A hydrophone calibration system and method based on acoustic contrast measurement

Abstract

This invention belongs to the field of hydrophone calibration technology, specifically relating to a hydrophone calibration system and method based on acoustic contrast measurement. It includes a sound source, a hydrophone under test, a standard scatterer, a positioning system, and a control and processing unit. A sound field is formed between the sound source and the hydrophone under test. The control and processing unit includes a signal generation module, a signal acquisition module, a data processing module, a memory, and a motion controller. The motion controller controls the displacement of the positioning system, whose bottom is connected to the sound source, the standard scatterer, and the hydrophone under test. This invention effectively eliminates environmental reflection interference, which is a common-mode signal, by performing differential calculations on the complex responses of two measurements, thereby accurately separating the sound field changes caused by the scatterer. By comparing the measured sound field changes with the theoretical scattered sound field calculated based on scattering theory, the absolute sensitivity of the hydrophone under test can be accurately determined.

Description

Technical Field

[0001] This invention belongs to the field of hydrophone calibration technology, specifically relating to a hydrophone calibration system and method based on acoustic contrast measurement. Background Technology

[0002] As a core component for underwater acoustic signal detection, the accuracy of hydrophones' sensitivity and other performance parameters is crucial, thus requiring regular calibration. Currently, the most common calibration technique in the industry is the comparative method. Its standard procedure involves comparing the responses of the hydrophone under test and a standard hydrophone in the same sound field within a large, professional anechoic tank. The accuracy of this method relies entirely on the anechoic tank's ability to suppress sound reflections, thereby simulating an ideal free sound field environment. To overcome reflection problems in limited spaces such as small water tanks, the industry has also developed the pulse method. This method involves emitting short acoustic pulses and using a time window to capture and analyze the first arriving direct sound signal. However, this method has an inherent drawback: when calibrating low-frequency signals, the longer wavelength requires a correspondingly longer duration of the acoustic pulse. This leads to easy temporal aliasing between direct and reflected sound in small water tanks, causing calibration failure.

[0003] In summary, existing hydrophone calibration technologies face two major technical bottlenecks: 1) accurate calibration of hydrophones is difficult to achieve in non-anechoic or limited anechoic environments; 2) existing technologies struggle to effectively calibrate low frequencies within confined spaces. Currently, precise hydrophone calibration heavily relies on specialized anechoic tanks to create an ideal free-field environment, resulting in high calibration costs and the inability to perform in-situ calibration. For already installed hydrophones, their performance drifts due to aging and environmental changes, but recalibration is not readily available. Once a hydrophone is in use, performance drift caused by environmental changes or aging cannot be corrected in a timely manner, leading to poor timeliness of calibration results that do not accurately reflect its performance under operating conditions. Furthermore, the entire calibration process is cumbersome, requiring professional personnel and precision instruments, resulting in high costs, and the effectiveness of low-frequency calibration using the pulse method in small water tanks is limited.

[0004] Therefore, the core technical problem to be solved by this invention is to provide a new method that can effectively suppress environmental reflection interference, thereby achieving accurate calibration of hydrophones in the full frequency band, especially the low frequency band, in ordinary water tanks, and ultimately achieving a low-cost, high-precision in-situ calibration. Summary of the Invention

[0005] This invention provides the following technical solution:

[0006] A hydrophone calibration system based on acoustic contrast measurement includes a sound source, a hydrophone under test, a standard scattering body, a positioning system, and a control and processing unit. The sound source and the hydrophone under test are located on the same straight line, forming a sound field between them. The control and processing unit includes a signal generation module, a signal acquisition module, a data processing module, a memory, and a motion controller. The motion controller controls the displacement of the positioning system, and the bottom of the positioning system is connected to the sound source, the standard scattering body, and the hydrophone under test.

[0007] Furthermore, the positioning system is used to ensure the spatial stability of the sound source and the hydrophone under test, and to control the movement of the standard scatterer between inside and outside the sound field.

[0008] Furthermore, the control and processing unit is electrically connected to the sound source, the hydrophone under test, and the positioning system.

[0009] Furthermore, the standard scatterer is a solid precision stainless steel sphere with high acoustic impedance.

