An underwater acoustic Doppler velocity measurement precision verification method and system

Abstract

The present application relates to the technical field of ultrasonic detection and signal measurement, and aims at solving the common problems in the prior art, such as uncontrollable environment, insufficient precision in shallow water and low speed, etc. The present application provides a method and system for verifying the precision of underwater acoustic Doppler velocity measurement. The method comprises the following steps: a host computer controls a three-axis motion module to drive an ultrasonic transducer to make controllable motion in still water, and the relative speed between the transducer and the stationary reflecting interface is taken as a traceable reference speed; waveform parameters are defined according to a flow measurement mode, a transmission signal is generated by an arbitrary waveform generator, and the transducer is driven by a power amplifier to emit sound waves; an oscilloscope acquires echo signals and completes analog-to-digital conversion under the control of a synchronous trigger signal; the host computer reads echo waveform data, and executes algorithm processing such as quadrature mixing, low-pass filtering and complex autocorrelation, etc., to obtain a measured speed; and the measured speed is compared with the reference speed to realize quantitative verification of the velocity measurement precision, and the method has the characteristics of high precision and strong stability.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic testing and signal measurement technology, specifically to a method and system for verifying the accuracy of underwater acoustic Doppler velocimetry. Background Technology

[0002] Acoustic Doppler velocimetry technology estimates the target velocity by emitting sound waves into a target area and receiving the echoes, based on the Doppler frequency shift, amplitude, and correlation characteristics of the echoes. It offers advantages such as not disturbing the flow field, flexible measurement methods, and a large velocity measurement range, and has been widely applied in equipment such as Doppler velocity logs (DVL) and acoustic Doppler current profilers (ADCP). To ensure the accuracy and reliability of the velocity measurement results, quantitative verification and evaluation of the accuracy of the acoustic Doppler velocimetry system is a crucial step in the instrument development and algorithm optimization process.

[0003] Currently, the commonly used methods for verifying the accuracy of acoustic velocities mainly include the following three: Field testing: Conducting on-site tests of velocity measuring equipment in real water bodies (such as rivers, lakes, and oceans) can reflect the comprehensive performance of the instrument under actual hydrological and dynamic environments. However, field testing conditions are complex, environmental factors (such as velocity profiles, water temperature gradients, suspended solids concentrations, and water turbulence) are uncontrollable, the repeatability of measurement results is poor, and it is difficult to effectively separate systematic errors from environmental interference errors, making it unsuitable for fine-grained evaluation during the velocity measurement algorithm development stage.

[0004] Indoor water tank trailer test: A trailer is used to move the speed measuring device at a constant speed in a water tank, allowing for linear velocity calibration in a stable and controllable aquatic environment. This method avoids environmental interference to some extent and is suitable for preliminary performance verification of the instrument. However, it is limited by the size of the water tank, making it difficult to obtain high-precision measurement results under shallow water and low-speed conditions. Furthermore, the trailer's movement may introduce mechanical vibrations, causing additional interference to the echo signal and affecting the independent evaluation of the algorithm's accuracy.

[0005] Hardware-in-the-loop (HIL) simulation testing: This method simulates echo signals with Doppler frequency shift using a signal source or simulation platform, and then feeds them into a velocimetry algorithm for processing and evaluation. This method has advantages such as good repeatability, flexible parameter configuration, and ease of quantitative analysis, and is widely used in the algorithm development stage. However, it completely ignores the actual propagation process of sound waves in water and the coupling effect between the transducer and the medium. It fails to reflect the influence of actual transducer transmission and reception characteristics, sound field distribution, boundary reflection, and water scattering on velocimetry accuracy, leading to a significant gap between simulation results and actual performance.

[0006] In summary, existing methods suffer from common problems in velocity measurement accuracy verification, such as uncontrollable environment, poor repeatability (field testing), insufficient accuracy in shallow water and low speed (water tank trailer testing), and missing acoustic propagation process (physical simulation). These problems make it difficult to simultaneously meet the comprehensive requirements of reproducing real physical processes, high accuracy and repeatability, and rapid algorithm verification under shallow water and low speed conditions.

[0007] Therefore, there is an urgent need to propose a speed measurement accuracy verification device and method that can realistically reproduce the entire process of sound wave emission, propagation in water, scattering and echo reception under controlled indoor conditions, while possessing high-precision motion simulation and traceable reference speed, so as to provide a reliable and efficient experimental platform for Doppler speed measurement algorithm research and instrument calibration. Summary of the Invention

[0008] In view of this, the present invention provides an underwater acoustic Doppler velocity measurement accuracy verification method and system to solve the problems of uncontrollable environment, poor repeatability, insufficient accuracy in shallow water and low speed, and missing acoustic propagation process in velocity measurement accuracy verification.

[0009] In a first aspect, the present invention provides a method for verifying the accuracy of underwater acoustic Doppler velocity measurement, the method comprising: S1: Real-time acquisition of the moving speed and position information of the motion mechanism, and determination of a reference speed based on the moving speed and position information; S2: Determine the flow measurement working mode according to the target requirements, configure waveform parameters under preset engineering constraints, and control the ultrasonic transducer to emit sound waves in the experimental liquid medium based on the waveform parameters; S3: Control the signal acquisition device to synchronously acquire the echo signal received by the ultrasonic transducer, and receive the echo waveform data obtained by the signal acquisition device after performing analog-to-digital conversion based on the echo signal; S4: Perform Doppler velocity measurement algorithm processing on the echo waveform data to calculate the measured velocity, compare the measured velocity with the reference velocity, and output the velocity measurement accuracy verification result based on the comparison result.

