JPL2007

This instrument was at JPL to provide simultaneously recorded atmospheric spectra during the OCO thermal-vacuum testing period. The instrument was subsequently moved to Lamont, Oklahoma.

The wind speed and direction sensor was faulty for the entire time series. It is possible that the wind speed values are valid but noisy, but the wind direction values are not.

The magnitude of the ghosts caused by the laser sampling board have not yet been quantified, but they likely cause a constant bias in XCO2 of <1 ppm over the entire time series.

Wunch, D., P. O. Wennberg, G. C. Toon, G. Keppel-Aleks, and Y. G. Yavin (2009), Emissions of greenhouse gases from a North American megacity, Geophysical Research Letters, 36(15), 1-5, doi:10.1029/2009GL039825. Available from: http://www.agu.org/pubs/crossref/200...GL039825.shtml

JPL2011

This instrument was at JPL to provide simultaneously recorded atmospheric spectra during the OCO-2 thermal-vacuum testing period. The instrument was subsequently moved to Indianpolis, Indiana.

The red filter, which prevents aliased spectral information from folding back onto the Si detector spectra, was removed to reduce the channeling in the A-band spectra on April 19, 2012. After this date, the oxygen B-band spectra are not useable (the A-band spectra are fine).

Data from this instrument are not affected by ghosts caused by laser sampling errors.

Lauder

Please refer to the official output file header information (ascii files) for the two Lauder FTS instruments attached below

Tsukuba

  • Tsukuba 120 HR (old FTS, now at Rikubetsu after upgrading), two-letter site name: tj (Dec. 25, 2008 - Mar. 22, 2010)

The bias for the Tsukuba data measured with an old FTS (Bruker IFS 120 HR) using the 2010 aircraft calibration campaign over Tsukuba was estimated. We did three overpasses and a bias for the Tsukuba FTS value obtained with the TCCON common data processing is -1.48 ppm +/- 0.50 ppm (1 sigma) for XCO2. The 1.48 ppm bias was added to these XCO2 data.

A bias for XCH4 likely exists but its magnitude has not yet been estimated.

Tanaka, T., Y. Miyamoto, I. Morino, T. Machida, T. Nagahama, Y. Sawa, H. Matsueda, D. Wunch, S. Kawakami, and O. Uchino (2012), Aircraft measurements of carbon dioxide and methane for the calibration of ground-based high-resolution Fourier Transform Spectrometers and a comparison to GOSAT data measured over Tsukuba and Moshiri, Atmospheric Measurement Techniques, 5(8), 2003–2012, doi:10.5194/amt-5-2003-2012 (Version of GGG2009 was used in this paper.). Available from: http://www.atmos-meas-tech.net/5/2003/2012/

The Tsukuba 120 HR instrument did not measure wavenumbers below 6000 cm-1, and so it was missing CO, N2O, HF, some H2O and HDO windows and one CH4 window. As such, the H2O, HDO and CH4 are not directly comparable to the standard TCCON retrievals and the H2O retrievals cannot be considered calibrated.

  • Tsukuba 125 HR (new FTS), two-letter site name: tk (Apr. 08, 2010 -present)

New FTS (IFS 125 HR) started operation from Apr. 08, 2010. However, spectra were affect by a laser sampling error from Apr. 08, 2010 to Jul. 28, 2011 and by a lot of aftershock after a very huge earthquake with 9.0 magnitude occurred on Mar. 11, 2011 from Apr. 11, 2011 to Jul. 28, 2011. Therefore, we are releasing the data without ghost and earthquake effects from Aug. 4 2011.

[Problematic XCO data from Apr. 13, 2012 to Aug. 27, 2012, from Sep. 13, 2012 to Jan. 11, 2013, and Feb. 22, 2013 and Jun. 6, 2013]
Problematic XCO data with poor data quality were found on dates from Apr. 13, 2012 to Aug 27, 2012 and from Sep. 13, 2012 to Jan. 11, 2013. Please DON'T USE the Tsukuba 125 HR XCO data from Apr. 13, 2012 to Aug. 27, 2012 and from Sep. 13, 2012 to Jan. 11, 2013.
The XCO data on dates Feb. 22, 2013 and Jun. 6, 2013 were also problematic. In their data invalid value (-9999.9) was inserted.

 

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Park Falls

New laser detector boards were installed on June 23, 2011 to eliminate the effect of mis-sampling ('ghosts'). The magnitude of the change has not yet been fully quantified, but the earlier data are likely too high by ~0.8±0.4 ppm in XCO2.

