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Tunnel and traffic monitoring

Visibility monitoring

Visibility monitoring is used to control the ventilation of a tunnel during normal operation in order to ensure sufficient visibility for tunnel users. Whether ventilation using jet fans is required, and if so with what capacity, depends on the measured visibility values. Visibility is expressed as an absorbance coefficient, which describes the loss of light caused by air pollution.

JES ELEKTROTECHNIK, a DURAG GROUP company, offers sensors in this area with two different measuring methods: the traditional transmission method and the more modern scattered light method, which with its greater reliability and easier handling has established itself as the standard in Central Europe.

The measuring system consists of a sensor that emits and receives light and an optical reflector, which must be mounted on the tunnel wall at a distance of approx. 10 m and aligned with one another.


During the measurement, the optical transmission of the air along this open measuring section in the tunnel is determined and used to calculate the absorbance coefficient.

In contrast to the transmission method, the measurement in the scattered light method takes place in a single device. Depending on the design, the device can be mounted on the tunnel wall or outside the tunnel driving space in a niche or service room where it is always accessible.


The sensor measures the intensity of the light that is scattered at a certain angle when it encounters the air extracted from the tunnel and uses it to calculate the absorbance coefficient. 

The newly developed IoT-capable smart/AQM sensor can be equipped with up to 3 different gas sensors (CO, NO, NO2) for complete measurement monitoring of air quality in tunnels.