[0010] In one optional implementation, determining a reference speed based on the moving speed and location information specifically includes: The system receives the actual speed values ​​and real-time positions uploaded in real time by the position feedback units of each axis of the motion mechanism, and uses them as input data for the moving speed and position information. When the position information indicates that the ultrasonic transducer is in a preset effective speed measurement range, the corresponding moving speed is decomposed by coordinate decomposition to extract the radial component along the sound beam direction, and the reference speed is output.

[0011] In one optional implementation, the step of determining the flow measurement working mode according to the target requirements and configuring waveform parameters under preset engineering constraints includes: The preset engineering constraints are input with at least one of the following: speed measurement range, distance measurement range, layer thickness, and encoding form. Based on the preset engineering constraints, one of the following is selected as the flow measurement working mode: narrowband speed measurement mode, pulse coherent speed measurement mode, and wideband coded speed measurement mode. At least one of the following is determined: carrier frequency, transmission interval, pulse length, symbol width, repetition count, and signal amplitude. The configuration data of the waveform parameters is then output.

[0012] In one optional implementation, step S3 specifically includes: A trigger output configuration command is sent to the waveform generator, causing the waveform generator to generate a synchronous trigger signal from its trigger output channel while simultaneously outputting the transmission signal, and outputting it to the trigger input terminal of the signal acquisition device; the signal acquisition device uses the arrival time of the synchronous trigger signal as a sampling start flag, and performs analog-to-digital conversion on the analog echo electrical signal output by the receiving terminal of the ultrasonic transducer, converting the continuous analog quantity into discrete digital echo waveform data.

[0013] In one optional implementation, the step of performing Doppler velocimetry algorithm processing on the echo waveform data to calculate the measured velocity includes: Using the echo waveform data as algorithm input, the echo waveform data is first preprocessed by removing DC offset and bandpass filtering, and the preprocessed time-domain echo data is output. Generate one cosine local oscillator signal and one sine local oscillator signal with the same frequency as the transmitted carrier. Multiply the preprocessed time-domain echo data with the cosine local oscillator signal and the sine local oscillator signal respectively to obtain in-phase and quadrature components containing high-frequency components and Doppler frequency components. A low-pass filter with a cutoff frequency set between the Doppler frequency offset range and the carrier frequency is used to perform low-pass filtering on the in-phase component and the quadrature component respectively, filtering out high-frequency components, extracting the in-phase component and the quadrature component that only contain Doppler frequency offset information, and then orthogonally synthesizing the two components to obtain a complex signal. Perform complex autocorrelation operation on the complex signal, take two consecutive sets of echo data segments with the same duration and fixed time delay, calculate the complex conjugate product of the two data segments and calculate the time mean, and output a complex autocorrelation function value; Calculate the phase angle of the complex autocorrelation function value, divide the phase angle by the fixed time delay to obtain the Doppler angular frequency, and then convert it into the Doppler frequency shift; substitute the Doppler frequency shift, the sound speed in the liquid medium and the carrier frequency into the Doppler radial velocity relationship to calculate the radial velocity in the direction of sound wave propagation, and output the measured velocity.

[0014] In one optional implementation, comparing the measured speed with the reference speed and outputting a speed measurement accuracy verification result based on the comparison result includes: Within the same effective speed measurement interval, the sampled values ​​of the measured speed at multiple times are compared with the sampled values ​​of the reference speed at the corresponding times. The speed deviation and root mean square error between the two are calculated, and the calculation results are used as data output to quantitatively characterize the speed measurement accuracy.

[0015] Secondly, the present invention provides an underwater acoustic Doppler velocimeter accuracy verification system for performing an underwater acoustic Doppler velocimeter accuracy verification method as described in the first aspect and any optional embodiment, comprising: A computer for performing the steps of the method as described in the first aspect and any alternative implementation; The motion mechanism is composed of three-axis linear modules, each axis is equipped with a position feedback unit, which is used to drive the ultrasonic transducer to move in the liquid medium and feed back the actual speed value and real-time position to the computer. An ultrasonic transducer, installed at the end of the motion mechanism, is used to emit sound waves and receive echo signals in the experimental liquid medium. A waveform generator, which is communicatively connected to the computer, is used to receive the waveform parameters and generate a transmission signal and a synchronization trigger signal to drive the ultrasonic transducer. A signal acquisition device, connected to the ultrasonic transducer and the signal source, is used to acquire the echo signal under the control of the synchronous trigger signal, perform analog-to-digital conversion, and output echo waveform data to the computer.

[0016] In one optional embodiment, the motion mechanism is a three-axis linear module assembly, including an X-axis, a Y-axis, and a Z-axis; The X-axis serves as the primary direction of motion, while the Y and Z axes are used to adjust the horizontal position and water depth of the ultrasonic transducer. The motion trajectory of the motion mechanism includes an acceleration segment, a constant speed segment, and a deceleration segment, with the constant speed segment serving as the effective speed measurement range.

