Ocean current meter high time resolution flow velocity measurement method

Abstract

The invention discloses a high-time-resolution flow velocity measurement method for an ocean current meter, and belongs to the technical field of ocean observation. According to the method, optical scattering signals are collected and converted into electric signals for preprocessing, the preprocessed electric signals are subjected to primary FFT to obtain Doppler frequency fd1, system characteristics of an optical flow meter and fd1 are used for constructing a standard Doppler signal function, the correlation between the standard Doppler signal function and the electric signals collected next time is verified, and if not, a predicted frequency sequence is generated till the correlation reaches the standard; determining an optimal frequency calculation speed value v1; signals are collected again at a fixed time interval, fd2 is obtained through secondary FFT, a new standard Doppler signal function is constructed, and a speed value v2 is obtained through calculation after the correlation is verified; and through continuous frequency sequence recursion verification, FFT is executed again only when a fixed time interval is reached or the correlation is lower than a threshold value, the flow velocity is predicted, corrected and updated at other moments, and high-time-resolution flow velocity data is output.

Description

Technical Field

[0001] This invention belongs to the field of marine observation technology, specifically to the field of high temporal resolution current velocity measurement technology for marine optical current meters, and further to the field of signal processing technology for high-resolution measurement of marine dynamic parameters. Background Technology

[0002] In the field of marine flow velocity measurement, commonly used methods typically rely on suspended particles or bubbles in the fluid. Currently widely used equipment includes acoustic Doppler velocimeters, acoustic Doppler velocimeter profilers, particle image velocimeters, and laser Doppler velocimeters. Among these, acoustic Doppler velocimeters rely on signals reflected from sound wave scatterers to invert flow velocity. Their advantage lies in their ability to operate normally in low-concentration water bodies. However, limited by the principle of acoustic Doppler velocimetry, this equipment requires a long sampling period, and signal processing averaging is necessary, resulting in low temporal resolution and difficulty in accurately capturing rapid dynamic changes in the flow field.

[0003] While laser Doppler velocimeters can achieve high measurement accuracy, their use in marine environments faces significant limitations. The low particle concentration in ocean waters and the attenuation of optical signals during transmission result in insufficient effective sampling rates, failing to meet the demands for continuous and efficient measurements in certain scenarios. Furthermore, existing flow velocity measurement methods share common problems in signal processing, generally relying on frequent Fast Fourier Transform (FFT) calculations to determine frequency drift and flow velocity. This approach not only consumes significant memory but also prolongs computation time, directly limiting the real-time performance of the measurement process and reducing temporal resolution. It also significantly increases the difficulty of implementing edge computing in flow velocity measurement systems, impacting ease of use and making it unsuitable for applications with stringent requirements for computational efficiency and memory usage, such as embedded systems or real-time observation systems. Summary of the Invention

[0004] The purpose of this invention is to provide a high temporal resolution current velocity measurement method for ocean current meters, which solves the problems of low measurement temporal resolution, insufficient effective sampling rate, and high computational and memory consumption caused by frequent fast Fourier transforms in existing optical current meters, thus affecting real-time performance and edge computing implementation.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A high-time-resolution method for measuring ocean current velocity using a current meter includes the following steps:

[0007] Acquire optical scattering signals, convert the optical scattering signals into electrical signals and preprocess them to obtain preprocessed electrical signals;

[0008] Perform an initial Fast Fourier Transform on the preprocessed electrical signal to obtain a signal with a Doppler frequency f. d1 The frequency signal is the center peak value;

[0009] Utilizing the characteristics of the optical current meter system and the Doppler frequency f d1 Construct a standard Doppler signal function, verify the cross-correlation between the standard Doppler signal function and the next acquired and converted electrical signal, determine the optimal frequency based on the correlation results, and calculate the velocity value v1.

[0010] The optical scattering signal is reacquired at fixed time intervals and converted into a corresponding electrical signal. A second fast Fourier transform is then performed on this electrical signal to obtain the Doppler frequency f. d2 The optical current meter system characteristics and the Doppler frequency f are utilized. d2 Construct a new standard Doppler signal function;

[0011] The correlation between the new standard Doppler signal function and the corresponding electrical signal is verified, and the new optimal frequency is determined based on the correlation results, and the velocity value v2 is calculated.

