Wave Characteristic Measurement from Moving Platforms
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Solution Overview
Problem
Conventional underwater acoustic measurement systems, such as acoustic Doppler current profilers and wave directional spectrum devices, face challenges in accurately measuring wave characteristics like direction, height, and period due to contamination from vertical currents and instrument motion, especially when operating from moving platforms.
Innovation Solution
A system that combines an acoustic Doppler current profiler with an earth reference sensor to determine wave characteristics by transforming data into a fixed reference frame, accounting for platform motion and currents, allowing for the calculation of directional and non-directional wave spectra and derived parameters like significant wave height and peak period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional acoustic Doppler current profilers are used to measure wave characteristics, then the measurement can be performed from a moving platform, but the accuracy is degraded due to contamination from vertical currents and instrument motion
Solution Approach 1:
The measurement process is segmented into distinct reference frame transformations: first transforming from the moving platform reference frame to the earth-fixed reference frame using platform motion data, then separately processing the water velocity measurements. This segmentation allows independent correction of platform motion effects from actual water motion measurements, thereby maintaining measurement accuracy while operating from moving platforms.
Solution Approach 2:
An earth-fixed reference frame is introduced as an intermediary coordinate system between the moving platform and the water mass. By transforming all measurements into this intermediate reference frame that is fixed to the earth rather than the moving platform, the system can separate platform motion from water motion, enabling accurate wave characteristic measurement despite platform movement.
2Measurement precision
If pitch and roll buoys are used to measure wave directional spectra, then wave direction can be obtained, but the device complexity and cost increase, and they are vulnerable to weather and theft
Solution Approach 1:
The acoustic Doppler current profiler is designed to perform multiple functions: it measures both current velocity profiles and wave characteristics including directional spectra. By utilizing the same transducer array and signal processing system for both current and wave measurements, the system eliminates the need for separate specialized wave measurement instruments, thereby reducing device complexity and cost while maintaining measurement accuracy.
Solution Approach 2:
The system merges wave measurement capabilities with the existing current profiler platform. By combining wave directional spectrum measurement with current velocity measurement in a single integrated system, the patent eliminates the need for separate pitch and roll buoys, reducing overall system complexity, cost, and vulnerability while maintaining the ability to measure wave characteristics.
3Measurement precision
If PUV triplets are used to measure wave characteristics, then pressure and horizontal velocity can be measured, but they are only useful in shallow water due to decay of wave velocity and pressure with increased water depth
Solution Approach 1:
The system transitions from measuring only horizontal velocity components (as in PUV triplets) to measuring three-dimensional velocity vectors using acoustic beams oriented in multiple directions including vertical components. By utilizing the vertical dimension of acoustic beam propagation and measuring vertical velocity components, the system can detect wave orbital motion at greater depths where horizontal velocity decay has occurred, thereby extending the operational depth range.
Solution Approach 2:
The patent replaces the mechanical PUV triplet system with an acoustic Doppler-based measurement system. The acoustic method uses sound wave propagation and Doppler shift measurements rather than mechanical pressure and velocity sensors, allowing measurements to be taken at greater depths where mechanical sensors would be ineffective due to signal decay. This substitution enables deep-water wave measurement capability.
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 precise measurement of wave characteristics from moving platforms, compensating for platform motion and currents, thereby improving the accuracy of wave direction, height, and period determination.
Implementation Method 1
acoustic Doppler current profiler...measure the component of velocity projected along the beam axis
Implementation Method 2
Doppler sonar to measure currents in a fluid medium is well-established
Data Source
AI summary
A system and a method for determining one or more wave characteristics from a moving platform are disclosed. A sonar system, such as an Acoustic Doppler Current Profiler, can profile the water motion relative to the platform, and an earth reference can determine a measure of the platform motion relative to a fixed earth reference. Both water profile and earth reference measurements can be synergistically employed to compensate for motion of the platform. Directional wave spectra and non-directional wave spectrum can be computed and translated via linear wave theory to surface height spectra and used to calculate characteristics, such as significant wave height, peak period, and peak direction.