JP7532308B2 - Underwater sound field measuring system and underwater sound field measuring method - Google Patents

Description

This disclosure relates to an underwater sound field measurement system and an underwater sound field measurement method.

Ships and other vessels generate sounds underwater, which become underwater noise. Underwater noise is measured, for example, by placing hydrophones underwater.

Japanese Patent Application Publication No. 10-81297

There is growing international momentum for the introduction of underwater noise regulations due to the impact of underwater noise on marine life. When evaluating underwater noise, the underwater sound field state (e.g. sound pressure contour) is important. With conventional methods, it has been difficult to create sound pressure contours with high accuracy.

For example, Patent Document 1 discloses an underwater vehicle for acquiring underwater data and a relay buoy placed on the ocean nearby, but it is difficult to evaluate the sound field using observations made by a single underwater vehicle.

This disclosure has been made in light of these circumstances, and aims to provide an underwater sound field measurement system and an underwater sound field measurement method that can improve the accuracy of evaluating underwater sound fields.

A first aspect of the present disclosure is an underwater sound field measurement system that includes a plurality of underwater vehicles each having a sound pressure meter and arranged at a predetermined position relative to a measurement target, and a processing unit that estimates the underwater sound field generated by the measurement target based on the measurement results of each of the underwater vehicles.

A second aspect of the present disclosure is an underwater sound field measurement method that includes the steps of placing an underwater vehicle having a sound pressure meter at each of predetermined positions relative to a measurement object, and estimating the underwater sound field generated by the measurement object based on the measurement results of each of the underwater vehicles.

This disclosure has the effect of improving the accuracy of underwater sound field evaluation.

FIG. 1 is a diagram showing a schematic configuration of an underwater sound field measuring system according to an embodiment of the present disclosure. FIG. 2 is a diagram illustrating an example of a hardware configuration of a processing device according to an embodiment of the present disclosure. FIG. 2 is a diagram illustrating an example of a sound pressure contour map according to an embodiment of the present disclosure. FIG. 2 is a diagram illustrating an example of a sound pressure contour map according to an embodiment of the present disclosure. 11 is a flowchart illustrating an example of a procedure for a sound pressure contour map generation process according to an embodiment of the present disclosure. FIG. 1 is a diagram illustrating an example of the configuration of an underwater sound field measuring system according to an embodiment of the present disclosure. FIG. 1 is a diagram illustrating an example of the configuration of an underwater sound field measuring system according to an embodiment of the present disclosure.

Below, an embodiment of the underwater sound field measurement system and underwater sound field measurement method according to the present disclosure will be described with reference to the drawings.

Figure 1 is a diagram showing a schematic configuration of an underwater sound field measurement system 1 according to an embodiment of the present disclosure. In this embodiment, a ship on the ocean is the measurement target 2. Note that the measurement target 2 is not limited to a ship. As shown in Figure 1, multiple underwater vehicles 3 are placed in the sea. The underwater vehicles 3 are, for example, UUVs (Unmanned Underwater Vehicles). Note that the underwater vehicles 3 are not limited to UUVs. Figure 1 shows a configuration in which 12 underwater vehicles 3 are provided, but the configuration is not limited to Figure 1 as long as multiple underwater vehicles 3 are provided.

The underwater vehicle 3 has a sound pressure meter. Specifically, the sound pressure meter is a hydrophone that can measure sound pressure underwater. The hydrophone measures the sound pressure around the underwater vehicle 3 on which it is mounted. In other words, the hydrophone measures the sound pressure at the position of the underwater vehicle 3 in the sound field generated underwater by the measurement target 2.

The underwater vehicle 3 is placed at a predetermined position relative to the measurement target 2. That is, the underwater vehicle 3 is placed at a predetermined position in the sea. The predetermined position is set in advance relative to the sea. In this embodiment, the predetermined position is set on a horizontal plane a predetermined distance away from the measurement target 2 (i.e., the sea surface) as shown in FIG. 1. The horizontal plane is a plane perpendicular to the direction of gravity (a plane parallel to the sea surface). For example, the horizontal plane is set at a position 100 m away from the sea surface toward the seabed.

