Underwater Detection Device and Bubble Detection Method

Abstract

The problem lies in providing an underwater detection device and a bubble detection method capable of more accurately detecting the state of bubbles. The solution lies in that the bubble detection device (1) includes: a transmitting wave part (11) that transmits acoustic waves to a transmitting wave region (11a) in water; a receiving wave part (12) that receives acoustic waves after being reflected by bubbles existing in the transmitting wave region (11a) and then being reflected by bubbles existing in a receiving wave region (12a) different from the transmitting wave region (11a); and a bubble determination part that determines the state of bubbles in water based on the received signal received by the receiving wave part (12).

Description

Technical Field

[0001] The present invention relates to an underwater detection device and a bubble detection method for transmitting sound waves into water and detecting the state of bubbles in water based on the echoes thereof. Background Art

[0002] Conventionally, marine echo sounders or Doppler sonars are known, which measure ultrasonic waves reflected by an object to detect the distance to the object, the speed of a ship, etc. In such a device, if the ultrasonic waves are blocked by bubbles, it is not possible to appropriately measure the distance to the object, the speed of the ship, etc. To avoid such a situation, in such a device, a configuration capable of detecting the generation state of bubbles and controlling the measurement operation can be used.

[0003] As a bubble detection device for detecting the generation state of bubbles, for example, the following bubble detection device is known, which includes: an oscillator that transmits ultrasonic waves and receives the reflected waves thereof; a signal processing unit that performs signal processing on a received signal based on the reflected waves from water and calculates the frequency distribution of the received signal; and a storage unit that stores a reference frequency distribution reflecting the state of bubbles. In this bubble detection device, for the obtained frequency distribution, the difference from the reference frequency distribution stored in the storage unit is calculated, and when the difference is within a specified range, it is determined that the size and density of the bubbles are the same as those of the bubbles in the reference frequency distribution. For example, in the following Patent Document 1, a bubble detection device having the same configuration as described above is described.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2015-102416 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] In the device as described above, if the reflected waves from bubbles and the reflected waves from objects other than bubbles existing in water are mixed, it is difficult to accurately detect the state of bubbles.

[0009] In view of this problem, an object of the present invention is to provide an underwater detection device and a bubble detection method capable of more accurately detecting the state of bubbles.

[0010] Means for Solving the Problems

[0011] A first aspect of the present invention relates to an underwater detection device. The underwater detection device according to this aspect includes: a first oscillator that transmits sound waves to a first area in water; a second oscillator that receives the sound waves reflected by bubbles present in the first area and then reflected by bubbles present in a second area different from the first area; and a bubble determination unit that determines the state of bubbles in water based on the received signal received by the second oscillator.

[0012] According to the underwater detection device according to this aspect, the first area is different from the second area. Therefore, when there are no bubbles in the water, the reflected wave of the sound wave transmitted by the first oscillator is hardly received by the second oscillator. Even if there are objects other than bubbles in the first area, the reflected wave from the object hardly enters the second oscillator. On the other hand, when there are bubbles in the water, the sound wave transmitted by the first oscillator hits the bubbles and undergoes diffuse reflection repeatedly, thereby propagating to the second area. Thus, the reflected wave that propagates to the second area enters the second oscillator and is received by the second oscillator. In this case, even if there are objects other than bubbles mixed in the first area, the reflected wave from the object hardly enters the second oscillator directly.

[0013] Therefore, according to the underwater detection device according to this aspect, based on the received signal received by the second oscillator after the sound wave transmitted from the first oscillator is reflected by bubbles present in the first area and then reflected by bubbles present in the second area, the state of bubbles in water can be accurately determined.

[0014] In the underwater detection device according to this aspect, it can be configured such that the central axis of the transmission beam of the first oscillator is not parallel to the central axis of the reception beam of the second oscillator. Thus, even when the first oscillator and the second oscillator are close to each other, the first area and the second area can be appropriately separated. Therefore, the first oscillator and the second oscillator can be provided together on the bottom of a ship or the like. In addition, when the first oscillator and the second oscillator are provided in a single transceiver, the first oscillator and the second oscillator can be compactly accommodated in the transceiver.

[0015] In this case, it can be configured such that the transmission wavefront of the first oscillator and the reception wavefront of the second oscillator are inclined at a predetermined angle from a state of facing the same direction to a state of facing each other.

[0016] The underwater detection device according to this aspect can be configured to further include: a speed calculation unit that calculates the ship speed; and a display unit that displays the ship speed calculated by the speed calculation unit and information related to the state of bubbles determined by the bubble determination unit. Thus, when the user visually grasps the ship speed, the user can confirm the state of bubbles. Therefore, the user can grasp the influence of bubbles on the ship speed.

[0017] In this case, the underwater detection device according to this method can be configured such that on the display unit, the ship speed and information related to the state of the bubbles are displayed side by side. Thus, the user can visually compare the ship speed and the information related to the state of the bubbles. Therefore, the user can smoothly grasp the influence of the bubbles on the ship speed.

[0018] In this case, the underwater detection device according to this method can be configured such that based on the state of the bubbles in the water determined by the bubble determination unit, whether to display the ship speed on the display unit is switched. If there are a large number of bubbles in the water, the ship speed calculated by the speed calculation unit may sometimes be inaccurate. In such a case, for example, by making the display of the ship speed disappear, it is possible to suppress the display of inaccurate ship speed.

[0019] In the underwater detection device according to this method, it can be configured such that the speed calculation unit calculates the ship speed when the bubble determination unit determines that there are no bubbles in the water. If there are a large number of bubbles in the water, the ship speed calculated by the speed calculation unit may sometimes be inaccurate. In such a case, by not performing the calculation of the ship speed, it is possible to suppress the useless calculation process of the ship speed.

[0020] The underwater detection device according to this method can be configured to include: a frequency conversion unit that performs frequency conversion on the received signal received by the second oscillator to generate frequency data, and the bubble determination unit determines the state of the bubbles in the water based on the frequency data generated by the frequency conversion unit. Thus, compared with the method of evaluating the intensity of the received signal, it is possible to exclude noise in a frequency band different from the frequency of the sound wave that is the object of the received wave, and therefore it is possible to accurately determine the state of the bubbles in the water.

[0021] In this case, it can be configured such that when an amplitude equal to or greater than a specified threshold value is generated in the frequency data, the bubble determination unit determines that there are bubbles in the water. When there are no bubbles in the water, although an amplitude based on noise is generated in the frequency data, an amplitude equal to or greater than the specified threshold value is not generated. On the other hand, when there are bubbles in the water, in the frequency data, the amplitude based on noise overlaps with the amplitude based on the sound wave from the bubbles. Therefore, in this case, an amplitude equal to or greater than the specified threshold value is generated in the frequency data. Therefore, by determining whether an amplitude equal to or greater than the specified threshold value is generated, it is possible to determine whether there are bubbles in the water.

[0022] In this case, it can be configured that: in the frequency data, when an amplitude above the specified threshold is generated in a frequency band within a specified range including the frequency of the sound wave transmitted from the first oscillator, the bubble determination unit determines that there are bubbles in the water. If the transmitted sound wave is scattered by bubbles, the frequency of the scattered sound wave is included near the transmission frequency of the transmitted sound wave. Therefore, if the determination is made in a frequency band within a specified range including the transmission frequency, it is possible to determine more accurately whether there are bubbles in the water.

[0023] In the underwater detection device according to this embodiment, it can be configured that: the bubble determination unit determines the amount of bubbles present in the water based on the signal amount of an amplitude above a specified threshold in the frequency data. Thereby, it is possible to further determine the degree of bubbles present in the water.

[0024] The underwater detection device according to this embodiment can be configured that: among the first region and the second region, one region faces the bow direction and the other region faces the stern direction.

[0025] The second embodiment of the present invention relates to a bubble detection method. The bubble detection method according to this embodiment transmits a sound wave to a transmission wave region in the water, receives the sound wave reflected by bubbles present in the transmission wave region and then reflected by bubbles present in a reception wave region different from the transmission wave region, and determines the state of the bubbles in the water based on the reception wave state of the received sound wave.

[0026] According to the bubble detection method according to this embodiment, it has the same effect as the first embodiment.

[0027] Advantages of the Invention

[0028] As described above, according to the present invention, it is possible to provide an underwater detection device and a bubble detection method that can more accurately detect the state of bubbles.

[0029] The advantages and significance of the present invention will become clearer through the description of the embodiments shown below. However, the embodiments shown below are merely examples when implementing the present invention, and the present invention is not limited at all to the forms described in the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram for explaining the configuration and operation of the bubble detection device according to Embodiment 1.

[0031] Figure 2 It is a block diagram showing the configuration of the bubble detection device according to Embodiment 1.

[0032] Figure 3 It is a flowchart showing the bubble detection process according to Embodiment 1.

[0033] Figure 4 It is a schematic diagram showing the usage state of the ship speed measuring device related to Embodiment 2.

[0034] Figure 5 It is a schematic diagram showing the configuration of the transceiver related to Embodiment 2.

[0035] Figure 6 It is a block diagram showing the configuration of the ship speed measuring device related to Embodiment 2.

[0036] Figure 7 It is a block diagram showing the configuration of the signal processing circuit related to Embodiment 2.

[0037] Figure 8 It is a timing chart schematically showing the transmission wave timing and reception wave timing of the first transceiver unit and the transmission wave timing and reception wave timing of the second transceiver unit related to Embodiment 2.

[0038] Figure 9 The (a) of [Figure number] is a diagram showing an example of frequency data based on the first speed signal or the second speed signal obtained in the case where there are no bubbles in water related to Embodiment 2. Figure 9 The (b) of [Figure number] is a diagram showing an example of frequency data based on the first bubble signal or the second bubble signal obtained in the case where there are no bubbles in water related to Embodiment 2.

