Lake test method based on target intensity measurement of underwater acoustic transponder

Abstract

The invention discloses an on-lake test method based on target intensity measurement of an underwater acoustic transponder. The method comprises the following steps: (1) preparation work of a measurement test; (2) the arrangement position of the equipment needs to meet sound field conditions; (3) setting emission signal design conditions; (4) measuring method; (5) measuring; the measurement method comprises the following steps: under the condition of a free field and a far field, calculating a sound intensity value by converting a sound pressure value capable of being directly measured into a sound pressure at a position of 1m, and calculating a target intensity value according to a formula (4); the # imgabs0 # performs Fourier analysis processing on the time domain signal to obtain an incident signal frequency spectrum pi (f) and an echo signal frequency spectrum pr (f); spherical wave correction is carried out on a frequency spectrum signal, an incident signal is converted to a target sound center, a # imgabs 1 # scattered echo signal is converted to a position 1m away from the target sound center: pr (f). R, and a target intensity value # imgabs 2 # can be obtained according to a formula (5). The method is suitable for underwater acoustic transponder target intensity measurement lake / sea tests, the far-field condition is easily met, the measurement method is convenient and efficient, and the method conforms to the actual use scene.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater acoustic detection and identification, and specifically relates to a lake test method based on underwater acoustic transponder target intensity measurement. Background Art

[0002] As we all know, when sound waves hit an object, they will undergo physical processes such as emission, scattering and diffraction, resulting in the generation of secondary waves distributed throughout the space, which are composed of reflected waves, scattered waves and diffracted waves. The secondary waves in a certain direction reach the receiving point and are received. Active sonar achieves target detection and target identification by receiving such echo signals. Therefore, the strength of the target echo and the amount of target information it carries play a very important role in the work of active sonar.

[0003] Target strength is an important parameter in the active sonar equation. To optimize the design of sonar or to reasonably apply sonar using the active sonar equation, it is necessary to first estimate the target strength value. Target strength measurement technology is an important science and technology in the fields of sonar technology, hydroacoustics and ocean detection, and has broad application prospects in military and civilian fields. The early traditional hydroacoustic target strength measurement methods include direct measurement method and indirect measurement method (comparison method). The direct method needs to measure three physical quantities: sound source level, echo intensity and propagation loss. The key is how to accurately measure the propagation loss, which requires accurate measurement of the distance between the sound source and the target, and determines the corresponding propagation loss according to the actual hydrological conditions. For lake / sea field operations, it is relatively difficult. The indirect method (comparison method) requires a reference target with a known target strength, but the reference target with a high degree of fidelity is difficult to manufacture. The lake test method based on hydroacoustic transponder target strength measurement proposed by the present invention does not need to determine the propagation loss, does not need to do complex absolute calibration work, and is simple to measure, thereby improving measurement accuracy and efficiency.

[0004] In active target detection tests, an acoustic transponder is generally used to simulate an active target. The acoustic transponder collects the radiated acoustic signal of the transmitting transducer, sets the target strength through the control software, and finally uses another transmitting transducer to radiate the acoustic signal. In the whole process, accurate measurement of the target strength is indispensable for a successful test. In addition, accurate measurement of target strength is a complex but extremely critical process, which plays a vital role in the field of ocean exploration. Summary of the invention

[0005] In view of the above technical deficiencies, the present invention proposes a lake test method based on the underwater acoustic transponder target intensity measurement on the basis of the national standard GB / T 31014-2014 "Laboratory method for underwater acoustic target intensity measurement", which is suitable for lake / sea tests of underwater acoustic transponder target intensity measurement, can easily meet far-field conditions, and the measurement method is convenient and efficient, and conforms to actual usage scenarios.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a lake test method based on target intensity measurement of a hydroacoustic transponder, comprising the following contents:

[0007] (1) Preparation for measurement test; (2) Equipment placement should meet the acoustic field conditions; (3) Transmitted signal design conditions; (4) Measurement method; (5) Measurement steps;

[0008] The measurement method is as follows: Under free field and far field conditions, the sound intensity value can be calculated by converting the sound pressure value that can be directly measured into the sound pressure at 1m, and the target intensity value is calculated according to formula (4).

