Underwater acoustic positioning system and underwater acoustic positioning method

Abstract

To provide an underwater acoustic positioning system and an underwater acoustic positioning method that are capable of improving the positioning accuracy of an acoustic apparatus such as a transmitter.SOLUTION: An underwater acoustic positioning system includes a shipboard station and a positioning device. The shipboard station includes a communication unit that receives an acoustic signal transmitted by an acoustic apparatus, a positioning unit that positions the position of the shipboard station, and a creation unit that creates positioning request information for positioning that includes the acoustic signal received by the communication unit and position information on the shipboard station positioned by the positioning unit. The communication unit transmits the positioning request information created by the creation unit to the positioning device. The positioning device includes a receiving unit that receives the positioning request information transmitted from the shipboard station and a signal processing unit that derives the position of the acoustic apparatus based on the acoustic signal and position information on the shipboard station included in the positioning request information received by the receiving unit.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an underwater acoustic positioning system and an underwater acoustic positioning method.

Background Art

[0002] Regarding an aerial drone, there is known one that carries an underwater drone, flies to a target water area, separates the underwater drone after landing in the target water area, makes the underwater drone submerge, recovers the underwater drone after the work of the underwater drone is completed, and takes off from the water (hereinafter referred to as "hydro-aerial combined drone") (see, for example, Non-Patent Document 1). The hydro-aerial combined drone has a function of acoustic positioning. For example, a sound wave is transmitted from a transmitter attached to the underwater drone and received by an underwater microphone (hydrophone) on the aerial drone side. The aerial drone automatically analyzes the received signal and calculates the position of the underwater drone. The calculation result of the position of the underwater drone is sent to a land-based base together with the camera images of the aerial drone and the underwater drone. At the base, the position is displayed on a map.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described technology, in the case of an aerial drone, the analysis of the received signal (acoustic signal) from the transmitter attached to the underwater drone and the process of calculating the position of the underwater drone (transmitter) are performed by the CPU (Central Processing Unit) of the embedded board mounted on the aerial drone. Since the size of the aerial drone cannot be increased significantly, it is difficult for the CPU of the embedded board mounted on the aerial drone to perform complex and advanced processing. For this reason, the calculation accuracy of the position of the transmitter calculated by the aerial drone is not necessarily high. An object of the present invention is to provide an underwater acoustic positioning system and an underwater acoustic positioning method capable of improving the positioning accuracy of the position of an acoustic device such as a transmitter.

Means for Solving the Problems

[0005] (1) One aspect of the present invention is an underwater acoustic positioning system including a ship station and a positioning device. The ship station includes a first communication unit that receives an acoustic signal transmitted by an acoustic device, a positioning unit that measures the position of the ship station, and a creation unit that creates positioning request information for positioning including the acoustic signal received by the first communication unit and the position information of the ship station measured by the positioning unit. Either via a mobile phone line or a satellite communication line, The ship station further includes a second communication unit that transmits the positioning request information created by the creation unit to the positioning device. The positioning device includes a receiving unit that receives the positioning request information transmitted by the ship station, and based on the time difference of the acoustic signals received on three or more channels included in the positioning request information received by the receiving unit, the transmission cycle of the acoustic signal transmitted by the acoustic device, and the position information of the ship station. In the SSBL method The underwater acoustic positioning system includes a signal processing unit that derives the position of the acoustic device. ( 2 ) One aspect of the present invention is the underwater acoustic positioning system described in the above (1 ) to ). In this system, when the number of samples of the transmission cycle of the acoustic signal transmitted by the acoustic device is a power of 2, the signal processing unit performs a fast Fourier transform on the acoustic signal with the number of samples (power of 2) of the transmission cycle of the acoustic signal transmitted by the acoustic device, and based on the result of the fast Fourier transform of the acoustic signal, derives the position of the acoustic device. ( 3 )One aspect of the present invention is that in the underwater acoustic positioning system described above in (1 ) to ), when the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device is not a power of 2, the signal processing unit performs a fast Fourier transform on the acoustic signal with the number of samples being a power of 2 in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device, and derives the position of the acoustic device based on the result of performing the fast Fourier transform on the acoustic signal. ( 4 )One aspect of the present invention is that in the underwater acoustic positioning system according to any one of the above (1) to the above ( 3 ), the signal processing unit calculates the cross-correlation function between the acoustic signals transmitted by the acoustic device on a plurality of channels. ( 5 )One aspect of the present invention is that in the underwater acoustic positioning system according to any one of the above (1) to the above ( 4 ), the first communication unit receives the uncompressed acoustic signal, or the reversibly compressed acoustic signal, or the irreversibly compressed acoustic signal transmitted by the acoustic device.

