Ultrasonic device, ultrasonic incident angle calculation method, and program

Abstract

To provide an ultrasonic device, an ultrasonic incident angle calculation method, and a program, which can more accurately calculate an incident angle of ultrasonic waves on fish.SOLUTION: An ultrasonic device 1 includes: an ultrasonic transducer 10 that sequentially transmits a plurality of transmission waves toward a fish and generates an echo signal for each of the transmission waves; a fish echo tracking portion 32 that tracks in time an echo of the fish from the echo signals; a fish speed calculation portion 33 that calculates a swimming speed of the tracked fish from the tracked echoes of the fish; an ultrasonic incident angle calculation portion 34 that calculates an ultrasonic incident angle θ of the plurality of transmission waves on the tracked fish on the basis of a position of the fish relative to the ultrasonic transducer 10; and an angle correction portion 35 that corrects the ultrasonic incident angle θ on the basis of the swimming speed of the fish.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an ultrasonic device for fish detection, an ultrasonic incident angle calculation method for calculating the incident angle of ultrasonic waves with respect to fish, and a program for causing a computer to execute a function for calculating the incident angle of ultrasonic waves with respect to fish.

Background Art

[0002] Conventionally, a device for transmitting a transmission wave into water and measuring the size of a fish based on the reflected wave thereof has been known. In the echo signal from the fish, peaks occur at the timings when the reflected waves from the swim bladder, back, and belly are received. For example, the distance from the back to the swim bladder (upper body height) of the fish can be calculated from the time difference between the peak from the back and the peak from the swim bladder. Alternatively, the distance from the back to the belly (body height) of the fish can be calculated from the time difference between the peak from the back and the peak from the belly. By applying the distances between these parts to a predetermined calculation formula, the size (body length, weight, etc.) of the fish can be calculated.

[0003] However, the distance between the parts calculated from the fish can vary depending on the incident angle of the ultrasonic waves with respect to the fish. For example, when the ultrasonic waves are transmitted directly downward, the incident angle of the ultrasonic waves incident on the fish is larger when the fish swims diagonally downward than when the fish swims horizontally. Therefore, the distance between the parts calculated when the fish swims diagonally downward is larger than the distance between the parts calculated when the same fish swims horizontally. Thus, even for the same fish, if there is a difference in the calculation result of the distance between the parts depending on the swimming direction, the size of the fish cannot be accurately calculated.

[0004] Such a problem can be solved by calculating the incident angle of the ultrasonic waves with respect to the fish from the swimming direction of the fish and calculating the size of the fish based on the calculated incident angle and the distance between the above parts. The following Patent Document 1 discloses this type of fish body size calculation device.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2022-158950 Summary of the Invention Problems to be Solved by the Invention

[0006] However, the posture of the fish, that is, the orientation connecting the tip of the upper jaw from the fork of the tail (the concave central part of the tail fin), is not necessarily parallel to the swimming direction of the fish. When the posture of the fish tilts up and down with respect to the swimming direction, the incident angle of the ultrasonic wave with respect to the fish changes accordingly. Therefore, it may happen that the incident angle of the ultrasonic wave cannot be accurately calculated only from the swimming direction of the fish.

[0007] In view of such problems, an object of the present invention is to provide an ultrasonic device, an ultrasonic incident angle calculation method, and a program capable of more accurately calculating the incident angle of an ultrasonic wave with respect to a fish. Means for Solving the Problems

[0008] A first aspect of the present invention relates to an ultrasonic device for fish detection. The ultrasonic device according to this aspect continuously transmits a plurality of transmission waves toward a fish, an ultrasonic transceiver that generates an echo signal for each transmission wave, a fish echo tracking unit that temporally tracks the echo of the fish from the echo signal, a fish speed calculation unit that calculates the swimming speed of the tracked fish from the tracked fish echo, an ultrasonic incident angle calculation unit that calculates the ultrasonic incident angle of the plurality of transmission waves with respect to the tracked fish based on the position of the fish with respect to the ultrasonic transceiver, and an angle correction unit that corrects the ultrasonic incident angle based on the swimming speed of the fish.

[0009] As a result of intensive research, the inventor has found that the posture of a fish changes according to the swimming speed of the fish. That is, the inventor has found that the posture of the fish is not necessarily parallel to the swimming direction, and depending on the swimming speed, it tilts from the swimming direction. Furthermore, the inventor has found that this tilt changes according to the swimming speed of the fish. From this, the ultrasonic incident angle of the transmitted wave with respect to the fish can change depending on the swimming speed of the fish. Based on this finding, the inventor considered that by further taking into account the tilt of the posture due to the swimming speed of the fish, the ultrasonic incident angle with respect to the fish can be calculated more accurately.

[0010] According to the ultrasonic device according to this aspect, the ultrasonic incident angle calculated based on the position of the fish with respect to the ultrasonic transmitter / receiver is corrected based on the swimming speed of the fish by the above finding. Therefore, the ultrasonic incident angle with respect to the fish can be calculated more accurately.

[0011] In the ultrasonic device according to this aspect, the angle correction unit may be configured to correct the ultrasonic incident angle with a correction value that changes as a function of the swimming speed.

[0012] The tilt of the fish's posture with respect to the swimming direction changes according to a predetermined function in response to a change in the swimming speed. Therefore, according to this configuration, the ultrasonic incident angle can be appropriately corrected with a correction value that changes as a function of the swimming speed.

[0013] In this configuration, the correction value may be obtained from the relationship between a predetermined correction value and the swimming speed of the fish.

[0014] According to this configuration, the correction value of the ultrasonic incident angle can be smoothly obtained from the relationship between the predetermined correction value and the swimming speed of the fish based on the above function.

[0015] In the ultrasonic device according to this aspect, the angle correction unit may be configured to correct the ultrasonic incident angle with a correction value that linearly changes with the swimming speed.

[0016] The relationship between the swimming speed of the fish and the correction value (the inclination of the fish's posture with respect to the swimming direction) can be approximated by a predetermined correlation line. Therefore, according to this configuration, the ultrasonic incident angle can be appropriately corrected by the correction value that linearly changes with the swimming speed.

[0017] In the ultrasonic device according to this aspect, when v is the swimming speed and a and b are coefficients determined in advance according to the fish species, the angle correction unit may be configured to correct the ultrasonic incident angle with a correction value according to the formula a×v + b.

[0018] The above-mentioned correlation line is different for each fish species. Therefore, when the correlation line is expressed as a×v + b from the coefficients a, b and the swimming speed of the fish, the coefficients a, b are different for each fish species. Therefore, according to this configuration, since the correction value is obtained by the formula a×v + b from the coefficients a, b determined in advance for each fish species, the ultrasonic incident angle with respect to the fish can be appropriately corrected for each fish species.

[0019] In the ultrasonic device according to this aspect, the angle correction unit may be configured to correct the ultrasonic incident angle when the swimming speed is lower than the threshold speed, and not correct the ultrasonic incident angle when the swimming speed is equal to or higher than the threshold speed.

[0020] The posture of the fish inclines with respect to the swimming direction of the fish in the range where the swimming speed is low, but becomes substantially parallel to the swimming direction of the fish in the range where the swimming speed is high. Therefore, according to this configuration, since the ultrasonic incidence is corrected only when the swimming speed is lower than the threshold speed, the ultrasonic incident angle can be smoothly corrected according to the swimming speed.

[0021] In the ultrasonic device according to this aspect, the fish speed calculation unit may be further configured to normalize the swimming speed by the size of the fish.

[0022] The swimming speed of a fish is said to be proportional to the body length of the fish. The body length of the fish has a predetermined correlation with various fish sizes such as the upper body height and body height. Therefore, according to this configuration, the correction value of the ultrasonic incident angle is obtained from the relationship between the swimming speed of the fish and the correction value when the swimming speed is normalized by the fish size, so that the correction value can be appropriately obtained.

