Design and deployment of a prototype multicomponent distributed acoustic sensing loop array

Abstract

In 2016-2017 a range of analyses and applications of a geometrical model of fibre-optic (DAS) data for arbitrary fibre shapes was described. Amongst those applications was a multicomponent estimation scheme based on a careful accounting, and combined useage, of the varying fibre directions associated with a shaped cable layout. In 2018 a prototype shaped DAS fibre array was buried at the Containment and Monitoring Institute Field Research Station in Newell County AB to put some of these ideas and their feasibility to the test. The loop was illuminated from several directions, and shot records were analyzed to assess if directional sensitivity is sufficient to permit multiple components of strain to be estimated simultaneously. By picking a P-wave arrival and comparing it to an analytic model, we conclude with a cautious "yes". The size of the loop (roughly 10m on a side) was chosen to accommodate standard DAS gauge lengths; at this size, horizontal but not vertical strain rate components were sensed. Future versions designed for gauge lengths on the order of 2m will permit 6-component estimation.

Distributed Acoustic Sensing (DAS) for Natural Microseismicity Studies: A Case Study From Antarctica

“…However, if we assume that at the scale of the array the S ‐waves can be approximated as plane waves, we can approximate the triangular array as a point sensor by correcting for the spatial distribution, similar to the approach of Innanen et al. (2019). We then need to determine how any amplitude changes or polarity reversals recorded on the three sides of the array relate to the polarization of the S waves.…”

“…Using the triangular array partially alleviates for the inherent single component nature of DAS fiber because it records strain in a 2D plane rather than a 1D line, albeit with measurements at different orientations not at precisely the same location. However, if we assume that at the scale of the array the S-waves can be approximated as plane waves, we can approximate the triangular array as a point sensor by correcting for the spatial distribution, similar to the approach of Innanen et al (2019). We then need to determine how any amplitude changes or polarity reversals recorded on the three sides of the array relate to the polarization of the S waves.…”