The spectral region near 3 mm is shown to be most promising for remote sensing of methane emissions. Parameters of radiation of a tunable repetitively-pulsed mini-ТЕА СО2 laser and generators of its harmonics to be used in the helicopter-borne differential absorption lidar are estimated. A possibility of detecting remotely methane emissions from a pipe line is studied by numerical simulation. Possibility of detecting emissions of different intensity at a distance up to 1 km is analyzed when using third harmonic of the ТЕА СО2 laser in an airborne lidar. The use of third harmonic of the ТЕА СО2 laser allows methane emissions from a pipe line to be detected and measured with the mean measurement error of 10 to 15% for methane concentrations varying from its background level to the explosion-hazardous one.