Interferometric rail roughness measurement at train operational speed

Measuring rail roughness in view of reducing rolling noise emission is a challenge for field instrumentation. Direct measurements can be carried out with contacting relative displacement measuring systems. However, the rail length that can be covered is limited and surveying a wide network turns out not to be practical. On the other hand, indirect methods based on acceleration measurements may be used for monitoring purposes. In this paper, the feasibility of roughness measurements based on interferometric techniques is discussed. Such a measurement could be carried out at normal train operation speed. The problems of optical measurements in real-time conditions are taken in due consideration. A key point of the discussion is the use of a system for vibration attenuation to be mounted under a vehicle to suspend the optical sensing device. The structure for a complete measurement device is proposed together with the expected performance.