An underwater low-frequency noise comprehensive test system

Abstract

The application provides an underwater low-frequency noise comprehensive test system, which comprises an underwater vehicle platform, an environment sensing calibration module, a fixed underwater measurement array, an adaptive signal processing module, a three-dimensional positioning module and a target feature extraction and analysis module; the underwater vehicle platform is used for maneuvering deployment and recovery of the fixed underwater measurement array; the environment sensing calibration module is used for obtaining underwater environment characteristic benchmarks; the fixed underwater measurement array is used for receiving underwater target radiation noise; the adaptive signal processing module is used for extracting target noise signals; the three-dimensional positioning module is used for three-dimensional positioning of the vehicle, the measurement array and the underwater target; and the target feature extraction and analysis module is used for processing the target noise signals to extract noise features; through cooperative work of the underwater vehicle and the fixed measurement array, the scheme realizes high-precision, comparability and multi-dimensional comprehensive test of underwater low-frequency noise in a complex environment.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic testing systems, and more particularly to an underwater low-frequency noise comprehensive testing system. Background Technology

[0002] Low-frequency noise from underwater targets is crucial for identifying the type, operational status, and acoustic characteristics of underwater equipment. Therefore, high-precision and reliable measurement of low-frequency noise is of great significance in fields such as marine monitoring, seabed resource exploration, and underwater equipment evaluation. Traditional underwater noise measurement often relies on fixed hydrophones, towed arrays, or single-point vector hydrophones. While these methods can achieve basic sound pressure reception, they suffer from limitations in complex aquatic environments, including limited coverage, insufficient azimuth resolution, weak anti-interference performance, and difficulty in simultaneously capturing near-field and far-field information.

[0003] Meanwhile, underwater acoustic signals are affected by temperature, salinity, and depth structures, ocean current disturbances, seabed reflections, and multipath effects during propagation, making stable observation and precise localization of low-frequency noise more difficult. Current technologies struggle to achieve comprehensive multi-angle, multi-distance, and full-space measurements of target low-frequency noise, and lack real-time acoustic calibration and localization fusion capabilities for dynamic environmental changes. This results in distorted noise characteristics and insufficient localization accuracy, limiting the in-depth analysis and application of underwater target acoustic characteristics.

[0004] A review of publicly available technical solutions reveals that CN117889949A proposes a novel low-frequency three-dimensional differential pressure vector hydrophone. Its structure includes a piezoelectric ceramic tube, a PVC six-way tube, a copper tube, a piezoelectric ceramic ring, a pre-embedded nut, a positioning rod, and a vulcanized cable. The piezoelectric tube, acting as an array unit, is symmetrically placed along the X, Y, and Z directions of the PVC six-way tube. Vibration velocity information is obtained by differentially analyzing two closely spaced sound pressure array elements, thereby receiving the sound signal. The piezoelectric ring is placed outside the PVC piezoelectric tube and is connected in parallel to collect sound pressure information in the sound field, generating a vector hydrophone sound pressure signal. After underwater acoustic signal processing, the target location can be directly obtained. The vector hydrophone device is small in size, compact in structure, and easy to install and deploy. It also has advantages such as good directivity, high sensitivity, and low self-noise when operating in the low-frequency band. However, this solution focuses on optimizing the structure of a single vector hydrophone and can only achieve low-frequency sound pressure and vibration velocity measurements at local points. It cannot meet the requirements for testing the target noise characteristics under large-scale, multi-angle, and dynamic conditions. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of current systems by proposing a comprehensive underwater low-frequency noise testing system.

[0006] The present invention adopts the following technical solution:

[0007] An underwater low-frequency noise comprehensive testing system includes an underwater vehicle platform, an environmental perception calibration module, a bottom-mounted fixed measurement array, an adaptive signal processing module, a three-dimensional positioning module, and a target feature extraction and analysis module.

[0008] The underwater vehicle platform is used to maneuverably carry and deploy a fixed underwater measurement array, and to achieve precise positioning of the fixed underwater measurement array through acoustic source signal transmission with the fixed underwater measurement array; the environmental perception calibration module is used to provide an environmental calibration basis for underwater acoustic propagation and noise analysis; the fixed underwater measurement array is used to receive underwater target noise and reference acoustic source signals emitted by the vehicle at a preset water depth for a long period of time.

[0009] The underwater vehicle platform includes a payload deployment unit, an active sound source transmission unit, and a positioning information acquisition unit. The payload deployment unit is used to carry, release, and retrieve the underwater fixed measurement array. The active sound source transmission unit is used to transmit active reference sound source signals to the underwater fixed measurement array to achieve precise positioning of the underwater fixed measurement array. The positioning information acquisition unit is used to acquire the current position information of the underwater vehicle in real time.

[0010] The environmental perception calibration module includes a sound velocity profile measurement unit, an underwater acoustic attenuation measurement unit, and a background noise reference measurement unit. The sound velocity profile measurement unit is used to measure the sound velocity profile at various depths underwater in real time in conjunction with a CTD sensor array. The underwater acoustic attenuation measurement unit is used to calculate the underwater acoustic absorption coefficient at different frequency bands by transmitting a sweep frequency signal to the bottom and receiving the reflected echo from the bottom. The background noise reference measurement unit is used to obtain the background noise power spectral density in the underwater environment in real time.

[0011] Furthermore, the active sound source transmitting unit adaptively selects the optimal operating frequency band as the transmission frequency band of the active reference sound source signal under different underwater test environments. The specific working process of the active sound source transmitting unit is as follows:

[0012] S1: In the initial stage of testing, after the vehicle platform releases the underwater fixed measurement array, the vehicle returns to the predetermined navigation position, and the availability index of each frequency band is calculated:

[0013] ;

[0014] in, For the transmission frequency band The corresponding availability index at that time For the transmission frequency band The power spectrum of the sound source at that time For the transmission frequency band Background noise power spectrum at that time For the transmission frequency band The underwater acoustic absorption coefficient at that time, The propagation distance is the estimated distance from the vehicle to the center of the underwater fixed measurement array during the initial stage of the test.

