Underwater sound vertical line array element sensitivity in-situ calibration method based on high-precision synchronous clock
By combining a high-precision synchronization clock and an omnidirectional sound source, in-situ calibration of the underwater acoustic detection array elements was achieved, solving the problems of high cost and environmental impact of array element sensitivity calibration, and providing accurate array element performance testing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-09
- Publication Date
- 2026-03-31
AI Technical Summary
Existing technologies for underwater acoustic detection arrays suffer from high costs, complex procedures, and are affected by the marine environment, making accurate calibration difficult to achieve in real-world environments.
A high-precision synchronous clock is used to provide a time reference. Combined with an omnidirectional sound source, a standard hydrophone, and a CTD, in-situ calibration of the vertical linear array elements is achieved by measuring the sound source level and time interval data.
Without changing the array position, accurate calibration of the sensitivity of the underwater acoustic detection array was achieved, providing array element performance testing in a real-world environment and ensuring the sonar system is in good working order.
Smart Images
Figure CN121762012A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of underwater acoustic array element hydrophone sensitivity calibration technology, specifically relating to an in-situ calibration method for the sensitivity of underwater acoustic vertical linear array elements based on a high-precision synchronous clock. Background Technology
[0002] A hydrophone array is a series of transducers connected in series, primarily used for underwater target detection, identification, localization, and measurement of underwater radiated noise. The types of hydrophones that make up the array vary depending on the underwater deployment method. Detection arrays, compared to individual hydrophones, have higher spatial gain, improving the signal-to-noise ratio of the received signal. They are often used for broadband radiated noise measurement of low-noise targets. However, radiated noise source-level measurements depend on the accuracy of the array element sensitivity calibration. Therefore, sensitivity calibration of the array elements in an underwater acoustic detection array is of significant engineering importance.
[0003] For the sensitivity calibration of array elements after linear array formation, existing technologies generally employ comparative calibration or in-tube calibration. Among them, the free-field comparative method uses a calibrated sound source to calibrate the sensitivity of the hydrophone, which includes sound field requirements, deployment preparation, precautions for calibrating the sound source, uncertainty analysis, etc., but it has drawbacks such as being complicated and difficult to implement.
[0004] Because the physical structure and subsequent electronic systems of the hydrophone can affect the actual sensitivity and amplitude-phase consistency of the array elements after arraying, and because the sensitivity of the hydrophone elements in the actual marine environment is affected by seawater temperature and pressure, its sensitivity will change to some extent. If the sensitivity of the hydrophone needs to be calibrated in the laboratory before each experiment, the cost will be high, and the process of calibrating the sensitivity of long arrays will be cumbersome. Summary of the Invention
[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an accurate time reference by using a high-precision synchronous clock, and to provide a solution with small calibration error and high feasibility for in-situ sensitivity calibration of underwater acoustic vertical linear arrays.
[0006] To achieve the above objectives, this invention provides an in-situ calibration method for the sensitivity of underwater acoustic vertical linear array elements based on a high-precision synchronous clock, comprising the following steps:
[0007] Step 1: Construct a standard hydrophone device and vertical linear array for measuring the sound power of omnidirectional sound sources;
[0008] Step 2: Lower the CTD to a depth exceeding the vertical linear array depth, then lift and retrieve it, and measure the average sound velocity;
[0009] Step 3: Control the omnidirectional sound source to emit a signal, use a standard hydrophone to measure the sound source level at different frequencies in real time and record the LFM ranging signal waveform to calibrate the sound source level of the omnidirectional sound source;
[0010] Step 4: The vertical linear array receives the LFM signal, stores the LFM signal waveform and open-circuit voltage data at each frequency point in the storage system, and obtains the time interval data after data processing;
[0011] Step 5: Calculate the sensitivity of each linear array element based on the average sound velocity, sound source level data, open circuit voltage data at each frequency point, and time interval data to achieve in-situ calibration.
[0012] Based on the above technical content, the present invention has the following beneficial effects:
[0013] This invention achieves in-situ calibration of the sensitivity of vertical linear array elements by arranging an omnidirectional sound source, a standard hydrophone, a CTD, and a vertical linear array equipped with a high-precision synchronization clock system underwater, while keeping the experimental environment unchanged.
