System and method for measuring acoustic scattering intensity from a target in the sea

Abstract

The application discloses a system and method for measuring sound scattering intensity of a target in sea, which is composed of a mobile platform, a transmitting system, a receiving system and a supporting device. The system can be used to measure the sound scattering intensity of a medium or small scale target in a wide sea area by using the mobile platform. The platform used in the measuring system is movable and can be applied flexibly in a wide area, and is not affected by the water depth and environmental noise of a fixed water platform area. The platform has low hardware requirement and relatively low test cost, and the measuring method has strong operability. The calculation method considers practicability and accuracy, and the direct wave and echo signal is convenient to extract and process, so that the sound scattering intensity of the target in a transmitting-receiving combined mode and a transmitting-receiving separated mode can be obtained.

Description

Technical Field

[0001] This invention relates to underwater acoustic measurement, and in particular to a system and method for measuring the acoustic scattering intensity of a target in the sea. Background Technology

[0002] Underwater target echo characteristics are a crucial information source for active sonar, and one of the important means of understanding target characteristics is measuring the acoustic scattering intensity of underwater targets. Currently, the most common measurements are conducted in water tanks and lake test stations, using fixed platforms for hoisting and measurement. However, due to limitations in water area and depth, it is difficult to conduct acoustic scattering tests on large and medium-scale scaled models. At sea, acoustic scattering measurements are currently mainly conducted on full-scale targets using large measurement vessels with dedicated test platforms in motion. Because the underwater incident attitude and receiving azimuth of the target are difficult to control, the effective measurement azimuth and frequency band data obtained are also relatively limited. Furthermore, sea trials of large dedicated measurement vessels are costly. Therefore, it is necessary to develop a flexible and controllable marine measurement system and method that does not have high requirements for the measurement platform and can complete acoustic scattering measurements of medium-scale scaled models in wide waters. Summary of the Invention

[0003] The purpose of this invention is to provide a system and method for measuring the acoustic scattering intensity of marine targets. This system can utilize a mobile platform in open sea areas to measure the acoustic scattering intensity of small- to medium-sized targets in both combined and separate transmitting / receiving configurations. The platform used in this measurement system is mobile and flexible in its application area, unaffected by water depth and environmental noise in areas with fixed platforms. The platform has low hardware requirements and relatively low testing costs. The measurement method is highly operable, and the calculation method balances practicality and accuracy. Direct wave and echo signals are easy to extract and process, facilitating the determination of the acoustic scattering intensity of the target in both combined and separate transmitting / receiving configurations.

[0004] The technical solution of the present invention is as follows:

[0005] On the one hand, the present invention provides a system for measuring the acoustic scattering intensity of a target in the sea, characterized in that it includes a mobile platform at sea consisting of a measuring vessel and a target vessel;

[0006] The survey vessel is used to deploy a launch system and a receiving system, and is equipped with launch and receiving equipment as well as the ability to lower targets into the water.

[0007] The target vessel is used to mount and control the attitude of the target under test in the water. It only needs to meet the underwater target mounting capacity and does not require the ability to launch the target into the water. The target under test is equipped with a magnetic compass, a thruster and a target motion controller. The magnetic compass is used to monitor the horizontal and vertical attitude of the target under test. The thruster is used to drive the target to rotate. The target motion controller (16) is used to monitor and adjust the attitude of the target.

[0008] Furthermore, the transmission system includes a signal generator, a power amplifier, and a transmission array;

[0009] The signal generator is used to generate single-frequency and linear frequency modulated signals, and can import files of arbitrary waveform signals, and set parameters such as pulse interval, pulse length, signal amplitude, and waveform resolution.

[0010] The power amplifier is matched with the transmission array according to the transmission signal frequency band, and different amplification levels are available for selection;

[0011] The aforementioned transmitting array is suspended and fixed at one end of the measuring vessel by steel cables. For low-frequency signals, a vertical multi-element transmitting array composed of multiple elements is used to construct a low-frequency, highly directional sound source; for high-frequency signals, a transmitting transducer with a relatively stable frequency response and a high source level is used.

[0012] The receiving system includes a receiving linear array, a charge amplifier, and a data acquisition unit;

[0013] The receiving array includes a vertical receiving array with both transmitting and receiving components and two underwater buoy receiving arrays with separate transmitting and receiving components. The lower end of the vertical receiving array is counterweighted with steel ropes, and the upper end is suspended from the bow of the measuring vessel (1) with steel ropes to obtain the vertical spatial sound field distribution, and then a highly directional receiving signal is formed by beamforming.

