Surface Wave Phase Velocity Uncertainties Analysis on Roadside DAS: Influence of Cable and Ground Coupling

Cavity-related geohazards can have devastating effects on the economy by the deterioration of the infrastructure transportation network (roads, railways, embankments, airports, etc.).

This makes the cavity-prone area mapping in urban context an increasing priority into a near future, and there is a need for monitoring of the near-surface (0–50 m) conditions along transportation infrastructure network.

Telecom-Distributed Acoustic

Sensing is a recent breakthrough from the field of opto-electronics which has shown it is possible to use existing telecommunication fiber optic already deployed in cities to record seismic signals. Therefore, the use of T-DAS for monitoring the subsurface using seismic methods such as passive roadside MASW is appealing.

However, questions regarding measurement uncertainties are still opened.

In this study, we analyze from a controlled experiment the influence of fiber optic coupling on measurement uncertainties.

Our results show that way the cable is coupled to the ground has more influence on phase velocity uncertainties than the way the fiber optic is coupled to the cable itself. The differences are observed at high frequencies (>30 Hz). Because most existing telecommunication fiber optic cable lie within pipes, it is most likely that T-DAS is not suited to study shallow small-scales heterogeneities using such techniques.