Ultrasonic device and ultrasound incidence angle calculation method

Abstract

An ultrasonic device (1) including an ultrasonic transducer (10), a fish echo tracking module (32), a fish speed calculation module (33), an ultrasound incidence angle calculation module (34), and an angle adjustment module (35) is disclosed. The ultrasonic transducer sequentially transmits a plurality of transmission waves toward a fish and generates an echo signal for each of the plurality of transmission waves. The fish echo tracking module tracks in time an echo of the fish from the echo signals. The fish speed calculation module calculates a swimming speed of the tracked fish from the tracked echoes of the fish. The ultrasound incidence angle calculation module calculates an ultrasound incidence angle of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer. The angle adjustment module adjusts the ultrasound incidence angle based on the swimming speed of the fish.

Description

ULTRASONIC DEVICE AND ULTRASOUND INCIDENCE ANGLE CALCULATION METHOD

[0001] The present disclosure relates to an ultrasonic device for fish detection, an ultrasound incidence angle calculation method for calculating an incidence angle of ultrasonic waves on fish, and a program that causes a computer to calculate an incidence angle of ultrasonic waves on fish.Background

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

[0003] However, the distance between the parts calculated from the fish can vary depending on the incidence angle of ultrasonic wave on the fish. For example, when the ultrasonic wave is transmitted straight down, the incidence angle of the ultrasonic wave on the fish is larger when the fish swims diagonally down than when the fish swims horizontally. Therefore, the distance between the parts calculated when the fish swims diagonally down is larger than the distance between the parts calculated when the same fish swims horizontally. Thus, even for the same fish, if the result of calculating the distance between the parts differs depending on the swimming direction, the size of the fish cannot be accurately calculated.

[0004] This problem can be solved by calculating the incidence angle of the ultrasonic wave on the fish from the swimming direction of the fish and calculating the size of the fish based on the calculated incidence angle and the distance between the parts. The following Patent Document 1 discloses this kind of fish body size calculation device.

[0005] Patent Document 1: JP2022-158950

[0006] However, the posture of the fish, that is, the direction in which the tip of the upper jaw is connected to the forked caudal fin (i.e., the concave center of the caudal fin), is not necessarily parallel to the swimming direction of the fish. When the posture of the fish is tilted up or down with respect to the swimming direction, the incidence angle of the ultrasonic wave on the fish changes by that amount. Therefore, it is possible that the incidence angle of the ultrasonic wave cannot be accurately calculated only from the swimming direction of the fish.

[0007] In view of this problem, it is an object of the present disclosure to provide an ultrasonic device, an ultrasound incidence angle calculation method and a program capable of more accurately calculating the incidence angle of the ultrasonic wave on the fish.Summary

[0008] The first aspect of the present disclosure relates to an ultrasonic device for fish detection. The ultrasonic device according to this aspect includes an ultrasonic transducer, a fish echo tracking module, a fish speed calculation module, an ultrasound incidence angle calculation module, and an angle adjustment module. The ultrasonic transducer is configured to sequentially transmit a plurality of transmission waves toward a fish and generate an echo signal for each of the plurality of transmission waves. The fish echo tracking module is configured to track in time an echo of the fish from the echo signals. The fish speed calculation module is configured to calculate a swimming speed of the tracked fish from the tracked echoes of the fish. The ultrasound incidence angle calculation module is configured to calculate an ultrasound incidence angle of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer. The angle adjustment module is configured to adjust the ultrasound incidence angle based on the swimming speed of the fish.

[0009] As a result of research, the inventor found that a posture of the fish changes according to the swimming speed of the fish. That is, the inventor found that the posture of the fish is not necessarily parallel to a swimming direction, but tilts from the swimming direction depending on the swimming speed. Furthermore, the inventor found that this tilt inclination varies according to the swimming speed of the fish. Thus, the ultrasound incidence angle of the transmission wave on the fish may vary according to the swimming speed of the fish. Based on this knowledge, the inventor thought that the incidence angle of an ultrasonic wave on the fish can be calculated more accurately by adding the inclination of the posture according to the swimming speed of the fish.

[0010] According to the ultrasonic device of the first aspect, the incidence angle of the ultrasonic wave calculated based on the position of the fish relative to the ultrasonic transducer is adjusted based on the swimming speed of the fish according to the above knowledge. Therefore, the incidence angle of the ultrasonic wave with respect to the fish can be calculated more accurately.

[0011] In the ultrasonic device according to an embodiment, the angle adjustment module may be configured to adjust the ultrasound incidence angle with an adjustment value that changes as a function of the swimming speed.