A plurality of predetermined positions are set on a horizontal plane. Specifically, the predetermined positions are arranged in a grid pattern on the horizontal plane. For this reason, as shown in FIG. 1, the underwater vehicles 3 are arranged in a grid pattern. This makes it possible to measure sound pressure at the predetermined positions. This makes it possible to evaluate the sound field state on the horizontal plane, as described below. The spacing of the grid (i.e., the spacing between the predetermined positions) is set based on the size of the measurement target 2 and the resolution of the sound field to be estimated. Note that the arrangement of the underwater vehicles 3 is not limited to a horizontal plane. The individual arrangements are also not limited to a grid pattern.

Specific configuration examples of the underwater vehicle 3 include, for example, a measurement system, a position measurement unit, an inertial navigation system, and an acoustic communication device. The measurement system is a system that measures sound pressure, and includes the above-mentioned sound pressure meter as a sensor. The measurement system may also include an amplifier and a data recording unit.

The position measurement unit is a GPS. That is, the position measurement unit can measure the current position on the earth. For example, an inertial navigation system detects acceleration with an accelerometer, and finds speed by integrating the acceleration, and distance by integrating the speed. Also, a gyro is used to detect direction. Then, based on the traveled distance and direction, the traveled distance from the starting point is calculated. That is, when the underwater vehicle 3 is on the ocean, the position measurement unit measures its own position, and when it dives into the sea, the current position measured by the position measurement unit is used as the starting point. Then, when in the sea, the underwater vehicle 3 determines its own position in the sea from the starting point using underwater navigation. As a result, each underwater vehicle 3 moves to its corresponding predetermined position.

The acoustic communication device is capable of communicating with other devices by acoustic communication. For example, each underwater vehicle 3 is capable of communicating with a designated parent unit. If there is a limit to the acoustic communication distance, a repeater may be used to relay the communication. Time synchronization may be achieved using the acoustic communication function. In this case, for example, a predetermined signal (time stamp) is transmitted from the parent unit to each underwater vehicle 3 to achieve time synchronization. As long as time synchronization is achieved, the method is not limited to using the acoustic communication function.

Next, we will explain the processing device (processing unit) 5.

FIG. 2 is a diagram showing an example of a hardware configuration of the processing device 5 according to the present embodiment.
2, the processing device 5 is a computer system, and includes, for example, a CPU 11, a ROM (Read Only Memory) 12 for storing programs executed by the CPU 11, a RAM (Random Access Memory) 13 that functions as a work area when each program is executed, a hard disk drive (HDD) 14 as a large-capacity storage device, and a communication unit 15 for connecting to a network or the like. Note that a solid-state drive (SSD) may be used as the large-capacity storage device. These units are connected via a bus 18.

The processing device 5 may also include an input unit such as a keyboard and mouse, and a display unit such as a liquid crystal display device for displaying data.

The storage medium for storing the programs executed by the CPU 11 is not limited to the ROM 12. For example, it may be other auxiliary storage devices such as a magnetic disk, a magneto-optical disk, or a semiconductor memory.

A series of processing steps for realizing the various functions described below are recorded in the form of a program on the hard disk drive 14, etc., and the CPU 11 reads this program into the RAM 13, etc., and executes information processing and arithmetic processing to realize the various functions described below. The program may be pre-installed in the ROM 12 or other storage medium, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, semiconductor memories, etc.

The processing device (processing unit) 5 estimates the underwater sound field generated by the measurement target 2 based on the measurement results of each underwater vehicle 3. That is, the processing device 5 estimates the sound field state on the horizontal plane. The sound field state is represented, for example, by a sound pressure contour. For this reason, the processing device 5 calculates a sound pressure contour map.

