Abstract: A narrow-linewidth, variable-wavelength, active, absorbing LIDAR (Light Detection and Ranging) system and method. The linewidth of the source and detector is sufficiently narrow to produce a reasonable signal-to-noise ratio for the system. The central wavelength of the source and detector can be synchronously changed. The system comprises a tunable light-emitting source and uses the absorption of light to determine the chemical composition of the item being detected. A wavelength tunable filter synchronized to the tunable source reduces or eliminates background noise and thus increases the level of detection for low concentrations of the substance to be detected.

Abstract: A detector that can detect a gas which has leaked, particularly from buried and or exposed pipelines. The detector can be placed on an aircraft and flown at heights, e.g. up to about 500 feet, or other heights, and at relatively high speeds along the length of the pipeline. A tunable light source is programmed to switch between a first frequency, which is known to be absorbed by the gas in question, and a second frequency, which is known not to be as readily absorbed by the gas in question. A laser rangefinder is also provided to measure the distance between the pipeline and the detector. A computer is preferably provided to interpret readings from the sensors, based on distances measured by the laser rangefinder. A GPS receiver is also preferably provided.