JP7590002B2 - Sound wave direction detection device, underwater vehicle device, sound wave direction detection method and program - Google Patents

Description

The present invention relates to an underwater vehicle device, a sound wave direction detection device, a sound wave direction detection method, and a program.

Advances in computer technology are leading to a trend towards smaller underwater vehicles. Reducing the size of an underwater vehicle makes it possible to reduce manufacturing costs. Another benefit is that the possibility of such a small underwater vehicle being detected by sonar, which is an acoustic sensor, radar, which is a radio wave sensor, optical sensors, etc. is reduced.

In order to miniaturize the underwater vehicle, the passive sonar mounted on it must also be miniaturized. For this reason, it is difficult to obtain directionality by arranging acoustic sensors (electrostrictive transducers) that convert acoustic signals into electrical signals in an array and eliminate the effects of the noise generated by the propeller at the rear of the underwater vehicle.

It is possible to measure and estimate the frequency level of the propeller sound corresponding to the speed and depth of the underwater vehicle during the manufacturing stage. However, a more accurate method of distinguishing between underwater noise, which varies greatly due to waves and other factors, and the propeller sound is to directly measure the frequency level of the propeller sound using passive sonar.

Patent Document 1 discloses an underwater vehicle detection device that converts an analog received signal from an acoustic sensor into a digital signal, converts it into a signal (amplitude spectrum) for each frequency component using a Fast Fourier Transform (FFT), generates a cardioid type directivity for each predetermined frequency component based on the signal for each frequency component in a directivity forming section, calculates a directivity ratio, which is the ratio of the signal level in the maximum sensitivity direction to the signal level in the minimum sensitivity direction, for each predetermined frequency component based on the cardioid type directivity, and synthesizes the directivity ratios calculated for each predetermined frequency component to generate a directivity ratio distribution that represents the distribution of the directivity ratios for each frequency component.

JP 2013-160564 A

As mentioned above, for miniaturized underwater vehicles, the passive sonar mounted on them must be miniaturized, so it is difficult to eliminate the effect of the propulsion unit at the rear of the underwater vehicle on the sound of the ship's movement by arranging the acoustic sensors in an array to obtain directionality.

The object of the present invention is therefore to provide an apparatus, method, and program that can eliminate or suppress the effects of propeller noise from the rear propeller of an underwater vehicle, and prevent the propeller noise from deteriorating the accuracy of detecting the direction of arrival of sound waves emitted by the vessel.

According to the present invention, there is provided a sound wave arrival direction detection device for an underwater vehicle having a passive sonar and a propeller at the rear, which sets the insensitive direction of the cardioid directivity of the passive sonar to the rear direction of the underwater vehicle, receives a received signal from the passive sonar, calculates the reception level of the propeller sound based on the reception level that excludes the propeller sound from the propeller, and detects the arrival direction of the sound waves with the influence of the propeller sound corrected.

According to the present invention, there is provided a method for detecting the direction of arrival of a sound wave in an underwater vehicle having a passive sonar and a thruster at its rear, the method including: providing the passive sonar with a cardioid directivity with an insensitive direction toward the rear of the underwater vehicle;
receiving a received wave signal from the passive sonar, and calculating a received wave level of the propeller sound based on a received wave level excluding the propeller sound from the propeller;
The present invention provides a method for detecting the direction of arrival of sound waves, the method comprising the steps of: detecting the direction of arrival of sound waves after correcting the influence of the propeller sound;

According to the present invention, a computer mounted on an underwater vehicle having a passive sonar and a thruster at its rear performs a process of giving the passive sonar a cardioid directivity with an insensitive direction toward the rear of the underwater vehicle;
receiving a received wave signal by the passive sonar, calculating a received wave level of the propeller sound based on a received wave level excluding the propeller sound from the propeller, and detecting an incoming direction of the sound wave with the influence of the propeller sound corrected. Furthermore, according to the present invention, there is provided a computer-readable recording medium (e.g., a semiconductor storage such as a RAM (Random Access Memory), a ROM (Read Only Memory), or an EEPROM (Electrically Erasable and Programmable ROM)), a HDD (Hard Disk Drive), an SSD (Solid State Drive), a CD (Compact Disc), or a DVD (Digital Versatile Disc) storing the above program.

The present invention makes it possible to eliminate or suppress the effects of propeller noise from the rear propeller of an underwater vehicle, and to avoid deterioration in the accuracy of detecting the direction of arrival of sound waves emitted by a vessel, caused by the propeller noise.

FIG. 1 is a diagram illustrating an overview of an underwater vehicle according to an embodiment of the present invention. FIG. 1 is a diagram illustrating a passive sonar according to an embodiment of the present invention. FIG. 1 is a diagram illustrating an embodiment of the present invention. FIG. 1 is a diagram illustrating an embodiment of the present invention. FIG. 1 is a diagram illustrating a problem to be solved by the present invention. FIG. 2 is a diagram for explaining the directionality of an omnidirectional receiver of a passive sonar. FIG. 1 is a diagram showing the directivity (distribution of direction-sensitivity) of an omnidirectional receiver of a passive sonar. FIG. 2 is a diagram for explaining a schematic diagram of cardioid directivity. FIG. 1 is a diagram showing cardioid directivity (distribution of direction-sensitivity). 1A to 1C are diagrams for explaining the directivity of each receiver of a passive sonar, and FIG. 1D is a diagram showing the configuration of a direction correction device according to an embodiment of the present invention. 4 is a flowchart showing the operation of the direction correction device according to the embodiment of the present invention. FIG. 1 is a diagram illustrating an embodiment of the present invention. 13A and 13B are diagrams showing the level (frequency distribution) of a received signal from an omnidirectional receiver and the level (frequency distribution) of a received signal from a cardioid receiver. 9A and 9B are diagrams showing the level (frequency distribution) of a received signal of a non-directional receiver and the direction (frequency distribution) of the non-directional received signal in the positional relationship of FIG. 8. 13A and 13B are diagrams showing the level (frequency distribution) of a signal received by an omnidirectional receiver and the direction (frequency distribution) of the omnidirectional received signal. FIG. 1 is a diagram illustrating an embodiment of the present invention. FIG. 1 is a diagram illustrating an embodiment of the present invention. FIG. 1 is a diagram illustrating an embodiment of the present invention.