[0015] S2: Use the frequency band corresponding to the maximum value of the current availability index as the center frequency of the active reference sound source signal in the initial stage of the test;

[0016] S3: During the test, an adaptive adjustment cycle is set, and at the end of each adaptive adjustment cycle, the position information of the underwater vehicle is obtained to calculate the current propagation distance, and the availability index of each frequency band is recalculated. If the availability index of a new frequency band is greater than the switching threshold, the active reference sound source is switched to the new frequency band to complete the transmission; otherwise, the current frequency band is maintained.

[0017] Furthermore, the switching threshold can be set to 1.5 times the availability index of the current transmission band.

[0018] Furthermore, the underwater fixed measurement array includes a hydrophone array element unit, an array synchronization unit, and a sound source sampling buffer unit; the hydrophone array element unit consists of multiple hydrophones arranged in an array, each of which can receive sound pressure signals from underwater; the array synchronization unit is used to achieve time synchronization calibration between different hydrophones; the sound source sampling buffer unit is used to filter and preprocess the sound pressure signals acquired by the hydrophones in the measurement array and buffer them.

[0019] Furthermore, the adaptive signal processing module includes an active sound source separation unit, a background noise suppression unit, and a target signal extraction unit. The active sound source separation unit is used to accurately extract and remove the active reference sound source signal component from the sound pressure signal received by the underwater fixed measurement array based on the emission time, center frequency, and reference sound source signal characteristics provided by the active sound source emission unit. The background noise suppression unit is used to adaptively filter the sound pressure signal after removing the active sound source based on the background noise power spectral density provided by the environmental perception calibration module to suppress environmental background noise. The target signal extraction unit is used to output the target noise signal after active sound source separation and background noise suppression.

[0020] Furthermore, the three-dimensional positioning module includes an array calibration unit, a target positioning unit, and a fusion position output unit. The array calibration unit is used to calculate the propagation distance and azimuth angle between the vehicle and each hydrophone based on the arrival time of the active reference sound source signal and the sound speed profile, and accordingly calculates the actual spatial coordinates of each hydrophone in the underwater fixed measurement array, correcting the displacement, tilt, and deformation of the underwater fixed measurement array after deployment in the initial stage of the test. The target positioning unit is used to measure the azimuth and pitch angles of the underwater target relative to each hydrophone through beamforming based on the target noise signal acquired by each hydrophone, obtain the distance between each hydrophone and the underwater target through the time delay difference of the pure target noise signal acquired by each hydrophone, and calculate the underwater target position by combining the current actual spatial coordinates of each hydrophone. The fusion position output unit is used to perform a unified coordinate system transformation on the position of the underwater vehicle, the position of the underwater fixed measurement array, and the position of the underwater target, and output the relative geometric relationship between the three.

[0021] Furthermore, the target feature extraction and analysis module includes a source noise extraction unit, a spectrum feature extraction unit, a time-domain modulation feature extraction unit, and a spatial pointing feature extraction unit. The source noise extraction unit is used to perform propagation inversion on the target noise signal to extract the source-level noise signal of the underwater target. The spectrum feature extraction unit is used to perform low-frequency spectrum analysis on the source-level noise signal to extract the power spectral density distribution, characteristic spectral lines, spectral peak positions, and spectral energy variation characteristics of the target in a preset low-frequency band, which is used to characterize the low-frequency radiated noise intensity and spectral structure characteristics of the underwater target. The time-domain modulation feature extraction unit is used to perform time-domain and time-frequency analysis on the source-level noise signal to extract the periodic modulation characteristics, amplitude fluctuation characteristics, and modulation frequency characteristics of the target noise, so as to reflect the time-frequency domain characteristics of the underwater target. The spatial pointing feature extraction unit is used to combine the target spatial position information output by the three-dimensional positioning module to extract the energy distribution characteristics and pointing variation characteristics of the source-level noise signal in different spatial directions, so as to reflect the spatial distribution law of the radiated noise of the underwater target.

[0022] The beneficial effects achieved by this invention are:

[0023] This invention combines the mobile deployment capability of an underwater vehicle platform with the stable receiving capability of a fixed underwater measurement array to construct a flexibly adjustable underwater acoustic testing system. It introduces modules such as environmental perception calibration, adaptive signal processing, and 3D positioning to perform real-time calibration and compensation for underwater sound propagation conditions, array geometry, and background noise. Based on this, it performs propagation inversion and multi-dimensional feature extraction on target noise, effectively reducing the impact of environmental changes and propagation effects on low-frequency noise test results. This improves the consistency, accuracy, and reliability of noise characteristics under different testing conditions, providing stable and unified technical support for the evaluation of low-frequency acoustic characteristics of underwater targets. Attached Figure Description

[0024] The invention will be further understood from the following description taken in conjunction with the accompanying drawings. The components in the drawings are not necessarily drawn to scale, but rather the emphasis is on illustrating the principles of the embodiments. In different views, the same reference numerals designate corresponding parts.

[0025] Figure 1 This is a schematic diagram of the overall modules of the present invention.

[0026] Figure 2 This is a schematic diagram of the working process of the active sound source emission unit of the present invention.

[0027] Figure 3 This is a schematic diagram comparing the signal-to-noise ratio improvement of the present invention's solution with that of the traditional solution.

[0028] Figure 4 This is a schematic diagram comparing the improvement in positioning error of the present invention with that of traditional solutions.

[0029] Figure 5 This is a schematic diagram comparing the improvement in repeatability consistency of the present invention's solution compared to traditional solutions. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Other systems, methods, and / or features of this embodiment will become apparent to those skilled in the art after reviewing the following detailed description. It is intended that all such additional systems, methods, features, and advantages are included within this specification, are included within the scope of the present invention, and are protected by the appended claims. Further features of the disclosed embodiments are described in the following detailed description, and these features will be apparent from the following detailed description.