[0012] Correlation is recursively verified using frequency sequences at continuous time intervals. The Fast Fourier Transform is re-executed only when the fixed time interval is reached or the signal correlation drops below a threshold. At other times, flow velocity is updated through prediction and correlation correction, outputting high-temporal-resolution flow velocity data.

[0013] In one possible implementation, when preprocessing the electrical signal converted from the optical scattering signal, filtering or amplification is used to process the electrical signal to obtain the preprocessed electrical signal; the characteristics of the optical current meter system and the Doppler frequency f are then utilized. d1 When constructing the standard Doppler signal function, white noise or Gaussian noise is added to the standard Doppler signal function to form a basic Doppler signal function containing noise.

[0014] In one possible implementation, when verifying the cross-correlation between the standard Doppler signal function and the next acquired and converted electrical signal, if the correlation does not meet the expected standard, based on the Doppler frequency f... d1 According to f d1 A predicted frequency sequence is generated by adding or subtracting a frequency interval of n, and the correlation between the predicted frequency sequence and the electrical signal is verified step by step until the correlation reaches the expected standard to determine the optimal frequency, where n is a positive integer.

[0015] In one possible implementation, when verifying the correlation between the new standard Doppler signal function and the corresponding electrical signal, if the correlation does not meet the expected standard, based on the Doppler frequency f... d2 According to f d2 A new predicted frequency sequence is generated by adding or subtracting a frequency interval of n. The correlation between the new predicted frequency sequence and the electrical signal is verified step by step until the correlation reaches the expected standard to determine the new optimal frequency, where n is a positive integer.

[0016] In one possible implementation, the characteristics of the optical current meter system are utilized in conjunction with the Doppler frequency f. d1 When constructing the standard Doppler signal function, the amplitude, the number of fringes of the measurement volume, the transit time of the particle through the measurement volume, the particle arrival time, and any time the particle passes through the fringes are called, combined with the Doppler frequency f. d1 The standard Doppler signal function is constructed.

[0017] In one possible implementation, the characteristics of the optical current meter system are utilized in conjunction with the Doppler frequency f. d2 When constructing a new standard Doppler signal function, the amplitude, the number of fringes in the measurement volume, the transit time of the particle through the measurement volume, the particle arrival time, and any time the particle passes through the fringes are called, combined with the Doppler frequency f. d2 The new standard Doppler signal function is then constructed.

[0018] In one possible implementation, when calculating the speed value v1 or speed value v2, the corresponding speed value v1 or speed value v2 is calculated respectively by using the determined optimal frequency or the new optimal frequency, based on the unique correspondence between speed and frequency.

[0019] In one possible implementation, when re-acquiring the optical scattering signal at fixed time intervals, frequency prediction and velocity calculation are continuously performed at unit time intervals within a preset time range, and the sampling rate is set to the reciprocal of the unit time. When verifying the correlation between the standard Doppler signal function or the new standard Doppler signal function and the corresponding electrical signal, a correlation function is used to describe the degree of correlation between the values ​​of the two signals at different times, and the result of the correlation function is used to determine whether the correlation meets the expected standard.

[0020] In one possible implementation, after outputting high temporal resolution flow velocity data, the flow velocity data is applied to scenarios such as ocean flow velocity and turbulence monitoring, underwater robot attitude and velocity perception, estuary and lake and laboratory flow field research, or high-speed particle or bubble tracking and measurement.

[0021] In one possible implementation, the optical scattering signal is acquired in a marine environment by an ocean optical current meter, which includes a laser Doppler velocimeter.

[0022] Compared with existing technologies, the advantages of this invention are as follows: By introducing a prediction mechanism based on the correlation verification of the standard Doppler signal function, this invention re-executes the Fast Fourier Transform (FFT) only when a fixed time interval is reached or the signal correlation drops below a threshold. At other times, flow velocity updates are achieved through prediction and correlation correction, significantly reducing the number of FFT calls. This directly reduces the computational load and memory consumption in the signal processing process, making the flow velocity measurement system more easily adaptable to embedded systems or real-time observation systems. It also provides favorable conditions for the implementation of edge computing, solving the problems of poor real-time performance and high difficulty in edge computing caused by frequent FFT execution in traditional methods.