[0023] In this case, the size of the fish may be the size of the fish in the height direction of the fish (upper body height, body height, etc.).

[0024] Alternatively, the size of the fish may be the size of the fish in the length direction of the fish (body length, fork length of the tail, etc.).

[0025] In the ultrasonic device according to this aspect, the correction of the ultrasonic incident angle may vary depending on the fish species.

[0026] The relationship between the swimming speed of the fish and the correction value (the inclination of the fish's posture with respect to the swimming direction) varies depending on the fish species. Therefore, according to this configuration, the ultrasonic incident angle can be appropriately corrected.

[0027] The second aspect of the present invention relates to an ultrasonic incident angle calculation method for calculating the ultrasonic incident angle of a transmission wave with respect to a fish. The ultrasonic incident angle calculation method according to this aspect temporally tracks the echo of the fish from the echo signal generated by receiving, with the ultrasonic wave transceiver, the reflected wave of each transmission wave continuously transmitted from the ultrasonic wave transceiver toward the fish, calculates the swimming speed of the tracked fish from the tracked echo of the fish, calculates the ultrasonic incident angle of the plurality of transmission waves with respect to the tracked fish based on the position of the fish with respect to the ultrasonic wave transceiver, and corrects the ultrasonic incident angle based on the swimming speed of the fish.

[0028] According to the ultrasonic incident angle calculation method according to this aspect, similar to the first aspect, the ultrasonic incident angle with respect to the fish can be calculated more accurately.

[0029] The third aspect of the present invention relates to a program for causing a computer to execute processing functions. The program according to this aspect causes a computer to execute a function of temporally tracking the echo of a fish from echo signals generated by receiving, with the ultrasonic transmitter / receiver, reflected waves of each transmission wave continuously transmitted from the ultrasonic transmitter / receiver toward the fish, a function of calculating the swimming speed of the tracked fish from the tracked echo of the fish, a function of calculating the ultrasonic incident angle of the plurality of transmission waves with respect to the tracked fish based on the position of the fish with respect to the ultrasonic transmitter / receiver, and a function of correcting the ultrasonic incident angle based on the swimming speed of the fish.

[0030] According to the program according to this aspect, similar to the first aspect, the ultrasonic incident angle with respect to the fish can be calculated more accurately.

Advantages of the Invention

[0031] As described above, according to the present invention, it is possible to provide an ultrasonic device, an ultrasonic incident angle calculation method, and a program capable of more accurately calculating the incident angle of ultrasonic waves with respect to a fish.

[0032] The effects or significance of the present invention will become clearer from 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 to those described in the following embodiments at all.

Brief Description of the Drawings

[0033]

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DETAILED DESCRIPTION OF THE INVENTION

[0034] The functions realized by the components described in this specification may be implemented in a circuit or processing circuit including a general-purpose processor, a specific-purpose processor, an integrated circuit, ASICs (Application Specific Integrated Circuits), a CPU (a Central Processing Unit), a conventional circuit, and / or a combination thereof, programmed to realize the described functions. The processor includes transistors and other circuits and is regarded as a circuit or processing circuit. The processor may be a programmable processor that executes a program stored in a memory.

[0035] In this specification, a circuit, unit, and means are hardware programmed to realize the described functions or hardware that executes this function. The hardware may be any hardware disclosed in this specification or any hardware known to be programmed to realize the described functions or to execute this function.

[0036] When the hardware is a processor regarded as a type of circuit, the circuit, means, or unit is a combination of hardware and software used to configure the hardware and / or the processor.

[0037] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments show an example in which the present invention is applied to an ultrasonic device installed in a fish cage. However, the present invention is not limited to the following embodiments in any way.

[0038] FIG. 1 is a perspective view showing a usage form of the ultrasonic device 1.

[0039] As shown in FIG. 1, in this embodiment, the ultrasonic device 1 is used in a fish cage 2 installed in the sea for fish farming. The fish cage 2 includes a frame 3, a float 4, a net 5, and a pier 6.

[0040] The frame 3 is formed in a loop shape in plan view. A plurality of floats 4 are attached to the frame 3. Due to the buoyancy of the floats 4, the frame 3 floats on the water surface. The frame 3 is connected to a weight on the bottom of the water by a mooring rope (not shown).

[0041] The upper end of the net 5 is fixed to the frame 3. The net 5 is suspended from the frame 3 so as to partition the water and form a closed space. Fish are bred inside this closed space. A pier 6 for performing various operations in aquaculture is fixed on the frame 3.

[0042] A float 7 is floated approximately at the center inside the frame 3. The float 7 is connected to the pier 6 by a rope. An ultrasonic transmitter / receiver 10, a transmission / reception unit 20, and a signal processing unit 30 that constitute the ultrasonic device 1 are installed on this float 7. As will be described later, the ultrasonic device 1 further has an operation display unit 40 (see FIG. 2), but in FIG. 1, the illustration of the operation display unit 40 is omitted. The operation display unit 40 is an interface for operation input and display for the ultrasonic device 1. The operation display unit 40 may be detachable from the signal processing unit 30.

[0043] The ultrasonic transmitter / receiver 10 is arranged vertically downward and transmits ultrasonic waves (transmission waves TS) downward from near the water surface into the water. The ultrasonic transmitter / receiver 10 continuously transmits a plurality of transmission waves TS toward the fish and generates an echo signal for each transmission wave TS.

[0044] FIG. 2 is a block diagram showing the configuration of the ultrasonic device 1.

[0045] The ultrasonic device 1 includes an ultrasonic transmitter / receiver 10, a transmission / reception unit 20, a signal processing unit 30, and an operation display unit 40.

[0046] The ultrasonic transceiver 10 can mutually convert an electrical signal and ultrasonic vibrations. The ultrasonic transceiver 10 includes a transmitter 11 and a receiver 12. The transmitter 11 includes one element (ultrasonic vibrator), and the receiver 12 includes a plurality of elements (ultrasonic vibrators) divided into four reception channels.

[0047] The transmitter 11 transmits a pulsed transmission wave toward the water. In order to improve the resolution in the depth direction, it is preferable to transmit the transmission wave with a pulse as short as possible. Each reception channel of the receiver 12 receives a reflected wave reflected from an underwater target. The ultrasonic transceiver 10 transmits an electrical signal (echo signal) based on the received reflected wave to the transceiver unit 20.

[0048] The structure of the ultrasonic transceiver 10 can be changed as appropriate. For example, the ultrasonic transceiver 10 may be configured such that both transmission and reception are performed by a plurality of elements.

[0049] Based on the difference in the timing at which the four reception channels of the ultrasonic transceiver 10 receive the reflected wave, that is, the phase difference of the received reflected wave, the position of the target can be obtained. Thereby, three-dimensional detection by a known split beam method is realized. The position of the target is obtained by the signal processing unit 30. The signal processing unit 30 obtains the position of the target based on the phase difference of the echo signals of the target respectively output from the four reception channels in response to the transmission of one transmission wave.

[0050] The transceiver unit 20 is connected to the ultrasonic transceiver 10 via an electrical cable. The transceiver unit 20 outputs an electrical signal for causing the ultrasonic transceiver 10 to transmit a transmission wave to the ultrasonic transceiver 10 via the electrical cable. The transceiver unit 20 obtains the electrical signal acquired by the ultrasonic transceiver 10 based on the reflected wave via the electrical cable. The transceiver unit 20 converts the electrical signal acquired from the ultrasonic transceiver 10 into a received signal that is a digital signal and transmits it to the signal processing unit 30.

