Sonar Time-Reversed Chirp Signals for Bubble Scatter Suppression
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Solution Overview
Problem
SONAR systems face challenges in bubbly conditions due to acoustic backscatter from bubbles, which hinder the detection of real targets and require high-amplitude sources for effective clutter reduction techniques like TWIPS and BiaPSS.
Innovation Solution
Employing time-reversed chirp signals, either linear or logarithmic, emitted simultaneously and processed with matched filters to enhance linear target detection by suppressing bubble scatter, using a pair of up and down chirp pulses with partial or complete overlap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sonar techniques are used in bubbly conditions, then bubble scatter is suppressed through nonlinear pulsations, but high-amplitude sources are required which increase energy consumption and potential harm to marine life
Solution Approach 1:
The patent changes the temporal and spectral parameters of the sonar signal by using chirp signals with linearly varying frequency instead of traditional single-frequency or simple pulsed signals. This parameter change allows the system to achieve better target detection in bubbly waters through frequency diversity without requiring high amplitude, thus resolving the contradiction between measurement precision and energy consumption
Solution Approach 2:
The patent employs periodic transmission of chirp signals with specific timing relationships between upward and downward chirps. This periodic action with varying frequency over time enables the system to exploit temporal coherence for target enhancement while maintaining lower amplitude levels, addressing the energy consumption issue while preserving detection accuracy
2Measurement precision
If high-amplitude sources are used to drive bubbles to large nonlinear pulsations, then clutter reduction is achieved, but the system complexity and equipment requirements increase
Solution Approach 1:
The patent replaces the mechanical approach of using high-amplitude acoustic pulses to physically drive bubble pulsations with a signal processing approach using chirp signals and temporal coherence analysis. This substitution achieves clutter reduction through intelligent signal design and processing rather than brute-force acoustic energy, thereby reducing system complexity and equipment requirements
Solution Approach 2:
The patent introduces an intermediary processing stage that analyzes the temporal coherence characteristics of returned signals. This intermediary layer between signal transmission and target detection enables the system to distinguish targets from bubble clutter based on their different temporal coherence properties, achieving clutter reduction without requiring complex high-power acoustic sources
3Measurement precision
If time-reversed chirp signals are used to enhance linear target scatter, then target detection is improved, but the processing complexity increases
Solution Approach 1:
The patent applies time-reversal to the chirp signal, transmitting signals in reverse chronological order. This inversion technique exploits the property that linear targets preserve temporal coherence while bubbles do not, enabling enhanced target detection through simple correlation processing. The inversion approach maintains relatively simple processing requirements compared to more sophisticated adaptive filtering methods
Solution Approach 2:
The patent uses matched filtering which involves creating a copy of the transmitted chirp signal and correlating it with the received signal. This copying approach simplifies the processing by using the known transmitted waveform template to enhance target returns while suppressing incoherent bubble scatter, achieving good target detection without requiring complex real-time signal generation and analysis systems
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
Enhances target detection by suppressing bubble scatter and reducing noise, allowing for improved detection range and accuracy in bubbly waters without the need for high-amplitude sources.
Implementation Method 1
When insonified (i.e. subjected to acoustic energy from a SONAR transmitter), the backscatter from bubbles can hinder the detection of 'real' targets in the water
Implementation Method 2
the bubbles demonstrate their inherently nonlinear behaviour if they are of the correct size, which usually means they are close to their pulsation resonance
Implementation Method 3
it is possible to enhance the scatter from both linear targets and bubbles, with a greater effect on the former, owing to the difference between bubble responses, to an increasing or decreasing frequency sweep of the driving chirp signal
Data Source
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Figure 1(b)
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AI summary
Disclosed is a SONAR system operable to transmit a pair of pulses including an up-chirp signal and a down-chirp signal wherein the down-chirp signal is a time-reversed version of the up-chirp signal. Also disclosed is a related method of operation.