[0006] ( 6 )One aspect of the present invention is an underwater acoustic positioning method executed by an underwater acoustic positioning system including a ship station and a positioning device, wherein the ship station receives an acoustic signal transmitted by an acoustic device, the ship station measures a position, the ship station creates positioning request information for positioning including the acoustic signal and the position information of the ship station, and the ship station Either via a mobile phone line or a satellite communication line, transmits the positioning request information to the positioning device, the positioning device receives the positioning request information transmitted by the ship station, and the positioning device is based on the time difference of the acoustic signals received on 3 or more channels included in the positioning request information, the transmission period of the acoustic signal transmitted by the acoustic device, and the position information of the ship station In the SSBL method to derive the position of the acoustic device.

Advantages of the Invention

[0007] According to the present invention, an underwater acoustic positioning system and an underwater acoustic positioning method capable of improving the positioning accuracy of the position of an acoustic device such as a transmitter can be provided.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0009] Next, the underwater acoustic positioning system and the underwater acoustic positioning method according to the present embodiment will be described with reference to the drawings. The embodiments described below are merely examples, and the embodiments to which the present invention is applied are not limited to the following embodiments. In all the drawings for explaining the embodiments, those having the same function are denoted by the same reference numerals, and repeated explanations are omitted. In addition, “based on XX” as used in the present application means “based on at least XX”, and includes cases where it is based on another element in addition to XX. Also, “based on XX” is not limited to the case where XX is directly used, and includes cases where it is based on something obtained by performing arithmetic operations or processing on XX. “XX” is an arbitrary element (for example, arbitrary information).

[0010] (Embodiment) (Underwater Acoustic Positioning System) FIG. 1 is a diagram showing a configuration example of an underwater acoustic positioning system according to an embodiment of the present invention. In FIG. 1, an underwater acoustic positioning system 1 includes an aerial drone 10, an acoustic device 50, and a positioning device 100. The aerial drone 10 and the positioning device 100 communicate via a network NW. The network NW includes, for example, a mobile phone line, a satellite communication line, the Internet, a WAN (Wide Area Network), a LAN (Local Area Network), a provider device, a wireless base station, and the like.

[0011] An overview of the processing of the underwater acoustic positioning system 1 will be described. The acoustic device 50 is mounted on, for example, an underwater drone (not shown). When the underwater drone dives, the acoustic device 50 mounted on the underwater drone comes to be located underwater UW. The acoustic device 50 transmits acoustic signals on at least 3 channels. For example, the acoustic device 50 transmits an uncompressed (not compressed) acoustic signal underwater UW for about 10 milliseconds about once per second. The acoustic device 50 repeats the transmission and non-transmission of the acoustic signal. An example of the acoustic device 50 is a transmitter, a pinger, or a transponder. Hereinafter, as an example, the case where the acoustic device 50 transmits acoustic signals on 3 channels will be continued to be described. The aerial drone 10 is located on the water surface and receives the acoustic signals transmitted by the acoustic device 50 on 3 channels. Time synchronization is performed between the aerial drone 10 and the acoustic device 50. Since the acoustic device 50 repeats the transmission and non-transmission of the acoustic signal, the acoustic signals received by the aerial drone 10 may or may not include the acoustic signals transmitted by the acoustic device 50. The aerial drone 10 measures the position of its own aerial drone 10. The aerial drone 10 creates positioning request information for positioning, including each of the acoustic signals received on 3 channels and the position information of its own aerial drone 10. The aerial drone 10 transmits the created positioning request information to the positioning device 100. The positioning device 100 is located on land and receives the positioning request information transmitted by the water drone 10. For example, the positioning device 100 may be located at a location away from the water drone 10. The positioning device 100 derives the position of the acoustic device 50 based on each of the acoustic signals received on three channels included in the received positioning request information, the transmission period of the acoustic signal transmitted by the acoustic device 50, and the position information of the water drone 10. Here, the transmission period of the acoustic signal transmitted by the acoustic device 50 is preset in the positioning device 100. The positioning device 100, for example, uses the SSBL (Super Short Base Line) method to obtain the time difference of the acoustic signals received on three channels, and calculates the position of the acoustic device 50 based on the obtained time difference of the acoustic signals. The positioning device 100 outputs the derivation result of the position of the acoustic device.

[0012] Hereinafter, each of the water drone 10 and the positioning device 100 included in the underwater acoustic positioning system 1 will be sequentially described. FIG. 2 is a diagram showing details of the water drone and the positioning device included in the underwater acoustic positioning system of the present embodiment. (Water drone 10) The water drone 10 includes a housing (not shown) and a plurality of rotors (not shown). Each of the plurality of rotors rotates by a motor (not shown) to apply lift and propulsion force to the water drone 10. Further, by controlling the drive current supplied to each motor, the orientation and traveling direction of the water drone 10 can be controlled. An example of the water drone 10 is a ship station, an unmanned aerial vehicle on water, or an aerial drone. The water drone 10 is configured to include a smartphone, a mobile terminal, a personal computer, a tablet terminal device, or other information processing devices. The water drone 10 includes, for example, a first communication unit 12-1, a second communication unit 12-2, a positioning unit 14, a creation unit 16, a control unit 18, and a storage unit 20.

