Читать книгу Distributed Acoustic Sensing in Geophysics - Группа авторов - Страница 50

A challenge with DAS data sets is that there is only a single component detecting strain along the axial length of the fiber. Conventional VSP and earthquake seismic recordings are typically acquired with three components (3C): one vertical and two orthogonal horizontal components. (Exploration surface seismic is normally acquired with only vertical component geophones.) While there are 3C optical sensors available that can be spliced into a fiber‐optic cable, they are point sensors not directly related to DAS measurements. Research is ongoing to create 3C measurements using sets of helically wound fibers in a single cable; currently, they are not commercially available (Ning & Sava, 2018). However, this limitation restricts the ability of DAS data sets to locate the azimuthal direction of seismic waves hitting the fiber; in this way, it is quite similar to single‐component geophone data sets.