[0017] In one alternative implementation, the device further includes a switch for connecting the various communication devices within a local area network.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention controls the relative motion of an ultrasonic transducer and the experimental liquid medium through a high-precision motion mechanism. The relative velocity between the ultrasonic transducer and the reflecting interface (equivalent water body or bottom) is used to represent the flow velocity and bottom velocity, enabling quantitative calibration and accuracy verification of the Doppler velocimetry algorithm. Compared with traditional methods, this approach is suitable for the rapid development and verification of high-precision velocimetry algorithms in shallow water with low speeds. While maintaining experimental repeatability and environmental controllability, it can realistically reproduce the sound wave propagation and echo reception process, thus more reliably verifying the transducer performance and the accuracy of the velocimetry algorithm. This provides precise and traceable experimental evidence for the study of the mechanism and system calibration of acoustic Doppler flow measurement technology. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of an underwater acoustic Doppler velocity measurement accuracy verification system according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the underwater acoustic Doppler velocity measurement accuracy verification method according to an embodiment of the present invention. Figure 3 This is the speed running curve planned by the motion mechanism according to an embodiment of the present invention; Figure 4 The images show the time-domain waveform, echo correlation, and real-time speed curve results of the broadband coding speed measurement algorithm according to an embodiment of the present invention. Figure 5 The images show the time-domain waveform, echo correlation, and real-time velocity curve results of the pulse coherence velocimetry algorithm according to an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Figure 1 This is a schematic diagram of the structure of an underwater acoustic Doppler velocity measurement accuracy verification system according to an embodiment of the present invention, comprising: A computer is used to execute a method for verifying the accuracy of underwater acoustic Doppler velocimetry. The motion mechanism is composed of three-axis linear modules, each axis is equipped with a position feedback unit, which is used to drive the ultrasonic transducer to move in the liquid medium and feed back the actual speed value and real-time position to the computer. An ultrasonic transducer, installed at the end of the motion mechanism, is used to emit sound waves and receive echo signals in the experimental liquid medium. A waveform generator, which is communicatively connected to the computer, is used to receive the waveform parameters and generate a transmission signal and a synchronization trigger signal to drive the ultrasonic transducer. A signal acquisition device, connected to the ultrasonic transducer and the signal source, is used to acquire the echo signal under the control of the synchronous trigger signal, perform analog-to-digital conversion, and output echo waveform data to the computer.

[0023] Optionally, the motion mechanism is a three-axis linear module combination, including an X-axis, a Y-axis, and a Z-axis; wherein, the X-axis serves as the main direction of motion, and the Y-axis and Z-axis are used to adjust the horizontal position and water depth of the ultrasonic transducer; the motion trajectory of the motion mechanism includes an acceleration segment, a constant speed segment, and a deceleration segment, and the constant speed segment serves as the effective speed measurement range.

[0024] Optionally, it also includes: a switch for connecting various communication devices within a local area network.

[0025] In this embodiment, the ultrasonic transducer is fixed to the end of the Z-axis of the three-axis motion module using a clamp. The clamp is adjustable relative to the Z-axis direction, and the clamp is adjusted so that the sound beam direction of the ultrasonic transducer forms a 20° angle with the vertically downward direction. Water is filled into the experimental water tank to 4 / 5 of the tank depth, and the computer controls the Z-axis slider to move up and down to configure the water immersion depth of the ultrasonic transducer.

[0026] The motion mechanism consists of three linear modules: X, Y, and Z. The linear modules have a displacement accuracy of 0.02 mm and a speed measurement accuracy of up to 1 mm / s. Each linear module is equipped with a driver, and all three drivers are connected to the same controller. The controller is connected to a switch via an Ethernet port. The controller is primarily responsible for parsing the control commands issued by the computer and converting them into drive commands for the three linear modules. In actual use, the Y and Z axes are mainly used to adjust the initial position and water depth of the ultrasonic transducer, while the X axis, as the main direction of motion, is responsible for controlling the relative motion of the ultrasonic transducer. During the experiment, due to the limited number of computer network ports, a switch was used to connect the oscilloscope and the controller to the same local area network, enabling rapid communication between multiple devices.

[0027] The ultrasonic transducer's motion speed is controlled in segments. Starting from a stationary state, the ultrasonic transducer steadily accelerates to a set speed, and then maintains a constant speed for a certain period of time. This stage is the effective velocity measurement range, during which the echo signal has stable Doppler frequency shift characteristics. Afterward, the speed is gradually reduced to zero through a deceleration process, completing one motion cycle.

[0028] In practical use, the Y and Z axes of the motion mechanism are mainly used to adjust the initial position and water depth of the ultrasonic transducer, while the X-axis, as the main direction of motion, is responsible for controlling the relative motion of the ultrasonic transducer. Before conducting acoustic Doppler velocimetry verification, the motion path and speed control need to be planned reasonably. Due to the size limitation of the water tank, the maximum displacement of the ultrasonic transducer's X-axis is 1m. One velocity measurement cycle includes three stages: acceleration, stable velocity measurement, and deceleration. The stable velocity measurement stage is used to collect effective experimental data, while the acceleration and deceleration stages are used to achieve a smooth transition between different speeds, avoiding interference to the echo signal due to transient vibrations or impacts of the mechanical system. The ultrasonic transducer's motion speed adopts a segmented control method. First, the ultrasonic transducer starts from a stationary state and accelerates steadily to the set speed. Then, it maintains a constant speed for a certain period of time. This stage is the effective velocity measurement interval, during which the echo signal has stable Doppler frequency shift characteristics, which can be used to evaluate the accuracy of the velocity measurement algorithm. Afterward, the speed is gradually reduced to zero through a deceleration process, completing one motion cycle.

