Acoustic test system with underwater movement and fixed measurement array collaboration

Abstract

The invention provides an underwater moving and fixed measurement array collaborative acoustic test system. The system comprises an underwater vehicle platform, an underwater fixed measurement array, a space-time calibration module and a sound source control modulation module, the underwater vehicle platform is used for bearing the sound source transmitting equipment, the attitude sensor, the position beacon and the communication module; the underwater fixed measurement array is used for receiving a bottom layer target acoustic signal and a reference sound signal emitted by an aircraft platform; the space-time calibration module is used for realizing the consistency of test signals acquired from the aircraft platform and the measurement array; the sound source control modulation module is used for generating different acoustic test signals according to task requirements; according to the invention, the underwater vehicle platform and the underwater fixed measurement array are cooperatively fused to construct a reconfigurable, high-precision and time-space consistent acoustic test system, so that the underwater acoustic test capability with a larger coverage range, higher measurement precision and stronger data consistency under a complex sea area condition is realized.

Description

An acoustic testing system combining underwater mobile and fixed measurement arrays Technical Field

[0001] This invention relates to the field of underwater acoustic testing system technology, and in particular to an acoustic testing system that combines underwater mobile and fixed measurement arrays. Background Technology

[0002] With the increasing demands for tasks such as marine resource exploration, subsea engineering construction, underwater target identification, and marine environmental monitoring, the importance of underwater acoustic testing technology is becoming increasingly prominent. Traditional underwater acoustic testing mostly relies on fixed hydrophone arrays for data acquisition. Although this deployment method has advantages such as structural stability and strong long-term monitoring capabilities, its measurement coverage and observation angle are greatly limited in complex sea conditions, deep water areas, or large-scale measurement tasks due to the fixed array position and poor reconfigurability.

[0003] On the other hand, with the development of underwater vehicle technology, conducting mobile acoustic testing based on underwater vehicles is gradually becoming a trend. Underwater vehicles have advantages such as autonomous navigation, flexible maneuverability, and adaptability to multi-depth environments, and can form variable measurement geometry within the mission area. However, a single vehicle platform still has shortcomings in terms of sound source localization accuracy, multi-point reception capability, and long-term stability, making it difficult to meet the requirements of high-precision sound field inversion and multi-source data consistency.

[0004] In practical underwater acoustic testing, achieving high-precision time synchronization, unified spatial coordinates, and reliable data fusion under multi-platform, multi-node collaborative conditions is a major challenge currently facing the technology. Especially under conditions of complex and variable marine environments, significant time-varying sound velocity profiles, and limited communication bandwidth, traditional measurement systems struggle to simultaneously balance maneuverability and measurement accuracy.

[0005] Therefore, there is an urgent need for a collaborative testing system that combines the flexibility of a mobile platform with the stability of a fixed array measurement, thereby improving the coverage, parameter controllability, and data accuracy of underwater acoustic measurements.

[0006] A review of publicly available technical solutions reveals that CN114485645A proposes a UUV cluster cooperative positioning system and method based on ranging and information interaction. This system includes a master UUV, multiple slave UUVs, and a cooperative positioning device mounted on each slave UUV. The cooperative positioning device uses INS data from the slave UUVs for position estimation as the primary navigation unit and acoustic ranging and cooperative positioning message filtering as the secondary navigation unit. The cooperative positioning method includes: clock discipline within the master and slave UUVs; the master UUV periodically packaging its own position and position estimation covariance matrix into a cooperative positioning message and broadcasting it to the slave UUVs in the cluster; the slave UUVs receiving the cooperative positioning message; and the cooperative positioning device of the slave UUVs constructing state and measurement equations based on the data and calculating the cooperative positioning result using an extended Kalman filter. This invention considers the uncertainty in the position estimation of the main UUV itself and reconstructs the state vector of the slave UUV, thereby improving the overall positioning performance of the cluster. However, this scheme mainly addresses the collaborative positioning problem of the UUV cluster itself and does not involve the construction of the underwater fixed measurement array and its acoustic testing collaboration mechanism with the mobile platform. Therefore, it cannot perform high-precision, reconfigurable array-based measurement of the target sound field. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of current systems by proposing an acoustic testing system that combines underwater mobile and fixed measurement arrays.

[0008] The present invention adopts the following technical solution:

[0009] An underwater acoustic testing system integrating a mobile and fixed measurement array is disclosed. The system includes an underwater vehicle platform, a fixed underwater measurement array, a spatiotemporal calibration module, and a sound source control and modulation module. The underwater vehicle platform carries a sound source transmitting device, attitude sensors, a position beacon, and a communication module. The fixed underwater measurement array receives acoustic signals from underlying targets and reference acoustic signals transmitted by the vehicle platform. The spatiotemporal calibration module ensures consistency between the test signals acquired by the vehicle platform and the measurement array. The sound source control and modulation module generates different acoustic test signals according to mission requirements.

[0010] The sound source transmitting device is used to generate and transmit a preset acoustic test signal according to the instructions of the sound source control modulation module.

[0011] The attitude sensor is used to collect the attitude parameters of the underwater vehicle platform in real time.

[0012] The position beacon is used to obtain the real-time position coordinates of the vehicle platform.

[0013] The communication module is used to enable bidirectional communication between the underwater vehicle platform and the underwater fixed measurement array.

[0014] Furthermore, the underwater fixed measurement array includes multiple hydrophone nodes, which are used to receive acoustic signals generated by underwater targets and reference acoustic signals emitted by underwater vehicle platforms. The multiple hydrophone nodes are arranged in a preset spatial geometry. Each hydrophone node integrates a data buffer unit, a power management unit, and a self-test unit. The data buffer unit is used to locally store the raw acoustic signals collected by the hydrophones and attach a collection timestamp to the stored data. The power management unit is used to manage the energy consumption status of the hydrophone nodes. The self-test unit is used to detect the operating status of key components in the hydrophone nodes.

