Even with a flashlight or searchlight, navigation through dense smoke and fog is difficult, because visibility is severely limited due to absorption in in the visible spectrum and backscattering (Fig. 1 & Fig.2). Although it is possible to see through smoke and fog with thermal imaging cameras, but their dependency in temperature impairs navigation in great heat. This is especially problematic for emergency forces (e.g. firefighters) and for the observation of critical infrastructures. One solution to this problem is the use of wavelengths in the short-wavelength infrared (SWIR) spectrum, since increased fog and smoke penetration and thus increased visibility can be achieved here without temperature dependencies (Fig. 1).
The Goal of this project is the fabrication of a light and portable demonstrator, which provides better orientation indoors through fog and smoke via vision enhancement. Therefore, active optical imaging techniques are to be used, including the use of light sources with different wavelength within the SWIR spectrum.
For this purpose, e.g. self-developed illuminators made of SWIR LED arrays are used. In simulations, laboratory and field tests different wavelengths in the SWIR spectrum are investigated, to find the (cost-)effective compromise between power, transmission and scattering.
Special attention is paid to the utilization over short distances in smoky and foggy indoor areas. Accordingly, the angle of view of the SWIR sensor system, comprising a SWIR camera and a lens with SWIR antireflective coating, is wide. The illumination angle of the LED array is selected to match the angle of view of the camera, so that the recoded scene is entirely illuminated.
To provide optimal support for emergency forces, the demonstrator is built to be portable. Thus, the compact housing comes with side handles, optional battery operation as well as operation via a touchscreen embedded in the housing.
To provide optimal support for emergency forces, the demonstrator is built to be portable (Fig. 3). Thus, the compact housing comes with side handles, optional battery operation as well as operation via a touchscreen embedded in the housing. This device should be further optimized in terms of ease of use through cooperation with fire department emergency services.
The innovation of this project lies within the combination of a SWIR-sensor, the portability of the system and the investigation of different wavelengths for improved smoke and fog penetration, thus delivering a new method to assist emergency forces.
Along with the investigation over different wavelength the future use of polarized radiation will be used to suppress backscattering.
Project runtime: 10/2019 to 12/2023
• M. Mischung, J. Schmidt, E. Peters, M. Berger, M. Anders, M. Stephan, "Development and characterisation of a portable, active short-wave infrared camera system for vision enhancement through smoke and fog," Proc. SPIE 12271, Electro-optical and Infrared Systems: Technology and Applications XIX, 122710M (2 November 2022); https://doi.org/10.1117/12.2636216