JP2000221255A - Apparatus and method for passive sonar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus and a method for a passive sonar in which a noise can be removed optimally, even when the frequency characteristic of the noise generated by a passing ship or the like having a bed influence on the detection of a target signal is not uniform. SOLUTION: The frequency band of an acoustic signal from a receiving part is limited by a noise-level measuring part 1. The noise level in every direction of the acoustic signal in the limited frequency band is measured. Noise level data in every direction is outputted. On the basis of the noise level data and on the basis of reception level data which os calculated by a signal-level calculation part 2, a direction in which an S/N ratio becomes maximum is calculated by a direction calculation part 3 so as to be outputted as direction data. On the basis of the direction data, a directivity pattern is formed by directivity formation parts 5L, 5M, 5H in the direction in which the S/N ratio becomes maximum, and a target is searched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive sonar technique, and more particularly to a passive sonar apparatus and a passive sonar method for removing noise when a target is detected by underwater acoustics using a sonobuoy.

[0002]

2. Description of the Related Art Conventionally, in a passive sonar technique for detecting a target by using underwater acoustics using a sonobuoy, noise reduction is caused by the presence of a cruise ship, and the detection of an acoustic signal generated from a target is degraded. Improved detection when difficult (S
/ N ratio improvement).

For example, as disclosed in Japanese Patent Application Laid-Open No. Hei 10-222434, the S / N ratio is determined based on the azimuth characteristics of actual noise obtained by rotating a directivity pattern and the azimuth characteristics of a signal to be detected. A method of forming a directivity pattern in an azimuth at which the ratio becomes maximum has been proposed. FIG. 5 is a block diagram showing the configuration of a conventional passive sonar device, and FIG. Are respectively shown.

[0005] In FIG. 5, a wave receiving section 4 includes three types of wave receivers 4.
1, 42 and 43, which receive an underwater sound wave, convert the sound into an electric signal, and output an acoustic signal as an electric signal. Of the three types of receivers 41, 42, and 43, receiver 41 has omnidirectional directivity as shown in FIG. 6A, and receiver 42 is shown in FIG. The receiver 43 has a directivity represented by sin θ as shown in FIG. 6C. The noise level measuring unit 7 receives the acoustic signal from the wave receiving unit 4, forms a directivity pattern, and measures (actually measures) the directional characteristics of the received noise level. The signal level calculation unit 2 calculates the azimuth characteristic of the signal level to be formed and received, assuming that the target exists in the azimuth β. Direction calculator 8
Receives the azimuth characteristics of the noise level measured by the noise level measurement unit 7 and the azimuth characteristics of the signal level calculated by the signal level calculation unit 2 as input signals, and calculates the azimuth characteristics of the S / N ratio; The azimuth that provides the maximum S / N ratio is sent to the directivity forming unit 5. The directivity forming unit 5 rotates the directivity pattern based on the input azimuth at which the maximum S / N ratio is obtained, and uses the acoustic signal from the wave receiving unit 4 to obtain a sound obtained by the rotated directivity pattern. The signal is supplied to the frequency analyzer 6. The frequency analysis unit 6 performs a frequency analysis on the input acoustic signal.

Next, the operation of the conventional passive sonar device will be described. In the wave receiving unit 4, the wave receivers 41 and 42
And 43, the underwater sound wave is converted into an acoustic signal as an electric signal using a piezoelectric element (an element that converts a pressure change into an electric signal) and supplied to the noise level measuring unit 7 and the directivity forming unit 5, respectively. .

[0006] The noise level measuring section 7 measures the noise level using the acoustic signal input from the wave receiving section 4. The measurement of the noise level forms a directivity pattern based on the null direction (the direction of lowest sensitivity, hereinafter referred to as null direction),
The azimuth α in the null direction is performed by rotating the azimuth α from 0 to 360 ° at equal intervals, and the azimuth characteristic LN (α) is measured from the actual noise level of the azimuth in each null direction.
The measurement result of the azimuth characteristic of the noise level is output to the azimuth calculation unit 8. Here, regarding the formation of the directivity pattern,
It is formed in the same manner as the directivity forming unit 5, and the description will be made in the part of the directivity forming unit 5.