Washenfelder, R. A., G. C. Toon, J.-F. L. Blavier, Z. Yang, N. T. Allen, P. O. Wennberg, S. A. Vay, D. M. Matross, and B. C. Daube (2006), Carbon dioxide column abundances at the Wisconsin Tall Tower site, Journal of Geophysical Research, 111(D22), 1-11, doi:10.1029/2006JD007154. Available from: http://www.agu.org/pubs/crossref/200...JD007154.shtml

Bialystok

Prior to September 27, 2009, a laser sampling error ('ghosts') caused a bias in XCO2. On this date, the bias was minimized, and the magnitude of the effect quantified as being 0.96 ppm in XCO2. Data uploaded to the TCCON data archive have the XCO2 before September 27, 2009 corrected by +0.96 ppm. Because of the ghost minimization, there are likely to also be step-changes in other gases at this time, which has not been corrected. Nevertheless, caution should be applied when interpreting changes in other gases across this date.

The following reference should be used for the Bialystok site:

Messerschmidt, J., H. Chen, N. M. Deutscher, C. Gerbig, P. Grupe, K. Katrynski, F.-T. Koch, J. V. Lavrič, J. Notholt, C. Rödenbeck, W. Ruhe, T. Warneke, and C. Weinzierl (2012), Automated ground-based remote sensing measurements of greenhouse gases at the Białystok site in comparison with collocated in situ measurements and model data, Atmospheric Chemistry and Physics, 12(15), 6741–6755, doi:10.5194/acp-12-6741-2012. Available from: http://www.atmos-chem-phys.net/12/6741/2012/

Orleans

A ghost correction of +0.42 ppm in XCO2 is applied to the Orleans time series until October 12, 2011. Ghosts are likely to affect other species as well - this effect has not been quantified. The ghosts have subsequently been minimized and no correction is applied after 20111012.

Izana

Measurements from 2007-2010 are affected by laser sampling ghosts. This effect on the retrieved Xco2 was minimized (though not eliminated) by averaging pairs of scans and correcting the data using surface pressure measurements. Measurements recorded after 2010-11-30 use a new laser sampling board and are not affected by ghosts, and no averaging is performed.

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Bremen

Since the last GGG2009 release, the the pressure associated with some of the Bremen spectra has been updated . This is due to a correction implemented to account for the height difference between the pressure measured at the instrument, and that measured at Bremen airport. The Bremen airport meteorological data are used in the case where no in situ data are available at the time of the spectrum. This mostly affects the earliest data, and occasional spectra at other times. The affect of this on the retrievals has not yet been quantified, but the pressure difference between the airport and the instrument is generally ~3hPa, with the correction resulting in a decreased pressure (the instrument is at a higher altitude than the airport).

Some processing errors resulted in the exclusion of a number of spectra in the GGG2009 release, so there should be more data in the GGG2012 release.

The Bremen instrument is also likely affected by laser-sampling errors. No correction has been applied to any species for this effect, but the ghosts were minimized after the replacement of the ECL03 laser board on July 5, 2011, and then subsequently again in May 2012. Care should be taken interpreting any changes crossing these dates.

Data are provided from 2005 onwards. From 2007, we are confident in the quality of the data, and care should be taken with interpretation of the 2005-6 data. Every effort has been made to ensure that these data are comparable to those from later in the time series, but there could be some remaining timing errors induced by failure to synchronize the time, for example.

No DC correction is currently applied to Bremen data. This will be applied to data post-2008 in future releases, once some outstanding issues with this site and the processing invoking this correction are resolved. As a consequence the precision of the data will be expected to improve in future releases.

 

WARNING: PLEASE NOTE!!!!

Between May and September (inclusive) 2012, there appears to be an offset in the retrieved xGAS quantities. This period was when the HeNe laser was failing, but the exact cause for the step change is unknown. For the time being, it is recommended not to use data during this period, and a correction or resolution for this effect is being investigated. Some of these data are flagged (those uploaded in May/June 2013), but those previously included from the original GGG2012 release are not flagged. This includes 2 days in May 2012 (24th and 25th) that should be excluded from any analyses.
 

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Ny Alesund

The magnitude of potential laser-sampling biases for the instrument at Ny Alesund has not been quantified. The InGaAs spectra at this site have been acquired with a lower spectral resolution than other TCCON sites (30 cm OPD). This should not induce any offset in comparison to other sites, however, as no calibration overflight has occurred over Ny Alesund this is not certain and the potential magnitude of this effect is not quantified. Studies suggest, however, that the effect of running at a significantly lower resolution (1cm OPD) is < 0.1%, so we expect the effect to be somewhat smaller than that, and within the inter-site uncertainties of the network.