[0010] A calibration method for a hydrophone calibration system based on acoustic contrast measurement includes the following steps:

[0011] S1. System Initialization and Reference Sound Field Measurement: The control and processing unit uses a motion controller and positioning system to fix the sound source and the hydrophone under test in predetermined positions in the water, controls the standard scatterer to move out of the sound field, and the signal generation module generates an excitation signal to drive the sound source to emit a signal. The hydrophone under test measures the signal and performs a Fourier transform to obtain the reference complex frequency response V. A (f);

[0012] S2. Introduce a standard scatterer for comparative sound field measurement: Keeping the positions of the sound source and the hydrophone under test unchanged, use a positioning system to place the hydrophone under test into a predetermined position within the sound field. Drive the sound source again to emit the same signal as in step S1. The hydrophone under test measures and performs a Fourier transform to obtain the comparative complex frequency response V. B (f);

[0013] S3. Calculate the measured scattered field response: The data processing module calculates the response based on the reference complex frequency response V. A (f) and the contrasting complex frequency response V B (f) Calculate the measured scattering response ΔV meas (f);

[0014] S4. Calculate the theoretical scattered sound field: The data processing module calculates the theoretical scattered sound field P using acoustic scattering theory. scat,theo (f),

[0015]

[0016] Among them, P inc (f) represents the sound pressure amplitude of the incident sound field, k = 2πf / c is the wavenumber, where f is the frequency, c is the speed of sound in water, a is the radius of the standard scatterer, r is the distance between the sound center of the hydrophone under test and the center of the standard scatterer sphere, θ is the angle formed by the position of the hydrophone under test, the center of the standard scatterer sphere, and the incident direction of the sound source, and P m For an m-th order Legendre polynomial, j m and h m These are the m-th order spherical Bessel function and the first kind of spherical Hankel function, respectively. m ′ and h m ' and ' are the derivatives of the above spherical function with respect to its argument ka, respectively;

[0017] S5. Solving for the hydrophone sensitivity: Based on the calculation results of steps S3 and S4, the data processing module obtains the complex sensitivity curve S of the hydrophone under test by solving the following relationship. hyd (f):

[0018]

[0019] The obtained sensitivity is stored in the memory as the result of this calibration.

[0020] Furthermore, in step S1, the signal acquisition module acquires the response voltage signal v output by the hydrophone under test. A (t), the data processing module performs a Fourier transform on it to obtain the reference complex voltage spectrum V. A (f) is as follows:

[0021]

[0022] In the formula, S hyd (f) represents the unknown sensitivity of the hydrophone under test, P inc (f) is the sound pressure amplitude of the incident sound field, P refl (f) is the sound pressure amplitude of the reflected sound field in the environment.

[0023] Furthermore, in step S2, the signal acquisition module again acquires the response voltage signal v output by the hydrophone under test. B (t), the data processing module performs a Fourier transform on it to obtain the comparative complex voltage spectrum V. B (f) is as follows:

[0024]

[0025] In the formula, S hyd (f) represents the unknown sensitivity of the hydrophone under test, P A (f) is the sound pressure amplitude of the reference sound field, P scat(f) is the sound pressure amplitude of the scattered sound field.

[0026] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0027] This invention aims to eliminate the interference of environmental reflection on calibration results by introducing a standard scatterer and performing differential measurements, thereby freeing it from the dependence on professional anechoic tanks and enabling high-precision in-situ calibration that can be performed in ordinary water tanks or even at the sensor's working site. In addition, this method is committed to simplifying the calibration process and equipment requirements, improving calibration accuracy in complex environments while significantly reducing the economic and time costs of calibration, making the accuracy assurance of hydrophones throughout their entire life cycle more convenient and economical. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the geometric layout of the calibration system of the present invention in water;

[0029] Figure 2 This is a functional block diagram of the control and processing unit of the calibration system of the present invention;

[0030] Figure 3 This is a flowchart illustrating the specific workflow of the calibration method of the present invention.

