Passive Sonar Localization via Acoustic Correlation
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Solution Overview
Problem
Current passive sonar systems face challenges in accurately localizing underwater targets in range and depth, especially at longer ranges, due to sound refraction and the complexity of sound propagation paths, which affects the accuracy of existing techniques like narrowband and broadband autocorrelation processing.
Innovation Solution
The method involves receiving passive acoustic signals from an underwater target via multiple propagation paths, correlating the signals to identify correlation features, and using propagation models to select dominant paths and estimate range and depth, with a likelihood factor determining the accuracy of the localization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If narrowband or matched field processing is used to localize in range and depth, then localization accuracy is improved, but a large sonar array is required which is not practical for many applications
Solution Approach 1:
The patent extracts and utilizes only the necessary components for localization by focusing on correlation features from dominant propagation paths rather than requiring a complete large-scale array system. This allows achieving localization functionality with a more compact configuration.
Solution Approach 2:
The patent changes the processing approach from narrowband to broadband correlation processing, and shifts from requiring spatial array configuration to using temporal correlation analysis. This parameter change enables localization without the need for large physical array dimensions.
2Measurement precision
If broadband autocorrelation processing is used to identify time delay between direct and surface-reflected sound paths, then range and depth can be calculated, but performance is greatly degraded at moderate to high sea states due to scattering of surface-reflected sound
Solution Approach 1:
The patent converts the harmful effect of surface scattering into a beneficial feature by using the scattered energy from multiple paths as additional correlation features. Instead of treating surface scattering as noise to be rejected, the method identifies and utilizes correlation features from dominant paths including scattered components, thereby maintaining reliability in high sea states.
Solution Approach 2:
The patent implements dynamic selection of dominant propagation paths based on correlation strength and likelihood factors. The system adapts to changing sea conditions by identifying which paths remain dominant under various sea states, allowing continuous reliable localization despite varying environmental conditions.
3Measurement precision
If passive sonar systems use beamforming techniques with vertical beam steering to detect and localize submarines, then azimuth localization is achieved, but range and depth localization is not possible because the submarine can be positioned at an essentially infinite number of depths and ranges along the vertical beam steer angle
Solution Approach 1:
The patent adds temporal dimension to the spatial beamforming approach by incorporating time-delay correlation analysis. While beamforming provides azimuth information through spatial distribution, the correlation processing in the time domain extracts range and depth information, effectively adding temporal dimension to compensate for the loss of range-depth information in pure spatial processing.
Solution Approach 2:
The patent uses correlation features as an intermediary between the received passive sound and the final localization result. These correlation features serve as mediators that encode information about propagation paths, time delays, and path characteristics, enabling extraction of range and depth information that would otherwise be lost in conventional beamforming.
4Measurement precision
If sound propagation paths are analyzed to account for refraction effects at longer ranges, then localization accuracy is improved, but the complexity of identifying and processing multiple propagation paths increases
Solution Approach 1:
The patent applies partial action by focusing computational resources on identifying and processing only the dominant propagation paths rather than attempting to analyze all possible paths. By selecting and processing a subset of the most significant paths (direct, surface-reflected, bottom-reflected), the system achieves long-range localization accuracy without the excessive complexity of complete path analysis.
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 enhances the accuracy of range and depth localization by accounting for various sound propagation paths and refraction effects, providing a more reliable method for tracking underwater targets even in challenging sea states.
Implementation Method 1
receiving a passive acoustic signal generated by a target. The sound signal travels on at least two propagation paths, i.e., a first propagation path and a second propagation path, to the sonar system
Implementation Method 2
a tendency of the passive sound generated by the enemy submarine to bend (i.e., refract), primarily in a vertical direction, as the sound propagates through the water
Implementation Method 3
The signal received by a sonar element (i.e., sonar transducer), or a sonar array, is autocorrelated to identify a relative time delay between the passive sound arriving at the sonar element on a direct sound path and the passive sound arriving at the sonar element on a surface-reflected sound path
Data Source
Figure 1
Figure 2~2A
Figure 3
AI summary
A to method and system provide a range and depth localization of a passive sound generator, e.g., a submarine target. The method and system use an autocorrelation and/or a cross correlation to arrive at a plurality of range versus depth estimates, which are resolved and evaluated using likelihood factors in order to provide a range and depth localization.