[0029] In this embodiment, the signal voltage amplitude output by the waveform generator is relatively small and cannot be directly used to drive the ultrasonic transducer. It needs to be amplified by a power amplifier. Therefore, a power amplifier is required between the two. In practical applications, the input impedance of the power amplifier is set to 50Ω to match the output impedance of the arbitrary waveform generator, thereby improving signal transmission efficiency. The driving voltage is the product of the output voltage amplitude of the arbitrary waveform generator and the amplification factor of the power amplifier. For example, if the output signal amplitude of the arbitrary waveform generator is 5Vpp and the amplification gain is 20dB, and the output voltage of the power amplifier is 50Vpp, the output impedance of the power amplifier used in this system is the internal circuit impedance of the instrument connected in series with a 5Ω or 100Ω resistor. The two leads of the transducer are connected to the positive and negative terminals of the power amplifier output, respectively. The transducer leads are not polarity-sensitive. Here, the output resistor is set to be connected in series with a 5Ω resistor, so that the voltage division of the power amplifier output is mainly used to drive the transducer output.

[0030] In this embodiment, the signal acquisition device is a programmable oscilloscope. Its input signal is input through the oscilloscope probe, and the two clips of the oscilloscope probe are respectively connected to the two leads of the ultrasonic transducer. Because the power amplifier output voltage is relatively high and is simultaneously connected to the ultrasonic transducer, the input impedance of the programmable oscilloscope is set to 1MΩ. A high input impedance acquisition method is used, along with an attenuation probe, to prevent high-voltage transmission signals from damaging the acquisition channel. The trigger output channel of the arbitrary waveform generator is connected to the trigger input channel of the programmable oscilloscope to determine the flag indicating that echo acquisition has been activated. The programmable oscilloscope is connected to a switch via Ethernet to receive control commands from the computer and to upload echo signal information to the computer.

[0031] Figure 2 This is a flowchart of an underwater acoustic Doppler velocity measurement accuracy verification method according to an embodiment of the present invention. The flowchart includes the following steps: S1: Real-time acquisition of the moving speed and position information of the motion mechanism, and determination of a reference speed based on the moving speed and position information.

[0032] Optionally, determining a reference speed based on the moving speed and position information specifically includes: receiving the actual speed value and real-time position uploaded in real time by the position feedback unit of each axis of the motion mechanism as input data for the moving speed and position information; when the position information indicates that the ultrasonic transducer is in a preset effective speed measurement range, extracting the radial component along the sound beam direction from the corresponding moving speed through coordinate decomposition, and outputting the reference speed.

[0033] In this embodiment, the experimental environment is a standard acrylic water tank with dimensions of 1.2m × 1m × 1m, and is conducted according to the following... Figure 1 The schematic diagram shows the connection of each device. The ultrasonic transducer is fixed to the three-axis motion module by a clamp. The three-axis motion module is fixed to the water tank by a connector. The three-axis motion module is connected to the module drive controller. The output interface of the arbitrary waveform generator is connected to the input interface of the power amplifier. The output end of the power amplifier is connected to the two leads of the ultrasonic transducer. The trigger output interface of the arbitrary waveform generator is connected to the trigger input interface of the oscilloscope. The two leads of the ultrasonic transducer are connected to the input channel of the oscilloscope through the oscilloscope probe. The switch is connected to the oscilloscope, computer and module drive controller through a network cable. The arbitrary waveform generator is connected to the computer through USB.

[0034] The ultrasonic transducer is fixed to the bottom of the three-axis motion module by a clamp. The water tank is used to provide a stable liquid acoustic propagation environment. Pure water is injected into the water tank, and an appropriate amount of fine river sand is added as suspended particles to simulate a real river environment.

[0035] In this embodiment, during the motion process, the linear module drive controller collects the actual speed and position information of each axis in real time through the position feedback units equipped on each axis, and uploads it to the computer via Ethernet. The computer receives the actual speed values ​​and real-time positions uploaded in real time by the position feedback units of each axis of the motion mechanism as input data for movement speed and position information. When the position, speed, acceleration, and transducer attitude fed back by the motion mechanism all meet the preset stability conditions, the time period is determined as the effective speed measurement interval, and the radial component of the motion speed along the sound beam direction within the speed measurement interval is extracted as the reference speed. The reference speed is determined by the actual motion speed of the X-axis. Based on the relative motion relationship between the motion mechanism and the still water, the relative speed between the ultrasonic transducer and the reflecting interface is used to equivalently characterize the flow velocity or bottom velocity. This reference speed is measurable and traceable, and is used for comparative analysis with the measured speed obtained by the subsequent Doppler velocimetry algorithm.

[0036] S2: Determine the flow measurement working mode according to the target requirements, configure the waveform parameters under the preset engineering constraints, and control the ultrasonic transducer to emit sound waves in the experimental liquid medium based on the waveform parameters.

[0037] Optionally, the step of determining the flow measurement working mode according to the target requirements and configuring waveform parameters under preset engineering constraints includes: using at least one of the following preset engineering constraints as input: velocity range, distance range, layer thickness, and coding form; selecting one of the following as the flow measurement working mode from narrowband velocity measurement mode, pulse coherent velocity measurement mode, and wideband coded velocity measurement mode according to the preset engineering constraints, and determining at least one of the following: carrier frequency, transmission interval, pulse length, symbol width, repetition count, and signal amplitude, and outputting the configuration data of the waveform parameters.