[0031] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0032] Example 1:

[0033] like Figure 1, Figure 2 As shown, this embodiment provides an underwater low-frequency noise comprehensive testing system, which includes an underwater vehicle platform, an environmental perception calibration module, an underwater fixed measurement array, an adaptive signal processing module, a three-dimensional positioning module, and a target feature extraction and analysis module.

[0034] The underwater vehicle platform is used to maneuverably carry and deploy the underwater fixed measurement array, and to complete the precise positioning of the underwater fixed measurement array through the transmission of acoustic source signals between the platform and the underwater fixed measurement array; the environmental perception calibration module is used to provide an environmental calibration basis for underwater acoustic propagation and noise analysis; the underwater fixed measurement array is used to receive underwater target noise and reference acoustic source signals emitted by the vehicle at a preset water depth for a long period of time.

[0035] The underwater vehicle platform includes a payload deployment unit, an active sound source transmission unit, and a positioning information acquisition unit. The payload deployment unit is used to carry, release, and recover the underwater fixed measurement array. The active sound source transmission unit is used to transmit active reference sound source signals to the underwater fixed measurement array to achieve precise positioning of the underwater fixed measurement array. The positioning information acquisition unit is used to acquire the current position information of the underwater vehicle in real time.

[0036] The environmental perception calibration module includes a sound velocity profile measurement unit, an underwater acoustic attenuation measurement unit, and a background noise reference measurement unit. The sound velocity profile measurement unit is used to measure the sound velocity profile at various depths underwater in real time in conjunction with a CTD sensor array. The underwater acoustic attenuation measurement unit is used to calculate the underwater acoustic absorption coefficient at different frequency bands by transmitting a sweep frequency signal to the bottom and receiving the reflected echo from the bottom. The background noise reference measurement unit is used to obtain the background noise power spectral density in the underwater environment in real time.

[0037] Furthermore, the active sound source transmitting unit adaptively selects the optimal operating frequency band as the transmission frequency band of the active reference sound source signal under different underwater test environments. The specific working process of the active sound source transmitting unit is as follows:

[0038] S1: In the initial stage of testing, after the vehicle platform releases the underwater fixed measurement array, the vehicle returns to the predetermined navigation position, and the availability index of each frequency band is calculated:

[0039] ;

[0040] in, For the transmission frequency band The corresponding availability index at that time For the transmission frequency band The power spectrum of the sound source at that time For the transmission frequency band Background noise power spectrum at that time For the transmission frequency band The underwater acoustic absorption coefficient at that time, The propagation distance is the estimated distance from the vehicle to the center of the underwater fixed measurement array during the initial stage of the test.

[0041] S2: Use the frequency band corresponding to the maximum value of the current availability index as the center frequency of the active reference sound source signal in the initial stage of the test;

[0042] S3: During the test, an adaptive adjustment cycle is set, and at the end of each adaptive adjustment cycle, the position information of the underwater vehicle is obtained to calculate the current propagation distance, and the availability index of each frequency band is recalculated. If the availability index of a new frequency band is greater than the switching threshold, the active reference sound source is switched to the new frequency band to complete the transmission; otherwise, the current frequency band is maintained.

[0043] Furthermore, the underwater acoustic attenuation measurement unit specifically obtains the underwater acoustic absorption coefficient in the following manner: In the initial stage of the test, the underwater vehicle platform controls the active sound source transmitting unit to transmit a preset sweep frequency reference sound source signal towards the underwater fixed measurement array. The sweep frequency reference sound source signal covers a predetermined low-frequency test band. The hydrophone array elements of the underwater fixed measurement array synchronously receive the sweep frequency signal and its echo signal after reflection from the bottom of the water, and perform frequency domain analysis on the received amplitude of each frequency band. Based on the amplitude difference between the transmitted signal and the received echo signal in each frequency band, and combined with the propagation distance information, the underwater acoustic attenuation measurement unit calculates the equivalent underwater acoustic absorption coefficient in different frequency bands, which is used to characterize the underwater acoustic attenuation characteristics of the current test water area.

[0044] Furthermore, the background noise benchmark measurement unit specifically obtains the background noise power spectral density in the following manner: before the target noise test begins or during the time period when the target has not entered the measurement area, the underwater fixed measurement array continuously collects underwater environmental sound pressure signals; the background noise benchmark measurement unit performs time-domain sampling and frequency-domain transformation processing on the collected environmental sound pressure signals, calculates the noise power spectral density of each frequency band, and uses the power spectral density as the background noise benchmark of the current test environment, providing a noise reference basis for subsequent active sound source availability assessment and target noise extraction;

[0045] Furthermore, the switching threshold can be set to 1.5 times the availability index of the current transmission band;

[0046] This solution adaptively selects the transmission frequency band of the active reference sound source based on propagation distance, underwater acoustic absorption characteristics, and background noise level. This ensures that the active reference sound source always operates in a frequency range with better signal-to-noise ratio and lower propagation loss under different underwater environments and different test stages, thereby improving the reception stability and effective propagation distance of the reference sound source signal. At the same time, by dynamically adjusting the transmission frequency band during the test, the impact of environmental changes and vehicle movement on positioning and array calibration accuracy is reduced, improving the reliability and consistency of underwater fixed measurement array positioning and subsequent acoustic testing.

[0047] Furthermore, the underwater fixed measurement array includes a hydrophone array element unit, an array synchronization unit, and a sound source sampling buffer unit; the hydrophone array element unit consists of multiple hydrophones arranged in an array, each of which can receive sound pressure signals from underwater; the array synchronization unit is used to achieve time synchronization calibration between different hydrophones; the sound source sampling buffer unit is used to filter, preprocess, and buffer the sound pressure signals acquired by the hydrophones in the measurement array.

