Infrared (IR) Optical Gas Imaging (OGI) cameras are used to image gaseous compounds and detect gas leaks from equipment. A given IR camera may be more sensitive to one compound than another. Response Factor (RF) is a measure of an IR camera’s sensitivity for a given compound relative to a reference compound. For example, if the RF value for methane is 0.30 in reference to propane, it means that an image of methane is 30% as strong as propane for this particular camera, i.e., methane is less easily detected than propane. If propene’s RF is 1.47, the image of propene is 47% stronger than propane. When RF for a compound is very small, that compound may not be visible in the IR camera.

The values of RF are affected by the type of IR camera and the product of concentration (C) and optical pathlength (L), which is commonly denoted as CL with units of ppm-m. For example, CL=100,000 ppm-m could represent a parcel of pure gas (1,000,000 ppm) that is 0.1 meter deep, or 100,000 ppm that is 1 meter deep. For practical purposes, three CL values are used in this RF calculator: 2,000 ppm-m for a small/diluted gas plume, 100,000 ppm-m for a large/concentrated gas plume, and 20,000 ppm-m for a condition between the high and low CL. For more information on RF, please refer to paper # 93 in the Proceedings of Air Quality Measurement Methods and Technology, Chapel Hill, NC, March 15-17, 2016 (

This online RF Calculator is provided to the OGI user community by Providence Photonics free of charge. Users simply need to enter their email address in order to use this tool.

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Acknowledgement: the IR spectral data used to calculate the RF is downloaded on November 18, 2015 from the IR database maintained by Pacific Northwest National Lab (PNNL).