[0013] The first communication unit 12-1 is implemented by a communication module. The first communication unit 12-1 is installed, for example, at the lower part of the underwater drone 10 and receives underwater sounds (sound waves propagating in water). An example of the first communication unit 12-1 is a hydrophone. The first communication unit 12-1 receives the acoustic signals transmitted by the acoustic device 50 existing in the underwater UW in three channels. The second communication unit 12-2 is implemented by a communication module. The second communication unit 12-2 communicates with an external communication device via the network NW. The second communication unit 12-2 may communicate, for example, by a wireless communication method such as a mobile phone line or a satellite communication line. An example of the mobile phone line is the 5th Generation Mobile Communication System (5G). The second communication unit 12-2 transmits the positioning request information output by the creation unit 16. The storage unit 20 is implemented by an HDD (Hard Disk Drive), a flash memory, a RAM (Random Access Memory), a ROM (Read Only Memory), etc.

[0014] The positioning unit 14 is composed of a satellite positioning system such as a Global Navigation Satellite System (GNSS) and positions the position of the underwater drone 10. The Global Navigation Satellite System includes the Global Positioning System (GPS), GLONASS, Galileo, the Quasi-Zenith Satellite (QZSS), etc. The positioning unit 14 positions the position of the underwater drone 10. The creation unit 16 acquires the three-channel acoustic signal from the first communication unit 12-1 and acquires the position information of the underwater drone 10 from the positioning unit 14. The creation unit 16 creates positioning request information addressed to the positioning device 100 including the acquired three-channel acoustic signal and the position information of the underwater drone 10. The creation unit 16 outputs the created positioning request information to the second communication unit 12-2. The control unit 18 navigates the water drone 10 by controlling the drive current supplied to each motor. By controlling the drive current supplied to each motor, each of the plurality of rotors rotates, and the orientation and traveling direction of the water drone 10 can be controlled.

[0015] All or part of the positioning unit 14, the creation unit 16, and the control unit 18 are, for example, functional units (hereinafter referred to as software functional units) realized by a processor such as a CPU (Central Processing Unit) executing a program stored in the storage unit 20. Note that all or part of the positioning unit 14, the creation unit 16, and the control unit 18 may be realized by hardware such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), or FPGA (Field-Programmable Gate Array), or may be realized by a combination of a software functional unit and hardware.

[0016] (Positioning device 100) The positioning device 100 is realized as a smartphone, a mobile terminal, a personal computer, a tablet terminal device, or other information processing device. The positioning device 100 includes, for example, a communication unit 102, a signal processing unit 104, an output unit 106, and a storage unit 110. The communication unit 102 is realized by a communication module. The communication unit 102 communicates with an external communication device via the network NW. The communication unit 102 may communicate by a wireless communication method such as a mobile phone line or a satellite communication line, for example. The communication unit 102 receives the positioning request information transmitted by the water drone 10. The storage unit 110 is realized by an HDD, a flash memory, a RAM, a ROM, or the like. The storage unit 110 stores information for specifying the transmission cycle of the acoustic signal transmitted by the acoustic device 50.

[0017] The signal processing unit 104 acquires positioning request information from the communication unit 102. The signal processing unit 104 acquires the acoustic signals of three channels included in the acquired positioning request information and the position information of the water drone 10. The signal processing unit 104 acquires information specifying the transmission cycle of the acoustic signals transmitted by the acoustic device 50 from the storage unit 110. The signal processing unit 104 derives the position of the acoustic device 50 based on each of the acquired acoustic signals of three channels, the transmission cycle of the acoustic signals transmitted by the acoustic device 50, and the position information of the water drone 10. FIG. 3 is a diagram for explaining an example of the operation of the positioning device included in the underwater acoustic positioning system according to the present embodiment. FIG. 3 shows an example of the acoustic signals of three channels included in the positioning request information. In FIG. 3, the horizontal axis represents time [seconds]. The signal processing unit 104 cuts out each of the acoustic signals of three channels at a predetermined cycle. The signal processing unit 104 calculates the cross-correlation function between the cut-out waveform of each of the acoustic signals of three channels and the transmission pulse waveform. The signal processing unit 104 obtains the difference in reception times of the received pulses detected using each of the acoustic signals of three channels. The signal processing unit 104 obtains the position of the acoustic device 50 based on the difference in reception times of the received pulses.

