Passive sonar detection confidence determination device, passive sonar system and method, and program

Abstract

To increase the efficiency of a process of determining whether or not a received underwater sound wave is a ship-sailing sound radiated from an underwater sailing body and realize automatization in determining a likelihood (detection confidence factor).SOLUTION: The present invention includes: a noise averaging processing unit that determines the frequency spectrum of a signal received by a nondirectional first echo sounder receiver of a passive sonar that receives an underwater sound wave and calculates a signal-to-noise ratio on the basis of amplitude data for each frequency component; an azimuth calculation processing unit that determines the frequency spectrum of a signal received by a south-north directional second echo sounder receiver and an east-west directional third echo sounder receiver of the passive sonar and calculates the azimuth for each frequency component; an azimuth error processing unit that stores the azimuth calculation result for each frequency component in a storage unit for a prescribed number of times, and calculates the average value of difference as an azimuth error between the latest azimuth calculation result for each frequency component by the azimuth calculation processing unit and the azimuth calculation result for each frequency component for a prescribed number of times; and a detection confidence factor determination unit that calculates the determination value of the detection confidence factor of the ship-sailing sound of an underwater sailing body, on the basis of the absolute value of azimuth error for each frequency component.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a passive sonar detection confidence determination device, a passive sonar system and method, and a program.

Background Art

[0002] A general drop-type passive sonar includes three types of receivers (acoustic sensors): an eight-shaped directivity (NS directivity) in the north-south direction, an eight-shaped directivity (EW directivity) in the east-west direction, and an omnidirectional uniform directivity, that is, non-directivity. The electrical signals of the underwater sound waves received by each receiver are modulated and converted into RF (Radio Frequency) signals, which are wirelessly transmitted from the antenna to a processing device (for example, an on-board processing device in an aircraft).

[0003] In an on-board processing device mounted on an aircraft, a wireless signal wirelessly transmitted from a drop-type passive sonar is received by an antenna, demodulated, and converted into a baseband signal. Signal processing is performed on the underwater sound waves received by the non-directive receiver to detect the running sound radiated from an underwater vehicle. Also, in the on-board processing device, signal processing is performed on the underwater sound waves received by the NS directivity receiver and the EW directivity receiver of the drop-type passive sonar to calculate the arrival direction of the running sound of the underwater vehicle.

[0004] On the other hand, on the side of the underwater vehicle, in order to avoid being detected by the drop-type passive sonar, there is a tendency to quiet the running sounds such as engine sound, motor rotation sound, cooling water pump operation sound, and screw propeller rotation sound.

[0005] Regarding the improvement of signal processing aimed at improving the detection performance of the running sound of an underwater vehicle by a drop-type passive sonar, for example, the following patent documents are referred to.

[0006] Patent Document 1 discloses an underwater vehicle detection device that solves the problem of difficulty in detecting the presence of an underwater vehicle when the operating noise of the underwater vehicle propulsion machine (e.g., engine noise, motor rotation noise, cooling water pump operation noise, and screw rotation noise) is low. The device comprises: an acoustic sensor that converts sound waves generated from an underwater vehicle present in the water into electrical signals; a directional pattern forming unit that forms a cardioid directivity pattern for each predetermined frequency component based on the electrical signals; a directional pattern calculation unit that calculates a directivity ratio, which is the ratio of the signal level in the direction of maximum sensitivity to the signal level in the direction of minimum sensitivity, for each predetermined frequency component based on the cardioid directivity pattern formed by the directional pattern forming unit; and a directional pattern distribution generation unit that synthesizes the directional pattern calculated by the directional pattern calculation unit for each predetermined frequency component to generate a directional pattern distribution representing the distribution of directional patterns for each frequency component.

[0007] Furthermore, Patent Document 2 discloses a sonar device that addresses issues such as large azimuth calculation errors when performing long-duration integration processing to separate weak underwater sound waves radiated by an underwater vehicle from underwater noise and improve the signal-to-noise ratio (S / N ratio), by comprising: at least one S / N ratio calculation unit configured to calculate the S / N ratio of an acoustic signal received by an acoustic sensor; at least one integration processing unit configured to integrate the acoustic signal for a set integration time; at least one integration time selection unit configured to select the integration time based on the S / N ratio; and at least one azimuth calculation unit configured to calculate the azimuth of the received acoustic signal based on at least one acoustic signal integrated for the selected integration time. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2013-160564 [Patent Document 2] Japanese Patent Publication No. 2018-146353 [Overview of the project] [Problems that the invention aims to solve]

[0009] As mentioned above, the sounds of underwater vehicles, such as engine noise, motor rotation noise, cooling water pump operation noise, and propeller rotation noise, tend to become quieter.

[0010] For such underwater vehicles, there is a need to streamline the process of determining whether the underwater sound waves received by a deployable passive sonar are the vehicle's own sound, and to automate the determination of the likelihood (probability) that the sound is indeed emitted from the vehicle.