[0048] Furthermore, the adaptive signal processing module includes an active sound source separation unit, a background noise suppression unit, and a target signal extraction unit. The active sound source separation unit is used to accurately extract and remove the active reference sound source signal component from the sound pressure signal received by the underwater fixed measurement array based on the emission time, center frequency, and reference sound source signal characteristics provided by the active sound source emission unit. The background noise suppression unit is used to adaptively filter the sound pressure signal after removing the active sound source based on the background noise power spectral density provided by the environmental perception calibration module to suppress environmental background noise. The target signal extraction unit is used to output the target noise signal after active sound source separation and background noise suppression.

[0049] Example 2:

[0050] This embodiment should be understood to include at least all the features of any of the foregoing embodiments, and to further improve upon them;

[0051] This embodiment provides an underwater low-frequency noise comprehensive testing system, which includes an underwater vehicle platform, an environmental perception calibration module, an underwater fixed measurement array, an adaptive signal processing module, a three-dimensional positioning module, and a target feature extraction and analysis module;

[0052] Furthermore, the three-dimensional positioning module includes an array calibration unit, a target positioning unit, and a fusion position output unit. The array calibration unit is used to calculate the propagation distance and azimuth angle between the vehicle and each hydrophone based on the arrival time of the active reference sound source signal and the sound speed profile, and accordingly calculates the actual spatial coordinates of each hydrophone in the underwater fixed measurement array, correcting the displacement, tilt, and deformation of the underwater fixed measurement array after deployment in the initial stage of testing. The target positioning unit is used to measure the azimuth and pitch angles of the underwater target relative to each hydrophone through beamforming based on the target noise signal acquired by each hydrophone, obtain the distance between each hydrophone and the underwater target through the time delay difference of the target noise signal acquired by each hydrophone, and calculate the underwater target position by combining the current actual spatial coordinates of each hydrophone. The fusion position output unit is used to perform a unified coordinate system transformation on the position of the underwater vehicle, the position of the underwater fixed measurement array, and the position of the underwater target, and output the relative geometric relationship between the three.

[0053] Furthermore, the target feature extraction and analysis module includes a source noise extraction unit, a spectrum feature extraction unit, a time-domain modulation feature extraction unit, and a spatial pointing feature extraction unit. The source noise extraction unit is used to perform propagation inversion on the target noise signal to extract the source-level noise signal of the underwater target. The spectrum feature extraction unit is used to perform low-frequency spectrum analysis on the source-level noise signal to extract the power spectral density distribution, characteristic spectral lines, spectral peak positions, and spectral energy variation characteristics of the target in a preset low-frequency band, which is used to characterize the low-frequency radiated noise intensity and spectral structure characteristics of the underwater target. The time-domain modulation feature extraction unit is used to perform time-domain and time-frequency analysis on the source-level noise signal to extract the periodic modulation characteristics, amplitude fluctuation characteristics, and modulation frequency characteristics of the target noise, so as to reflect the time-frequency domain characteristics of the underwater target. The spatial pointing feature extraction unit is used to combine the target spatial position information output by the three-dimensional positioning module to extract the energy distribution characteristics and pointing variation characteristics of the source-level noise signal in different spatial directions, so as to reflect the spatial distribution law of the radiated noise of the underwater target.

[0054] Furthermore, the source noise extraction unit extracts the source-level noise signal in the following manner:

[0055] ;

[0056] in, The source-level noise signal, The target noise signal; The distance from the underwater target to the center of the fixed underwater measurement array. express The resulting geometric diffusion loss compensation term, in decibels, is used to correct the propagation attenuation caused by spherical diffusion. The acoustic propagation path from the underwater target to the fixed measurement array on the seabed; These are the path parameters along the sound propagation path; These are the depth coordinates corresponding to the depth location of the sound propagation path. The underwater acoustic absorption coefficient varies with depth. The underwater acoustic attenuation measurement unit obtains the absorption coefficient as a function of depth by performing measurement inversion based on a swept-frequency reference signal emitted by an active sound source. The underwater vehicle transmits a swept-frequency reference sound source signal covering a predetermined frequency band to a fixed underwater measurement array. The measurement array receives the reference sound source signal and the reflected echo signal from the seabed. The underwater acoustic attenuation measurement unit calculates the frequency band absorption loss based on the attenuation of the echo amplitude in each frequency band and the propagation distance. Furthermore, it uses sound velocity profile data obtained by the sound velocity profile measurement unit to correct the propagation path, thereby obtaining the underwater acoustic absorption coefficient as a function of depth. The above is for The inversion calculation process can be completed using the conventional echo attenuation inversion calculation method in the field of underwater acoustic propagation testing; , and All are sound level quantities in the decibel range and have uniform sound level dimensions;

[0057] This scheme introduces a source noise extraction unit into the target feature extraction and analysis module to perform propagation inversion on the target noise signal received by the underwater fixed measurement array, thereby obtaining the source-level noise characteristics of the underwater target. This effectively eliminates the influence of propagation distance, water absorption, and environmental stratification on the noise measurement results, making the noise characteristics obtained under different test conditions comparable and consistent. On this basis, by jointly extracting the spectral characteristics, temporal modulation characteristics, and spatial pointing characteristics of the source-level noise signal, a multi-dimensional characterization of the low-frequency radiated noise intensity, modulation law, and spatial distribution characteristics of the underwater target is achieved, improving the accuracy and reliability of underwater target noise characteristic analysis and providing a stable and unified data foundation for the evaluation and comparative analysis of the acoustic characteristics of underwater targets.

[0058] Example 3:

[0059] This embodiment should be understood to include at least all the features of any of the foregoing embodiments, and further provides specific engineering implementation details and parameter configuration schemes based thereon.

[0060] This embodiment provides an underwater low-frequency noise comprehensive testing system. The system includes an underwater vehicle platform, an environmental perception calibration module, a bottom fixed measurement array, an adaptive signal processing module, a three-dimensional positioning module, and a target feature extraction and analysis module. The modules work together to achieve high-precision comprehensive measurement of the low-frequency radiated noise of underwater targets.

