Field testing of multicomponent DAS sensing
Kevin W. Hall, Kristopher A. Innanen, Donald C. Lawton
We constructed an experimental directional DAS sensor (DDS) at the Containment and Monitoring Institutes Field Research Station (CaMI.FRS) in 2018. The sensor consists of two buried 10x10 m squares of straight and helically wound fibre, with the second square rotated forty-five degrees relative to the first. Three-component geophones were planted on the surface just outside of the corners of the DDS, and four source locations (Vibe Points) were acquired using a 5 m gauge length in the DAS interrogator. Building on work reported last year, where horizontal components of the geophone data were converted to strain-rate traces and visually compared to fibre strain-rate traces, we use directional strain-rate traces to estimate time-series of strain-rate-tensors for the DDS and surface geophones for the first direct ground-roll arrival across the DDS. The estimated tensors are almost identical for the straight and helically wound fibre after trace scaling, but the amplitudes of the geophone strain-rate tensors are higher than seen for the fibre results in some cases. We speculate this is because the geophones and the fibre are not co-located.