[0011] Therefore, the present invention was devised in view of the above problems, and its purpose is to provide a passive sonar detection confidence determination device, a passive sonar system, a passive sonar detection confidence determination method, and a program that streamline the process of determining whether or not received underwater sound waves are navigation sounds emitted from an underwater vehicle, and enable the automation of determining the likelihood (detection confidence) that they are such navigation sounds. [Means for solving the problem]

[0012] According to one embodiment of the present invention, a passive sonar detection confidence determination device is provided, comprising: a noise averaging processing unit that obtains the frequency spectrum of a signal received by an omnidirectional first receiver of a passive sonar that receives underwater sound waves and calculates a signal-to-noise ratio based on amplitude data for each frequency component; an orientation calculation processing unit that obtains the frequency spectrum of a signal received by a second receiver with north-south directivity and a third receiver with east-west directivity of the passive sonar and calculates the orientation for each frequency component; an orientation error processing unit that stores the orientation calculation results for each frequency component by the orientation calculation processing unit in a predetermined number of storage units for a predetermined number of times, and calculates the average value of the difference between the latest orientation calculation result for each frequency component by the orientation calculation processing unit and the orientation calculation results for each frequency component for the predetermined number of times as the orientation error; and a detection confidence determination processing unit that calculates a determination value for the detection confidence of the sound of an underwater vehicle based on the absolute value of the orientation error for each frequency component.

[0013] According to one embodiment of the present invention, a passive sonar system comprises a passive sonar that receives underwater sound waves and a passive sonar detection confidence level determination device. The passive sonar comprises a floating surface unit and an underwater unit suspended from the floating surface unit by a cable. The underwater unit includes an omnidirectional first receiver, a north-south directional second receiver, and an east-west directional third receiver. The underwater unit transmits the received signals from the first to third receivers to the floating surface unit, and the floating surface unit wirelessly transmits the received signals from the first to third receivers to the passive sonar detection confidence determination device. The passive sonar detection confidence determination device includes: a noise averaging processing unit that obtains the frequency spectrum of the received signal of the first receiver included in the radio signal transmitted from the passive sonar and calculates a signal-to-noise ratio based on amplitude data for each frequency component; a direction calculation processing unit that obtains the frequency spectrum of the received signals of the second receiver and the third receiver included in the radio signal and calculates the direction for each frequency component; a direction error processing unit that stores the direction calculation results for each frequency component by the direction calculation processing unit in a predetermined number of storage units for a predetermined number of times, and calculates the average value of the difference between the latest direction calculation result for each frequency component by the direction calculation processing unit and the predetermined number of direction calculation results for each frequency component as the direction error; and a detection confidence determination processing unit that calculates a detection confidence value for detecting the sound of an underwater vehicle based on the absolute value of the direction error for each frequency component.

[0014] According to one embodiment of the present invention, the first step is to obtain the frequency spectrum of a signal received by an omnidirectional first receiver of a passive sonar that receives underwater sound waves, and to calculate the signal-to-noise ratio based on the amplitude data for each frequency component, The second step involves obtaining the frequency spectrum of the signals received by the second receiver of the passive sonar, which is directional in the north-south direction, and the third receiver, which is directional in the east-west direction, respectively, and calculating the direction for each frequency component. A third step involves storing the direction calculation results for each frequency component obtained in the second step in a predetermined number of memory units, and calculating the average difference between the latest direction calculation result for each frequency component obtained in the second step and the predetermined number of direction calculation results for each frequency component as the direction error. A fourth step involves calculating a determination value for the detection confidence level of the underwater vehicle's navigation sound based on the absolute value of the azimuth error for each frequency component, A passive sonar detection confidence determination method is provided, which includes the following.

[0015] According to one embodiment of the present invention, a first process is performed to obtain the frequency spectrum of a signal received by an omnidirectional first receiver of a passive sonar that receives underwater sound waves, and to calculate the signal-to-noise ratio based on the amplitude data for each frequency component. A second process of obtaining the frequency spectra of the signals received by the second receiver with a north-south directivity and the third receiver with an east-west directivity of the passive sonar and calculating the azimuth for each frequency component, a third process of storing the azimuth calculation results for each frequency component obtained by the second process in a storage unit for a predetermined number of times, and calculating an average value of the differences between the latest azimuth calculation result for each frequency component obtained by the second process and the azimuth calculation results for each frequency component for the predetermined number of times as an azimuth error; and a fourth process of calculating a determination value of detection confidence for detecting the navigation sound of an underwater vehicle based on the absolute value of the azimuth error for each frequency component, and a program for causing a computer to execute these processes is provided. Further, according to the present invention, a computer-readable recording medium (for example, a semiconductor storage such as a RAM (Random Access Memory), a ROM (Read Only Memory), or an EEPROM (Electrically Erasable and Programmable ROM)), an HDD (Hard Disk Drive), a CD (Compact Disc), a DVD (Digital Versatile Disc)) storing the above program is provided. [Effect of the Invention]

[0016] According to the present invention, it is possible to improve the efficiency of the determination process as to whether the received underwater sound wave is the navigation sound of an underwater vehicle, and to automate the determination of the probability (detection confidence) that it is the navigation sound radiated from the underwater vehicle. [Brief Description of the Drawings]

[0017] [Figure 1A] It is a diagram schematically explaining an example of the system of an embodiment. [Figure 1B] It is a diagram schematically explaining the directivity of each receiver. [Figure 2] It is a diagram explaining an example of improvement in azimuth accuracy due to an integration effect. [Figure 3A] It is a diagram explaining an example of the configuration of an embodiment. [Figure 3B] This is a diagram for explaining Modification Example 1 of the configuration of the embodiment. [Figure 4] This is a diagram for explaining the processing content of the azimuth error processing of the embodiment. [Figure 5] This is a diagram for explaining the processing content of the detection confidence determination processing of the embodiment. [Figure 6] This is a diagram for explaining the embodiment.

