An Alternative to commercial optical fibre sensors for shallow ladslide monitoring – interferometric optical fibre sensing

Abstract

Optical fibre-based monitoring has settled in the field of geohazards monitoring. Interferometric optical fibre sensors are the least used in landslide monitoring, while classical approaches rely on Fibre Bragg Grating and Brillouin Optical Time Domain Reflectometry/Analysis. Landslide monitoring goes hand by hand with the development of technology. While authors tend to focus on the unprecedented accuracy and reduced costs of the sensor itself, the economic and practical aspects related to the interrogating systems are often disregarded. Recently, a simpler and significantly more cost-effective approach has been introduced through “integral coherent measurements” because they yield an integral of the signal response over the entire length of the optical fibre sensor. This sensing system proves to be suitable to provide an overall indication of the state of the entire monitored domain and yield indications of the onset of motion with a high temporal resolution. The sensor has been tested in controlled conditions as a monitoring tool in a downscaled landslide model. We exploit the large bandwidth and high frequency of acquisition in order to detect high frequency elastic waves. The proposed sensor is able to distinguish the vibration footprint generated by ground movement. The results obtained from the experimental tests demonstrate that the proposed sensing system is able to recognize the onset of motion some minutes before a visual indication of instability could be observed.