Profiling of CH4 background mixing ratio in the lower troposphere with Raman lidar
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Atmospheric Measurement Techniques
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We present the results of methane profiling in
the lower troposphere using LILAS Raman lidar from the
Lille University observatory platform (France). The lidar is
based on a frequency-tripled Nd:YAG laser, and nighttime
profiling up to 4000 with 100m height resolution is possible
for methane. Agreement between the measured photoncounting
rate in the CH4 Raman channel in the free troposphere
and numerical simulations for a typical CH4 background
mixing ratio (2 ppm) confirms that CH4 Raman scattering
is detected. The mixing ratio is calculated from the
ratio of methane (395.7 nm) and nitrogen (386.7 nm) Raman
backscatters, and within the planetary boundary layer,
an increase of the CH4 mixing ratio, up to a factor of 2, is
observed. Different possible interfering factors, such as leakage
of the elastic signal and aerosol fluorescence, have been
taken into consideration. Tests using backscattering from
clouds confirmed that the filters in the Raman channel provide
sufficient rejection of elastic scattering. The measured
methane profiles do not correlate with aerosol backscattering,
which corroborates the hypothesis that, in the planetary
boundary layer, not aerosol fluorescence but CH4 is
observed. However, the fluorescence contribution cannot be
completely excluded and, for future measurements, we plan
to install an additional control channel close to 393 nm,
where no strong Raman lines exist and only fluorescence can
be observed.
Como referenciar
VESELOVSKII, IGOR; GOLOUB, PHILIPPE; HU, QIAOYUN; PODVIN, THIERRY; WHITEMAN, DAVID N.; KORENSKIY, MIKHAEL; LANDULFO, EDUARDO. Profiling of CH4 background mixing ratio in the lower troposphere with Raman lidar: a feasibility experiment. Atmospheric Measurement Techniques, v. 12, n. 1, p. 119-128, 2019. DOI: 10.5194/amt-12-119-2019. Disponível em: http://repositorio.ipen.br/handle/123456789/30023. Acesso em: 30 Dec 2025.
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