[0023] This invention employs a two-stage correlation verification process—initial frequency sampling and fixed-time interval sampling—to continuously predict frequency and calculate velocity at unit time intervals, eliminating the need for a full Fast Fourier Transform (FFT) for each sampling. This significantly improves the temporal resolution of flow velocity measurement, enabling higher frequency flow velocity output under the same hardware conditions. It enhances the system's ability to capture dynamic changes in ocean current fields, overcoming the shortcomings of traditional acoustic or optical current meters, which suffer from low temporal resolution and difficulty in reflecting rapid changes in the flow field.

[0024] The standard Doppler signal function constructed in this invention can effectively verify the correlation of the acquired signals. Even in marine environments with low particle concentrations, it can accurately obtain frequency information and calculate current velocity through correlation recursion verification, without relying on high-sampling-rate optical detectors. This broadens the applicable scenarios of marine optical current meters, ensuring reliable velocity measurement even in low-particle-density marine environments, and solves the problem of insufficient effective sampling rate of traditional laser Doppler velocimeters in low-particle-density environments. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a standard Doppler signal function and frequency information diagram according to an embodiment of the present invention, wherein, Figure 1 (a) is the time-domain plot of the standard Doppler signal function. Figure 1 (b) is the frequency domain diagram of the standard Doppler signal function;

[0027] Figure 2 This is a diagram showing the basic Doppler signal function and frequency information of an embodiment of the present invention. The basic Doppler signal function is a Doppler signal function with non-zero noise. Figure 2 (a) is the time-domain plot of the basic Doppler signal function; Figure 2 (b) is the frequency domain plot of the basic Doppler signal function.

[0028] Figure 3 This is a correlation information and frequency information graph of the basic Doppler signal function and the standard Doppler signal function after correlation verification in an embodiment of the present invention. The basic Doppler signal function is a Doppler signal function with non-zero noise. Figure 3 (a) is a correlation diagram between the basic Doppler signal function and the standard Doppler signal function; Figure 3 (b) Frequency domain plot of the function after relevant verification.

[0029] Appendix Figure 4 This is a schematic diagram of the high temporal resolution processing flow of an embodiment of the present invention. The flow includes two main processes: initial frequency sampling and correlation calculation, and fixed time interval sampling and correlation verification. Detailed Implementation

[0030] 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 this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0031] Example:

[0032] It should be noted that the terms "comprising" and "having" and any variations thereof in the embodiments of the present invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0033] The high time resolution current velocity measurement method for ocean current meters provided in this embodiment of the invention includes the following steps:

[0034] Step 101: Acquire optical scattering signals, convert the optical scattering signals into electrical signals and preprocess them to obtain preprocessed electrical signals.

[0035] The optical scattering signal is collected by an ocean optical current meter in the marine environment, and the ocean optical current meter includes a laser Doppler velocimeter.

[0036] Step 102: Perform an initial fast Fourier transform on the preprocessed electrical signal to obtain the signal at the Doppler frequency f. d1 The frequency signal is the center peak value.

[0037] In the process of preprocessing the electrical signal converted from the optical scattering signal, the electrical signal is processed by filtering or amplification to obtain the preprocessed electrical signal.

[0038] Step 103: Utilize the characteristics of the optical current meter system and the Doppler frequency f d1 Construct a basic Doppler signal function, verify the cross-correlation between the basic Doppler signal function and the electrical signal acquired and converted in the next step, determine the optimal frequency based on the correlation results, and calculate the velocity value v1.

[0039] Among them, the characteristics of the optical current meter system and the Doppler frequency f are utilized. d1 When constructing the standard Doppler signal function, white noise or Gaussian noise is added to the standard Doppler signal function to form a basic Doppler signal function containing noise.

[0040] Specifically, when verifying the cross-correlation between the standard Doppler signal function and the next acquired and converted electrical signal, if the correlation does not meet the expected standard, based on the Doppler frequency f... d1 According to f d1 A predicted frequency sequence is generated by adding or subtracting a frequency interval of n, and the correlation between the predicted frequency sequence and the electrical signal is verified step by step until the correlation reaches the expected standard to determine the optimal frequency, where n is a positive integer.

[0041] Among them, the characteristics of the optical current meter system and the Doppler frequency f are utilized. d1 When constructing the standard Doppler signal function, the amplitude, the number of fringes of the measurement volume, the transit time of the particle through the measurement volume, the particle arrival time, and any time the particle passes through the fringes are called, combined with the Doppler frequency f. d1 The standard Doppler signal function is constructed.