An embodiment of the present invention will be described. According to one aspect of the present invention, a sound wave arrival direction detection device (direction correction device) mounted on an underwater vehicle having a passive sonar and a thruster at the rear has a directivity of the passive sonar with a non-sensitive direction set toward the rear of the underwater vehicle, receives a received signal from the passive sonar, calculates the level of the thruster sound based on the received wave level that excludes the thruster sound from the thruster, and detects the arrival direction of the sound wave with the influence of the thruster sound corrected.

In one aspect of the sound wave arrival direction detection device of the present invention, underwater sound waves received by an omnidirectional receiver equipped in a passive sonar are converted from analog signals to digital signals, and the time domain signal series is converted to the frequency domain to calculate the received wave level for each frequency component in the detection frequency band.

In one aspect of the present invention, the sound wave arrival direction detection device converts the underwater sound waves received by the non-directional receiver and the front and rear directional receivers equipped in the passive sonar from analog signals to digital signals, converts the time domain signal series into the frequency domain, calculates the received wave level for each frequency component in the detection frequency band, and calculates the received wave level of cardioid directivity with the insensitive direction set to the rear of the underwater vehicle.

Furthermore, in one embodiment of the sound wave arrival direction detection device of the present invention, the reception level of the propeller sound (such as the operating sound from the propeller at the rear of the underwater vehicle) for each frequency component is calculated from the difference between the omnidirectional reception level for each frequency component and the CARDIOID directional reception level.

In one embodiment of the sound wave arrival direction detection device of the present invention, the sound wave arrival direction is calculated by excluding the received wave level component of the propeller sound from the calculation result of the arrival direction (before correction) of the underwater sound waves received by the front-rear directional receiver and the left-right directional receiver.

<Embodiment>
Figures 1A and 1B are diagrams for explaining one embodiment. Figure 1A is a diagram showing an underwater vehicle equipped with a passive sonar. Figure 1B is a diagram for explaining the configuration of the passive sonar 2 in Figure 1A. Referring to Figure 1A, the underwater vehicle 1 is equipped with a passive sonar 2. When the underwater vehicle 1 navigates near the sea surface, the passive sonar 2 receives sound waves from other ships 5 to detect the direction of the other ships 5 and prevent collisions or to avoid being detected by the other ships 5.

As shown in Figure 1A, the underwater vehicle 1 is equipped with a propeller 3 at its rear end (rear). The propeller 3 is mounted on the rear of the underwater vehicle 1 and obtains propulsion by rotating a screw propeller (not shown). The rotation of the screw propeller generates cavitation noise (noise generated when bubbles are generated in the low-pressure area on the back of the blade as the propeller rotates faster and these bubbles collapse). The propeller sound 4 is sound waves generated by the rotation of the screw propeller inside the propeller 3.

In the passive sonar 2, the propeller sound 4 is a sound wave arriving from the rear. In other words, the propeller sound 4 is a noise source for the passive sonar 2. Although not particularly limited, in this embodiment, the propeller 3 is assumed to be a pump jet propulsion type propeller with a screw propeller covered by a shroud (not shown).

The ship 5 is the target whose sailing sound is detected by the passive sonar 2.

As shown in FIG. 1B, the passive sonar 2 is equipped with an omnidirectional receiver 12, a front-rear directional receiver 13, and a left-right directional receiver 14.

According to this embodiment, the sonic wave arrival direction detection device (direction correction device) implemented in the underwater vehicle 1 is configured to use the CARDIOID directivity of the passive sonar 2, which blocks sound waves arriving from a specific direction, and to measure the level of the sound (propeller sound 4) emitted by the propeller 3, thereby correcting the detection result of the arrival direction of the navigation sound arriving from the ship 5 to eliminate the influence of the propeller sound 4.

Figures 2A and 2B are diagrams explaining the detection of the direction of arrival of the navigation sound of a ship by the underwater vehicle 1. Figure 2A is a schematic plan view (XY plan view) of the underwater vehicle 1 navigating near the sea surface as seen from the Z-axis direction (above), and Figure 2B is a schematic side view showing the underwater vehicle 1 navigating near the sea surface.

As shown diagrammatically in FIG. 2A, the passive sonar 2 monitors the entire circumference in the horizontal direction (XY plane) to detect sound waves (sailing sounds) emitted by other ships 5, and determines the direction (referred to as "ship direction") 6 of the other ship 5 from the direction from which the sound waves arrive. This prevents collisions with other ships 5. The ship direction is, for example, the direction of the ship 5 as seen from the passive sonar 2, based on the bow direction of the underwater vehicle 1.

