Distributed Acoustic Sensing Using Reflector Pairs
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Solution Overview
Problem
Conventional fibre optical distributed acoustic sensing systems face limitations in acoustic bandwidth and sampling rate due to the need for waiting for backscattered light to travel the entire fibre length before injecting the next light pattern, which restricts detection rate and requires complex and costly systems.
Innovation Solution
The method involves injecting coherent light patterns into an optical fibre with multiple reflector pairs, allowing simultaneous propagation of multiple light patterns and separate detection of reflected signals from each reflector pair, regardless of light characteristics, to increase sampling rate and acoustic bandwidth without additional complexity or components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional DAS sensors use single light pattern injection with waiting for backscatter to travel entire fibre length, then measurement precision is maintained, but acoustic bandwidth and sampling rate are limited
Solution Approach 1:
The optical fibre is segmented into multiple sensing sections by introducing reflector pairs at specific locations. Each reflector pair reflects light locally, creating separate detection zones. This segmentation allows simultaneous propagation of multiple light patterns in different sections, eliminating the need to wait for backscatter to travel the entire fibre length and thereby increasing sampling rate.
Solution Approach 2:
Reflector pairs are introduced as intermediary elements that locally reflect light back toward the detector. These reflectors act as intermediaries between the injected light patterns and the detector, enabling local reflection and detection without requiring light to travel the full fibre length. This intermediary mechanism reduces the effective detection path length and increases the sampling rate.
2Productivity
If multiple light patterns are propagated simultaneously to increase sampling rate, then productivity improves, but signal detection and measurement becomes more complex
Solution Approach 1:
The fibre is divided into discrete sensing sections using reflector pairs, with each section independently detecting acoustic events. This spatial segmentation allows multiple light patterns to propagate simultaneously in different sections without significant signal overlap, simplifying the detection and separation of reflected signals compared to fully distributed sensing without reflectors.
Solution Approach 2:
Reflector pairs are strategically placed at specific locations where acoustic monitoring is needed, creating localized sensing zones with enhanced reflection properties. Each reflector pair provides strong local reflection signals that are distinct from signals in other sections, making it easier to separate and identify reflected light patterns from different locations, thereby reducing detection complexity.
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
This approach enables high-rate monitoring of selected locations along the fibre with increased acoustic bandwidth and sampling rate, reducing the time between light pattern launches and allowing for precise detection of strain, stress, and acoustic disturbances between reflector pairs, while ignoring weaker Rayleigh scattering noise.
Implementation Method 1
at least one optical fibre (33) adapted to guide light
Implementation Method 2
each reflector pair comprising two reflectors (A1, B1; A2, B2) spaced apart by an intra-reflector distance
Implementation Method 3
analyzing the detected phase of the received first and second reflected light patterns to determine strain and/or stress and/or acoustic disturbance
Data Source
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AI summary
It is provided a method of high rate fibre optical distributed acoustic sensing, the method comprising: injecting a first coherent light pattern comprising first light into an optical cable, the optical cable having at least a first reflector pair and a second reflector pair arranged at different positions along the optical cable; injecting a second coherent light pattern comprising second light into the optical cable while first backscatter light of the first light pattern is propagating in the optical cable; detecting first reflected light originating from reflection of the first light pattern from the first reflector pair and/or the second reflector pair; and, at a different interval in time: detecting second reflected light originating from reflection of the second light pattern from the first reflector pair and/or the second reflector pair.