[0014] The charge amplifier is used to amplify the received signal;

[0015] The aforementioned data acquisition device is used to display echo waveforms, monitor whether the signal is abnormal, make preliminary estimates of the echo arrival time and intensity, analyze interference, and avoid it in a timely manner.

[0016] Furthermore, it also includes supporting equipment, which includes:

[0017] A temperature, salinity, and depth gauge, suspended by a steel cable from the side of the survey vessel, is used to measure the seawater temperature, salinity, and depth at the location of the survey vessel.

[0018] The underwater mooring receiver array is composed of a buoy, an electronic cabin receiver, a receiver array, a buoy, an acoustic release device, and a counterweight, which are connected in series by steel cables.

[0019] Positioning devices are installed on the target ship and the measuring ship respectively, and are used to locate the positions of the transmitting, receiving and measured targets.

[0020] Furthermore, the buoy is used to provide buoyancy to the receiving array and is placed in a predetermined position, and the acoustic release device is used for underwater release and recovery of the receiving array.

[0021] Furthermore, the target vessel is only equipped with a lifting cable car and equipment to control the rotation of the target being measured, and the tonnage and deck working space of the target vessel can be smaller than those of the measuring vessel.

[0022] On the other hand, the present invention also provides a method for measuring the acoustic scattering intensity of a target in the sea, characterized by comprising the following steps:

[0023] Step 1. Install the transmitting and receiving systems on the survey vessel as the first mobile maritime platform and move it to calm waters; move the target vessel as the second mobile maritime platform to calm waters.

[0024] Step 2. Install wind speed and direction sensors on the survey vessel to monitor wind speed and direction, install ocean current meters to monitor seawater flow speed and stability, install temperature, salinity and depth meters to monitor seawater temperature, salinity and depth, and install positioning equipment.

[0025] Step 3. Select a suitable location in the seawater to place the underwater mooring receiving array, which consists of a buoy connected by steel cables, an electronic cabin receiver, a receiving array, a buoy, an acoustic release device, and a counterweight, as the receiving point for transmitting and receiving. The positioning equipment on the survey vessel will record the coordinates of the underwater mooring receiving array.

[0026] Step 4. Referring to the aforementioned mooring coordinates and local wind, wave, and current conditions, and according to the requirements for combined and separate transmission and reception testing, determine the positions of the measuring vessel and the target vessel, ensuring that the bow and stern of the measuring vessel and the target vessel are in a straight line with the current, and that the mooring receiving array is located in the separate transmission and reception orientation, i.e., the line connecting the transmitter and the target forms a certain angle with the line connecting the target and the receiver.

[0027] Step 5. After anchoring the bow of the measuring vessel, the transmitting array and vertical receiving array are suspended in the sea at the bow and stern of the measuring vessel using steel cables. The target to be measured is suspended in the sea at the stern of the target vessel using steel cables. The target to be measured is equipped with a propeller and a target motion electronic control cabin. The target vessel controls the rotation of the target to be measured via cables to measure the sound scattering intensity in different azimuths. Both the target to be measured and the transmitting array are equipped with magnetic compasses to monitor the horizontal and vertical attitude of the target to be measured. The vertical receiving array and the underwater receiving array are each counterweighted to maintain their vertical attitude. The lengths of the steel cables for the target to be measured, the transmitting array, and the vertical receiving array are marked with depth to ensure that the sound centers of the three are at the same depth.

[0028] Step 6. The target to be measured is lowered into the water and its center of gravity is adjusted at the crane on the stern deck platform of the measuring vessel. The load-bearing rope and control cable are handed over to the nearby target vessel. The traction rope of the measuring vessel is held in place by the support column on the side of the vessel. The crane is released, and the traction rope and load-bearing rope are slowly extended to the marked depth mark. After the traction rope is released, the target vessel carries the target away and the attitude of the two vessels is adjusted.

[0029] Step 7. The vertical receiving array is hoisted to a specified depth at the bow or side of the measuring vessel, and the transmitting array is hoisted to a specified depth. The attitude of the transmitting array is adjusted according to the magnetic compass installed on the transmitting array. GPS locators are installed at the point where the target is suspended on the target vessel and at the transmitting array and vertical receiving array on the measuring vessel. The positions of the three points are calibrated using these three GPS locators, the underwater attitude stability of the three is monitored, and the functions are debugged.

[0030] Step 8. Connect the instruments and equipment on the ship, check whether the static attitude and rotation state of the target under test (4) are normal, and check whether the vertical attitude of the multi-element transmitting array and the vertical receiving array is normal.