In a small underwater vehicle 1, there is no space for a passive sonar 2 to be equipped with a receiving array in which multiple receivers are arranged horizontally. For this reason, as shown in FIG. 1B, there are cases where only three receivers are used: an omnidirectional receiver 12, a front-rear directional receiver 13, and a left-right directional receiver 14. If the receiving array is not arranged horizontally, it is not possible to eliminate the influence of the propeller sound, which is the rotational sound of the propeller 3 (screw propeller) located at the rear of the underwater vehicle 1.

Figure 3 is a diagram explaining the propeller sound that affects the detection of the direction of arrival of the navigation sound of the ship 5 by the underwater vehicle 1. The ship navigation sound reception signal level (S1) 7 represents the level at which the passive sonar 2 detects the sound waves emitted when the ship 5 rotates its screw propeller to navigate. The propeller sound reception signal level (S2) 8 represents the level at which the passive sonar 2 detects the sound waves emitted by the propeller 3 when the underwater vehicle 1 navigates.

As shown in Figure 3, the direction of the resultant vector v of vector v1 (magnitude |v1| = S1: ship navigation sound reception signal level 7) in the direction from which the navigation sound of another ship 5 is coming (ship direction 6) and vector v2 (magnitude |v2| = S2: propeller sound reception signal level 8) in the direction from which the propeller sound 4 is coming is the direction detected by the passive sonar 2 for the other ship 5.

As a result, there is a problem in that the direction from which the navigation sound of another vessel 5 detected by the passive sonar 2 equipped on the underwater vehicle 1 comes (passive sonar detection direction 9) is closer to the rear of the underwater vehicle 1 than it actually is.

Figures 4A and 4B are diagrams showing the directionality of the omnidirectional receiver 12 of the passive sonar 2 equipped on the underwater vehicle 1. Figure 4A shows the directionality 10 of the omnidirectional receiver 12 in an XY plane view of the unmanned underwater vehicle 1 sailing near the sea surface, viewed from the Z-axis direction. Figure 4B is a diagram showing the direction (horizontal axis) and sensitivity (received wave level) (vertical axis) of the omnidirectional receiver 12. As shown in Figures 4A and 4B, the omnidirectional receiver 12 has a uniform directivity 10 over 360 degrees.

Figures 5A and 5B are diagrams showing CARDIOID directivity synthesized from the received signal of the passive sonar 2 equipped on the underwater vehicle 1. Figure 5A shows CARDIOID directivity 11 in an XY plane view of the underwater vehicle 1 navigating near the sea surface, viewed from the Z-axis direction. Figure 5B is a diagram showing the distribution of the direction (horizontal axis) and sensitivity (received wave level) (vertical axis) of CARDIOID directivity 11. In Figure 5B, the sensitivity (received wave level) has a characteristic of 1+cos(θ) for the direction θ, with maximum sensitivity at θ=0 and null (no sensitivity) at θ=π.

The omnidirectional receiver 12 equipped on the passive sonar 2 does not have horizontal directionality and is therefore affected by the propeller sound 4, but the CARDIOID directivity 11 blocks sound waves arriving from the rear and is therefore not affected by the propeller sound 4.

Figure 6 is a diagram for explaining the sound wave arrival direction detection device (also called "direction correction device") 24 of this embodiment. Figures 6 (A), (B), and (C) are diagrams showing the directivity patterns in the XY plane of the omnidirectional receiver 12, the front-rear directional receiver 13, and the left-right directional receiver 14. The omnidirectional pattern in Figure 6 (A) has uniform sensitivity over 360 degrees, which is shown as a circle (radius 1) in Figure 6 (A). In Figures 6 (B) and (C), the front-rear directional receiver 13 has directivity expressed as cosθ with respect to the direction θ, as shown in Figure 6 (B). The left-right directional receiver 14 has directivity expressed as sinθ, as shown in Figure 6 (C).

By adding the receiving level of the receiver of the omnidirectional pattern in Figure 6 (A) and the receiving level of the receiver of the directional pattern in Figure 6 (B), a directivity expressed as 1 + cosθ (cardioid type directivity) is obtained. For example, a cardioid type directional pattern has maximum sensitivity for θ = 0 and is insensitive (null) for θ = π.

Figure 6 (D) is a diagram showing the configuration of the direction correction device 24 of the passive sonar 2 equipped on the underwater vehicle 1 of the embodiment. In Figure 6 (D), the preamplifiers 15-1, 15-2, and 15-3 respectively amplify weak electrical signals (voltages) from the omnidirectional receiver 12, the front-rear directional receiver 13, and the left-right directional receiver 14, which convert underwater sound pressure into electrical signals (voltages) and output them.

Band pass filters (BPFs) 16-1, 16-2, and 16-3 receive the electrical signals from preamplifiers 15-1, 15-2, and 15-3, respectively, attenuate frequency components that are not subject to the subsequent FFT (Fast Fourier Transform) processing, and extract the frequency band that is subject to FFT processing.

Analog to Digital Converters (ADCs) 17-1, 17-2, and 17-3 convert the analog signals (voltages) output from the bandpass filters 16-1, 16-2, and 16-3, respectively, into digital signals (digital data).