[0018] Specifically, when the number of samples of the transmission cycle of the acoustic signals transmitted by the acoustic device 50 is a power of 2 for each of the acoustic signals of three channels, the signal processing unit 104 performs fast Fourier transform on each of the acoustic signals of three channels using the number of samples (power of 2) of the transmission cycle of the acoustic signals transmitted by the acoustic device 50. For example, the signal processing unit 104 may perform fast Fourier transform on each of the acoustic signals of three channels using 2048 samples of the transmission cycle of the acoustic signals transmitted by the acoustic device 50, or may perform fast Fourier transform using 1 / 2 or 1 / 4 of the number of samples of the transmission cycle of the acoustic signals transmitted by the acoustic device 50. By configuring in this way, it is possible to cut out at a relatively short cycle, so that the processing load of the positioning device 100 can be reduced. The signal processing unit 104 calculates a cross-correlation function by multiplying, on the frequency plane, the result of performing a fast Fourier transform on each of the three-channel acoustic signals by the transmission pulse waveform. The signal processing unit 104 detects the reception of a pulse based on the calculation result of the cross-correlation function. The signal processing unit 104 calculates the difference in reception times based on the detection result of the reception of the pulse. The signal processing unit 104 calculates the position of the acoustic device 50 based on the calculation result of the difference in reception times and the position information of the water drone 10. Here, the position coordinates of the acoustic device 50 and the first communication unit 12-1 can be expressed with the coordinates on the water drone 10 as the reference coordinate system. For example, the bow direction of the water drone 10 is the x-axis, the starboard direction is the y-axis, and the vertical direction is the z-axis. The signal processing unit 104 may perform conversion from the coordinates on the water drone 10 to the earth coordinates using, for example, a GNSS compass. The output unit 106 acquires the calculation result of the position of the acoustic device 50 from the signal processing unit 104. The output unit 106 outputs the acquired position information of the acoustic device 50. For example, the output unit 106 may output the position information of the acoustic device 50 by voice, may output it to another device (not shown), or may output it to a display unit (not shown). All or part of the signal processing unit 104 and the output unit 106 are, for example, functional units (hereinafter referred to as software functional units) realized by a processor such as a CPU executing a program stored in the storage unit 110. Note that all or part of the signal processing unit 104 and the output unit 106 may be realized by hardware such as an LSI, an ASIC, or an FPGA, or may be realized by a combination of a software functional unit and hardware.

[0019] (Operation of the underwater acoustic positioning system) FIG. 4 is a flowchart showing an example of the operation of the underwater acoustic positioning system according to the present embodiment. The case where the number of samples in the transmission period of the acoustic signal transmitted by the acoustic device 50 is a power of 2 will be described. (Step S1-1) In the water drone 10, the first communication unit 12-1 receives the acoustic signal transmitted by the acoustic device 50 in three channels. (Step S2-1) In the water drone 10, the positioning unit 14 measures the position of the water drone 10. (Step S3-1) In the water drone 10, the creation unit 16 acquires acoustic signals of three channels from the first communication unit 12-1 and acquires the position information of the water drone 10 from the positioning unit 14. The creation unit 16 creates positioning request information addressed to the positioning device 100, which includes the acquired acoustic signals of three channels and the position information of the water drone 10. (Step S4-1) In the water drone 10, the creation unit 16 outputs the created positioning request information to the second communication unit 12-2. The second communication unit 12-2 acquires the positioning request information output by the creation unit 16 and transmits the acquired positioning request information to the positioning device 100.

[0020] (Step S5-1) In the positioning device 100, the communication unit 102 receives the positioning request information transmitted by the water drone 10. The signal processing unit 104 acquires the positioning request information from the communication unit 102. The signal processing unit 104 acquires the acoustic signals of three channels included in the acquired positioning request information and the position information of the water drone 10. The signal processing unit 104 performs fast Fourier transform on each of the acoustic signals of three channels with the number of samples (power of 2) of the transmission cycle of the acoustic signals transmitted by the acoustic device 50. (Step S6-1) In the positioning device 100, the signal processing unit 104 calculates the cross-correlation function between the result (waveform) of Fourier transform of each of the acoustic signals of three channels and the transmission pulse waveform. (Step S7-1) In the positioning device 100, the signal processing unit 104 obtains the difference in reception times of the received pulses detected by each of the acoustic signals of three channels based on the calculation result of the cross-correlation function. (Step S8-1) In the positioning device 100, the signal processing unit 104 obtains the position of the acoustic device 50 based on the difference in reception times of the received pulses. (Step S9-1) In the positioning device 100, the output unit 106 acquires the calculation result of the position of the acoustic device 50 from the signal processing unit 104. The output unit 106 outputs the acquired position information of the acoustic device 50. In the above-described embodiment, the case where the acoustic device 50 transmits an uncompressed acoustic signal has been described, but the present invention is not limited to this example. For example, the acoustic device 50 may transmit a reversibly compressed acoustic signal or an irreversibly compressed acoustic signal. In the above-described embodiment, the case where the water drone 10 receives the acoustic signal transmitted by the acoustic device 50 in three channels has been described, but the present invention is not limited to this example. For example, the acoustic device 50 may transmit an acoustic signal in four or more channels, and the water drone 10 may receive the acoustic signal transmitted by the acoustic device 50 in four or more channels. By configuring in this way, even when time synchronization is not performed between the water drone 10 and the acoustic device 50, the positioning device 100 can obtain the position of the acoustic device 50.