[0031] Step 9. Set the frequency modulation signal, use a signal source and power amplifier to emit sound waves, the pulse width of the emitted signal covers the maximum length of the target, the pulse emission interval is at least 1.5 times the reverberation time, adjust the output voltage amplitude of the signal source, understand the conversion law between the output voltage of the signal source and the system's transmitter stage, and clarify the relationship between the highest output voltage and the maximum transmitter stage under the condition that the direct wave waveform is not distorted;

[0032] Step 10. Utilize the real-time display function of the trigger mode of the vertical receiving array and the collector to observe whether the received signal is normal. Under conditions where the influence of seabed currents and other interferences is minimal, collect the target echo signal under different frequency modulation signals. The collected data is the target scattered sound pressure at the vertical receiving array and the moored receiving array. Perform preliminary signal processing to evaluate the reliability of the measurement data. Repeat the measurement steps according to different frequency bands, different transmit and receive angles, and other test conditions, and measure the temperature, salinity, and depth of the seawater at regular intervals.

[0033] Step 11. After all operating condition tests are completed, retrieve the aforementioned underwater devices, including the transmitting array, vertical receiving array, underwater buoy receiving array, and the target under test, and return to port.

[0034] Step 12. Based on the target scattered acoustic pressure data collected from the vertical receiving linear array and the underwater buoy receiving array, the target acoustic scattering intensity is obtained by signal processing as follows:

[0035] Under the condition that the receiving array simultaneously satisfies the requirements of the transmitting array and the far-field condition of the measured target, the direct wave sound pressure level is:

[0036] The target echo sound pressure level of SPL-20lg(L1)(1) is:

[0037] SPL-20lg(L2)-20lg(L3)+TS(2)

[0038] In the formula, L1 is the distance between the transmitting sound source and the receiving array, L2 is the distance between the transmitting array and the target being measured, and L3 is the distance between the target being measured and the receiving array. When the transmitting and receiving are combined, the receiving array is the vertical receiving array on the measuring ship. When the transmitting and receiving are separated, the receiving array is the underwater buoy receiving array. The corresponding distances are estimated based on the wave arrival time and GPS coordinates.

[0039] The target acoustic scattering intensity is calculated using the direct wave reference method. Specifically, based on the acquired data, direct wave and echo data are extracted using a time window. A single-frequency long pulse signal is constructed as a reference signal. The direct wave and echo are convolved with the single-frequency reference signal, and their envelopes are obtained. The ratio of the direct wave to the target echo envelope amplitude is q. The target echo sound pressure level then has the following relationship:

[0040] SPL - 20lg(L1) = SPL - 20lg(L2) - 20lg(L3) + TS + 20lg(q) (3)

[0041] Therefore, the target acoustic scattering intensity TS is given by equation (4):

[0042] TS = - 20lg(L1) + 20lg(L2) + 20lg(L3) - 20lg(q) (4)

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] (1) The measurement platform of the measurement system of the present invention is movable, and a suitable test area with good background noise can be selected according to the sea conditions. It is not affected by the water depth and environmental noise of the fixed water platform area, and the measurement environment is better than that of the limited range and depth of the water area on the lake.

[0045] (2) The measurement platform of the present invention only requires one measurement vessel with the ability to launch and receive equipment and to lower the target into the water, and the other target vessel only needs to meet the underwater target loading capacity. Overall, the hardware requirements of the measurement platform are low and the measurement cost is lower than that of a large measurement vessel with a dedicated test moon pool platform.

[0046] (3) The measurement method of the present invention is highly operable, and the distance between the transmission and the target can be adjusted according to the actual echo effect. It is not limited by the area of ​​the test platform and is more flexible than fixed test platforms on lakes and at sea.

[0047] (4) The acoustic scattering intensity calculation of the present invention adopts the direct wave reference method. The direct wave and echo signals are easy to extract and process, and the acoustic scattering intensity of the combined transmit and receive and separate transmit and receive can be obtained. It has the characteristics of strong practicality and high accuracy. Attached Figure Description

[0048] Figure 1This is a three-dimensional schematic diagram of an embodiment of the acoustic scattering intensity measurement system for marine targets of the present invention;

[0049] Figure 2 This is a top view of an embodiment of the acoustic scattering intensity measurement system for marine targets of the present invention;

[0050] Figure 3 This is a flowchart of the acoustic scattering intensity signal processing for a target in the sea, according to an embodiment of the present invention.

[0051] Figure 4 This is a sound velocity diagram showing the change in sound velocity with depth according to an embodiment of the present invention;

[0052] Figure 5 The direct wave and echo of the time-domain signal after signal processing for measuring the cylindrical standard target in the sea, as described in this embodiment of the invention.