[0051] The transmitting and receiving unit 20 amplifies the electrical signals acquired by the above four receiving channels, and further filters them at the frequency of the transmission wave. The transmitting and receiving unit 20 converts the filtered electrical signals into received signals which are digital signals, and transmits them to the signal processing unit 30.

[0052] The signal processing unit 30 is configured as a known computer. The signal processing unit 30 is connected to the transmitting and receiving unit 20 by a communication cable. The signal processing unit 30 communicates with the transmitting and receiving unit 20 via the communication cable. The signal processing unit 30 receives the received signals from the transmitting and receiving unit 20 through the above communication, and sequentially stores the received received signals. The signal processing unit 30 performs fish size calculation processing using the received received signals.

[0053] The signal processing unit 30 includes an arithmetic processing circuit such as a CPU (Central Processing Unit), and storage media such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a hard disk. A program for realizing fish size calculation processing is stored in the storage media. By this program, the functions of a fish echo extraction unit 31, a fish echo tracking unit 32, a fish speed calculation unit 33, an ultrasonic incident angle calculation unit 34, an angle correction unit 35, and a fish size calculation unit 36 are imparted to the signal processing unit 30.

[0054] The fish echo extraction unit 31 extracts the fish echo from the echo signals output from the ultrasonic transceiver 10, and further acquires the position of the fish in water. In response to one transmission wave, echo signals are output from the four receiving channels respectively, and the received signals obtained by converting these echo signals into digital signals are input from the transmitting and receiving unit 20 to the signal processing unit 30. The fish echo extraction unit 31 extracts echo signals equal to or higher than a predetermined threshold value as fish echo signals. The threshold value is set so as to be able to extract fish echo signals.

[0055] FIG. 3 is a diagram showing an example of echo signals output from the ultrasonic transceiver 10.

[0056] For convenience, Fig. 3 shows the portion of the envelope of the echo signal output from one receiving channel by one transmission, near the fish echo signal. In the example of Fig. 3, the threshold value Th1 for extracting the fish echo is set to -60 dB.

[0057] In Figure 3, the horizontal axis represents the time from the transmission timing, and the vertical axis represents the target strength based on the echo signal. Target strength is a parameter that indicates the degree to which a portion of the reflected wave that is scattered when an ultrasonic wave (transmitted wave) hits a target returns in the direction of incidence, and is essentially equivalent to the intensity of the echo signal. Target strength is expressed in decibels. The distance from the ultrasonic transmitter / receiver 10 can be calculated by multiplying the time on the horizontal axis by the speed of sound in water and dividing the result by 2.

[0058] The fish echo signal contains multiple peaks P10 to P13, which are based on reflected waves from various parts of the fish, such as the back, swim bladder, and belly. Of these peaks, swim bladder peak P10 is the largest. The fish echo extraction unit 31 extracts the swim bladder peak P10, which is the largest peak, from the echo signals of the four receiving channels. The signal processing unit 30 identifies the position of the fish's swim bladder relative to the ultrasonic transmitter / receiver 10 using the split beam method based on the phase difference between these four swim bladder peaks P10 and the time from the transmission timing to the reception timing of these swim bladder peaks P10, i.e., the distance from the ultrasonic transmitter / receiver 10 to the swim bladder, and obtains the identified swim bladder position as the fish's position relative to the ultrasonic transmitter / receiver 10.

[0059] Note that the position of the fish does not necessarily have to be obtained as the position of the fish's swim bladder, and it may be obtained as the position of other parts, such as the position of the fish's back. For example, when the position of the fish's back is used as the position of the fish, the signal processing unit 30 performs the above processing on the peak P11 that is the peak from the back, thereby identifying the position of the fish's back with respect to the ultrasonic transceiver 10, and obtaining the identified position of the back as the position of the fish with respect to the ultrasonic transceiver 10. Similarly, the position of the fish may be obtained using the peak P12 from the dorsal fin or the peak P13 from the abdomen.

[0060] Returning to FIG. 2, the fish echo tracking unit 32 tracks the fish echo over time from the echo signal output from the ultrasonic transceiver 10. That is, when the position of the fish obtained by the fish echo extraction unit 31 in the current transmission wave is substantially the same as any of the positions of the fish obtained by the fish echo extraction unit 31 in the previous transmission wave, the fish echo tracking unit 32 estimates that the fish echo signals corresponding to the positions of these two fish at substantially the same position are echo signals from the same fish. In this way, the fish echo tracking unit 32 tracks the echo signals from the same fish over time.

[0061] Whether the positions of the fish in the previous and current times are substantially the same can be determined by whether these two fish positions are included within the range of the distance that the fish can swim during the transmission period of the transmission wave. The tracking of the fish may include, for example, prediction using a Kalman filter, and a sophisticated tracking algorithm for fish tracking may be adopted.

[0062] The fish speed calculation unit 33 calculates the swimming speed of the tracked fish from the fish echo tracked by the fish echo tracking unit 32. For example, the fish speed calculation unit 33 calculates the swimming speed of the fish at the current position of the fish based on the distance between the tracked positions of the fish in the current and previous times and the time difference between the timings at which these two fish positions were respectively obtained.

[0063] The ultrasonic incident angle calculation unit 34 calculates the ultrasonic incident angle of the transmission wave with respect to the tracked fish based on the position of the fish with respect to the ultrasonic transceiver 10.

[0064] FIG. 4 is a diagram schematically showing a method for calculating the ultrasonic incident angle of a transmission wave with respect to a tracked fish.

[0065] In FIG. 4, tracked fish F1 and F1' are illustrated. Fish F1 is a fish at which position P1 (the position of the swim bladder) was acquired in the current wave transmission, and fish F1' is a fish at which position P1 (the position of the swim bladder) was acquired in a past wave transmission. The ultrasonic incident angle calculation unit 34 acquires, as the swimming direction D1 of fish F1, the direction from the position P1 acquired in the previous wave transmission to the position P1 acquired in the current wave transmission. The ultrasonic incident angle calculation unit 34 calculates the ultrasonic incident angle θ from the angle θa formed between the straight line L1 connecting the position P1 of fish F1 and the ultrasonic transmitter / receiver 10 and the swimming direction D1 of fish F1 by the following formula.

[0066] Ultrasonic incident angle θ = 90° - included angle θa...(1)

[0067] That is, the ultrasonic incident angle θ is the supplementary angle of the angle θa formed between the straight line L1 and the swimming direction D1 of fish F1.

[0068] Similarly, the ultrasonic incident angle θ of the transmission wave with respect to fish F1' is acquired as the supplementary angle of the angle θa formed between the straight line L1' connecting the position P1 of fish F1' and the ultrasonic transmitter / receiver 10 and the swimming direction D1 of fish F1'. Note that the angle θa formed between the straight line connecting the position of the fish and the ultrasonic transmitter / receiver 10 and the swimming direction of the fish may be acquired as the ultrasonic incident angle θ.

[0069] Returning to FIG. 2, the angle correction unit 35 corrects the ultrasonic incident angle θ calculated by the ultrasonic incident angle calculation unit 34 based on the swimming speed of the fish calculated by the fish speed calculation unit 33.

[0070] That is, as described above, the ultrasonic incident angle calculation unit 34 calculates the supplementary angle of the angle θa formed by the straight line L1 connecting the position P1 of the fish and the ultrasonic transmitter / receiver 10 and the swimming direction D1 of the fish as the ultrasonic incident angle θ of the transmitted wave with respect to the fish. However, the posture of the fish is not necessarily parallel to the swimming direction D1 of the fish. When the posture of the fish is inclined vertically with respect to the swimming direction D1, the ultrasonic incident angle θ with respect to the fish changes accordingly. Therefore, when the ultrasonic incident angle θ is calculated from the swimming direction D1 of the fish in the ultrasonic incident angle calculation unit 34, the ultrasonic incident angle θ may become inaccurate.