On the other hand, based on the input target target azimuth β, the signal level calculator 2 assumes that the target target exists in the azimuth β, and calculates the signal of a signal that would be obtained when the directivity pattern is rotated. Calculate the reception level. The signal reception level is calculated by forming a directivity pattern based on the null direction and rotating the azimuth α in the null direction from 0 to 360 ° at evenly spaced angles. Azimuth characteristic LS (α, β) from the reception level of the azimuth signal
Is calculated. The calculation result of the azimuth characteristic of the signal level is output to the azimuth calculation unit 8.

The azimuth calculating section 8 has an azimuth characteristic L of the noise level.
The azimuth calculation is performed based on N (α) and the azimuth characteristic LS (α, β) of the signal level. The azimuth calculation is performed first while rotating the null direction azimuth α from 0 to 360 ° at equal intervals, dividing the signal level and noise level in each null direction azimuth, and calculating each azimuth as null. The azimuth characteristic of the S / N ratio which will be obtained by the directivity pattern as the direction is obtained.

Subsequently, the azimuth calculation unit 8 searches the azimuth αβ at which the S / N ratio becomes maximum from the calculated azimuth characteristics. The azimuth αβ at which the S / N ratio becomes the maximum is the null azimuth in which noise can be optimally removed.
Output the direction αβ.

The directivity forming unit 5 multiplies the acoustic signal input from the receiver 42 by cos αβ in the multiplier 51 based on the input data from the azimuth calculating unit 8, and inputs the result from the receiver 43. The multiplier 52 adds sin to the
The result of multiplication by αβ is added by the adder 53. The directivity at this time is represented by the following expression (1), and the directivity pattern is as shown in FIG. 6D. The acoustic signals obtained by the two receivers 42 and 43 are multiplied and added. Thus, the sound signal becomes the same as the sound signal obtained by the receiver having the directivity pattern of cos θ rotated by αβ. cosθcosαβ + sinθsinαβ = cos (θ−αβ) (1)

Further, the directivity forming section 5 multiplies the addition result obtained by the adder 53 by “−1” by the multiplier 54 and supplies the result to the adder 55, where the sound is output from the receiver 41. Add to signal. The directivity at this time is expressed by the following equation (2), and the cardioid (CARDIO) shown in FIG.
ID). 1-cos (θ-αβ) (2)

As described above, the directivity forming section 5 aims at removing noise by changing the input direction αβ from the acoustic signals output from the three receivers 41, 42 and 43 of the receiving section 4. A cardioid directivity that can rotate the directivity pattern in any direction can be obtained. The acoustic signal obtained by the directivity formed by the directivity forming unit 5 is supplied to the frequency analyzing unit 6 and subjected to frequency analysis.

As described above, by inputting the value of the target target azimuth β, the directivity pattern is rotated to measure the azimuth characteristic of the noise level, and the calculated signal level of the signal to be detected is calculated. The azimuth αβ that gives the maximum S / N ratio is obtained from the azimuth characteristics, the directional pattern is rotated in that azimuth, the noise of the rowing ship is received at a low reception sensitivity, and the signal of the target target is received at the reception sensitivity. Reception is performed at a high location to reduce the noise reception level of the cruise ship to remove noise.

[0014]

However, the conventional passive sonar device has the following problems. In a conventional passive sonar device, to improve the noise measurement to the overall (average) signal detection of the target,
Measurement is performed in the entire band (overall), and there is a problem that optimal noise elimination cannot be performed when the frequency characteristics of noise generated by a cruise ship or the like are not uniform. For example,
7 (A) and 7 (B) show the frequency characteristics and noise level of the noise generated by the cruise ship a or the cruise ship b. And 1
One of the two ships (Fig. 7 (B): a ship b) emits a strong level of noise in a high frequency band.
(A): When a rowing ship a) emits a strong level of noise in a low frequency band (however, the noise level in all bands is the same), noise reduction is performed on the high frequency of the target signal. When it is desired to remove the noise, it is more effective to remove the noise of the former ship b, but the noise level is the same since the noise is the same level because the noise is the same level. a and b are calculated with the same weight, and optimal noise removal is not performed.