Specifically, the processing device 5 acquires data measured by each underwater vehicle 3. The data is time-series waveform data of sound pressure. The data may be acquired automatically or may be input manually. The acquired data is then subjected to processing such as narrowband analysis and 1/n octave band analysis. After analyzing each piece of data, the coordinates of a specific position on a horizontal plane (the position of the underwater vehicle 3) are associated with the sound pressure data, and the sound field state is processed as a sound pressure contour map on the horizontal plane. Figure 3 shows an example of a sound pressure contour map. In Figure 3, the direction of the arrow P indicates a state in which the sound pressure is higher.

The sound pressure contour map may be displayed for each time or frequency. Furthermore, by continuously plotting each time or frequency, it is possible to create an animation of the sound pressure contour map in the horizontal plane.

The processing device 5 may be provided, for example, on the ship of the measurement target 2 or on a ship other than the measurement target 2 (for example, an unmanned vehicle), and may collect data from each underwater vehicle 3 online to estimate the sound field. Furthermore, data may be input to the processing device 5 by an operator or the like after the measurement by each underwater vehicle 3 is completed. The processing device 5 also acquires position information from each underwater vehicle.

Next, the selection of measurement data will be described.
Background noise exists underwater. Therefore, if the sound pressure generated by the measurement target 2 is buried in the background noise, the sound pressure generated by the measurement target 2 cannot be measured. For this reason, it is appropriate to select the measurement data used for sound field evaluation.

Specifically, the processing device 5 estimates the underwater sound field based on the measurement results of the underwater vehicle 3 located within an allowable distance from the measurement target 2. That is, the sound pressure contour map is generated using the measurement results of the underwater vehicle 3 located within an allowable distance from the measurement target 2.

The allowable distance is set based on the background noise level of the sea area. Specifically, the allowable distance is the distance R calculated by the distance attenuation equation in a spherical diffuse sound field as shown in equation (1). Note that equation (1) applies when the sea area is deep (the distance from the sea surface to the seabed), specifically when the distance from the measurement target 2 to the underwater vehicle 3 is equal to or less than the deep water of the sea area. For example, when the distance from the measurement target 2 to the underwater vehicle 3, which is assumed to be the furthest away, is equal to or less than the deep water of the sea area (i.e., the seabed is deep), equation (1) is applied.

In formula (1), R is the allowable distance [m], Ln is the background noise level [dB], and Ls is the sound pressure level [dB] at a position 1 m away from the measurement target 2.

On the other hand, when the seabed is shallow, specifically, when the distance from the measurement target 2 to the underwater vehicle 3 is greater than the depth of the sea area, formula (2) can be applied. For example, when the distance between the measurement target 2 and the underwater vehicle 3 that is assumed to be the furthest away is greater than the depth of the sea area (i.e., the seabed is shallow), formula (2) is applied.

In equation (2), h is the depth of the ocean [m].

The effects of background noise can be suppressed by using the measurement results of an underwater vehicle 3 located within an allowable distance from the measurement target 2 that is set based on the underwater background noise level. Furthermore, the allowable distance is set based on the water depth, allowing for more accurate sound field evaluation.

The selection of measurement data is not limited to the above, and can be applied in other ways. For example, the selection may be determined for each sound pressure measurement result. Specifically, the processing device 5 estimates the underwater sound field based on the measurement results of the underwater vehicle 3 in which the value obtained by subtracting the underwater background noise level from the measured sound pressure level is greater than 3 dB. That is, a sound pressure contour map is created using the sound pressure measurement results (sound pressure level Lp) that satisfy the condition sound pressure level Lp-background noise level Ln>3 dB. For measurement points that do not satisfy this condition, the corresponding positions on the map may be indicated by dotted lines or the like to distinguish them from measurement points that satisfy the condition. The left side of FIG. 4 shows the sound pressure contour map before the application of the condition, and the right side of FIG. 4 shows the sound pressure contour map after the application of the condition (including the dotted line L). In this way, when there is a possibility that the sound pressure measurement result is buried in the background noise, it can be displayed separately on the map.

