Non-destructive fiber-optic sensor system for the measurement of speed in road traffic

Abstract

Fiber-optic sensors offer an attractive option to existing sensors for the measurement of the vehicle speed in road traffic. This article describes the measuring scheme of two interferometric sensor units including input-output components for the measurement of the vehicle speed. The interferometric sensors operate on a principle of Mach-Zehnder interferometer. The sensors are constructed to detect a vibration caused by vehicles moving on roads. The sensor system processes the vibrational response, and the vehicle speed is calculated in a time domain. DFB laser was used with a wavelength of 1550 nm and output power of 1--5~mW. The solution provides very high sensitivity. The performance of the proposed system was verified by a series of experimental measurements of the speed. The vehicle speed was monitored by GPS. The highest relative difference of the evaluated speed against GPS data was 7.7 %, the smallest was 1.36 %. When recalculated on kph, the absolute error ranged in the tolerance ± 3 kph, which denotes segmental measuring systems in CZE.