[0009]

[0010] Perform Fourier analysis on the time domain signal to obtain the incident signal spectrum p i (f) and echo signal spectrum p r (f) Perform spherical wave correction on the spectrum signal and convert the incident signal to the target sound center: The scattered echo signal is converted to 1m away from the target sound center: p r (f)·r, the target strength value can be obtained according to formula (5):

[0011]

[0012] Preferably, the measurement test preparation is as follows:

[0013] ① Wipe the surface of the standard ball, soak it in water, and record the basic information of the standard ball, such as shape, size, and weight;

[0014] ② Wipe the surface of the transmitting transducer and standard hydrophone and soak them fully;

[0015] ③Record and measure the temperature and water depth in the lake.

[0016] Preferably, the equipment placement location should meet the following sound field conditions:

[0017] ① To measure the intensity of hydroacoustic targets in a lake, the measurement must be carried out under free field and far field conditions, and must comply with free field or equivalent free field conditions;

[0018] ② The target and the hydrophone should be in the far field of the transmitting transducer so that the sound waves incident on the target and the hydrophone are equivalent to plane waves, that is, they meet the following requirements:

[0019]

[0020] Where a1 and a2 represent the maximum linear dimensions of the radiating surface of the transmitting transducer and the target, respectively, in m, and λ is the wavelength of the sound wave in the lake corresponding to the measurement frequency, in m;

[0021] ③ The hydrophone should be in the far field of the target scattered echo, so that the scattered echo incident on the hydrophone is equivalent to a plane wave, that is, it satisfies:

[0022]

[0023] Where a3 represents the maximum linear dimension of the standard hydrophone, in m;

[0024] ④ The effective acoustic center of the transmitting transducer, hydrophone and target should be arranged on the same acoustic axis;

[0025] ⑤It is necessary to measure the background noise of the test sound field.

[0026] Preferably, the transmission signal design conditions are as follows:

[0027] ① The transmitted signal contains at least 3 cycles of steady-state waves;

[0028] ②During the measurement process, there is interference from reflected sound waves on the lake surface and bottom. The width of the transmitted pulse signal should be controlled so that the interference sound waves do not overlap with the incident sound waves and scattered echoes in the time domain.

[0029] ③The transmitted signal should be able to cover the target, that is, control the width of the transmitted pulse signal to meet

[0030]

[0031] Where a4 is the maximum linear dimension of the target in the projection plane perpendicular to the incident wave direction, in m, and c is the speed of sound in the lake, in m / s;

[0032] ④ The interval between transmitting signals should be no less than 1.5 times the length of the reverberation time in the lake;

[0033] ⑤The transmitting signal can be selected as single frequency pulse or broadband pulse.

[0034] Preferably, the measuring steps are as follows:

[0035] ①Preparation work;

[0036] ② Transmitting signal design;

[0037] ③Signal transmission;

[0038] ④ When the target is not placed in the sound field, a short pulse signal is emitted, and the arrival time of the interfering sound wave and the reverberation time in the lake are analyzed according to the time domain pulse sequence received by the hydrophone. The pulse width and pulse emission interval of the measurement signal are determined and recorded;

[0039] ⑤ When the target is not placed in the sound field, emit a pulse signal of a certain frequency (frequency band) and pulse width, measure the incident wave signal, control the trigger signal synchronization multiple times (preferably more than 8 times), collect and average the signal p i (n);

[0040] ⑥Press the target Figure 1 Place the target in the sound field as shown. The state of the measuring device and the sound field conditions should remain unchanged before and after the target is placed.