[0071] FIG. 5(a) is a diagram showing the acquisition state of the ultrasonic incident angle θ when the posture of the fish F1 is parallel to the swimming direction D1, and FIG. 5(b) is a diagram showing the acquisition state of the ultrasonic incident angle θ when the posture of the fish F1 is inclined downward by an angle θb from the swimming direction D1.

[0072] As shown in FIG. 5(a), when the posture of the fish F1 is parallel to the swimming direction D1 of the fish F1, the ultrasonic incident angle θ calculated by the above formula (1) coincides with the actual incident angle of the transmitted wave with respect to the fish F1, that is, the angle formed by the straight line L2 extending in the body height direction of the fish F1 from the position P1 and the straight line L1. On the other hand, as shown in FIG. 5(b), when the posture of the fish F1 is inclined downward by an angle θb from the swimming direction D1 of the fish F1, the ultrasonic incident angle θ calculated by the above formula (1) is smaller by an angle θb than the actual incident angle θ' of the transmitted wave with respect to the fish F1, that is, the angle θ' formed by the straight line L2 and the straight line L1.

[0073] When the posture of the fish F1 is not parallel to the swimming direction D1 as shown in FIG. 5(b), the angle correction unit 35 acquires the angle θb as a correction value, and corrects the ultrasonic incident angle θ calculated by the ultrasonic incident angle calculation unit 34 with the acquired correction value. In the example of FIG. 5(b), the angle correction unit 35 adds the angle θb, which is the correction value, to the ultrasonic incident angle θ calculated by the ultrasonic incident angle calculation unit 34 to obtain the corrected ultrasonic incident angle θ'. The method for acquiring the angle θb, which is the correction value, will be described later with reference to FIGS. 6(a) to 8(b).

[0074] Returning to FIG. 2, the fish size calculation unit 36 calculates the size of the fish based on the echo signal. For example, in the echo signal of the fish shown in FIG. 3, the fish size calculation unit 36 calculates the fish's upper body height (the distance from the back to the swim bladder) from the time difference between peak P10 at the swim bladder and peak P11 at the back. The fish size calculation unit 36 applies the calculated upper body height to a predetermined conversion formula to calculate the fish's fork length, body length, withers height, weight, etc. For example, the weight W of the fish can be calculated by applying the fish's upper body height UBH to the following conversion formula:

[0075] W=α·UBH β …(2)

[0076] The coefficients α and β in equation (2) differ depending on the fish species.

[0077] Here, even for the same fish, if the ultrasonic incident angle of the transmitted wave changes, the time difference between peak P10 on the swim bladder and peak P11 on the back will change. Therefore, the fish's upper body height UBH, calculated from the time difference between these peaks, will also change as the ultrasonic incident angle changes, and the calculated fish size will also change. Furthermore, the coefficients α and β in the above equation (2) are set based on the case where the ultrasonic incident angle to the fish is a predetermined angle.

[0078] Therefore, in order to accurately calculate the size of the fish in the fish cage 2, it is preferable to obtain the upper body height UBH from the echo signal of a fish whose ultrasonic incident angle θ' corrected by the angle correction unit 35 substantially matches the standard ultrasonic incident angle used as the setting standard for the above coefficients α and β, and then apply the obtained upper body height UBH to a predetermined conversion formula to calculate the size of the fish (fork length, body length, body height, weight, etc.).

[0079] The fish size calculation unit 36 extracts only the echo signals of fish in which the ultrasonic incident angle θ’ substantially matches the reference ultrasonic incident angle among the echo signals of fish acquired by a series of transmitted waves. The fish size calculation unit 36 calculates the upper body height UBH of the fish from the extracted echo signals of the fish, applies the calculated upper body height UBH to the conversion formula, and calculates the size of the fish (fork length, body length, body height, weight, etc.) corresponding to the extracted echo signals of the fish. The fish size calculation unit 36 acquires, for example, the median value of the calculated fish size (fork length, body length, body height, weight, etc.) as the fish size in the fish basket 2.

[0080] Next, a method for obtaining the correction value in the angle correction unit 35 of FIG. 2 will be described.

[0081] As a result of intensive research, the inventor has found that the posture of a fish changes depending on the swimming speed of the fish. That is, the inventor has found that the posture of the fish is not necessarily parallel to the swimming direction and may be inclined from the swimming direction depending on the swimming speed. Furthermore, the inventor has found that this inclination changes according to the swimming speed of the fish. From this, the ultrasonic incident angle of the transmitted wave with respect to the fish can change depending on the swimming speed of the fish. Based on this finding, the inventor thought that by further considering the inclination of the posture due to the swimming speed of the fish, the ultrasonic incident angle with respect to the fish can be calculated more accurately.

[0082] FIG. 6(a) is a graph showing the measurement results of the relationship between the swimming speed of fish and the posture of fish in a fish basket for breeding amberjack.

[0083] In FIG. 6(a), the horizontal axis represents the average value of the swimming speed of the fish (average swimming speed), and the vertical axis represents the average value of the inclination angle of the posture of the fish with respect to the swimming direction of the fish (average posture angle). The average posture angle on the vertical axis is a negative value when the posture (face) of the fish faces downward with respect to the swimming direction of the fish, and a positive value when the posture (face) of the fish faces upward with respect to the swimming direction of the fish. The measurement results in a plurality of different fish baskets are integrated in the measurement results of FIG. 6(a). The measurement results are plotted in the graph of FIG. 6(a).

[0084] As shown in Fig. 6(a), the posture of the fish (amberjack) was more downward with respect to the swimming direction as the swimming speed was lower, and approached being parallel to the swimming direction as the swimming speed increased. The correlation between the average swimming speed and the average posture angle can be defined by the correlation straight line L11, or can be defined by the correlation curve L12. According to the correlation straight line L11, the average posture angle of the fish (amberjack) can be expressed by the following formula from the swimming speed v.

[0085] Average posture angle = k×(v0 - v) …(3)

[0086] Here, v0 is the reference speed when the posture of the fish is parallel to the swimming direction. For example, the average swimming speed when the average posture angle is 0 in the correlation straight line L11 of Fig. 6(a) can be obtained as the reference speed v0. Also, k is a correction coefficient and corresponds to the slope of the correlation straight line L11.

[0087] The average posture angle shown on the vertical axis of Fig. 6(a) corresponds to the angle θb in Fig. 5(b). In formula (3), since the average posture angle has a negative value when the fish is downward, the value obtained by attaching a negative sign to the average posture angle calculated by formula (3) becomes the correction value for the ultrasonic incident angle θ. Therefore, the correction value can be calculated by the following formula.

[0088] Correction value = -k×(v0 - v) …(4)

[0089] Therefore, the corrected ultrasonic incident angle θ’ can be calculated by the following formula.

[0090] θ’ = θ - k×(v0 - v) …(5)

[0091] The angle correction unit 35 in Fig. 2 may correct the ultrasonic incident angle θ calculated by the ultrasonic incident angle calculation unit 34 using the swimming speed v of the fish calculated by the fish speed calculation unit 33 according to formula (5).

[0092] However, the correlation line L11 shown in Fig. 6(a) has a positive average attitude angle in a range where the average swimming speed is higher than the reference speed v0 which is the average swimming speed when the average attitude angle is 0. This indicates that in this speed range, the fish's attitude is upward with respect to the swimming direction. However, the actual attitude of the fish is maintained in a state almost parallel to the swimming direction in a range where the average swimming speed is higher than the reference speed v0. Therefore, when the fish's swimming speed is higher than the reference speed v0, it can be said that it is better not to correct the ultrasonic incident angle θ by the above formula (5).