[0039] Figure 10 The (a) of [Figure number] is a diagram showing an example of frequency data based on the first speed signal or the second speed signal obtained in the case where there are bubbles in water related to Embodiment 2. Figure 10 The (b) of [Figure number] is a diagram showing an example of frequency data based on the first bubble signal or the second bubble signal obtained in the case where there are bubbles in water related to Embodiment 2.

[0040] Figure 11 It is a curve graph of frequency data obtained from the first speed signal in the state where no bubbles are generated in the experiment of Embodiment 2.

[0041] Figure 12 It is a curve graph of frequency data obtained from the second bubble signal in the state where no bubbles are generated in the experiment of Embodiment 2.

[0042] Figure 13 It is a curve graph of frequency data obtained from the first speed signal in the state where a small amount of bubbles are generated in the experiment of Embodiment 2.

[0043] Figure 14It is a graph of frequency data obtained from the second bubble signal in a state where a small number of bubbles are generated, related to the experiment of Embodiment 2.

[0044] Figure 15 It is a graph of frequency data obtained from the first velocity signal in a state where a large number of bubbles are generated, related to the experiment of Embodiment 2.

[0045] Figure 16 It is a graph of frequency data obtained from the second bubble signal in a state where a large number of bubbles are generated, related to the experiment of Embodiment 2.

[0046] Figure 17 (a) of is a diagram schematically showing the display content of the display device when the current ship speed is calculated, related to Embodiment 2. Figure 17 (b) of is a diagram schematically showing the display content of the display device when the current ship speed is not calculated, related to Embodiment 2.

[0047] Figure 18 It is a flowchart showing the ship speed measurement process related to Embodiment 2.

[0048] Figure 19 (a) of Figure 19 (b) of is a diagram for explaining the method of determining the state of bubbles in water related to a modification example of Embodiment 2.

[0049] Figure 20 (a) of Figure 20 (b) of is a diagram for explaining the method of determining the state of bubbles in water related to a modification example of Embodiment 2.

[0050] Explanation of reference numerals:

[0051] 1 Bubble detection device (underwater detection device)

[0052] 2 Ship speed measurement device (underwater detection device)

[0053] 11 Transmission wave part (first oscillator)

[0054] 11a Transmission wave area (first area)

[0055] 12 Reception wave part (second oscillator)

[0056] 12a Reception wave area (second area)

[0057] 25a Bubble determination part

[0058] 111 First transceiver part (first oscillator, second oscillator)

[0059] 111a First region (first region, second region)

[0060] 111b Surface (transmitted wave surface, received wave surface)

[0061] 111c Central axis

[0062] 112 Second transmitting and receiving wave section (first oscillator, second oscillator)

[0063] 112a Second region (first region, second region)

[0064] 112b Surface (transmitted wave surface, received wave surface)

[0065] 112c Central axis

[0066] 130 Display device (display section)

[0067] 311 First frequency conversion section (frequency conversion section)

[0068] 312 Second frequency conversion section (frequency conversion section)

[0069] 330 Bubble determination section

[0070] 340 Speed calculation section. Detailed implementation mode

[0071] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Embodiment 1 is an example in which the present invention is applied to a bubble detection device, and Embodiment 2 is an example in which the present invention is applied to a ship speed measurement device. However, the following embodiments are one embodiment of the present invention, and the present invention is not limited to the following embodiments at all.

[0072] <Embodiment 1>

[0073] Figure 1 It is a schematic diagram for explaining the configuration and operation of the bubble detection device 1. Figure 1 The first state, the second state, and the third state represent the process in which the sound wave transmitted to the bubble propagates through diffuse reflection.

[0074] The bubble detection device 1 includes a transmitting wave section 11 and a receiving wave section 12. The transmitting wave section 11 and the receiving wave section 12 are, for example, oscillators. The transmitting wave section 11 and the receiving wave section 12 are positioned in water. The transmitting wave section 11 transmits a sound wave (for example, an ultrasonic wave) to the transmitting wave region 11a in water. The receiving wave section 12 receives the sound wave from the receiving wave region 12a in water different from the transmitting wave region 11a. The bubble detection device 1 determines the state of the bubble in water based on the received wave state of the receiving wave section 12.

[0075] In the case where there are bubbles in water, as shown in the first state, the sound wave transmitted from the transmitting wave section 11 is reflected by the bubbles in the transmitting wave region 11a. Next, as shown in the second state, the sound wave reflected by the bubbles in the transmitting wave region 11a propagates in the water and reaches other bubbles, and is reflected by the other bubbles. Through such diffuse reflection, the sound wave propagates successively among multiple bubbles. Then, as shown in the third state, the sound wave reflected by the bubbles in the receiving wave region 12a is received by the receiving wave section 12.

[0076] On the other hand, in the case where there are no bubbles in water, the sound wave transmitted from the transmitting wave section 11 is not reflected by the bubbles in the transmitting wave region 11a. In this case, the sound wave is hardly re-reflected in the receiving wave region 12a, so the receiving wave section 12 hardly receives the sound wave.

[0077] Figure 2 It is a block diagram showing the configuration of the bubble detection device 1.

[0078] The bubble detection device 1 includes a transceiver 10, a control device 20, and a display device 30. The transceiver 10 includes a transmitting wave section 11 and a receiving wave section 12. The control device 20 includes a transmitting amplifier 21, a receiving amplifier 22, a transmitting signal generation circuit 23, an A / D conversion circuit 24, and a signal processing circuit 25.

[0079] The signal processing circuit 25 includes an arithmetic processing circuit such as a CPU and a memory (storage medium), and executes a prescribed function through a program held in the memory. This program causes the signal processing circuit 25 to execute the function of the bubble determination section 25a. In addition, the function of the bubble determination section 25a can also be realized not by software but by a hardware configuration.

[0080] The signal processing circuit 25 sends an instruction signal to the transmitting signal generation circuit 23 at a prescribed timing. In response to the instruction from the signal processing circuit 25, the transmitting signal generation circuit 23 generates a transmitting signal for driving the transmitting wave section 11 and outputs it to the transmitting amplifier 21. The transmitting signal is, for example, a pulse signal of a prescribed frequency. The transmitting amplifier 21 amplifies the transmitting signal and outputs it to the transmitting wave section 11. Thus, the transmitting wave section 11 transmits a sound wave to the transmitting wave region 11a in water (refer to Figure 1 ).

[0081] The receiving wave section 12 receives the sound wave from the receiving wave region 12a in water (refer to Figure 1 ) and outputs the received signal to the receiving amplifier 22. The receiving amplifier 22 amplifies the received signal and outputs it to the A / D conversion circuit 24. The A / D conversion circuit 24 converts the received wave signal from analog to digital and outputs it to the signal processing circuit 25.

[0082] The bubble determination unit 25a of the signal processing circuit 25 detects the state of bubbles in water based on the received signal input from the A / D conversion circuit 24. For example, the bubble determination unit 25a determines whether a sound wave is received by the receiving wave unit 12 corresponding to the transmission of the sound wave from the transmission wave unit 11 based on the intensity of the received signal. The bubble determination unit 25a monitors the received wave signal during the period when it is assumed that the sound wave is received after the signal processing circuit 25 outputs an indication signal to the transmission signal generation circuit 23. Then, for example, when the intensity of the received signal exceeds a threshold value, the bubble determination unit 25a determines that there are bubbles in the water, and when the received signal does not exceed the threshold value, the bubble determination unit 25a determines that there are no bubbles in the water.

[0083] Figure 3 Flowchart showing the bubble detection process.

[0084] Figure 3 The bubble detection process shown starts automatically when the power supply of the bubble detection device 1 is turned on, or starts when the user inputs a start instruction to the bubble detection device 1.

[0085] If the bubble detection process starts, the transmission wave unit 11 transmits a sound wave to the transmission wave region 11a in the water (S1). After that, for a certain period, that is, during the period including the timing when the sound wave reflected by the bubble assumed to exist at a specified water depth position in the water reaches the receiving wave unit 12, the receiving wave unit 12 performs the action of receiving the sound wave from the receiving wave region 12a in the water (S2). Then, the bubble determination unit 25a determines the state of the bubbles in the water based on the received wave state of the receiving wave unit 12 (S3). Specifically, as described above, it is determined whether there are bubbles in the water according to whether the intensity of the received signal exceeds the threshold value. After that, the signal processing circuit 25 displays the determination result of step S3 on the display device 30 (S4).

[0086] In addition, the determination in step S3 is not limited to determining the presence or absence of bubbles. For example, it is also possible to determine the distribution of bubbles indicating in what depth there are many bubbles based on the width of the range (range on the time axis) of the received signal exceeding a threshold value. In addition, the determination of the state of the bubbles can also be performed based on other parameter values other than the intensity of the received signal. For example, the signal processing circuit 25 can also perform processing such as FFT (Fast Fourier Transformation) on the received signal to generate frequency data, and based on the generated frequency data, determine the state of the bubbles in the water. In this case, for example, it is also possible to determine the presence or absence of bubbles based on whether the amplitude of the frequency data exceeds a threshold value. In addition, in particular, it is also possible to determine the presence or absence of bubbles based on whether an amplitude exceeding a threshold value is generated in a frequency band including the frequency of the transmitted signal. In this case, it is also possible to determine the distribution of bubbles indicating in what depth there are many bubbles based on the magnitude and range (range on the frequency axis) of the amplitude exceeding the threshold value.

[0087] <Effects of Embodiment 1>

[0088] According to Embodiment 1, the following effects can be obtained.

