France has tested a new fibre optic sensing system for its railways that could act as a cavity or sink hole warning system on railway track beds and tunnels.

The Optical Backscatter Reflectometer (OBR) 4400 developed by Luna Technologies was tested by the French Public Works Research Laboratory in association with French National Railways.

The system will help in identifying embedded cavities, or sink holes that may induce soil collapse.

The OBR is the first ultra high-resolution optical time-domain reflectometry (OTDR) with backscatter-level sensitivity designed for component- and module-level reflectometry. The instrument has a small portable platform to measure reflections up to 2km.

During testing the locator detected a 5mm embedded cavity located 2m away from the sensing cable.

LUNA‘s OBR technique is proven to be more useful in detecting the embedded cavities and their sizes.