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| Titel |
A method to correct sampling ghosts in historic near-infrared Fourier transform spectrometer (FTS) measurements |
| VerfasserIn |
S. Dohe, V. Sherlock, F. Hase, M. Gisi, J. Robinson, E. Sepúlveda, M. Schneider, T. Blumenstock |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 8 ; Nr. 6, no. 8 (2013-08-13), S.1981-1992 |
| Datensatznummer |
250085033
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| Publikation (Nr.) |
 copernicus.org/amt-6-1981-2013.pdf |
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| Zusammenfassung |
| 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. In this study we investigate a
two-step scheme to correct these errors. In the first step the laser sampling
error (LSE) is estimated by determining the sampling shift which minimises
the magnitude of the signal intensity in selected, fully absorbed regions of
the solar spectrum. The LSE is estimated for every day with measurements
which meet certain selection criteria to derive the site-specific time series
of the LSEs. In the second step, this sequence of LSEs is used to resample
all the interferograms acquired at the site, and hence correct the sampling
errors. Measurements acquired at the Izaña and Lauder TCCON sites are
used to demonstrate the method. At both sites the sampling error histories
show changes in LSE due to instrument interventions (e.g. realignment).
Estimated LSEs are in good agreement with sampling errors inferred from the
ratio of primary and ghost spectral signatures in optically bandpass-limited
tungsten lamp spectra acquired at Lauder. The original time series of
Xair and XCO2 (XY: column-averaged
DMF of the target gas Y) at both sites show discrepancies of 0.2–0.5%
due to changes in the LSE associated with instrument interventions or changes
in the measurement sample rate. After resampling, discrepancies are reduced to
0.1% or less at Lauder and 0.2% at Izaña. In the latter case,
coincident changes in interferometer alignment may also have contributed to
the residual difference. In the future the proposed method will be used to
correct historical spectra at all TCCON sites. |
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