[0089] Since the transmission wave region 11a of the transmission wave unit 11 is different from the reception wave region 12a of the reception wave unit 12, when there are no bubbles in the water, the reflected wave of the sound wave transmitted by the transmission wave unit 11 is hardly received by the reception wave unit 12. In this case, even if there is an object other than a bubble in the transmission wave region 11a, the reflected wave from the object hardly enters the reception wave unit 12. On the other hand, when there are bubbles in the water, the sound wave transmitted by the transmission wave unit 11 hits the bubbles and undergoes diffuse reflection repeatedly, thereby propagating to the reception wave region 12a. As a result, the reflected wave of the sound wave enters the reception wave unit 12 and is received by the reception wave unit 12. In this case, even if an object other than a bubble is mixed in the transmission wave region 11a, the reflected wave from the object hardly enters the reception wave unit 12 directly.

[0090] Therefore, the bubble determination unit 25a can accurately determine the state of the bubbles in the water based on the reception wave state of the reception wave unit 12 (for example, whether the reception wave unit 12 receives a sound wave). As described above, according to the bubble detection device 1 of Embodiment 1, the state of the bubbles can be accurately detected.

[0091] <Embodiment 2>

[0092] In Embodiment 2, two wave transmitting and receiving units, i.e., the first wave transmitting and receiving unit 111 and the second wave transmitting and receiving unit 112, are used. The ship speed is measured by alternately transmitting waves using the first wave transmitting and receiving unit 111 and the second wave transmitting and receiving unit 112. The first wave transmitting and receiving unit 111 and the second wave transmitting and receiving unit 112 are used for measuring the ship speed and for detecting bubbles. The principle of bubble detection is the same as that in Embodiment 1 above. That is, based on whether a sound wave is received by the other when a sound wave is transmitted from one of the first wave transmitting and receiving unit 111 and the second wave transmitting and receiving unit 112, the state of bubbles in water (presence or absence of bubbles, etc.) is determined. Therefore, among the first wave transmitting and receiving unit 111 and the second wave transmitting and receiving unit 112, the wave transmitting and receiving unit that transmits the wave corresponds to the wave transmitting unit of the bubble detection device, and the other wave transmitting and receiving unit corresponds to the wave receiving unit of the bubble detection device. That is, in Embodiment 2, the wave transmitting unit and the wave receiving unit of the bubble detection device are switched between the first wave transmitting and receiving unit 111 and the second wave transmitting and receiving unit 112 in accordance with the timing of ship speed detection.

[0093] Figure 4 It is a schematic diagram showing the usage state of the ship speed measuring device 2 according to Embodiment 2.

[0094] In Figure 4 , the X - Y plane is the horizontal plane, and the positive direction of the Z - axis is the vertically downward direction. The longitudinal direction of the hull 40 is oriented in the X - axis direction, the bow 40a of the hull 40 is located on the positive side of the X - axis, and the stern 40b of the hull 40 is located on the negative side of the X - axis. In Figure 4 , for convenience, only the wave transceiver 110 among the components of the ship speed measuring device 2 is illustrated.

[0095] The wave transceiver 110 is disposed, for example, near the bottom of the hull 40 directly below the steering cabin 41 of the hull 40. In Figure 4 In the example shown, the wave transceiver 110 is positioned at the bottom of the hull slightly behind the center of the hull 40. Sound waves are transmitted from the wave transceiver 110 to the first area 111a and the second area 112a in the water. Here, ultrasonic waves are transmitted to the first area 111a and the second area 112a. The first area 111a faces the direction of the bow 40a, and the second area 112a faces the direction of the stern 40b. The transmitted ultrasonic waves are reflected by substances in the water, and the reflected waves (echoes) after being reflected by substances in the water are received by the wave transceiver 110. By the control device 120 (refer to Figure 6 ) arranged in the steering cabin 41 of the hull 40, etc., the ship speed of the hull 40 relative to the water (hereinafter simply referred to as "ship speed") is calculated.

[0096] Figure 5 It is a schematic diagram showing the configuration of the wave transceiver 110. In Figure 5 , the same X, Y, and Z axes as Figure 4 are shown.

[0097] The transceiver 110 includes a first transceiver unit 111, a second transceiver unit 112, and a housing 113. The first transceiver unit 111 is an oscillator that transmits sound waves to a first area 111a in water and receives sound waves from the first area 111a. The second transceiver unit 112 is also an oscillator that transmits sound waves to a second area 112a in water different from the first area 111a and receives sound waves from the second area 112a. The first transceiver unit 111 is positioned on the stern 40b side and transmits a first sound wave toward the bow 40a side. The second transceiver unit 112 is positioned on the bow 40a side and transmits a second sound wave toward the stern 40b side.

[0098] The housing 113 has a cylindrical outer shape. On the positive Z-axis side of the housing 113, a circular opening 113a is formed. The first sound wave transmitted from the first transceiver unit 111 and the second sound wave transmitted from the second transceiver unit 112 propagate into the water via the opening 113a. In addition, the first sound wave and the second sound wave reflected by plankton, particles, bubbles, etc. in the water are received by the first transceiver unit 111 and the second transceiver unit 112 via the opening 113a.

[0099] The first transceiver unit 111 transmits a first sound wave to a first area 111a in water (refer to Figure 4 ) and receives a sound wave including a reflected wave (echo) of the first sound wave from the first area 111a. The second transceiver unit 112 transmits a second sound wave to a second area 112a in water (refer to Figure 4 ) and receives a sound wave including a reflected wave (echo) of the second sound wave from the second area 112a.

[0100] The surface 111b of the first transceiver unit 111 for transmitting and receiving waves is inclined at an angle θ1 with respect to the Z-axis direction. Thus, the depression angle of the transmission wave direction and the reception wave direction of the first transceiver unit 111 becomes the angle θ1. In other words, the central axis 111c of the first area 111a (refer to Figure 4 ) is inclined at an angle θ1 with respect to the length direction (X-axis direction) of the hull 40. In addition, the surface 112b of the second transceiver unit 112 for transmitting and receiving waves is inclined at an angle θ2 with respect to the Z-axis direction. Thus, the depression angle of the transmission wave direction and the reception wave direction of the second transceiver unit 112 becomes the angle θ2. In other words, the central axis 112c of the second area 112a (refer to Figure 4 ) is inclined at an angle θ2 with respect to the length direction (X-axis direction) of the hull 40.

[0101] The central axis 111c of the transmitting beam and the receiving beam of the first transceiver unit 111 is not parallel to the central axis 112c of the transmitting beam and the receiving beam of the second transceiver unit 112. The surface 111b of the first transceiver unit 111 and the surface 112b of the second transceiver unit 112 are inclined at 90° - θ1 and 90° - θ2, respectively, from the state of facing the same direction to the state of facing each other.

[0102] In Embodiment 2, the angle θ1 is equal to the angle θ2. The angles θ1 and θ2 are set, for example, to about 50° to 80°.

[0103] The first transceiver unit 111 has a directivity that expands within a specified angular range with respect to the central axis 111c. Specifically, the divergence angle of the sound wave transmitted from the first transceiver unit 111 and the divergence angle of the sound wave received by the first transceiver unit 111 are about 1° to 6°. Similarly, the second transceiver unit 112 has a directivity that expands within a specified angular range with respect to the central axis 112c. Specifically, the divergence angle of the sound wave transmitted from the second transceiver unit 112 and the divergence angle of the sound wave received by the second transceiver unit 112 are about 1° to 6°.

[0104] The first sound wave transmitted from the first transceiver unit 111 is reflected by plankton, fine particles, etc. within the first area 111a (see Figure 4 ), returns to the first transceiver unit 111, and is received. In addition, the second sound wave transmitted from the second transceiver unit 112 is reflected by plankton, fine particles, etc. within the second area 112a (see Figure 4 ), returns to the second transceiver unit 112, and is received. At this time, corresponding to the ship speed of the hull 40, the frequency of the received sound wave changes due to the Doppler effect. Therefore, by using the signal based on the first sound wave transmitted from the first transceiver unit 111 and received by the first transceiver unit 111 (hereinafter referred to as the "first speed signal") and the signal based on the second sound wave transmitted from the second transceiver unit 112 and received by the second transceiver unit 112 (hereinafter referred to as the "second speed signal"), the ship speed can be calculated.

[0105] In the calculation of the ship speed, both the first speed signal and the second speed signal are used. Thus, even if the hull 40 tilts in the fore-and-aft direction, the ship speed can be accurately calculated. That is, if the hull 40 tilts in the fore-and-aft direction due to the influence of waves or the like, the transmission wave direction of the sound waves transmitted from the first wave transceiver 111 and the second wave transceiver 112 changes. Along with this, the Doppler frequency shift amount (the difference between the frequency at the time of transmission wave and the frequency at the time of reception wave) generated in the reflected waves of the respective sound waves changes. For example, if the Doppler frequency shift amount of the reflected wave received by the first wave transceiver 111 increases corresponding to the tilt of the hull 40, the Doppler frequency shift amount of the reflected wave received by the second wave transceiver 112 decreases. Therefore, the frequencies of the first speed signal and the second speed signal respectively increase and decrease by frequencies corresponding to the tilt of the hull 40. Therefore, by averaging the speeds calculated based on the Doppler frequency shift amounts of the respective frequencies of the first speed signal and the second speed signal, the ship speed that suppresses the influence of the tilt of the hull 40 can be calculated. Thus, regardless of whether the hull 40 tilts or not, the ship speed can be accurately calculated.

[0106] Furthermore, in the case where there are bubbles in the water, similar to the case described in Figure 1 the sound waves transmitted from one wave transceiver are diffusely reflected by the bubbles in the water and then received by the other wave transceiver.