No DC/solar intensity variation correction is currently applied to Ny Alesund data. Since the installation of the new electronics, more spectra have been acquired in non-clear sky scenes, and future updates will include correction (when available) and filtering based on solar intensity variations.

In October 2012 the instrument was upgraded from a Bruker 120HR to a Bruker 120/5HR, with the installation of new electronics.

Note that the majority of data (pre-October 2012) were acquired with the IFS120HR, where the ghosts are expected to be negligible. The ghosts were minimised with the installation of the new electronics.

On June 25, 2013, the resolution was changed to be 45 cm max OPD, along with changing PHR to 1cm (instead of 4cm-1).

Ascension Island

Solar tracker mirror degradation in 2012 and 2013

Ascension Island is a very rough environment. The solar tracker mirrors suffered from degradation due to sea salt corrosion and dust from the very beginning (May 22, 2012). The reflectivity of the mirrors was reduced from nearly 100% to about 30-40% in the infrared (25% in the visible). This reduced the number of spectra per day and also the signal-to-noise-ratio of the spectra that were measured. Still, about 50% of the measured spectra (the ones that were submitted to the TCCON database) appeared to be usable for further analysis.

The 2nd measurement period with new protected-gold mirrors started from mid-March 2013. The new mirrors performed much better than the first set at the beginning. Howver, they still suffered from the harsh environment. By the end of June 2013, the mirrors were too degraded for further measurements. The instrument was then shut down until the next planned maintenance in August 2013.

The problem was finally solved with the introduction of specially designed rugged mirrors in August 2013. There are three distinct periods with respect to the different types of mirrors that were used:

  • 20120522-20120831: original unprotected gold mirrors (no cleaning)
  • 20130317-20130618: protected gold mirrors (cleaning every 1-2 weeks)
  • 20130911-today:      rugged mirrors (cleaning every 1-2 weeks)

The mirrors need to be cleaned regularly to remove dust from the surface. Otherwise, the solar tracker would become unable to track the sun
after 3-4 weeks. The effects of cleaning may be visible in the data, for example in the form of a sudden decrease in noise or an increase in the number of measurements per day.

Laser sampling errors  

The Ascension Island FTS should not suffer from laser sampling errors (aka ghosts). The upgraded ECL04 laser board was installed just before the deployment to Ascension Island (March 2012). Another check during the 1st maintenance visit in March 2013 revealed no ghosts.

Timing issues with pre-GGG2014 data

Due to a bug in the preprocessing software, time stamps in the spectrum files were offset by about 105-110 seconds. This caused a slight dependency on solar zenith angle in the retrieved total columns. However, since this affects all columns in a similar way, the actual x_gas was not affected!

The bug was found and eliminated in August 2014 and the whole dataset was reprocessed. So, only the GGG2012 data that had been uploaded to the TCCON database before this date was affected by this bug. The GGG2014 data for Ascension Island was never affected!

Reunion Island

The Reunion Island XCO2 data have a residual airmass dependence even after the known TCCON-wide airmass dependence is removed. The cause of this is still under investigation.
Measurements at Reunion began in September 2011 with an upgraded laser board (ECL04).  The complete Reunion Island dataset should essentially be unaffected by the laser-sampling ghosts.
From August 2 2012 until November 12 2012, a linearly increasing time correction (tcorr) was applied to compensate for a deviating computer clock which was not receiving NTP time updates during this period.
The daily spread of the retrieved Xgas from November 26 2012 until December 13 2012 is considerably larger due to a degrading laser tube. To reflect this, the errors for Xco2 are about three times larger during this period compared with the errors obtained during optimal operation.
The bad laser tube was replaced on February 18 2013.

From October 10 2014 until November 20 2014 a too large iris was used (0.8 mm instead of 0.5 mm) for the measurements, this resulted in saturation of the detector at low solar zenith angles.
The measurements which were affected by this saturation of the detector have been flaged based on the value of their corresponding SIA.  The value of "SIA" (solar intensity average) in the Reunion Island data is the mean detector voltage during a measurement, and has a range of 0 V to 0.7 V.  We consider measurements with an SIA > 0.5 V to be saturated.