Mode for Carrying Out the Invention

[0018] Embodiments of the present invention will be described. By signal - processing the underwater sound waves received by a dropped - type passive sonar dropped from an aircraft into the sea, signals with a large S / N (Signal to Noise ratio) for each frequency component that seems to be the running sound of an underwater vehicle are detected, and by continuously monitoring for a long time whether the sound - wave arrival azimuth is a specific azimuth, it may be determined whether it is the running sound of an underwater vehicle. According to this embodiment, by evaluating in advance whether the arrival azimuth of the underwater sound wave is a specific direction, the running sound radiated by the underwater vehicle can be automatically discriminated efficiently.

[0019] That is, in this embodiment, when detecting the running sound radiated when an underwater vehicle runs by a dropped - type passive sonar, signal processing is performed on the underwater sound wave received by the dropped - type passive sonar to automatically determine whether it is the running sound radiated from the underwater vehicle. The probability (detection confidence) that it is the running sound radiated from the underwater vehicle is automatically determined. As a method for automatically determining the detection confidence, the fact that an underwater sound wave is arriving from a specific direction is numerically evaluated.

[0020] By adding and integrating the received signals, the S / N of the received signals is improved. As a result of the improvement of the S / N of the received signals, the azimuth calculation error is improved.

[0021] When receiving the running sound of an underwater vehicle with improved S / N from a specific direction, the azimuth calculation error becomes smaller.

[0022] Therefore, underwater sound wave signals with small direction calculation errors are likely to be navigation sounds originating from an underwater vehicle.

[0023] In the passive sonar detection confidence determination device of this embodiment, in the signal processing of a deployable passive sonar, underwater sound waves are automatically determined to have a high probability (detection confidence) of being navigation sounds originating from an underwater vehicle if the difference between the latest arrival direction calculation result and the average value of the direction calculation results over a certain period of time is small.

[0024] Figure 1A is a schematic diagram showing an example of a passive sonar system according to an embodiment. In Figure 1A, the underwater vehicle 2 is an object navigating underwater that is detected by the passive sonar detection confidence determination device 100. The drop-type passive sonar 4 is dropped onto the sea surface 1 from an aircraft 3.

[0025] When the drop-type passive sonar 4 is dropped onto the sea surface 1, it separates into a surface section 4A and an underwater section 4B equipped with a receiver.

[0026] The underwater sound wave signal (electrical signal) received by the underwater unit 4B of the droppable passive sonar 4 (also called the "droppable passive sonar underwater unit") is transmitted to the surface unit 4A of the droppable passive sonar 4 (also called the "droppable passive sonar surface unit") and wirelessly transmitted to the aircraft 3. The aircraft 3 receives the signal (radio wave) wirelessly transmitted from the surface unit 4A of the droppable passive sonar 4, detects the sound emitted by the underwater vehicle 2, and detects the underwater vehicle 2.

[0027] Aircraft 3 is equipped with, as an onboard processing unit, at least a radio communication device (not shown) that receives and demodulates signals (radio waves) transmitted wirelessly from the surface unit 4A of the droppable passive sonar 4, and a passive sonar detection confidence determination device 100.

[0028] The surface unit 4A of the drop-type passive sonar 4 receives the electrical signal of the underwater sound wave received by the underwater unit 4B, for example via a wire, converts it into an RF (Radio Frequency) signal, and transmits it wirelessly to the aircraft 3 via an antenna (not shown).

[0029] The underwater section 4B of the drop-type passive sonar is equipped with an OMNI directional receiver 7, an NS directional receiver 8, and an EW directional receiver 9, whose respective directivity is schematically shown in Figure 1B. Receivers 7, 8, and 9 convert the received underwater sound waves into electrical signals and transmit them to the surface section 4A via a wired connection, for example, through a signal transmission line (not shown) arranged on the suspension cable 5. Although not particularly limited, receivers 7, 8, and 9 may be configured to convert the received underwater sound waves into electrical signals and transmit these electrical signals in parallel to the surface section 4A.

[0030] In the aquatic section 4A, the received signals from receivers 7, 8, and 9, which are transmitted in parallel from the underwater section 4B, are modulated (for example, frequency modulation (FM)) and transmitted wirelessly via the antenna.

[0031] In Figure 1A, the navigation sound 6 is the underwater sound wave of mechanical operating sounds such as engine noise, motor rotation noise, cooling water pump operation noise, and screw propeller rotation noise emitted by the underwater vehicle 2.

[0032] Figure 1B illustrates the directivity of each receiver in the underwater section 4B of the drop-type passive sonar 4 shown in Figure 1A. In Figure 1B, the OMNI directional receiver 7 is equipped with an electrostrictive transducer that has uniform directivity in all directions, i.e., omnidirectional, and converts the received underwater sound waves into electrical signals.

[0033] The NS directional receiver 8 is equipped with an electrostrictive transducer having an eight-shaped directivity (NS directivity) in the north-south direction, and converts underwater sound waves into electrical signals.

[0034] The EW directional receiver 9 is an electrostrictive transducer with an eight-shaped directivity (EW directivity) in the east-west direction, and converts underwater sound waves into electrical signals.