[0093] From this, when the swimming speed v of the fish calculated by the fish speed calculation unit 33 is less than or equal to the reference speed v0 (threshold speed), the angle correction unit 35 in Fig. 2 applies the above formula (5) to correct the ultrasonic incident angle θ. When the swimming speed v is higher than the reference speed v0 (threshold speed), the ultrasonic incident angle θ calculated by the ultrasonic incident angle calculation unit 34 may be directly used as the ultrasonic incident angle of the transmitted wave with respect to the fish without performing the correction by formula (5). That is, the angle correction unit 35 may perform correction processing according to the following formula.

[0094] If v>v0θ’=θ …(6) If v≦v0θ’=θ-k×(v0-v) …(7)

[0095] It should be noted that the swimming speed of the fish is said to be proportional to the body length of the fish. Therefore, the horizontal axis in Fig. 6(a) may be normalized by the body length of the fish. In this case, the graph in Fig. 6(a) changes as shown in Fig. 6(b). In Fig. 6(b), the average swimming speed at each plot in Fig. 6(a) is normalized by the average body length (gauge value) of the fish at these plots. In the graph of Fig. 6(b), the correlation between the average swimming speed and the average attitude angle is higher than that in the graph of Fig. 6(a).

[0096] In the graph of Fig. 6(b), the correlation relationship between the average swimming speed and the average attitude angle can be defined by the correlation line L21 or the correlation curve L22. According to the correlation line L21, the above formula (5) is transformed into the following formula.

[0097] θ'=θ-k×{v 0_FL -(v / FL)} …(8)

[0098] where v 0_FL is the reference speed when the fish's posture is parallel to the swimming direction, and corresponds to the average swimming speed when the average posture angle on the correlation line L21 is 0. Also, FL is the average body length of the fish in each plot.

[0099] In this case, the above equations (6) and (7) are transformed into the following equations, respectively.

[0100] If v / FL>v 0_FL θ'=θ …(9) If v / FL≦v 0_FL θ'=θ-k×{v 0_FL -(v / FL)}…(10)

[0101] The angle correction unit 35 may perform correction processing according to the above equations (9) and (10). As described above, the correlation between the average swimming speed and the average attitude angle is higher in the graph of Fig. 6(b) than in the graph of Fig. 6(a). From this point of view, it is estimated that the ultrasonic incident angle θ can be corrected more accurately by using the above equations (9) and (10).

[0102] On the other hand, in equations (9) and (10), it is necessary to calculate the body length FL of the fish from the echo signals. In this case, the fish speed calculation unit 33 calculates the body length FL of the fish from the echo signals extracted by the fish echo extraction unit 31. The body length FL of the fish can be calculated, for example, by applying the upper body height of the fish calculated from the time difference between peaks P10 and P11 in Figure 3 to a predetermined conversion formula.

[0103] However, as described above, since the swimming posture of the fish is not necessarily parallel to the swimming direction of the fish, the calculation result of the upper body height based on the above time difference may include errors. Therefore, this error may affect the correction according to the above formulas (9) and (10). Further, the correction of the ultrasonic incident angle θ is performed to calculate the size of the fish such as the body length and weight of the fish. Therefore, calculating the body length FL of the fish first for the correction of the ultrasonic incident angle θ does not follow the series of calculation processes.

[0104] From these points, the angle correction unit 35 may perform the correction process of the ultrasonic incident angle θ according to the above formulas (6) and (7). Alternatively, after the angle correction unit 35 performs the correction process of the ultrasonic incident angle θ according to the above formulas (9) and (10), the fish size calculation unit 36 may calculate the body length FL of the fish again using the corrected ultrasonic incident angle θ'.

[0105] Also, when performing daily measurements, the average value of the fish body length estimated the previous day may be used as the body length FL in the above formulas (9) and (10) to perform the correction process of the ultrasonic incident angle θ. Alternatively, after obtaining the body length FL etc. once without correcting the incident angle θ, the body length FL may be used as the body length FL in the above formulas (9) and (10) to correct the ultrasonic incident angle θ, and the body length FL etc. may be estimated again using the corrected ultrasonic incident angle θ'.

[0106] In the graph of FIG. 6(b), the average swimming speed is normalized by the average body length of the fish, but the average swimming speed may be normalized by other fish sizes such as the upper body height, body height, and fork length of the fish. When the average swimming speed is normalized by the upper body height of the fish, the fish speed calculation unit 33 calculates the upper body height of the fish from the fish echo signal extracted by the fish echo extraction unit 31 as described above. Also, when the average swimming speed is normalized by the body height or fork length of the fish, the fish speed calculation unit 33 applies the upper body height calculated from the fish echo signal to a predetermined conversion formula to calculate the body height or fork length of the fish.

[0107] Fig. 7(a) is a graph showing the measurement results of the relationship between the swimming speed of fish and the posture of fish in an aquarium for raising yellowtail. Fig. 7(b) is a graph obtained by normalizing the horizontal axis of the graph in Fig. 7(a) with the average body length of the fish. In Fig. 7(b), the average swimming speed at each plot in Fig. 7(a) is normalized with the average body length of the fish at these plots.

[0108] Fig. 8(a) is a graph showing the measurement results of the relationship between the swimming speed of fish and the posture of fish in an aquarium for raising mackerel. Fig. 8(b) is a graph obtained by normalizing the horizontal axis of the graph in Fig. 8(a) with the average body length of the fish. In Fig. 8(b), the average swimming speed at each plot in Fig. 8(a) is normalized with the average body length of the fish at these plots.

[0109] For yellowtail and mackerel as well, based on the correlation line L11 in Figs. 7(a) and 8(a), the ultrasonic incident angle θ can be corrected from the above formulas (6) and (7). However, as can be seen by comparing Figs. 6(a), 7(a) and 8(a), the slopes of the correlation lines L11 are different among amberjack, yellowtail and mackerel, and also the reference speeds v0 are different. Therefore, when using the above formulas (6) and (7) for correcting the ultrasonic incident angle θ, the coefficient k and the reference speed v0 may be changed according to the fish species.

[0110] Similarly, for yellowtail and mackerel as well, based on the correlation line L21 in Figs. 7(b) and 8(b), the ultrasonic incident angle θ can be corrected from the above formulas (9) and (10). Also in this case, the slopes of the correlation lines L21 are different among amberjack, yellowtail and mackerel, and also the reference speed v 0_FL is different, so the coefficient k and the reference speed v 0_FL may be changed according to the fish species.

[0111] Note that the above formula (4), which is the calculation formula for the correction value based on the correlation line L11 in Figs. 6(a), 7(a) and 8(a), is transformed as follows.

[0112] Correction value = -k×(v0 - v) = k×v - k×v0 = a1×v + b1…(11)

[0113] Therefore, the above formula (7), which is the calculation formula for the corrected ultrasonic incident angle θ', is transformed as follows.

[0114] If v ≦ v0 θ' = θ + a1 × v + b1 …(12)

[0115] Therefore, when correcting the ultrasonic incident angle θ based on the correlation straight line L11, the coefficients a1 and b1 in formula (12) may be changed for each fish species.

[0116] Also, the calculation formula for the correction value based on the correlation straight line L21 in FIGS. 6(b), 7(b), and 8(b) is as follows.

[0117] Correction value = -k × {v 0_FL - (v / FL)} = a2 × v + b2…(13)

[0118] Therefore, the above formula (10), which is the calculation formula for the corrected ultrasonic incident angle θ', is transformed as follows.

[0119] If v / FL ≦ v 0_FL θ' = θ + a2 × v + b2 …(14)

[0120] Therefore, when correcting the ultrasonic incident angle θ based on the normalized correlation straight line L21, the coefficients a2 and b2 in formula (14) may be changed for each fish species.

