Finding Acoustic Sources with a Multi-Component Linear Array

We describe data interpretation tools for a sensor array combining a fiber-optic DAS array with a sparse array of two-component (2C) point sensors. Depending on the application, the point sensors can be electric or fiber-optic, with fiber-optic sensors preferrable for long-term deployyment. We show how a linear array of multi-component sensors can identify and track any source of acoustic energy whether or not the orientations of the multi-component sensors are known a priori. The orientation of the two transverse axes of any 2C sensor is found relative to all other 2C sensors. The estimates of the “relative orientation” improves with the number of source points registered. A moving source or a sequence of microseismic events can be followed in “relative 3D space” where all reconstructed source locations are correctly positioned relative to each other, but rotated by a fixed, unknown angle around the axis of the linear array. The absolute orientation of the 2C sensors and absolute location in 3C space can be found by either assuming the direction to at-least one of the sources, or by assuming that, e.g., the moving object observed is moving at a constant depth in a near-horizontal plane.