[0021] According to the underwater acoustic positioning system according to the embodiment, the underwater acoustic positioning system 1 includes a water drone 10 as a ship station and a positioning device 100. The water drone 10 includes a first communication unit 12-1 that receives an acoustic signal transmitted by the acoustic device 50, a positioning unit 14 that measures the position of the ship station, a creation unit 16 that creates positioning request information for positioning including the acoustic signal received by the first communication unit 12-1 and the position information of the water drone 10 measured by the positioning unit 14, and a second communication unit 12-2 that transmits the positioning request information created by the creation unit 16 to the positioning device 100. The positioning device 100 includes a communication unit 102 as a receiving unit that receives the positioning request information transmitted by the water drone 10, and a signal processing unit 104 that derives the position of the acoustic device 50 based on the acoustic signal and the position information of the water drone 10 included in the positioning request information received by the communication unit 102. By configuring in this way, the positioning device 100 can derive the position of the acoustic device 50 using a high-performance CPU based on the acoustic signal and the position information of the water drone 10 included in the positioning request information transmitted by the water drone 10, so that the positioning accuracy of the position of the acoustic device 50 can be improved.

[0022] In the underwater acoustic positioning system 1, the second communication unit 12-2 transmits positioning request information to the positioning device 100 via either a mobile phone line or a satellite communication line. With this configuration, the underwater drone 10 can transmit the positioning request information to the positioning device 100 at high speed via either a mobile phone line or a satellite communication line. Therefore, the positioning device 100 can derive the position information of the acoustic device 50 almost in real time. Specifically, the acoustic signal received by the first communication unit 12-1 installed at the lower part of the underwater drone 10 floating on the water surface is transmitted from the second communication unit 12-2 to the land-based positioning device 100 via a high-speed communication line such as a mobile phone line or a satellite communication line. Assuming that the sampling frequency of the acoustic signal received by the positioning device 100 is 300 kHz and there are 4 channels of 2-byte data per sample, the required transmission speed is 19.2 [Mbps]. This transmission speed is a bandwidth that can be easily achieved, for example, using a 5G line. With this configuration, signals that had to be processed by a device (such as an underwater drone) wired to a hydrophone can be processed using the rich resources of the remotely installed land-based positioning device 100, enabling processing in an advanced and highly accurate manner.

[0023] In the underwater acoustic positioning system 1, when the number of samples in the transmission period of the acoustic signal transmitted by the acoustic device 50 is a power of 2, the signal processing unit 104 performs a fast Fourier transform on the acoustic signal with the number of samples in the transmission period of the acoustic signal transmitted by the acoustic device 50 (a power of 2), and derives the position of the acoustic device 50 based on the result of the fast Fourier transform of the acoustic signal. With this configuration, the positioning device 100 can perform a fast Fourier transform on the acoustic signal with the number of samples in the transmission period of the acoustic signal transmitted by the acoustic device 50 (a power of 2). Therefore, the positioning device 100 can derive the position of the acoustic device 50 based on the result of the fast Fourier transform of the acoustic signal with the number of samples in the transmission period of the acoustic signal transmitted by the acoustic device 50. Conventionally, the position of an underwater drone is calculated by performing the following processes. The acoustic signal received by the hydrophone is cut out, for example, every about 8 mS (2048 samples), and the correlation with the transmission pulse waveform is calculated. That is, a fast Fourier transform is applied every 8 mS, and multiplication is performed on the frequency plane. The transmission pulse waveform is, for example, a chirp signal with a length of 800 samples (3.2 mS). When the reception of the pulse is detected, the position of the underwater drone is calculated by calculating the difference in reception times at each channel. According to this process, if there is no disturbance in the received waveform due to reflected waves or the like, the position calculation can be performed without problems. However, if there are interfering waves, it may not be possible to accurately determine the position of the received pulse.