[0042] Step 104: Reacquire the optical scattering signal at fixed time intervals and convert it into the corresponding electrical signal. Perform a second Fast Fourier Transform on the electrical signal to obtain the Doppler frequency f. d2 The optical current meter system characteristics and the Doppler frequency f are utilized. d2 Construct a new standard Doppler signal function.

[0043] Among them, the characteristics of the optical current meter system and the Doppler frequency f are utilized. d2When constructing a new standard Doppler signal function, the amplitude, the number of fringes in the measurement volume, the transit time of the particle through the measurement volume, the particle arrival time, and any time the particle passes through the fringes are called, combined with the Doppler frequency f. d2 The new standard Doppler signal function is then constructed.

[0044] When the optical scattering signal is reacquired at fixed time intervals, frequency prediction and velocity calculation are continuously performed at unit time intervals within a preset time range, and the sampling rate is set to the reciprocal of the unit time.

[0045] Step 105: Verify the correlation between the new standard Doppler signal function and the corresponding electrical signal, determine the new optimal frequency based on the correlation results, and calculate the velocity value v2.

[0046] Specifically, when verifying the correlation between the new standard Doppler signal function and the corresponding electrical signal, if the correlation does not meet the expected standard, based on the Doppler frequency f... d2 According to f d2 A new predicted frequency sequence is generated by adding or subtracting a frequency interval of n. The correlation between the new predicted frequency sequence and the electrical signal is verified step by step until the correlation reaches the expected standard to determine the new optimal frequency, where n is a positive integer.

[0047] When calculating the speed value v1 or speed value v2, based on the unique correspondence between speed and frequency, the corresponding speed value v1 or speed value v2 is calculated by the determined optimal frequency or the new optimal frequency.

[0048] When verifying the correlation between the standard Doppler signal function or the new standard Doppler signal function and the corresponding electrical signal, a correlation function is used to describe the degree of correlation between the values ​​of the two signals at different times, and the result of the correlation function is used to determine whether the correlation meets the expected standard.

[0049] Step 106: Perform correlation recursion verification using frequency sequences of continuous time intervals. Only when the fixed time interval is reached or the signal correlation drops below the threshold will the fast Fourier transform be re-executed. At other times, flow velocity will be updated through prediction and correlation correction, and high time resolution flow velocity data will be output.

[0050] Among them, after outputting high temporal resolution flow velocity data, the flow velocity data is applied to ocean flow velocity and turbulence monitoring, underwater robot attitude and velocity perception, estuary and lake and laboratory flow field research, or high-speed particle or bubble tracking and measurement scenarios.

[0051] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0052] The high time resolution current velocity measurement method for ocean current meters provided in this embodiment of the invention includes:

[0053] Procedure 1: Initial frequency sampling and correlation calculation:

[0054] First, an optical ocean current meter is tested. During this process, optical scattering signals are collected. These optical scattering signals are converted into electrical signals by a photodetector. The acquisition system then collects these electrical signals and performs preliminary data processing. Common processing methods include simple filtering and amplification. Other types of data processing can also be performed according to actual needs. The processing methods are not limited to the filtering and amplification mentioned above.

[0055] Next, an initial FFT transformation is performed on the processed electrical signal to obtain the signal at the Doppler frequency f. d1 The frequency signal is the center peak value. Then, the characteristics of the optical current meter system and the initially obtained Doppler frequency f are used... d1 The basic Doppler signal function is constructed. When constructing this function, white noise, Gaussian noise, or other noise signals not mentioned in this invention can be added to the noise component. This Doppler signal function can be denoted as y1, and its specific expression is as follows:

[0056] y1=id×exp(-(2×2^(0.5)×(t-t0) / tao)^2)+ia×exp(-(2×2^(0.5)×(t-t0) / tao)^2)×cos(2×π×fd1×(t-t0))+noise;

[0057] Where id and ia are amplitudes; fs is the sampling rate; Nf is the number of fringes in the measurement volume; f d1 The Doppler frequency reflects the particle velocity; tao is the finite transit time of the particle through the measuring volume, which can be expressed using Nf / f. d1 The calculation shows that t is any time it takes for the particle to pass through the stripe; t0 is the time when the particle arrives; and noise is any noise signal that can be set. If it is a standard Doppler signal function, noise can be set to 0.

