Distributed Acoustic Sensing Signal Processing With Spread Spectrum Pulses
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Solution Overview
Problem
Existing distributed acoustic sensing (DAS) systems face limitations in operational range and signal-to-noise ratio due to the use of traditional pulse methods, which either distort measurements for large acoustic strains or require reduced spatial resolution when increasing energy per measurement.
Innovation Solution
The use of spread spectrum pulses in DAS systems, where scattered signals are interfered with a local oscillator to generate modulated carrier signals, followed by pulse compression, enhances signal-to-noise ratio and operational range without reducing spatial resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the duration of each pulse is increased to increase energy per measurement, then the signal-to-noise ratio is improved, but the spatial resolution of the system is decreased
Solution Approach 1:
The patent applies spread spectrum modulation to the optical pulse, spreading its spectral content over a wide bandwidth. This allows the pulse to maintain high energy content (improving signal-to-noise ratio) while the wide bandwidth preserves fine temporal resolution (maintaining spatial resolution). The key parameter change is transforming the pulse from a narrowband signal to a wideband spread spectrum signal.
Solution Approach 2:
The patent uses pseudorandom binary sequence modulation to periodically switch the phase of the optical carrier. This periodic modulation spreads the pulse energy across a wide frequency spectrum while maintaining the ability to correlate and compress the signal later, thereby improving signal-to-noise ratio without sacrificing spatial resolution.
2Measurement precision
If traditional pulse methods are used to increase energy per measurement, then signal-to-noise ratio improves, but operational range is limited
Solution Approach 1:
The patent transforms the optical pulse into a spread spectrum signal by modulating it with a pseudorandom binary sequence. This parameter change spreads the spectral content over a wide bandwidth, allowing the pulse to carry high energy while maintaining temporal resolution. The result is improved signal-to-noise ratio that enables extended operational range without the trade-offs of traditional pulse methods.
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 the signal-to-noise ratio and operational range of DAS systems, providing better strain measurements with maintained spatial resolution through pulse compression and spread spectrum techniques.
Implementation Method 1
a scattered signal that was scattered at a scattering location along an optical path is received and interfered with a local oscillator signal to generate a first carrier signal
Implementation Method 2
These discontinuities lead to scattering of laser light passing through the optical fiber, particularly by Rayleigh scattering
Data Source
AI summary
Disclosed are signal processing methods for an optical detection system, and corresponding systems. An example is a signal processing method for a distributed acoustic sensing system which utilizes spread spectrum pulses transmitted along an optical path, where a scattered signal that was scattered at a scattering location along an optical path is received and interfered with a local oscillator signal to generate a first carrier signal that is modulated by a phase difference between the local oscillator and scattered signals. The first carrier signal is then processed to generate a second carrier signal that is modulated by a spatial differential of the phase difference. Pulse compression is then performed on the second carrier signal. The spatial differential of the phase difference is directly related to the strain (or acoustic environment) of the optical path at the scattering location, and so enables the strain at the scattering location to be estimated.