[0024] For example, the acoustic device 50 attached to the underwater drone transmits (emits) an acoustic signal (acoustic pulse) usually once per second. The surface drone 10 repeatedly receives a similar waveform with a period of one second. Therefore, in order to obtain the reception time difference between channels, it is ideal to be able to compare the entire one second rather than every 8 mS as described above. However, if the entire one second is compared, a fast Fourier transform process with about 300,000 samples needs to be performed, so the processing power of the embedded processor directly connected to the hydrophone is insufficient. Therefore, it is difficult to process in real time. In the underwater acoustic positioning system 1 according to this embodiment, the surface drone 10 transmits the waveform of the received acoustic signal as it is to the positioning device 100 installed at the land base. The positioning device 100 performs a fast Fourier transform process of about 300,000 samples based on the waveform of the acoustic signal transmitted by the surface drone 10. Since the positioning device 100 installed at the land base can be equipped with a high-performance computer, it is possible to perform the processing within one second even with a fast Fourier transform process of about 300,000 samples. That is, the positioning device 100 can perform the positioning process in real time, and it is possible to display the position on the map with high accuracy and in real time in combination with other information.

[0025] Note that the positioning device 100 does not need to perform fast Fourier transform processing with a number of samples approximately equal to one times the number of samples in the transmission cycle of the acoustic signal (acoustic pulse) transmitted by the acoustic device 50, and may perform fast Fourier transform processing with a number of samples approximately equal to an integer multiple of the number of samples in the same cycle. Also, in view of the purpose of a series of processes, even if it is somewhat smaller (shorter) than the number of samples in the same cycle as the transmission cycle of the acoustic signal (acoustic pulse) transmitted by the acoustic device 50, the purpose can be sufficiently achieved. Therefore, for example, the fast Fourier transform processing with a number of samples approximately equal to one-half of the number of samples in the same cycle as the transmission cycle of the acoustic signal (acoustic pulse) transmitted by the acoustic device 50 may be calculated about two times, or the fast Fourier transform processing with a number of samples approximately equal to one-fourth of the number of samples in the same cycle as the transmission cycle of the acoustic signal (acoustic pulse) transmitted by the acoustic device 50 may be calculated about four times.

[0026] In the underwater acoustic positioning system 1, the signal processing unit 104 calculates the cross-correlation function between the acoustic signals transmitted by the acoustic device 50 on a plurality of channels. By configuring in this way, since the positioning device 100 can calculate the cross-correlation function between the acoustic signals transmitted by the acoustic device 50 on a plurality of channels, the difference in reception times on each channel can be calculated. For this reason, the positioning device 100 can calculate the position of the acoustic device 50.

[0027] In the underwater acoustic positioning system 1, the first communication unit 12-1 receives an uncompressed acoustic signal, or a reversibly compressed acoustic signal, or an irreversibly compressed acoustic signal transmitted by the acoustic device 50. By configuring in this way, the positioning device 100 can derive the position of the acoustic device 50 based on the uncompressed acoustic signal, or the reversibly compressed acoustic signal, or the irreversibly compressed acoustic signal transmitted by the acoustic device 50.

[0028] (Modification of the embodiment) (Underwater acoustic positioning system) The configuration example of the underwater acoustic positioning system 1a in the modification of the embodiment can apply FIG. 1. However, instead of the positioning device 100, a positioning device 100a is provided. The outline of the processing of the underwater acoustic positioning system 1a will be described. The acoustic device 50 is attached to, for example, an underwater drone (not shown). When the underwater drone dives, the acoustic device 50 attached to the underwater drone comes to be located in the underwater UW. The acoustic device 50 transmits acoustic signals in at least 3 channels. For example, the acoustic device 50 transmits an uncompressed (not compressed) acoustic signal into the underwater UW for about 10 milliseconds once per second. The acoustic device 50 repeats the transmission and non - transmission of the acoustic signal. The surface drone 10 is located on the water surface and receives the acoustic signals transmitted by the acoustic device 50 in 3 channels. The surface drone 10 measures its own position on the water surface. The surface drone 10 creates positioning request information for positioning, which includes the acoustic signals received in at least 3 channels and the position information of the surface drone 10 itself. The surface drone 10 transmits the created positioning request information to the positioning device 100a. The positioning device 100a is located on land and receives the positioning request information transmitted by the surface drone 10. The positioning device 100a derives the position of the acoustic device 50 based on each of the acoustic signals received in 3 channels included in the received positioning request information, a value near the number of samples of the transmission period of the acoustic signals transmitted by the acoustic device 50, and the position information of the surface drone 10. Here, the transmission period of the acoustic signals transmitted by the acoustic device 50 is preset in the positioning device 100a. The positioning device 100a, for example, obtains the time difference of the acoustic signals received in 3 channels by the SSBL method, and calculates the position of the acoustic device 50 based on the obtained time difference of the acoustic signals. The positioning device 100a outputs the derivation result of the position of the acoustic device.

[0029] Hereinafter, among the surface drone 10 and the positioning device 100a included in the underwater acoustic positioning system 1a, a positioning device 100a different from the embodiment will be described. FIG. 5 is a diagram showing details of a surface drone and a positioning device included in an underwater acoustic positioning system according to a modification of the embodiment. (Positioning device) The positioning device 100a is realized as a smartphone, a mobile terminal, a personal computer, a tablet terminal device, or other information processing device. The positioning device 100a includes, for example, a communication unit 102, a signal processing unit 104a, an output unit 106, and a storage unit 110.