Next, an example of the above-mentioned sound pressure contour map generation process will be described with reference to FIG. 5. FIG. 5 is a flowchart showing an example of the procedure of the sound pressure contour map generation process according to this embodiment. The flow shown in FIG. 5 is executed, for example, when an instruction to create the map is received.

First, measurement data is acquired from each underwater vehicle 3 (S101).

Next, data analysis is performed (S102). The data analysis is, for example, narrowband analysis or 1/n octave band analysis.

The coordinates of a specific position on the horizontal plane (the position of the underwater vehicle 3) are associated with the sound pressure data to generate a sound pressure contour map (S103).

However, as long as it is possible to estimate the underwater sound field using data measured by the underwater vehicle 3, the process is not limited to the above.

Next, we will explain how to adjust the position of the underwater vehicle 3.

As mentioned above, the underwater vehicle 3 is placed at a predetermined position. The predetermined position is set corresponding to the area for which a contour map is to be created. However, if there is a deviation between the set predetermined position and the actual position of the underwater vehicle 3, there is a possibility that sound pressure will be measured at a position that is different from the predetermined position. In such a case, it is possible to perform a deviation correction.

Specifically, when a predetermined position and the placement position of the corresponding underwater vehicle 3 are separated by a predetermined value or more, the processing device 5 estimates the underwater sound field by taking the sound pressure measurement position of the underwater vehicle 3 as the placement position. The predetermined value, which is the criterion for judging the amount of deviation, is, for example, the straight-line distance between the predetermined position and the placement position of the corresponding underwater vehicle 3. This predetermined value is set, for example, based on the distance at which the sound pressure is expected to change by more than an allowable value. Then, when a deviation of more than the predetermined value occurs, a sound pressure contour map is created with the measured sound pressure as the measurement result at the actual placement position, not as the measurement result at the predetermined position. This makes it possible to generate a sound pressure contour map by correlating the sound pressure measurement result with the actual measurement point.

The adjustment for the deviation is not limited to the above. For example, the underwater vehicle 3 may be moved. For example, as shown in FIG. 6, the parent unit 4 is installed on the ocean, and the position of the parent unit 4 is set as the reference position. By installing the parent unit 4 on the ocean, the current position can be grasped by GPS. The parent unit 4 also has an underwater communication function and can communicate with each underwater vehicle 3. Then, the reference position (parent unit position) is associated with each predetermined position. Specifically, when the reference position is at a preset position (ideal state), each predetermined position relative to the reference position is set as the reference arrangement position. That is, when the reference position is at a preset position (ideal state), each predetermined position coincides with each reference position. However, when the parent unit 4 on the ocean is swept away by waves, the position of the parent unit 4 on the ocean deviates from the original ideal position. Then, since the position of the parent unit 4 after movement is set as the reference position, each reference arrangement position also deviates relatively from each predetermined position. Since each underwater vehicle 3 is controlled to be placed at a predetermined position, a deviation occurs between the reference placement position and the placement position of the corresponding underwater vehicle 3. Therefore, when the reference placement position and the placement position of the underwater vehicle 3 (i.e., the predetermined position) are separated by a predetermined value or more, the underwater vehicle 3 is moved to the reference placement position. This makes it possible to maintain the positional relationship between the reference position and the placement position of each underwater vehicle 3. Whether or not a deviation has occurred can be determined by whether or not the reference position, which is the position of the parent unit, has deviated from the ideal position by a predetermined value or more. The movement adjustment function may be provided in the underwater sound field measurement system 1 as an adjustment unit (adjustment device). The function of the parent unit 4 may be provided in a ship (e.g., an unmanned vehicle) different from the measurement target 2 as shown in FIG. 6, or may be provided in the ship of the measurement target 2 as shown in FIG. 7.

When current location information of each underwater vehicle 3 can be obtained, the deviation may be adjusted based on the current location information.

