We all know that most gases, such as methane, sulphur hexafluoride (SF6), carbon monoxide and hundreds of others, are invisible to the naked eye like those in the air around us, but can they be seen with a thermal camera? The answer is: some thermal camera energies. Most infrared thermal camera cannot directly detect gases, but optical gas thermal camera are highly specialized infrared thermal camera that can filter wavebands and show certain gases.

1. How does optical gas imaging work?

Many gas compounds can absorb infrared energy, but only within a certain wavelength range. Most hydrocarbons (such as benzene, butane, and methane) absorb radiation near the 3.3 micron wavelength, while compounds such as SF6 absorb energy near the 10.6 micron wavelength. (Many hydrocarbons have multiple absorption peaks in the infrared spectrum, such as methane, which absorbs energy near the 7.7 micron wavelength, but which can only be easily detected by band filter optical gas thermal camera.) The optical gas thermal camera uses a unique spectral filter mounted in front of the detector to limit the wavelength of radiation allowed to pass to an extremely narrow wavelength range - known as bandpass filtering. Within this very narrow wavelength range (for specific gases), the optical gas thermal camera can show the location of the plume (which usually looks like a cloud) by preventing energy from reaching the infrared detector. The energy of the wavelength at which the cloud is located is absorbed by the gas.

2. Can the thermal camera show all the gases?

Since the optical gas thermal camera shows the absorption of infrared energy by a gas, the optical gas thermal camera cannot image a gas directly if it does not absorb the infrared radiation being filtered out of the bandpass. For example, there is no way to directly image inert gases such as helium, oxygen and nitrogen. And even if a thermal camera can show a particular gas, such as hydrocarbon gas, it may not be able to show another gas with vastly different infrared absorption characteristics.

3. Can infrared imaging identify gases?

Optical gas thermal camera is ideal for detecting gas leaks. However, this method is not suitable for gas identification -- to identify a gas, one must know in advance the spectral filter which is applicable to the specific absorption band of the gas. The thermal camera was also unable to distinguish one gas from another in the series of gases being examined. For example, thermal camera used to display hydrocarbon gases cannot distinguish which ones are detected.