A method of measuring the concentration of a gas in a target environment using a laser lidar system, comprises directing a laser beam towards an environment containing the gas, tuning the laser wavelength over a wavelength range including the absorption line of the gas, and measuring intensity of laser light returned from the environment containing the gas, as a result of scattering as a function of time. The intensity vs time is then converted into gas absorption vs wavelength, and the gas absorption vs wavelength is used to determine the concentration of the gas in the target environment.