A phase-difference-based underwater acoustic tomography method for measuring flow

Abstract

The application discloses an underwater acoustic tomography flow measurement method based on phase difference. The method comprises the following steps: collecting bidirectional propagation acoustic signals of a water area to be measured, and extracting the propagation time and phase change of the bidirectional propagation acoustic signals; establishing the relationship among the phase change of the bidirectional propagation acoustic signals, the propagation time of the bidirectional propagation acoustic signals, the average flow velocity of the water area to be measured and the average sound velocity of the water area to be measured through wave acoustic, and inversely deriving the average flow velocity of the water area to be measured and the average sound velocity of the water area to be measured through the relationship. The purpose of the application is to provide an underwater acoustic tomography flow measurement method based on phase difference, which is more suitable for use in acoustic tomography technology with lower frequency. The uncertainty in flow velocity measurement can be reduced by simultaneously considering the time difference and the phase difference, and the automatic and high-precision flow measurement technology is promoted. The application is suitable for flow velocity measurement of water areas such as river channels, estuaries and bay areas.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic measurement technology, and in particular to an underwater acoustic tomography method based on phase difference. Background Technology

[0002] Since Munk and Wunsch formally proposed "marine acoustic tomography" in 1979, the technology has continued to develop and has been tested and applied in coastal areas, rivers, and estuaries. Compared with traditional current measurement techniques, acoustic tomography has advantages such as high precision, large-scale measurement, and high degree of automation, and has high application prospects and research value.

[0003] Current acoustic tomography techniques mostly invert water flow velocity by measuring the time difference between the propagation of acoustic signals upstream and downstream. For example, Chinese patent document CN116558585A discloses an acoustic tomography flow measurement technique based on the travel time difference of acoustic signals. This method has high accuracy for high flow velocities, but due to the theoretical limit of accuracy in time delay estimation after matched filtering, the error is relatively large for low flow velocities (such as flow velocities below 0.1 m / s). Therefore, there is a need to study an acoustic tomography flow measurement theory and method more suitable for low flow velocity measurements.

[0004] Wave acoustics theory is more suitable for analyzing lower-frequency sound waves than X-ray acoustics theory. Time-of-flight acoustic tomography (TOC) flow measurement is derived from ultrasonic X-ray acoustics theory, which provides an approximate solution to the wave equation under high-frequency conditions and is suitable for analyzing high-frequency sound waves. However, when using lower-frequency sound waves in TOC flow measurement, errors are inevitable. Therefore, it is necessary to research a flow measurement theory and method more suitable for low-frequency acoustic tomography.

[0005] In conclusion, it is essential to invent an acoustic tomography technique that is more suitable for low flow rates and low-frequency signals and has higher accuracy. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose an underwater acoustic tomography method based on phase difference, which is more suitable for use in acoustic tomography at lower frequencies. Simultaneously considering time difference and phase difference can reduce the uncertainty in flow velocity measurement, promoting automation and high-precision flow measurement technology. This invention is applicable to flow velocity measurement in waterways, estuaries, bays, and other water bodies.

[0007] According to one aspect of the present invention, an underwater acoustic tomography method based on phase difference is provided, comprising:

[0008] Collect bidirectional acoustic signals from the water body to be measured, extract the propagation time and phase changes of the bidirectional acoustic signals, and note the phase change here. satisfy

[0009] By establishing the relationship between the phase change of the bidirectional propagating sound signal, the propagation time of the bidirectional propagating sound signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test through wave acoustics, the average flow velocity and the average sound velocity of the water body under test can be obtained by inversion through this relationship.

[0010] In the above technical solution, the novel underwater acoustic tomography theory based on phase difference starts from the theory of wave acoustics and takes into account the influence of the two-way propagation time of the acoustic signal and the phase difference of the two-way propagation on the velocity inversion. To a certain extent, it makes up for the error of relying solely on time delay estimation after matched filtering, and improves the accuracy of low-frequency acoustic tomography flow measurement and acoustic tomography low velocity flow measurement technology.