[0031] The markings in the image are as follows:

[0032] 1-Sound source; 2-Hydrophone under test; 3-Standard scatterer; 4-Positioning system; 5-Control and processing unit; 51-Signal generation module; 52-Signal acquisition module; 53-Data processing module; 54-Memory; 55-Motion controller. Detailed Implementation

[0033] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings, so that those skilled in the art can more clearly understand how to practice the present invention. Although the present invention has been described in conjunction with its preferred embodiments, these embodiments are merely illustrative and not intended to limit the scope of the invention.

[0034] As attached Figure 1As shown, a hydrophone calibration system based on acoustic contrast measurement includes a sound source 1, a hydrophone under test 2, a standard scattering object 3, a positioning system 4, and a control and processing unit 5. The sound source 1 and the hydrophone under test 2 are located on the same straight line, forming a sound field between them. The control and processing unit 5 includes a signal generation module 51, a signal acquisition module 52, a data processing module 53, a memory 54, and a motion controller 55. The motion controller 55 controls the displacement of the positioning system 4. The bottom of the positioning system 4 is connected to the sound source 1, the standard scattering object 3, and the hydrophone under test 2, respectively. That is, the bottom of the positioning system 4 is provided with corresponding fixing mechanisms for connecting the sound source 1, the standard scattering object 3, and the hydrophone under test 2.

[0035] Specifically, the positioning system 4 is used to ensure the spatial stability of the sound source 1 and the hydrophone 2 under test, and to control the movement of the standard scatterer 3 between inside and outside the sound field. That is, the positioning system 4 can control the standard scatterer 3 to move between predetermined positions inside and outside the sound field path with high precision and high repeatability.

[0036] Specifically, the control and processing unit 5 is electrically connected to the sound source 1, the hydrophone under test 2, and the positioning system 4. That is, the control and processing unit 5 is the control center of the calibration system, automatically controls the entire calibration process, can drive the sound source 1 to emit sound signals, collect the response signals of the hydrophone under test 2, control the movement of the positioning system 4, and perform calculations on the sensitivity of the hydrophone under test 2.

[0037] Specifically, the standard scatterer 3 is a solid precision stainless steel ball with high acoustic impedance, which is beneficial for subsequent hydrophone calibration.

[0038] A calibration method for a hydrophone calibration system based on acoustic contrast measurement includes the following steps:

[0039] S1. System Initialization and Reference Sound Field Measurement: The control and processing unit 5 uses the motion controller 55 and the positioning system 4 to fix the sound source 1 and the hydrophone under test 2 in predetermined positions in the water. It controls the standard scatterer 3 to move out of the sound field, i.e., the standard scatterer 3 is at position A. The signal generation module 51 generates an excitation signal to drive the sound source 1 to emit a signal, which is measured by the hydrophone under test 2 and subjected to Fourier transform to obtain the reference complex frequency response V. A (f);

[0040] S2. Introduce a standard scatterer for comparative sound field measurement: Keeping the positions of sound source 1 and hydrophone 2 unchanged, use positioning system 4 to place hydrophone 2 into a predetermined position within the sound field, i.e., standard scatterer 3 is at position B, which is located on the line connecting sound source 1 and hydrophone 2. Drive sound source 1 again to emit the same excitation signal as in step S1. The hydrophone 2 measures and performs a Fourier transform to obtain the comparative complex frequency response V.B (f);

[0041] S3. Calculate the measured scattered field response: The data processing module 53 calculates the response based on the reference complex frequency response V. A (f) and the contrasting complex frequency response V B (f) Calculate the measured scattering response ΔV meas (f); that is, the data processing module 53 calculates the difference between the complex voltage spectrum of the two measurements. This difference operation is the key to the present invention. It completely cancels out the unchanging reference sound field, which includes direct sound and environmental reflections, as a common-mode signal, thereby eliminating the interference of environmental reflections.

