Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).
1.645 µm differential absorption lidar measurements of atmospheric methane using an Er:YAG laser
Dimitri Edouart,Fabien Gibert,and Claire Cénac
Abstract. A differential absorption lidar (DIAL) based on an Er:YAG laser was used to retrieve methane concentration profiles within the mixed layer along a near-horizontal line of sight (4° above the horizontal) from the École Polytechnique site, directed northward toward the western part of the city of Paris. The achieved precision remains below 1 % up to a range of 3.5 km for profiles with a spatio-temporal resolution of 470 m / 20 min. The measurements were compared with in situ observations from an ICOS site located 5 km from the lidar. The lidar successfully captured the late stage of the dispersion of a methane plume originating from a fire occurred at a waste-sorting facility in the city of Paris, in good agreement with the in situ measurements. Both random and systematic errors in the lidar measurements are dominated by uncertainties in the ON wavelength measurement.
Received: 13 Feb 2026 – Discussion started: 16 Apr 2026
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The authors report on a DIAL system operating in the 1.645 um region to detect methane. The results are compared to a ICOS site and successfully measured increased concentrations of methane created by a fire. The work is well described and the results are impressive. I recommend publication of this manuscript with some minor changes.
Line 83.
“The wavelength measurement alternates between the two DFBs using a fiber switch (sSWT) toggling every 10 s, thereby tracking the slow drift of each seeder locked to the laser cavity.”
Line 180
“The Licel acquisition module integrates 2000 laser shots for both ON and OFF wavelengths in real time, resulting in ON and OFF profiles recorded with a temporal resolution of 4 s.”
Please clarify the above two statements. Is that 4s for both, or 2 sec each? Where did 10 sec go?
Figure 3. Switching the axis of the range is confusing
Line 259
“The uncertainty bars of the ICOS measurements represent the dispersion of the measurements within each hourly interval.”
Why not match the resolution of the lidar system? Is there a limitation, or is this a choice?
Line 267.
“The differences in methane concentration between the ICOS measurements (at 100 m) and the lidar measurements averaged over one hour up to a range of 3.5 km remain below 50 ppb. A fire occurred at a waste sorting facility located in the city of Paris on the evening of April 7..”
Roughly how far from the point sensor (at 100 m) is the center of mass of the lidar results?
Figure 6. Can you highlight the region in the left image used in the right image. The error bars and overlap is very difficult to see at the plum tail, maybe include zoomed in insert.
Laboratoire de Météorologie Dynamique (LMD/IPSL), École polytechnique, Institut polytechnique de Paris, Sorbonne Université, École normale supérieure, PSL Research University, CNRS, École des Ponts, Palaiseau, France
Laboratoire de Météorologie Dynamique (LMD/IPSL), École polytechnique, Institut polytechnique de Paris, Sorbonne Université, École normale supérieure, PSL Research University, CNRS, École des Ponts, Palaiseau, France
Claire Cénac
Laboratoire de Météorologie Dynamique (LMD/IPSL), École polytechnique, Institut polytechnique de Paris, Sorbonne Université, École normale supérieure, PSL Research University, CNRS, École des Ponts, Palaiseau, France
A differential absorption lidar (DIAL) based on an Er:YAG laser measured methane mixing ratio profiles along a quasi-horizontal path. A precision better than 1 % was achieved up to 3.5 km with a spatiotemporal resolution of 470 m / 20 min. The measurements were compared with in-situ instruments. An analysis of random and systematic errors shows that the main limitation is the uncertainty in the ON wavelength.
A differential absorption lidar (DIAL) based on an Er:YAG laser measured methane mixing ratio...
The authors report on a DIAL system operating in the 1.645 um region to detect methane. The results are compared to a ICOS site and successfully measured increased concentrations of methane created by a fire. The work is well described and the results are impressive. I recommend publication of this manuscript with some minor changes.
Line 83.
“The wavelength measurement alternates between the two DFBs using a fiber switch (sSWT) toggling every 10 s, thereby tracking the slow drift of each seeder locked to the laser cavity.”
Line 180
“The Licel acquisition module integrates 2000 laser shots for both ON and OFF wavelengths in real time, resulting in ON and OFF profiles recorded with a temporal resolution of 4 s.”
Please clarify the above two statements. Is that 4s for both, or 2 sec each? Where did 10 sec go?
Figure 3. Switching the axis of the range is confusing
Line 259
“The uncertainty bars of the ICOS measurements represent the dispersion of the measurements within each hourly interval.”
Why not match the resolution of the lidar system? Is there a limitation, or is this a choice?
Line 267.
“The differences in methane concentration between the ICOS measurements (at 100 m) and the lidar measurements averaged over one hour up to a range of 3.5 km remain below 50 ppb. A fire occurred at a waste sorting facility located in the city of Paris on the evening of April 7..”
Roughly how far from the point sensor (at 100 m) is the center of mass of the lidar results?
Figure 6. Can you highlight the region in the left image used in the right image. The error bars and overlap is very difficult to see at the plum tail, maybe include zoomed in insert.