Polarization-Based Fiber Optic System for Debris Flow Early Warning: On-Field Demonstration

Naturally occurring mass transport events can endanger human life and infrastructure integrity, especially in mountain areas often affected by landslides, debris flows, and avalanches. Currently available hazard detection systems can greatly help with the timely warning (within a few seconds) of ongoing, potentially dangerous events, but can often be inaccurate, unreliable and, due to the need for in-situ power supply, difficult to operate. Modern optical fiber sensing techniques, on the other hand, can provide exceptional accuracy but require longer measurement time and increased complexity and cost, which makes them unsuitable for such time- and cost-sensitive applications. In this paper, we present an on-field demonstration of a previously developed polarization-based optical fiber early-warning system. A mountain gully in the Valle d'Aosta region, in Italy, is used as a validation testbed to show the reliability of our approach in detecting anomalous vibration phenomena, and its robustness against the background noise associated, for instance, with car traffic or animal wildlife in the monitored area. Our findings show that the rate of variation of the state of polarization induced by real-life, hazardous rockfall events on the optical fiber is orders of magnitudes higher than the average variation rate recorded in normal conditions, thus making the proposed system a promising alternative in the mountain hazards sensors world. Moreover, we show that the system has great potential for increased accuracy in the monitoring of event dynamics by using different optical fibers in separate sections of the site, which can also be a source of additional cost reduction.