[0107] That is, the first sound wave transmitted from the first wave transceiver 111 is repeatedly reflected by a plurality of bubbles existing between the first area 111a and the second area 112a, and propagates to the second area 112a through the diffuse reflection by these plurality of bubbles. In this way, the sound wave propagated to the second area 112a is reflected by the bubbles existing in the second area 112a and received by the second wave transceiver 112. Similarly, the second sound wave transmitted from the second wave transceiver 112 is repeatedly reflected by a plurality of bubbles existing between the second area 112a and the first area 111a, and propagates to the first area 111a through the diffuse reflection by these plurality of bubbles. In this way, the sound wave propagated to the first area 111a is reflected by the bubbles existing in the first area 111a and received by the first wave transceiver 111.

[0108] Therefore, by using the signal based on the first sound wave transmitted from the first wave transceiver 111 and received by the second wave transceiver 112 (hereinafter referred to as the "second bubble signal"), and the signal based on the second sound wave transmitted from the second wave transceiver 112 and received by the first wave transceiver 111 (hereinafter referred to as the "first bubble signal"), the state of the bubbles in the water can be determined.

[0109] Figure 6 is a block diagram showing the configuration of the ship speed measuring device 2.

[0110] The ship speed measuring device 2 includes a transceiver 110, a control device 120, and a display device 130. The control device 120 includes a first switching circuit 201, a second switching circuit 202, a first transmission amplifier 211, a second transmission amplifier 212, a transmission signal generation circuit 213, a first reception amplifier 221, a second reception amplifier 222, a first A / D conversion circuit 231, a second A / D conversion circuit 232, and a signal processing circuit 240. The control device 120 and the display device 130 are provided in the steering room 41 of the hull 40 (refer to Figure 4 ).

[0111] In response to an instruction from the signal processing circuit 240, the transmission signal generation circuit 213 generates a transmission signal for driving the first transceiver unit 111 and outputs it to the first transmission amplifier 211, and generates a transmission signal for driving the second transceiver unit 112 and outputs it to the second transmission amplifier 212. In Embodiment 2, the transmission signal generation circuit 213 generates a transmission signal such that the frequencies of the first sound wave and the second sound wave are F (MHz). The first transmission amplifier 211 amplifies the transmission signal and outputs it to the first switching circuit 201. The second transmission amplifier 212 amplifies the transmission signal and outputs it to the second switching circuit 202.

[0112] In response to the transmission signal from the first switching circuit 201, the first transceiver unit 111 transmits a first sound wave (ultrasonic pulse) into the water. In response to the transmission signal from the second switching circuit 202, the second transceiver unit 112 transmits a second sound wave (ultrasonic pulse) into the water. The first transceiver unit 111 and the second transceiver unit 112 receive the reflected wave (echo) after the ultrasonic pulse is reflected by plankton, particles, bubbles, etc. in the water, and convert it into an electrical signal. Thereby, a reception signal is generated. The first transceiver unit 111 and the second transceiver unit 112 respectively output the reception signal corresponding to the received sound wave to the first switching circuit 201 and the second switching circuit 202.

[0113] When the transmission signal is output from the first transmission amplifier 211, the first switching circuit 201 relays the transmission signal and outputs it to the first transceiver unit 111. In addition, when the reception signal is output from the first transceiver unit 111, the first switching circuit 201 relays the reception signal and outputs it to the first reception amplifier 221. Similarly, when the transmission signal is output from the second transmission amplifier 212, the second switching circuit 202 relays the transmission signal and outputs it to the second transceiver unit 112. In addition, when the reception signal is output from the second transceiver unit 112, the second switching circuit 202 relays the reception signal and outputs it to the second reception amplifier 222.

[0114] The first receiving amplifier 221 amplifies the received signal output from the first switching circuit 201 and outputs it to the first A / D conversion circuit 231. The second receiving amplifier 222 amplifies the received signal output from the second switching circuit 202 and outputs it to the second A / D conversion circuit 232. The first A / D conversion circuit 231 converts the analog received signal output from the first receiving amplifier 221 into a digital received signal and outputs it to the signal processing circuit 240. The second A / D conversion circuit 232 converts the analog received signal output from the second receiving amplifier 222 into a digital received signal and outputs it to the signal processing circuit 240.

[0115] Based on the received signals output from the first A / D conversion circuit 231 and the second A / D conversion circuit 232, the signal processing circuit 240 calculates the ship speed and determines the state of the bubbles. Then, the signal processing circuit 240 outputs the calculated ship speed, the determination result of the state of the bubbles, etc. to the display device 130.

[0116] The display device 130 is a display such as a liquid crystal display. The display device 130 displays the ship speed, the determination result, etc. output from the signal processing circuit 240. Regarding the display content of the display device 130, it will be described later with reference to Figure 17 (a) and (b).

[0117] Figure 7 is a block diagram showing the configuration of the signal processing circuit 240.

[0118] The signal processing circuit 25 includes an arithmetic processing circuit such as a CPU and a memory (storage medium), and executes a prescribed function through a program held in the memory. In Figure 7 it, the functions executed by the signal processing circuit 25 through this program are shown as functional modules. In addition, part or all of these functions may be implemented not by software but by a hardware configuration.

[0119] The signal processing circuit 240 includes a timing setting unit 301, a first frequency conversion unit 311, a second frequency conversion unit 312, a first Doppler measurement unit 321, a second Doppler measurement unit 322, a bubble determination unit 330, and a speed calculation unit 340.

[0120] The timing setting unit 301 sends an instruction to the transmission signal generation circuit 213 to cause it to generate a transmission signal. At this time, the timing setting unit 301 sends an instruction to cause it to generate a transmission signal in such a manner that the transmission wave timing of the first sound wave is different from the transmission wave timing of the second sound wave. Regarding the transmission wave timing, it will be described later with reference to Figure 8 it.

[0121] The first frequency conversion unit 311 performs frequency conversion on the received signal input from the first A / D conversion circuit 231 through fast Fourier transform (FFT). The second frequency conversion unit 312 performs frequency conversion on the received signal input from the second A / D conversion circuit 232 through fast Fourier transform (FFT).

[0122] Here, in the received signal input from the first transceiver unit 111, there is the received signal (first velocity signal) of the first acoustic wave received by the first transceiver unit 111 and the received signal (first bubble signal) of the second acoustic wave received by the first transceiver unit 111. The first frequency conversion unit 311 outputs the frequency data obtained by performing frequency conversion on the first velocity signal to the first Doppler measurement unit 321, and outputs the frequency data obtained by performing frequency conversion on the first bubble signal to the bubble determination unit 330.

[0123] Similarly, in the received signal input from the second transceiver unit 112, there is the received signal (second velocity signal) of the second acoustic wave received by the second transceiver unit 112 and the received signal (second bubble signal) of the first acoustic wave received by the second transceiver unit 112. The second frequency conversion unit 312 outputs the frequency data obtained by performing frequency conversion on the second velocity signal to the second Doppler measurement unit 322, and outputs the frequency data obtained by performing frequency conversion on the second bubble signal to the bubble determination unit 330.

[0124] The first Doppler measurement unit 321 measures the offset (Doppler shift amount) of the frequency of the amplitude that becomes a peak (maximum value) from the transmission frequency F of the first acoustic wave in the frequency data of the first velocity signal output from the first frequency conversion unit 311, and outputs the measured offset amount to the velocity calculation unit 340. Similarly, the second Doppler measurement unit 322 measures the offset (Doppler shift amount) of the frequency of the amplitude that becomes a peak (maximum value) from the transmission frequency F of the second acoustic wave in the frequency data of the second velocity signal output from the second frequency conversion unit 312, and outputs the measured offset amount to the velocity calculation unit 340.

[0125] The bubble determination unit 330 determines the state of the bubble based on the frequency data of the first bubble signal output from the first frequency conversion unit 311 and the frequency data of the second bubble signal output from the second frequency conversion unit 312. Specifically, when the amplitude above a prescribed threshold value is generated in the frequency data of the first bubble signal, the bubble determination unit 330 determines that a bubble is generated when obtaining the corresponding second velocity signal. Similarly, when the amplitude above a prescribed threshold value is generated in the frequency data of the second bubble signal, the bubble determination unit 330 determines that a bubble is generated when obtaining the corresponding first velocity signal. The bubble determination unit 330 outputs the determination result to the velocity calculation unit 340 and the display device 130. Regarding the method for determining bubbles, refer to Figure 9in (a) to Figure 10 explain (b).

[0126] The speed calculation unit 340 calculates the ship speed based on the first transceiver unit 111 based on the frequency offset output from the first Doppler measurement unit 321, and calculates the ship speed based on the second transceiver unit 112 based on the frequency offset output from the second Doppler measurement unit 322. Then, the speed calculation unit 340 uses the ship speed based on the first transceiver unit 111 for a specified period amount and the ship speed based on the second transceiver unit 112 for a specified period amount to calculate the current ship speed. The speed calculation unit 340 outputs the current ship speed calculated in this way to the display device 130.

[0127] Here, when there are bubbles in the water, the sound wave reflected by plankton, fine particles, etc. may be affected by the bubbles. In this case, the first speed signal and the second speed signal deteriorate, and an appropriate ship speed cannot be obtained. Therefore, in the second embodiment, a bubble determination unit 330 is provided, and the first speed signal and the second speed signal at the timing when bubbles are detected are not used to calculate the ship speed at that timing.

[0128] Figure 8 is a timing chart schematically showing the transmission wave timing and reception wave timing of the first transceiver unit 111 and the transmission wave timing and reception wave timing of the second transceiver unit 112.