[0035] Figure 2 shows the correlation between the S / N improvement effect of additive integration in a received signal and the direction calculation error. When the reproducibility of the input signal is high, the S / N is improved by performing n measurements of the waveform under the same conditions and performing additive integration considering the starting point and phase. That is, the amplitude of the signal becomes n times larger with the additive integration of n signal components, but the amplitude of the noise becomes √n times larger with the additive integration of n noise components, and the S / N is improved by n / √n = √n times. Note that when performing multiple integrals with the same integration time and accumulating the integral values ​​of each integral, the integration time of the additive integration corresponds to the sum of the integration times of each of the multiple integrals.

[0036] In Figure 2, 11 represents the signal-to-noise ratio (S / N) of the engine noise (6 in Figure 1A) in dB. An example of S / N improvement is shown when the summation integral of mechanical engine noise (S) and random underwater noise (N) is performed with a 1-second period, as shown on the horizontal axis for integration time (seconds).

[0037] TIFF0007859731000001.tif16150 ...(1)

[0038] Expressing equation (1) in decibels (dB), TIFF0007859731000002.tif19150...(2)

[0039] Equation (1) above corresponds to the fact that the noise width of random noise is inversely proportional to the square root of the number of integrations (integration time). Furthermore, from equation (2) above, if the integration time is n times the unit integration time, then the S / N ratio for one integration (unit integration time) is: TIFF0007859731000003.tif15153 ...(3) The signal-to-noise ratio (S / N) improves as follows: As shown in Figure 2, assuming a unit integration time of 1 second, the S / N ratio improves by 10 dB, 20 dB, and 25 dB when the integration time is set to, for example, 10 seconds, 100 seconds, and 320 seconds. Thus, the S / N ratio increases as the number of integrations increases (the integration time increases).

[0040] In Figure 2, 12 represents the direction calculation error (deg) of the approaching direction of the navigation sound 6 received by the underwater section 4B of the drop-type passive sonar 4. The direction calculation error (deg) is given by the following equation (4).

[0041] Direction calculation error (deg)=90deg - arctan(S / N)(deg) ···(4)

[0042] Here, y(deg) is the principal value of the arctangent function y=arctan(S / N): -π / 2(90deg). <y<π / 2(90deg)とされる(arctanはtan -1 (Also written as ). However, since S / N > 0, 0 <y<π / 2(90deg)である。

[0043] From equation (4) and Figure 2, it can be seen that the direction calculation error (deg) tends to decrease as the signal-to-noise ratio (S / N) improves.

[0044] Figure 3A illustrates an example of the configuration of a passive sonar detection confidence determination system. In this configuration example, a radio communication device 23 installed on the surface section 4A of the drop-type passive sonar 4 receives electrical signals of underwater sound waves received by the OMNI directional receiver 7, NS directional receiver 8, and EW directional receiver 9 in the underwater section 4B and transmits them wirelessly to the radio communication device 24 on the aircraft 3. The radio communication device 23 may FM modulate the received signals (analog signals) from receivers 7, 8, and 9 and transmit them via an antenna as radio signals in a predetermined VHF (Very High Frequency) / UHF (Ultra High Frequency) band. In this case, the radio communication device 23 may also frequency-division multiplex (FDM) the FM-modulated signals from receivers 7, 8, and 9 for wireless transmission.

[0045] The radio communication device 24 of aircraft 3 receives and demodulates the signal wirelessly transmitted from radio communication device 23, and outputs the OMNI, NS, and EW components of the analog signal in parallel. In the passive sonar detection confidence determination device 100, the low-pass filters (LPFs) 12-1 to 12-3 allow frequency components of the OMNI, NS, and EW components of the analog signal output from radio communication device 24 to pass through, for example, frequency components below half the sampling frequency of the A / D conversion (Nyquist frequency), and block frequency components above half the sampling frequency.

[0046] The A / D converters 13-1 to 13-3 convert the electrical signals output by the low-pass filters (LPFs) 12-1 to 12-3 into digital waveform data. The clock signals supplied to the A / D converters 13-1 to 13-3 are either identical clock signals or clock signals with synchronized edges.

[0047] The OMNI, NS, and EW digital signals output from the A / D converters 13-1 to 13-3 are supplied to the FFT (Fast Fourier Transform) processing units 14-1 to 14-3.

[0048] The FFT processing units 14-1 to 14-3 convert the time-domain digital waveform data (time-series data) of the OMNI component, NS component, and EW component into frequency spectra, respectively. The frequency components have amplitude and phase components. The FFT processing units 14-1 to 14-3 may also use DFT (Discrete Fourier Transform).

[0049] The integration processing units 15-1 to 15-3 perform integration over a predetermined period of time on the level data (amplitude data) for each frequency component of the waveform data of the OMNI, NS, and EW components, which are the calculation results of the FFT processing units 14-1 to 14-3. As explained with reference to Figure 2, the signal-to-noise ratio (S / N) is improved for each frequency component through the effect of additive integration.

[0050] The noise averaging processing unit 16 calculates the ratio of the level value of each frequency component to the average value for the level data of each frequency component of the digital waveform data of the OMNI component, and calculates the S / N ratio of the average value (noise equivalent level value) and the level data of each frequency component (signal equivalent level value). The noise averaging processing unit 16 detects frequency components whose calculated S / N ratio exceeds a predetermined value as candidates for the navigation sound 6 emitted by the underwater vehicle 2. The noise averaging processing unit 16 outputs the frequency components of the detected candidate navigation sound 6 to the display control unit 21.

[0051] The direction calculation processing unit 17 calculates the direction angle using the arctangent function for the level data of each frequency component of the waveform data from the NS directional receiver 8 and the EW directional receiver 9.