[0015] Furthermore, the spatiotemporal calibration module includes a time synchronization unit, a spatial baseline calibration unit, and a coordinate unification unit; the time synchronization unit is used to achieve high-precision time synchronization between the underwater vehicle platform and each node of the underwater fixed measurement array; the spatial baseline calibration unit is used to establish a precise spatial baseline relationship between the vehicle platform and the measurement array nodes; the coordinate unification unit is used to convert the position information of the vehicle platform, each hydrophone node, and the underwater target to a unified measurement coordinate system.

[0016] Furthermore, the sound source control modulation module includes a waveform generation unit, a power control unit, a transmission timing unit, and a signal encoding unit. The waveform generation unit is used to generate different types of acoustic signal waveforms according to the test task, including single-frequency continuous wave (CW), linear frequency modulated (LFM) signal, M-sequence, chirp signal, and multi-frequency combination signal. The power control unit is used to adaptively adjust the transmission power according to the test distance and environmental conditions. The transmission timing unit is used to precisely control the transmission time of the acoustic signal to ensure strict synchronization with the sampling timing of the measurement array. The signal encoding unit is used to perform feature encoding on the transmitted signal to facilitate signal identification and matched filtering at the receiving end.

[0017] Furthermore, the time synchronization unit employs a bidirectional time transfer protocol to achieve high-precision time synchronization, specifically including the following steps:

[0018] S11: Initial clock synchronization: When the system starts up, the surface mother ship initializes and synchronizes the master clock of the underwater unmanned vehicle platform and the underwater fixed measurement array through GPS or Beidou satellite timing system; each hydrophone node obtains the initial time reference from the master clock.

[0019] S12: Two-way time signal exchange: The underwater unmanned vehicle platform is in time... Transmit a synchronization signal to the target hydrophone node; the target node at time... Upon receiving the signal, the local timestamp is recorded; the target node at time... Send a response signal; the spacecraft platform at any time A response signal was received;

[0020] S13: Clock Offset Calculation: Calculate the clock offset and one-way propagation time based on the four timestamps.

[0021] ;

[0022] ;

[0023] in, This represents the clock offset between the hydrophone node and the vehicle platform. The one-way propagation time of the sound signal;

[0024] S14: Time-varying sound speed compensation: Based on real-time measured water temperature, salinity, and depth parameters, the equivalent sound speed along the propagation path is calculated, and the propagation time is corrected.

[0025] ;

[0026] ;

[0027] in, For reference speed of sound, The equivalent speed of sound along the propagation path. , and These are the coefficients representing the effects of temperature, salinity, and depth on the speed of sound. This is the difference between the measured temperature and the reference temperature. This represents the difference between the measured salinity and the reference salinity. The difference between the measured depth and the reference depth. To correct the one-way propagation time of the acoustic signal;

[0028] Recalculate the precise clock offset using the corrected propagation time:

[0029] ;

[0030] in, This is the precise clock offset after correction for the speed of sound. This is the precise clock offset before sound speed correction;

[0031] S15: Timestamp Correction: A series of corrected clock offset measurements are obtained through multiple bidirectional time transfers. and the corresponding measurement time Clock drift rate is estimated using linear regression:

[0032] ;

[0033] in, For the first Clock drift rate of each node; The average value at measurement time. This represents the average value of the clock offset.

[0034] After obtaining the clock drift rate, the timestamps of all subsequent sampled data are corrected in real time:

[0035]

[0036] in, For the first The node Corrected timestamps for each sampling point This is the original timestamp. This is the most recently measured clock offset. The reference time for estimating the clock drift rate;

[0037] S16: Periodic Synchronization Update: The system repeats steps S12 to S15 every preset time interval to perform a new round of bidirectional time transfer and update the clock offset. and drift rate To ensure synchronization accuracy during long-term operation; when the cumulative number of updates exceeds a preset threshold, the most recent N update values ​​are used for sliding window linear regression, where N is the preset number of updates within a period, and the update values ​​include increasing the clock offset and drift rate to improve the accuracy of drift rate estimation.

[0038] The beneficial effects achieved by this invention are:

[0039] This invention constructs a reconfigurable and scalable underwater acoustic testing system by synergistically integrating an underwater vehicle platform with a fixed underwater measurement array. It achieves high-precision, multi-node system-level time consistency through bidirectional time transfer, dynamic sound velocity compensation, and clock drift correction. Combined with a spatial baseline calibration method based on multi-constraint optimization, it significantly improves the calibration accuracy of array node positions and vehicle positions. Through a unified coordinate system transformation and adaptive sound source control mechanism, this invention can acquire more stable and accurate acoustic measurement data under complex sea conditions and time-varying sound channels, thereby improving the overall accuracy and reliability of underwater sound field inversion, propagation loss measurement, and target acoustic characteristic analysis. Attached Figure Description

[0040] 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.

[0041] Figure 1 is a schematic diagram of the overall modules of the present invention.

[0042] Figure 2 is a schematic diagram of the time synchronization unit of the present invention.

[0043] Figure 3 is a schematic diagram of the working process of the spatial baseline calibration unit of the present invention.

[0044] Figure 4 is a schematic diagram comparing the positioning error index of the system of the present invention and the traditional solution.

[0045] Figure 5 is a schematic diagram comparing the performance of the system of the present invention and the traditional solution in terms of clock drift cumulative error index.

[0046] Figure 6 is a schematic diagram comparing the performance of the system of the present invention and the traditional solution in terms of array geometry calibration accuracy. Detailed Implementation

[0047] 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.

[0048] 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 invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0049] Example 1:

[0050] As shown in Figures 1, 2, and 3, this embodiment provides an acoustic testing system that coordinates an underwater mobile and fixed measurement array. The system includes an underwater vehicle platform, a fixed underwater measurement array, a spatiotemporal calibration module, and a sound source control and modulation module. The underwater vehicle platform carries a sound source transmitting device, attitude sensor, position beacon, and communication module. The fixed underwater measurement array receives acoustic signals from the underlying target and reference acoustic signals transmitted by the vehicle platform. The spatiotemporal calibration module ensures consistency between the test signals acquired by the vehicle platform and the measurement array. The sound source control and modulation module generates different acoustic test signals according to mission requirements.