[0129] In Figure 8 , as the time interval from when the sound wave is transmitted from the first transceiver unit 111 or the second transceiver unit 112 until the reflected wave of the sound wave is received, the periods P1 to P4 are shown. In the periods P1 and P3, the first transceiver unit 111 transmits the first sound wave, and in the periods P2 and P4, the second transceiver unit 112 transmits the second sound wave.

[0130] If the first sound wave is transmitted from the first transceiver unit 111 at time T1, the first sound wave is reflected by plankton and fine particles in the water and is received by the first transceiver unit 111 near time T2. As a result, the first speed signal is output from the first transceiver unit 111. At this time, if there are bubbles in the water, the first sound wave is diffusely reflected by the bubbles and is received by the second transceiver unit 112 near time T2. As a result, the second bubble signal is output from the second transceiver unit 112. The second bubble signal is used when determining the state of the bubbles, and based on the determination result of the bubbles based on the second bubble signal, it is determined whether the ship speed calculated based on the first speed signal is appropriate. In this way, the processing of the transmitted wave and received wave in the period P1 ends.

[0131] Next, if the second sound wave is transmitted from the second transceiver unit 112 at time T3, the second sound wave is reflected by the plankton and particles in the water, and is received by the second transceiver unit 112 around time T4. Thus, the second speed signal is output from the second transceiver unit 112. At this time, if there are bubbles in the water, the second sound wave is diffusely reflected by the bubbles, and is received by the first transceiver unit 111 around time T4. Thus, the first bubble signal is output from the first transceiver unit 111. The first bubble signal is used when determining the state of the bubble, and whether the ship speed calculated based on the second speed signal is appropriate is determined based on the determination result of the bubble based on the first bubble signal. In this way, the processing of the transmission wave and the reception wave in period P2 is completed.

[0132] In this manner, the cycle in which the first transceiver unit 111 transmits the first sound wave and the cycle in which the second transceiver unit 112 transmits the second sound wave are repeated alternately.

[0133] Next, refer to Figure 9 (a)~ Figure 10 (b) of the present invention will now be described the calculation of the ship speed by the speed calculation unit 340 and the determination of the state of the bubbles by the bubble determination unit 330.

[0134] Figure 9 The graph of (a) is a diagram showing an example of frequency data based on the first velocity signal or the second velocity signal obtained when there are no bubbles in water.

[0135] If there are no bubbles in the water, the amplitude becomes significantly larger near the transmission frequency F of the first and second sound waves, and the frequency width of the large amplitude portion is narrow. Therefore, the frequency of the peak (maximum) amplitude can be easily and appropriately determined.

[0136] The first Doppler measurement unit 321 is Figure 9 In the frequency data obtained by frequency conversion of the first speed signal shown in (a), the amplitude peak is measured to what extent it is offset from the transmission frequency F of the first sound wave. The speed calculation unit 340 calculates the ship speed based on the first transceiver unit 111 based on the frequency offset (Doppler shift amount). Similarly, the second Doppler measurement unit 322 calculates the ship speed based on the first transceiver unit 111. Figure 9 In the frequency data obtained by frequency-converting the second speed signal shown in (a), the amplitude peak is measured to what extent it is shifted from the transmission frequency F of the second sound wave. The speed calculation unit 340 calculates the ship speed by the second transceiver unit 112 based on the frequency shift amount (Doppler shift amount).

[0137] Figure 9 The graph of (b) is a diagram showing an example of frequency data based on the first bubble signal or the second bubble signal obtained when there are no bubbles in water.

[0138] The bubble determination unit 330 determines whether an amplitude equal to or greater than a specified threshold value Ath has occurred in the frequency data of the first bubble signal as shown in Figure 9 (b). The threshold value Ath is set to be able to distinguish noise from the amplitude based on bubbles. That is, the threshold value Ath is set to be greater than the amplitude of the noise generated in the absence of bubbles and less than the amplitude that may be generated in the presence of a specified amount of bubbles. The threshold value Ath can be appropriately adjusted according to the amount of bubbles to be detected.

[0139] In Figure 9 the case of the graph in (b), since an amplitude equal to or greater than the threshold value Ath has not occurred, it is determined that no bubbles have been generated. Therefore, it is determined that the second speed signal obtained at the same timing as the first bubble signal in this case is appropriate, and the ship speed based on the second speed signal is appropriate.

[0140] Similarly, the bubble determination unit 330 determines whether an amplitude equal to or greater than a specified threshold value Ath has occurred in the frequency data of the second bubble signal as shown in Figure 9 (b). In Figure 9 the case of the graph in (b), since an amplitude equal to or greater than the threshold value Ath has not occurred, it is determined that no bubbles have been generated. Therefore, it is determined that the first speed signal obtained at the same timing as the second bubble signal in this case is appropriate, and the ship speed based on the first speed signal is appropriate.

[0141] Figure 10 The graph in (a) shows an example of the frequency data based on the first speed signal or the second speed signal obtained when there are bubbles in the water.

[0142] If there are bubbles in the water, the sound wave reflected by the bubbles returns to the transceiver unit that sent the sound wave. Therefore, near the transmission frequency F, the amplitude becomes significantly larger, and the width of the frequency range where the amplitude increases becomes wider. Therefore, it is difficult to determine the frequency of the amplitude that becomes the peak (maximum value), and the calculation accuracy of the ship speed may decrease.

[0143] Figure 10 The graph in (b) shows an example of the frequency data based on the first bubble signal or the second bubble signal obtained when there are bubbles in the water.

[0144] In Figure 10 the case of the frequency data of the first bubble signal as shown in (b), since an amplitude equal to or greater than the threshold value Ath has occurred, it is determined that bubbles have been generated. Therefore, it is determined that the second speed signal obtained at the same timing as the first bubble signal in this case is greatly deteriorated for calculating the speed, and the ship speed based on the second speed signal is inappropriate.

[0145] Similarly, in the case of the frequency data based on the second bubble signal as shown in (b) of Figure 10 , since an amplitude above the threshold Ath is generated, it is determined that a bubble has been generated. Therefore, it is determined that the first velocity signal obtained at the same timing as the second bubble signal in this case is greatly deteriorated for calculating the velocity, and the ship speed based on the first velocity signal is inappropriate.

[0146] Next, referring to Figure 11 - 16 , the experiments conducted by the inventors will be described.

[0147] The inventors artificially created a state where no bubbles were generated, a state where a small number of bubbles were generated, and a state where a large number of bubbles were generated for actual seawater. At this time, the water ship speed was 0 kn in the state where no bubbles were generated, approximately 4 kn in the state where a small number of bubbles were generated, and approximately 5 kn in the state where a large number of bubbles were generated. Then, in each state, the inventors caused the first acoustic wave to be transmitted from the first transceiver unit 111 at a transmission frequency of F0 (Hz), and the reflected wave (echo) was received by the first transceiver unit 111 and the second transceiver unit 112. Then, the inventors performed fast Fourier transform (FFT) on the first velocity signal of the first transceiver unit 111 and the second bubble signal of the second transceiver unit 112, respectively, and obtained the frequency data.

[0148] Figure 11 is a graph of the frequency data obtained from the first velocity signal in the state where no bubbles were generated. In Figure 11 , the frequency data obtained by averaging the frequency data based on the first velocity signal for a specified period amount is shown. As described above, the ship speed was set to 0 kn in the state where no bubbles were generated. In addition, according to the experimental results shown in Figure 11 , at the same frequency F0 as the first acoustic wave, the amplitude becomes large in a narrow frequency width. Therefore, in this case, it can be seen that the ship speed can be appropriately obtained based on the first velocity signal.

[0149] Figure 12 is a graph of the frequency data obtained from the second bubble signal in the state where no bubbles were generated. In Figure 12 , the frequency data obtained by averaging the frequency data based on the second bubble signal for a specified period amount is shown. As shown in Figure 12 , although there are noise components in the frequency data based on the second bubble signal, the frequency band where the amplitude becomes large does not clearly exist. Therefore, in this case, it can be seen that the state of the bubbles can be appropriately determined based on the second bubble signal.

[0150] Figure 13It is a graph of frequency data obtained based on the first velocity signal in a state where a small number of bubbles are generated. As described above, the ship speed is set to approximately 4 kn in a state where a small number of bubbles are generated. Thus, the Doppler frequency shift amount ΔFc (Hz) with respect to the transmission frequency F0 of the first sound wave is calculated. Additionally, according to Figure 13 the experimental results shown, the amplitude becomes larger near the frequency offset by ΔFa (Hz) from the transmission frequency F0 of the first sound wave. Then, if ΔFc and ΔFa in this case are compared, it can be seen that ΔFc and ΔFa are approximately the same value. Therefore, in this case, it can also be known that the ship speed can be appropriately obtained based on the first velocity signal.

[0151] Figure 14 It is a graph of frequency data obtained based on the second bubble signal in a state where a small number of bubbles are generated. In Figure 14 this case, compared with Figure 12 , the amplitude becomes larger near the transmission frequency F0 of the first sound wave. This can be considered because: due to the small number of bubbles present in the water, the first sound wave transmitted by the first transceiver unit 111 is received by the second transceiver unit 112. In this case, as Figure 14 shown, by setting the amplitude threshold Ath, the state of the bubbles can be determined. That is, since the amplitude of the overall frequency data is smaller than the threshold Ath, it can be judged that there are substantially no bubbles in the water that affect the calculation result of the ship speed, and it can be known that the ship speed based on the first velocity signal is appropriate.