[0038] In this embodiment, based on the actual speed measurement method, the transmission waveform parameters of the driving ultrasonic transducer for the arbitrary waveform generator are configured on the computer, including continuous sine waves, pulse waves, pseudo-random coded signals, or coherent pulse train signals. The output interface of the arbitrary waveform generator is connected to the input interface of the power amplifier, the trigger output mode of the arbitrary waveform generator is configured, and the trigger output channel of the arbitrary waveform generator is connected to the trigger input interface of the oscilloscope.

[0039] Based on the measurement requirements, the input and output impedance and amplification factor of the power amplifier are configured appropriately. The output voltage after amplification is about 60Vpp. The positive and negative terminals of the power amplifier are connected to the two leads of the ultrasonic transducer, respectively.

[0040] In this embodiment, the carrier frequency of the velocity measurement signal is set according to the operating frequency of the ultrasonic transducer. The ultrasonic transducer used in this system operates at a frequency of 1MHz. The flow measurement mode is determined based on verification requirements. Parameters such as the transmission interval, pulse length, symbol width, repetition count, and signal amplitude of the velocity measurement signal are determined under engineering constraints such as velocity range, distance range, layer thickness, and encoding format. After setting the parameters, an output channel for transmitting the signal is set, and the output impedance of this channel is configured to 50Ω to match the subsequent power amplifier. Simultaneously, the trigger output mode of the arbitrary waveform generator is set as a flag to enable echo acquisition on the oscilloscope.

[0041] The arbitrary waveform generator connects to a computer via USB, enabling visualized waveform design and efficient control through the computer's host software. The output signal voltage amplitude of the arbitrary waveform generator is relatively small and cannot be directly used to drive the ultrasonic transducer; it requires amplification by a power amplifier. The power amplifier's input impedance is set to 50Ω to match the output impedance of the arbitrary waveform generator, improving signal transmission efficiency. The driving voltage is the product of the arbitrary waveform generator's output voltage amplitude and the power amplifier's amplification factor. The power amplifier's output is connected to the two leads of the ultrasonic transducer; the voltage divider at the power amplifier's output is primarily used to drive the transducer.

[0042] S3: Control the signal acquisition device to synchronously acquire the echo signal received by the ultrasonic transducer, and receive the echo waveform data obtained by the signal acquisition device after performing analog-to-digital conversion based on the echo signal.

[0043] Optionally, the specific steps include: sending a trigger output configuration command to the waveform generator, causing the waveform generator to generate a synchronous trigger signal from its trigger output channel while outputting the transmission signal, and outputting it to the trigger input terminal of the signal acquisition device; the signal acquisition device uses the arrival time of the synchronous trigger signal as a sampling start flag to perform analog-to-digital conversion on the analog echo electrical signal output by the receiving terminal of the ultrasonic transducer, converting the continuous analog quantity into discrete digital echo waveform data.

[0044] In this embodiment, the two leads of the ultrasonic transducer are connected to the input channel of the oscilloscope through the oscilloscope probe. The echo signal is received by the ultrasonic transducer and sent to the oscilloscope for sampling and display. The oscilloscope is connected to the switch via Ethernet, and the oscilloscope and computer exchange commands and data.

[0045] In this embodiment, the computer sends a trigger output configuration command to the arbitrary waveform generator. Simultaneously with outputting the transmission signal, the arbitrary waveform generator generates a synchronous trigger signal from its trigger output channel and outputs it to the trigger input terminal of the oscilloscope. The oscilloscope uses the arrival time of the synchronous trigger signal as a sampling start flag to perform analog-to-digital conversion on the analog echo signal output from the ultrasonic transducer receiver, converting the continuous analog quantity into discrete digital echo waveform data.

[0046] The oscilloscope is connected to a switch via Ethernet. A computer-written acquisition program accesses the oscilloscope's resources via the VISA (Virtual Instrument Software Architecture) interface and TCP / IP protocol. After the connection is established, an initialization command is sent to configure key acquisition parameters of the oscilloscope, such as channel selection, sampling rate, vertical sensitivity, and time base, ensuring the integrity of the sampled signal. Simultaneously, the input trigger source, trigger level, and trigger mode are set via the SCPI (Standard Commands for Programmable Instruments) protocol. After configuration, the computer waits for the oscilloscope's trigger flag. Upon triggering, an acquisition control command is sent to initiate waveform acquisition. After acquisition, the waveform data stored on the oscilloscope is read via the SCPI protocol and transmitted back to the computer in binary format. This binary data contains a complete array of sampling points. The computer decodes, normalizes, and reconstructs the timing of the waveform data, extracting the echo waveform data of the corresponding channel. The echo waveform data is then processed by a Doppler velocimetry algorithm for velocity calculation. After successfully completing one acquisition cycle, the program jumps back to the oscilloscope trigger flag judgment command, waiting to process the next echo signal. After the computer runs the acquisition program, it will output the current measurement results in a loop and save them in the computer's cache workspace. Start the motion mechanism to begin the test. After the speed measurement experiment is completed, pause the motion mechanism and export the cached measurement data from the workspace.

