Phased Array Transducer Velocity Ambiguity Resolution
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Solution Overview
Problem
Current velocity measurement systems, such as acoustic Doppler current profilers, face challenges in achieving accurate velocity measurements due to trade-offs between maximum profiling range, temporal resolution, and spatial resolution, as well as issues with measurement bias, particularly in large-scale features like temperature and salinity interfaces.
Innovation Solution
The method involves transmitting a first set of signals with a bandwidth broader than the system's bandwidth to obtain an initial velocity estimate, followed by transmitting a second set of signals with a narrower bandwidth to obtain multiple possible velocity estimates, and selecting one based on the initial estimate, using a phased array transducer to resolve ambiguity and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single narrowband pulse is used for velocity measurement, then the system bandwidth is matched to the measuring system, but velocity ambiguity cannot be resolved and measurement accuracy deteriorates
Solution Approach 1:
The velocity measurement process is segmented into two distinct stages: first transmitting a broadband signal to obtain an unambiguous initial velocity estimate, then transmitting a narrowband signal to obtain precise velocity measurements. This segmentation allows each signal type to fulfill its optimal function without compromise.
Solution Approach 2:
A preliminary velocity estimate is obtained using a broadband signal before performing the main velocity measurement with a narrowband signal. This preliminary action provides crucial information that resolves the velocity ambiguity that would otherwise plague narrowband measurements.
2Measurement precision
If broadband signals are transmitted to resolve velocity ambiguity, then velocity accuracy improves, but the system operates beyond its nominal bandwidth causing potential distortion
Solution Approach 1:
The measurement process is divided into two signal transmission phases: a broadband phase for ambiguity resolution and a narrowband phase for precise measurement. This segmentation ensures that broadband signals are only used when necessary for resolving ambiguity, minimizing distortion risks.
Solution Approach 2:
The broadband signal is transmitted with intentionally excessive bandwidth beyond the system's nominal bandwidth. While this may cause some distortion, the brief duration and targeted use (only for ambiguity resolution) limits the harmful effects while achieving the goal of resolving velocity ambiguity.
3Measurement precision
If multiple velocity estimates are obtained with narrowband signals, then measurement precision improves, but velocity ambiguity increases
Solution Approach 1:
The initial broadband velocity estimate serves as feedback information that guides the selection among multiple narrowband velocity estimates. This feedback mechanism resolves the ambiguity by providing a reference against which the narrowband estimates can be compared and validated.
Solution Approach 2:
The broadband velocity estimate is obtained as a preliminary action before processing multiple narrowband estimates. This preliminary estimate establishes the correct velocity range, allowing subsequent narrowband measurements to be interpreted unambiguously.
4Measurement precision
If signal bandwidth is increased to improve velocity resolution, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The signal processing is segmented into two distinct processing chains: one for broadband signals focused on ambiguity resolution and another for narrowband signals focused on precise measurement. This segmentation allows each processing chain to be optimized independently, managing overall system complexity.
Solution Approach 2:
The measuring system is designed to handle both broadband and narrowband signals through a unified processing framework. This multi-functionality allows the system to leverage the strengths of both signal types without requiring completely separate processing systems, thereby managing complexity.
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 and reliability of velocity measurements by reducing bias and improving resolution, allowing for more precise determination of velocity components in fluid media, such as water currents.
Implementation Method 1
The received sound has a Doppler frequency shift proportionate to the relative velocity between the scatters and the transducer
Implementation Method 2
transducer to generate pulses of sound (which when downconverted to human hearing frequencies sound like 'pings') that backscatter as echoes from plankton, small particles, and small-scale inhomogeneities in the water
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
Systems and methods for measuring velocity in fluid are disclosed. In one aspect, a method (900) comprises transmitting a first set of signals of a bandwidth broader than the measuring system, receiving echoes from the first set of signals, obtaining a first velocity estimate based on the echoes, transmitting a second set of signals of a bandwidth narrower than the measuring system, receiving echoes from the second set of signals, obtaining velocity estimates based on the echoes from the second set of signals, selecting one of the velocity estimates based on the first velocity estimate. In another aspect, a method (280) comprises removing substantially a bias related to a first velocity from raw velocity estimates. In another aspect, a method (1900) comprises obtaining a velocity estimate for each of a set of transmitted pings, calculating a velocity based on the sum of the velocity estimates.