[0011] In some embodiments, the propagation time and phase changes of the bidirectional propagating acoustic signal are extracted, specifically:

[0012] The collected bidirectional propagating acoustic signal is passed through a matched filter to extract the propagation time of the bidirectional propagating acoustic signal, and the phase change of the bidirectional propagating acoustic signal is calculated using the FFT cross-spectral method.

[0013] In the above technical solution, since the Fourier transform is a mapping relationship between the time domain and the frequency domain, the FFT cross-spectral method theoretically has no phase difference measurement error.

[0014] In some embodiments, wave acoustics is used to establish the relationship between the phase change of the bidirectional propagating sound signal, the propagation time of the bidirectional propagating sound signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test. This relationship is then used to invert the average flow velocity and the average sound velocity of the water body under test.

[0015] Specifically:

[0016] Establish acoustic expressions for the transmission and reception positions based on the transmission and reception positions of bidirectional propagating acoustic signals;

[0017] Define the propagation direction of a bidirectional acoustic signal, and derive the phase change of the bidirectional acoustic signal based on wave acoustic theory. The propagation time t of the two-way propagating sound signal + t - The acoustic relationship between the average flow velocity u and the average sound velocity C0 of the water body to be measured;

[0018] The average flow velocity u and the average sound velocity C0 of the water body under test are obtained by simultaneously solving the acoustic relations.

[0019] In the above technical solution, the purpose of this setting is not only to take advantage of the fact that wave acoustics is more suitable for low-frequency sound waves than X-ray acoustics, but also to take into account the time difference term and the phase difference term, which to a certain extent makes up for the error of time delay estimation after relying solely on matched filtering. Therefore, it is more suitable for low-frequency acoustic tomography flow measurement and to improve the accuracy of acoustic tomography low-velocity flow measurement technology.

[0020] In some embodiments, the bidirectional propagating acoustic signal is a broadband chirp signal.

[0021] The purpose of this configuration in the above technical solution is that chirp signals have strong correlation characteristics, and the FFT cross-spectral method has high applicability to chirp signals.

[0022] In some embodiments, the propagation direction of the bidirectional acoustic signal forms a certain angle θ with the direction of water flow in the water body to be measured.

[0023] In the above technical solution, the included angle θ ranges from 0° to 90°. This is designed to prevent the flow velocity direction from being perpendicular to the line connecting the sound station.

[0024] In some embodiments, wave acoustics is used to establish the relationship between the phase change of the bidirectional propagating sound signal, the propagation time of the bidirectional propagating sound signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test. This relationship is then used to invert the relationship to obtain the average flow velocity and the average sound velocity of the water body under test.

[0025] This also includes:

[0026] The average temperature of the water body under test is calculated using the empirical formula for sound velocity obtained through inversion.

[0027] In the above technical solution, the novel underwater acoustic tomography method based on phase difference can simultaneously monitor the average flow velocity of the water body and the temperature of the water body under test.

[0028] According to another aspect of the present invention, an underwater acoustic tomography system based on phase difference is proposed, comprising a data acquisition module and a velocity measurement module connected in sequence.

[0029] This acquisition module is used to collect bidirectional propagating acoustic signals from the water area under test, extract the propagation time and phase changes of the bidirectional propagating acoustic signals, and here the phase... satisfy

[0030] This velocity measurement module is used to establish the relationship between the phase change of the bidirectional propagating acoustic signal, the propagation time of the bidirectional propagating acoustic signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test through wave acoustics. The average flow velocity and average sound velocity of the water body under test are then obtained through inversion of this relationship. In the above technical solution, this underwater acoustic tomography system based on phase difference simultaneously calculates the bidirectional propagation time difference and the phase change difference of the acoustic signal, and inverts the average sound velocity and average flow velocity, which to some extent compensates for the error of relying solely on time delay estimation after matched filtering, and improves the accuracy of low-frequency acoustic tomography and low-velocity acoustic tomography techniques. According to another aspect of the present invention, an underwater acoustic tomography device based on phase difference is proposed, comprising:

[0031] At least one processor; and,

[0032] A memory communicatively connected to the at least one processor; wherein,

[0033] The memory stores instructions that can be executed by the at least one processor, which enables the at least one processor to perform the above-described underwater acoustic tomography method based on phase difference.