[0012] The inclination of the posture of the fish with respect to the swimming direction may change with a predetermined function according to the change of the swimming speed. Therefore, according to this configuration, the ultrasound incidence angle can be properly adjusted with the adjustment value that changes as a function of the swimming speed.

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

[0014] According to this configuration, the adjustment value of the ultrasound incidence angle can be smoothly obtained from the predetermined relation between adjustment value and swimming speed of the fish based on said function.

[0015] In the ultrasonic device according to an embodiment, the angle adjustment module may be configured to adjust the ultrasound incidence angle with an adjustment value that changes linearly with the swimming speed.

[0016] The relation between the swimming speed of the fish and the adjustment value (the inclination of the posture of the fish with respect to the swimming direction) can be approximated by a predetermined correlation line. Therefore, according to this configuration, the ultrasound incidence angle can be properly adjusted with the adjustment value that changes linearly with the swimming speed.

[0017] In the ultrasonic device according to an embodiment, the angle adjustment module may be configured to adjust the ultrasound incidence angle with an adjustment value according to equation a×v+b, where (v) is the swimming speed, and (a) and (b) are coefficients predetermined by fish species.

[0018] The correlation line described above is different for each fish species. Therefore, when the correlation line is expressed as a×v+b from the coefficients (a) and (b) and the swimming speed (v) of the fish, the coefficients (a) and (b) are different for each fish species. Therefore, according to this configuration, since the adjustment value is obtained from the coefficients (a) and (b) predetermined for each fish species by the equation a×v+b, the ultrasound incidence angle on the fish can be adjusted appropriately for each fish species.

[0019] In the ultrasonic device according to an embodiment, the angle adjustment module may be configured to adjust the ultrasound incidence angle when the swimming speed is below a threshold speed, and not adjust the ultrasound incidence angle when the swimming speed is above the threshold speed.

[0020] The posture of the fish is inclined with respect to the swimming direction of the fish in a range where the swimming speed is low but is almost parallel to the swimming direction of the fish in a range where the swimming speed is high. Therefore, according to this configuration, since the ultrasound incidence angle is only adjusted when the swimming speed is lower than the threshold speed, the ultrasound incidence angle can be smoothly adjusted according to the swimming speed.

[0021] In the ultrasonic device according to an embodiment, the fish speed calculation module may further be configured to normalize the swimming speed with a fish size of the fish.

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

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

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

[0025] In the ultrasonic device according to an embodiment, the adjustment of the ultrasound incidence angle may depend on fish species.

[0026] The relation between the swimming speed of the fish and the adjustment value (the inclination of the posture of the fish with respect to the swimming direction) differs for each species of fish. Therefore, with this configuration, the ultrasound incidence angle can be properly adjusted.

[0027] The second aspect of the present disclosure relates to an ultrasound incidence angle calculation method. The method according to this aspect comprises tracking in time an echo of a fish from echo signals generated by receiving with an ultrasonic transducer reflection wave of each transmission wave of a plurality of transmission waves sequentially transmitted toward the fish with the ultrasonic transducer; calculating a swimming speed of the tracked fish from the tracked echoes of the fish; calculating an ultrasound incidence angle of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer; and adjusting the ultrasound incidence angle based on the swimming speed of the fish.

[0028] According to the ultrasound incidence angle calculation method of the second aspect, the ultrasound incidence angle on the fish can be calculated more accurately as in the first aspect.

[0029] The third aspect of the present disclosure relates to a program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of the second aspect. Specifically, the program according to the third aspect causes the computer to track in time an echo of a fish from echo signals generated by receiving with an ultrasonic transducer reflection wave of each transmission wave of a plurality of transmission waves sequentially transmitted toward the fish with the ultrasonic transducer; calculate a swimming speed of the tracked fish from the tracked echoes of the fish; calculate an ultrasound incidence angle of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer; and adjust the ultrasound incidence angle based on the swimming speed of the fish.

[0030] According to the program of the third aspect, the ultrasound incidence angle on the fish can be calculated more accurately as in the first aspect.

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

[0032] The effect or significance of the present disclosure will become more apparent in the description of the following embodiments. However, the following embodiments are only examples of the embodiments of the present disclosure, and the present disclosure is not limited in any way to those described in the following embodiments.