The FFTs 18-1, 18-2, and 18-3 convert the digital data (digital signal waveform) x(t) output from the AD converters 17-1, 17-2, and 17-3 into the frequency domain. In this case, a short-time FFT may be used, which divides x(t) into short time intervals and analyzes the frequency of each time interval. In this case, a window function w(t) is sequentially shifted by mS and multiplied by the digital signal waveform x(t), to extract a portion of the digital signal waveform (discrete-time signal) x(t) for the time interval mS ≦t ≦ (mS+N-1), and a finite-length signal (time frame) with the time origin moved to the beginning of the extracted time interval is generated.
x _m (t)=[x ₀ ,x ₁ ,…,x _N-1 ] (m=1,2,…) ・・・(1)
Here, m is the time frame index, S is the frame shift amount, and N is the frame length (for example, N is a power of 2). A short term Fourier transform (short term FFT) is performed by applying FFT to this finite length signal of length N. A Hamming window or the like may be used as a window function.

・・・(3)
で与えられる。なお、ｉ番目の周波数成分の振幅I_i(ｍ)は、ｉ番目の周波数成分の受波レベルともいう。また、ｍ番目のフレームの周波数スペクトルにおいて、ｉ番目の周波数成分の位相θi(m)は、逆正接関数tan^-1を用いて

・・・(4)
で求まる。N/2+1番目はナイキスト周波数（サンプリング周波数の半分）のデータであり、ｙ_i(ｉ＝N/2+2～N)は、2～N/2の成分の複素共役が逆順に入っている。FFTのかわりにDFT（Discrete Fourier Transform:離散フーリエ変換）を用いてもよい。 FFT calculation result of the mth frame x _m (t)
y _m (t)=FFT(x _m (t))=[y ₀ ,y ₁ ,.., y _N-1 ] ・・・(2)
In the above, the first frequency component (bin number 1) _y0 is a DC (direct current) component. The i-th frequency component _yi (i = 1 to (N/2-1)) is a complex number, with the real part Re(yi) and the imaginary part Im(yi), in the frequency spectrum of the m-th frame,
The amplitude I _i (m) of the i-th frequency component is

...(3)
The amplitude I _i (m) of the i-th frequency component is also called the received wave level of the i-th frequency component. In addition, the phase θi(m) of the i-th frequency component in the frequency spectrum of the m-th frame is given by using the arctangent function tan ^-1.

...(4)
The N/2+1th data is the Nyquist frequency (half the sampling frequency), and y _i (i = N/2+2 to N) contains the complex conjugates of the components 2 to N/2 in reverse order. DFT (Discrete Fourier Transform) may be used instead of FFT.

・・・(5)
なお、周波数成分毎の振幅の時系列Ｉ_i(τ)（τ＝1,2,…）は、離散時間サンプリングであるため、積分演算は加算演算となる。 The amplitude of each frequency component, which is the result of the FFT calculation, may be integrated (moving averaged) for several seconds to several tens of seconds (N samples), for example, to improve the signal to noise ratio (SNR). For the FFT calculation result for each frame, the time average of a time width B is calculated centered on a certain point s for the time series of the amplitude _Ii (m) (m = 1, 2, ...) of each frequency component (i), and the average value is set as the value at the certain point s.

...(5)
It should be noted that the time series I _i (τ) (τ=1, 2, . . . ) of the amplitude for each frequency component is a discrete time sampling, and therefore the integral operation becomes an addition operation.

・・・(6) If the noise component is σ, the signal-to-noise ratio (SNR) is given by:

...(6)

The moving average improves the S/N ratio. For example, averaging four samples increases the S/N ratio by 6 dB (decibels). In this way, the moving average is effective against underwater noise that originates from natural phenomena, but since the propeller sound 4 is a mechanical operating sound and not noise (random noise), performing the moving average cannot be expected to improve the S/N ratio.

The CARDIOID directional synthesis unit 19 adds the amplitude (received wave level) of each frequency component of the received signal of the omnidirectional receiver 12 and the amplitude (received wave level) of each frequency component of the received signal of the front-rear directional receiver 13.

The propeller sound level calculation unit 20 calculates the propeller sound by subtracting data corresponding to the amplitude (received wave level) of each frequency component of the CARDIOID directivity from the amplitude (received wave level) of each frequency component of the received signal of the omnidirectional receiver 12.

The wave receiving direction calculation unit 21 applies an arctangent (tan −1 ) function to the ratio between the amplitude (wave receiving level) of each frequency component of the wave receiving signal of the front-rear directional receiver 13 and the amplitude (wave receiving level) of each frequency component of the wave receiving signal of the left-right directional receiver ¹⁴ , and calculates the principal value as the direction (angle:
Convert to degree.

The received signal detection unit 22 sets a threshold value for the ratio of the amplitude (received wave level) of each frequency component of the received signal from the omnidirectional receiver 12 to the average value in the frequency band, and detects the amplitude (received wave level) of each frequency component that exceeds the threshold value as the sailing sound of the ship 5.

The wave receiving direction correction calculation unit 23 calculates the ship direction 6, which eliminates the influence of the propeller sound 4, from the amplitude (wave receiving level) of each frequency component of the wave receiving signal of the non-directional receiver 12, obtained by the propeller sound level calculation unit 20 and the direction data of each frequency component obtained by the wave receiving direction calculation unit 21, as shown in Figure 3.

Figure 7 is a flowchart explaining the processing of the passive sonar direction correction device 24 in Figure 6.

<Step 1-1> (Converting sound waves received by the omnidirectional receiver 12 into amplitudes for each frequency component):
The non-directional received signal received by the non-directional receiver 12 and converted into an electrical signal is amplified by the preamplifier 15-1, unnecessary frequency band signals are attenuated by the bandpass filter 16-1, and converted into digital data by the AD converter 17-1. The time domain digital data is converted into the frequency domain by the FFT 18-1 to obtain the amplitude value for each frequency component, and the signal-to-noise ratio is improved by calculating a moving average for each frequency component for a predetermined number of samples.