[0152] Figure 15 It is a graph of frequency data obtained based on the first velocity signal in a state where a large number of bubbles are generated. As described above, the ship speed is set to approximately 5 kn in a state where a large number of bubbles are generated. Thus, the Doppler frequency shift amount ΔFc (Hz) with respect to the transmission frequency F0 of the first sound wave is calculated. Additionally, according to Figure 15 the experimental results shown, the amplitude becomes larger near the frequency offset by ΔFa (Hz) from the transmission frequency F0 of the first sound wave. Then, if ΔFc and ΔFa in this case are compared, it can be seen that it cannot be said that ΔFc and ΔFa are approximately the same value. Therefore, in this case, it can be known that the ship speed cannot be appropriately obtained based on the first velocity signal.

[0153] Figure 16 It is a graph of frequency data obtained based on the second bubble signal in a state where a large number of bubbles are generated. In Figure 16 this case, compared with Figure 14 , the amplitude becomes even larger near the transmission frequency F0 of the first sound wave. In this case, also as Figure 16As shown, by setting the amplitude threshold Ath, the state of the bubbles can be determined. That is, since the amplitude of a part of the frequency data is equal to or greater than the threshold Ath, it can be determined that there are bubbles in the water that affect the calculation result of the ship speed, and it can be known that the ship speed obtained at the same timing is inappropriate.

[0154] Next, referring to Figure 17 (a) and (b) of, the display content of the display device 130 will be described.

[0155] In the second embodiment, as described above, based on the first bubble signal, it is determined whether the second speed signal obtained at the same timing is appropriate, and based on the second bubble signal, it is determined whether the first speed signal obtained at the same timing is appropriate. Further, in the second embodiment, the average is calculated based on the first speed signal and the second speed signal determined to be appropriate in the immediately preceding specified period, and the current ship speed is calculated. At this time, as long as it is determined by the bubble determination unit 330 that there are no bubbles in the water based on the first bubble signal and the second bubble signal in the immediately preceding specified period, the speed calculation unit 340 calculates the current ship speed. That is, when it is determined based on the first bubble signal and the second bubble signal in the immediately preceding specified period that there are bubbles in the water and the current ship speed is inappropriate, the current ship speed is not calculated and is not displayed on the display device 130.

[0156] Figure 17 (a) of is a diagram schematically showing the display content of the display device 130 when the current ship speed is calculated based on the ship speed in the immediately preceding specified period. The ship speed display area 131 is an area for displaying the ship speed, and the bubble information display area 132 is an area for displaying information related to the state of the bubbles determined by the bubble determination unit 330. The ship speed display area 131 and the bubble information display area 132 are arranged side by side vertically. In Figure 17 (a) of the case, since the current ship speed has been calculated, the ship speed is displayed in the ship speed display area 131, and a message "No bubbles generated" is displayed in the bubble information display area 132.

[0157] Figure 17 (b) of is a diagram schematically showing the display content of the display device 130 when the current ship speed is not calculated based on the ship speed in the immediately preceding specified period. In this case, in the ship speed display area 131, a diagonal line indicating that the current ship speed has not been calculated is displayed. In the bubble information display area 132, a message "Bubbles generated, ship speed may be inaccurate" is displayed.

[0158] In addition, the display method of the ship speed and the presence or absence of bubbles is not limited to Figure 17The display methods of (a) and (b). For example, it can also be that when the ship speed is calculated, the bubble information is not displayed, and only when the ship speed is not calculated, the bubble information is displayed. In this case, it can also be that only characters such as "bubble" are displayed in the ship speed display area 131 or near it.

[0159] Figure 18 It is a flowchart showing the ship speed measurement process.

[0160] Figure 18 The ship speed measurement process shown starts automatically when the power supply of the ship speed measurement device 2 is turned on. Or it can also be started by the user inputting a start instruction for ship speed measurement to the ship speed measurement device 2. Figure 18 The process.

[0161] If the ship speed measurement process starts, the signal processing circuit 240 causes the first wave transceiver unit 111 to send the first sound wave (S11) to the first area 111a in the water. Then, the signal processing circuit 240 causes the first wave transceiver unit 111 to receive the sound wave from the first area 111a (the reflected wave of the first sound wave), and causes the second wave transceiver unit 112 to receive the sound wave (S12) from the second area 112a. Thus, a first speed signal is output from the first wave transceiver unit 111, and a second bubble signal is output from the second wave transceiver unit 112. The processing of steps S11 and S12 corresponds to Figure 8 One cycle of the transmitted wave based on the first wave transceiver unit 111 shown.

[0162] Next, the signal processing circuit 240 causes the second wave transceiver unit 112 to send the second sound wave (S13) to the second area 112a in the water. Then, the signal processing circuit 240 causes the second wave transceiver unit 112 to receive the sound wave from the second area 112a (the reflected wave of the second sound wave), and causes the first wave transceiver unit 111 to receive the sound wave (S14) from the first area 111a. Thus, a second speed signal is output from the second wave transceiver unit 112, and a first bubble signal is output from the first wave transceiver unit 111. The processing of steps S13 and S14 corresponds to Figure 8 One cycle of the transmitted wave based on the second wave transceiver unit 112 shown.

[0163] Next, the signal processing circuit 240 calculates the ship speed based on the first speed signal obtained in step S12 and calculates the ship speed based on the second speed signal obtained in step S14. Furthermore, the signal processing circuit 240 determines the state of the bubbles based on the second bubble signal obtained in step S12 and determines the state of the bubbles based on the first bubble signal obtained in step S14. The signal processing circuit 240 stores the calculated ship speed and the determination result of the bubbles in correspondence with each other in the memory (S15). The signal processing circuit 240 repeats the processing of steps S11 to S15 until the ship speed calculation operation ends (S16). Thus, the ship speed and the determination result of the bubbles obtained in each cycle are sequentially stored in the memory of the signal processing circuit 240.

[0164] After that, as described above, as long as the bubble determination unit 330 determines that there are no bubbles in the water based on the first bubble signal and the second bubble signal in a specified cycle, the speed calculation unit 340 calculates the current ship speed. The speed calculation unit 340 calculates the average based on the first speed signal and the second speed signal determined to be appropriate in the specified cycle and calculates the current ship speed. Then, when the signal processing circuit 240 calculates the current ship speed, the calculated ship speed and the bubble information based on the determination result of the bubbles are Figure 17 displayed on the display device 130 as shown in (a) of. In addition, when the signal processing circuit 240 does not calculate the current ship speed, a diagonal line indicating that the ship speed has not been calculated is Figure 17 displayed in the ship speed display area 131 as shown in (b) of, and the bubble information is Figure 17 displayed in the bubble information display area 132 as shown in (b) of.

[0165] <Effects of Embodiment 2>

[0166] According to Embodiment 2, the following effects can be obtained.

[0167] The first region 111a of the first transceiver unit 111 is different from the second region 112a of the second transceiver unit 112. Therefore, when there are no bubbles in the water, the reflected wave of the sound wave transmitted by the first transceiver unit 111 is hardly received by the second transceiver unit 112, and even if there is an object other than a bubble in the first region 111a, the reflected wave from the object hardly enters the second transceiver unit 112. Similarly, when there are no bubbles in the water, the reflected wave of the sound wave transmitted by the second transceiver unit 112 is hardly received by the first transceiver unit 111, and even if there is an object other than a bubble in the second region 112a, the reflected wave from the object hardly enters the first transceiver unit 111.

[0168] On the other hand, in the presence of air bubbles in water, the sound wave transmitted by the first transmitting and receiving wave section 111 hits the air bubbles and undergoes diffuse reflection repeatedly, thus propagating to the second region 112a. As a result, the reflected wave propagating to the second region 112a enters the second transmitting and receiving wave section 112 and is received by the second transmitting and receiving wave section 112. In this case, even if objects other than air bubbles are mixed in the first region 111a, the reflected wave from this object hardly directly enters the second transmitting and receiving wave section 112. Similarly, in the presence of air bubbles in water, the sound wave transmitted by the second transmitting and receiving wave section 112 hits the air bubbles and undergoes diffuse reflection repeatedly, thus propagating to the first region 111a. As a result, the reflected wave propagating to the first region 111a enters the first transmitting and receiving wave section 111 and is received by the first transmitting and receiving wave section 111. In this case, even if objects other than air bubbles are mixed in the second region 112a, the reflected wave from this object hardly directly enters the first transmitting and receiving wave section 111.

[0169] Therefore, according to Embodiment 2, based on at least one of the first received signal (the first air bubble signal) received by the first transmitting and receiving wave section 111, which is the sound wave transmitted by the second transmitting and receiving wave section 112, reflected by the air bubbles present in the second region 112a, and then reflected by the air bubbles present in the first region 111a, and the second received signal (the second air bubble signal) received by the second transmitting and receiving wave section 112, which is the sound wave transmitted by the first transmitting and receiving wave section 111, reflected by the air bubbles present in the first region 111a, and then reflected by the air bubbles present in the second region 112a, the state of the air bubbles in water can be accurately determined.

[0170] In addition, the ship speed can be calculated based on the received signal (the first speed signal) of the reflected wave of the first sound wave received by the first transmitting and receiving wave section 111 and the received signal (the second speed signal) of the reflected wave of the second sound wave received by the second transmitting and receiving wave section 112. That is, in Embodiment 2, the first transmitting and receiving wave section 111 and the second transmitting and receiving wave section 112 are used for both determining the state of air bubbles and calculating the ship speed. Therefore, in the ship speed measuring device 2 equipped with the first transmitting and receiving wave section 111 and the second transmitting and receiving wave section 112, the state of air bubbles can be detected without adding an additional structure.