The present invention has been made in view of such a problem, and an object of the present invention is to solve the problem that the frequency characteristics of noise generated by a cruise ship or the like adversely affecting the detection of a target signal are not uniform. Another object of the present invention is to provide a passive sonar device and a passive sonar method capable of optimally removing noise.

[0016]

Means for Solving the Problems In order to solve the above problems, the present invention has the following constitution. The gist of the invention according to claim 1 is a passive sonar device that performs a target detection by forming a directivity pattern having different sensitivities in respective directions from an audio signal, and a filter unit that limits a frequency band of the audio signal, Noise level measuring means for measuring a noise level in each direction of the acoustic signal in the limited frequency band and outputting noise level data in each direction, and receiving each direction when a target exists in a specified direction. Receiving level calculating means for calculating a level and outputting received level data in each direction; and obtaining an S / N ratio in each direction from the received level data and the noise level data, and a direction in which the S / N ratio is maximized. Azimuth calculating means for calculating azimuth data and outputting the result as azimuth data; Consists in Passhibusona apparatus characterized and. The gist of the invention described in claim 2 is that the filter means limits the acoustic signal to a plurality of frequency bands, and the directivity forming means is provided for each of the plurality of frequency bands. 1 is a passive sonar device. The gist of the invention according to claim 3 is that the noise level measuring means and the azimuth calculating means process the measurement of the noise level and the calculation of the azimuth in time series for each of the plurality of frequency bands. Item 1. The passive sonar device according to item 1 or 2. The gist of the invention according to claim 4 is a passive sonar method for detecting a target by forming a directional pattern having different sensitivities in respective directions from an audio signal, wherein a frequency band of the audio signal is limited. Measure the noise level in each direction of the sound signal in the specified frequency band, output noise level data in each direction, calculate the reception level in each direction when the target is present in the specified direction, and calculate each direction. The S / N ratio of each azimuth is calculated from the reception level data and the noise level data, and the azimuth at which the S / N ratio becomes maximum is calculated and output as azimuth data. The passive sonar method is characterized in that the directivity pattern is formed in an azimuth at which the S / N ratio becomes maximum according to data. The gist of the invention according to claim 5 is that the acoustic signal is limited to a plurality of frequency bands and the directivity pattern is formed for each of the plurality of frequency bands. Exists. The gist of the invention according to claim 6 resides in the passive sonar method according to claim 4 or 5, wherein the measurement of the noise level and the calculation of the direction are processed in time series for each of the plurality of frequency bands.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an entire configuration of an embodiment of a passive sonar device and a passive sonar method according to the present invention, and FIG.
FIG. 3 is a flowchart showing a flow of operation of the block diagram of FIG. 3, FIG. 3 is a diagram showing a positional relationship between a target target and a ship, and FIG. 4 is a diagram showing an output graph of each azimuth characteristic.
FIG. 7 is a diagram showing the frequency characteristics of noise and the noise level in the low band (L), the middle band (M), and the high band (H) of the cruise ship.

The receiving unit 4 shown in FIG. 1 has a non-directional receiver 41, a receiver 42 having directivity cos θ, and a directivity sin θ
, Respectively, receives underwater sound waves, converts them into acoustic signals as electric signals, and outputs them to the noise level measuring unit 1 and the directivity forming units 5L, 5M, and 5H, respectively. I do. In this embodiment, the wave receiving unit 4 is installed in the sea as a sonobuoy, and the obtained acoustic signal is transmitted by radio, and the noise level measuring unit 1, the signal level calculating unit 2, the azimuth calculating unit 3, the directivity forming For example, an aircraft equipped with the units 5L, 5M, 5H and the frequency analysis units 6L, 6M, 6H is configured to receive them.

