Principle

Detection principle

Each gas has its own absorption spectrum and can present typical absorption lines 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 lines which enables them to be identified from several gases.

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 on the targeted line.

The evaluation of the quantity of gas is carried out by a three differential infra-red imaging process: spatial, spectral, and temporal fields.

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…