[0053] Labels in the diagram: 1. Survey vessel; 2. Target vessel; 3. Transmission array; 4. Target being measured; 5. Vertical receiving array; 6. Mooring receiving array; 7. Buoy; 8. Receiving array electronics compartment; 9. Buoy; 10. Acoustic release device; 11. Counterweight; 12. GPS locator; 13. Magnetic compass; 14. Temperature, salinity, and depth gauge; 15. Thruster; 16. Target motion control compartment; 17. Anchor; 18. Direct wave; 19. Target echo. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] For examples, please refer to Figure 1 and Figure 2 As shown in the figure, the underwater target acoustic scattering intensity measurement system of the present invention consists of a mobile offshore platform, a transmitting system, a receiving system, and supporting equipment.

[0056] The aforementioned mobile maritime platform includes a survey vessel 1 and a target vessel 2.

[0057] The measurement vessel 1 is used to house the launch system and receiving system and their supporting equipment. The stern deck platform is equipped with cranes, hinges, load-bearing cables and other equipment for hoisting the target and launch array. There is a winch on the bow side for hoisting cables, ensuring that the platform has sufficient hoisting capacity and working space.

[0058] The aforementioned transmission system mainly consists of a signal generator, a power amplifier, and a transmission array 3 (not shown in the figure). The signal generator should be able to generate single-frequency and linear frequency modulated signals, import files of arbitrary waveform signals, and set parameters such as pulse interval, pulse length, signal amplitude, and waveform resolution. The power amplifier should be matched with the transmission array according to the frequency band of the transmitted signal and should have different amplification levels to choose from. For low-frequency signals, the transmission array 3 uses a vertical multi-element transmission array composed of multiple elements to construct a low-frequency, highly directional sound source. For high-frequency signals, a transmitting transducer with a relatively stable frequency response and a high source level is used, which is suspended and fixed to one end of the measuring vessel 1 by steel rope.

[0059] The receiving system mainly consists of a receiving linear array, a charge amplifier, and a data acquisition unit (not shown in the figure). The receiving linear array includes a vertical receiving linear array 5 with both transceiver and receiver on the measuring vessel 1 and two separate transceiver and receiver receiving linear arrays on the underwater buoy. The vertical receiving linear array 5 is composed of multiple hydrophones. The lower end of the vertical receiving linear array 5 is ballasted by a steel cable 11, and the upper end is suspended from the bow of the measuring vessel 1 by a steel cable to obtain the vertical spatial sound field distribution. Then, through beamforming, a highly directional receiving signal can be obtained, reducing channel interference. The charge amplifier can amplify the received signal, and the sensitivity is set corresponding to the array elements of the receiving array. The number of channels of the data acquisition unit should meet the signal acquisition requirements of the number of array elements and hydrophones. Parameters such as sampling rate and acquisition duration can be set to meet the synchronous triggering conditions. It can display the echo waveform in real time, monitor whether the signal is abnormal, and preliminarily estimate the arrival time and intensity of the echo, analyze the interference situation, and avoid it in time.

[0060] The supporting equipment mainly includes marine positioning equipment, a temperature, salinity, and depth gauge 14, a magnetic compass 13, a voltage stabilizer (not shown in the figure), a mooring receiver array, a buoy 7, an acoustic release device 10, and a counterweight 11. The marine positioning equipment includes three GPS locators 12. One GPS locator 12 is installed on the platform of the target vessel 2, and two GPS locators 12 are respectively installed on the bow and stern of the survey vessel 1 to locate the position of the transmitting, receiving, and measured target. The temperature, salinity, and depth gauge 14 is suspended by a steel cable on the side of the survey vessel 1 and is used to measure marine environmental information parameters such as seawater temperature, salinity, and depth at the survey vessel 1.

[0061] The underwater mooring receiving array is formed by connecting the buoy 9, the electronic cabin receiver 8, the receiving array 6, the buoy 7, the acoustic release device 10, and the counterweight 11 with steel cables in that order. The buoy 7 is used to provide buoyancy to the receiving array 6 and is placed in a predetermined position. The acoustic release device 10 is used for underwater release and recovery of the receiving array 6.

[0062] The target ship 2 is used to mount and control the measured attitude of the target 4. The target 4 is equipped with a magnetic compass 13, a thruster 15 and a target motion controller 16. The magnetic compass 13 is used to monitor the horizontal and vertical attitude of the target 4. The thruster 15 and the target motion controller 16 are used to adjust the attitude in time before measurement.

[0063] Example

[0064] The survey vessel 1 has a displacement of approximately 1,000 tons, while the target vessel 2 has a displacement of 300 tons.