[0034] In the above technical solution, to better operate and process the method, the method is stored in memory, and the processor executes the stored method. It should be noted that the principle and effect of each step have been described above and will not be elaborated upon here.

[0035] According to another aspect of the present invention, a computer-readable storage medium is provided, which stores a computer program that, when executed by a processor, implements the above-described underwater acoustic tomography method based on phase difference.

[0036] In the above technical solution, to better operate and use the method, the method is stored in a computer-readable storage medium and implemented using a processor. It should be noted that the principle and effect of each step have been described above and will not be elaborated upon here. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic flowchart of an embodiment of the underwater acoustic tomography current measurement method based on phase difference of the present invention;

[0039] Figure 2 This is a schematic diagram of a water area according to an embodiment of the underwater acoustic tomography current measurement method based on phase difference of the present invention. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] This invention provides an underwater acoustic tomography method for current measurement based on phase difference, which is more suitable for use in low-frequency acoustic tomography techniques. By simultaneously considering time difference and phase difference, the uncertainty in velocity measurement can be reduced, promoting automation and high-precision current measurement technology. This invention is applicable to velocity measurement in waterways, estuaries, bays, and other similar bodies of water.

[0042] Example 1

[0043] Please see Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the underwater acoustic tomography current measurement method based on phase difference of the present invention. It should be noted that if substantially the same results are obtained, the method of the present invention is not necessarily identical. Figure 1 The illustrated process sequence is limited. For example... Figure 1 As shown, the method includes the following steps:

[0044] S101: Collect the bidirectional propagating acoustic signal from the water area to be measured, extract the propagation time and phase changes of the bidirectional propagating acoustic signal, and the phase change here. satisfy

[0045] In this embodiment, the propagation time and phase changes of the bidirectional propagating acoustic signal are extracted, specifically:

[0046] The collected bidirectional propagating acoustic signal is passed through a matched filter to extract the propagation time of the bidirectional propagating acoustic signal, and the phase change of the bidirectional propagating acoustic signal is calculated using the FFT cross-spectral method.

[0047] S102: Establish the relationship between the phase change of the bidirectional propagating sound signal, the propagation time of the bidirectional propagating sound signal, the water flow velocity of the water body to be measured, and the average sound velocity of the water body to be measured through wave acoustics. The average flow velocity and the average sound velocity of the water body to be measured are obtained by inversion through this relationship.

[0048] In this embodiment, the relationship between the phase change of the bidirectional propagating sound signal, the propagation time of the bidirectional propagating sound signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test is established through wave acoustics. The average flow velocity and the average sound velocity of the water body under test are then obtained by inversion using this relationship. Specifically:

[0049] Establish acoustic expressions for the transmission and reception positions based on the transmission and reception positions of bidirectional propagating acoustic signals;

[0050] Define the propagation direction of a bidirectional acoustic signal, and derive the phase change of the bidirectional acoustic signal based on wave acoustic theory. and The propagation time t of a two-way propagating sound signal + and t - The acoustic relationship between the average flow velocity u and the average sound velocity C0 of the water body under test;

[0051] The average flow velocity u and the average sound velocity C0 of the water body under test are obtained by simultaneously solving the acoustic relations.

[0052] In this embodiment, the bidirectional propagating acoustic signal is a chirp signal with a frequency of 40kHz to 80kHz.