<Step 1-2> (Converting the sound waves received by the front-rear directional receiver 13 into levels for each frequency component):
The front-rear directional received signal received by the front-rear directional receiver 13 and converted into an electric signal is amplified by a preamplifier 15-2, unnecessary frequency band signals are attenuated by a bandpass filter 16-2, and converted into digital data by an AD converter 17-2. The time domain digital data is converted into the frequency domain by an FFT 18-2 to obtain the amplitude value for each frequency component, and a moving average is calculated for each frequency component for a predetermined number of samples for the amplitude value for each frequency component to improve the S/N ratio.

<Step 1-3> (Converting the sound waves received by the left/right directional receiver 14 into levels for each frequency component):
The left-right directional received signal received by the left-right directional receiver 14 and converted into an electric signal is amplified by a preamplifier 15-3, unnecessary frequency band signals are attenuated by a bandpass filter 16-3, and converted into digital data by an AD converter 17-3. The time domain data is converted into the frequency domain by an FFT 18-3, and the signal-to-noise ratio is improved by calculating a moving average for each frequency component for a predetermined number of samples of the amplitude value for each frequency component.

<Step 2-1> (Calculate digital data for each frequency component of CARDIOID directivity):
By subtracting the amplitude of each frequency component of the received signal of the front/rear directional receiver 13 from the amplitude of each frequency component of the received signal of the omnidirectional receiver 12, the amplitude of each frequency component of the CARDIOID directivity shown in Figures 5A and 5B can be obtained.

As shown in Figures 5A and 5B, the amplitude (level) of each frequency component of the CARDIOID directivity has no directivity (sensitivity) in the direction of ±180°, which is the direction from which the propeller sound 4 arrives.

Figures 9 (A) and (B) show the amplitude (received wave level) of each frequency component of the received signal of the omnidirectional receiver 12 and the amplitude (received wave level) of each frequency component of the CARDIOID directivity, with the horizontal axis being frequency and the vertical axis being the received wave level. As shown in Figure 9 (B), the level of each frequency component of the CARDIOID directivity, compared to the level of each frequency component of the received signal of the omnidirectional receiver 12 shown in Figure 9 (A), excludes each frequency component of the propeller sound 4, so compared to the level of each frequency component of the received signal of the omnidirectional receiver 12, the received wave level tends to be smaller by the amount corresponding to each frequency component of the propeller sound 4.

<Step 2-2> (Calculate digital data for each frequency component of the propeller sound):
In the propeller sound level calculation unit 20, the amplitude (receiving level) of each frequency component of the propeller sound 4 is obtained by subtracting the amplitude (receiving level) of each frequency component of the CARDIOID-directional sound wave from the amplitude (receiving level) of each frequency component of the reception signal of the non-directional receiver 12. At this time, the CARDIOID directivity has a horizontal direction directivity as shown by reference numeral 11 in Fig. 5B, and the receiving sensitivity (level) differs depending on the direction.

The propeller sound level calculation unit 20 performs correction on the level of each frequency component of the CARDIOID directivity (CARDIOID directivity level) using the following formula, and calculates the propeller sound level by subtracting the corrected result from the omnidirectional level.

Propulsion sound level = Omnidirectional level - CARDIOID directional level / (cosθ ₂ + 1) ... (7)

In the above formula (7), _θ2 is the _θ2 of the passive sonar detection direction 9 in Figure 3, and is calculated in step 2-3 described later. The CARDIOID directivity (CARDIOID curve) 11 is expressed in polar coordinates as follows, where r is the distance from the origin and θ is the angle (radian).
r=a(1+cosθ)...(8)
(In FIG. 5B, a=1). The second term of the above equation (7) is expressed as follows:
a = r/(1 + cosθ) ... (9)
This corresponds to the calculation where θ = _θ2 .

The difference between the reception level for each non-directional frequency component in Figure 9 (A) (example of frequency distribution) and the reception level for each frequency component of the CARDIOID directional reception signal in Figure 9 (B) (levels corrected for direction) is the reception signal of the propeller sound 4 in Figure 1, and corresponds to the propeller sound reception signal level (S2) 8 in Figure 3.

The level (example of frequency distribution) of the CARDIOID directional received signal in Figure 9 (B) corresponds to the ship navigation sound received signal level (S1) 7 in Figure 3.

<Step 2-3> (Calculate the wave receiving direction for each frequency component):
In the receiving direction calculation unit 21, the ratio of the amplitude of each frequency component of the receiving signal of the front/rear directional receiver 13 to the amplitude of each frequency component of the receiving signal of the left/right directional receiver 14 is converted into a direction (angle) using an arctangent function, thereby calculating the passive sonar detection direction (θ ₂ ) 9 shown in Figure 12.

12, the amplitude of each frequency component of the received signal of the front-rear directional receiver 13 (FIG. 6) is the distance between A and C, and is calculated by the following equation (10). In FIG. 12, the diameter of each circle is set to 1.
AC=cos( _θ2 ) ...(10)

In FIG. 12, the amplitude of each frequency component of the received signal of the left/right directional receiver 14 (FIG. 6) corresponds to the distance between A and B.
AB = sin( _θ2 ) ... (11)

From the formulas (10) and (11),
θ ₂ = tan ^-1 (AB/AC) ...(12)
Here, θ ₂ is the principal value of the arctangent function tan ⁻¹ (−π/2<θ ₂ <π/2).

