Fiber Optic Signal Stacking for Distributed Acoustic Sensing Noise Reduction
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Solution Overview
Problem
Distributed acoustic sensing systems, particularly those relying on Rayleigh backscattering, suffer from low signal-to-noise ratios due to random statistical noise, which limits their precision in applications requiring high accuracy, such as seismic monitoring.
Innovation Solution
The method involves transmitting optical signals into a fiber optic cable with multiple parallel fiber lengths, collecting and processing reflected signals from each segment to generate seismic traces, and stacking these traces to enhance the signal-to-noise ratio while maintaining the simplicity and low cost of the hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple light pulses at different frequencies and wavelengths are fired into the fiber, then the signal to noise ratio is improved, but the complexity of data processing and optical components increases
Solution Approach 1:
The patent divides the fiber into multiple segments and processes signals from each segment separately. By segmenting the fiber and using time-domain gating to isolate backscattered light from different segments, the system can stack signals from multiple segments to improve signal-to-noise ratio without requiring multiple light sources or complex spectral processing
Solution Approach 2:
The patent combines signals from multiple fiber segments through coherent stacking in the time domain. By synchronizing and summing the backscattered signals from different segments, the system achieves signal-to-noise ratio improvement through constructive interference of the signal while random noise averages out, eliminating the need for multiple wavelengths
2Device complexity
If distributed acoustic sensing systems rely on Rayleigh backscattering, then the system maintains simplicity and low cost, but the signal to noise ratio becomes low due to random statistical noise
Solution Approach 1:
The patent implements continuous monitoring by firing repeated laser pulses at the same wavelength and stacking the resulting signals. This continuous action allows accumulation of signal energy over multiple pulses while the random noise averages out, improving signal-to-noise ratio without changing the basic Rayleigh backscattering mechanism or hardware complexity
Solution Approach 2:
The system performs preliminary signal conditioning and time-domain gating to isolate useful backscattered signals from noise before stacking. By pre-processing each pulse's signal to extract only the relevant time windows corresponding to different fiber segments, the system prepares clean signals for stacking that will accumulate constructively
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 significantly improves the signal-to-noise ratio by effectively eliminating random noise, allowing for more precise analysis of seismic data and maintaining the cost-effectiveness of the system.
Implementation Method 1
Because the cables typically comprise optically conducting fiber containing a plurality of backscattering inhomogeneities along the length of the fiber, such systems allow the distributed measurement of axial strain along an optical fiber by measuring backscattered light from a laser pulse input into the fiber
Data Source
AI summary
A method for obtaining information about a subsurface formation from acoustic signals that contain information about the subsurface formation, comprises a) transmitting an optical signal into a fiber optic cable (14) that includes a sensing apparatus (20) comprising a plurality of substantially parallel fiber lengths (24), b) collecting from the sensing apparatus a plurality of received optical signals, each received signal comprising a portion of the transmitted signal that has been reflected from a different segment of a cable length, wherein the different segments are each in different cable lengths and correspond to a single selected location along the sensing cable, and c) processing the collected signals so as to obtain information about an acoustic signal received at the different segments. The cable may be ribbon cable and the lateral distance between the different segments may be less than 10 meters.