[0171] As Figure 5As shown, the central axis 111c of the transmission beam and reception beam of the first transceiver unit 111 is not parallel to the central axis 112c of the transmission beam and reception beam of the second transceiver unit 112. Thus, even when the first transceiver unit 111 and the second transceiver unit 112 are close to each other, the first region 111a and the second region 112a can be appropriately separated. Therefore, the first transceiver unit 111 and the second transceiver unit 112 can be provided together on the bottom of a ship or the like. In addition, when the first transceiver unit 111 and the second transceiver unit 112 are provided in a single transceiver 110, the first transceiver unit 111 and the second transceiver unit 112 can be compactly accommodated in the transceiver 110.

[0172] As Figure 17 shown in (a) and (b) of, the signal processing circuit 240 causes the display device 130 to display the ship speed calculated by the speed calculation unit 340 and the information related to the state of the bubbles determined by the bubble determination unit 330. Thus, when the user visually grasps the ship speed, the user can confirm the state of the bubbles. Therefore, the user can grasp the influence of the bubbles on the ship speed.

[0173] In addition, the signal processing circuit 240 causes the display device 130 to display the ship speed and the information related to the state of the bubbles side by side. Thus, the user can visually compare the ship speed and the information related to the state of the bubbles. Therefore, the user can smoothly grasp the influence of the bubbles on the ship speed.

[0174] As Figure 17 shown in (a) and (b) of, the signal processing circuit 240 switches whether to display the ship speed on the display device 130 based on the state of the bubbles in the water determined by the bubble determination unit 330. Specifically, the bubble determination unit 330 determines whether there are bubbles currently based on the first bubble signal and the second bubble signal of a prescribed periodic quantity. If it is determined that no bubbles are currently generated in the water, the speed calculation unit 340 calculates the average as the current ship speed. On the other hand, if it is determined that bubbles are currently generated in the water, the speed calculation unit 340 does not calculate the current ship speed. Then, as Figure 17 shown in (a) and (b) of, the signal processing circuit 240 displays the ship speed in the ship speed display area 131 when no bubbles are generated, and displays a diagonal line in the ship speed display area 131 when bubbles are generated. If there are a large number of bubbles in the water, the ship speed calculated by the speed calculation unit 340 may be inaccurate. In such a case, by making the display of the ship speed disappear, it is possible to suppress the display of an inaccurate ship speed.

[0175] In addition, there is no need to arrange the first transmitting / receiving wave unit 111 and the second transmitting / receiving wave unit 112 at the bow 40a where the influence of bubbles is small in order to avoid displaying inaccurate ship speeds. Therefore, there is no need to arrange wiring over a long distance from a display device 130 or the like arranged in the steering room 41 or the like to the first transmitting / receiving wave unit 111 and the second transmitting / receiving wave unit 112 arranged at the bow 40a. Therefore, the installation cost of the first transmitting / receiving wave unit 111 and the second transmitting / receiving wave unit 112 can be significantly reduced.

[0176] When the bubble determination unit 330 determines that there are no bubbles in the water, the speed calculation unit 340 calculates the current ship speed (average). If there are a large number of bubbles in the water, the ship speed calculated by the speed calculation unit 340 may be inaccurate. According to the configuration of Embodiment 2, in such a case, useless calculation processing of the ship speed can be suppressed. In addition, in this case, there is no need to arrange the first transmitting / receiving wave unit 111 and the second transmitting / receiving wave unit 112 at the bow 40a in order to avoid calculating an inaccurate ship speed. Therefore, the installation cost of the first transmitting / receiving wave unit 111 and the second transmitting / receiving wave unit 112 can be significantly reduced.

[0177] The first frequency conversion unit 311 and the second frequency conversion unit 312 respectively perform frequency conversion on the first bubble signal and the second bubble signal. Then, the bubble determination unit 330 determines the state of bubbles in the water based on the frequency data obtained by performing frequency conversion on the first bubble signal and the second bubble signal. Thereby, compared with the method of evaluating the intensities of the first bubble signal and the second bubble signal, noise in a frequency band different from the frequency of the sound wave that is the object of the received wave can be excluded, and thus the state of bubbles in the water can be determined with high precision.

[0178] As described with reference to Figure 9 the graph of (b) and Figure 10 the graph of (b), when the bubble determination unit 330 generates an amplitude equal to or greater than a threshold value Ath in the frequency data based on the first bubble signal and the second bubble signal, it is determined that there are bubbles in the water. When there are no bubbles in the water, although an amplitude based on noise is generated in the frequency data based on the first bubble signal and the second bubble signal, an amplitude equal to or greater than the threshold value Ath is not generated. On the other hand, when there are bubbles in the water, in the frequency data based on the first bubble signal and the second bubble signal, the amplitude based on noise overlaps with the amplitude based on the sound wave from the bubbles. Therefore, in this case, an amplitude equal to or greater than the threshold value Ath is generated in the frequency data. Therefore, by determining whether an amplitude equal to or greater than the threshold value Ath is generated, it is possible to determine whether there are bubbles in the water.

[0179] The first region 111a of the first wave transmitting and receiving unit 111 faces the bow 40a side, and the second region 112a of the second wave transmitting and receiving unit 112 faces the stern 40b side. In this way, if one of the two regions faces the bow 40a side and the other faces the stern 40b side, the frequency shift between the transmitted wave and the received wave when the acoustic wave is transmitted in the bow 40a direction and the frequency shift between the transmitted wave and the received wave when the acoustic wave is transmitted in the stern 40b direction can be measured by each wave transmitting and receiving unit respectively. Therefore, even when the hull 40 tilts forward and backward during navigation, the ship speed can be appropriately calculated by averaging the frequency shifts in each direction. In addition, the two wave transmitting and receiving units configured for such a purpose can be used also for detecting bubbles. Therefore, simplification of the configuration can be achieved, and the ship speed and bubbles can be detected appropriately.

[0180] <Modification Example>

[0181] In the above-described Second Embodiment, as described with reference to Figure 9 the graph of (b) and Figure 10 the graph of (b), when an amplitude equal to or greater than the threshold Ath is generated in the frequency data, it is determined that there are bubbles in the water. However, the method for determining bubbles is not limited to this. For example, as shown in the graph of (a) of Figure 19 , when the signal area (hatched portion) of the amplitude equal to or greater than the threshold Ath in the frequency data exceeds a specified value, it is determined that there are bubbles in the water. In addition, as shown in the graph of (b) of Figure 19 , when the signal area (hatched portion) of the amplitude equal to or greater than the threshold Ath in the frequency band F1 in the frequency data exceeds a specified value, it is determined that there are bubbles in the water.

[0182] In addition, as shown in the graph of (a) of Figure 20 , when an amplitude equal to or greater than the threshold Ath is generated in the frequency band FB within a specified range including the transmission frequency F of the original acoustic wave in the frequency data, it is determined that there are bubbles in the water. If the transmitted acoustic wave is scattered by bubbles, the frequency of the scattered acoustic wave is included near the transmission frequency F of the transmitted acoustic wave. Therefore, if the determination is made in the frequency band FB within a specified range including the transmission frequency F, it is possible to determine more accurately whether there are bubbles in the water.

[0183] In addition, as shown in the graph of (b) of Figure 20 , when the signal area (hatched portion) of the amplitude equal to or greater than the threshold Ath in the frequency band FB of the frequency data exceeds a specified value, it is determined that there are bubbles in the water.

[0184] In addition, in the above-described Embodiments 1 and 2, the presence or absence of bubbles is determined based on the received signal of the sound wave scattered by the bubbles. However, the state of the bubbles to be determined is not limited to the presence or absence of bubbles. For example, the amount of bubbles may also be determined based on the received signal of the sound wave scattered by the bubbles. In this case, for example, in the configuration of Embodiment 2, in the Figure 10 frequency data shown in the graph of (b), based on the signal amount of the amplitude above the threshold Ath, the amount of bubbles present in the water is determined in the bubble determination unit 330.

[0185] Here, the signal amount of the amplitude above the threshold Ath can be obtained, for example, as the area of the shaded region in the graph of (b) of Figure 19 (the total amount of the amplitudes of the respective frequency components included in the frequency band F1). Alternatively, the area of the shaded region in the graph of (a) of Figure 19 may also be used as the signal amount of the amplitude above the threshold Ath.

[0186] In this way, when determining the amount of bubbles present in the water, information related to the amount of bubbles may also be displayed on the display device 130. In this case, the amount of bubbles may be displayed by a ratio that continuously changes according to the amount, or may be displayed in three levels of "many", "medium", and "few" based on the magnitude relationship between two thresholds and the determination result of the amount of bubbles. It is not limited to three levels, and the amount of bubbles may also be displayed by other numbers of levels. Thereby, the user can grasp the degree of bubbles present in the water.

[0187] In addition, in the above-described Embodiment 2, the amplitude threshold Ath is a fixed value, but it is not limited thereto. The threshold Ath may also be determined based on the signal strength of the speed signal each time a determination is made based on the bubble signal. For example, it may also be that when determining based on the second bubble signal, the threshold Ath used in the determination of the second bubble signal is determined based on the signal strength of the first speed signal. Similarly, it may also be that when determining based on the first bubble signal, the threshold Ath used in the determination of the first bubble signal is determined based on the signal strength of the second speed signal.

[0188] In addition, in the above-described Embodiment 1, when determining bubbles, if the intensity of the received signal of the receiving wave unit 12 is large, it is determined that there are bubbles in the water. However, it is not limited thereto, and the same bubble determination as that of the ship speed measurement device 2 of the above-described Embodiment 2 may also be performed.

[0189] For example, it may also be that a frequency conversion unit is provided in the bubble detection device 1, and the received signal of the receiving wave unit 12 is frequency-converted by the frequency conversion unit. Then, it may also be that the bubble determination unit 25a determines the state of the bubbles in the water based on the frequency data obtained by the frequency conversion by the frequency conversion unit.