As described above, according to the underwater sound field measurement system and underwater sound field measurement method of this embodiment, the underwater vehicle 3 is used to measure sound pressure at multiple predetermined positions to estimate the underwater sound field generated by the measurement target 2, thereby improving the evaluation accuracy of the underwater sound field. As the underwater vehicle 3 is used to measure sound pressure at multiple predetermined positions to estimate the underwater sound field generated by the measurement target 2, the evaluation accuracy of the underwater sound field can be improved.

For example, when measuring sound pressure by suspending a hydrophone from a buoy, it is difficult to measure sound pressure directly below the object of observation because the hydrophone is above the buoy. Also, when raising the hydrophone from the seabed using an anchor or the like, it is costly to install and maintain equipment such as laying a cable on the seabed. Compared to these methods, the method according to this embodiment can measure sound pressure directly below the measurement object 2, improving the accuracy of sound field evaluation. In addition, data with a good signal-to-noise ratio can be obtained. Although noise can be generated when using a cable, this noise can also be suppressed. There is no need to lay a cable on the seabed, and large-scale construction work is suppressed.

The underwater vehicle 3 is used to measure sound pressure at multiple predetermined positions to estimate the underwater sound field generated by the measurement target 2, thereby improving the accuracy of the evaluation of the underwater sound field.The underwater vehicle 3 is used to measure sound pressure at multiple predetermined positions to estimate the underwater sound field generated by the measurement target 2, thereby improving the accuracy of the evaluation of the underwater sound field.

This disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the invention. It is also possible to combine the various embodiments.

The underwater sound field measuring system and the underwater sound field measuring method described in each of the above-described embodiments can be understood, for example, as follows.
The underwater sound field measurement system (1) of the present disclosure comprises a plurality of underwater vehicles (3) each arranged at a predetermined position relative to a measurement object (2) and equipped with a sound pressure meter, and a processing unit (5) that estimates the underwater sound field generated by the measurement object based on the measurement results of each of the underwater vehicles.

The underwater sound field measurement system according to the present disclosure uses an underwater vehicle to measure sound pressure at multiple predetermined positions to estimate the underwater sound field generated by the measurement object, thereby improving the accuracy of the evaluation of the underwater sound field. In addition, sound pressure can be measured directly below the measurement object. For example, it is possible to obtain data with a good signal-to-noise ratio compared to measurements made by suspending a hydrophone from a buoy.

In the underwater sound field measurement system according to the present disclosure, each of the underwater vehicles may be disposed at a predetermined position on a horizontal plane a predetermined distance away from the measurement target, and the processing unit may estimate the sound field state on the horizontal plane.

The underwater sound field measurement system according to the present disclosure allows the sound field on a horizontal plane to be evaluated by placing underwater vehicles at predetermined positions on the horizontal plane a predetermined distance away from the measurement target.

In the underwater sound field measurement system according to the present disclosure, the underwater vehicles may be arranged in a lattice pattern.

The underwater sound field measurement system according to the present disclosure allows the underwater vehicles to be arranged in a lattice pattern, making it possible to effectively evaluate the underwater sound field.

In the underwater sound field measurement system according to the present disclosure, each of the underwater vehicles may be time-synchronized based on a predetermined signal.

According to the underwater sound field measurement system of the present disclosure, each underwater vehicle is time-synchronized, allowing the underwater sound field to be evaluated more accurately using each measurement result.

In the underwater sound field measurement system according to the present disclosure, the processing unit may estimate the underwater sound field based on the measurement results of the underwater vehicle located within an allowable distance from the measurement target, and the allowable distance may be set based on the underwater background noise level.

The underwater sound field measurement system according to the present disclosure can suppress the effects of background noise by using the measurement results of an underwater vehicle located within an allowable distance from the measurement target that is set based on the underwater background noise level.

In the underwater sound field measurement system according to the present disclosure, the allowable distance may be set based on the water depth.

According to the underwater sound field measurement system disclosed herein, the attenuation of the sound field changes depending on the water depth, so by selecting the measurement results to be used depending on the water depth, it is possible to more accurately evaluate the sound field.