[0014] Meanwhile, this invention calibrates the sensitivity of hydrophones in the underwater acoustic detection array directly in a marine or lake environment without changing the array's location. By closely mimicking real-world conditions, it tests the receiving performance of the installed underwater acoustic detection array, effectively determining the actual performance and consistency of the hydrophone elements. This provides accurate data references for the implementation of algorithms such as signal processing in the underwater acoustic detection array, ensuring the sonar system operates in good condition.
[0015] Other advantages, objectives, and features of the invention will be set forth in the following description and will be apparent to those skilled in the art in some respects, or may be learned by practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description
[0016] Figure 1 This is an overall schematic diagram of an embodiment of this application;
[0017] Figure 2 This is a specific deployment example diagram of the Yellow Sea test experiment in this application;
[0018] Figure 3 for Figure 2 A schematic diagram of an LFM signal emitted by an omnidirectional sound source;
[0019] Figure 4 This is a timing diagram of the received signals of a vertical linear array.
[0020] Figure 5The following is a graph showing the sensitivity data of three representative array elements at different frequencies in the test examples of this application;
[0021] Figure 6 This is a sensitivity calibration comparison chart of three representative array elements in the test examples of this application. Detailed Implementation
[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0023] This application provides an embodiment of a method for in-situ sensitivity calibration of underwater vertical linear array elements based on a high-precision synchronous clock, including the following steps:
[0024] S1. Construct a device for measuring the sound power of an omnidirectional sound source, such as... Figure 1 As shown, this involves assembling an omnidirectional sound source and a standard hydrophone using a rigid support on an experimental vessel (deployment vessel) and then deploying them underwater at a certain depth using ropes.
[0025] Next, the omnidirectional sound source and the standard hydrophone are fixed on a rigid bracket. The straight-line distance between the sound center of the omnidirectional sound source and the standard hydrophone is measured and recorded using a steel tape measure, and this distance is set to be no less than 1m.
[0026] The rigid straight rod is flexibly lowered into the water using a cantilever crane and placed on the experimental vessel, at the same depth as the first element of the vertical array. If the first element is far from the water surface, it is placed as close to the depth of the first element as possible, depending on the specific circumstances.
[0027] S2. Differential GPS is used to synchronize the time of the omnidirectional sound source and the synchronization clock of the vertical line array. The two synchronization clocks are synchronized using GPS second pulses, and the synchronization error is less than 10µs.
[0028] S3. Construct a vertical line array, including placing the vertical line array underwater at a certain distance from the experimental vessel.
[0029] Furthermore, the vertical line array is positioned no more than 1500 meters away from the experimental vessel. The first element of the vertical line array is connected to the buoy frame, and the last element is connected to the seabed release device and the sinker, which can contact the seabed.
[0030] S4. Deploy the CTD to measure the speed of sound, including lowering the CTD from the experimental ship to a depth exceeding the length of the linear array and then retrieving it.
[0031] Furthermore, during the CTD deployment and retrieval process, the CTD records the sound velocity at different profiles between the omnidirectional sound source and the vertical linear array, and then the average value of the sound velocity at different depths is taken as the average sound velocity.
[0032] S5. Control the omnidirectional sound source to emit signals, and use a standard hydrophone to measure the sound source level at different frequencies in real time and record the LFM ranging signal waveform to calibrate the sound source level of the omnidirectional sound source.
[0033] Furthermore, each cycle of the signal emitted by the omnidirectional sound source includes an active emission phase and a silent observation phase.
[0034] Furthermore, the signal in the main transmission phase adopts a composite waveform design, including a PPS second pulse, an LFM ranging signal, and a single-frequency short pulse train sequence (characteristic frequency sequence). Its triggering method is triggered by the rising edge of the second pulse, and its structure is as follows:
[0035] When the rising edge of the first PPS second pulse arrives, the LFM ranging signal is transmitted. After a preset time, the characteristic frequency signal is transmitted according to the 1 / 3 octave band criterion. Finally, the LFM ranging signal is transmitted again to finish. The next PPS second pulse is the silent observation phase, and the signal is continuously transmitted according to the above pattern.
[0036] While the omnidirectional sound source emits LFM and frequency signals, a standard hydrophone receives the waveform of the LFM signal and the open-circuit voltage of the frequency signal. Using the LFM signal data, the distance between the standard hydrophone and the omnidirectional sound source can be determined. Since the sensitivity of the standard hydrophone is known, the distance can be calculated using the formula: The source level L of an omnidirectional sound source can be measured. sp Real-time calibration is achieved.