[0041] ⑦ Adjust the placement posture of the target to meet the specified incident angle requirements;

[0042] ⑧Emit a pulse signal of the same frequency (frequency band) and pulse width. If the incident wave and the scattered echo acoustic signal have no time domain overlap, directly measure the sample scattered echo, synchronize multiple times (preferably more than 8 times), collect and average, and record the signal p r (n); otherwise, measure the incident wave, scattered echo superimposed acoustic signal, synchronously collect multiple times and average and record the signal p a (n), and obtain the sample scattered echo signal p r (n):p r (n) = p a (n)-p i (n);

[0043] ⑨For signal p i (n) and p r (n) Perform Fourier analysis to obtain the spectrum p i (f) and p r (f), calculate the target intensity TS(f) at the frequency (frequency band) according to formula (4);

[0044] ⑩ Transmit the signal of the next frequency (frequency band) and pulse width, and repeat the process from ⑤ to ⑨ until the measurement of the target intensity at all frequencies (frequency bands) and pulse widths is completed.

[0045] Compared with the prior art, the beneficial effects achieved by the present invention are: the present invention is suitable for lake / sea tests for measuring target intensity of hydroacoustic transponders, it is easy to meet far-field conditions, the measurement method is convenient and efficient, and it conforms to actual usage scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic diagram of a lake test for measuring target strength of a transponder in the present invention;

[0047] Figure 2 This is the on-lake measurement process of the target intensity of the hydroacoustic transponder in the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] Example 1

[0050] A lake test method based on hydroacoustic transponder target intensity measurement, including the following contents:

[0051] (1) Measurement test preparation

[0052] ① Wipe the surface of the standard ball, soak it in water, and record basic information such as shape, size, and weight of the standard ball.

[0053] ② Wipe the surface of the transmitting transducer and standard hydrophone and soak them fully.

[0054] ③Record and measure the temperature and water depth in the lake.

[0055] (2) Equipment placement should meet sound field conditions

[0056] ① To measure the intensity of hydroacoustic targets in a lake, the measurement must be carried out under free field and far field conditions, and must comply with free field or equivalent free field conditions;

[0057] ② The target and the hydrophone should be in the far field of the transmitting transducer so that the sound waves incident on the target and the hydrophone are equivalent to plane waves, that is, they meet the following requirements:

[0058]

[0059] Where a1 and a2 represent the maximum dimensions of the radiating surface of the transmitting transducer and the target, respectively, in m, and λ is the wavelength of the sound wave in the lake corresponding to the measurement frequency, in m.

[0060] ③ The hydrophone should be in the far field of the target scattered echo, so that the scattered echo incident on the hydrophone is equivalent to a plane wave, that is, it satisfies:

[0061]

[0062] Where a3 represents the maximum linear dimension of the standard hydrophone, in meters.

[0063] ④ The effective acoustic center of the transmitting transducer, hydrophone and target should be arranged on the same acoustic axis;

[0064] ⑤It is necessary to measure the background noise of the test sound field.

[0065] (3) Transmitting signal design conditions

[0066] ① The transmitted signal contains at least 3 cycles of steady-state waves;

[0067] ②During the measurement process, there is interference from reflected sound waves on the lake surface and bottom. The width of the transmitted pulse signal should be controlled so that the interference sound waves do not overlap with the incident sound waves and scattered echoes in the time domain.

[0068] ③The transmitted signal should be able to cover the target, that is, control the width of the transmitted pulse signal to meet

[0069]

[0070] Where a4 is the maximum linear dimension of the target in the projection plane perpendicular to the incident wave direction, in m, and c is the speed of sound in the lake, in m / s;

[0071] ④ The interval between transmitting signals should be no less than 1.5 times the length of the reverberation time in the lake;

[0072] ⑤The transmitting signal can be selected as single frequency pulse or broadband pulse.

[0073] (4) Measurement method

[0074] Under free field and far field conditions, the sound intensity value can be calculated by converting the sound pressure value that can be directly measured into the sound pressure at 1m. The target intensity value is calculated according to formula (4).