[0121] The angle correction unit 35 may calculate the correction value used for correcting the ultrasonic incident angle θ from the above formula (11) or formula (13). Alternatively, the angle correction unit 35 may hold, as a table, the relationship between the correction value determined in advance based on these formulas and the swimming speed of the fish, and obtain the correction value from this table.

[0122] FIG. 9 is a diagram showing the configuration of a table that defines the relationship between the correction value and the swimming speed of the fish.

[0123] In the table, the swimming speed of the fish is associated with the correction value based on the above formula (11) or (13). The swimming speed is subdivided into predetermined speed intervals. The swimming speed range to which the correction value is associated is v1 to v n When the above formula (11) is used to construct the table, the swimming speed v n corresponds to the reference speed v0. As shown in equation (6), if the swimming speed exceeds the reference speed v0, the ultrasonic incident angle θ is not corrected. Therefore, the table contains the swimming speed v n Similarly, when the above formula (13) is used to construct the table, the swimming speed v n v / FL is the reference speed v 0_FL This corresponds to the swimming speed when the swimming speed v n A correction value of 0 may be associated with the higher speed range.

[0124] The angle correction unit 35 identifies in the table the swimming speed of the fish that is closest to the swimming speed calculated by the fish speed calculation unit 33. The angle correction unit 35 acquires the correction value associated with the identified swimming speed as the correction value for the ultrasonic incident angle θ for the fish. The angle correction unit 35 adds the acquired correction value to the ultrasonic incident angle θ calculated by the ultrasonic incident angle calculation unit 34 to calculate the corrected ultrasonic incident angle θ'.

[0125] As described above, the correlation between the swimming speed of a fish (average swimming speed) and the tilt of the fish's posture relative to the swimming direction (average posture angle) differs for each fish species. For this reason, the table of FIG. 9 may be prepared in the angle correction unit 35 for each fish species. Note that, depending on the fish species, the posture of the fish may be facing upward relative to the swimming direction when the swimming speed is low. For such fish species, the signs of the coefficients a1, a2, b1, and b2 of the correction values may be adjusted according to the correlation between the average swimming speed and the average posture angle, and the table of FIG. 9 may be adjusted accordingly.

[0126] Note that the correction value (average attitude angle) may be obtained from the correlation curves L12 and L22 instead of the correlation lines L11 and L21. For example, the angle correction unit 35 may hold a function representing the correlation curves L12 and L22, apply the swimming speed of the fish to this function, and calculate the correction value (average attitude angle) of this fish. Alternatively, similar to the case of FIG. 9, the angle correction unit 35 may hold a table corresponding to the correlation curves L12 and L22, and obtain the correction value corresponding to the swimming speed of the fish from this table.

[0127] In these cases as well, the angle correction unit 35 may add the obtained correction value to the ultrasonic incident angle θ calculated by the ultrasonic incident angle calculation unit 34 to obtain the corrected ultrasonic incident angle θ'. Also, in these cases as well, similar to the above, the function or table is held by the angle correction unit 35 for each fish species. The angle correction unit 35 corrects the ultrasonic incident angle θ using the function or table corresponding to the specified fish species.

[0128] FIG. 10 is a flowchart showing the calculation process of the size of the fish.

[0129] Prior to the process of FIG. 10, the signal processing unit 30 stores, in time series, a plurality of echo signals for a certain period (for example, for several hours) obtained by each reception channel in a series of carrier waves. The signal processing unit 30 executes the process of FIG. 10 for these echo signals. The fish species of the target fish, that is, the fish cultured in the net cage 2, is input via the operation display unit 40. The signal processing unit 30 executes the process of FIG. 10 using the function or table corresponding to the input fish species.

[0130] In the flowchart of FIG. 10, steps S12, S13, S14, S15, S16, and S17 are respectively executed by the functions of the fish echo extraction unit 31, fish echo tracking unit 32, fish speed calculation unit 33, ultrasonic incident angle calculation unit 34, angle correction unit 35, and fish size calculation unit 36 in FIG. 2. Hereinafter, the description will be made assuming that the signal processing unit 30 performs the process of FIG. 10 by these functions. Steps S12 to S16 correspond to the calculation process of the ultrasonic incident angle of the transmission wave with respect to the fish.

[0131] The signal processing unit 30 sets echo signals for a certain period in time series as processing targets in order (S11). The signal processing unit 30 extracts fish echoes from the echo signals set as processing targets, and obtains the positions of the fish by the split beam method described above (S12). The signal processing unit 30 temporally tracks the fish echoes (fish positions) from the obtained fish positions as described above (S13).

[0132] The signal processing unit 30 calculates the swimming speed of the fish from the tracked fish echoes as described above (S14). The signal processing unit 30 calculates the swimming direction of the fish from the tracked fish echoes, and calculates the ultrasonic incident angle θ based on the swimming direction (S15). The signal processing unit 30 corrects the calculated ultrasonic incident angle θ based on the swimming speed of the fish (S16). Specifically, as described above, the signal processing unit 30 obtains a correction value based on the swimming speed, adds the obtained correction value to the ultrasonic incident angle θ, and calculates the corrected ultrasonic incident angle θ'.

[0133] The signal processing unit 30 calculates the size of the fish (such as the upper body height, body height, body length, fork length of the tail, weight, etc.) only for the fish echo signals in which the corrected ultrasonic incident angle θ' is near a predetermined angle (for example, within a range of plus or minus several degrees with respect to the predetermined angle) among the fish echo signals extracted in step S12, and stores the calculated size of the fish (S17). The information processing unit 30 calculates the upper body height of the fish, for example, from the time difference between peaks P10 and P11 in FIG. 4, and applies the calculated upper body height to a predetermined conversion formula to calculate the size of the fish.

[0134] Here, the predetermined angle in step S17 is the ultrasonic incident angle assumed in the mathematical formula used for calculating the upper body height and other sizes. For example, when the mathematical formula used for calculating the upper body height and other sizes is defined assuming that the transmitted wave is incident perpendicular to the back of the fish, the predetermined angle is set to 0°. The predetermined angle can be set to a preferred angle for each fish species.

[0135] The signal processing unit 30 determines whether or not the processing of steps S12 to S17 has been completed for all echo signals for a certain period of time (S18). If unprocessed echo signals remain (S18: NO), the signal processing unit 30 sets the next echo signal to be processed (S11) and performs the processing from step S12 onwards.

[0136] When the processing of steps S12 to S17 has been completed for all echo signals for a certain period of time (S18: YES), the signal processing unit 30 executes a process of displaying the fish size on the operation and display unit 40 (S19). For example, the signal processing unit 30 calculates the median or average of each of the fish sizes (body height, body height, body length, fork length, weight, etc.) stored in step S17, and displays these calculation results on the operation and display unit 40. This causes the signal processing unit 30 to end the processing of FIG. 10.

[0137] The inventors performed the following measurements to confirm the effectiveness of the correction process in step S16. The inventors calculated the weights of fish cultured in the fish pen 2 by performing the process of FIG. 10 on multiple days. The correction in step S16 used the above equations (9) and (10). For the fish body length FL in equations (9) and (10), the fish body length calculated for each fish was used for each fish by omitting step S16 of FIG. 10 (correction of the ultrasonic incident angle). For comparison, the inventors actually weighed fish cultured in the same fish pen 2 on multiple days to obtain the fish weights. Furthermore, as a comparative example, the inventors calculated the weights of fish cultured in the same fish pen 2 by performing the process of FIG. 10 in which step S16 (correction of the ultrasonic incident angle) was omitted. The inventors then compared these calculation results with the weighing results to confirm the effectiveness of the correction process in step S16.

[0138] 11(a) and 11(b) are graphs showing the measurement results of the embodiment and the comparative example in comparison with the actual calibration results.