[0053] In this embodiment, the propagation direction of the bidirectional acoustic signal forms a certain angle θ with the direction of water flow in the water body to be measured.

[0054] In this embodiment, the relationship between the phase change of the bidirectional propagating sound signal, the propagation time of the bidirectional propagating sound signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test is established through wave acoustics. The water flow velocity and the average sound velocity of the water body under test are then obtained through inversion using this relationship. The method further includes:

[0055] S103: The average temperature of the water body under test is calculated using the empirical formula for sound velocity, based on the water flow velocity and the average sound velocity of the water body obtained through inversion.

[0056] To further explain, this embodiment will begin with a detailed description of the method proposed in this embodiment, starting with the data acquisition hardware. Specifically:

[0057] Please see Figure 2 , Figure 2 This represents a body of water to be measured. Two acoustic stations, A and B, are deployed in this body of water to collect bidirectional propagating acoustic signals, where 'flow' represents the direction of water flow within the body of water. This acoustic station is an acoustic transceiver system, capable of transmitting and receiving acoustic signals.

[0058] (1) Acoustic sites A and B

[0059] Acoustic stations A and B are separated by a straight-line distance L, and the line connecting them forms an angle θ with the river channel. Acoustic stations A and B consist of an above-water section 1 and an underwater section 2. The underwater section 2 is the acoustic probe, composed of a transmitting transducer and a receiving hydrophone, or a combined transducer and transceiver, used for transmitting and receiving acoustic signals. The above-water section 1 is the circuit hardware, housing the system control and data processing center, including an industrial computer, a data acquisition system, a power amplifier, a filter amplifier board, a GPS synchronization module, and a network supply module. The industrial computer connects to the data acquisition system to generate and receive analog signals. The network supply module connects to the industrial computer for data exchange between stations and between stations and the server, as well as remote control. The above-water section 1 of acoustic stations A and B can be deployed on shore or on surface buoys.

[0060] (2) Collect underwater acoustic data in the water area to be tested and extract the time and phase changes of signal propagation.

[0061] Underwater acoustic data is collected from the water area to be measured, and the time and phase changes of signal propagation are extracted. The underwater acoustic data consists of chirp signals transmitted and received between acoustic stations A and B. In this embodiment, the signal used is a chirp signal in the range of 40kHz to 80kHz. The two stations process and analyze the collected underwater acoustic data respectively. The received acoustic signal is passed through a matched filter to extract the signal propagation time data t. + t - The phase change of the signal is calculated using the FFT cross-spectral method. Phase change here satisfy

[0062] The FFT cross-spectral method is as follows:

[0063] For two signals with the same frequency, as expressed in the following expressions:

[0064]

[0065]

[0066] Where n = 0, 1, 2, ..., L-1. A1 and A2 are the amplitudes of the two signals, respectively, f m For signal frequency, Let T be the initial phase of the two signals. s The sampling period.

[0067] Performing an L-point DFT on x(n) yields the spectrum:

[0068]

[0069] in, A k1 and These represent the amplitude and phase in the spectrum, respectively.

[0070] Similarly, for y(n), we have:

[0071]

[0072] The cross-power spectrum of X(k) and Y(k) is:

[0073]

[0074] but

[0075]

[0076] The phase difference between the two signals can then be calculated.

[0077] By taking x(n) as the transmitted signal and y(n) as the received signal, the phase change of the acoustic signal from transmission to reception can be calculated. and

[0078] (3) Data transmission

[0079] This embodiment uses a network supply module to transmit data between stations, enabling each station to have real-time signal propagation time and phase changes. This allows for local real-time calculation and display of flow velocity, with the results uploaded to the server in real time. Considering the computational burden on the industrial computers at each station, a data processing server can also be set up to collect the processing results from both stations and perform calculations on the server.

[0080] (4) Calculate the propagation time difference and phase difference of the two-way propagation of the acoustic signal, and invert the flow velocity of the water body to be measured.

