Abstract: Leaks in natural gas pipelines are detected by an airborne gas cell correlation radiometer having two channels, one to detect methane and the other to detect nitrous oxide. The channel outputs are compared in order to detect anomalies in their relative magnitude, an increase in methane concentration relative to nitrous oxide concentration being indicative of a gas leakage in the area from which the radiometer receives radiation.

Abstract: A resonance lamp of improved efficiency and stability is provided, using radio frequency excitation applied axially of the lamp, which is matched to the radio frequency source by making it part of an initially high Q tuned circuit resonant at the source frequency. This resonance promotes starting of the lamp, while the damping applied by the lamp circuit during running provides stabilization. A feedback circuit sensing lamp current or light output from a rare gas filling of the lamp provides longer term stability. The lamp may include a heated side arm containing a source of molecular gas which can be excited to provide radiation from an atomic species of interest, and the heating of the side arm is controlled not only by feedback from a temperature sensor but also by feedback from an optical detector sensitive to the radiation of interest.