[0065] A vertical seven-element transmitter array 3, composed of seven elements, is used to construct a low-frequency, highly directional sound source with an operating frequency range of 1k-4kHz. It is suspended and fixed to the stern of the measuring vessel 1 by steel cables.

[0066] The vertical receiving array 5 includes a combined receiving array 6 on the survey vessel 1 and a separate receiving array 5 on the underwater buoy, and is composed of 32 hydrophones.

[0067] The method for measuring the scattered acoustic field using the above-mentioned underwater target acoustic scattering intensity measurement system includes the following steps:

[0068] 1) Based on nautical charts and sea condition forecasts, obtain information about the test area, including surrounding sea depth and island / reef distribution, ocean current and tidal strength and direction, wind and wave weather changes, etc. Select a wide sea area with relatively small currents and calm sea conditions as the test site to reduce interference from underwater equipment movement and the impact of changes in equipment depth and position. (Refer to...) Figure 4 The average sea depth in the area is 150m and the speed of sound is around 1530m / s.

[0069] 2) The measuring vessel 1 and the target vessel 2 sail to the predetermined test location, use wind speed and direction sensors to monitor wind and waves, use ocean current meters to monitor current speed and its stability, and use temperature, salinity and depth gauge 14 to measure seawater temperature, salinity and depth to assess the feasibility of the test environment.

[0070] 3) On the survey vessel 1, the float 9, electronic compartment 8, receiving array 6, buoy 7, acoustic release device 10, and counterweight 11 are connected in series to form a mooring receiving array. After debugging, a suitable position is selected as the receiving point for separate transmission and reception and the mooring array is lowered into the water in sequence. Its GPS coordinates are recorded. Multiple mooring receiving arrays can be placed according to the required separation angle.

[0071] 4) Based on the coordinates of the mooring and the local wind, wave and current conditions, determine the positions of the measuring vessel 1 and the target vessel 2 according to the requirements of the combined and separate receiving and transmitting tests, so that the bow and stern of the measuring vessel 1 and the target vessel 2 are in a straight line with the current, and the mooring receiving array is at the separate angle position.

[0072] 5) After the bow of the measuring vessel 1 is anchored, the target 4, the seven-element transmitting array 3, and the vertical receiving array 5 are assembled. The target 4 is a standard steel cylinder, 6m long and 30cm in diameter, with thrusters 15 at both ends and an internal electronic control cabin 16, allowing the target vessel 2 to control the rotation of the target 4 via cables to measure the sound scattering intensity in different azimuths. Magnetic compasses 13 are installed on the target 4 and the transmitting array 3 to monitor the horizontal and vertical attitudes respectively. All receiving arrays 5 and 6 are counterweighted 11 to maintain their vertical attitude. The cable lengths of the target 4, the transmitting array 3, and the receiving array 5 are marked at a depth of 50m to ensure that the sound centers of the three are at the same depth.

[0073] 6) The target 4 to be measured is lowered into the water and its center of gravity is adjusted at the crane on the stern deck platform of the measuring vessel 1. The load-bearing rope and control cable are handed over to the nearby target vessel 2. The traction rope of the measuring vessel 1 is pulled by the side column of the ship, the crane is released, and the traction rope and load-bearing rope are slowly lengthened to the marked depth mark. After the traction rope is released, the target vessel 2 moves away and the attitude of the two vessels is adjusted.

[0074] 7) Hoist the vertical receiving array 5 to the designated depth at the bow or side of survey vessel 1, taking care to prevent the receiving array cable from getting tangled with anchor chains or other equipment. Hoist the seven-element transmitting array 3 to the designated depth at the crane on the stern deck platform of survey vessel 1, and adjust the attitude of the transmitting array according to the magnetic compass 13. Install GPS 12 at the target suspension point on target vessel 2 and at the transmitting and receiving arrays on survey vessel 1, and use the three-point GPS 12 to calibrate the positions of the three points in a straight line. Monitor the underwater attitude stability of the three components and perform functional debugging.

[0075] 8) Connect the instruments and equipment on board, including signal source, power amplifier, multi-channel signal acquisition device, charge amplifier, voltage regulator, GPS signal, etc., and perform functional debugging.

[0076] 9) Check whether the stationary attitude and rotation status of the target 4 are normal, and check whether the vertical attitude of the transmitting array 3 and the receiving array 5 are normal.

[0077] 10) Set up a 1k-4kHz linear frequency modulated signal and use a signal source and power amplifier to emit sound waves. The pulse width of the emitted signal should be 10ms to cover the maximum length of the target, and the pulse emission interval should be at least 1.5 times greater than the reverberation time. Adjust the output voltage amplitude of the signal source, understand the conversion law between the output voltage of the signal source and the system's transmitter stage, and determine the maximum output voltage and the maximum transmitter stage under the condition that the direct wave waveform is not distorted.