[0030] The signal processing unit 104a acquires positioning request information from the communication unit 102. The signal processing unit 104a acquires the three-channel acoustic signals included in the acquired positioning request information and the position information of the underwater drone 10. The signal processing unit 104a acquires information for specifying the transmission cycle of the acoustic signals transmitted by the acoustic device 50 from the storage unit 110. The signal processing unit 104a derives the position of the acoustic device 50 based on each of the acquired three-channel acoustic signals, a value in the vicinity of the number of samples of the transmission cycle of the acoustic signals transmitted by the acoustic device 50, and the position information of the underwater drone 10. The signal processing unit 104a extracts each of the three-channel acoustic signals at a predetermined cycle. The signal processing unit 104a calculates the cross-correlation function between the waveform obtained by extracting each of the three-channel acoustic signals and the transmission pulse waveform. The signal processing unit 104a obtains the difference in reception times of the received pulses detected using each of the three-channel acoustic signals. The signal processing unit 104a obtains the position of the acoustic device 50 based on the difference in reception times of the received pulses.

[0031] Specifically, when the number of samples of the transmission cycle of the acoustic signals transmitted by the acoustic device 50 is not a power of 2, the signal processing unit 104a obtains a power of 2 in the vicinity of the number of samples of the transmission cycle. For example, when the number of samples of the transmission cycle of the acoustic signals transmitted by the acoustic device 50 is not a power of 2, the signal processing unit 104a obtains the nearest power of 2 to the number of samples of the transmission cycle. The signal processing unit 104a performs a fast Fourier transform on the acoustic signal with the number of samples of a power of 2 in the vicinity of the number of samples of the transmission period obtained, at the number of samples of a power of 2 in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50. For example, the signal processing unit 104a may perform a fast Fourier transform on each of the three-channel acoustic signals with 2048 samples in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50, or may perform a fast Fourier transform with 1 / 2 or 1 / 4 of the number of samples of a value (power of 2) in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50. By configuring in this way, it can be cut out in a relatively short period, so the processing load of the positioning device 100a can be reduced. The signal processing unit 104a calculates the cross-correlation function by multiplying the result of performing a fast Fourier transform on each of the three-channel acoustic signals and the transmission pulse waveform on the frequency plane. The signal processing unit 104a detects the reception of the pulse based on the calculation result of the cross-correlation function. The signal processing unit 104a calculates the difference in reception time based on the detection result of the reception of the pulse. The signal processing unit 104a calculates the position of the acoustic device 50 based on the calculation result of the difference in reception time and the position information of the underwater drone 10. Here, the position coordinates of the acoustic device 50 and the first communication unit 12-1 can be represented with the coordinates on the underwater drone 10 as the reference coordinate system. For example, the bow direction of the underwater drone 10 is the x-axis, the starboard direction is the y-axis, and the vertical direction is the z-axis. The signal processing unit 104a may perform conversion from the coordinates on the underwater drone 10 to the earth coordinates using, for example, a GNSS compass. All or part of the signal processing unit 104a is, for example, a functional unit (hereinafter referred to as a software functional unit) realized by a processor such as a CPU executing a program stored in the storage unit 110. Note that all or part of the signal processing unit 104a may be realized by hardware such as an LSI, an ASIC, or an FPGA, or may be realized by a combination of a software functional unit and hardware.

[0032] (Operation of the underwater acoustic positioning system) FIG. 6 is a flowchart showing an example of the operation of an underwater acoustic positioning system according to a modification of the embodiment. Here, as an example, the case where the acoustic device 50 transmits an acoustic signal in three channels will be described. Since steps S1-1 to S4-2 and S6-2 to S8-2 can apply steps S1-1 to S4-1 and S6-1 to S8-1 in FIG. 4, the description here is omitted. (Step S5-2) In the positioning device 100a, the communication unit 102 receives the positioning request information transmitted by the water drone 10. The signal processing unit 104a acquires the positioning request information from the communication unit 102. The signal processing unit 104a acquires the three-channel acoustic signal included in the acquired positioning request information and the position information of the water drone 10. When the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50 is not a power of 2, the signal processing unit 104a obtains a power of 2 in the vicinity of the number of samples of the transmission period. The signal processing unit 104a performs fast Fourier transform on the acoustic signal with the number of samples of a power of 2 in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50.