In the underwater sound field measurement system according to the present disclosure, when the predetermined position and the corresponding placement position of the underwater vehicle are separated by a predetermined value or more, the processing unit may estimate the underwater sound field by taking the sound pressure measurement position of the underwater vehicle as the placement position.

According to the underwater sound field measurement system of the present disclosure, when there is a discrepancy between the set predetermined position and the actual placement position of the underwater vehicle, the sound field can be evaluated more accurately by setting the sound pressure measurement position of the underwater vehicle to the actual placement position rather than setting the sound pressure measurement position of the underwater vehicle to the predetermined position.

The underwater sound field measurement system according to the present disclosure may include an adjustment unit that moves the underwater vehicle to a reference position when the reference position is a position of the underwater vehicle corresponding to a reference position and the position of the underwater vehicle is separated by a predetermined value or more.

According to the underwater sound field measurement system of the present disclosure, if the position of the underwater vehicle is misaligned with respect to a reference position (e.g., the parent unit (4)), the sound field can be evaluated more accurately by moving the underwater vehicle to the reference position.

In the underwater sound field measurement system according to the present disclosure, the processing unit may estimate the underwater sound field based on the measurement results of the underwater vehicle in which the measured sound pressure level minus the underwater background noise level is greater than 3 dB.

The underwater sound field measurement system of the present disclosure allows for more accurate evaluation of the sound field because sound pressure measurement results that are significantly affected by background noise levels that are not the subject of measurement are excluded from the sound field estimation.

The underwater sound field measurement method disclosed herein includes the steps of placing an underwater vehicle having a sound pressure meter at each of the predetermined positions relative to the measurement object, and estimating the underwater sound field generated by the measurement object based on the measurement results of each of the underwater vehicles.

1: Underwater sound field measurement system 2: Measurement target 3: Underwater vehicle 4: Main unit 11: CPU
12: ROM
13: RAM
14: Hard disk drive 15: Communication unit 18: Bus L: Dotted line

Claims (10)

a plurality of underwater vehicles each having a sound pressure meter and disposed at a predetermined position relative to a measurement target;
a processing unit that estimates an underwater sound field generated by the measurement target based on the measurement results of each of the underwater vehicles;
An underwater sound field measurement system comprising: each of the underwater vehicles is disposed at a predetermined position on a horizontal plane at a predetermined distance from the measurement target;
The underwater sound field measuring system according to claim 1 , wherein the processing unit estimates the sound field state on the horizontal plane. The underwater sound field measurement system according to claim 2, wherein the underwater vehicles are arranged in a grid pattern. An underwater sound field measurement system according to any one of claims 1 to 3, in which each of the underwater vehicles is time-synchronized based on a predetermined signal. The processing unit estimates an underwater sound field based on a measurement result of the underwater vehicle located within a tolerable distance from the measurement target,
5. The underwater sound field measuring system according to claim 1, wherein the permissible distance is set based on an underwater background noise level. The underwater sound field measurement system of claim 5, wherein the allowable distance is set based on the water depth. The underwater sound field measurement system according to any one of claims 1 to 6, wherein the processing unit estimates the underwater sound field by taking the sound pressure measurement position of the underwater vehicle as the placement position when the predetermined position and the placement position of the corresponding underwater vehicle are separated by a predetermined value or more. The underwater sound field measurement system according to any one of claims 1 to 7, further comprising an adjustment unit that moves the underwater vehicle to a reference position when a reference position, which is a position of the underwater vehicle corresponding to a reference position, is separated from the position of the underwater vehicle by a predetermined value or more. The underwater sound field measurement system according to any one of claims 1 to 8, wherein the processing unit estimates the underwater sound field based on the measurement results of the underwater vehicle in which the measured sound pressure level minus the underwater background noise level is greater than 3 dB. placing an underwater vehicle having a sound pressure meter at each of the predetermined positions relative to the measurement target;
estimating an underwater sound field generated by the measurement target based on the measurement results of each of the underwater vehicles;
The underwater sound field measuring method includes: