Spatial Averaging for Coherent Distributed Acoustic Sensing
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Solution Overview
Problem
Coherent distributed acoustic sensing (DAS) systems face instability in phase measurement due to Rayleigh fading and noise, particularly at certain fiber locations, leading to low signal strength and instability in strain detection.
Innovation Solution
A moving average method using polarization combining output is employed to reduce Rayleigh fading, involving location grouping, internal phase alignment, and inter-group phase alignment, which strengthens the signal and reduces fading by rotating complex signals to align with reference directions and combining them efficiently, thereby reducing calculation complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase calculation is performed directly from the complex signal at each fiber location, then the phase measurement can be obtained, but the measurement becomes unstable due to Rayleigh fading and noise at certain locations
Solution Approach 1:
The patent combines complex signals from multiple fiber locations through spatial averaging. By merging signals from N adjacent locations before phase calculation, the system reduces the impact of Rayleigh fading and noise at individual locations, thereby improving phase measurement stability and reliability simultaneously
Solution Approach 2:
The patent divides the fiber into segments of N adjacent locations for spatial averaging. This segmentation allows the system to process signals in groups, where each group's average reduces local fading effects while preserving the overall phase information across the fiber
2Measurement precision
If spatial averaging is performed across multiple fiber locations, then the signal quality improves and fading is reduced, but the calculation complexity increases
Solution Approach 1:
The patent performs preliminary phase alignment by calculating and applying phase rotation values to each location's complex signal before the spatial averaging operation. This preliminary action ensures that signals are properly aligned in phase, preventing destructive interference and reducing the need for complex iterative optimization during the averaging process
Solution Approach 2:
The patent transforms the complex signal parameters by applying phase rotation values to align signals before averaging. This parameter transformation simplifies the averaging operation by ensuring all signals contribute constructively, reducing computational complexity while maintaining measurement accuracy
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 improves signal quality by maintaining phase continuity and preserving ultra-low frequency information, reducing the possibility of fading and enhancing the accuracy of strain detection along the optical fiber.
Implementation Method 1
DAS systems exploit a Rayleigh scattering effect in optical fiber to detect changes in the fiber strain
Implementation Method 2
Coherent DAS extracts the phase from the complex signal to detect the strain
Data Source
AI summary
A spatial averaging method for a coherent distributed acoustic sensing (DAS) system that employs differential beating and polarization combining of signals for two locations along a length of optical sensing fiber to determine phase change in-between every location along the length of the optical sensing fiber and a moving average using polarization combining output to reduce any Rayleigh fading before phase determination.