[0052] The direction error processing unit 18 stores the direction data for each frequency component calculated by the direction calculation processing unit 17 in memory (storage unit) 20 for a predetermined period of time (corresponding to the number of times the FFT process is executed), and calculates the direction error as the average value of the difference between the latest direction calculation result for each frequency component and the direction calculation results for the predetermined period of time.

[0053] The detection confidence determination processing unit 19 calculates a determination value for the degree of confidence (detection confidence) of detecting the navigation sound 6 of the underwater vehicle 2 from the absolute value of the azimuth error for each frequency component. The detection confidence determination processing unit 19 outputs the determination result of the detection confidence for each frequency component to the display control unit 21.

[0054] The display control unit 21 receives the candidate frequency components of the navigation sound 6 detected by the noise averaging processing unit 16 and the detection confidence determination results for each frequency component of the navigation sound 6 calculated by the detection confidence determination processing unit 19, and outputs the received information to the display device 22 in a predetermined display format. At that time, the display control unit 21 may display the candidate frequency components of the navigation sound 6 of the underwater vehicle 2 on the screen of the display device 22, and display the detection confidence determination value together with the frequency components on the screen.

[0055] Figure 3B illustrates a modified version of Figure 3A. In the example of Figure 3B, the low-pass filters (LPFs) 12-1 to 12-3 and A / D converters 13-1 to 13-3 of the passive sonar detection confidence determination device 100 of the aircraft 3 in Figure 3A are placed on the surface section 4A of the drop-type passive sonar 4. For the received signals (OMNI component) from the OMNI directional receiver 7, the received signals (NS component) from the NS directional receiver 8, and the received signals (EW component) from the EW directional receiver 9 in the underwater section 4B, the low-pass filters (LPFs) 12-1 to 12-3 pass the low-frequency components of each signal, and the OMNI, NS, and EW components, converted into digital signals by the A / D converters 13-1 to 13-3, are input in parallel to the radio communication device 23' on the surface section 4A. The wireless communication device 23' modulates the OMNI, NS, and EW components of the input digital signal and transmits it wirelessly via an antenna (not shown). In this case, the wireless communication device 23' may also perform time-division multiplexing (TDM) on the digitized OMNI, NS, and EW components, and then modulate the time-division multiplexed digital signal (for example, GMSK (Gaussian Filtered Minimum Shift Keying) modulation) for wireless transmission. The digital modulation is not limited to GMSK modulation (band-limiting the digital signal through a Gaussian filter and then performing FM modulation), but may also be performed using amplitude shift keying (ASK), frequency shift keying (FSK), quadrature amplitude modulation (QAM), etc.

[0056] In the aircraft 3's radio communication device 24', the signal transmitted wirelessly from the radio communication device 23' is received and demodulated, and the OMNI, NS, and EW components, which are time-division multiplexed from the baseband signal (digital signal), are separated (demultiplexed) and supplied in parallel to the FFT processing units 14-1 to 14-3. The passive sonar detection confidence determination device 100' has the same configuration as the passive sonar detection confidence determination device 100 in Figure 3A, but without the low-pass filters (LPFs) 12-1 to 12-3 and the A / D converters 13-1 to 13-3. The processing of each processing unit is the same as the corresponding processing unit in the passive sonar detection confidence determination device 100 in Figure 3A, so a description is omitted.

[0057] In Figure 3B, the low-pass filters (LPFs) 12-1 to 12-3 and A / D converters 13-1 to 13-3 are located on the surface section 4A of the deployable passive sonar 4. However, as a further modification, the low-pass filters (LPFs) 12-1 to 12-3 and A / D converters 13-1 to 13-3 may be located on the underwater section 4B of the deployable passive sonar 4. In this case, the OMNI, NS, and EW components, which are the received signals from the OMNI directional receiver 7, NS directional receiver 8, and EW directional receiver 9 in the underwater section 4B, are digitally transmitted to the wireless communication device 23' on the surface section 4A.

[0058] Next, the operation of this embodiment will be described with reference to Figure 3A (the operation of the configuration shown in Figure 3B is similar).

[0059] The underwater sound waves, including the navigation sound 6, emitted by the underwater vehicle 2 are received by the OMNI directional receiver 7, NS directional receiver 8, and EW directional receiver 9 in the underwater section 4B of the deployable passive sonar 4, converted into electrical signals, and transmitted to the surface section 4A of the deployable passive sonar 4. The radio communication device 23 in the surface section 4A of the deployable passive sonar 4 then wirelessly transmits the received signals (analog electrical signals) from the OMNI directional receiver 7, NS directional receiver 8, and EW directional receiver 9.

[0060] The electrical signal of the underwater sound wave received by the OMNI directional receiver 7 is processed by the LPF 12-1 to remove high-frequency components and then converted into digital data by the A / D converter 13-1.

[0061] The FFT processing unit 14-1 converts the digital data into level data for each frequency component, and the integration processing unit 15-1 improves the S / N ratio through additive integration. The noise averaging processing unit 16 converts the level data for each frequency into S / N values ​​for each frequency. The noise averaging processing unit 16 detects frequency components whose S / N ratio exceeds a certain value as candidates for the navigation sound 6 emitted by the underwater vehicle 2.

[0062] The electrical signals of underwater sound waves received by the NS directional receiver 8 and the EW directional receiver 9 are filtered to remove high-frequency components using low-pass filters (LPFs) 12-2 and 12-3. The analog signals are converted into digital data using A / D converters 13-2 and 13-3.

