Autonomous Underwater Positioning via Acoustic Phase Difference
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Solution Overview
Problem
Current underwater navigation systems for autonomous underwater vehicles are expensive, operationally limiting, and require pre-programmed geophysical positions and synchronization of timing information, making them impractical for widespread use, especially in areas where GPS is unavailable or unreliable.
Innovation Solution
A single-point reference system using underwater acoustic modems to determine the geophysical position of autonomous underwater systems by exchanging broadband acoustic signals, allowing for flexible communication and eliminating the need for pre-programming or synchronization, with a method that involves monitoring depth and transmitting range, bearing, and geophysical position data within a single signal exchange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LBL systems are used for underwater positioning, then positioning precision is improved, but device complexity and deployment cost increase due to requiring extensive preparation and surface expression
Solution Approach 1:
The patent extracts the positioning function from complex LBL systems by using a single acoustic transponder instead of multiple beacons. The mobile system performs self-positioning by analyzing the phase difference of acoustic signals received from the single transponder, eliminating the need for extensive beacon deployment while maintaining positioning capability
Solution Approach 2:
The mobile autonomous system performs self-positioning by processing acoustic signals independently. The system uses its own sensors and computational resources to determine its position based on phase difference measurements, without requiring external processing or complex coordination between multiple beacons
2Extent of automation
If inertial navigation is used, then autonomous operation is improved, but measurement precision deteriorates due to drift rate of 1 nm/hour without compensation
Solution Approach 1:
The patent introduces acoustic feedback mechanisms where the mobile system continuously receives acoustic signals from the transponder and measures phase differences to update its position. This feedback loop compensates for inertial drift by providing periodic corrections based on actual acoustic measurements rather than relying solely on inertial sensors
3Measurement precision
If GPS surface fix is used, then positioning precision is improved, but adaptability deteriorates due to limitations on sea state capability and time spent on surface
Solution Approach 1:
The patent replaces the mechanical/optical GPS system with an acoustic-based positioning system. Instead of relying on satellite radio waves that require line-of-sight and stable sea conditions, the system uses acoustic signals that can propagate through water regardless of sea state, enabling positioning in all ocean conditions
4Ease of operation
If acoustic signals are used for positioning, then ease of operation is improved, but measurement precision deteriorates due to errors from average sound speed assumptions
Solution Approach 1:
The patent uses partial action by measuring only the phase difference of acoustic signals at the mobile system's location, rather than requiring complete timing information or multiple signal paths. This partial measurement approach simplifies the system while providing sufficient precision for navigation by focusing on the relative phase information that directly indicates position
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 reliable and cost-effective determination of the geophysical position of autonomous underwater systems without pre-programming or synchronization, providing flexible communication and reducing the need for above-water visibility, thus improving navigation efficiency and reducing operational costs.
Implementation Method 1
The relationship between time delay and range is well understood in acoustics. There is a direct and well-understood relationship between the speed of sound and the range between transmit and receive components.
Implementation Method 2
the bearing of the request signal is determined by analyzing the signals received at the array of transducers
Data Source
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AI summary
Method and apparatus for determining the geophysical position of an autonomous underwater system utilizing underwater acoustic modems that exchange underwater acoustic signals. An exchange of broadband acoustic signals is initiated between the autonomous system of unknown geophysical position and a base system of known geophysical position wherein the depths of both systems is known. A bearing calculation is made on one of the signals transmitted between the systems with the use of an array of hydrophones on either the autonomous or base system. The range between the two systems is determined by measuring the time of travel of at least one signal. By the acoustic transmission and sharing of information about the known depths of the systems, the known geophysical position of the base system, and the range between the systems, sufficient data is gathered and used to determine the geophysical position of the autonomous system.