[0139] In FIGS. 11(a) and 11(b), the weight of the fish calculated by the process of FIG. 10 is indicated by an unfilled circle, and the actual weighing result of the fish is indicated by an unfilled square. Also, the weight of the fish according to the comparative example is indicated by a black triangle. The weights of these fish are all the median values of the weights of a plurality of fish obtained on the same day. The graph of FIG. 11(a) shows the measurement result of amberjack for the fish (the fish to be measured) bred in the fish basket 2, and the graph of FIG. 11(b) shows the measurement result of yellowtail for the fish (the fish to be measured) bred in the fish basket 2.

[0140] As shown in FIGS. 11(a) and 11(b), in either case where the target fish is amberjack or yellowtail, the weight of the fish calculated by the process of FIG. 10 is closer to the actual weighing result of the fish than the weight of the fish according to the comparative example calculated by omitting step S16. Thereby, the effectiveness of the correction process in step S16 of FIG. 10 was confirmed.

[0141] <Effects of the Embodiment> According to the embodiment, the following effects can be achieved.

[0142] As shown in FIG. 2, the ultrasonic device 1 includes an ultrasonic transceiver 10 that continuously transmits a plurality of transmission waves toward the fish and generates an echo signal for each transmission wave, a fish echo tracking unit 32 that temporally tracks the fish echo from the echo signal, a fish speed calculation unit 33 that calculates the swimming speed of the tracked fish from the tracked fish echo, an ultrasonic incident angle calculation unit 34 that calculates the ultrasonic incident angle θ of the plurality of transmission waves with respect to the tracked fish based on the position of the fish with respect to the ultrasonic transceiver 10, and an angle correction unit 35 that corrects the ultrasonic incident angle θ based on the swimming speed of the fish.

[0143] According to this configuration, as described above, the ultrasonic incident angle θ calculated based on the position of the fish with respect to the ultrasonic transceiver 10 is corrected based on the swimming speed of the fish. Specifically, the angle θb shown in FIG. 5(b) is obtained as a correction value based on the swimming speed of the fish, and the ultrasonic incident angle θ is corrected by this correction value. Therefore, the ultrasonic incident angle with respect to the fish can be calculated more accurately.

[0144] As explained with reference to Figures 6(a), (b), 7(a), (b), and 8(a), (b), the angle correction unit 35 corrects the ultrasonic incident angle θ with a correction value (average attitude angle) that changes as a function of the swimming speed (average swimming speed).

[0145] As described above, the tilt of the fish's posture relative to the swimming direction changes according to a predetermined function in response to changes in swimming speed. Therefore, with this configuration, the ultrasonic incident angle can be appropriately corrected using a correction value that changes as a function of swimming speed.

[0146] As shown in FIG. 9, the correction value for correcting the ultrasonic wave incident angle θ may be obtained from a table that defines the relationship between a predetermined correction value and the swimming speed of the fish.

[0147] According to this configuration, the correction value for the ultrasonic wave incident angle θ can be smoothly obtained from a table that defines the relationship between a predetermined correction value and the swimming speed of the fish.

[0148] As described with reference to Figures 6(a), (b), 7(a), (b), and 8(a), (b), the angle correction unit 35 may correct the ultrasonic incident angle θ using a correction value (average attitude angle) that changes linearly with the swimming speed (average swimming speed).

[0149] As described above, the relationship between the swimming speed of the fish and the correction value (the inclination of the fish's posture relative to the swimming direction) can be approximated by the predetermined correlation lines L11 and L21. Therefore, with this configuration, the ultrasonic incident angle θ can be appropriately corrected by the correction value that changes linearly with the swimming speed in accordance with the correlation lines L11 and L21.

[0150] As shown in the above equations (11) and (13), the angle correction unit 35 may correct the ultrasonic incident angle θ using a correction value according to the equation a×v+b, where v is the swimming speed and a and b are coefficients predetermined depending on the fish species.

[0151] As shown in Figures 6(a) and 6(b), 7(a) and 7(b), and 8(a) and 8(b), the correlation lines L11 and L21 differ for each fish species. Therefore, when the correlation lines L11 and L21 are expressed as a × v + b using coefficient a (slope) and coefficient b (intercept) and the fish swimming speed v, the coefficients a and b differ for each fish species. Therefore, with this configuration, a correction value is obtained using the formula a × v + b from the coefficients a and b that are predetermined for each fish species, so the ultrasonic incident angle θ with respect to the fish can be appropriately corrected for each fish species.

[0152] As shown in the above equations (6), (7) and (9), (10), the angle correction unit 35 calculates the swimming speed by adjusting the reference speeds v0 and v1. 0_FL If the swimming speed is lower than the reference speed v0, v 0_FL If the velocity is equal to or greater than the threshold velocity, the ultrasonic wave incident angle θ may not be corrected.

[0153] As described above, the posture of the fish is tilted relative to the swimming direction D1 when the swimming speed is low, but is approximately parallel to the swimming direction D1 when the swimming speed is high. Therefore, with this configuration, the ultrasonic wave incident angle θ is corrected only when the swimming speed is lower than the threshold speed, so the ultrasonic wave incident angle θ can be smoothly corrected according to the swimming speed of the fish.

[0154] As described with reference to FIGS. 6(b), 7(b) and 8(b), the fish speed calculation unit 33 may be further configured to normalize the swimming speed by the size of the fish.

[0155] It is said that the swimming speed of a fish is proportional to its body length. Fish body length has a predetermined correlation with various fish dimensions, such as upper body height and body height. Therefore, with this configuration, the correction value for the ultrasonic incident angle θ can be obtained from the relationship between the swimming speed of the fish when the swimming speed is normalized by the fish size and the correction value, making it possible to obtain an appropriate correction value.

[0156] In this case, the size of the fish used for standardization may be the size of the fish in the height direction of the fish (body height, withers height, etc.), as described above.

[0157] Alternatively, the size of the fish used for standardization may be the size of the fish in the longitudinal direction of the fish (body length, fork length, etc.), as described above.

[0158] Furthermore, as described above, the correction of the ultrasonic wave incident angle θ may differ depending on the fish species.

[0159] As shown in Figures 6(a) and 6(b), 7(a) and 7(b), and 8(a) and 8(b), the relationship between the swimming speed (average swimming speed) and the correction value (average attitude angle) differs for each fish species. Therefore, by changing the correction of the ultrasonic incident angle θ depending on the fish species, the ultrasonic incident angle θ can be properly corrected.

[0160] As shown in Figure 10, the ultrasonic incident angle calculation method executed by the signal processing unit 30 (computer) using a program stored in the signal processing unit 30 includes step S13 of tracking the fish echo over time from the echo signals generated when the ultrasonic transmitter / receiver 10 receives the reflected waves of each transmitted wave continuously transmitted from the ultrasonic transmitter / receiver 10 toward the fish, step S14 of calculating the swimming speed of the tracked fish from the echo of the tracked fish, step S15 of calculating the ultrasonic incident angle θ of the multiple transmitted waves relative to the tracked fish based on the position of the fish relative to the ultrasonic transmitter / receiver 10, and step S16 of correcting the ultrasonic incident angle θ based on the swimming speed of the fish.

[0161] According to this ultrasonic wave incident angle calculation method, as described above, the ultrasonic wave incident angle on the fish can be accurately calculated.

[0162] <Example of change> The present invention is not limited to the above-described embodiment, and various modifications to the embodiment of the present invention are possible in addition to the above-described configuration.