[0051] The sound source transmitting device is used to generate and transmit a preset acoustic test signal according to the instructions of the sound source control modulation module;

[0052] The attitude sensor is used to collect the attitude parameters of the underwater vehicle platform in real time;

[0053] The position beacon is used to obtain the real-time position coordinates of the vehicle platform;

[0054] The communication module is used to enable bidirectional communication between the underwater vehicle platform and the underwater fixed measurement array.

[0055] The underwater fixed measurement array includes multiple hydrophone nodes, which are used to receive acoustic signals generated by underwater targets and reference acoustic signals emitted by underwater vehicle platforms. The multiple hydrophone nodes are arranged in a preset spatial geometry. Each hydrophone node integrates a data buffer unit, a power management unit, and a self-test unit. The data buffer unit is used to locally store the raw acoustic signals collected by the hydrophones and append a timestamp to the stored data. The power management unit is used to manage the energy consumption status of the hydrophone nodes. The self-test unit is used to detect the operational status of key components within the hydrophone nodes.

[0056] The spatiotemporal calibration module includes a time synchronization unit, a spatial baseline calibration unit, and a coordinate unification unit. The time synchronization unit is used to achieve high-precision time synchronization between the underwater vehicle platform and each node of the underwater fixed measurement array. The spatial baseline calibration unit is used to establish a precise spatial baseline relationship between the vehicle platform and the measurement array nodes. The coordinate unification unit is used to convert the position information of the vehicle platform, each hydrophone node, and the underwater target to a unified measurement coordinate system.

[0057] The sound source control modulation module includes a waveform generation unit, a power control unit, a transmission timing unit, and a signal encoding unit. The waveform generation unit generates different types of acoustic signal waveforms according to the test task, including single-frequency continuous wave (CW), linear frequency modulated (LFM) signals, M-sequences, chirp signals, and multi-frequency combination signals. The power control unit adaptively adjusts the transmission power based on the test distance and environmental conditions. The transmission timing unit precisely controls the transmission time of the acoustic signals to ensure strict synchronization with the sampling timing of the measurement array. The signal encoding unit performs feature encoding on the transmitted signals, facilitating signal identification and matched filtering at the receiving end.

[0058] Furthermore, the time synchronization unit employs a bidirectional time transfer protocol to achieve high-precision time synchronization, specifically including the following steps:

[0059] S11: Initial clock synchronization: When the system starts up, the surface mother ship initializes and synchronizes the master clock of the underwater unmanned vehicle platform and the underwater fixed measurement array through GPS or Beidou satellite timing system; each hydrophone node obtains the initial time reference from the master clock.

[0060] S12: Two-way time signal exchange: The underwater unmanned vehicle platform is in time... Transmit a synchronization signal to the target hydrophone node; the target node at time... Upon receiving the signal, the local timestamp is recorded; the target node at time... Send a response signal; the spacecraft platform at any time A response signal was received;

[0061] S13: Clock Offset Calculation: Calculate the clock offset and one-way propagation time based on the four timestamps.

[0062] ;

[0063] ;

[0064] in, This represents the clock offset between the hydrophone node and the vehicle platform. The one-way propagation time of the sound signal;

[0065] S14: Time-varying sound speed compensation: Based on real-time measured water temperature, salinity, and depth parameters, the equivalent sound speed along the propagation path is calculated, and the propagation time is corrected.

[0066] ;

[0067] ;

[0068] in, For reference speed of sound, The equivalent speed of sound along the propagation path. , and These are the influence coefficients of temperature, salinity, and depth on the speed of sound, respectively, with units of (m / s) / ℃, (m / s) / salinity unit, and (m / s) / m, used to characterize the linear compensation contribution of temperature, salinity, and depth changes to the speed of sound. This is the difference between the measured temperature and the reference temperature. This represents the difference between the measured salinity and the reference salinity. The difference between the measured depth and the reference depth. To correct the one-way propagation time of the acoustic signal;

[0069] Recalculate the precise clock offset using the corrected propagation time:

[0070] ;

[0071] in, This is the precise clock offset after correction for the speed of sound. This is the precise clock offset before sound speed correction;

[0072] S15: Timestamp Correction: A series of corrected clock offset measurements are obtained through multiple bidirectional time transfers. and the corresponding measurement time Clock drift rate is estimated using linear regression:

[0073] ;

[0074] in, For the first Clock drift rate of each node; The average value at measurement time. This represents the average value of the clock offset.

[0075] After obtaining the clock drift rate, the timestamps of all subsequent sampled data are corrected in real time:

[0076]

[0077] in, For the first The node Corrected timestamps for each sampling point This is the original timestamp. This is the most recently measured clock offset. The reference time for estimating the clock drift rate;

[0078] S16: Periodic Synchronization Update: The system repeats steps S12 to S15 every preset time interval to perform a new round of bidirectional time transfer and update the clock offset. and drift rate To ensure synchronization accuracy during long-term operation; when the cumulative number of updates exceeds a preset threshold, the most recent N update values ​​are used for sliding window linear regression, where N is the number of updates within a preset period, and the update values ​​include increasing the clock offset and drift rate to improve the accuracy of drift rate estimation;

[0079] Specifically, the reference temperature, reference salinity, and reference depth are preset reference state parameters, and their values ​​can be determined based on a preset empirical sound velocity model or calibration experiments; , and The reference state parameters can be obtained using existing empirical models or experimental calibration methods for underwater acoustic velocity.

[0080] This scheme introduces a two-way time transfer mechanism to achieve high-precision clock alignment between the underwater unmanned vehicle platform and each node of the underwater fixed measurement array without requiring precise prior knowledge of the propagation delay. Furthermore, by combining sound speed time-varying compensation based on temperature, salinity, and depth parameters, it effectively suppresses the impact of changes in the aquatic environment on the propagation time of the acoustic signal. Through linear regression modeling of multiple synchronization results, it estimates and corrects node clock drift in real time, enabling the system to maintain a stable and consistent time reference even under long-term operation. This significantly improves the time consistency and fusionability of multi-node acoustic test data, providing a reliable time basis for subsequent time difference measurements, array beamforming, and sound field inversion.