[0037] The above formula is the measurement correction formula for the sound source level (sound pressure level at a reference distance of 1m) in a free field, 20lgU FP -M0 equals the sound pressure level produced by the omnidirectional sound source at 1m, but due to spherical wave attenuation, a distance correction term of 20lgd needs to be added to finally obtain the source level L of the omnidirectional sound source. sp The parameters are defined as follows:
[0038] —The emitted sound level of the calibrated omnidirectional sound source, in dB, with a reference value of 1 μPa·m; U FP —Standard hydrophone output open-circuit voltage, in volts; — The distance between an omnidirectional sound source and the sound center of a standard hydrophone, in meters; —The sensitivity level of a standard hydrophone at this frequency, in dB.
[0039] S6. The vertical linear array receives LFM signals, including storing the LFM signal waveforms received by the vertical linear array elements and the open-circuit voltage data at each frequency point to the storage system via cables. The data is then processed by the host computer to obtain the time interval data.
[0040] Furthermore, the vertical linear array and the omnidirectional sound source are time-synchronized (world time synchronization). The waveform measured by the vertical linear array is matched and filtered with the waveform recorded by the standard hydrophone to obtain the correlation peak.
[0041] If the vertical linear array elements are composed of self-contained hydrophones, then the world time at the correlation peak is the time when the LFM ranging signal arrives at the vertical linear array element. Subtracting the transmission time of the LFM signal from this time gives the time interval data.
[0042] If the array elements of a vertical line array are triggered to receive signals by the rising edge of a PPS second pulse, the time interval data can be obtained by calculating the time difference between the correlation peak and the rising edge trigger.
[0043] S7. After data acquisition, the sensitivity of each linear array element can be obtained by using time interval data, average sound velocity data, sound source level data, and open-circuit voltage data, combined with formulas, thereby achieving in-situ calibration. Specifically:
[0044] Substituting the measured source level data of each frequency signal from the omnidirectional sound source, the open-circuit voltage of the different frequency signals received by each element of the vertical linear array directly obtained from the array elements, the average sound velocity, and the time interval data into the following formula, the sensitivity of each vertical linear array element can be obtained:
[0045]
[0046] In this formula, the sum of the first three terms on the right-hand side represents the sum of the array elements in... take The voltage measured at a distance is equivalent to the receiving voltage level at a reference distance of 1 m. Then subtract the source level L. sp (i.e., the sound pressure level at 1 m), yielding the "difference between voltage level and sound pressure level", which is the logarithmic form of the voltage-to-sound-pressure ratio, satisfying the definition of hydrophone sensitivity.
[0047] The parameters are defined as follows:
[0048] —The sensitivity level of the hydrophone calibrated by the underwater acoustic detection array is measured in dB, with a reference value of 1 V / μPa; —The emitted sound level of a calibrated omnidirectional sound source, in dB, with a reference value of 1 μPa·m; —The open-circuit voltage value at a certain frequency point in the output signal of the i-th hydrophone element, in V; —The average speed of sound measured at the depth position of the i-th hydrophone element, in m / s; —The absolute time delay (time interval) between the emitted signal from the omnidirectional sound source and the output signal of the hydrophone to be calibrated, in seconds.
[0049] like Figures 2-6 As shown, based on the same concept as the above embodiments, this application provides a specific experimental process and results in the Yellow Sea, and the implementation details are as follows:
[0050] (1) On-site environmental conditions: The wave height in the sea area is about 0.5m, the wind speed is 5.5m / s, the ambient temperature is 26℃, and there is light rain. The sea area is open, far from the shipping channel, and there are no other ships around. The water depth is about 37m.
[0051] (2) Example of device model selection and placement:
[0052] An omnidirectional sound source was connected to a standard hydrophone using a rigid straight rod, with a straight-line distance of 1 meter between them. The rigid straight rod was then flexibly lowered using a cantilever crane to a depth of at least 10 meters underwater from the experimental vessel. A Beidou positioning antenna was also fixed within 2 meters of the cantilever crane's suspension rope.
[0053] The vertical array elements of the Yellow Sea sea trial consist of three self-contained hydrophones, model icListen HF SC2-ETH. The omnidirectional sound source is model T150, with parameters of 1kHz-10kHz, Sv=148dB@10kHz, and is traced to the National Defense Underwater Acoustic Level 1 Metrology Station.