[0075]

[0076] Perform Fourier analysis on the time domain signal to obtain the incident signal spectrum p i (f) and echo signal spectrum p r (f) Perform spherical wave correction on the spectrum signal and convert the incident signal to the target sound center: The scattered echo signal is converted to 1m away from the target sound center: p r (f)·r, the target strength value can be obtained according to formula (5):

[0077]

[0078] (5) Measurement steps: Figure 2 shown.

[0079] ①Preparation work;

[0080] ② Transmitting signal design;

[0081] ③Signal transmission;

[0082] ④ When the target is not placed in the sound field, a short pulse signal is emitted, and the arrival time of the interfering sound wave and the reverberation time in the lake are analyzed according to the time domain pulse sequence received by the hydrophone. The pulse width and pulse emission interval of the measurement signal are determined and recorded.

[0083] ⑤5⑤ When the target is not placed in the sound field, emit a pulse signal of a certain frequency (frequency band) and pulse width, measure the incident wave signal, control the trigger signal synchronization multiple times (preferably more than 8 times), collect and average the signal p i (n).

[0084] ⑥Press the target Figure 1 Place the target into the sound field as shown. The state of the measuring device and the sound field conditions should remain unchanged before and after the target is placed.

[0085] ⑦ Adjust the placement of the target to meet the specified incident angle requirements.

[0086] ⑧Emit a pulse signal of the same frequency (frequency band) and pulse width. If the incident wave and the scattered echo acoustic signal have no time domain overlap, directly measure the sample scattered echo, synchronize multiple times (preferably more than 8 times), collect and average, and record the signal p r Otherwise, measure the incident wave, scattered echo and superimposed acoustic signal, collect multiple times synchronously and average them to record the signal p a (n), and obtain the sample scattered echo signal p r (n):p r (n) = p a (n)-p i (n).

[0087] ⑨For signal p i (n) and p r (n) Perform Fourier analysis to obtain the spectrum p i (f) and p r (f), calculate the target intensity TS(f) at this frequency (frequency band) according to formula (4).

[0088] ⑩ Transmit the signal of the next frequency (frequency band) and pulse width, and repeat the process from ⑤ to ⑨ until the measurement of the target intensity at all frequencies (frequency bands) and pulse widths is completed.

[0089] Example 2

[0090] like Figure 1 As shown in Table 1, the complete test equipment for the lake test of transponder target strength measurement consists of 2 transmitting transducers, 1 standard ball, 1 standard hydrophone, a hanging device and a measuring device. The measuring device consists of a signal generator, a power amplifier, a bandpass filter, a signal collector and control software. The specific equipment composition is shown in Table 1.

[0091] Table 1 Detailed equipment composition

[0092]

[0093]

[0094]

[0095] Although specific embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit thereof, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lake test method based on hydroacoustic transponder target intensity measurement, characterized in that: Includes the following: (1) Preparation for measurement test; (2) Equipment placement should meet the acoustic field conditions; (3) Transmitted signal design conditions; (4) Measurement method; (5) Measurement steps; The measurement method is as follows: Under free field and far field conditions, the sound intensity value can be calculated by converting the sound pressure value that can be directly measured into the sound pressure at 1m, and the target intensity value is calculated according to formula (4); Perform Fourier analysis on the time domain signal to obtain the incident signal spectrum p i (f) and echo signal spectrum p r (f) Perform spherical wave correction on the spectrum signal and convert the incident signal to the target sound center: The scattered echo signal is converted to 1m away from the target sound center: p r (f)·r, the target strength value can be obtained according to formula (5):

2. The lake test method based on hydroacoustic transponder target intensity measurement according to claim 1 is characterized in that: The measurement test preparations shown are as follows: ① Wipe the surface of the standard ball, soak it in water, and record the basic information of the standard ball, such as shape, size, and weight; ② Wipe the surface of the transmitting transducer and standard hydrophone and soak them fully; ③Record and measure the temperature and water depth in the lake.