[0081] Example 2:

[0082] This embodiment should be understood to include at least all the features of any of the foregoing embodiments, and to further improve upon them;

[0083] This embodiment provides an acoustic testing system that coordinates an underwater mobile and fixed measurement array. The system includes an underwater vehicle platform, a fixed underwater measurement array, a spatiotemporal calibration module, and a sound source control and modulation module. The underwater vehicle platform carries a sound source transmitting device, attitude sensors, a position beacon, and a communication module. The fixed underwater measurement array receives acoustic signals from underlying targets and reference acoustic signals transmitted by the vehicle platform. The spatiotemporal calibration module ensures consistency between the test signals acquired by the vehicle platform and the measurement array. The sound source control and modulation module generates different acoustic test signals according to mission requirements.

[0084] The underwater fixed measurement array includes multiple hydrophone nodes, which are used to receive acoustic signals generated by underwater targets and reference acoustic signals emitted by underwater vehicle platforms. The multiple hydrophone nodes are arranged in a preset spatial geometry. Each hydrophone node integrates a data buffer unit, a power management unit, and a self-test unit. The data buffer unit is used to locally store the raw acoustic signals collected by the hydrophones and append a timestamp to the stored data. The power management unit is used to manage the energy consumption status of the hydrophone nodes. The self-test unit is used to detect the operational status of key components within the hydrophone nodes.

[0085] The spatiotemporal calibration module includes a time synchronization unit, a spatial baseline calibration unit, and a coordinate unification unit. The time synchronization unit is used to achieve high-precision time synchronization between the underwater vehicle platform and each node of the underwater fixed measurement array. The spatial baseline calibration unit is used to establish a precise spatial baseline relationship between the vehicle platform and the measurement array nodes. The coordinate unification unit is used to convert the position information of the vehicle platform, each hydrophone node, and the underwater target to a unified measurement coordinate system.

[0086] Preferably, the hydrophone node further includes an acoustic transmission unit for measuring the distance between nodes, used to send ranging acoustic signals to adjacent hydrophone nodes during the spatial baseline calibration phase;

[0087] Furthermore, the workflow of the space baseline calibration unit specifically includes the following steps:

[0088] S21: Initial Information Acquisition and Distance Measurement: During the system deployment phase, the pre-calibration position coordinates of each hydrophone node are recorded as prior information. The pre-calibration position can be obtained through water surface GPS positioning and depth sensor measurement, with an initial accuracy of ±2 to 5 meters; at the same time, the reference distance between each hydrophone node is recorded as a geometric constraint.

[0089] The underwater unmanned vehicle platform sequentially transmits reference acoustic signals to each hydrophone node via a sound source transmitter. Preferably, a linear frequency modulated (LFM) signal is used, with a frequency range of 8 kHz to 12 kHz and a duration of 50 to 100 milliseconds. After receiving the reference acoustic signals, each hydrophone node extracts the arrival time through matched filtering and calculates the distance observation value from the vehicle to the node.

[0090]

[0091] in, For the spacecraft to reach the Distance observations of each node, For the first The time when each node receives a signal The time when the spacecraft transmits a signal. The equivalent speed of sound along the propagation path;

[0092] Preferably, the final distance observation result can be obtained by repeatedly measuring each node 3 to 5 times and taking the average value. At the same time, the observation standard deviation of the distance observation value can be calculated based on the multiple distance measurement results of the node to evaluate the stability and reliability of the distance measurement result.

[0093] S22: Cross-ranging acquisition between hydrophone nodes: To enhance the stability of the array's internal geometry, cross-ranging is performed between hydrophone nodes during the spatial baseline calibration phase, including:

[0094] S221: The system designates a hydrophone node as a transmitting node in a preset order;

[0095] S222: This transmitting node sends ranging acoustic signals to 4 to 8 adjacent hydrophone nodes in spatial location through its acoustic transmitting unit;

[0096] S223: Adjacent hydrophone nodes receive signals and calculate the propagation time between nodes to obtain the observed distance between nodes;

[0097] S23: Constructing a multi-constraint joint optimization model: Establishing a comprehensive objective function that includes distance observation residuals, node spacing constraints, and prior location constraints.

[0098] ;

[0099] in, For the comprehensive objective function, For the vehicle's position, For the first The estimated true location of each node. For the first The estimated true location of each node. This is the weighting coefficient, and its value is the reciprocal of the observed standard deviation; These are the observed distances between nodes. For node pairs in cross-distance measurement, For the set of node pairs to perform cross ranging, For the first The pre-calibrated position of each node. and For regularization parameters;

[0100] Preferably, when there is sufficient cross-distance measurement data between nodes, take to , to ;

[0101] S24: Iterative Optimization Solution: The comprehensive objective function obtained in the previous step is iteratively solved using the least squares method. After each iteration updates the node position estimation, it is checked whether the new estimated true position meets the physical constraints. The physical constraints include: minimum node spacing constraint to prevent non-physical overlap of node positions; node depth range constraint to limit node depth to a reasonable range; and overall array deformation constraint to suppress non-realistic overall stretching or twisting. The iterative convergence condition is: the position change between two adjacent iterations is less than 0.01 to 0.05 meters, or the relative change of the comprehensive objective function is less than... to Or, it may reach the maximum number of iterations;

[0102] S25: Output: Obtain the iteratively optimized positioning accuracy index, which includes the vehicle position and the position of each hydrophone node, and transmit the positioning accuracy index to the coordinate unification unit for subsequent acoustic data processing.

[0103] This scheme, through the aforementioned spatial baseline calibration process, introduces cross-ranging constraints between hydrophone nodes based on the underwater vehicle's maneuvering ranging, and constructs a multi-constraint joint optimization model in conjunction with the pre-calibrated node positions. This achieves precise calibration of the real spatial geometry of the underwater fixed measurement array. The method effectively suppresses the influence of array deployment errors, ranging noise, and local abnormal nodes on the overall geometric solution results. While ensuring physical feasibility, it significantly improves the stability and accuracy of array node position estimation. This provides a reliable spatial baseline foundation for subsequent acoustic data fusion processing, sound field reconstruction, and propagation characteristic analysis in a unified coordinate system, thereby enhancing the measurement accuracy and engineering applicability of the entire acoustic testing system.