[0061] Furthermore, the underwater vehicle platform uses a modular autonomous underwater vehicle as its carrier, with an overall length of 4.2 to 5.8 meters, a diameter of 0.53 to 0.68 meters, a maximum underwater speed of no less than 6 knots, an endurance of no less than 72 hours, and a maximum operating depth of 300 to 500 meters. The appropriate specifications and models can be selected based on the actual test depth. The navigation system of the underwater vehicle platform adopts a combination of inertial navigation and Doppler velocities. The gyroscope zero-bias stability of the inertial navigation unit is better than 0.01 degrees per hour, the accelerometer zero-bias stability is better than 50 microgravity, and the Doppler velocities have a velocity measurement accuracy better than ±0.3%. The underwater positioning accuracy of the vehicle can reach 0.1% to 0.15% of the range. As a variant implementation, the navigation system can also adopt a combination of inertial navigation and an acoustic long baseline positioning system, or a combination of inertial navigation and an ultra-short baseline positioning system, to adapt to different marine environmental conditions and positioning accuracy requirements.

[0062] Furthermore, the load deployment unit adopts an electric push rod release mechanism with a push rod stroke of 150 mm to 200 mm, a maximum thrust of not less than 500 Newtons, a release response time of less than 2 seconds, and the ability to carry a fixed underwater measurement array with a mass of 80 kg to 150 kg. The release mechanism is equipped with a pressure sensor and a displacement sensor to monitor the release status. The pressure sensor has a range of 0 to 5 MPa and an accuracy of 0.1% of full scale, while the displacement sensor has a resolution of 0.1 mm. As a variant implementation, the load deployment unit can also adopt a hydraulically driven release mechanism or a pneumatically driven release mechanism. The hydraulically driven release mechanism is suitable for deployment scenarios with larger loads, while the pneumatically driven release mechanism is suitable for applications requiring higher response speeds.

[0063] Furthermore, the active sound source emitting unit employs a piezoelectric ceramic transducer array with an operating frequency range of 50 Hz to 2000 Hz and a sound source level of not less than 185 dB (reference value is 1 μPa at 1 meter). The emission directivity is omnidirectional or controllable, with an adjustable directivity range of ±30 degrees. The transducer array consists of 4 to 8 piezoelectric ceramic transducer units, with a unit diameter of 80 mm to 120 mm, and is encapsulated in a titanium alloy shell to adapt to the high-pressure underwater environment. As a variant implementation, the active sound source emitting unit can also employ a magnetostrictive transducer or an electric transducer. The magnetostrictive transducer has higher power density and a wider operating frequency band, while the electric transducer has better emission efficiency in the extremely low frequency band.

[0064] Furthermore, the positioning information acquisition unit integrates a global satellite navigation system receiver and an underwater acoustic communication device. The satellite navigation receiver supports multi-system and multi-frequency signal processing, with a surface positioning accuracy better than 2 meters. The underwater acoustic communication device operates at a frequency of 8 kHz to 16 kHz, has a communication distance of not less than 5,000 meters, and a communication rate of 80 bits per second to 500 bits per second. It is used to acquire satellite positioning information when the vehicle surfaces and transmit it to the underwater measurement array via an underwater acoustic link.

[0065] Furthermore, the sound velocity profile measurement unit in the environmental perception calibration module adopts an integrated temperature, salinity, and depth sensor group. The temperature measurement range is -2 degrees Celsius to 35 degrees Celsius with an accuracy of ±0.002 degrees Celsius; the conductivity measurement range is 0 to 7 Siemens per meter with an accuracy of ±0.0003 Siemens per meter; the pressure measurement range is 0 to 60 MPa with an accuracy of 0.01% of full scale; and the sampling frequency is 1 Hz to 24 Hz. It can realize the calculation of sound velocity from the water surface to the bottom of the water, and the sound velocity calculation accuracy is better than ±0.05 meters per second. As a modified implementation, the sound velocity profile measurement unit can also use a direct sound velocity meter for measurement. The direct sound velocity meter directly obtains the sound velocity value by measuring the propagation time of the ultrasonic wave over a known distance, and the measurement accuracy can reach ±0.02 meters per second, but the cost is relatively high.

[0066] Furthermore, the underwater acoustic attenuation measurement unit adopts a broadband swept-frequency signal transmission and reception method, with a swept-frequency range covering 10 Hz to 1000 Hz and a swept-frequency period of 5 seconds to 20 seconds. The underwater acoustic absorption coefficient of each frequency band is calculated by analyzing the amplitude attenuation characteristics of the reflected echo signal from the seabed. The absorption coefficient measurement accuracy is better than ±0.5 dB per kilometer. The background noise reference measurement unit adopts a low self-noise hydrophone with a self-noise level lower than the zero-order noise spectrum of the ocean. Its sensitivity is -170 dB (reference value is 1 volt per micropascal) to -195 dB, the operating frequency band is 1 Hz to 10000 Hz, and the dynamic range is not less than 120 dB. It is used to silently collect environmental background noise samples for no less than 600 seconds before the test.

[0067] Furthermore, the hydrophone array elements in the underwater fixed measurement array adopt a square or circular planar array layout, with 16 to 64 elements, an element spacing of 3 to 8 meters, and an array aperture of 12 to 56 meters. Each hydrophone element adopts a piezoelectric ceramic cylindrical structure, with a sensitivity of -180 dB to -195 dB (reference value is 1 volt per micropascal), an operating frequency band of 5 Hz to 2000 Hz, a pressure withstand depth of not less than 500 meters, and a self-noise equivalent sound pressure level more than 10 dB lower than the zero-order spectrum of the ocean. As a modified embodiment, the hydrophone array elements can also use vector hydrophones instead of scalar hydrophones. Vector hydrophones can simultaneously acquire sound pressure and particle velocity information, and have two-dimensional or three-dimensional directivity measurement capabilities, which helps to improve the spatial resolution and anti-interference performance in the low-frequency band.