Figure 8 shows an example of the positional relationship when the sound of two ships sailing is detected by a passive sonar 2 equipped on an underwater vehicle 1. Figures 9 (A) and (B) show an example of the frequency distribution of the received signal of the omnidirectional receiver and the frequency distribution of the CARDIOID directional received signal in the positional relationship shown in Figure 8. Figures 10 (A) and (B) show an example of the frequency distribution of the received signal of the omnidirectional receiver and an example of the calculation of the sound arrival direction of the received signal of the omnidirectional receiver in the positional relationship shown in Figure 8.

Figure 10 (B) shows an example of the calculation results of the passive sonar detection direction when two ships, ship (1) 25 and ship (2) 27 shown in Figure 8, are present (the horizontal axis is frequency, and the vertical axis is direction (deg.)

In FIG. 10(B), the ship direction (1) 26 is a direction of 45 degrees, and the result of calculating the detection direction of the frequency components of the sailing sound of ship (1) 25 is a direction of approximately 55 degrees.

The ship direction (2) 28 is a direction of 90 degrees, and the result of calculating the detection direction of the frequency components of the sailing sound of ship (2) 27 is a direction of approximately 100 degrees.

Since the underwater vehicle has the structure shown in FIG. 1, the result of calculating the detection direction of the frequency components of the propeller sound 4 is roughly as follows:
120deg to 180deg, and
-120deg～-180deg
This is the direction.

In this way, even if the receiving transducer is a simple passive sonar 2 that does not have an array arrangement structure, if there are frequency characteristics for the navigation sounds of ship (1) 25 and ship (2) 27 in Figure 8, it is possible to distinguish and calculate the direction of arrival of the navigation sounds of multiple ships.

The calculation result of the wave receiving direction for each frequency component is the passive sonar detection direction 9 in Figure 3, and to calculate the ship direction 6, a correction calculation of the wave receiving direction for each frequency component is required. This will be explained with reference to Figure 7 again.

<Step 3> (Detection of received signal by threshold value):
The non-directional receiver 12 calculates an average value of the amplitude level for each frequency component in a frequency band for the amplitude level (received wave level) for each frequency component of the received signal.

Frequency components whose ratios between each frequency component and the average value exceed a predetermined threshold value are detected as the sailing sound of the ship 5.

The reasons for using values and ratios are as follows:

The noise level in the ocean fluctuates depending on weather and sea conditions, and the level of noise generated by the propulsion sound 4 and friction between the underwater vehicle 1 and seawater fluctuates depending on the speed of the underwater vehicle 1, so the average level of each frequency component in the frequency band is considered to correspond to the noise level. By converting the absolute level value into an S/N ratio, the threshold is made valid for all conditions.

Figure 11 (A) shows an example of detection of a received signal when the threshold value 30 is set to three times the average value of the frequency band. When the speed of the underwater vehicle 1 is slow, the propeller sound 4 is small, and the sailing sound of the ship 5 is loud, as shown in the example of Figure 11 (B), the frequency component of the propeller direction 29 can be removed and the passive sonar detection directions of the ship direction (1) 26 and the ship direction (2) 28 can be extracted. The following explanation will be given again with reference to Figure 7.

<Step 5> (Calculate the correction value for the receiving direction for each frequency component):
The amplitude level of each frequency component of the thruster sound 4 calculated by the thruster sound level calculation unit 20 corresponds to the thruster received signal level (S2) 8 in FIG.

The calculation results of the sound wave arrival direction for each frequency component calculated by the wave receiving direction calculation unit 21 correspond to the passive sonar detection direction 9 (θ ₂ ) in FIG.

The amplitude level of each omnidirectional frequency component corresponds to the ship navigation sound reception signal level (S1) 7 in Figure 3.

The amplitude level for each frequency component of the CARDIOID directivity (level corrected for the receiving direction) corresponds to the receiving signal level (S3) in Figure 13.

13, the ship direction 6 (θ ₁ ) is calculated by the following calculation: In FIG. 13, S3 corresponds to AF, and S4 corresponds to AG.

S4=S3×cos( _θ2 )...(13)

In FIG. 13, S2 corresponds to A-E, and S5 corresponds to A-H. Therefore,
S5=(S2+S4)...(14)

In FIG. 13, S6 corresponds to HD.
S6=S3×sin( _θ2 )...(15)

therefore,
θ ₁ = tan ^-1 (S6/S5) ...(16)
In addition, in the formula (16), θ ₁ is the principal value of the arctangent function tan ⁻¹ (−π/2<θ ₁ <π/2).

The ship direction (θ ₁ ) 6 is calculated for each frequency component, but from the CARDIOID directivity shown in FIG. 5B, it is roughly
120deg to 180deg, and
-120deg～-180deg
The received signal coming from the propeller direction 29 (see FIG. 10) is considered to be the propeller sound 4 or the sailing sound of the ship 5 located behind (ship 5 in FIG. 3 or ship (1) 25 in FIG. 8).

The level of the received signal is attenuated by the CARDIOID directivity 11 in Fig. 5B, and the difference between the ship sailing sound received signal level (S1) 7 and the propeller sound received signal level (S2) 8 in Fig. 13 becomes small. Therefore, the ship direction 6 (θ ₁ ) cannot be calculated accurately. Therefore, the passive sonar detection direction 9 is calculated without calculating the correction value for each frequency component.
-120deg～+120deg
It is conceivable to perform correction calculations for the receiving direction for each frequency component (step 5) only for the levels of frequency components in the range.