[0104] Example 3:

[0105] This embodiment should be understood to include at least all the features of any of the foregoing embodiments, and to further improve upon them. The present invention will be described in detail below with reference to specific parameter configurations, technical implementation details, comparative verification data and alternative solutions.

[0106] In this embodiment, the underwater vehicle platform adopts a torpedo-shaped design with a total length of 2400 mm to 3200 mm, a diameter of 320 mm to 450 mm, and a dry weight in air of 180 kg to 320 kg. It uses aluminum alloy or titanium alloy pressure-resistant shell material, has a maximum operating depth of 500 m to 1500 m, and can operate continuously for 12 hours to 48 hours at a speed of 5 knots. As an alternative shape, a flat or disc-shaped design can be adopted to reduce the drag coefficient by about 15% to 25%, or a modular splicing structure can be adopted to facilitate transportation and on-site assembly.

[0107] The sound source emitting device employs a piezoelectric ceramic transducer array with 4 to 12 transducers, each with a unit diameter of 60 mm to 120 mm. The operating frequency range covers 1 kHz to 50 kHz, and the emitted sound source level can reach 185 dB to 210 dB at the center frequency. It supports switching between omnidirectional and directional emission modes. As a transducer alternative, the piezoelectric ceramic transducer can be replaced with an electromagnetic transducer or a magnetostrictive transducer. Magnetostrictive transducers offer higher electroacoustic conversion efficiency in the low-frequency band (approximately 10% to 20% improvement) but increase volume by approximately 30% to 50%. Electromagnetic transducers have a simpler structure and lower cost (approximately 40% to 60%) but increase power consumption by approximately 25% to 40%.

[0108] The attitude sensor employs a combination of a fiber optic gyroscope inertial measurement unit and an electronic compass. The fiber optic gyroscope exhibits zero-bias stability better than 0.01 to 0.05 degrees per hour, scale factor stability better than 20 to 100 ppm, angle measurement accuracy of 0.01 to 0.05 degrees, heading accuracy of 0.1 to 0.5 degrees, an update frequency of 100 to 400 Hz, and data output latency of less than 5 to 20 milliseconds. As an alternative to inertial measurement, a MEMS inertial measurement unit can replace the fiber optic gyroscope, reducing costs by 60% to 80%, but decreasing angular velocity measurement accuracy to 0.1 to 1 degree per hour. This is suitable for shallow water testing scenarios or short-term measurement tasks with lower accuracy requirements.

[0109] The location beacon employs a long-baseline acoustic positioning system combined with inertial navigation, achieving a positioning accuracy of 0.1 to 0.5 meters within a slant range of 1000 to 3000 meters. The positioning update rate is 0.2 Hz to 2 Hz, the beacon operates at a frequency of 20 kHz to 30 kHz, and its transmission power is 175 dB to 190 dB. A four-element receiver array is used for direction of arrival calculation, with an azimuth resolution better than 0.5 to 2 degrees. As an alternative positioning system, an ultra-short baseline system can replace the long-baseline system, reducing installation and commissioning time by 70% to 85% but decreasing positioning accuracy to 0.5 to 2 meters. This is suitable for test missions with high mobility requirements. Alternatively, a combined inertial and Doppler velocimeter trajectory calculation scheme can be used to provide backup positioning capability in case of beacon failure.

[0110] The communication module employs an underwater acoustic communicator to achieve bidirectional data transmission between the underwater vehicle platform and the fixed underwater measurement array. It operates in dual-band frequencies of 8kHz to 16kHz or 24kHz to 32kHz, with an adaptive communication rate ranging from 200bps to 9600bps. The communication distance can reach 2000 meters to 8000 meters in typical marine environments, and the bit error rate is less than 0.1% to 1% with a signal-to-noise ratio greater than 10dB. It supports both time-division multiple access (TDMA) and code-division multiple access (CDMA) networking modes. As an alternative communication solution, an optical communication module can replace the underwater acoustic communicator in short-range, high-speed transmission scenarios. Optical communication rates can reach 1Mbps to 10Mbps, but the effective communication distance is limited to 50 meters to 200 meters. Alternatively, a cable-controlled communication method can be used to achieve unlimited-distance, high-speed transmission, but this sacrifices the vehicle's maneuverability and autonomy.

[0111] In this embodiment, the underwater fixed measurement array consists of 16 to 64 hydrophone nodes, arranged in a square or hexagonal array layout, with the node spacing adjustable from 50 meters to 500 meters, and the array coverage area ranging from 0.25 square kilometers to 25 square kilometers. As an alternative to the array layout, a random sparse array layout can be used to expand the coverage area by approximately 30% to 60% while maintaining spatial sampling diversity with the same number of nodes, or a multi-layer vertical array layout can be used to obtain the vertical distribution characteristics of the sound field for sound velocity profile inversion, or a ring array layout can be used to achieve omnidirectional equal-precision measurements suitable for sound source localization tasks.

[0112] The hydrophone node uses a cylindrical piezoelectric ceramic hydrophone with a sensitivity of -185dB to -205dB (reference 1V / μPa), an operating frequency range of 10Hz to 100kHz, and selectable omnidirectional or cardioid polarization. The noise floor equivalent sound pressure level at 1kHz is 15dB to 25dB below sea state zero, and the dynamic range is not less than 100dB to 130dB. As an alternative to the hydrophone type, fiber optic hydrophones can be used instead of piezoelectric ceramic hydrophones. They have the advantages of strong anti-electromagnetic interference capability and high sensitivity, which is about 10dB to 20dB higher, but the cost increases by 200% to 400% and requires a matching opto-demodulation system and a dedicated optical cable.