[0047] S4: Perform Doppler velocity measurement algorithm processing on the echo waveform data to calculate the measured velocity, compare the measured velocity with the reference velocity, and output the velocity measurement accuracy verification result based on the comparison result.

[0048] Optionally, the step of performing Doppler velocimetry algorithm processing on the echo waveform data to calculate the measured speed includes: using the echo waveform data as algorithm input, firstly performing DC offset removal and bandpass filtering preprocessing on the echo waveform data, and outputting preprocessed time-domain echo data; generating one cosine local oscillator signal and one sine local oscillator signal with the same frequency as the transmitted carrier, multiplying the preprocessed time-domain echo data by the cosine local oscillator signal and the sine local oscillator signal respectively to obtain in-phase and quadrature components containing high-frequency components and Doppler frequency components; and using a low-pass filter with a cutoff frequency set between the Doppler frequency offset range and the carrier frequency to perform low-pass filtering on the in-phase and quadrature components respectively. The process involves filtering out high-frequency components, extracting only the in-phase and quadrature components containing Doppler frequency offset information, and orthogonally combining the two components to obtain a complex signal. A complex autocorrelation operation is performed on the complex signal. Two consecutive echo data segments with the same duration and fixed delay are taken, and the complex conjugate product of the two data segments is calculated and its time average is taken to output a complex autocorrelation function value. The phase angle of the complex autocorrelation function value is calculated, and this phase angle is divided by the fixed delay to obtain the Doppler angular frequency, which is then converted into a Doppler frequency shift. The Doppler frequency shift, the speed of sound in the liquid medium, and the carrier frequency are substituted into the Doppler radial velocity relationship to calculate the radial velocity in the direction of sound wave propagation, and the measured velocity is output.

[0049] Optionally, comparing the measured speed with the reference speed and outputting a speed measurement accuracy verification result based on the comparison result includes: within the same effective speed measurement interval, performing difference calculations on the sampled values ​​of the measured speed at multiple times and the sampled values ​​of the reference speed at the corresponding times, calculating the speed deviation and root mean square error between the two, and outputting the calculation result as data to quantitatively characterize the speed measurement accuracy.

[0050] In this embodiment, the Doppler velocimetry algorithm is implemented in the host computer software. The raw signal acquired by the oscilloscope is first preprocessed and denoised by a script program to remove high-frequency noise interference and DC offset, thereby improving signal quality. The preprocessed signal is down-converted to baseband using digital quadrature mixing technology. In-phase and quadrature components are obtained by multiplying the signal with the local oscillator signal (cos, sin). The mixed signal is then filtered by a low-pass filter (such as Butterworth or FIR) to remove high-frequency components, extracting the effective frequency offset signal. The Doppler frequency offset signal is then reconstructed into a complex form. ,in, This represents the reconstructed complex form of the Doppler frequency offset signal; Indicates the in-phase component. Represents the imaginary unit; This represents the quadrature-phase component. The formula preserves amplitude and phase information. Next, complex autocorrelation is calculated on the complex signal, and the phase change is calculated based on the average of the complex conjugate products under time delay and data length. Based on the linear relationship between phase difference and time delay, Doppler estimation is achieved, yielding the flow velocity measurement result. The entire signal processing flow can be flexibly controlled via scripting, making it suitable for rapid verification and testing of velocity measurement algorithms and waveforms.

[0051] In this embodiment, before conducting acoustic Doppler velocities verification, the motion path and speed control need to be planned. Due to the size limitation of the water tank, the maximum displacement of the ultrasonic transducer's X-axis is 1m, and the speed range is 0.001m / s to 0.3m / s. The transducer's motion speed adopts a segmented control method. For example... Figure 3 As shown, the transducer first accelerates steadily from a stationary state to a set speed, and then maintains a constant speed. This stage is the effective speed measurement range, during which the echo signal has stable Doppler frequency shift characteristics, which can be used to evaluate the accuracy of the speed measurement algorithm. Afterwards, the speed is gradually reduced to zero through a deceleration process, completing one motion cycle. By writing a control script program on a computer to set the operating parameters of the motion mechanism, including displacement, velocity, and acceleration, the repeatable and stable operation of the above speed trajectory can be achieved.

[0052] The arbitrary waveform generator and power amplifier outputs are activated. The computer starts the oscilloscope acquisition program and the three-axis motion module control program. The computer acquires data in real time and calculates the flow velocity information. The specific signal processing flow is as follows: The flow velocity depends on the Doppler frequency shift generated by the echo. The formula for calculating the Doppler radial velocity is as follows: In the formula, The magnitude of the radial velocity measured by the transducer. This is the operating frequency of the ultrasonic transducer. The Doppler shift frequency, This is the speed of sound underwater, typically 1500 m / s.

[0053] Frequency offset can be calculated from the echo data. The echo signal carrying the Doppler frequency offset is: In the formula, The amplitude of the echo signal. This is the angular frequency corresponding to the local oscillator signal. The angular frequency corresponding to the Doppler shift frequency. This represents the initial phase angle of the echo signal. The host computer software generates cosine and sine local oscillator signals. , Complex correlation processing requires that the phase difference between the two mixing signals be constant, and the two local oscillator signals be multiplied by the echo digital signal respectively.

[0054] The expression for the mixed signal is: , .