[0042] S4. Calculation of theoretical scattered sound field: Based on the pre-stored system geometric parameters, the physical parameters of the standard scatterer 3, and the real-time measured water medium parameters, the data processing module 53 calculates the theoretical scattered sound field P using acoustic scattering theory. scat,theo (f), where a rigid sphere with radius a is taken as an example of a standard scatterer 3, when a plane wave P inc (f) The theoretical scattered sound field P generated at a point at a distance r from the center of the sphere and at an angle θ with the incident direction upon incidence. scat,theo (f) can be given precisely by the following series solution:

[0043]

[0044] Among them, P inc (f) represents the sound pressure amplitude of the incident sound field, k = 2πf / c is the wavenumber, where f is the frequency, c is the speed of sound in water, a is the radius of the standard scatterer 3, r is the distance between the sound center of the hydrophone 2 under test and the center of the standard scatterer 3, θ is the angle formed by the position of the hydrophone 2 under test, the center of the standard scatterer 3, and the incident direction of the sound source 1, and P m For an m-th order Legendre polynomial, j m and h m These are the m-th order spherical Bessel function and the first kind of spherical Hankel function, respectively. m ′ and h m ' and ' are the derivatives of the above spherical function with respect to its argument ka, respectively;

[0045] S5. Solving for the hydrophone sensitivity: Based on the calculation results of steps S3 and S4, the data processing module 53 obtains the complex sensitivity curve S of the hydrophone under test 2 by solving the following relationship. hyd (f):

[0046]

[0047] That is, the sensitivity is approximately equal to the measured scattered field response / theoretical scattered sound field. The obtained sensitivity, which includes amplitude and phase information, is stored in memory 54 as the result of this calibration.

[0048] Specifically, in step S1, at the hydrophone 2 under test, the total sound field P A (f) is the incident sound field P inc (f) and ambient reflected sound field P refl Linear superposition of (f):

[0049]

[0050] Signal acquisition module 52 acquires the response voltage signal v output by the hydrophone under test 2. A (t), the data processing module 53 performs a Fourier transform on it to obtain the reference complex voltage spectrum V. A (f) is as follows:

[0051]

[0052] In the formula, S hyd (f) represents the unknown sensitivity of the hydrophone 2 under test, P inc (f) is the sound pressure amplitude of the incident sound field, P refl (f) is the sound pressure amplitude of the reflected sound field in the environment.

[0053] Specifically, in step S2, at the hydrophone 2 under test, the total sound field P B (f) is the reference sound field P A (f) and the scattered sound field P scat Linear superposition of (f):

[0054]

[0055] Signal acquisition module 52 again acquires the response voltage signal v output by the hydrophone under test 2. B (t), the data processing module 53 performs a Fourier transform on it to obtain the comparative complex voltage spectrum V. B (f) is as follows:

[0056]

[0057] In the formula, S hyd (f) represents the unknown sensitivity of the hydrophone 2 under test, P A (f) is the sound pressure amplitude of the reference sound field, P scat (f) is the sound pressure amplitude of the scattered sound field.

[0058] This invention eliminates complex environmental reflections as common-mode noise by measuring the "relative change" rather than the "absolute value" of the sound field, thereby significantly improving calibration accuracy in non-ideal environments. This breakthrough fundamentally solves the problem of in-situ calibration in traditional techniques, making high-precision calibration possible in ordinary water tanks or even on-site, eliminating the need for expensive anechoic tanks and significantly reducing system cost and operational complexity. This method allows for convenient periodic performance reviews of deployed hydrophones, real-time compensation for performance drift caused by device aging or environmental changes, and ensures measurement accuracy throughout their lifespan. Furthermore, compared to the reverberant tank method, which can only measure "random incident sensitivity" and cannot provide phase information, this invention can accurately calibrate the more practical "free-field sensitivity," including amplitude and phase, in most underwater acoustic applications, providing complete and crucial fundamental parameters for hydrophone directivity and array applications.

[0059] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications and substitutions based on the technical solutions and inventive concepts provided by the present invention should be covered within the scope of protection of the present invention.

Claims

1. A hydrophone calibration system based on acoustic contrast measurement, characterized in that: The device includes a sound source (1), a hydrophone under test (2), a standard scattering body (3), a positioning system (4), and a control and processing unit (5). The sound source (1) and the hydrophone under test (2) are located on the same straight line, and a sound field is formed between the sound source (1) and the hydrophone under test (2). The control and processing unit (5) includes a signal generation module (51), a signal acquisition module (52), a data processing module (53), a memory (54), and a motion controller (55). The motion controller (55) controls the displacement of the positioning system (4). The bottom of the positioning system (4) is connected to the sound source (1), the standard scattering body (3), and the hydrophone under test (2), respectively.