[0113] The data cache unit uses industrial-grade solid-state storage with a storage capacity of 64GB to 512GB, a data write speed of no less than 50MB / s to 200MB / s, a sampling rate of 8kHz to 192kHz, a sampling accuracy of 16-bit to 24-bit, and each sampled data is appended with a 64-bit timestamp with a timestamp resolution of 1 microsecond to 10 microseconds. As an alternative storage solution, mechanical hard disk storage can be used to expand the capacity to 2TB to 8TB, but additional vibration reduction and isolation design is required to adapt to underwater vibration. Alternatively, memory caching can be used in conjunction with real-time upload to reduce local storage requirements, but higher requirements are placed on the reliability of the communication link.

[0114] The power management unit supports three levels of power consumption switching, including standby mode power consumption of less than 0.1 watts, low-speed sampling mode power consumption of 0.5 watts to 2 watts, and full-speed sampling mode power consumption of 3 watts to 15 watts. The power supply adopts a high-energy-density lithium battery pack with a battery capacity of 50Ah to 200Ah. The continuous working time of a single node in low-speed sampling mode can reach 30 days to 180 days. As an alternative power supply solution, submarine cable power supply can be used to replace battery power supply to achieve indefinite continuous operation, but additional cable laying and protection engineering investment is required. Alternatively, ocean current power generation or thermoelectric power generation devices can be used to achieve partial energy self-sufficiency and extend the endurance by about 20% to 50%.

[0115] The self-test unit has five functions: hydrophone sensitivity verification, memory health detection, battery power monitoring, cabin leakage detection, and communication link testing. The self-test cycle can be set from 1 hour to 24 hours. Abnormal conditions are automatically reported and a backup node activation mechanism is triggered. The hydrophone sensitivity verification uses a built-in reference sound source excitation method to detect whether the sensitivity deviation exceeds ±3dB.

[0116] In this embodiment, the time synchronization unit adopts a bidirectional time transfer protocol to achieve high-precision time synchronization. The initial clock source uses a high-precision temperature-controlled crystal oscillator with a frequency accuracy better than one part per million to one part per ten million and a daily drift rate of less than 0.1 ppm to 1 ppm. After bidirectional time transfer compensation, the time synchronization accuracy of each node reaches 1 microsecond to 10 microseconds, and the synchronization update cycle is adjustable from 10 seconds to 300 seconds. As an alternative clock source, a chip-level atomic clock can be used to replace the temperature-controlled crystal oscillator to reduce the daily drift rate to below 0.01 ppm, but the cost increases by about 300% to 500%. Alternatively, a temperature-compensated crystal oscillator can be used to reduce the cost by about 50% to 70%, but the daily drift rate increases to 1 ppm to 10 ppm.

[0117] The spatial baseline calibration unit uses a linear frequency modulated (LFM) signal for ranging, with a center frequency of 8 kHz to 15 kHz, a bandwidth of 2 kHz to 6 kHz, a pulse duration of 50 ms to 200 ms, and a ranging repetition frequency of 0.5 Hz to 2 Hz. In typical marine environments, the single ranging accuracy is better than 0.1 m to 0.5 m, and after averaging multiple measurements, it can reach 0.02 m to 0.1 m. As an alternative ranging signal, an M-sequence pseudo-random coded signal can be used to replace the LFM signal to improve the ranging robustness in multipath environments by about 15% to 30%, but the signal processing complexity increases by 30% to 50%. Alternatively, an orthogonal frequency division multiplexing (OFDM) signal can be used to integrate ranging and communication to improve spectrum utilization efficiency.

[0118] The coordinate unification unit supports bidirectional conversion between the geographic coordinate system and the local Cartesian coordinate system. The coordinate origin can be set at the array geometric center or a specified hydrophone node position. The coordinate conversion accuracy is better than 0.01 meters to 0.05 meters. It supports real-time calculation of the trajectory of moving targets based on Doppler velocity measurement, with velocity estimation accuracy better than 0.1 m / s to 0.5 m / s. As an alternative to coordinate conversion, an ellipsoidal coordinate system or a UTM projected coordinate system can be used to meet the coordinate continuity requirements of large-scale cross-regional measurement tasks.

[0119] In this embodiment, the waveform generation unit uses direct digital synthesis technology to generate test signal waveforms. The digital-to-analog conversion resolution is 16-bit to 24-bit, the output sampling rate is 96kHz to 384kHz, the waveform storage depth supports 32M to 256M sampling points, and it can generate single-frequency continuous wave signals with a frequency range of 100Hz to 50kHz, linear frequency modulated signals with a bandwidth of 100Hz to 20kHz, M-sequence orders of 7 to 15, and multi-frequency combination signals supporting the superposition of up to 16 frequency components. As an alternative to waveform generation, an arbitrary waveform generator can be used to replace direct digital synthesis to support more complex custom waveforms, but the cost increases by about 100% to 200%.

[0120] The power control unit supports 10 to 100 levels of fine-tuning of transmit power, with an adjustment step size of 1dB to 3dB. The difference between the maximum and minimum transmit power is not less than 30dB to 60dB. The power adjustment response time is less than 10 milliseconds to 50 milliseconds. It has overcurrent and overtemperature protection functions, automatically reducing power protection when the transducer temperature exceeds 65 degrees Celsius or the drive current exceeds 120% of the rated value.

[0121] The timing control accuracy of the transmission timing unit is better than 1 microsecond to 10 microseconds. It supports three working modes: single transmission, periodic transmission, and triggered transmission. The periodic transmission interval can be set from 100 milliseconds to 60 seconds, and the triggered transmission delay can be set from 0 milliseconds to 1000 milliseconds. As an alternative to timing control, an external trigger synchronization method can be used to achieve strict timing coordination with other measurement devices.

[0122] The signal encoding unit supports three encoding methods: Barker code, M-sequence, and Gold sequence. The encoding length ranges from 7 to 1023 bits. The encoding modulation method includes two options: binary phase shift keying (BPS) and quadrature phase shift keying (QPS). The matched filter gain at the receiver ranges from 8 dB to 30 dB.