[0055] As can be seen from the above formula, both mixing signals contain an angular frequency of ω. The high-frequency components and angular frequencies are The Doppler frequency components are required. The Doppler offset angular frequency must be determined. It is necessary to filter out the two mixing signals. The high-frequency components are measured in a speed range generally within 10 m / s. According to the Doppler radial velocity formula, the corresponding Doppler frequency deviation is less than 13.3 kHz. A 5th-order Butterworth low-pass filter is designed accordingly, with a -3 dB cutoff frequency of 50 kHz.

[0056] The two signals after filtering are: , The complex correlation operation uses two sets of echo pulses with a duration of T, and the pulse delay is... This involves performing autocorrelation calculations using two consecutive sets of echoes. The two filtered signals are then orthogonally synthesized to form a complex signal. .

[0057] The autocorrelation function is: .

[0058] The Doppler frequency shift expression for the complex correlation algorithm is: .

[0059] After determining the Doppler frequency shift, the Doppler velocity can be calculated using the Doppler radial velocity formula.

[0060] In this embodiment, within the effective speed measurement range, let the first... The Doppler velocity measurement results at each sampling time are as follows: The standard radial velocity is The speed measurement error for: according to Figure 1 As shown, the ultrasonic transducer mainly moves along the X-axis of the motion mechanism, and the angle between the sound beam emitted by the ultrasonic transducer and the vertical direction is [value missing]. The standard radial velocity is: in, The actual speed along the X-axis is fed back by the motion mechanism.

[0061] In this embodiment, within the effective velocity measurement range, the Doppler velocity measurement results are compared point by point with the standard radial flow velocity, and the average error, root mean square error, standard deviation of error, and maximum absolute error are further calculated to evaluate the systematic deviation, overall accuracy, repeatability, and maximum deviation of the Doppler velocity measurement results relative to the standard radial flow velocity.

[0062] The average error is: , used to characterize system bias; The root mean square error is: , used to characterize the overall speed measurement accuracy; The standard deviation of the error is: , used to characterize repeatability; The maximum absolute error is: , is used to characterize the maximum degree of deviation.

[0063] In the broadband coded speed measurement mode, the time-domain waveform, echo correlation, and real-time speed curve results are shown in the image. Figure 4 As shown, in pulse coherent velocimetry mode, the time-domain waveform, echo correlation, and real-time velocity curve results are as follows: Figure 5 As shown, the time-domain waveform can reflect the reception time of the reflected echo, the echo correlation graph can be used to analyze the changing trend of the echo correlation, and the real-time velocity curve result image can be used to observe the real-time changes in velocity magnitude.

[0064] The underwater acoustic Doppler velocimetry accuracy verification system built by this invention can achieve repeatable measurements of displacement, velocity, and motion trajectory under program control. Based on an arbitrary waveform generator, arbitrary waveform signals can be designed, which facilitates, quickly, and flexibly verifies the measurement accuracy and calculation speed of the acoustic Doppler velocimetry waveform and algorithm, thereby providing experimental basis for the optimized design of underwater acoustic Doppler velocimetry algorithms.

[0065] This invention is based on the principle of relative motion. A motion mechanism drives an ultrasonic transducer to move in still water. The relative velocity between the ultrasonic transducer and the reflecting interface (equivalent water body or bottom) effectively represents the flow velocity and bottom velocity, realistically reproducing the sound wave propagation and echo reception process. This allows for more reliable verification of the accuracy of the velocity measurement algorithm in real-world applications. The relative velocity is controlled by a motion module under computer control according to set acceleration, speed, and displacement parameters. The motion controller provides real-time feedback of the actual velocity and position information of each axis, thus obtaining a measurable and traceable reference velocity. The device uses a computer to control the transducer's transmission and reception. An arbitrary waveform generator serves as the signal source, allowing the computer to import the waveform parameters to be tested. A programmable oscilloscope acts as the signal acquisition device, converting the electrical signals received by the transducer into waveform data that the computer can analyze. The echo data is processed in the computer, and the measurement results are output. This device is suitable for testing and verifying various acoustic Doppler velocimetry methods, such as narrowband velocimetry, pulse coherent velocimetry, and broadband coded velocimetry. It features good repeatability, high accuracy, and strong stability. By comparing and analyzing the acoustic Doppler velocimetry results with the reference speed, it enables quantitative evaluation and verification of velocimetry accuracy, providing a convenient and reliable solution for verifying the accuracy of underwater acoustic Doppler velocimetry.

[0066] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for verifying the accuracy of underwater acoustic Doppler velocimeters, characterized in that, The method includes: S1: Real-time acquisition of the moving speed and position information of the motion mechanism, and determination of a reference speed based on the moving speed and position information; S2: Determine the flow measurement working mode according to the target requirements, configure waveform parameters under preset engineering constraints, and control the ultrasonic transducer to emit sound waves in the experimental liquid medium based on the waveform parameters; S3: Control the signal acquisition device to synchronously acquire the echo signal received by the ultrasonic transducer, and receive the echo waveform data obtained by the signal acquisition device after performing analog-to-digital conversion based on the echo signal; S4: Perform Doppler velocity measurement algorithm processing on the echo waveform data to calculate the measured velocity, compare the measured velocity with the reference velocity, and output the velocity measurement accuracy verification result based on the comparison result.

