Distributed Acoustic Sensing Direction Determination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Typical single-fiber distributed acoustic sensing (DAS) systems fail to accurately determine the direction of travel of acoustic waves due to ambiguities, with location of impact being the only available datum.
Innovation Solution
A DAS system comprising an optical time domain reflectometer (OTDR) and multiple acoustic-sensing optical fibers with known relative positions, arranged in a diverging pattern, and a processor that determines the propagation direction of acoustic waves by analyzing return optical signals using a fixed or switchable optical coupler.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single optical fiber is used for acoustic sensing, then the device complexity is reduced, but the measurement precision of wave propagation direction is insufficient
Solution Approach 1:
The single optical fiber is segmented into multiple virtual sensing zones along its length, with each zone acting as an independent acoustic sensor. This segmentation allows the system to determine wave propagation direction by comparing signals from different segments, resolving the contradiction between using a single fiber and achieving directional measurement precision.
Solution Approach 2:
The patent transforms the one-dimensional single fiber into a multi-dimensional sensing array by utilizing spatial distribution of multiple fibers or segments. This dimensional expansion enables the system to resolve wave propagation direction in addition to location, overcoming the limitation of single-fiber systems.
2Measurement precision
If multiple acoustic-sensing optical fibers are used to determine propagation direction, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
Multiple optical fibers are merged into a unified DAS system controlled by a single OTDR, sharing common control and processing resources. This merging approach enables directional measurement precision while reducing overall system complexity compared to having separate systems for each fiber.
Solution Approach 2:
The OTDR and processing system serve multiple functions: locating acoustic events, determining propagation direction, and characterizing wave properties. This multi-functionality reduces the need for separate specialized devices, thereby managing complexity while achieving precise directional measurement.
3Measurement precision
If optical fibers are positioned in diverging pattern with long lengths, then the coverage area and sensitivity are improved, but the ease of operation and installation become more difficult
Solution Approach 1:
The system dynamically adjusts sensing parameters and fiber coupling configurations based on the diverging pattern geometry and acoustic event location. This dynamic adaptation optimizes sensitivity for long-distance events while simplifying the operational complexity of deploying diverging fiber patterns.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides directional wave propagation information, enhancing the localization of acoustic/seismic events and increasing sensitivity, allowing for more effective monitoring of infrastructure and geographic regions with a single OTDR unit.
Implementation Method 1
In this approach, optical fibers are positioned in the area or structure to be monitored, and this approach is based upon, for example, Rayleigh backscattering. Here, a coherent laser pulse is sent along an optical fiber, and scattering sites within the optical fiber cause the optical fiber to act as a distributed interferometer.
Data Source
AI summary
A DAS system may include an OTDR, and acoustic-sensing optical fibers coupled to the OTDR. The acoustic-sensing optical fibers may have known relative positions within an acoustic wave transmitting medium. The DAS system may also include a processor cooperating with the OTDR to determine a propagation direction of an acoustic wave from an acoustic event in the acoustic wave transmitting medium based upon the known relative positions of the acoustic-sensing optical fibers.