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Gas cell spectrum study and determination of
the concentration of carbon monoxide inside the
gas cell
Atmospheric Remote Sensing and Molecular
Spectroscopy (Vietnam School of Earth Observation)
Quy Nhon, Vietnam, 26-31 August 2018
Yao Té (yao-veng.te@sorbonne-universite.fr)
Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères
LERMA-IPSL, SU/CNRS/Observatoire de Paris/IPSL, UMR 8112
Case 76, 4 Place Jussieu, 75005 Paris, France
Recording of the gas cell spectrum
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
Picture of the FTS-Paris spectrometer
IR spectrum of the FTS-Paris instrument
H2O
H2O
H2O
CO2
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
IR spectrum of the FTS-Paris instrument
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
IR spectrum of the FTS-Paris instrument
H2O
H2O
H2O
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
IR spectrum of the FTS-Paris instrument under vacuum
H2O
H2O
H2O
CO2
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
Ambient air spectrum
Under vacuum spectrum
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
Gas cell inside the FTS-Paris spectrometer
Gas cell spectrum recorded by of the FTS-Paris instrument
H2O
H2O
H2O
CO2
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
Under vacuum spectrum
Gas cell spectrum
CO
CO
Gas cell spectrum + optical filter
CO2
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
CO
Effect of spectral resolution
Gas cell spectrum + optical filter
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
Res = 0.1 cm-1
Res = 0.2 cm-1
Res = 1.0 cm-1
Res = 5.0 cm-1
[resolution]
Effect of integration time
Gas cell spectrum + optical filter
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
4 scans spectrum
16 scans spectrum
[co-addition]
𝐺𝑎𝑖𝑛 = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑐𝑎𝑛𝑠
Analyse of the gas cell spectrum
Transmission spectrum of gas cell
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
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Transmission spectrum of gas cell
Study of the absorption line R(17)
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
?
Instructions and Hints
1 - Remember the Beer-Lambert law 𝑰 𝝂 = 𝑰𝟎(𝝂)𝒆−𝒏𝝈𝝂𝑳
2 - For small absorption :
- First order approximation of 𝒆−𝒏𝝈𝝂𝑳 𝒆−𝒏𝝈𝝂𝑳 ≈ 𝟏 − 𝒏𝝈𝝂𝑳
- Integration of 𝟏 − Τ𝑰 𝑰𝟎 introducing 𝑺 = 𝟎∞𝝈𝝂 𝒅𝝂
𝟎∞(𝟏 − Τ𝑰 𝑰𝟎) 𝒅𝝂 ≈ 𝒏𝝈𝝂𝑺
3 - Calculation of the absorption line area in units of squares
≈ 𝟒𝟏 𝒕𝒊𝒍𝒆𝒔4 - Determine the physical units of one square on the paper
Y axis : 9 tiles for 2% absorption
X axis : 6 tiles for 0.2 cm-1 𝟏 𝒕𝒊𝒍𝒆 = 𝟕. 𝟒𝟏 × 𝟏𝟎−𝟓 𝒄𝒎−𝟏
5 - Determine the particle number density n (m-3) and then the CO partial
pressure inside the cell
𝒏 =𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔
𝒗𝒐𝒍𝒖𝒎𝒆=
𝒊𝒏𝒕𝒆𝒈𝒓𝒂𝒍
𝑳𝑺= 𝟏. 𝟑𝟏𝟕 × 𝟏𝟎𝟐𝟑 𝒎−𝟑
𝒑 =𝑵𝒌𝑻
𝑽𝒐𝒍𝒖𝒎𝒆= 𝒏𝒌𝑻 = 𝟓𝟑𝟔 𝑷𝒂
Té et al., Tutorials on Gas cell spectrum study, Quy Nhon, 26-31 August 2018
𝐿 = 20 𝑐𝑚𝑆 = 1.153 × 10−21 𝑐𝑚−1/(𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠. 𝑐𝑚−2)𝑘 = 1.38 × 10−38 𝑚2. 𝑘𝑔. 𝑠−2. 𝐾−1
𝑇 = 295 ± 1𝐾
How to determine the CO concentration from the R(17) line ?
Thank you for your attention
2018 Annual Joint NDACC-IRWG & TCCON meeting
June 11-15, 2018 @ Mexico
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