[0078] 11) Utilize the real-time display function of receiver arrays 6 and 5 and the trigger mode of the data acquisition unit to observe whether the received signal is normal, analyze interference such as ocean currents and static electricity, minimize controllable interference on the ship, and ensure that the interface reverberation and incident and scattered sound waves do not overlap in the time domain, so that the distance between the measuring ship and the target ship can be adjusted appropriately.

[0079] 12) Under conditions of minimal interference from seabed currents and other disturbances, target echo signal acquisition was conducted under different frequency modulation signals. The target 4 rotated once, and data acquisition was continuous. Preliminary signal processing was performed to assess the reliability of the measurement data. The measurement steps were repeated according to the test conditions of different frequency band linear frequency modulation signals and different setting angles. Seawater temperature, salinity, and depth were measured at regular intervals, and changes in wind, waves, currents, and GPS coordinates were observed.

[0080] 13) After all working condition tests are completed, the underwater devices, such as the transmitting array 3, receiving arrays 5 and 6, the target under test 4, and the mooring, are recovered in sequence and the ship returns to port.

[0081] 14) See Figure 4 The signal processing was performed as follows to obtain the acoustic scattering intensity of targets in different orientations at different frequencies and angles:

[0082] The acoustic scattering intensity of target 4 was measured using the direct wave reference method. Under the condition that both the transmitting array and the far-field condition of target 4 are met by receiving arrays 5 and 6, the sound pressure level of the direct wave, according to the spherical wave propagation law, is:

[0083] The sound pressure level of the target echo SPL-20lg(L1)(1) is:

[0084] SPL-20lg(L2)-20lg(L3)+TS(2)

[0085] In the formula, SPL is the transmitting sound source level, L1 is the distance between the transmitting array 3 and the vertical receiving array 5, L2 is the distance between the transmitting array 3 and the target 4, and L3 is the distance between the target 4 and the vertical receiving array 5. (See also...) Figure 2 When the transmitting and receiving are combined, the receiving array is taken as the vertical receiving array 5 on the survey vessel 1, and correspondingly, L1 = D1, L2 = D2, L3 = D1 + D2; when the transmitting and receiving are separated, the receiving array 6 is taken as the underwater buoy receiving array 6, and then L1 = D3, L2 = D2, L3 = D4. The distance of each segment is estimated based on the wave arrival time and GPS coordinates.

[0086] Assuming the ratio q of the envelope amplitude of the direct wave to the target echo, the following relationship holds:

[0087] SPL - 20lg(L1) = SPL - 20lg(L2) - 20lg(L3) + TS + 20lg(q) (3)

[0088] The target acoustic scattering intensity is

[0089] TS = - 20lg(L1) + 20lg(L2) + 20lg(L3) - 20lg(q) (4)

[0090] Therefore, by obtaining the distances between each point and the ratio of the direct wave to the target echo envelope amplitude obtained through signal processing methods such as time windowing, matched filtering, and Hilbert transform, the acoustic scattering intensity at the combined transmitting and receiving positions and at different separation angles can be obtained. This avoids or reduces the influence of the transmitting source level, signal amplitude fluctuations, and environmental interference on the measurement results, thereby improving accuracy and practicality.

[0091] In this embodiment, the direct wave and cylindrical echo obtained by the receiving array signal processing of the measuring vessel 1 are described in reference. Figure 5 According to formula (4), the intensity of the cylindrical horizontal target 4 at 3kHz is 4.4dB, the theoretical value is 3.6dB, and the error is 0.8dB.

[0092] Experiments show that the measurement system of the present invention uses a mobile platform with flexible application areas, is not affected by the water depth and environmental noise of the fixed water platform area, has low platform hardware requirements, relatively low testing costs, strong operability of the measurement method, and a calculation method that balances practicality and accuracy. The direct wave and echo signals are easy to extract and process, making it easy to obtain the acoustic scattering intensity of the target under test with both transmit and receive combined and separate transmit and receive.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for measuring the acoustic scattering intensity of a target in the sea, characterized in that, Including a mobile maritime platform consisting of a survey vessel (1) and a target vessel (2); The survey vessel (1) is used to deploy the launch system and the receiving system, and has the ability to launch and receive equipment as well as to lower the target into the water; The target vessel (2) is used to mount and control the attitude of the target (4) in the water. It only needs to meet the underwater target mounting capacity and does not require the ability to launch the target into the water. The target (4) is equipped with a magnetic compass (13), a thruster (15) and a target motion control cabin (16). The magnetic compass (13) is used to monitor the horizontal and vertical attitude of the target (4). The thruster (15) is used to drive the target to rotate. The target motion control cabin (16) is used to monitor and adjust the target attitude.