[0063] The FFT processing units 14-2 and 14-3 convert the time-domain digital waveform data of the NS component and EW component into level data (amplitude data) for each frequency component.

[0064] The integration processing units 15-1 to 15-3 improve the signal-to-noise ratio (S / N) of the level data (amplitude data) for each frequency component of the frequency spectrum output from the FFT processing units 14-1 to 14-3 by the additive integration effect explained with reference to Figure 2.

[0065] The direction calculation processing unit 17 receives the summation and integration results of the level data (amplitude data) for each frequency component of the NS component and EW component output from the integration processing units 15-2 and 15-3, respectively, and converts the summation and integration of the level data (amplitude data) for each frequency into sound wave arrival direction values ​​for each frequency. Note that any known method can be used for the direction calculation process that calculates the sound wave arrival direction based on the level difference of the received signals from the NS directional receiver 8 and the EW directional receiver 9.

[0066] The direction error processing unit 18 stores the sound wave arrival direction values ​​for each frequency component obtained by the direction calculation processing unit 17 in a table format (also called a "memory table") in the memory 20, as shown in Figure 4.

[0067] In the table in Figure 4, the horizontal axis represents the frequency component number (frequency bin number), and the vertical axis represents time (number of past FFT operations). Figure 4 shows an example of a table stored in memory 20 with 16 past FFT operations and 128 FFT frequency bins.

[0068] The results of the direction calculation process performed by the direction calculation processing unit 17, based on the frequency-specific level data of the frequency spectrum most recently calculated by the FFT processing units 14-2 and 14-3, are stored in the memory table's T(0) row in the order of frequencies F(1) to F(128). The results of the direction calculation process performed by the FFT processing units 14-2 and 14-3 15 periods prior are stored in the memory table's T(15) row in the order of frequencies F(1) to F(128). Note that F(1) is the DC (Direct Current) component, and F(128) is the amplitude spectrum (level data) of the Nyquist frequency.

[0069] The direction error processing unit 18 calculates the average value D(X) of the difference between the result of the latest direction calculation process and the direction calculation results for each frequency component over the past 15 times, for each frequency component F(1) to F(128) on the horizontal axis. D(X)=Σ((F(X),T0)-(F(X),T(K)))÷15 TIFF0007859731000004.tif14150...(5)

[0070] In equation (5), X is the frequency bin number for each frequency component from 1 to 128. (F(X),T(0)) is F(X) at time T(0) in the table in Figure 4. (F(X), T(K))(K=1~15) represents F(X) at time T(K)(K=1~15) in the table in Figure 4.

[0071] The detection confidence determination processing unit 19 determines the detection confidence level in nine stages, A to I, as shown in Figure 5, based on the absolute value of the average value D(X) of the azimuth error for each frequency component obtained by the azimuth error processing unit 18.

[0072] Detection confidence level A: The absolute value of the average azimuthal error D(X) for each frequency component is less than 4 degrees (Y branch in step S1), and the signal-to-noise ratio is 23 dB or higher.

[0073] Detection confidence B: The absolute value of the average azimuthal error D(X) for each frequency component is less than 8 degrees (Y branch in step S2), and the signal-to-noise ratio is 17 dB or higher.

[0074] Detection confidence C: The absolute value of the average azimuthal error D(X) for each frequency component is less than 12 degrees (Y branch in step S3), and the signal-to-noise ratio is 13 dB or higher.

[0075] Detection confidence D: The absolute value of the average azimuthal error D(X) for each frequency component is less than 16 degrees (Y branch in step S4), and the signal-to-noise ratio is 11 dB or higher.

[0076] Detection confidence E: The absolute value of the average azimuthal error D(X) for each frequency component is less than 20 degrees (Y branch in step S5), and the signal-to-noise ratio is 9 dB or higher.

[0077] Detection confidence F: The absolute value of the average azimuthal error D(X) for each frequency component is less than 24 degrees (Y branch in step S6), and the signal-to-noise ratio is 7 dB or higher.

[0078] Detection confidence G: The absolute value of the average azimuthal error D(X) for each frequency component is less than 28 degrees (Y branch in step S7), and the signal-to-noise ratio is 5 dB or higher.

[0079] Detection confidence H: The absolute value of the average azimuthal error D(X) for each frequency component is less than 32 degrees (Y branch in step S8), and the signal-to-noise ratio is 4 dB or higher.

[0080] Detection confidence I: The absolute value of the average azimuthal error D(X) for each frequency component is 32 degrees or greater (N branch in step S8), and the signal-to-noise ratio is less than 4 dB.

[0081] It should be noted that the detection confidence level is not limited to nine levels. For example, the detection confidence level for the N branch in step S7 may be set to H, resulting in eight levels.

[0082] If the detection confidence level is ranked into multiple stages as described above, the display control unit 21 may color-code (or assign a grayscale) each stage and mark the candidate frequency components of the underwater vehicle 2's navigation sound 6 displayed on the display device 22 screen with a color (or grayscale) corresponding to the detection confidence level of the frequency component.