[0123] To verify the performance advantages of the system described in this invention, as shown in Figures 4, 5, and 6, a comparative test was conducted at a near-shore test site. The test area had a water depth of 80 to 120 meters, a silty seabed, and sea state 2 to 3 during the test. The water temperature vertical profile showed a negative gradient distribution, with surface water temperature ranging from 22 to 25 degrees Celsius and bottom water temperature ranging from 15 to 18 degrees Celsius.

[0124] Comparative Example 1 adopts a traditional fixed array working mode. The array consists of 24 hydrophone nodes with a node spacing of 100 meters. The pre-deployed coordinates are directly used as the node positions without performing vehicle-to-vehicle collaborative calibration. Time synchronization relies solely on the initial satellite time synchronization without dynamic update compensation.

[0125] Comparative Example 2 adopts a single-vehicle maneuvering measurement mode. The vehicle is equipped with an integrated transceiver acoustic measurement system and sails at a constant speed along a preset route. The receiving array is a 4-element linear array with a baseline length of 0.5 meters, and it is not coordinated with the underwater fixed array.

[0126] The system of this invention adopts the collaborative working mode described in the embodiments, in which the vehicle works together with a fixed array of 32 hydrophone nodes to perform a complete spatiotemporal calibration process before testing.

[0127] Regarding the sound source localization accuracy, the root mean square error of sound source localization in Comparative Example 1 is 3.2 meters to 5.8 meters, the root mean square error of sound source localization in Comparative Example 2 is 1.5 meters to 2.8 meters, and the root mean square error of sound source localization in the system of the present invention is 0.3 meters to 0.6 meters, which is an improvement of 82% to 90% and 60% to 79% compared with Comparative Example 1 and Comparative Example 2, respectively.

[0128] Regarding time synchronization accuracy, after 8 hours of continuous operation, the cumulative error of clock drift at each node in Comparative Example 1 reached 15 to 80 microseconds. Since Comparative Example 2 only involves a single aircraft and does not involve multi-node synchronization issues, the system of this invention maintains the clock synchronization error of each node within the range of 2 to 8 microseconds after 24 hours of continuous operation, meeting the requirements for high-precision arrival time difference measurement.

[0129] Regarding the accuracy of array geometry calibration, the node position error of Comparative Example 1, which relies on pre-placed coordinates, is 1.5 meters to 4.2 meters. Comparative Example 2 does not involve fixed array calibration. After multi-constraint joint optimization, the node position estimation error of the system of this invention is reduced to 0.08 meters to 0.25 meters, which is 85% to 95% higher than that of Comparative Example 1.

[0130] In terms of coverage and measurement efficiency, the coverage of Comparative Example 1 array is fixed at about 0.24 square kilometers, while Comparative Example 2 vehicle maneuver measurement covers about 0.5 square kilometers per hour, but the data quality is affected by the attitude stability of the vehicle. The fixed array of the present invention provides stable spatial coverage of about 0.32 square kilometers, while the vehicle can expand the boundary of the measurement area. The overall measurement efficiency is improved by 40% to 120% compared with the single mode.

[0131] In specific implementations, the following technical means can be modified and replaced according to the actual application scenario.

[0132] Regarding the type of underwater vehicle platform, in addition to the torpedo-type autonomous underwater vehicle described in this embodiment, it can be replaced with a gliding underwater vehicle to achieve low-power, long-endurance operation, with its endurance extended to 7 to 30 days, but its speed reduced to 0.5 to 2 knots. Alternatively, it can be replaced with a cable-controlled underwater robot to achieve real-time control and high-bandwidth data transmission rates of up to 10 Mbps to 100 Mbps, but its operating range is limited by the cable length. Or, it can be replaced with a wave glider combined with a towed sound source to achieve surface remote control and solar power supply, suitable for long-term monitoring tasks.

[0133] Regarding time synchronization technology, in addition to the bidirectional time transfer protocol described in this embodiment, it can be replaced by unidirectional broadcast synchronization in conjunction with a high-precision atomic clock to simplify the communication process and reduce synchronization communication overhead by about 50% to 70%, or by underwater time synchronization technology based on the common-view method to improve the parallel synchronization efficiency of multiple nodes and reduce the total calibration time by about 30% to 50%, or by fully coherent phase-locked loop technology to achieve phase locking of the sampling clock and achieve sub-microsecond level synchronization accuracy.

[0134] Regarding data fusion algorithms, in addition to the multi-constraint least squares optimization described in this embodiment, it can be replaced by extended Kalman filtering to achieve recursive real-time estimation suitable for dynamic tracking scenarios, or by particle filtering to handle strong nonlinear and non-Gaussian noise scenarios to improve robustness by about 20% to 40%, or by factor graph optimization to achieve global consistency constraints suitable for large-scale arrays with more than 100 nodes.

[0135] The underwater mobile and fixed measurement array coordinated acoustic testing system described in this embodiment has achieved significant results in practical applications.

[0136] In terms of sound field measurement, the system can achieve propagation loss measurement accuracy better than 1dB to 2dB and sound source level inversion accuracy better than 2dB to 3dB in the range of 100 meters to 5000 meters. The multipath structure resolution capability can distinguish sound ray paths with arrival time differences greater than 0.5 milliseconds to 2 milliseconds.

[0137] In terms of target localization, the system's three-dimensional positioning accuracy for cooperative targets is better than 0.5 to 1 meter within a distance of 1000 meters and better than 1 to 2 meters within a distance of 3000 meters. The root mean square error of the tracking position of moving targets is less than 1 to 3 meters, and the root mean square error of velocity estimation is less than 0.2 m / s to 0.5 m / s.

[0138] In terms of system reliability, the mean time between failures (MTBF) of the underwater fixed array nodes is greater than 2,000 to 5,000 hours, the continuous operation time of the vehicle platform is greater than 12 to 36 hours, and the overall system availability is greater than 95% to 99%.

[0139] In terms of deployment efficiency, the fixed array deployment time is 4 to 12 hours, the vehicle launch preparation time is 0.5 to 2 hours, the spatiotemporal calibration process takes 0.5 to 2 hours, and the first acquisition of valid measurement data takes 6 to 16 hours after the system enters the water.