[0033] According to the underwater acoustic positioning system 1a according to the modification of the embodiment, in the positioning device 100a, when the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50 is not a power of 2, the signal processing unit 104a performs fast Fourier transform on the acoustic signal with the number of samples of a power of 2 in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50, and derives the position of the acoustic device 50 based on the result of performing fast Fourier transform on the acoustic signal. By configuring in this way, even when the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50 is not a power of 2, the positioning device 100a can perform fast Fourier transform on the acoustic signal with the number of samples of a power of 2 in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50. Therefore, the positioning device 100a can derive the position of the acoustic device 50 based on the result of performing fast Fourier transform on the acoustic signal with the number of samples of a power of 2 in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device 50.

[0034] According to the underwater acoustic positioning system of the present embodiment and the underwater acoustic positioning system of the modified example of the embodiment, by improving the positioning accuracy of the position of the acoustic device in water, it is assumed that the ocean and ocean resources can be conserved for sustainable development and can be used in a sustainable manner. Therefore, it becomes possible to contribute to Goal 14, "Conserve the oceans' bounty," of the Sustainable Development Goals (SDGs) led by the United Nations.

[0035] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present invention are also included. For example, a computer program for realizing the functions of each of the above-described devices may be recorded on a computer-readable recording medium, and the computer program recorded on this recording medium may be read into a computer system and executed. Here, the "computer system" may include hardware such as an OS and peripheral devices. In addition, the "computer-readable recording medium" refers to a writable non-volatile memory such as a flexible disk, a magneto-optical disk, a ROM, a flash memory, a portable medium such as a DVD, and a storage device such as a hard disk built into a computer system. Furthermore, the "computer-readable recording medium" also includes a volatile memory (for example, DRAM (Dynamic Random Access Memory)) inside a computer system that becomes a server or a client when a computer program is transmitted via a network such as the Internet or a communication line such as a telephone line, and holds the program for a certain period of time. Also, the above program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. Further, the program may be for realizing a part of the functions described above. Furthermore, it may be a so-called difference file (difference program) that can realize the functions described above in combination with a program already recorded in the computer system.

Explanation of Signs

[0036] 10…Aerial drone, 12-1…First communication unit, 12-2…Second communication unit, 14…Positioning unit, 16…Creation unit, 18…Control unit, 20…Memory unit, 50…Acoustic device, 100, 100a…Positioning device, 102…Communication unit, 104, 104a…Signal processing unit, 106…Output unit

Claims

1. An underwater acoustic positioning system comprising a shipboard station and a positioning device, wherein the shipboard station includes a first communication unit that receives an acoustic signal transmitted by an acoustic device, a positioning unit that measures the position of the shipboard station, a creation unit that creates positioning request information for positioning, including the acoustic signal received by the first communication unit and the position information of the shipboard station measured by the positioning unit, a second communication unit that transmits the positioning request information created by the creation unit to the positioning device via either a mobile phone line or a satellite communication line and the positioning device includes a receiving unit that receives the positioning request information transmitted by the shipboard station, a signal processing unit that derives the position of the acoustic device in the SSBL method based on the time difference of the acoustic signals received on three or more channels included in the positioning request information received by the receiving unit, the transmission period of the acoustic signal transmitted by the acoustic device, and the position information of the shipboard station An underwater acoustic positioning system.

2. When the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device is a power of 2, the signal processing unit performs a fast Fourier transform on the acoustic signal with the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device, and derives the position of the acoustic device based on the result of the fast Fourier transform of the acoustic signal. The underwater acoustic positioning system according to Claim 1.

3. When the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device is not a power of 2, the signal processing unit performs a fast Fourier transform on the acoustic signal with the number of samples of a power of 2 in the vicinity of the number of samples of the transmission period of the acoustic signal transmitted by the acoustic device, and derives the position of the acoustic device based on the result of the fast Fourier transform of the acoustic signal. The underwater acoustic positioning system according to Claim 1.

4. The signal processing unit calculates a cross-correlation function between acoustic signals transmitted by the acoustic device on a plurality of channels. The underwater acoustic positioning system according to any one of Claims 1 to 3.

5. The first communication unit receives the uncompressed acoustic signal, the reversibly compressed acoustic signal, or the irreversibly compressed acoustic signal transmitted by the acoustic device. The underwater acoustic positioning system according to any one of Claims 1 to 4.

6. An underwater acoustic positioning method executed by an underwater acoustic positioning system comprising a shipboard station and a positioning device, wherein the shipboard station receives an acoustic signal transmitted by an acoustic device, the shipboard station measures its position, The ship station creates positioning request information for positioning, including the acoustic signal and the position information of the ship station. The ship station transmits the positioning request information to a positioning device via either a mobile phone line or a satellite communication line. The positioning device receives the positioning request information transmitted by the ship station. An underwater acoustic positioning method in which the positioning device derives the position of the acoustic device in the SSBL method based on the time difference of the acoustic signals received on three or more channels included in the positioning request information, the transmission period of the acoustic signals transmitted by the acoustic device, and the position information of the ship station.

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