[0081] Assuming the distance between the sound wave transmitter and receiver is L, and the sound wave propagates from the transmitter to the receiver, according to wave acoustics, the sound wave at x = L can be expressed as:

[0082]

[0083] Where P represents sound pressure; t is time, in seconds; A L ω represents the sound pressure level; ω is the angular frequency; c represents the speed of sound, in m / s.

[0084] The phase change during sound wave propagation is as follows:

[0085]

[0086] The two acoustic stations are station A and station B. Assuming the direction of the acoustic signal propagation from station A to station B is positive, the phase change during this process is influenced by the water flow. It should be expressed as:

[0087]

[0088] Where C0 is the average sound speed of the water area being measured, u is the magnitude of the flow velocity of the water area being measured, and θ represents the angle between the direction of the water flow and the line connecting the two stations.

[0089] Similarly, as the sound signal is emitted from station B and propagates to station A, the phase change is as follows:

[0090]

[0091] in,

[0092] Combining equations (3) and (4), we can obtain the magnitudes of the flow velocity and the average sound velocity as follows:

[0093]

[0094]

[0095] The wave nature of sound waves causes the time difference to satisfy:

[0096]

[0097] Therefore, equation (6) can be simplified to:

[0098]

[0099] Therefore, the propagation time difference and phase change difference between the two stations can be used to calculate the flow velocity of the water area to be measured using equation (5), the average sound velocity can be calculated using equation (8), and the average temperature of the area to be measured can be calculated using the empirical formula for sound velocity. The empirical formula for sound velocity can be referred to in existing technology and will not be elaborated here. In this novel underwater acoustic tomography theory based on phase difference, starting from the theory of wave acoustics, the influence of the two-way propagation time and the phase difference of the two-way propagation of the sound signal on the flow velocity inversion is considered, which theoretically improves the accuracy of low-frequency acoustic tomography flow measurement and acoustic tomography low-velocity flow measurement technology.

[0100] Example 2

[0101] An underwater acoustic tomography system based on phase difference includes a data acquisition module and a velocity measurement module connected in sequence.

[0102] This acquisition module is used to collect bidirectional propagating acoustic signals from the water area under test, extract the propagation time and phase changes of the bidirectional propagating acoustic signals, and here the phase... satisfy

[0103] This velocity measurement module is used to establish the relationship between the phase change of the bidirectional propagating sound signal and the propagation time of the bidirectional propagating sound signal, the water flow velocity of the water body under test, and the average sound velocity of the water body under test through wave acoustics. The water flow velocity and the average sound velocity of the water body under test are obtained by inversion through this relationship.

[0104] In this embodiment, the novel underwater acoustic tomography theory based on phase difference, starting from the theory of wave acoustics, considers the influence of the bidirectional propagation time and phase difference of the acoustic signal on the velocity inversion, thus improving the accuracy of low-frequency acoustic tomography and low-velocity acoustic tomography. It should be noted that the steps performed by each module of this system correspond one-to-one with the steps of the underwater acoustic tomography method based on phase difference described in one embodiment, and will not be elaborated further here.

[0105] Example 3

[0106] An underwater acoustic tomography device based on phase difference includes:

[0107] At least one processor; and,

[0108] A memory communicatively connected to the at least one processor; wherein,

[0109] The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the underwater acoustic tomography method based on phase difference as described in one embodiment.

[0110] In the above technical solution, in order to better operate and process the method described in one of the embodiments, the method is stored in a memory, and the stored method is executed by a processor. It should be noted that the principle and effect of each step have been described above and will not be elaborated further here.

[0111] Example 4

[0112] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described underwater acoustic tomography method based on phase difference.

[0113] In this embodiment, to better operate and use the method described in one of the embodiments, the above method is stored in a computer-readable storage medium, and the above method is implemented using a processor. It should be noted that the principle and effect of each step have been described above and will not be elaborated further here.