2. The hydrophone calibration system based on acoustic contrast measurement according to claim 1, characterized in that: The positioning system (4) is used to ensure the spatial position stability of the sound source (1) and the hydrophone (2) under test, and to control the movement of the standard scatterer (3) between the sound field and the outside of the sound field.

3. The hydrophone calibration system based on acoustic contrast measurement according to claim 1, characterized in that: The control and processing unit (5) is electrically connected to the sound source (1), the hydrophone under test (2), and the positioning system (4).

4. The hydrophone calibration system based on acoustic contrast measurement according to claim 1, characterized in that: The standard scatterer (3) is a solid precision stainless steel ball with high acoustic impedance.

5. A calibration method for a hydrophone calibration system based on acoustic contrast measurement as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. System initialization and reference sound field measurement: The control and processing unit (5) fixes the sound source (1) and the hydrophone under test (2) in a predetermined position in the water through the motion controller (55) and the positioning system (4), controls the standard scatterer (3) to move out of the sound field, and the signal generation module (51) generates an excitation signal to drive the sound source (1) to emit a signal. The reference complex frequency response V is obtained by measuring and performing Fourier transform on the hydrophone under test (2). A (f); S2. Introduce a standard scatterer and perform a comparative sound field measurement: Keep the positions of the sound source (1) and the hydrophone under test (2) unchanged, use the positioning system (4) to place the hydrophone under test (2) into a predetermined position within the sound field, and drive the sound source (1) again to emit the same signal as in step S1. The comparative complex frequency response V is obtained by measuring and performing a Fourier transform on the hydrophone under test (2). B (f); S3. Calculate the measured scattered field response: The data processing module (53) calculates the response based on the reference complex frequency response V. A (f) and the contrasting complex frequency response V B (f) Calculate the measured scattering response ΔV meas (f); S4. Calculate the theoretical scattered sound field: The theoretical scattered sound field P is calculated by the data processing module (53) using acoustic scattering theory. scat,theo (f), Among them, P inc (f) represents the sound pressure amplitude of the incident sound field, k = 2πf / c represents the wave number, where f is the frequency, c is the speed of sound in water, a is the radius of the standard scatterer (3), r is the distance between the sound center of the hydrophone (2) under test and the center of the standard scatterer (3), θ is the angle formed by the position of the hydrophone (2) under test, the center of the standard scatterer (3), and the incident direction of the sound source (1), and P m For an m-th order Legendre polynomial, j m and h m These are the m-th order spherical Bessel function and the first kind of spherical Hankel function, respectively. m ′ and h m ' and ' are the derivatives of the above spherical function with respect to its argument ka, respectively; S5. Solving for the hydrophone sensitivity: Based on the calculation results of steps S3 and S4, the data processing module (53) obtains the complex sensitivity curve S of the hydrophone under test (2) by solving the following relationship. hyd (f): The obtained sensitivity is stored in memory (54) as the result of this calibration.

6. The calibration method for a hydrophone calibration system based on acoustic contrast measurement according to claim 5, characterized in that: In step S1, the signal acquisition module (52) acquires the response voltage signal v output by the hydrophone under test (2). A (t), the data processing module (53) performs a Fourier transform on it to obtain the reference complex voltage spectrum V. A (f) is as follows: In the formula, S hyd (f) represents the unknown sensitivity of the hydrophone (2) under test, P inc (f) is the sound pressure amplitude of the incident sound field, P refl (f) is the sound pressure amplitude of the ambient reflected sound field.

7. The calibration method for a hydrophone calibration system based on acoustic contrast measurement according to claim 6, characterized in that: In step S2, the signal acquisition module (52) acquires the response voltage signal v output by the hydrophone under test (2) again. B (t), the data processing module (53) performs a Fourier transform on it to obtain the comparative complex voltage spectrum V. B (f) is as follows: In the formula, S hyd (f) represents the unknown sensitivity of the hydrophone (2) under test, P A (f) is the sound pressure amplitude of the reference sound field, P scat (f) is the sound pressure amplitude of the scattered sound field.

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