The noise level measuring unit 1 receives an acoustic signal from the wave receiving unit 4, forms a directional pattern, and specifies a low band (L), a medium band (M), and a high band specified for the received noise. (H)
The noise level data LNL (α) corresponding to the low band (L) frequency and the noise level data corresponding to the middle band (M) frequency are measured (actually measured) for the azimuth characteristic of the noise level for each of the three bands of frequencies. The noise level data LNH (α) corresponding to the LNM (α) and high frequency (H) frequencies is transmitted. Here, the "azimuth characteristic" refers to a characteristic obtained when the azimuth is changed from 0 to 360 degrees with respect to the null direction of the directivity pattern (the direction of lowest sensitivity, hereinafter referred to as null direction). is there.

The signal level calculator 2 determines that the target is the azimuth β
, The azimuth characteristic of the received signal level is calculated, and the signal level data LS (α, β) is transmitted.

The azimuth calculation unit 3 includes the noise level data LNL (α) and the noise level data L
NM (α), the noise level data LNH (α), and the azimuth characteristic LS (α, β) calculated by the signal level calculation unit 2 are received as input signals, and the low band (L), the middle band (M), The azimuth characteristic of the S / N ratio is calculated for each of the three frequency bands of the high band (H), and the azimuth data αβL that provides the maximum S / N ratio in the low band (L) frequency band and the mid band (M) Maximum S / in frequency band
Forming azimuth data αβM as the N ratio and azimuth data αβH as the maximum S / N ratio in the high frequency band (H),
Direction data αβL, direction data αβM, direction data αβ
H is sent to the directivity forming units 5L, 5M, and 5H, respectively.

The directivity forming units 5L, 5M, and 5H receive the acoustic signal from the wave receiving unit 4 and the azimuth data αβ from the azimuth calculating unit 3.
L, αβM, and αβH, respectively, to form rotated directional patterns, and to convert the acoustic signals obtained by the formed directivities into frequency analysis units 6L, 6L.
M, 6H, respectively, and the frequency analysis units 6L, 6M,
6H performs frequency analysis on the input acoustic signal.

Next, the operation of this embodiment will be described. The sound waves emitted from the target, the ship, etc. propagate through the water and reach the wave receiving unit 4, where the wave receivers 41, 4 of the wave receiving unit 4
2 and 43 are converted into an acoustic signal which is an electric signal, and the noise level measuring unit 1 and the directivity forming units 5L, 5L
M, 5H.

First, the noise level measuring section 1 temporarily stores the acoustic signal input from the wave receiving section 4. By temporarily storing the acoustic signal, the same acoustic signal is used for measurement in all directions, and the measurement of the directional characteristics of the noise level can be accurately performed.

The noise level measuring unit 1 measures the noise level using the temporarily stored acoustic signal in accordance with the flowchart of FIG. 2A, and obtains the noise level data LNL (LNL) corresponding to the low band (L) frequency. α), noise level data LNM (α) corresponding to the frequency of the middle band (M), high band (H)
Of the noise level data LNH (α) corresponding to the frequency First, the directional α in the null direction is set to 0 ° (Step 101), a directivity pattern in which the directional α in the null direction is set to 0 ° (Step 102), and a filter that passes the low frequency band (L) is formed. Multiplication (step 103) (In order to obtain noise level data corresponding to the frequency of the middle band (M) or the high band (H), a filter that passes the frequency band of the middle band (M) or the high band (H) is used. ), And the directivity pattern with the null direction azimuth α being 0 ° and the noise level obtained in the low frequency band (L) are measured (step 104). Since the noise level in the real environment is likely to fluctuate, the noise level is measured by averaging several measurements in order to perform stable measurement. The directivity pattern is formed by the same method as the directivity forming section 5 of the conventional passive sonar device shown in FIG.

Although the same result can be obtained even if the order of forming the filter and the directivity pattern is reversed, it is necessary to apply a filter to the acoustic signal of each receiver when the order is reversed. There is.

