Increasing the Quantitative Credibility of Open-Path Fourier Transform Infrared (FT-IR) Spectroscopic Data, with Focus on Several Properties of the Background Spectrum

Shao, Limin; Wang, Wan-Ping; Griffiths, Peter R.; Leytem, April B.

doi:10.1366/12-06901

Cited by 11 publications

(5 citation statements)

References 22 publications

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“…Similar intercomparison measurements between conventional active, open-path sensors are rare but have shown agreement of typically 1-20% (Thoma et al, 2005;Hak et al, 2005;Smith et al, 2011;Shao et al, 2013;Conde et al, 2014;Reiche et al, 2014;Thalman et al, 2015). Here, we find agreement between two DCS instruments that is an order of magnitude better and is comparable to that achieved with highly-calibrated, state-of-the-art, solarlooking FTIRs that retrieve vertical column measurements (Messerschmidt et al, 2011;Frey et al, 2015;Hedelius et al, 2016); however, open-path DCS does not require instrumentspecific calibrations (e.g.…”

Section: Introductionsupporting

confidence: 72%

Reply to Editor and Reviewer Comments

Waxman¹

2017

Preprint

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We present the first quantitative intercomparison between two open-path dual comb spectroscopy (DCS) instruments which were operated across adjacent 2-km open-air paths over a two-week period. We used DCS to measure the atmospheric absorption spectrum in the near infrared from 6021 to 6388 cm −1 (1565 to 1661 nm), corresponding to a 367 cm −1 bandwidth, at 0.0067 cm −1 sample spacing. The measured absorption spectra agree with each other to within 5×10 −4 without any external calibration of either instrument. The absorption spectra are fit to retrieve concentrations for carbon dioxide (CO 2), methane (CH 4), water (H 2 O), and deuterated water (HDO). The retrieved dry mole fractions agree to 0.14% (0.57 ppm) for CO 2 , 0.35% (7 ppb) for CH 4 , and 0.40% (36 ppm) for H 2 O over the two-week measurement campaign, which included 23 °C outdoor temperature variations and periods of strong atmospheric turbulence. This agreement is at least an order of magnitude better than conventional active-source open-path instrument intercomparisons and is particularly relevant to future regional flux measurements as it allows accurate comparisons of open-path DCS data across locations and time. We additionally compare the open-path DCS retrievals to a WMO-calibrated cavity ringdown point sensor located along the path with good agreement. Short-term and long-term differences between the two systems are attributed, respectively, to spatial sampling discrepancies and to inaccuracies in the current spectral database used to fit the DCS data. Finally, the two-week measurement campaign yields diurnal cycles of CO 2 and CH 4 that are consistent with the presence of local sources of CO 2 and absence of local sources of CH 4 .

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Section: Introductionsupporting

confidence: 72%

Reply to Editor and Reviewer Comments

Waxman¹

2017

Preprint

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“…Similar intercomparison measurements between conventional active open-path sensors are rare but have shown agreement of typically 1-20 % (Thoma et al, 2005;Hak et al, 2005;Smith et al, 2011;Shao et al, 2013;Conde et al, 2014;Reiche et al, 2014;Thalman et al, 2015). Here, we find agreement between two DCS instruments that is an order of magnitude better and is comparable to that achieved with highly calibrated, state-of-the-art solar-looking FTS systems that retrieve vertical column measurements (Messerschmidt et al, 2011;Frey et al, 2015;Hedelius et al, 2016); how-ever, open-path DCS does not require instrument-specific calibrations (e.g., of the instrument line shape) and provides a very different capability by retrieving the dry mole fractions across regional, kilometer-scale paths over day and night on a mobile platform.…”