In this case, in step 4, it is determined whether the wave receiving direction found in step 3 is within the range of -120deg to +120deg, and if it is within the range, the wave receiving direction correction calculation for each frequency component in step 5 is performed, and if the wave receiving direction is outside the range of -120deg to +120deg, the wave receiving direction correction calculation for each frequency component may not be performed. In this case, it may be possible to output a message indicating that the wave receiving direction correction calculation for each frequency component will not be performed.

The passive sonar detection direction 9 is
+120deg to +180deg, and
-120deg～-180deg
Regarding the level of the frequency components, since no correction calculation for the detection direction is performed, the accuracy of the direction is reduced. However, if a ship 5 (Figure 3) is present, it is possible to obtain an approximate value of the ship direction 6 for the amplitude level of the frequency components of the sailing sound of the ship 5.

FIG. 14 is a diagram for explaining an embodiment of the present invention, and is a diagram for explaining the configuration when implemented in a computer device (data processing device, processor device) 40. Referring to FIG. 14, the computer device 40 includes a processor 41, a memory 42 such as a semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), or an EEPROM (Electrically Erasable Programmable Read-Only Memory) (or a HDD (Hard Disk Drive) or an SSD (Solid State Drive)), a display device 43, and an interface 44 (bus interface) that connects to the FFTs 18-1 to 18-3 in FIG. 6. The processor 41 executes the program 45 stored in the memory 42 to execute the processes of the CARDIOID directivity synthesis unit 19, the propeller sound level calculation unit 20, the receiving direction calculation unit 21, the receiving signal detection unit 22, and the receiving direction correction calculation unit 23 in FIG. 6. The processor 41 may be a DSP (Digital Signal Processor). In this case, the processor 41 may perform FFT calculations, and in this case, the interface 44 (bus interface) is connected to the AD converters 17-1 to 17-3 in FIG. 6.

As explained above, the embodiment provides the following effects:

In a simplified passive sonar 2 (small passive sonar with a non-array arrangement equipped on a small underwater vehicle 1) equipped on an underwater vehicle 1, the direction of the detected ship's navigation sound is corrected to eliminate the influence of the propeller sound 4 arriving from the rear of the underwater vehicle 1, thereby improving the accuracy of detecting the direction of the navigation sound arriving from the ship. Note that the present invention is suitable for application to unmanned underwater vehicles (UUVs) and the like, but is not limited thereto and can of course be applied to manned underwater vehicles.

The disclosure of Patent Document 1 above is incorporated herein by reference. Modifications and adjustments of the embodiments and examples are possible within the framework of the entire disclosure of the present invention (including the scope of the claims), and further based on the basic technical ideas. Furthermore, various combinations and selections of the various disclosed elements (including each element of each claim, each element of each example, each element of each drawing, etc.) are possible within the framework of the scope of the claims of the present invention. In other words, the present invention naturally includes various modifications and alterations that a person skilled in the art would be able to make in accordance with the entire disclosure, including the scope of the claims, and the technical ideas.

1 Underwater vehicle 2 Passive sonar 3 Propeller 4 Propeller sound 5 Ship 6 Ship direction 7 Ship navigation sound reception signal level (S1)
8. Propulsion sound receiving signal level (S2)
9 Passive sonar detection direction 10 Directivity of omnidirectional receiver 11 CARDIOID directivity 12 Omnidirectional receiver 13 Front-rear directional receiver 14 Left-right directional receiver 15-1 to 15-3 Preamplifier 16-1 to 16-3 Bandpass filter 17-1 to 17-3 AD converter 18-1 to 18-3 FFT
19 CARDIOID directivity synthesis unit 20 Propulsion unit sound level calculation unit 21 Receiving direction calculation unit 22 Receiving signal detection unit 23 Receiving direction correction calculation unit 24 Sound wave arrival direction detection device (direction correction device)
25 Ship (1) (First Ship)
26 Ship Direction (1) (First Ship Direction)
27 Ship (2) (Second Ship)
28 Ship Direction (2) (Second Ship Direction)
29 Thruster direction 30 Threshold 40 Computer device 41 Processor 42 Memory 43 Display device 44 Interface 45 Program

Claims (7)

