Atmospheric Remote Sensing and Molecular Spectroscopy ...€¦ · Spectroscopy (Vietnam School of...

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

?

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