Multipath Angle of Arrival Determination in Passive Sonar
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Solution Overview
Problem
Conventional passive sonar systems face difficulties in accurately localizing and tracking underwater vessels at longer ranges due to the bending of sound waves in water, making it challenging to determine the correct vertical angle of arrival, which is essential for range and depth estimation.
Innovation Solution
The method involves performing autocorrelation and cross-correlation on signals received from multiple receive beams to determine multipath angles of arrival, allowing for the separation and analysis of signal components from different paths, thereby improving the accuracy of range and depth estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-path techniques are used to determine vertical angle of arrival, then the system remains simple, but localization accuracy deteriorates due to sound wave bending and multipath effects
Solution Approach 1:
The patent segments the received signal into multiple distinct paths using autocorrelation and cross-correlation techniques. By identifying separate arrival times and characteristics of different signal paths (direct path, surface reflected path, bottom reflected path), the system can analyze each path independently to determine accurate angle of arrival information despite sound wave bending effects.
Solution Approach 2:
The patent introduces correlation functions (autocorrelation and cross-correlation) as intermediary mathematical tools to extract path information from the composite received signal. These correlation operations serve as mediators that separate and identify individual signal paths based on their temporal and spatial characteristics, enabling accurate angle determination without direct physical separation of paths.
2Reliability
If passive sonar systems use beam-forming techniques with receive beams, then they remain covert and undetectable, but localization in depth and range becomes impossible at short ranges
Solution Approach 1:
The patent transitions from analyzing only the spatial direction (azimuth) of incoming signals to analyzing the temporal dimension as well. By examining arrival times of different signal paths and using correlation techniques across time delays, the system extracts depth and range information from the temporal structure of multipath signals, adding a time dimension to the traditional spatial beam-forming approach.
3Productivity
If passive sound propagates through water at longer ranges, then the sound bends vertically due to refraction, but this makes determining the correct vertical angle of arrival even more difficult
Solution Approach 1:
The patent converts the harmful effect of sound wave bending and multipath propagation into a beneficial source of information. Instead of treating refraction and multiple paths as obstacles that obscure the true angle of arrival, the system uses the distinctive temporal and spatial patterns of multipath signals (identified through correlation analysis) to infer accurate angle information and compensate for refraction effects.
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 enables more precise localization and tracking of underwater vessels by effectively separating and analyzing signals from multiple paths, overcoming the limitations of single-path techniques and improving range and depth estimation accuracy.
Implementation Method 1
an underwater vessel (i.e., a submarine) generates sound, which is generally referred to as passive sound, as it travels through the water
Implementation Method 2
performing an autocorrelation on a first signal received at a first received beam from a signal source, performing a cross-correlation between the first signal and a second signal received at a second receive beam from the signal source
Data Source
AI summary
In one aspect, a method to determine multipath angles of arrival includes performing an autocorrelation on a first signal received at a first received beam from a signal source, performing a cross-correlation between the first signal and a second signal received at a second receive beam from the signal source, and determining an angle of arrival for a first path from the signal source and an angle of arrival for a second path from the signal source based on the autocorrelation and the cross-correlation.