2. The underwater acoustic Doppler velocity measurement accuracy verification method according to claim 1, characterized in that, Determining a reference speed based on the aforementioned movement speed and location information specifically includes: The system receives the actual speed values ​​and real-time positions uploaded in real time by the position feedback units of each axis of the motion mechanism, and uses them as input data for the moving speed and position information. When the position information indicates that the ultrasonic transducer is in a preset effective speed measurement range, the corresponding moving speed is decomposed by coordinate decomposition to extract the radial component along the sound beam direction, and the reference speed is output.

3. The underwater acoustic Doppler velocity measurement accuracy verification method according to claim 1, characterized in that, The process of determining the flow measurement working mode based on target requirements and configuring waveform parameters under preset engineering constraints includes: The preset engineering constraints are input with at least one of the following: speed measurement range, distance measurement range, layer thickness, and encoding form. Based on the preset engineering constraints, one of the following is selected as the flow measurement working mode: narrowband speed measurement mode, pulse coherent speed measurement mode, and wideband coded speed measurement mode. At least one of the following is determined: carrier frequency, transmission interval, pulse length, symbol width, repetition count, and signal amplitude. The configuration data of the waveform parameters is then output.

4. The underwater acoustic Doppler velocity measurement accuracy verification method according to claim 1, characterized in that, Step S3 specifically includes: A trigger output configuration command is sent to the waveform generator, causing the waveform generator to generate a synchronous trigger signal from its trigger output channel while simultaneously outputting the transmission signal, and outputting it to the trigger input terminal of the signal acquisition device; the signal acquisition device uses the arrival time of the synchronous trigger signal as a sampling start flag, and performs analog-to-digital conversion on the analog echo electrical signal output by the receiving terminal of the ultrasonic transducer, converting the continuous analog quantity into discrete digital echo waveform data.

5. The underwater acoustic Doppler velocity measurement accuracy verification method according to claim 1, characterized in that, The process of performing Doppler velocimetry algorithm processing on the echo waveform data to calculate the measured velocity includes: Using the echo waveform data as algorithm input, the echo waveform data is first preprocessed by removing DC offset and bandpass filtering, and the preprocessed time-domain echo data is output. Generate one cosine local oscillator signal and one sine local oscillator signal with the same frequency as the transmitted carrier. Multiply the preprocessed time-domain echo data with the cosine local oscillator signal and the sine local oscillator signal respectively to obtain in-phase and quadrature components containing high-frequency components and Doppler frequency components. A low-pass filter with a cutoff frequency set between the Doppler frequency offset range and the carrier frequency is used to perform low-pass filtering on the in-phase component and the quadrature component respectively, filtering out high-frequency components, extracting the in-phase component and the quadrature component that only contain Doppler frequency offset information, and then orthogonally synthesizing the two components to obtain a complex signal. Perform complex autocorrelation operation on the complex signal, take two consecutive sets of echo data segments with the same duration and fixed time delay, calculate the complex conjugate product of the two data segments and calculate the time mean, and output a complex autocorrelation function value; Calculate the phase angle of the complex autocorrelation function value, divide the phase angle by the fixed time delay to obtain the Doppler angular frequency, and then convert it into the Doppler frequency shift; substitute the Doppler frequency shift, the sound speed in the liquid medium and the carrier frequency into the Doppler radial velocity relationship to calculate the radial velocity in the direction of sound wave propagation, and output the measured velocity.

6. The underwater acoustic Doppler velocity measurement accuracy verification method according to claim 1, characterized in that, The step of comparing the measured speed with the reference speed and outputting a speed measurement accuracy verification result based on the comparison result includes: Within the same effective speed measurement interval, the sampled values ​​of the measured speed at multiple times are compared with the sampled values ​​of the reference speed at the corresponding times. The speed deviation and root mean square error between the two are calculated, and the calculation results are used as data output to quantitatively characterize the speed measurement accuracy.

7. An underwater acoustic Doppler velocimeter accuracy verification system, used to execute the underwater acoustic Doppler velocimeter accuracy verification method as described in any one of claims 1-6, characterized in that, include: A computer for performing the steps of the method as described in any one of claims 1 to 6; The motion mechanism is composed of three linear modules, each axis is equipped with a position feedback unit, which is used to drive the ultrasonic transducer to move in the liquid medium and feed back the actual speed value and real-time position to the computer. An ultrasonic transducer, installed at the end of the motion mechanism, is used to emit sound waves and receive echo signals in the experimental liquid medium. A waveform generator, which is communicatively connected to the computer, is used to receive the waveform parameters and generate a transmission signal and a synchronization trigger signal to drive the ultrasonic transducer. A signal acquisition device, connected to the ultrasonic transducer and the signal source, is used to acquire the echo signal under the control of the synchronous trigger signal, perform analog-to-digital conversion, and output echo waveform data to the computer.

8. The underwater acoustic Doppler velocity measurement accuracy verification system according to claim 7, characterized in that, The motion mechanism is a three-axis linear module assembly, including the X-axis, Y-axis and Z-axis; The X-axis serves as the primary direction of motion, while the Y and Z axes are used to adjust the horizontal position and water depth of the ultrasonic transducer. The motion trajectory of the motion mechanism includes an acceleration segment, a constant speed segment, and a deceleration segment, with the constant speed segment serving as the effective speed measurement range.

9. The underwater acoustic Doppler velocity measurement accuracy verification system according to claim 7, characterized in that, Also includes: A switch is used to connect various communication devices within a local area network (LAN).

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