Next, the noise level measurement section 1 sends the measured noise level data LNL (α) (α = 0 °) to the azimuth calculation section 3 (step 105). Subsequently, the value of the azimuth α is shifted by a certain angle d (step 106), and it is determined whether or not the azimuth α is 360 ° or more (step 10).
7) When the angle is less than 360 °, the azimuth α in the null direction is d.
Is formed in the same manner (step 102), a filter for passing the low frequency band (L) is applied (step 103), and the azimuth α in the null direction is set to d.
The noise level obtained in the directivity pattern and the low frequency band (L) is measured (step 104), and the noise level data LNL (α) (α = d °) is transmitted (step 105).

Here, the value of the angle d of the shift amount of the azimuth α is optimally the same as the azimuth accuracy desired by the operator. For example, if the operator wants to obtain with an accuracy of 10 degrees, the angle d is set to 10 degrees. In the noise measurement process, the null direction azimuth α is sequentially increased by an angle d, and the measurement and transmission of the noise level in each direction are repeated in the null direction azimuth α of 0 to 360 ° ( Steps 102 to 107).

For reference, as shown in FIG. 3, the wave receiving section 4 (Sonobuoy) of the passive sonar device is located at the position indicated by 20, and the ships a and b are connected to the wave receiving section 4 (20). On the other hand, it is assumed that the target target 30 exists in the azimuth rotated by 70 ° and 310 ° clockwise from the north direction, and that the target 30 exists in the azimuth rotated 170 ° (= β) clockwise from the north direction. In this case, the azimuth characteristic of the noise level as shown in FIG. 4A can be obtained by measurement. Here, it can be seen that the lowest noise level is obtained by directing the direction of the lowest sensitivity (null direction) between the rowing ships a and b (azimuth 30 °).

The signal level calculator 2 shown in FIG. 1 is obtained when the directivity pattern is rotated, based on the input target target direction β, assuming that the target is present in the direction β. The reception level of the brazing signal is calculated according to the flowchart shown in FIG.
Send S (α, β).

First, the signal level calculation unit 2 sets the azimuth α in the null direction to 0 ° (step 201), and obtains the signal level LS (α, α,
β) is calculated based on the following equation (step 202). LS (α, β) = 1−cos (β−α) (3) Therefore, the signal level LS when the null direction azimuth α = 0
(0, β) is obtained from equation (4) by substituting α = 0 into equation (3). LS (0, β) = 1−cos (β−0) (4)

After outputting the data of the signal level LS (0, β) calculated by the equation (4) to the azimuth calculating section 3 (step 203), the signal level calculating section 2 changes the value of the azimuth α by a certain angle d. Shift (step 204), and it is determined whether the azimuth α after the shift is equal to or greater than 360 ° (step 2).
05) If the angle is less than 360 °, step 202 is performed again.
To 204 are executed. Hereinafter, in the same manner as above,
The signal level calculation section 2 sequentially increases the azimuth α in the null direction by an angle d, calculates a signal level that would be obtained in a directivity pattern having each azimuth as a null direction, and sends out the calculation result. , The orientation α in the null direction is 0 to 3
Repeat in the range of 60 °. The signal level is an assumed level, and is not related to the frequency band in this calculation.

Therefore, as shown in FIG. 3, the signal level calculator 2 determines that the target 30 is 1 clockwise from the north direction.
If the signal exists in a direction rotated by 70 ° (= β), 170 ° is substituted for β in the equation (3) to obtain a signal level characteristic as shown in FIG. In FIG. 4B, when the null direction is directed to the azimuth of 170 °, that is, the direction of the target 30, the signal of the target 30 is not received.