[0058] After constructing the basic Doppler signal function, the constructed standard Doppler signal function is used as the signal correlation function to verify the cross-correlation and stability between this function and the next acquired signal. The signal correlation function used for verification is R(s,t)=E(X(s)*Y(t)), which describes the degree of correlation between the values ​​of random signals X(s) and Y(t) at any two different times s and t. If the correlation is found to fail to meet the expected standard after verification, a predicted frequency sequence is generated based on this, and the sequence has the form f. d1±n×Δf, where n takes the value of a positive integer such as 1, 2, or 3. The correlation between the predicted frequency sequence and the next acquired signal is then progressively verified until the correlation reaches the expected standard. When the correlation between the predicted frequency and the signal reaches its optimal state, the optimal frequency f is output. d1 ±n×Δf, and calculate the velocity value v1 based on this frequency. In the subsequent certain time T, the operation is carried out in the above frequency prediction manner at unit time intervals of Δt, so as to continuously obtain the velocity value. At this time, the sampling rate of the measurement is 1 / Δt.

[0059] Process 2: Fixed time interval sampling and correlation verification

[0060] The optical signal is reacquired at time intervals T, and a second FFT transformation is performed on the reacquired optical signal to obtain the Doppler frequency f. d2 Then, using the obtained Doppler frequency f d2 Construct the basic Doppler signal function, that is, construct a new correlation function y2. The specific expression of y2 is y2=id×exp(-(2×2^(0.5)×(t-t0) / tao)^2)+ia×exp(-(2×2^(0.5)×(t-t0) / tao)^2)×cos(2×π×f d2 ×(t-t0))+noise.

[0061] After construction, the correlation function y2 is verified with the signal acquired at the previous time step. Simultaneously, the constructed standard Doppler signal function is used as the signal correlation function to verify its cross-correlation and stability with the next acquired signal. If the verification results show that the correlation fails to meet the expected standard, a new predicted frequency sequence is generated based on this, with the form f. d2 ±n×Δf, where n takes the value of a positive integer such as 1, 2, or 3. The correlation between this new predicted frequency sequence and the corresponding acquired signal is then progressively verified until the correlation reaches the expected standard. The optimal frequency is then determined based on the correlation. After determining the optimal frequency, the corresponding frequency f is output. d2 ±n×Δf, and calculate the velocity value v2 based on this frequency.

[0062] Finally, the velocity calculation and update steps are performed. This is based on the frequency sequence f obtained over continuous time intervals. d1 f d2 f d3Correlation recursion verification is performed. During the verification process, the FFT transformation is only re-executed when the set time interval T is reached or the signal correlation drops below the threshold. At other times, the flow rate is updated through frequency prediction and correlation correction. This method can significantly reduce the number of FFT transformations, thereby reducing the system's memory usage and improving the temporal resolution of flow rate measurement.

[0063] In summary, this invention establishes a current velocity prediction mechanism and model based on correlation verification by utilizing the temporal correlation of signals. Between adjacent time points, correlation verification replaces the complete FFT calculation, thereby achieving high-frequency updates of current velocity. This reduces the number of FFT operations, improving computational efficiency, as the FFT transformation is only performed when correlation fails, significantly reducing computational load and memory consumption. This makes the method suitable for embedded systems, systems requiring edge computing, or real-time observation systems, and can also be applied to other related systems not mentioned above. Through the fast correlation verification mechanism, this invention also improves the temporal resolution and real-time performance of current velocity measurement, achieving higher temporal resolution current velocity output under the same hardware conditions, thus enhancing the ability to capture dynamic changes in ocean current fields. Furthermore, this method does not rely on high-sampling-rate optical detectors, making it suitable for optical velocimetry in low-particle-density marine environments, enabling reliable current velocity measurement in these environments.

[0064] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to specific data.

[0065] The following describes the flow velocity measurement method of the present invention in detail using an actual ocean optical current meter measurement process as an example. For ease of subsequent description, this embodiment uses LDV as an abbreviation for laser Doppler current meter, and the signal collected by this device is called ordinary LDV signal (ordinary Doppler signal). The Doppler signals constructed based on the frequency signal obtained from the initial FFT are respectively called basic LDV signal (basic Doppler signal) and standard LDV signal (standard Doppler signal).

[0066] The high time resolution current velocity measurement method for ocean current meters provided in this embodiment of the invention includes:

[0067] First, the measurement system acquires the scattered light signal at a sampling frequency fs, performs an initial FFT transform on the scattered light signal, and obtains the main frequency f through the transform. d1 In a practical application, the system used a sampling frequency fs of 12.5MHz to acquire signals, and the initial set main frequency f... d1 It is 10000Hz.