3. A lake test method based on hydroacoustic transponder target intensity measurement according to claim 1, characterized in that: The equipment placement location should meet the following sound field conditions: ① To measure the intensity of hydroacoustic targets in a lake, the measurement must be carried out under free field and far field conditions, and must comply with free field or equivalent free field conditions; ② The target and the hydrophone should be in the far field of the transmitting transducer so that the sound waves incident on the target and the hydrophone are equivalent to plane waves, that is, they meet the following requirements: Where a1 and a2 represent the maximum linear dimensions of the radiating surface of the transmitting transducer and the target, respectively, in m, and λ is the wavelength of the sound wave in the lake corresponding to the measurement frequency, in m; ③ The hydrophone should be in the far field of the target scattered echo, so that the scattered echo incident on the hydrophone is equivalent to a plane wave, that is, it satisfies: Where a3 represents the maximum linear dimension of the standard hydrophone, in m; ④ The effective acoustic center of the transmitting transducer, hydrophone and target should be arranged on the same acoustic axis; ⑤It is necessary to measure the background noise of the test sound field.

4. The lake test method based on hydroacoustic transponder target intensity measurement according to claim 1 is characterized in that: The transmission signal design conditions are as follows: ① The transmitted signal contains at least 3 cycles of steady-state waves; ②During the measurement process, there is interference from reflected sound waves on the lake surface and bottom. The width of the transmitted pulse signal should be controlled so that the interference sound waves do not overlap with the incident sound waves and scattered echoes in the time domain. ③The transmitted signal should be able to cover the target, that is, control the width of the transmitted pulse signal to meet Where a4 is the maximum linear dimension of the target in the projection plane perpendicular to the incident wave direction, in m, and c is the speed of sound in the lake, in m / s; ④ The interval between transmitting signals should be no less than 1.5 times the length of the reverberation time in the lake; ⑤The transmitting signal can be selected as single frequency pulse or broadband pulse.

5. The lake test method based on hydroacoustic transponder target intensity measurement according to claim 1 is characterized in that: The measurement steps are as follows: ①Preparation work; ② Transmitting signal design; ③Signal transmission; ④ When the target is not placed in the sound field, a short pulse signal is emitted, and the arrival time of the interfering sound wave and the reverberation time in the lake are analyzed according to the time domain pulse sequence received by the hydrophone; Determine the pulse width and pulse emission interval of the measurement signal and record them; ⑤ When the target is not placed in the sound field, emit a pulse signal of a certain frequency (frequency band) and pulse width, measure the incident wave signal, control the trigger signal synchronization multiple times (preferably more than 8 times), collect and average the signal p i (n); ⑥ Place the target in the sound field as shown in Figure 1. The state of the measurement device and the sound field conditions should remain unchanged before and after the target is placed; ⑦ Adjust the placement posture of the target to meet the specified incident angle requirements; ⑧Emit a pulse signal of the same frequency (frequency band) and pulse width. If the incident wave and the scattered echo acoustic signal have no time domain overlap, directly measure the sample scattered echo, synchronize multiple times (preferably more than 8 times), collect and average, and record the signal p r (n); otherwise, measure the incident wave, scattered echo superimposed acoustic signal, synchronously collect multiple times and average and record the signal p a (n), and obtain the sample scattered echo signal p r (n):p r (n) = p a (n)-p i (n); ⑨For signal p i (n) and p r (n) Perform Fourier analysis to obtain the spectrum p i (f) and p r (f), calculate the target intensity TS(f) at the frequency (frequency band) according to formula (4); ⑩ Transmit the signal of the next frequency (frequency band) and pulse width, and repeat the process from ⑤ to ⑨ until the measurement of the target intensity at all frequencies (frequency bands) and pulse widths is completed.

Images