[0083] Figure 6 illustrates the configuration when a passive sonar detection confidence determination device 100, an onboard processing unit equipped on an aircraft 3 that detects the sound 6 of an underwater vehicle 2 from underwater sound waves received by a drop-type passive sonar 4, is implemented in a computer device 200. Referring to Figure 6, the computer device 200 includes a processor 201, memory 202 such as semiconductor memory (or HDD (Hard Disk Drive)) such as RAM (Random Access Memory), ROM (Read Only Memory), or EEPROM (Electrically Erasable Programmable Read-Only Memory), a display device 203, and an interface 204 (bus interface) for connecting to a wireless receiver. The processor 201 may be a DSP (Digital Signal Processor). The display device 203 corresponds to the display device 22 in Figures 3A and 3B.

[0084] By executing the program stored in memory 202, the processor 201 performs the following processes: FFT processing units 14-1 to 14-3, integration processing units 15-1 to 15-3, noise averaging processing unit 16, direction calculation processing unit 17, direction error processing unit 18, and detection confidence determination processing unit 19. The processor 201 is instructed to perform the following: noise averaging processing, which calculates a signal-to-noise ratio based on amplitude data for each frequency component by obtaining a frequency spectrum from the received signal of the OMNI directional receiver 7 of the underwater section 4B of the passive sonar that receives sound waves underwater using FFT; direction calculation processing, which calculates the direction for each frequency component by obtaining a frequency spectrum from the received signals of the NS directional receiver 8 and EW directional receiver 9 of the underwater section 4B of the passive sonar using FFT; direction error processing, which stores the direction calculation results for each frequency component obtained by the direction calculation processing in the memory (storage unit) 20 for a predetermined number of times, and calculates the direction error as the average value of the difference between the latest direction calculation result for each frequency component obtained by the direction calculation processing and the direction calculation results for the predetermined number of times; detection confidence determination processing, which calculates a determination value of the detection confidence level for detecting the sound of an underwater vehicle based on the absolute value of the direction error for each frequency component; and display control, which displays the detection confidence level on the display device 203.

[0085] The above-described embodiment provides, for example, the following effects:

[0086] (a) With respect to underwater sound waves received by the drop-type passive sonar 4, the confidence level of detection can be quantitatively and automatically determined when sound waves arriving from a specific direction are detected as the sound of the underwater vehicle 2 6.

[0087] (b) Background noise such as the sound of waves on the sea surface coming from an unspecified number of directions, and noise such as artifact noise that occurs accidentally in an electrical circuit, can be distinguished from the sound of an underwater vehicle by automatically determining whether they are coming from a specific direction, even if the signal-to-noise ratio for each frequency component is large.

[0088] Furthermore, the disclosures in Patent Documents 1 and 2 mentioned above are incorporated herein by reference. Within the framework of the full disclosure of the present invention (including the claims), further modifications and adjustments to the embodiments or examples are possible based on the fundamental technical concept. Also, within the framework of the claims of the present invention, various combinations or selections of various disclosed elements (including each element of each claim, each element of each embodiment, each element of each drawing, etc.) are possible. In other words, the present invention naturally includes various modifications and alterations that a person skilled in the art could make in accordance with the full disclosure, including the claims, and the technical concept. [Explanation of Symbols]

[0089] 1 sea level 2 Underwater vehicle 3 aircraft 4. Drop-type passive sonar 4A Surface-mounted (Surface-mounted passive sonar) 4B Underwater Unit (Deployable Passive Sonar Underwater Unit) 5. Suspension Cable 6. Sound of sailing 7 OMNI Directional Receiver 8 NS directional receiver 9 EW directional receiver 10. Passive sonar detection confidence level determination device 11 S / N 12 Direction calculation error 12-1~12-3 Low-pass filter 13-1~13-3 A / D Converters 14-1~14-3 FFT Processing Unit 15-1~15-3 Integral Processing Section 16. Noise averaging processing unit 17 Direction Calculation Processing Unit 18. Directional Error Processing Unit 19 Detection confidence determination processing unit 20 Memory (storage unit) 21 Display Control Unit 22 Display device 23, 23' Wireless communication device 24, 24' Wireless communication equipment 100, 100' Passive Sonar Detection Confidence Determination Device 200 Computer devices 201 Processor 202 memory 203 Display device 204 Interface

Claims

1. A noise averaging processing unit calculates the signal-to-noise ratio based on amplitude data for each frequency component, obtained by determining the frequency spectrum of the signal received by the omnidirectional first receiver of a passive sonar that receives underwater sound waves, The passive sonar includes a second receiver with north-south directivity and a third receiver with east-west directivity, respectively, and a direction calculation processing unit that calculates the direction for each frequency component by obtaining the frequency spectrum of the signals received by these receivers. A direction error processing unit stores the direction calculation results for each frequency component by the direction calculation processing unit in a predetermined storage unit for a set number of times, and calculates the average difference between the latest direction calculation result for each frequency component by the direction calculation processing unit and the predetermined number of direction calculation results for each frequency component as the direction error. A detection confidence determination processing unit calculates a determination value for the detection confidence of the underwater vehicle's sound based on the absolute value of the directional error for each frequency component, A passive sonar detection confidence determination device equipped with [a specific feature].

2. The passive sonar detection confidence determination device according to claim 1, wherein the detection confidence determination processing unit determines which of a plurality of predetermined adjacent divisions the absolute value of the azimuth error for each frequency component falls into, and outputs a detection confidence level that is set in advance corresponding to the division.

3. The passive sonar detection confidence determination device according to claim 1, wherein the noise averaging processing unit considers frequency components in which the signal-to-noise ratio exceeds a predetermined value as candidates for the navigation sound emitted by the underwater vehicle.