[0068] Next, utilizing the characteristics of the optical current meter system and the initially obtained frequency fd1 Construct the basic Doppler signal function, denoted as y1, with the specific expression: y1=id×exp(-(2×2^(0.5)×(t-t0) / tao)^2)+ia×exp(-(2×2^(0.5)×(t-t0) / tao)^2)×cos(2×π×f d1 ×(t-t0))+noise.

[0069] In this embodiment, id=ia=100; the number of stripes on the measuring body Nf=70; tao=Nf / f d1 =7 / 1000; t0 is the time when the particle arrives, denoted as the time zero when the particle's center point reaches the midpoint of the stripe; t is any time it takes for the particle to pass through the stripe, with intervals of 1 / fs, denoted as -200 / f d1 Up to 200 / f d1 between.

[0070] When constructing the standard Doppler signal function, noise is set to 0. The expression for the standard Doppler signal function is then: y1=id×exp(-(2×2^(0.5)×(t-t0) / tao)^2)+ia×exp(-(2×2^(0.5)×(t-t0) / tao)^2)×cos(2×π×f d1 ×(t-t0)),

[0071] The time-domain plot of the function is as follows Figure 1 As shown in (a), after performing an FFT transform on the standard Doppler signal function, its frequency domain diagram can be obtained, as shown in [image missing]. Figure 1 As shown in (b).

[0072] When constructing the basic Doppler signal function, noise is set as a random noise signal with an amplitude 10 times that of the LDV signal, i.e., the noise signal function amplitude is set to 1000. The expression for the basic Doppler signal function is then y1=id×exp(-(2×2^(0.5)×(t-t0) / tao)^2)+ia×exp(-(2×2^(0.5)×(t-t0) / tao)^2)×cos(2×π×f d1 ×(t-t0))+1000*randn,

[0073] Where randn represents the random noise signal. This basic Doppler signal function corresponds to the ordinary LDV signal acquired in actual use, which is also the acquired signal that needs to be processed subsequently. The basic Doppler signal function and frequency information constructed in this invention are as follows: Figure 2 As shown, the time-domain plot of the basic Doppler signal function is as follows. Figure 2 (a) The frequency domain diagram is Figure 2(b).

[0074] Subsequently, the constructed standard Doppler signal function was used as the signal correlation function to verify its correlation with the basic Doppler signal function. This verification process confirms the cross-correlation and stability between the acquired signal and the standard Doppler signal function in practical applications. The signal correlation function used for verification is R(s,t)=E(X(s)*Y(t)), which describes the degree of correlation between the values ​​of random signals X(s) and Y(t) at any two different times s and t.

[0075] Correlation information and frequency information, such as Figure 3 As shown, where Figure 3 (a) shows the correlation between the basic Doppler signal function and the standard Doppler signal function. It can be observed that the signal amplitude is strongest when there is no data offset, corresponding to the state where the particle center point reaches the midpoint of the fringe without any offset. After performing an FFT transform on the correlated signal, the frequency domain plot of the function after correlation verification is obtained, as shown below. Figure 3 As shown in (b), the peak frequency in the figure can well reflect the initial main frequency f. d1 In this embodiment, the initial frequency f d1 The frequency was 10000Hz. After correlation verification, the demodulated frequency information was 9987.49, with an overall relative error of 0.125%. This demonstrates that the standard Doppler signal function constructed using the initially obtained frequency fd1 as the signal correlation function, after correlation verification, can effectively reflect the frequency characteristics of the measured signal, i.e., the ordinary Doppler signal function.

[0076] Next, the constructed standard Doppler signal function is used as the signal correlation function to predict the frequency distribution at the next moment. First, a new signal is acquired, and then the cross-correlation between the acquired signal and the standard Doppler signal function is verified. If the signal correlation meets the expected standard, the initial dominant frequency f is output. d1 The frequency characteristic information of the signal under test is used as the basis for calculating the velocity value of the signal under test, and then the velocity value is output. If the correlation fails to meet the expected standard, a predicted frequency sequence is generated based on this, and the sequence is in the form of f. d1 ±n×Δf, where n is a positive integer such as 1, 2, 3, etc., and Δf can be subdivided according to actual needs. In this embodiment, based on error calculation and actual requirements, Δf is set to 12.5Hz. Then, the correlation between the predicted frequency sequence and the acquired signal is gradually verified until the correlation reaches the expected standard. When the correlation between the predicted frequency and the signal is at its optimal state, the optimal frequency, f, is output. d1±n×Δf, and calculate the velocity value v1 based on this frequency. It should be noted that the velocity vi (i takes the value 1, 2, 3, etc.) is related to the frequency, and the correspondence between the two is unique.