[0068] Furthermore, the array synchronization unit uses a high-stability isothermal crystal oscillator as the time base source, with a frequency stability better than ±1 x 10^-9 per day, and the time synchronization error between each array element channel is less than 1 microsecond; the sound source sampling buffer unit uses a 24-bit analog-to-digital converter with a sampling frequency of 48 kHz to 96 kHz, a dynamic range of not less than 120 dB, and a built-in storage capacity of not less than 256 gigabytes, capable of continuously recording multi-channel acoustic data for no less than 48 hours.

[0069] Furthermore, the active sound source separation unit in the adaptive signal processing module employs an adaptive filtering algorithm to accurately remove the reference sound source signal. The filter order is from 128 to 512, and the convergence factor is adaptively adjusted from 0.001 to 0.1, with a signal separation degree better than 35 dB. The background noise suppression unit employs a Wiener filtering method based on power spectrum estimation or a noise suppression method based on subspace decomposition, with a noise suppression amount of 15 dB to 25 dB and a target signal distortion of less than 3%. As a modified implementation, the background noise suppression unit can also employ a noise suppression method based on deep learning, achieving more accurate noise estimation and suppression through a pre-trained neural network model, exhibiting better adaptability in non-stationary noise environments.

[0070] Furthermore, the array calibration unit in the three-dimensional positioning module calculates the actual three-dimensional spatial coordinates of each hydrophone array element based on the time difference of arrival and sound velocity profile data of the active reference sound source signal, using the least squares method or extended Kalman filter algorithm, with a coordinate calculation accuracy better than ±0.3 meters; the target positioning unit uses conventional beamforming or adaptive beamforming methods to estimate the target azimuth, with an azimuth resolution better than 3 degrees, an elevation angle estimation accuracy better than 5 degrees, and uses a time delay difference positioning method for target distance estimation, with a distance estimation accuracy better than 2% of the target distance.

[0071] Furthermore, the spectral feature extraction unit in the target feature extraction and analysis module uses Fast Fourier Transform or high-resolution spectral estimation methods to perform spectral analysis on the source-level noise signal, with a frequency resolution better than 0.5 Hz. It can extract the power spectral density distribution and characteristic spectral lines in the 10 Hz to 500 Hz frequency band, and the frequency identification accuracy of the characteristic spectral lines is better than ±0.2 Hz. The time-domain modulation feature extraction unit uses envelope demodulation and cyclostationary analysis methods to extract the modulation features of the target noise, with a modulation frequency resolution better than 0.1 Hz. It can identify periodic modulation components such as propeller blade frequency and shaft frequency. The spatial pointing feature extraction unit combines target position information and multi-channel signal data, and uses beam power spectrum analysis to extract the energy distribution of target radiated noise in different azimuth and pitch angle directions, with an angular resolution better than 5 degrees.

[0072] like Figure 3 , Figure 4 and Figure 5 As shown, to verify the beneficial effects of the underwater low-frequency noise comprehensive testing system described in this invention, a systematic comparative test experiment was conducted in a certain sea area. The average water depth of the test area was about 180 meters, the sea state conditions were level 2 to 3, the seawater temperature was 18.2 degrees Celsius, and the salinity was 34.5‰. During the test, the power spectral density of the ambient background noise was about 42 dB to 48 dB (reference value is 1 micropascal squared per hertz). The test target was a certain type of diesel-powered underwater vehicle with a displacement of about 850 tons and a speed range of 5 to 8 knots. The main radiated noise was concentrated in the low-frequency band of 20 Hz to 400 Hz, of which the main engine fundamental frequency was about 62 Hz and the propeller blade frequency was about 8.3 Hz.

[0073] This experiment used three measurement schemes for comparison and verification: The system of this invention is configured as a 4.5-meter-class autonomous underwater vehicle equipped with a 16-element square underwater fixed measurement array (element spacing 5 meters, array aperture 20 meters), with a hydrophone sensitivity of -190dB, a sampling rate of 48kHz, an active sound source emission unit operating frequency range of 50Hz to 500Hz, and a sound source level of 185dB; Comparative Example 1 uses a traditional single-point hydrophone measurement scheme, using a single piezoelectric ceramic hydrophone with a sensitivity of -185dB placed at a fixed position on the seabed; Comparative Example 2 uses a traditional towed array measurement scheme, using a 32-element linear array (element spacing 0.75 meters) towed by a surface vessel at a speed of 4 knots, with basic background noise suppression function.

[0074] The test lasted for 8 hours. The target's distance gradually decreased from 3,500 meters to 500 meters and then back to 3,000 meters. A total of 480 sets of valid data were collected. Each set of data included 16 channels of sound pressure signals, environmental parameter records, target position information, and processed feature data. The data collection interval was 60 seconds, covering three typical test stages: target approach, horizontal alignment, and target departure. This fully verified the system's measurement performance under different distance and orientation conditions.

[0075] The detailed experimental steps include:

[0076] Step 1: System Deployment and Initialization

[0077] The underwater vehicle platform (4.5 meters long, 0.53 meters in diameter, and a maximum operating depth of 300 meters) carries an underwater fixed measurement array and dives to the test area. After reaching the predetermined position, it uses an electric push rod release mechanism (180 mm push rod stroke, 500 N maximum thrust) to deploy the 16-element square array to the seabed and anchor it. The vehicle then returns to its initial position (approximately 200 meters from the center of the array). The positioning information acquisition unit obtains the vehicle's position in real time through a combination of inertial navigation and Doppler velocity measurement, achieving a positioning accuracy of 0.12% of the range.

