A unique mobile remote sensing system is described which has been developed by British Gas for measuring the concentration of natural gas when released into the atmosphere. The system is based on UV Raman LIDAR and is used principally for research associated with atmospheric dispersion. Signals are monitored arising from both hydrocarbons and atmospheric nitrogen. These signals are combined to determine the concentration of natural gas in air without the need to measure short-term system variables such as atmospheric transmission losses or laser pulse energy. Three-dimensional information on the extent of the gas cloud is normally obtained. Details of improvements to data acquisition and processing techniques are included to illustrate the improved performance and specifications of the system.