A sound wave arrival direction detection device for an underwater vehicle having a passive sonar and a thruster at its rear,
A first means for calculating a non-directional reception level of a reception signal by the passive sonar that receives a sound wave;
A second means for calculating a cardioid directivity receiving level from the receiving signal,
The insensitive direction of the cardioid (CARDIOID) directivity is set in the rear direction of the underwater vehicle,
A third means for calculating a receiving direction of the received signal;
a fourth means for calculating a reception level of a propeller sound from the propeller based on the non-directional reception level of the reception signal, the cardioid directional reception level and the reception direction;
A fifth means for detecting the direction of arrival of the sound waves, with the influence of the propeller sound corrected, based on the non-directional receiving wave level and the receiving wave level of the propeller sound;
Equipped with
The passive sonar,
a first omnidirectional receiver;
A second wave receiver having directivity in the forward and backward directions of the traveling direction of the underwater vehicle;
a third wave receiver having directivity to the left and right of the traveling direction of the underwater vehicle;
Equipped with
The first means converts the received signal of the first receiver into a frequency domain and calculates a non-directional received wave level by the first receiver for each frequency component in a predetermined frequency band;
The second means calculates a cardioid directivity wave receiving level for each frequency component based on the non-directional wave receiving level by the first wave receiver for each frequency component and the wave receiving level by the second wave receiver for each frequency component,
The third means calculates a wave receiving direction for each frequency component based on a wave receiving level at the second wave receiver for each frequency component in the predetermined frequency band and at the third wave receiver for each frequency component,
The fourth means calculates the receiving level of the propeller sound for each frequency component based on the omnidirectional receiving level for each frequency component, the cardioid directional receiving level for each frequency component, and the receiving direction for each frequency component . Calculating an average value of the received wave level for each of the frequency components of the received wave signal of the first receiver;
The sound wave arrival direction detection device according to claim 1, further comprising a means for detecting the arrival direction of the sound waves emitted by a ship for frequency components where the ratio of the received wave level of each frequency component to the average value exceeds a predetermined threshold value. the fifth means calculates a first value (S4) and a second value (S6) which are projections of the corrected value (S3) onto the forward/rearward and left/right axes of the traveling direction of the underwater vehicle, based on a value (S3) obtained by correcting the wave receiving level for each frequency component of the cardioid directivity according to the wave receiving direction for each frequency component and the wave receiving direction for each frequency component;
3. The sound wave arrival direction detection device according to claim 1, further comprising: a third value (S5 ) obtained by adding the second value (S6) and the received wave level (S2) of the propeller sound, and an arctangent function is used to calculate the arrival direction of the sound wave emitted by the ship for the second value (S6). An underwater vehicle comprising the sound wave direction detection device according to any one of claims 1 to 3 . A method for detecting the direction of arrival of sound waves in an underwater vehicle having a passive sonar and a thruster at its rear, comprising:
A first step of calculating a non-directional reception level of a reception signal by the passive sonar that receives a sound wave;
A second step of calculating a received wave level of a cardioid directivity from the received wave signal, the received wave level having a direction of insensitivity set to a rear direction of the underwater vehicle;
A third step of calculating a receiving direction of the received signal;
a fourth step of calculating a reception level of a propeller sound from the propeller based on the non-directional reception level of the reception signal, the cardioid directional reception level and the reception direction;
A fifth step of detecting the direction of arrival of the sound waves, with the influence of the propeller sound corrected, based on the non-directional receiving wave level and the receiving wave level of the propeller sound;
having
The passive sonar,
a first omnidirectional receiver;
A second wave receiver having directivity in the forward and backward directions of the traveling direction of the underwater vehicle;
a third wave receiver having directivity to the left and right of the traveling direction of the underwater vehicle;
having
In the first step, a received signal of the first receiver is converted into a frequency domain, and a non-directional received wave level by the first receiver for each frequency component in a predetermined frequency band is calculated;
In the second step, a cardioid receiving level for each frequency component is calculated based on the non-directional receiving level by the first receiver for each frequency component and the receiving level by the second receiver for each frequency component;
In the third step, a wave receiving direction for each frequency component is calculated based on a wave receiving level for each frequency component in the second wave receiver and a wave receiving level for each frequency component in the predetermined frequency band at the third wave receiver,
The fourth step of the sound wave arrival direction detection method includes calculating a reception level of the propeller sound for each frequency component based on an omnidirectional reception level for each frequency component, a cardioid directional reception level for each frequency component, and a reception direction for each frequency component . Calculating an average value of the received wave level for each of the frequency components of the received wave signal of the first receiver;
The sound wave arrival direction detection method according to claim 5, further comprising a means for detecting the arrival direction of the sound waves emitted by a ship for frequency components where the ratio of the received wave level of each frequency component to the average value exceeds a predetermined threshold value. A computer mounted on an underwater vehicle equipped with a passive sonar and a thruster at the rear,
A first process of calculating a non-directional reception level of a reception signal by the passive sonar that receives a sound wave;
A second process of calculating a received wave level of a cardioid directivity from the received wave signal, the insensitive direction of which is set to the rear direction of the underwater vehicle;
A third process of calculating a receiving direction of the received signal;
A fourth process of calculating a reception level of a propeller sound from the propeller based on the non-directional reception level of the reception signal, the cardioid directional reception level and the reception direction;
A fifth process of detecting the direction of arrival of the sound wave, with the influence of the propeller sound corrected, based on the non-directional receiving wave level and the receiving wave level of the propeller sound;
A program for executing
The passive sonar,
a first omnidirectional receiver;
A second wave receiver having directivity in the forward and backward directions of the traveling direction of the underwater vehicle;
a third wave receiver having directivity to the left and right of the traveling direction of the underwater vehicle;
Equipped with
The first processing includes converting a received signal of the first receiver into a frequency domain and calculating a non-directional received wave level by the first receiver for each frequency component in a predetermined frequency band;
The second process calculates a cardioid directivity wave receiving level for each frequency component based on the non-directional wave receiving level by the first wave receiver for each frequency component and the wave receiving level by the second wave receiver for each frequency component;
The third process calculates a wave receiving direction for each frequency component based on a wave receiving level at the second wave receiver for each frequency component in the predetermined frequency band and at the third wave receiver for each frequency component,
The fourth processing is a program for calculating a receiving level of the propeller sound for each frequency component based on an omnidirectional receiving level for each frequency component, a cardioid directional receiving level for each frequency component, and a receiving direction for each frequency component .

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