[0140] This embodiment, through detailed technical parameter configuration, comparative verification data, and explanation of alternative solutions, fully demonstrates the technical advantages and engineering feasibility of the system of the present invention in achieving high-precision and reconfigurable underwater acoustic testing in complex marine environments.

[0141] 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 acoustic testing system that combines underwater mobile and fixed measurement arrays, characterized in that, The system includes an underwater vehicle platform, a bottom-mounted fixed measurement array, a spatiotemporal calibration module, and a sound source control and modulation module; the underwater vehicle platform is used to carry the sound source transmitting equipment, attitude sensors, position beacons, and communication modules; the bottom-mounted fixed measurement array is used to receive acoustic signals from the underlying target and reference acoustic signals transmitted by the vehicle platform; The spatiotemporal calibration module is used to ensure consistency between the test signals acquired by the underwater vehicle platform and the measurement array; the acoustic source control modulation module is used to generate different acoustic test signals according to mission requirements; the acoustic source transmitting device is used to generate and transmit preset acoustic test signals according to the instructions of the acoustic source control modulation module; the attitude sensor is used to collect the attitude parameters of the underwater vehicle platform in real time; the position beacon is used to obtain the real-time position coordinates of the vehicle platform; and the communication module is used to realize bidirectional communication between the underwater vehicle platform and the underwater fixed measurement array.

2. The acoustic testing system for underwater mobile and fixed measurement arrays in coordination according to claim 1, characterized in that, The underwater fixed measurement array includes multiple hydrophone nodes, which are used to receive acoustic signals generated by underwater targets and reference acoustic signals emitted by underwater vehicle platforms. The multiple hydrophone nodes are arranged in a preset spatial geometry. Each hydrophone node integrates a data buffer unit, a power management unit, and a self-test unit. The data buffer unit is used to locally store the raw acoustic signals collected by the hydrophones and to attach a collection timestamp to the stored data. The power consumption management unit is used to manage the power consumption status of the hydrophone node; the self-testing unit is used to detect the operating status of key components in the hydrophone node.

3. The acoustic testing system for underwater mobile and fixed measurement arrays in coordination according to claim 1, characterized in that, The spatiotemporal calibration module includes a time synchronization unit, a spatial baseline calibration unit, and a coordinate unification unit. The time synchronization unit is used to achieve high-precision time synchronization between the underwater vehicle platform and each node of the underwater fixed measurement array. The spatial baseline calibration unit is used to establish a precise spatial baseline relationship between the vehicle platform and the measurement array nodes. The coordinate unification unit is used to convert the position information of the vehicle platform, each hydrophone node, and the underwater target to a unified measurement coordinate system.

4. The acoustic testing system for underwater mobile and fixed measurement arrays in coordination according to claim 1, characterized in that, The sound source control modulation module includes a waveform generation unit, a power control unit, a transmission timing unit, and a signal encoding unit. The waveform generation unit is used to generate different types of acoustic signal waveforms according to the test task, including single-frequency continuous wave (CW), linear frequency modulated (LFM) signal, M-sequence, chirp signal, and multi-frequency combination signal. The power control unit is used to adaptively adjust the transmission power according to the test distance and environmental conditions. The transmission timing unit is used to precisely control the transmission time of the acoustic signal to ensure strict synchronization with the sampling timing of the measurement array. The signal encoding unit is used to perform feature encoding on the transmitted signal to facilitate signal identification and matched filtering at the receiving end.

5. The acoustic testing system for underwater mobile and fixed measurement arrays in coordination according to claim 3, characterized in that, The time synchronization unit employs a bidirectional time transfer protocol to achieve high-precision time synchronization, specifically including the following steps: S11: Initial clock synchronization: When the system starts, the surface mother ship initializes and synchronizes the master clocks of the underwater unmanned vehicle platform and the underwater fixed measurement array via GPS or Beidou satellite timing system; each hydrophone node obtains the initial time reference from the master clock; S12: Bidirectional time signal exchange: The underwater unmanned vehicle platform at time... Transmit a synchronization signal to the target hydrophone node; the target node at time... Upon receiving the signal, the local timestamp is recorded; the target node at time... Send a response signal; the spacecraft platform at any time Received acknowledgment signal; S13: Clock offset calculation: Calculate the clock offset and one-way propagation time based on the four timestamps: ； ;in, This represents the clock offset between the hydrophone node and the vehicle platform. S14: Time-varying sound speed compensation: Based on real-time measured water temperature, salinity, and depth parameters, the equivalent sound speed along the propagation path is calculated, and the propagation time is corrected. ； ;in, For reference speed of sound, The equivalent speed of sound along the propagation path. 、 and These are the coefficients representing the effects of temperature, salinity, and depth on the speed of sound. This is the difference between the measured temperature and the reference temperature. This represents the difference between the measured salinity and the reference salinity. The difference between the measured depth and the reference depth. To correct the one-way propagation time of the acoustic signal, the precise clock offset is recalculated using the corrected propagation time. ;in, This is the precise clock offset after correction for the speed of sound. S15: Time stamp correction: A series of corrected clock offset measurements are obtained through multiple bidirectional time transfers. and the corresponding measurement time Clock drift rate is estimated using linear regression: ;in, For the first Clock drift rate of each node; The average value at measurement time. This represents the average clock offset; after obtaining the clock drift rate, the timestamps of all subsequent sampled data are corrected in real time. in, For the first The node Corrected timestamps for each sampling point This is the original timestamp. This is the most recently measured clock offset. Reference time for clock drift rate estimation; S16: Periodic synchronization update: The system repeats steps S12 to S15 every preset time interval to perform a new round of bidirectional time transfer and update the clock offset. and drift rate To ensure synchronization accuracy during long-term operation; when the cumulative number of updates exceeds a preset threshold, the most recent N update values ​​are used for sliding window linear regression, where N is the preset number of updates within a period, and the update values ​​include increasing the clock offset and drift rate to improve the accuracy of drift rate estimation.

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