[0190] At this time, it is also possible to refer to Figure 9 the (b) part of Figure 10 and as described in the curve graph of the (b) part of Figure 20 when the bubble determination unit 25a generates an amplitude above a specified threshold in the frequency data, it is determined that there are bubbles in the water. Additionally, it is also possible to refer to Figure 19 the (a) part of Figure 20 and as described in the curve graph of the (b) part of

[0191] when the bubble determination unit 25a generates an amplitude above a specified threshold in a frequency band within a specified range including the transmission frequency of the sound wave transmitted by the transmission wave unit 11, it is determined that there are bubbles in the water. Additionally, it is also possible to refer to

[0192] the (a), (b) parts of

[0193] and as described in the curve graph of the (b) part of Figure 5As shown, the surface 111b of the first wave transmitting / receiving section 111 and the surface 112b of the second wave transmitting / receiving section 112 are inclined from the state of facing the same direction toward the direction of facing each other, but are not limited thereto. The surface 111b and the surface 112b may also be inclined from the state of facing the same direction toward the direction opposite to the direction of facing each other.

[0194] In addition, the central axis 111c of the first region 111a and the central axis 112c of the second region 112a may also be parallel to each other. That is, the surface 111b of the first wave transmitting / receiving section 111 and the surface 112b of the second wave transmitting / receiving section 112 may also be parallel to each other. In this case, the first wave transmitting / receiving section 111 and the second wave transmitting / receiving section 112 are arranged such that a predetermined distance is provided between the first wave transmitting / receiving section 111 and the second wave transmitting / receiving section 112 so that the first region 111a and the second region 112a do not overlap.

[0195] In addition, in the above-described Embodiment 1, the display device 30 may be omitted. In this case, the determination result of the state of the bubbles by the bubble determination unit 25a is transmitted to an external display device, and the determination result of the state of the bubbles is displayed on the external display device. In addition, in the above-described Embodiment 2, the display device 130 may be omitted. In this case, the ship speed calculated by the speed calculation unit 340 and the determination result of the state of the bubbles by the bubble determination unit 330 are transmitted to an external display device, and the ship speed and the determination result of the state of the bubbles are displayed on the external display device.

[0196] In addition, in the above-described Embodiment 2, in the speed calculation unit 340, the ship speed relative to water is calculated as the ship speed, but the ship speed relative to the ground may also be calculated. The ship speed relative to water is calculated based on the reflected waves from plankton and fine particles, but the ship speed relative to the ground is calculated based on the reflected waves from the seabed. In the case of the ship speed relative to the ground, similar to the ship speed relative to water, in the frequency data obtained by respectively performing frequency conversion on the first speed signal and the second speed signal, the frequency shift relative to the original sound wave is measured, and the ship speed relative to the ground is calculated based on the measured frequency shift amount.

[0197] In this way, in the case of calculating the ship speed relative to the ground, it is also determined whether the ship speed relative to the ground calculated in each cycle is appropriate based on the bubble signal obtained corresponding to the transmission of the sound wave for calculating the ship speed relative to the ground. Then, the current ship speed relative to the ground is calculated based on the ship speeds relative to the ground in a plurality of cycles up to the present.

[0198] In addition, in the above-described Embodiment 2, in the case of further calculating the ship speed relative to the ground, the speed of the ocean current may also be calculated based on the ship speed relative to water and the ship speed relative to the ground.

[0199] In addition, in the above-described Embodiment 2, the determination of the state of the bubbles in the water is based on both the second acoustic wave received by the first transceiver unit 111 and the first acoustic wave received by the second transceiver unit 112. However, the determination of the state of the bubbles in the water may also be based on either the second acoustic wave received by the first transceiver unit 111 or the first acoustic wave received by the second transceiver unit 112. In this case, frequency conversion is performed on either the signal of the second acoustic wave received by the first transceiver unit 111 (the first bubble signal) or the signal of the first acoustic wave received by the second transceiver unit 112 (the second bubble signal), and the state of the bubbles is determined based on the generated frequency data.

[0200] In addition, in the above-described Embodiment 2, the ship speed measuring device 2 may further include: a correction unit that corrects the first speed signal based on the second bubble signal and corrects the second speed signal based on the first bubble signal. For example, the correction unit subtracts the frequency data generated by performing frequency conversion on the second bubble signal from the frequency data generated by performing frequency conversion on the first speed signal, calculates the frequency data based on the corrected first speed signal, subtracts the frequency data generated by performing frequency conversion on the first bubble signal from the frequency data generated by performing frequency conversion on the second speed signal, and calculates the frequency data based on the corrected second speed signal. Then, the speed calculation unit 340 calculates the ship speed based on the corrected first speed signal and the second speed signal. Thereby, the influence of the bubbles on the signals (the first speed signal and the second speed signal) used for calculating the ship speed is suppressed, and it is possible to expect a more accurate calculation of the ship speed.

[0201] Furthermore, in the above-described Embodiment 2, the measurement of the ship speed is aborted according to the state of the bubbles, so the measurement result of the ship speed is not affected by the bubbles. Therefore, there is no need to arrange the first transceiver unit 111 and the second transceiver unit 112 at the bow 40a in order to avoid the influence of the bubbles. Therefore, there is no need to lay long wiring cables between the first transceiver unit 111 and the second transceiver unit 112 and the control device 120 arranged in the steering room 41 or the like, and the installation cost of the ship speed measuring device 2 can be significantly reduced.

[0202] In addition, in the above-described Embodiment 2, as Figure 7As shown, the received signals are directly input from the first A / D conversion circuit 231 and the second A / D conversion circuit 232 to the signal processing circuit 240, but a buffer memory may also be provided between the first A / D conversion circuit 231, the second A / D conversion circuit 232, and the signal processing circuit 240. In this case, the frequency conversion unit and the Doppler measurement unit are regarded as one system, and the received signals are read out from the buffer memory in a time-division manner and processed by the frequency conversion unit and the Doppler measurement unit. The speed calculation unit 340 calculates the ship speed based on the first speed signal and the second speed signal according to the Doppler frequency shift amounts received in a time-division manner. In addition, the bubble determination unit 330 determines bubbles based on the first bubble signal and the second bubble signal according to the frequency data received in a time-division manner.

[0203] In addition, in the above-described Embodiment 2, the configuration in the case where the bubble detection device according to the present invention is applied to the ship speed measurement device 2 is shown, but the bubble detection device according to the present invention is not limited to being applied to the ship speed measurement device 2, and can also be appropriately applied to other devices such as a target detection device for detecting an object in water or an underwater detection device. For example, when the bubble detection device is applied to the target detection device, the screen (detection screen) indicating the detection result of the target may be invalidated corresponding to the generation of a specified amount or more of bubbles in water.

[0204] The embodiments of the present invention can be appropriately modified in various ways within the scope described in the claims.

Claims

1. An underwater detection device is provided on a ship, characterized in that Comprising: A first oscillator that transmits acoustic waves to a first area in water; A second oscillator that receives the acoustic waves reflected by bubbles present in the first area and then reflected by bubbles present in a second area different from the first area; And A bubble determination unit that determines the state of bubbles in water based on a received signal output from the second oscillator corresponding to the acoustic waves transmitted by the first oscillator.

2. The underwater detection device according to claim 1, wherein The central axis of the transmission beam of the first oscillator is not parallel to the central axis of the reception beam of the second oscillator.

3. The underwater detection device according to claim 2, wherein The transmission wavefront of the first oscillator and the reception wavefront of the second oscillator are inclined at a prescribed angle from a state of facing the same direction to a state of facing each other.

4. The underwater detection device according to any one of claims 1 to 3, characterized in that Further comprising: A speed calculation unit that calculates the ship speed; and A display unit that displays the ship speed calculated by the speed calculation unit and information related to the state of bubbles determined by the bubble determination unit.

5. The underwater detection device according to claim 4, wherein On the display unit, the ship speed and the information related to the state of bubbles are displayed side by side.

6. The underwater detection device according to claim 5, wherein Based on the state of bubbles in water determined by the bubble determination unit, it is switched whether to display the ship speed on the display unit.

7. The underwater detection device according to claim 4, wherein The speed calculation unit calculates the ship speed when the bubble determination unit determines that there are no bubbles in water.

8. The underwater detection device according to any one of claims 1 to 3, characterized in that, Comprising: A frequency conversion unit that performs frequency conversion on the received signal received by the second oscillator to generate frequency data, The bubble determination unit determines the state of bubbles in water based on the frequency data generated by the frequency conversion unit.

9. The underwater detection device according to claim 8, wherein When an amplitude equal to or greater than a prescribed threshold is generated in the frequency data, the bubble determination unit determines that there are bubbles in water.

10. The underwater detection device according to claim 9, wherein In the frequency data, when an amplitude equal to or greater than the prescribed threshold is generated in a frequency band within a prescribed range including the frequency of the acoustic waves transmitted from the first oscillator, the bubble determination unit determines that there are bubbles in water.

11. The underwater detection device according to claim 8, wherein The bubble determination unit determines the amount of bubbles present in water based on the amount of signals having an amplitude equal to or greater than a prescribed threshold in the frequency data.

12. The underwater detection device according to any one of claims 1 to 3, wherein Among the first area and the second area, one area faces the bow direction and the other area faces the stern direction.

13. A bubble detection method, characterized in that Acoustic waves are transmitted from the bottom of the ship to a transmission wave area in water, The transmitted acoustic waves are received after being reflected by bubbles present in the transmission wave area and then reflected by bubbles present in a reception wave area different from the transmission wave area. Based on the received wave state of the said sound wave, determine the state of the bubbles in water.

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