2. The acoustic scattering intensity measurement system for marine targets according to claim 1, characterized in that, The aforementioned transmission system includes a signal generator, a power amplifier, and a transmission array (3); The signal generator is used to generate single-frequency and linear frequency modulated signals, and can import files of arbitrary waveform signals, and set parameters such as pulse interval, pulse length, signal amplitude, and waveform resolution. The power amplifier is matched with the transmission array according to the transmission signal frequency band, and different amplification levels are available for selection; The aforementioned transmitting array (3) is suspended and fixed at one end of the measuring vessel (1) by steel rope. For low-frequency signals, a vertical multi-element transmitting array composed of multiple arrays is used to construct a low-frequency, highly directional sound source. For high-frequency signals, a transmitting transducer with a relatively stable frequency response and a high source level is used. The receiving system includes a receiving linear array, a charge amplifier, and a data acquisition unit; The receiving array includes a vertical receiving array (5) with both transmitting and receiving functions and two underwater buoy receiving arrays with separate transmitting and receiving functions. The lower end of the vertical receiving array (5) is ballasted by a steel cable (11), and the upper end is suspended by a steel cable from the bow of the measuring vessel (1) to obtain the vertical spatial sound field distribution, and then a highly directional receiving signal is formed by beamforming. The charge amplifier is used to amplify the received signal; The aforementioned data acquisition device is used to display echo waveforms, monitor whether the signal is abnormal, make preliminary estimates of the echo arrival time and intensity, analyze interference, and avoid it in a timely manner.

3. The underwater target acoustic scattering intensity measurement system according to claim 1, characterized in that, It also includes supporting equipment, which includes: A temperature, salinity and depth meter (14) is suspended by a steel cable on the side of the measuring vessel (1) to measure the seawater temperature, salinity and depth at the measuring vessel (1); The underwater buoy receiving array is composed of a buoy (9), an electronic cabin receiver (8), a receiving linear array (6), a buoy (7), an acoustic release device (10), and a counterweight (11) connected in series by steel cables; Positioning devices are installed on the target ship (2) and the measuring ship (1) respectively, and are used to locate the position of the transmitting, receiving and measured target.

4. The underwater target acoustic scattering intensity measurement system according to claim 3, characterized in that, The float (7) is used to provide buoyancy to the receiving array (6) and is placed in a predetermined position. The acoustic release device (10) is used for underwater release and recovery of the receiving array (6).

5. The underwater target acoustic scattering intensity measurement system according to claim 1, characterized in that, The target vessel (2) is only equipped with a lifting cable car and equipment to control the rotation of the target (4). The tonnage and deck working space of the target vessel (2) are smaller than those of the measuring vessel (1).