4. A passive sonar detection confidence determination device according to claim 3, comprising a display control unit that receives the frequency components of candidate navigation sounds of the underwater vehicle detected by the noise averaging unit and the detection confidence level of the underwater vehicle's navigation sounds for each frequency component determined by the detection confidence determination unit, and controls the display of the frequency components of candidate navigation sounds of the underwater vehicle and the detection confidence level corresponding to the frequency components on a display device.

5. A passive sonar that receives underwater sound waves, A passive sonar detection confidence level determination device, Equipped with, The aforementioned passive sonar is, The part floating on the surface of the sea, The underwater section is suspended by a cable from the above-water section, Equipped with, The underwater section comprises an omnidirectional first receiver, a north-south directional second receiver, and an east-west directional third receiver. The received signals from the first to third receivers are transmitted to the water surface, The aquatic unit wirelessly transmits the received signals received by the first to third receivers to the passive sonar detection confidence determination device. The passive sonar detection confidence determination device is, A noise averaging processing unit that obtains the frequency spectrum of the received signal of the first receiver contained in the radio signal transmitted from the passive sonar and calculates the signal-to-noise ratio based on the amplitude data for each frequency component, An orientation calculation processing unit that obtains the frequency spectra of the received signals from the second receiver and the third receiver included in the aforementioned wireless signal and calculates the orientation for each frequency component, A direction error processing unit stores the direction calculation results for each frequency component by the direction calculation processing unit in a predetermined storage unit for a set number of times, and calculates the average difference between the latest direction calculation result for each frequency component by the direction calculation processing unit and the predetermined number of direction calculation results for each frequency component as the direction error. A detection confidence determination processing unit calculates a detection confidence determination value for detecting the sound of an underwater vehicle based on the absolute value of the directional error for each frequency component, A passive sonar system equipped with [feature / feature].

6. The passive sonar system according to claim 5, wherein the detection confidence determination processing unit determines which of a plurality of predetermined adjacent divisions the absolute value of the azimuth error for each frequency component falls into, and outputs a detection confidence level that is set in advance for the division.

7. The noise averaging processing unit detects frequency components in which the signal-to-noise ratio exceeds a predetermined value as candidates for the sound emitted by the underwater vehicle. The passive sonar system according to claim 5, comprising a display control unit that receives the frequency components of candidate sounds of the underwater vehicle detected by the noise averaging unit and the detection confidence level of the underwater vehicle's sounds for each frequency component determined by the detection confidence level determination unit, and controls the display of the frequency components of candidate sounds of the underwater vehicle and the detection confidence level corresponding to the frequency components on a display device.

8. The passive sonar detection confidence determination device is mounted on an aircraft. The passive sonar is dropped onto the sea surface from the aircraft, according to claim 5.

9. The first step involves obtaining the frequency spectrum of the signal received by the omnidirectional first receiver of a passive sonar that receives underwater sound waves, and calculating the signal-to-noise ratio based on the amplitude data for each frequency component. The second step involves obtaining the frequency spectrum of the signals received by the second receiver, which is directional in the north-south direction, and the third receiver, which is directional in the east-west direction, of the passive sonar, and calculating the direction for each frequency component. A third step involves storing the direction calculation results for each frequency component obtained in the second step in a predetermined number of memory units, and calculating the average difference between the latest direction calculation result for each frequency component obtained in the second step and the predetermined number of direction calculation results for each frequency component as the direction error. A fourth step is to calculate a determination value for the detection confidence level of the sound of the underwater vehicle being detected based on the absolute value of the directional error for each frequency component, A passive sonar detection confidence level determination method including [the specified method].

10. The passive sonar detection confidence determination method according to claim 9, the fourth step being to determine which of a plurality of predetermined adjacent divisions the absolute value of the azimuth error for each frequency component falls into, and to output a detection confidence level that is set in advance for the division.

11. In the first step described above, frequency components in which the signal-to-noise ratio exceeds a predetermined value are detected as candidates for the sound emitted by the underwater vehicle. The passive sonar detection confidence determination method according to claim 9, further comprising the step of receiving the frequency components of candidate navigation sounds of the underwater vehicle detected in the first step and the detection confidence level of the underwater vehicle's navigation sounds for each frequency component determined in the fourth step, and performing control to display the frequency components of candidate navigation sounds of the underwater vehicle and the detection confidence level corresponding to the frequency components on a display device.

12. A first process involves obtaining the frequency spectrum of a signal received by an omnidirectional first receiver of a passive sonar that receives underwater sound waves, and calculating the signal-to-noise ratio based on the amplitude data for each frequency component. A second process involves obtaining the frequency spectrum of the signals received by the second receiver of the passive sonar, which is directional in the north-south direction, and the third receiver, which is directional in the east-west direction, respectively, and calculating the direction for each frequency component. The third process involves storing the direction calculation results for each frequency component obtained by the second process in a predetermined number of memory units, and calculating the average difference between the latest direction calculation result for each frequency component obtained by the second process and the predetermined number of direction calculation results as the direction error. A fourth process involves calculating a determination value for the detection confidence level of the underwater vehicle's navigation sound based on the absolute value of the directional error for each frequency component, A program that causes a computer to execute something.

13. The program according to claim 12, wherein the fourth process determines which of a plurality of non-overlapping categories the absolute value of the azimuthal error for each frequency component belongs to, and outputs a detection confidence level set corresponding to the category.

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