[0077] In this embodiment, the time T is set to 10 minutes, and the operation is carried out in units of time Δt = 1 ms, following the frequency prediction method described above, continuously obtaining velocity values. The sampling rate is 1000 Hz. Optical signals are re-acquired in units of time interval T. If the acquired signal has weak correlation with the standard Doppler signal function, a second FFT transformation is performed on the re-acquired optical signal to obtain the Doppler frequency f. d2 .

[0078] Using the obtained frequency f d2 Construct the basic Doppler signal function, that is, construct a new correlation function y2. The specific expression of y2 is y2=idexp(-(22^(0.5)(t-t0) / tao)^2)+iaexp(-(22^(0.5)(t-t0) / tao)^2)cos(2πf d2 (t-t0))+noise. In this embodiment, id=ia=100 is still set; the number of stripes of the measuring body Nf=70; tao=Nf / f d1 =7 / 1000; t0 is the zero point when the particle center reaches the midpoint of the stripe; t=1 / fs, ranging from -200 / f d2 Up to 200 / f d2 between.

[0079] When noise is set to 0, y2 is the standard Doppler signal function, and its expression is y2=id×exp(-(2×2^(0.5)×(t-t0) / tao)^2)+ia×exp(-(2×2^(0.5)×(t-t0) / tao)^2)×cos(2×π×f d2 ×(t-t0)),

[0080] The time-domain plot of this function and Figure 1 (a) has a similar form, but in the frequency domain plot of the standard Doppler signal function obtained after performing an FFT transform, the frequency becomes f. d2 Using the constructed standard Doppler signal function as the signal correlation function, the correlation between the signal acquired within the current time interval T and the signal acquired in the next time interval is verified. The results of this correlation verification are consistent with... Figure 3 (a) is similar in form; if the correlation fails to meet the expected criteria, a new predicted frequency sequence is generated based on this, which has the form f. d2±n×Δf, where n is a positive integer such as 1, 2, or 3. In this embodiment, Δf is also set to 12.5Hz. The correlation between the new predicted frequency sequence and the corresponding acquired signal is verified step by step until the correlation reaches the expected standard. When the correlation between the predicted frequency and the signal is optimal, the optimal frequency, f, is output. d2 ±n×Δf, and calculate the velocity value v2 based on this frequency.

[0081] The next step is to solve for and update the velocity, using the frequency sequence f obtained over continuous time intervals. d1 f d2 f d3 Correlation recursion verification is performed. During the verification process, the FFT transformation is only re-executed when a set time interval T is reached or the signal correlation drops below a threshold. At other times, flow rate is updated through frequency prediction and correlation correction. This method significantly reduces the number of FFT transformations, thereby reducing system memory usage and improving the temporal resolution of flow rate measurement.

[0082] The main process steps of the flow velocity measurement in this invention are as follows: Figure 4 As shown, the process includes two steps: initial frequency sampling and correlation calculation (Step 1) and fixed time interval sampling and correlation verification (Step 2). After completing these two steps, the velocity is finally calculated and the output is updated. By calculating the rate of change of flow velocity using continuous time series, a high-time-resolution flow velocity curve can be generated. Since the probability of abrupt changes in flow velocity over time is very small, practical verification shows that this method can improve the time resolution by about 100 times while reducing the number of FFT calls by more than 50%, significantly improving the dynamic response capability of the optical current meter.

[0083] This invention has a wide range of applications and can be widely used in many fields, including ocean current and turbulence monitoring, underwater robot attitude and velocity sensing, estuarine and lake flow field research and laboratory flow field research, and high-speed particle or bubble tracking and measurement.