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Karlsruhe

Before Aug. 2012,the Karlsruhe instrument did not measure wavenumbers below 5000 cm-1, and so it was missing CO, N2O, HF, and some H2O and HDO windows. As such, the H2O and HDO during this period were not directly comparable to the standard TCCON retrievals and the H2O retrievals cannot be considered calibrated. Since Aug. 2012, the whole TCCON bandpass is covered. The current configuration differs from the standard TCCON setup in that the 4000 to 5300 cm-1 is observed with a cryogenic InSb detector and the 5300 to 9500 cm-1 region with an InGaAs detector. The spectrometer is operated vented and we expect that the complete Karlsruhe time series is essentially unaffected by ghost issues (ECL03 2009-08/2010, ECL04 08/2010-present).

Four Corners

The instrument at Four Corners was installed in March 2011, and was dedicated to TCCON measurements. It operated continuously until we had a laser failure in February 2012. This resulted in a data gap of ~1 month, and any variability in the data before February could be the result of the laser degradation. Another gap in the data occured in June, 2013, due to a software failure. The instrument resumed measurements in mid August. The operations in Four Corners ended in October, 2013.

May 5 to 18, 2013 has higher random noise, likely due to a laser stability problem. We recommend that results during this time frame to be used with caution. The instrument does not have an aperture stop behind the input window, this resulting in saturation of the InGaAs detector around local noon. We made a quality control for saturated spectra and removed them, but please be aware of this problem and be cautious when using noontime data.

The Four Corners FTS does not suffer from laser sampling errors (ghosts). The upgraded laser board was installed just before the deployment to Four Corners. Another check during the tracker realignment visit in May 2013 revealed no ghosts.

NOTE: A first data set was submitted for the March 1, 2011 to May 31, 2013 time frame. The second data set submitted recently is meant to replace the first one. It contains the full data set acquired in Four Corners: March 1, 2011 to September 31, 2013. In addition, it is clean of saturated spectra and we do recommend to the users to  stop using data from the first submission.

The instrument is scheduled to be deployed to Manaus, Brazil in January, 2014.

Bias of the pre-GGG2014 data

All 4C TCCON retrievals are high biased by ~0.28% due to an error in the surface pressure used in the retrievals. This error does not affect the GGG2014 data.  Please contact PI for details

Garmisch

From November, 27 2008 to May, 7 2009 the spectra and therefore the resulting mixing ratios are affected by saturation of the InGaAs Detector.

The early Garmisch spectra are affected by laser missampling errors. No correction has been applied to any species for this effect. The sampling errors were reduced by the ECL03 laserboard exchange onJuly, 20 2009 but due to the unknown effect where the sampling errors reappear in evacuated conditions a small sampling error was present up to August, 9 2010.

Indianapolis

The JPL2011 instrument was moved to Indianapolis, IN as part of the INFLUX campaign and recorded spectra from August 23, 2012 to December 1, 2012.  It has now returned to JPL for thermal-vacuum testing of the OCO-2 flight spare.

Saga

New laser detector boards ECL04 were installed on July 27, 2011 to eliminate the effect of mis-sampling ('ghosts'). The ghosts have subsequently been minimized and no correction is applied. The laser was exchanged on January 12, 2013.

To protect gold mirrors of the solar tracker from degradation, a high transmission glass is used for a cover of the solar tracker. Spectra with enough signal-to-noise ratio can be obtained with the protection glass.

Dryden

The JPL2011 instrument is now located at Dryden Flight Research Facility in support of OCO-2 and has been operational since July 20, 2013.

Caltech

The Caltech instrument has been running since September 20, 2012. There are several things to note about the Caltech data:

  1. The data were processed with a different version of the interferogram processing code as the rest of the TCCON data. This is primarily to address the fact that the Caltech instrument does not have a solar tracker that records solar intensity variations. The new version of the processing code calculates solar intensity variations from the DC levels recorded on the instrument (NIR) detectors themselves.
  2. The data do not suffer from laser sampling errors ('ghosts') as the instrument was delivered with the new laser sampling hardware.
  3. This instrument has been through several lasers, most of which failed due to faulty manufacturing. As a result, the data between April 30 and May 22, 2013 are much noisier than the rest due to a slow laser failure.

 

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 lh20040629_20110228_v2.txt Preview
Lauder 120HR release notes 2013-03-15
12.81 kB13:10, 14 Mar 2013v.sherlockActions
 ll20100202_20121231.txt Preview
Lauder 125HR release notes 2013-03-15
10.92 kB13:10, 14 Mar 2013v.sherlockActions
 read_gator_output.m
A MATLAB script to read the .tbl format from the GATOR database that hosts the TCCON data.
1499 bytes15:18, 16 Oct 2012dwunchActions
 Wunch_TCCON_Update_20121008.pdf
Update notes on the TCCON GGG2012 data release.
2.31 MB08:30, 17 Oct 2012dwunchActions