[0078] Step 2: Environmental parameter calibration and data collection:

[0079] The environmental perception calibration module was activated: The sound velocity profile measurement unit used an integrated temperature, salinity, and depth sensor group (temperature accuracy ±0.002℃, conductivity accuracy ±0.0003S / m, pressure accuracy 0.01%FS) to perform continuous profile measurements from the water surface to the bottom, and calculated the sound velocity profile data (the average sound velocity in this measurement was 1498m / s); the underwater acoustic attenuation measurement unit emitted a 20Hz to 1000Hz sweep frequency signal (sweep period 10 seconds) and calculated the absorption coefficient of each frequency band based on the seabed reflected echo; the background noise benchmark measurement unit used a low self-noise hydrophone (self-noise below the zero order spectrum of the ocean, sensitivity -192dB) to silently collect 800 seconds of environmental background noise samples before the target arrived.

[0080] Step 3: Precise Array Positioning and Calibration

[0081] The active sound source transmitting unit adaptively selects the optimal transmission frequency band based on availability indicators. Initially, 125Hz is selected as the reference sound source center frequency (sound source level 185dB), transmitting positioning signals to each hydrophone in the array. The array calibration unit, based on the signal arrival time difference (synchronization error of each channel less than 1 microsecond) and sound velocity profile data, uses an extended Kalman filter algorithm to calculate the actual three-dimensional spatial coordinates of each array element, correcting displacement and tilt deviations during array deployment. After calibration, the positioning accuracy reaches ±0.3 meters, meeting the requirements for subsequent beamforming and target positioning.

[0082] Step 4: Synchronous acquisition of target signal

[0083] The test target approaches the measurement array from a distance of 3500 meters at a speed of 5 to 8 knots. The underwater fixed measurement array continuously receives the low-frequency noise signal radiated by the target. The array synchronization unit uses a high-stability temperature-controlled crystal oscillator (frequency stability ±1×10⁻⁻⁻⁴). 9( / day) Ensures 16-channel time synchronization. The sound source sampling buffer unit uses a 24-bit analog-to-digital converter (sampling rate 48kHz, dynamic range 120dB) for multi-channel synchronous acquisition. The built-in 256GB storage enables continuous recording throughout the entire process. The test lasted for 8 hours, with the target distance changing from 3500 meters to 500 meters and then moving further away to 3000 meters.

[0084] Step 5: Adaptive signal processing:

[0085] The adaptive signal processing module performs three levels of processing on the acquired signal: the active sound source separation unit uses an adaptive filtering algorithm (filter order 256, convergence factor 0.015) to accurately remove the local sound source component from the mixed signal, achieving a separation degree of 38dB; the background noise suppression unit uses Wiener filtering based on the pre-acquired environmental noise spectrum for adaptive filtering, achieving a noise suppression amount of 22dB and a target signal distortion of less than 2.5%; the target signal extraction unit outputs a clean target noise signal, with the average signal-to-noise ratio improved by 18.5 to 22.3dB after processing.

[0086] Step 6: 3D positioning and trajectory calculation:

[0087] The target positioning unit uses an adaptive beamforming method based on clean signals to estimate the target's azimuth (azimuth resolution 2.8 degrees, pitch angle estimation accuracy 4.2 degrees), and calculates the target distance by combining the time delay difference of each channel (distance estimation accuracy is better than 1.8% of the target distance). The fusion position output unit transforms the vehicle position, array position and target position to a unified coordinate system, and outputs the target's three-dimensional motion trajectory in real time, with a positioning update rate of 10Hz and trajectory calculation accuracy improved by 65% ​​compared to Comparative Example 2.

[0088] Step 7: Multidimensional extraction of noise features:

[0089] The target feature extraction and analysis module completes multi-dimensional feature analysis: the source noise extraction unit calculates the target source level through propagation inversion (eliminating the influence of propagation distance and water absorption); the spectrum feature extraction unit uses a high-resolution spectrum estimation method (frequency resolution 0.4Hz) to identify five characteristic spectral lines, including the 62Hz main engine fundamental frequency and 124Hz / 186Hz / 248Hz harmonics; the time-domain modulation feature extraction unit extracts the propeller blade frequency modulation of 8.3Hz (modulation frequency resolution 0.08Hz); and the spatial pointing feature extraction unit analyzes the energy distribution of noise in different directions (angular resolution 4 degrees).

[0090] Step 8: Data Statistics and Effect Verification

[0091] Statistical analysis was performed on 480 sets of data from three measurement schemes: Compared with Comparative Example 1 (single-point hydrophone), the signal-to-noise ratio of this system was improved by 18.5 to 22.3 dB, the positioning accuracy was improved from ±12 meters to ±0.8 meters, the standard deviation of repeated measurements was reduced from 3.2 dB to 0.7 dB, and the effective measurement distance was extended from 1500 meters to 3200 meters; compared with Comparative Example 2 (towed array), the signal-to-noise ratio was improved by 8.2 to 11.5 dB, with a particularly significant improvement of 14.2 dB in the low-frequency band (20 to 100 Hz), a 65% improvement in trajectory calculation accuracy, and a 58% improvement in source-level measurement consistency, fully verifying the beneficial effects of the system of this invention.

[0092] The content disclosed above is only a preferred and feasible embodiment of the present invention, and is not intended to limit the scope of protection of the present invention. Therefore, all equivalent technical changes made based on the content of the present invention specification and drawings are included within the scope of protection of the present invention. Furthermore, the elements therein can be updated as technology develops.

Claims

1. An underwater low-frequency noise comprehensive testing system, characterized in that, The system includes an underwater vehicle platform, an environmental perception and calibration module, an underwater fixed measurement array, an adaptive signal processing module, a three-dimensional positioning module, and a target feature extraction and analysis module. The underwater vehicle platform is used to maneuverably carry and deploy the underwater fixed measurement array, and to complete the precise positioning of the underwater fixed measurement array through the transmission of acoustic source signals between the platform and the underwater fixed measurement array; the environmental perception calibration module is used to provide an environmental calibration basis for underwater acoustic propagation and noise analysis; the underwater fixed measurement array is used to receive underwater target noise and reference acoustic source signals emitted by the vehicle at a preset water depth for a long period of time. The underwater vehicle platform includes a payload deployment unit, an active sound source transmission unit, and a positioning information acquisition unit. The payload deployment unit is used to carry, release, and retrieve the underwater fixed measurement array. The active sound source transmission unit is used to transmit active reference sound source signals to the underwater fixed measurement array to achieve precise positioning of the underwater fixed measurement array. The positioning information acquisition unit is used to acquire the current position information of the underwater vehicle in real time.