[0114] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made based on the content of the present invention specification and drawings, or direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for underwater acoustic tomography based on phase difference, characterized in that, include: Collect bidirectional acoustic signals from the water body to be measured, and extract the propagation time and phase changes of the bidirectional acoustic signals; By establishing the relationship between the phase change of a two-way propagating sound signal, the propagation time of the two-way propagating sound signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test using wave acoustics, the average flow velocity and the average sound velocity of the water body under test can be obtained by inversion using this relationship. Specifically: Establish acoustic expressions for the transmission and reception positions based on the transmission and reception positions of bidirectional propagating acoustic signals; Define the propagation direction of a bidirectional acoustic signal, and derive the phase change of the bidirectional acoustic signal based on wave acoustic theory. , Propagation time of bidirectional sound signals , and the average flow velocity of the water body to be measured and the average speed of sound in the water body to be measured Acoustic relations; The average flow velocity of the water body under test is obtained by simultaneously solving the acoustic relations. and the average speed of sound in the water body to be measured .

2. The underwater acoustic tomography current measurement method based on phase difference as described in claim 1, characterized in that, Extract the propagation time and phase changes of the bidirectional propagating acoustic signal, specifically: The collected bidirectional propagating acoustic signal is passed through a matched filter to extract the propagation time of the bidirectional propagating acoustic signal, and the phase change of the bidirectional propagating acoustic signal is calculated using the FFT cross-spectral method.

3. The underwater acoustic tomography current measurement method based on phase difference as described in claim 1, characterized in that, The bidirectional propagating acoustic signal is a broadband chirp signal.

4. The underwater acoustic tomography method based on phase difference as described in claim 1, characterized in that, The propagation direction of the bidirectional acoustic signal forms a certain angle with the direction of water flow in the water area to be measured. ,0°≤ <90°.

5. The underwater acoustic tomography current measurement method based on phase difference as described in claim 1, characterized in that, The relationship between the phase change of a two-way propagating sound signal, the propagation time of the two-way propagating sound signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test is established through wave acoustics. The average flow velocity and average sound velocity of the water body under test are then obtained through inversion using this relationship. The process also includes: The average temperature of the water body under test is calculated using the empirical formula for sound velocity obtained through inversion.

6. An underwater acoustic tomography system based on phase difference, characterized in that, This includes a data acquisition module and a speed measurement module connected in sequence; This acquisition module is used to collect bidirectional propagating acoustic signals from the water area under test, extract the propagation time and phase changes of the bidirectional propagating acoustic signals, and here the phase change... Satisfy 0≤ ≤ ; This velocity measurement module is used to establish the relationship between the phase change of a two-way propagating sound signal, the propagation time of the two-way propagating sound signal, the average flow velocity of the water body under test, and the average sound velocity of the water body under test through wave acoustics. The average flow velocity and average sound velocity of the water body under test are then obtained through inversion using this relationship. Specifically: Establish acoustic expressions for the transmission and reception positions based on the transmission and reception positions of bidirectional propagating acoustic signals; Define the propagation direction of a bidirectional acoustic signal, and derive the phase change of the bidirectional acoustic signal based on wave acoustic theory. , Propagation time of bidirectional sound signals , and the average flow velocity of the water body to be measured and the average speed of sound in the water body to be measured Acoustic relations; The average flow velocity of the water body under test is obtained by simultaneously solving the acoustic relations. and the average speed of sound in the water body to be measured .

7. An underwater acoustic tomography device based on phase difference, characterized in that, include: At least one processor; as well as, A memory communicatively connected to the at least one processor; wherein, The memory stores instructions executable by the at least one processor, which, when executed by the at least one processor, enables the at least one processor to perform the underwater acoustic tomography method based on phase difference as described in any one of claims 1 to 5.

8. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the underwater acoustic tomography method based on phase difference as described in any one of claims 1 to 5.

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