Novel remote gas monitoring and imaging in the IR spectral region

Real-time gas imaging is of great interest in many contexts. Inspection of leaks from chemical installations, petrochemical plants, tank farms or pipelines has economical, environmental and security aspects. Easily deployable surveillance techniques for assessing sites of accidents involving gas tankers or trains are desirable for public safety considerations. In the indoor working environment, gas flow monitoring around room ventilation ports, extraction hoods, etc., is useful for optimizing the construction and adjustment of installations. Emissions of geophysical origin (volcanoes, geothermal installations or mines) as well as natural emissions of greenhouse gases from agriculture, swamps, etc., are also interesting to assess. Useful spectroscopic absorption features of the molecules of interest occur in the visible or infrared spectral regions. The vibrational-rotational fundamental bands in the IR region are particularly suitable for sensitive detection. Two new developments in IR gas monitoring and imaging are reported in the present paper. The first is a passive technique employing the natural thermal background radiation in a gas correlation scheme. The second one is an active technique where a multi-wavelength dial scheme employing an OPO transmitter is developed for simultaneous measurements of different hydrocarbons and interferents.