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. We present the results of methane profiling in the lowertroposphere using LILAS Raman lidar from the Lille University observatoryplatform (France). The lidar is based on a frequency-tripled Nd:YAG laser, and nighttimeprofiling up to 4000 with 100 m height resolution is possible for methane.Agreement between the measured photon-counting rate in the CH4 Ramanchannel in the free troposphere and numerical simulations for a typical CH4 background mixing ratio (2 ppm) confirms that CH4 Ramanscattering is detected. The mixing ratio is calculated from the ratio ofmethane (395.7 nm) and nitrogen (386.7 nm) Raman backscatters, and within theplanetary boundary layer, an increase of the CH4 mixing ratio, up to afactor of 2, is observed. Different possible interfering factors, such asleakage of the elastic signal and aerosol fluorescence, have been taken intoconsideration. Tests using backscattering from clouds confirmed that thefilters in the Raman channel provide sufficient rejection of elasticscattering. The measured methane profiles do not correlate with aerosolbackscattering, which corroborates the hypothesis that, in the planetary boundary layer, notaerosol fluorescence but CH4 is observed. However, the fluorescencecontribution cannot be completely excluded and, for future measurements, weplan to install an additional control channel close to 393 nm, where no strongRaman lines exist and only fluorescence can be observed.

Profiling of CH&lt;sub&gt;4&lt;/sub&gt; background mixing ratio in the lower troposphere with Raman lidar: a feasibility experiment

Profiling of CH<sub>4</sub> background mixing ratio in the lower troposphere with Raman lidar: a feasibility experiment