Each gas has its own absorption spectrum and presents typical absorption peaks in infra-red bands II (3 to 5 µm MWIR) and bands III (8 to 14 µm LWIR). Second Sight® operates in band III, in order to use the particular peaks to enables the identification of a vast majority of gas.
The Second Sight® measurement principle uses the scene background as an infra-red source, and image processing algorithms to highlight the presence of a gas cloud in line of sight.
The evaluation of the quantity of gas is carried out by a three differential infra-red imaging process: spatial, spectral, and temporal fields. The originality of the gas classification function is based on spectral analysis with low resolution and a wide bandwidth allowing for quick analysis without deterioration of the signal to noise ratio.
In particular, spatial differentiation enables the luminescence of the gas cloud to be eliminated and to only take its transmission into account. This characteristic enables Second Sight® to detect the gas even when it is at an ambient temperature.
Spectral differentiation exploits the spectral nature of the gas, which is isolated through the successive utilization of several filters. The comparison of channels enables a value corresponding to the gas cloud concentration integrated along the line of sight to be obtained.