A geometrical model of DAS fibre response

Kris Innanen

ABSTRACT

A geometrical model of the shape and response of a buried DAS fibre, which allows for both a helical wind and arbitrary curvature of the cable, is a tool for analysis and appraisal of DAS experiments. The model takes as input vectors describing the cable shape and (optionally) the parameters of the helix. As output, the model generates arc-length, fibre positioning, and tangent information, with (optionally) a gauge length imposed. Five example applications of the model are presented: (1) the fibre may be embedded in modelled 3D elastic wave field and its response computed; (2) the 3C vector wave is reconstructed along the fibre within defined reconsruction windows; (3) the six components of tensor strain are reconstructed similarly; (4) the cosθ directionality rule for P-wave displacement is generalized to the arbitrarily curved fibre; and (5) the cos 2 θ directionality rule for P-wave strain is similarly generalized.

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