Distributed Acoustic Sensing Spatial Averaging SNR
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Solution Overview
Problem
Distributed Acoustic Sensing (DAS) faces challenges in increasing the signal-to-noise ratio (SNR) due to limitations in temporal averaging, laser power, and coding methods, which restrict the detection length and sensitivity of acoustic vibrations in optical fibers.
Innovation Solution
Spatial averaging is employed by using an optical fiber with multiple spatial channels, where multiple laser pulses are launched and signals are digitally added across these channels to enhance the SNR without increasing power or using coding, assuming identical responses to acoustic vibrations across channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temporal averaging is used to increase SNR, then signal-to-noise ratio improves, but it is not applicable in DAS because successive OTDR traces are not identical
Solution Approach 1:
The patent transitions from temporal averaging (time dimension) to spatial averaging (space dimension). Instead of averaging successive OTDR traces over time, the invention launches N laser pulses into N spatial channels simultaneously and averages the signals from these parallel spatial channels, thereby resolving the limitation that temporal averaging cannot be applied when successive traces are not identical.
2Measurement precision
If laser pulse power is increased to improve SNR, then signal quality improves, but nonlinear interactions with the optical fiber occur that detrimentally affect the signal
Solution Approach 1:
The patent divides a single high-power laser pulse into N separate lower-power laser pulses and launches them into N spatial channels simultaneously. This segmentation allows the system to achieve the desired signal strength through spatial parallelism rather than temporal power concentration, thereby avoiding nonlinear optical interactions that would occur with excessive power in a single channel.
3Measurement precision
If multiple spatial channels are used for spatial averaging, then SNR increases by a factor of N^1/2, but the system complexity increases
Solution Approach 1:
The patent combines N spatial channels into a single optical fiber using a demultiplexer at the transmitter and a multiplexer at the receiver. This merging approach allows the system to achieve N-fold SNR improvement through spatial parallelism while maintaining a compact single-fiber architecture, thereby managing system complexity through integrated optical components rather than requiring N separate fibers.
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 method increases the SNR by a factor of N^1/2, allowing for longer detection lengths and improved sensitivity of acoustic vibrations without the limitations of conventional methods, and can be combined with Raman amplification for further enhancement.
Implementation Method 1
If an acoustic vibration makes physical contact with the optical fiber at a spatial point along its length, due to the photoelastic effect, the phase of the Rayleigh backscattered light at that point will be directly proportional to the acoustic vibration's amplitude.
Implementation Method 2
an OTDR 'trace' is measured, i.e., Rayleigh backscattered light is measured at every spatial point along the optical fiber's length using a time of flight analysis
Implementation Method 3
a laser pulse is launched into the optical fiber and, similar to conventional OTDR, an OTDR 'trace' is measured
Data Source
AI summary
A system to perform distributed acoustic sensing (DAS) in an environment with acoustic vibrations present includes at least an optical fiber positioned in said environment, wherein the optical fiber comprises N spatial channels and N laser pulses are launched into the N spatial channels of the optical fiber and propagate over a fiber length; and one or more sensors to measure N signals of acoustic vibration amplitude and frequency from each of N spatial channels, wherein the N signals are digitally added for spatial averaging and applied to determine DAS.