Section: Introductionmentioning

confidence: 82%

Intercomparison of open-path trace gas measurements with two dual-frequency-comb spectrometers

et al. 2017

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Abstract. We present the first quantitative intercomparison between two open-path dual-comb spectroscopy (DCS) instruments which were operated across adjacent 2 km openair paths over a 2-week period. We used DCS to measure the atmospheric absorption spectrum in the near infrared from 6023 to 6376 cm −1 (1568 to 1660 nm), corresponding to a 355 cm −1 bandwidth, at 0.0067 cm −1 sample spacing. The measured absorption spectra agree with each other to within 5 × 10 −4 in absorbance without any external calibration of either instrument. The absorption spectra are fit to retrieve path-integrated concentrations for carbon dioxide (CO 2 ), methane (CH 4 ), water (H 2 O), and deuterated water (HDO). The retrieved dry mole fractions agree to 0.14 % (0.57 ppm) for CO 2 , 0.35 % (7 ppb) for CH 4 , and 0.40 % (36 ppm) for H 2 O at ∼ 30 s integration time over the 2-week measurement campaign, which included 24 • C outdoor temperature variations and periods of strong atmospheric turbulence. This agreement is at least an order of magnitude better than conventional active-source open-path instrument intercomparisons and is particularly relevant to future regional flux measurements as it allows accurate comparisons of open-path DCS data across locations and time. We additionally compare the open-path DCS retrievals to a World Meteorological Organization (WMO)-calibrated cavity ring-down point sensor located along the path with good agreement. Shortterm and long-term differences between the open-path DCS and point sensor are attributed, respectively, to spatial sampling discrepancies and to inaccuracies in the current spectral database used to fit the DCS data. Finally, the 2-week measurement campaign yields diurnal cycles of CO 2 and CH 4 that are consistent with the presence of local sources of CO 2 and absence of local sources of CH 4 .

show abstract

“…Similar intercomparison measurements between conventional active, open-path sensors are rare but have shown agreement of typically 1–20% (Thoma et al, 2005; Hak et al, 2005; Smith et al, 2011; Shao et al, 2013; Conde et al, 2014; Reiche et al, 2014; Thalman et al, 2015). Here, we find agreement between two DCS instruments that is an order of magnitude better and is comparable to that achieved with highly-calibrated, state-of-the-art, solar-looking FTIRs that retrieve vertical column measurements (Messerschmidt et al, 2011; Frey et al, 2015; Hedelius et al, 2016); however, open-path DCS does not require instrument-specific calibrations (e.g.…”

Section: Introductionmentioning

confidence: 90%

Intercomparison of Open-Path Trace Gas Measurements with Two Dual Frequency Comb Spectrometers

Waxman¹,

Cossel²,

Truong³

et al. 2017

Preprint

View full text Add to dashboard Cite

We present the first quantitative intercomparison between two open-path dual comb spectroscopy (DCS) instruments which were operated across adjacent 2-km open-air paths over a two-week period. We used DCS to measure the atmospheric absorption spectrum in the near infrared from 6021 to 6388 cm−1 (1565 to 1661 nm), corresponding to a 367 cm−1 bandwidth, at 0.0067 cm−1 sample spacing. The measured absorption spectra agree with each other to within 5×10−4 without any external calibration of either instrument. The absorption spectra are fit to retrieve concentrations for carbon dioxide (CO2), methane (CH4), water (H2O), and deuterated water (HDO). The retrieved dry mole fractions agree to 0.14% (0.57 ppm) for CO2, 0.35% (7 ppb) for CH4, and 0.40% (36 ppm) for H2O over the two-week measurement campaign, which included 23 °C outdoor temperature variations and periods of strong atmospheric turbulence. This agreement is at least an order of magnitude better than conventional active-source open-path instrument intercomparisons and is particularly relevant to future regional flux measurements as it allows accurate comparisons of open-path DCS data across locations and time. We additionally compare the open-path DCS retrievals to a WMO-calibrated cavity ringdown point sensor located along the path with good agreement. Short-term and long-term differences between the two systems are attributed, respectively, to spatial sampling discrepancies and to inaccuracies in the current spectral database used to fit the DCS data. Finally, the two-week measurement campaign yields diurnal cycles of CO2 and CH4 that are consistent with the presence of local sources of CO2 and absence of local sources of CH4.

show abstract

Increasing the Quantitative Credibility of Open-Path Fourier Transform Infrared (FT-IR) Spectroscopic Data, with Focus on Several Properties of the Background Spectrum

Cited by 11 publications

References 22 publications

Reply to Editor and Reviewer Comments

Reply to Editor and Reviewer Comments

Intercomparison of open-path trace gas measurements with two dual-frequency-comb spectrometers

Intercomparison of Open-Path Trace Gas Measurements with Two Dual Frequency Comb Spectrometers

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