[0054] like Figure 2 As shown, the first array element is approximately 10m above the sea surface, followed by subsequent array elements spaced 10m apart. The vertical array is fixed by anchoring the tail array element with sinkers and pulling the first array element with buoys. The assembled vertical linear array is then deployed at sea. Before deployment, the vertical linear array and the omnidirectional sound source are synchronized in time by receiving GNSS second pulses via differential GPS.
[0055] The deployment vessel is equipped with monitoring equipment, including: a receiver, a host computer, a USB-4431, a power amplifier, and an oscilloscope. The USB-4431 is a signal transmitter and data acquisition unit, responsible for acquiring data from omnidirectional sound sources, standard hydrophones, and CTDs.
[0056] The CTD is slowly lowered vertically into the seabed and then lifted out. During this process, the CTD records the sound velocity at different water depth profiles to obtain the average sound velocity at different profiles.
[0057] The host computer on the deployment vessel controls the power amplifier to regularly transmit signals starting at the rising edge of the second pulse, with each cycle lasting 2 seconds. The first second is the active transmission phase, and the second is the silent observation phase. For example... Figure 3 As shown, firstly, an LFM ranging signal with a duration of 100ms is transmitted, with its frequency varying linearly within the range of 7–10kHz. After a 100ms silence period, characteristic frequencies are selected within the 1–10kHz band according to the 1 / 3 octave band criterion, and single-frequency short pulse sequences are transmitted in an alternating pattern of high and low frequencies (e.g., arranged in the pattern of 1kHz, 4kHz, 1.25kHz, 5kHz, 1.6kHz, 6.3kHz, 2kHz, 8kHz, 2.5kHz, 10kHz, 3.15kHz). Each frequency pulse train sequence transmits a 10-cycle sine wave, with the pulse duration adaptively adjusted according to the center frequency, and a 20ms guard interval is set between adjacent pulse trains. Finally, after a 100ms interval, an LFM measurement signal of 3.15–10kHz is transmitted to conclude the transmission.
[0058] After receiving the LFM ranging signal, the standard hydrophone calculates the actual distance to the omnidirectional sound source and records the signal waveform, saving it to the storage system. It also receives the open-circuit voltage of the characteristic frequency points in the 1-10kHz frequency band selected by the subsequent 1 / 3 octave band criterion. Since the sensitivity of the standard hydrophone is known, the source level of the omnidirectional sound source under different characteristic frequency point signals can be calculated, realizing the source level calibration of the omnidirectional sound source. The data obtained are shown in Table 1.
[0059] Table 1. Yellow Sea Test Sound Source Level Calibration Data
[0060]
[0061] like Figure 4 The diagram shows the timing sequence of a vertical linear array, where t1, t2, and t3 represent the time intervals between signal arrivals calculated for array elements A, B, and C, respectively. The specific calculation steps are as follows:
[0062] Before deploying the omnidirectional sound source and the vertical linear array, a synchronization clock is used to synchronize time, thus synchronizing world time. After deployment, the vertical linear array composed of self-contained hydrophones begins to continuously receive and store external signals, including waveform information.
[0063] An omnidirectional sound source transmits an LFM ranging signal at the rising edge of the PPS second pulse and records the transmission time as UTC 1. A standard hydrophone receives the waveform information of this LFM signal and stores it in the host computer. After a period of time, the vertical linear array also receives the waveform information of this LFM ranging signal and stores it.
[0064] After the experiment, the waveform information received by the standard hydrophone and the vertical linear array will be matched and filtered to obtain the correlation peak. The arrival time of the ranging signal will then be recorded as UTC 2.
[0065] Subtracting World Time 1 from World Time 2 gives the time interval between the transmission of a ranging signal and its reception by the vertical linear array. Figure 4 The values are represented as t1, t2, and t3.
[0066] The distance between the omnidirectional sound source and the array element can be obtained by multiplying the measured time interval by the average sound speed. Table 2 shows the LFM ranging results of three representative array elements.
[0067] Table 2. LFM ranging data for three representative array elements.
[0068]
[0069] Finally, the collected data is processed using a formula. The sensitivity of the linear array elements was calculated, and the sensitivity of the vertical linear array elements was calibrated in situ using an omnidirectional sound source. The calibration results of the representative array element 1967 are shown in Table 3.
[0070] Table 3. Array element calibration data for 1967
[0071]
[0072] It is worth noting that all equipment used in the experiment has been traced, and the measurement uncertainties have been determined. Uncertainty analysis yielded the following results: Figure 5 , Figure 6 As shown, the sensitivity deviation of most frequency points of each array element is less than 2dB, with a maximum of 2.3dB, which is within a reasonable uncertainty range compared with the laboratory measurement results.
