Underwater Vehicle Navigation via ADCP Current Profiles
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Solution Overview
Problem
Underwater vehicles face challenges in navigation when they lose access to satellite positioning systems, such as GPS, and need to accurately determine their position and velocity without external references, especially during transitions from the surface to the bottom of a body of water.
Innovation Solution
The system employs an Acoustic Doppler Current Profiler (ADCP) to measure current profiles and uses a processor to construct earth-referenced current profiles, shifting observed water profiles to a fixed grid of depth cells and differencing successive profiles to derive vehicle velocity estimates, which can be used for navigation until an earth-referenced velocity is available, incorporating a Kalman filter for optimal data weighting and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ADCP measures current profiles using acoustic beams, then water velocities can be measured, but the measurement precision deteriorates when GPS is unavailable and vehicle velocity is unknown
Solution Approach 1:
The patent introduces an intermediary processing system that uses sequential current profile measurements as mediators to infer vehicle velocity. By differencing successive current profiles and accumulating the differences, the system derives navigation information without direct GPS input, resolving the contradiction between maintaining measurement precision and ensuring navigation reliability in GPS-denied environments
Solution Approach 2:
The system implements feedback by using derived velocity estimates to improve subsequent current profile measurements. The accumulated velocity information feeds back into the measurement system, allowing the ADCP to better interpret successive profiles and maintain measurement precision even without external GPS references
2Reliability
If the system uses sequential observed water profiles to derive velocity, then navigation capability is maintained without GPS, but noise and uncertainty increase
Solution Approach 1:
The system performs preliminary actions by taking multiple sequential current profile measurements before deriving velocity. By accumulating measurements over time and space, the system builds up sufficient data to compute reliable velocity estimates, reducing the noise and uncertainty that would otherwise plague single-point measurements in GPS-denied environments
Solution Approach 2:
The patent merges multiple sequential current profile measurements into a unified velocity estimate. By combining information from successive profiles through differencing and accumulation operations, the system achieves reliable navigation capability while averaging out random noise and uncertainties present in individual measurements
3Measurement precision
If the system accumulates velocity changes from differenced profiles, then position estimation improves, but error accumulation occurs over time
Solution Approach 1:
The system employs periodic action by using bottom track measurements as periodic reference points to reset and correct the accumulated velocity estimates. When bottom track becomes available, it provides an external reference that corrects drift errors, allowing the system to maintain position estimation precision while preventing long-term error accumulation through periodic recalibration
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 method enables accurate navigation of underwater vehicles by providing a water column-derived estimate of vehicle velocity, reducing noise and uncertainty, and improving position estimation, even when GPS is unavailable, by combining current profile data with bottom track measurements for enhanced accuracy.
Implementation Method 1
An important category ofscientific instrumentation relates to precision underwater acoustics. With advanced transducers that transmit sound pulses and receive resulting echoes, water velocities in individual cells in a water column can be measured. This type of measurement is known in the industry as a current profile. As described in U.S. Pat. No. 6,052,334, the use of Doppler sonar to measure currents in a fluid medium is well-established.
Implementation Method 2
The processor is configured to get a water column derived estimate of change in vehicle velocity by differencing successive observed profiles and averages over the fixed grid of depth cells. The processor is further configured to determine a water column derived estimate of vehicle velocity by accumulating the initial earth reference vehicle velocity and subsequent changes in the vehicle velocity.
Data Source
AI summary
Underwater vehicles may fix their position from GPS at the surface of the water and use bottom track for dead reckoning once it has descended to within tracking range of the bottom of a body of water. This disclosure describes a method and system for navigation through the water through depths where GPS is not available using current profiles from sonar systems including acoustic Doppler current profilers (ADCP). This extrapolation of earth referenced current profiles can provide a way to estimate vehicle motion below the surface before the vehicle reaches the bottom. Once bottom track is achieved, the corrected reference for vehicle motion improves the vehicle position estimate. A Kalman filter updates vehicle position and current profile estimates during descent, and the bottom track when the bottom comes within range to enable navigation of underwater vehicles.