Passive seismological approaches for localizing near-surface fiber-optic cables with DAS

Accurate knowledge of fiber-optic cable geometry is important for many applications of distributed acoustic sensing (DAS). However, the true positions of buried or installed fibers are often uncertain due to slack, bends, or deviations from documented routes. We present two passive, seismology-based approaches for cable localization that exploit information contained in DAS recordings. The approaches are evaluated based on synthetic tests under controlled conditions. Case A employs ambient noise cross-correlations with reference points to estimate relative travel times, whereas Case B uses the differential arrivals of plane waves from distant earthquakes with linearly independent slowness vectors. Both methods can be formulated using a least-squares approach that allows for the joint estimation of propagation velocity and geometry, thereby providing consistent solutions in the presence of noisy or uncertain travel-time measurements. Synthetic experiments show that cable positions can be recovered with an accuracy in the order of 100 m, even when apparent velocities are uncertain or the medium exhibits heterogeneity. The two methods provide independent geometric constraints that complement other sources of information on cable routing, although additional uncertainties are expected in field applications.