[0073] The combined standard uncertainty was calculated. Expanding uncertainty (2.2dB) (K=2). As shown in Table 4, the expanded uncertainty of the in-situ calibration of the hydrophone using the omnidirectional sound source method for underwater acoustic detection array during the Yellow Sea sea trial was 2.2dB, which confirms the feasibility of the method in this application.
[0074] Table 4 Summary of Uncertainty Sources and Combined Uncertainty Table
[0075]
[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims
1. A method for in-situ calibration of the sensitivity of underwater acoustic vertical linear array elements based on a high-precision synchronous clock, characterized in that, Includes the following steps: Step 1: Construct a standard hydrophone device and vertical linear array for measuring the sound power of omnidirectional sound sources; Step 2: Lower the CTD to a depth exceeding the vertical linear array depth, then lift and retrieve it, and measure the average sound velocity; Step 3: Control the omnidirectional sound source to emit a signal, use a standard hydrophone to measure the sound source level at different frequencies in real time and record the LFM ranging signal waveform to calibrate the sound source level of the omnidirectional sound source; Step 4: The vertical linear array receives the LFM signal, stores the LFM signal waveform and open-circuit voltage data at each frequency point in the storage system, and obtains the time interval data after data processing; Step 5: Calculate the sensitivity of each linear array element based on the average sound velocity, sound source level data, open circuit voltage data at each frequency point, and time interval data to achieve in-situ calibration.
2. The method according to claim 1, characterized in that, Step 1 includes: Step 1.1: Construct a device for measuring the sound power of an omnidirectional sound source, including deploying an omnidirectional sound source and a standard hydrophone combination underwater on the experimental vessel; Step 1.2: Synchronize the vertical linear array with the omnidirectional sound source using a synchronization clock; Step 1.3: Construct a vertical line array and place it underwater at a predetermined distance from the experimental vessel.
3. The method according to claim 2, characterized in that, In step 1.1, the specific deployment method is as follows: A rigid bracket is used to fix the omnidirectional sound source and the standard hydrophone together, and the straight-line distance between the two is not less than one meter. The rigid straight rod was flexibly suspended and lowered into the water by the experimental vessel, and was located at the same depth as the first element of the vertical linear array.
4. The method according to claim 2 or 3, characterized in that, Step 1.3 specifically includes: The first element of the vertical line array is connected to the buoy frame, and the last element is connected to the seabed release device and the sinker. The vertical line array is deployed underwater at a distance of no more than 1,500 meters from the experimental vessel, and the vertical line array is fixed by anchoring the last element with the sinker and pulling the first element with the buoy.
5. The method according to claim 1, characterized in that, During the CTD lowering and retrieval process in step 2, the sound velocity at different profiles between the omnidirectional sound source and the vertical linear array is continuously recorded, and then the average value of the sound velocity at different depths is taken as the average sound velocity.
6. The method according to claim 1, characterized in that, In step 3, each cycle of the signal emitted by the omnidirectional sound source includes an active emission phase and a silent observation phase.
7. The method according to claim 6, characterized in that, During the main transmission phase, when the rising edge of the first PPS second pulse arrives, the LFM ranging signal is transmitted. After a preset time, the characteristic frequency signal is transmitted according to the 1 / 3 octave band criterion. Finally, the LFM ranging signal is transmitted again to finish the transmission.
8. The method according to claim 1, characterized in that, The calculation method for the time interval data includes: The waveform measured by the vertical linear array is matched and filtered with the waveform recorded by the standard hydrophone to obtain the correlation peak; If the vertical linear array elements are composed of self-contained hydrophones, then the world time at the correlation peak is the time when the LFM ranging signal arrives at the vertical linear array element. Subtracting the transmission time of the LFM signal from this time gives the time interval data. If the array elements of the vertical line array are triggered to receive signals by the rising edge of a PPS second pulse, the time interval data is obtained by calculating the time difference between the correlation peak and the rising edge trigger.
9. The method according to claim 1 or 8, characterized in that, Step 5 specifically involves: Based on the source level data of each frequency signal of the omnidirectional sound source obtained from the source level calibration, the open-circuit voltage of each array element receiving different frequency signals directly obtained from the vertical linear array elements, the average sound velocity and time interval data, the sensitivity of each vertical linear array element is calculated, thereby achieving in-situ calibration.