6. A method for measuring the acoustic scattering intensity of a target in the sea, characterized in that, Includes the following steps: Step 1. Install the transmitting and receiving systems on the survey vessel as the first mobile maritime platform and move it to calm waters; move the target vessel as the second mobile maritime platform to calm waters. Step 2. Install wind speed and direction sensors on the survey vessel to monitor wind speed and direction, install ocean current meters to monitor seawater flow speed and stability, install temperature, salinity and depth meters to monitor seawater temperature, salinity and depth, and install positioning equipment. Step 3. Select a suitable location to place the submersible receiving array, which consists of a steel cable connecting a buoy (9), an electronic cabin receiver (8), a submersible receiving array (6), a buoy (7), an acoustic release device (10), and a counterweight (11), into the sea as a separate receiving point for transmitting and receiving. The positioning equipment on the survey vessel (1) records the coordinates of the submersible receiving array. Step 4. Referring to the coordinates of the mooring and the local wind, wave and current conditions, and according to the requirements of the combined and separate transmission and reception test, determine the positions of the measuring vessel (1) and the target vessel (2), so that the bow and stern of the measuring vessel (1) and the target vessel (2) are in a straight line with the current, and the mooring receiving array is located in the separate transmission and reception orientation, that is, the connection line between the transmitter and the target and the connection line between the target and the receiver form a certain angle; Step 5. After anchoring the bow of the measuring vessel (1), the transmitting array (3) and the vertical receiving array (5) are distributed and suspended in the sea at the bow and stern of the measuring vessel (1) by steel cables; the target (4) to be measured is suspended in the sea at the stern of the target vessel (2) by steel cables. The target (4) is equipped with a propeller (15) and a target motion control cabin (16). The target vessel (2) controls the rotation of the target (4) by cable in order to measure the sound scattering intensity in different directions; the target (4) and the transmitting array (3) are both equipped with magnetic compasses (13) to monitor the horizontal and vertical attitude of the target (4). The vertical receiving array (5) and the moored receiving array (6) are each weighed (11) to maintain the vertical attitude; the lengths of the steel cables of the target (4), the transmitting array (3) and the vertical receiving array (5) are marked with depth to ensure that the sound centers of the three have the same depth; Step 6. The target (4) to be measured is lowered into the water and its center of gravity is adjusted at the crane on the stern deck platform of the measuring vessel (1). The load-bearing rope and control cable are handed over to the nearby target vessel (2). The traction rope of the measuring vessel (1) is pulled by the side column of the ship. The crane is unhooked. The traction rope and load-bearing rope are slowly lengthened to the marked depth mark. After the traction rope is unhooked, the target vessel (2) carries the target away and the attitude of the two vessels is adjusted. Step 7. The vertical receiving array (5) is suspended to the specified depth at the bow or side of the measuring vessel (1), and the transmitting array (3) is suspended to the specified depth. The attitude of the transmitting array (3) is adjusted according to the magnetic compass (13) installed on the transmitting array (3). GPS locators (12) are installed at the location where the target (4) is suspended on the target vessel (2) and at the transmitting array (3) and vertical receiving array (5) on the measuring vessel (1). The three GPS locators (12) are used to calibrate the position of the three points in a straight line, monitor the underwater attitude stability of the three, and perform functional debugging. Step 8. Connect the instruments and equipment on the ship, check whether the static attitude and rotation state of the target under test (4) are normal, and check whether the vertical attitude of the transmitting array (3) and the vertical receiving array (5) are normal. Step 9. Set the frequency modulation signal, use a signal source and power amplifier to emit sound waves, the pulse width of the emitted signal covers the maximum length of the target, the pulse emission interval is at least 1.5 times the reverberation time, adjust the output voltage amplitude of the signal source, understand the conversion law between the output voltage of the signal source and the system's transmitter stage, and clarify the relationship between the highest output voltage and the maximum transmitter stage under the condition that the direct wave waveform is not distorted; Step 10. Using the trigger mode real-time display function of the vertical receiving array (5) and the collector, observe whether the received signal is normal. Under the condition that the seabed current and other interferences are less affected, collect the target echo signal under different frequency modulation signals. The collected data is the target scattered sound pressure at the vertical receiving array (5) and the moored receiving array. The reliability of the measurement data is initially evaluated by signal processing. The measurement steps are repeated according to different frequency bands, different transmit and receive angles and other test conditions. The temperature, salinity and depth of the seawater are measured at regular intervals. Step 11. After all working condition tests are completed, the underwater devices, including the transmitting array (3), vertical receiving array (5), underwater buoy receiving array (6), and the target under test (4), are retrieved in sequence and returned to port. Step 12. Based on the collected target scattered acoustic pressure data from the vertical receiving linear array (5) and the underwater buoy receiving array, the target acoustic scattering intensity is obtained by signal processing as follows: Under the condition that the receiving array simultaneously satisfies the requirements of the transmitting array and the far-field condition of the measured target, the direct wave sound pressure level is: SPL-20lg(L1)(1) The target echo sound pressure level is: In the formula SPL-20lg(L2)-20lg(L3)+TS(2), L1 is the distance between the transmitting sound source and the receiving array, L2 is the distance between the transmitting array (3) and the target (4) being measured, and L3 is the distance between the target (4) being measured and the receiving array. When the transmitting and receiving are combined, the receiving array is the vertical receiving line array (5) on the measuring vessel (1). When the transmitting and receiving are separated, the receiving array is the underwater buoy receiving array (6). The corresponding distance is estimated based on the wave arrival time and GPS coordinates. The target acoustic scattering intensity is calculated using the direct wave reference method. Specifically, based on the acquired data, direct wave and echo data are extracted using a time window. A single-frequency long pulse signal is constructed as a reference signal. The direct wave and echo are convolved with the single-frequency reference signal, and their envelopes are obtained. The ratio of the direct wave to the target echo envelope amplitude is q. The target echo sound pressure level then has the following relationship: SPL - 20lg(L1) = SPL - 20lg(L2) - 20lg(L3) + TS + 20lg(q) (3) Therefore, the target acoustic scattering intensity TS is given by equation (4): TS = - 20lg(L1) + 20lg(L2) + 20lg(L3) - 20lg(q) (4).

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