NOVELTY - A gas imaging system for imaging a plume of a fugitive gas, includes a bi-selector assembly for providing separate first and second paths for transmittal of electromagnetic energies; first and second narrow band pass filters for passing electromagnetic energies of first and second wavelengths, respectively; an imager for capturing image data; and a processor for correlating and processing the first and second image data.    USE - For imaging a plume of a fugitive gas (claimed), e.g. sulfur hexafluoride or gaseous hydrocarbons.    ADVANTAGE - The inventive gas imaging system is portable and economical in detecting and imaging gas leaks.    DETAILED DESCRIPTION - A gas imaging system for imaging a plume of a fugitive gas, comprises a bi-spectral selector assembly for providing separate first and second paths for transmittal of electromagnetic energies emanating from the scene of interest. A first narrow band pass filter is provided in the first path for passing electromagnetic energy of a first wavelength corresponding to an electromagnetic wavelength absorption characteristic of the gas to the substantial exclusion of other electromagnetic energy. A second narrow band pass filter is provided in the second path for passing electromagnetic energy of a second wavelength in proximity of the first wavelength and to the exclusion of electromagnetic energy passed by the first narrow band pass filter. An imager is provided for capturing first and second image data of the scene of interest as represented by electromagnetic energies having traversed the first and second narrow band pass filters (28, 29) respectively. A processor is provided in data communication with the imager for correlating and processing the first and the second image data, and providing displayable data including an indication of the plume of gas.    An INDEPENDENT CLAIM is also included for a method for detecting a fugitive gas comprising receiving image radiation indicative of a scene comprising a plume of the fugitive gas. A first filter is used for filtering the received image radiation such that only spectral components of the radiation in a narrow wavelength band centered at an absorption wavelength of the gas are passed to provide a first image radiation. A second filter is used for filtering the received image radiation such that only spectral components of the radiation in a narrow wavelength band centered in proximity of the absorption wavelength of the gas are passed to provide a second image radiation. The first image radiation and the second image radiation are sensed and first and second image data are provided, respectively. The first and the second image data are correlated. An image of the fugitive gas plume is generated in dependence upon the correlated first and second image data.    DESCRIPTION OF DRAWING(S) - The figure is a plan view diagram of a bi-spectral selector assembly in combination with an infrared camera in the gas imaging system of the invention.    Lens structures (20, 21)    Incident mirrors (22, 23)    Infrared optical assemblies (26, 27)    Narrow band pass filters (28, 29)    Separator assembly (106)