DAS Doppler Shift Analysis for Moving Object Tracking
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Solution Overview
Problem
Current distributed acoustic sensing (DAS) systems struggle to provide detailed information about moving objects, particularly aircraft and land vehicles, as they typically only indicate the presence of a vehicle at a specific location along the optical fibre without providing information on its movement, speed, or direction.
Innovation Solution
A DAS apparatus that analyzes measurement signals from optical fibre sensing portions to detect a Doppler shift, allowing for the identification of moving objects by processing frequency changes over time, which indicates the object's velocity, direction, and proximity, enabling the tracking of objects along the fibre.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional DAS systems are used to detect moving objects, then the presence of objects can be indicated at specific locations, but detailed information about movement, speed, and direction cannot be provided
Solution Approach 1:
The patent applies parameter changes by analyzing frequency shifts (Doppler shift) in the acoustic signals detected by the DAS system. By detecting changes in the frequency parameter of the backscattered light signal caused by moving objects, the system extracts movement information including speed and direction, thereby resolving the contradiction between providing detailed movement information and maintaining detection precision
Solution Approach 2:
The patent uses acoustic signals as an intermediary to transfer information about moving objects to the DAS system. The acoustic waves generated or scattered by moving objects interact with the optical field in the fibre, creating frequency-modulated backscatter signals that carry movement information, thus enabling the detection of detailed object characteristics without compromising precision
2Area of stationary object
If DAS systems analyze acoustic signals from multiple sensing portions, then coverage area increases, but the ability to distinguish moving object characteristics deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the optical fibre into multiple discrete sensing portions along its length. Each sensing portion independently detects acoustic signals, and the system processes signals from different segments to determine the spatial distribution and movement characteristics of objects. This segmentation enables both wide monitoring coverage through multiple segments and precise object identification by analyzing the spatial pattern of detected signals
Solution Approach 2:
The patent uses feedback by comparing acoustic signals detected at different sensing portions and analyzing the temporal and spatial relationships between them. By processing the feedback information from multiple sensing zones, the system can distinguish moving object characteristics such as direction of travel and speed, maintaining identification accuracy while expanding monitoring coverage
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
Enables the detection of moving objects with improved accuracy, including aircraft and land vehicles, by determining their speed, direction, and proximity, providing detailed information about their movement and position relative to the fibre.
Implementation Method 1
Coherent light is launched into an optical fibre and any light which is Rayleigh backscattered within the optical fibre is detected and analysed
Implementation Method 2
a processor configured to analyse said measurement signals to identify a signal characteristic of a Doppler shift so as to detect a moving object
Data Source
AI summary
A system for moving object (402) detection is provided, the system comprising a fiber optic interrogator (106) adapted to provide distributed acoustic sensing on a optic fiber (104), for example arranged along a border. The measurement signals from each of a plurality of sensing portions (404, 406, 408, 410, 412) of said fiber are analyzed to determined a characteristic of a Doppler shift. The characteristic of a Doppler shift may be a generally continuous decrease in detected frequency. By detecting the time at which the rate of change of frequency is at a maximum for each of the sensing portions the time of closest approach (ti, t2, t3, t4, t5) of the object to those sensing portions can be determined with the sensing portion the object approaches closest to showing the greatest value of maximum rate of change of frequency. The distance of closest approach and velocity can be determined.