[0084] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0085] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-temporal-resolution current velocity measurement method for ocean current meters, characterized in that, Includes the following steps: Acquire optical scattering signals, convert the optical scattering signals into electrical signals and preprocess them to obtain preprocessed electrical signals; Perform an initial Fast Fourier Transform on the preprocessed electrical signal to obtain a signal with a Doppler frequency f. d1 The frequency signal is the center peak value; Utilizing the characteristics of the optical current meter system and the Doppler frequency f d1 Construct a standard Doppler signal function, verify the cross-correlation between the standard Doppler signal function and the next acquired and converted electrical signal, determine the optimal frequency based on the correlation results, and calculate the velocity value v1. The optical scattering signal is reacquired at fixed time intervals and converted into a corresponding electrical signal. A second fast Fourier transform is then performed on this electrical signal to obtain the Doppler frequency f. d2 The optical current meter system characteristics and the Doppler frequency f are utilized. d2 Construct a new standard Doppler signal function; The correlation between the new standard Doppler signal function and the corresponding electrical signal is verified, and the new optimal frequency is determined based on the correlation results, and the velocity value v2 is calculated. Correlation is recursively verified using frequency sequences at continuous time intervals. The Fast Fourier Transform is re-executed only when the fixed time interval is reached or the signal correlation drops below a threshold. At other times, flow velocity is updated through prediction and correlation correction, outputting high-temporal-resolution flow velocity data.

2. The high temporal resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, When preprocessing the electrical signal converted from the optical scattering signal, filtering or amplification is used to process the electrical signal to obtain the preprocessed electrical signal; the characteristics of the optical current meter system and the Doppler frequency f are then utilized. d1 When constructing the standard Doppler signal function, white noise or Gaussian noise is added to the standard Doppler signal function to form a basic Doppler signal function containing noise.

3. The high time resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, When verifying the cross-correlation between the standard Doppler signal function and the next acquired and converted electrical signal, if the correlation does not meet the expected standard, based on the Doppler frequency f... d1 According to f d1 A predicted frequency sequence is generated by adding or subtracting a frequency interval of n, and the correlation between the predicted frequency sequence and the electrical signal is verified step by step until the correlation reaches the expected standard to determine the optimal frequency, where n is a positive integer.

4. The high time resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, When verifying the correlation between the new standard Doppler signal function and the corresponding electrical signal, if the correlation does not meet the expected standard, based on the Doppler frequency f... d2 According to f d2 A new predicted frequency sequence is generated by adding or subtracting a frequency interval of n. The correlation between the new predicted frequency sequence and the electrical signal is verified step by step until the correlation reaches the expected standard to determine the new optimal frequency, where n is a positive integer.

5. The high time resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, Utilizing the characteristics of the optical current meter system and the Doppler frequency f d1 When constructing the standard Doppler signal function, the amplitude, the number of fringes of the measurement volume, the transit time of the particle through the measurement volume, the particle arrival time, and any time the particle passes through the fringes are called, combined with the Doppler frequency f. d1 The standard Doppler signal function is constructed.

6. The high time resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, Utilizing the characteristics of the optical current meter system and the Doppler frequency f d2 When constructing a new standard Doppler signal function, the amplitude, the number of fringes in the measurement volume, the transit time of the particle through the measurement volume, the particle arrival time, and any time the particle passes through the fringes are called, combined with the Doppler frequency f. d2 The new standard Doppler signal function is then constructed.

7. The high time resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, When calculating the velocity value v1 or the velocity value v2, based on the unique correspondence between velocity and frequency, the corresponding velocity value v1 or the velocity value v2 is calculated by the determined optimal frequency or the new optimal frequency, respectively.

8. The high time resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, When re-acquiring optical scattering signals at fixed time intervals, frequency prediction and velocity calculation are continuously performed at unit time intervals within a preset time range, and the sampling rate is set to the reciprocal of the unit time. When verifying the correlation between the standard Doppler signal function or the new basic Doppler signal function and the corresponding electrical signal, a correlation function is used to describe the degree of correlation between the values ​​of the two signals at different times, and the result of the correlation function is used to determine whether the correlation meets the expected standard.

9. The high time resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, After outputting high temporal resolution flow velocity data, the flow velocity data is applied to ocean flow velocity and turbulence monitoring, underwater robot attitude and velocity perception, estuary and lake and laboratory flow field research, or high-speed particle or bubble tracking and measurement scenarios.

10. The high temporal resolution current velocity measurement method for ocean current meters according to claim 1, characterized in that, The optical scattering signal is collected in the marine environment by an ocean optical current meter, which includes a laser Doppler velocimeter.

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