The azimuth calculator 3 calculates the noise level LNL (α) sent from the noise level measuring unit 1 and the signal level LS (α, β) sent from the signal level calculator 2.
The azimuth calculation is performed according to the flowchart shown in FIG. That is, the azimuth calculation unit 3 first sets the null azimuth α to 0 ° (step 301), and calculates the S / N ratio SN (α, β) that would be obtained by the directivity pattern in this case by the following equation. Calculation is performed based on the calculation (step 302). SNL (α, β) = LS (α, β) / LNL (α) (5) Therefore, SN (0, β) when the azimuth α = 0 in the null direction
Is obtained from equation (6) by substituting α = 0 into equation (5). SNL (0, β) = LS (0, β) / LNL (0) (6)

After temporarily storing the data of SNL (0, β) calculated by the equation (6), the azimuth calculation unit 3 shifts the value of the azimuth α by a certain angle d (step 303).
It is determined whether or not the azimuth α after the shift is equal to or greater than 360 ° (step 304), and if it is less than 360 °, the processing of steps 302 to 303 is executed again.

Hereinafter, in the same manner as described above, the azimuth calculating unit 3
The directional α in the null direction is sequentially increased by the angle d, and the calculation of the S / N ratio that can be obtained by the directivity pattern in which each directional is the null direction is performed.
Repeat within 360 °. Thereby, the azimuth calculation unit 3
4A shows the azimuth characteristics as shown in FIG. 4 (C) from the results of FIGS. 4 (A) and 4 (B) in the case where the ships A and B and the target 30 exist at the positions as shown in FIG. Get.

The azimuth calculation unit 3 searches the azimuth αβL at which the S / N ratio becomes maximum from the calculated azimuth characteristics (step 305). The azimuth αβL at which the S / N ratio becomes maximum is the null azimuth in which noise can be optimally removed in the low frequency band (L). Because the maximum S / N ratio means that the ratio of the signal level to the noise level is maximum, and the azimuth αβ at which the S / N ratio is maximum.
If the directivity pattern is rotated in the direction of L and an acoustic signal can be obtained, noise will be reduced. The azimuth αβL at which the obtained S / N ratio becomes the maximum is determined by the directivity forming unit 5.
L (step 306).

The directivity forming unit 5L changes the null direction to the azimuth αβ based on the azimuth αβL at which the input S / N ratio becomes the maximum.
A directivity pattern is set to L, and an acoustic signal obtained by the directivity pattern is output to the frequency analysis unit 6L. The frequency analysis unit 6L analyzes the frequency of the input acoustic signal. Here, the frequency analysis unit 6L only needs to analyze the set frequency band (low band (L)). This is because other frequency bands are not optimally denoised. Further, since the ship-going ship and the like move with the lapse of time and the state of the noise level changes, the entire process in the noise level measuring unit 1, the signal level calculating unit 2, and the azimuth calculating unit 3 is repeated at regular time intervals. . That is, the null direction is reviewed at a fixed time, and the directivity pattern is rotated.

Up to this point, the operation of forming a directional pattern in the null direction αβL in the low frequency band (L) and performing frequency analysis has been described. Similarly, in FIG.
03) is changed for the middle band (M) and the high band (H) by changing the filter to pass the middle band (M) or the high band (H).

In FIG. 1, the configuration of the noise level measuring unit 1 and the azimuth calculating unit 3 is one because the azimuth calculation is performed at fixed time intervals, so that the calculation of the low band (L) is executed. This is because the calculation of the middle range (M) and the high range (H) can be performed when not performed.

In this embodiment, the frequency band is divided into three parts. However, the same effect can be obtained by dividing the frequency band into two parts or four or more parts. The number of divisions of the frequency band is determined by the hardware scale and the expected effect. The effect is increased by increasing the number of divisions, but the directivity forming unit 5L,
5M and 5H and the frequency analysis units 6L, 6M and 6H are required by the number of divisions, and the hardware scale becomes large.

If the frequency of the target signal is known, only the band containing that frequency needs to be processed, so that it is not necessary to perform the processing in multiple divisions and the hardware scale can be reduced. It is.

According to this embodiment, noise reduction while waiting in a fixed direction can be realized. The reason is that once the azimuth of the target target is set, the optimum noise removal can always be performed even if the cruise ship moves and the situation of the noise level changes. This is a noise reduction method that is effective when the direction of existence of the target target is determined or estimated in the operation of target detection.