[0163] For example, in the above embodiment, as shown in formulas (6) and (7), the reference speed v0 when the average attitude angle becomes 0 on the correlation line L11 was set as the threshold speed for determining whether to execute correction. However, the method for setting the threshold speed is not limited to this. The threshold speed may be set near the upper limit of the range of swimming speeds (average swimming speed) for which it can be assumed appropriate to use the correlation line L11 to obtain the correction value (average attitude angle). Similarly, when using the correlation line L21 for correction, the threshold speed may be set near the upper limit of the range of normalized swimming speeds (average swimming speed) for which it can be assumed appropriate to use the correlation line L21 to obtain the correction value (average attitude angle).

[0164] Also, in the above embodiment, as a method of using the correlation curves L12 and L22 for correcting the ultrasonic incident angle θ, a method of using the correlation function representing the correlation curves L12 and L22 or a table corresponding to the correlation curves L12 and L22 was described. However, the method of using the correlation curves L12 and L22 for correction is not limited to this. For example, similar to the case of using formulas (6), (7) and formulas (9), (10), when the swimming speed of the fish is higher than a predetermined threshold speed, correction based on the correlation curves L12 and L22 may not be necessary. In this case, the threshold speed may be set, for example, near the lower limit value of the range of swimming speeds (average swimming speed) for which it is assumed that the correction values (average attitude angles) of the correlation curves L12 and L22 converge substantially to 0°.

[0165] Also, in the flowchart of FIG. 10, together with the ultrasonic incident angle calculation process (S12 to S16), the fish size calculation process (S17) and the display process (S19) were performed as a series of processes. However, the fish size calculation process (S17) and the display process (S19) may be performed separately from the ultrasonic incident angle calculation process (S12 to S16).

[0166] In this case, the signal processing unit 30 stores the corrected ultrasonic incident angle θ' obtained for each echo signal in steps S12 to S16, linking it to the corresponding fish echo signal. Then, when executing the process of calculating and displaying the fish size, the signal processing unit 30 reads out the echo signals for a predetermined period, including the fish echo signals, and the corrected ultrasonic incident angle θ' linked to each fish echo signal, and calculates the fish size by the same process as in step S17. Then, the signal processing unit 30 displays the calculated fish size on the operation and display unit 40.

[0167] Alternatively, the calculation and display of the fish size may be performed by an external computer separate from the signal processing unit 30. In this case, the signal processing unit 30 stores the corrected ultrasonic incident angle θ' obtained for each echo signal in steps S12 to S16, as described above, in association with the corresponding fish echo signal. The external computer also acquires echo signals for a predetermined period, including fish echo signals, from the signal processing unit 30, and the corrected ultrasonic incident angle θ' associated with each fish echo signal. The external computer then calculates the fish size using a process similar to step S17 and displays the calculated fish size on its display.

[0168] Furthermore, the number of receiving channels of the ultrasonic transmitter / receiver 10 is not limited to four, and may be five or more. In this case, the position of the fish relative to the ultrasonic transmitter / receiver 10 can be calculated by processing based on the split beam method. The number of receiving channels of the ultrasonic transmitter / receiver 10 can be changed as appropriate, as long as the position of the fish relative to the ultrasonic transmitter / receiver 10 can be calculated. Furthermore, the position of the fish relative to the ultrasonic transmitter / receiver 10 may be calculated based on the echo signal by a method other than the split beam method. For example, the position of the fish can also be calculated by estimating the speed and angle of incidence using the single beam method.

[0169] Furthermore, in the above embodiment, the ultrasonic transmitter / receiver 10 is arranged facing vertically downward so that the transmission wave (ultrasound wave) is transmitted downward from the water surface side into the water, but the ultrasonic transmitter / receiver 10 may also be placed at the bottom of the net 5 and the transmission wave (ultrasound wave) may be transmitted vertically upward toward the water surface above.

[0170] Furthermore, the fish from which data is acquired are not limited to fish cultivated in aquaculture farms (for example, fish pens 2). For example, if the species of a school of fish can be inferred by a fisherman or can be identified using a conventional fish finder that can identify the fish species, the ultrasonic transmitter / receiver 10 may be attached to the bottom of a fishing boat, and the ultrasonic device 1 may be used as a device for estimating the size of the fish in the school of fish.

[0171] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the claims. [Explanation of symbols]

[0172] 1 Ultrasonic device 10 Ultrasonic Transducer 32 Fish echo tracking unit 33 Fish speed calculation section 34 Ultrasonic incident angle calculation section 35 Angle correction unit

Claims

1. An ultrasonic device for fish detection, comprising: an ultrasonic transceiver that continuously transmits a plurality of transmission waves toward fish and generates an echo signal for each transmission wave; a fish echo tracking unit that temporally tracks the fish echo from the echo signal; a fish speed calculation unit that calculates the swimming speed of the tracked fish from the tracked fish echo; an ultrasonic incident angle calculation unit that calculates the ultrasonic incident angle of the plurality of transmission waves with respect to the tracked fish based on the position of the fish with respect to the ultrasonic transceiver; an angle correction unit that corrects the ultrasonic incident angle based on the swimming speed of the fish. An ultrasonic device characterized by the above.

2. The ultrasonic device according to claim 1, wherein the angle correction unit corrects the ultrasonic incident angle with a correction value that changes as a function of the swimming speed. An ultrasonic device characterized by the above.

3. The ultrasonic device according to claim 2, wherein the correction value is obtained from a relationship between a predetermined correction value and the swimming speed of the fish. An ultrasonic device characterized by the above.

4. The ultrasonic device according to claim 1, wherein the angle correction unit corrects the ultrasonic incident angle with a correction value that linearly changes with the swimming speed. An ultrasonic device characterized by the above.

5. The ultrasonic device according to claim 1, wherein the angle correction unit corrects the ultrasonic incident angle with a correction value according to the formula a×v + b, where v is the swimming speed and a and b are coefficients predetermined according to the fish species. An ultrasonic device characterized by the above.

6. The ultrasonic device according to claim 1, wherein the angle correction unit corrects the ultrasonic incident angle when the swimming speed is lower than a threshold speed, and does not correct the ultrasonic incident angle when the swimming speed is equal to or higher than the threshold speed. An ultrasonic device characterized by the above.

7. The ultrasonic device according to any one of claims 1 to 6, wherein the fish speed calculation unit further normalizes the swimming speed with the size of the fish. An ultrasonic device characterized by the above.

8. The ultrasonic device according to claim 7, wherein the size of the fish is the size of the fish in the height direction of the fish. An ultrasonic device characterized by the above.

9. The ultrasonic device according to claim 7, wherein the size of the fish is the size of the fish in the length direction of the fish. An ultrasonic device characterized by the above.

10. The ultrasonic device according to claim 1, wherein the correction of the ultrasonic incident angle varies depending on the fish species. An ultrasonic device characterized by the following.

11. Tracking the echo of the fish in time from the echo signals generated by receiving, with the ultrasonic transmitter / receiver, the reflected waves of each transmission wave continuously transmitted from the ultrasonic transmitter / receiver toward the fish, Calculating the swimming speed of the tracked fish from the tracked echo of the fish, Calculating the ultrasonic incident angle of the plurality of transmission waves with respect to the tracked fish based on the position of the fish with respect to the ultrasonic transmitter / receiver, Correcting the ultrasonic incident angle based on the swimming speed of the fish, An ultrasonic incident angle calculation method characterized by the above.

12. A function of tracking the echo of the fish in time from the echo signals generated by receiving, with the ultrasonic transmitter / receiver, the reflected waves of each transmission wave continuously transmitted from the ultrasonic transmitter / receiver toward the fish, A function of calculating the swimming speed of the tracked fish from the tracked echo of the fish, A function of calculating the ultrasonic incident angle of the plurality of transmission waves with respect to the tracked fish based on the position of the fish with respect to the ultrasonic transmitter / receiver, A program for causing a computer to execute a function of correcting the ultrasonic incident angle based on the swimming speed of the fish.

Images