2. The underwater low-frequency noise comprehensive testing system according to claim 1, characterized in that, The environmental perception calibration module includes a sound velocity profile measurement unit, an underwater acoustic attenuation measurement unit, and a background noise reference measurement unit. The sound velocity profile measurement unit is used to measure the sound velocity profile at various depths underwater in real time in conjunction with a CTD sensor array. The underwater acoustic attenuation measurement unit is used to calculate the underwater acoustic absorption coefficient at different frequency bands by transmitting a sweep frequency signal to the bottom and receiving the reflected echo from the bottom. The background noise reference measurement unit is used to obtain the background noise power spectral density in the underwater environment in real time.

3. The underwater low-frequency noise comprehensive testing system according to claim 1, characterized in that, The active sound source transmitting unit adaptively selects the optimal operating frequency band as the transmission frequency band of the active reference sound source signal under different underwater test environments. The specific working process of the active sound source transmitting unit is as follows: S1: In the initial stage of testing, after the vehicle platform releases the underwater fixed measurement array, the vehicle returns to the predetermined navigation position, and the availability index of each frequency band is calculated: ； in, For the transmission frequency band The corresponding availability index at that time For the transmission frequency band The power spectrum of the sound source at that time For the transmission frequency band Background noise power spectrum at that time For the transmission frequency band The underwater acoustic absorption coefficient at that time, The propagation distance is the estimated distance from the vehicle to the center of the underwater fixed measurement array during the initial stage of the test. S2: Use the frequency band corresponding to the maximum value of the current availability index as the center frequency of the active reference sound source signal in the initial stage of the test; S3: During the test, an adaptive adjustment cycle is set, and at the end of each adaptive adjustment cycle, the position information of the underwater vehicle is obtained to calculate the current propagation distance, and the availability index of each frequency band is recalculated. If the availability index of a new frequency band is greater than the switching threshold, the active reference sound source is switched to the new frequency band to complete the transmission; otherwise, the current frequency band is maintained.

4. The underwater low-frequency noise comprehensive testing system according to claim 1, characterized in that, The underwater fixed measurement array includes a hydrophone array element unit, an array synchronization unit, and a sound source sampling buffer unit. The hydrophone array element unit consists of multiple hydrophones arranged in an array, and each hydrophone can receive sound pressure signals from underwater. The array synchronization unit is used to achieve time synchronization calibration between different hydrophones. The sound source sampling buffer unit is used to filter and preprocess the sound pressure signals acquired by the hydrophones in the measurement array and buffer them.

5. The underwater low-frequency noise comprehensive testing system according to claim 1, characterized in that, The adaptive signal processing module includes an active sound source separation unit, a background noise suppression unit, and a target signal extraction unit; The active sound source separation unit is used to accurately extract and remove the active reference sound source signal component from the sound pressure signal received by the underwater fixed measurement array based on the emission time, center frequency and reference sound source signal characteristics provided by the active sound source emission unit. The background noise suppression unit is used to adaptively filter the sound pressure signal after removing the active sound source based on the background noise power spectral density provided by the environmental perception calibration module, thereby suppressing environmental background noise; the target signal extraction unit is used to output the target noise signal after active sound source separation and background noise suppression.

6. The underwater low-frequency noise comprehensive testing system according to claim 1, characterized in that, The three-dimensional positioning module includes an array calibration unit, a target positioning unit, and a fusion position output unit. The array calibration unit is used to calculate the propagation distance and azimuth angle between the vehicle and each hydrophone based on the arrival time of the active reference sound source signal and the sound speed profile, and accordingly calculates the actual spatial coordinates of each hydrophone in the underwater fixed measurement array, correcting the displacement, tilt, and deformation of the underwater fixed measurement array after deployment in the initial stage of the test. The target positioning unit is used to measure the azimuth and pitch angles of the underwater target relative to each hydrophone through beamforming based on the target noise signal acquired by each hydrophone, obtain the distance between each hydrophone and the underwater target through the time delay difference of the pure target noise signal acquired by each hydrophone, and calculate the position of the underwater target by combining the current actual spatial coordinates of each hydrophone. The fusion position output unit is used to perform a unified coordinate system transformation on the position of the underwater vehicle, the position of the underwater fixed measurement array, and the position of the underwater target, and output the relative geometric relationship between the three.

7. The underwater low-frequency noise comprehensive testing system according to claim 1, characterized in that, The target feature extraction and analysis module includes a source noise extraction unit, a spectrum feature extraction unit, a time-domain modulation feature extraction unit, and a spatial pointing feature extraction unit. The source noise extraction unit performs propagation inversion on the target noise signal to extract the source-level noise signal of the underwater target. The spectrum feature extraction unit performs low-frequency spectrum analysis on the source-level noise signal to extract the power spectral density distribution, characteristic spectral lines, spectral peak positions, and spectral energy variation characteristics of the target within a preset low-frequency band, characterizing the low-frequency radiated noise intensity and spectral structure characteristics of the underwater target. The time-domain modulation feature extraction unit performs time-domain and time-frequency analysis on the source-level noise signal to extract the periodic modulation characteristics, amplitude fluctuation characteristics, and modulation frequency characteristics of the target noise, reflecting the time-frequency domain characteristics of the underwater target. The spatial pointing feature extraction unit combines the target spatial position information output by the three-dimensional positioning module to extract the energy distribution characteristics and pointing variation characteristics of the source-level noise signal in different spatial directions, reflecting the spatial distribution law of the radiated noise of the underwater target.

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