Since the passive sonar apparatus and the passive sonar method according to the embodiment are configured as described above, even when the frequency characteristics of noise generated by a ship-going ship or the like are not uniform, the passive sonar apparatus and the passive sonar method are optimal for the target signal. This has the effect of making it possible to effectively remove noise.

In the present embodiment, the present invention is not limited to this, and can be applied to a passive sonar device and a passive sonar method suitable for applying the present invention. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, but can be set to numbers, positions, shapes, and the like suitable for carrying out the present invention. In each drawing, the same components are denoted by the same reference numerals.

[0046]

According to the present invention, the frequency band is divided,
When the frequency characteristics of the noise generated by the cruise ship are not uniform because the directivity pattern is rotated in the direction that maximizes the S / N ratio of the target signal in each frequency band and the sound waves are received. In addition, there is an effect that optimal noise removal can be performed on the target signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a passive sonar device and a passive sonar method according to an embodiment of the present invention.

FIG. 2 is a flowchart showing the operation flow of the block diagram of FIG. 1;

FIG. 3 is a diagram showing a positional relationship between a target target and a cruise ship.

FIG. 4 is a diagram illustrating frequency characteristics of noise of a rowing ship and a noise level in each band.

FIG. 5 is a block diagram showing a configuration of a conventional passive sonar device.

FIG. 6 is a diagram illustrating a pattern of directivity in a receiver and a directivity forming process.

FIG. 7 is a diagram illustrating frequency characteristics of noise of a rowing ship and noise levels in a low band (L), a middle band (M), and a high band (H).

[Explanation of symbols]

 Reference Signs List 1 noise level measuring unit 2 signal level calculating unit 3 direction calculating unit 4 receiving unit 5, 5L, 5M, 5H directivity forming unit 6, 6L, 6M, 6H frequency analyzing unit 7 noise level measuring unit 8 direction calculating unit 30 target Target 41 Receiver having non-directional directivity 42 Receiver having directivity represented by cos θ 43 Receiver having directivity represented by sin θ 51 Multiplier 52 Multiplier 53 Adder 54 Multiplication Container 55 Adder

Claims (6)

[Claims] 1. A passive sonar device for detecting a target by forming a directional pattern having different sensitivities in respective directions from an acoustic signal, wherein: a filter means for limiting a frequency band of the acoustic signal; A noise level measuring means for measuring a noise level in each direction of the sound signal in a band and outputting noise level data in each direction; and calculating a reception level in each direction when a target exists in a specified direction. Receiving level calculating means for outputting receiving level data in each direction; calculating an S / N ratio in each direction from the receiving level data and the noise level data; calculating a direction in which the S / N ratio is maximum; Azimuth calculating means for outputting data as data, and directivity forming means for forming a directional pattern in an azimuth at which the S / N ratio is maximized based on the azimuth data. That Passhibusona apparatus. 2. The passive sonar device according to claim 1, wherein said filter means limits said acoustic signal to a plurality of frequency bands, and said directivity forming means is provided for each of said plurality of frequency bands. . 3. The noise level measuring means and the azimuth calculating means process the measurement of the noise level and the calculation of the azimuth for each of the plurality of frequency bands in a time series. Passive sonar device. 4. A passive sonar method for detecting a target by forming a directional pattern having different sensitivities in respective directions from an acoustic signal, wherein the frequency band of the acoustic signal is limited. Measures the noise level in each direction of the audio signal, outputs noise level data in each direction, calculates the reception level in each direction when the target exists in the specified direction, and outputs the reception level data in each direction The S / N ratio of each direction is obtained from the reception level data and the noise level data, the direction at which the S / N ratio becomes maximum is calculated and output as direction data, and the S / N ratio is calculated based on the direction data. A passive sonar method, wherein the directional pattern is formed in an orientation in which is maximum. 5. The passive sonar method according to claim 4, wherein the acoustic signal is limited to a plurality of frequency bands, and the directivity pattern is formed for each of the plurality of frequency bands. 6. The passive sonar method according to claim 4, wherein the measurement of the noise level and the calculation of the azimuth are processed in time series for each of the plurality of frequency bands.