[0033] FIG. 1 is a perspective view showing a use of an ultrasonic device according to an embodiment.FIG. 2 is a block diagram showing a configuration of the ultrasonic device according to an embodiment.FIG. 3 is a diagram showing an example of an echo signal outputted from an ultrasonic transducer according to an embodiment.FIG. 4 is a diagram schematically showing a method for calculating an ultrasound incidence angle of a transmission wave on a tracked fish according to an embodiment.FIG. 5A is a diagram showing an acquisition of the ultrasound incidence angle in a state when a posture of the fish is parallel to a swimming direction according to an embodiment. FIG. 5B is a diagram showing an acquisition of the ultrasound incidence angle in a state when the posture of the fish is tilted downward from the swimming direction according to an embodiment.FIG. 6A is a graph showing a measurement result of measuring a relation between a swimming speed of the fish and a posture of the fish in a fish tank for breeding amberjack according to an embodiment. FIG. 6B is a graph showing a measurement result of measuring a relation between the swimming speed normalized by a body length of the fish and the posture of the fish in the fish tank for breeding the amberjack according to an embodiment.FIG. 7A is a graph showing a measurement result of measuring a relation between a swimming speed of the fish and a posture of the fish in a fish tank for breeding yellowtail according to an embodiment. FIG. 7B is a graph showing a measurement result of measuring a relation between the swimming speed normalized by a body length of the fish and the posture of the fish in the fish tank for breeding the yellowtail according to an embodiment.FIG. 8A is a graph showing a measurement result of measuring a relation between a swimming speed of the fish and a posture of the fish in a fish tank for breeding mackerel according to an embodiment. FIG. 8B is a graph showing a measurement result of measuring a relation between the swimming speed normalized by a body length of the fish and the posture of the fish in the fish tank for breeding the mackerel according to an embodiment.FIG. 9 is a diagram showing a structure of a table defining a relation between an adjustment value and a swimming speed of the fish according to an embodiment.FIG. 10 is a flowchart showing a process for calculating the size of a fish according to an embodiment.FIG. 11A and FIG. 11B are graphs showing measurement results of an embodiment and a comparative example, and actual measurement results from catch.DETAILED DESCRIPTION

[0034] The functionality of the elements disclosed herein may be implemented using circuitry or processing circuitry which includes general purpose processors, special purpose processors, integrated circuits, ASICs (“Application Specific Integrated Circuits”), conventional circuitry and / or combinations thereof which are configured or programmed to perform the disclosed functionality. Processors are considered processing circuitry or circuitry as they include transistors and other circuitry therein.

[0035] In the disclosure, the circuitry, units, or means are hardware that carry out or are programmed to perform the recited functionality. The hardware may be any hardware disclosed herein or otherwise known which is programmed or configured to carry out the recited functionality.

[0036] When the hardware is a processor which may be considered a type of circuitry, the circuitry, means, or units are a combination of hardware and software, the software being used to configure the hardware and / or processor.

[0037] Embodiments of the present disclosure will now be described with reference to the drawings. In the following embodiments, the present disclosure is applied to an ultrasonic device installed in a fish tank. However, the present disclosure is not limited in any way to the following embodiments.

[0038] FIG. 1 is a perspective view showing the use of an ultrasonic device 1.

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

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

[0041] The upper end of net 5 is fixed to the frame 3. The net 5 is suspended from the frame 3 so as to partition the water to form a closed space. Fish are raised in the closed space. The pier 6 is fixed on the frame 3 for carrying out various operations related to aquaculture.

[0042] A float 7 is floated on a substantially central part inside the frame 3. The float 7 is connected to pier 6 by a rope. An ultrasonic transducer 10, a transceiver unit 20 and a signal processing unit 30 constituting the ultrasonic device 1 are installed on the float 7. As described later, the ultrasonic device 1 may further include an operation display unit 40 (see FIG. 2), but the operation display unit 40 is not shown in FIG. 1. The operation display unit 40 is an interface for operation input and display related to the ultrasonic device 1. The operation display unit 40 may be detachable from the signal processing unit 30.

[0043] The ultrasonic transducer 10 may be arranged vertically downward and transmit an ultrasonic wave (transmission wave TS) downward from the vicinity of the water surface toward the water. The ultrasonic transducer 10 sequentially transmits a plurality of transmission waves TS toward fish and generates an echo signal for each of the plurality of transmission waves TS.

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

[0045] The ultrasonic device 1 includes the ultrasonic transducer 10, the transceiver unit 20, the signal processing unit 30, and the operation display unit 40.

[0046] The ultrasonic transducer 10 can mutually convert electric signals and ultrasonic vibrations. The ultrasonic transducer 10 includes a transmitter 11 and a receiver 12. The transmitter 11 may include one element (ultrasonic oscillator), and the receiver 12 may include a plurality of elements (ultrasonic oscillators) divided for example into four receiving channels.

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

[0048] The structure of the ultrasonic transducer 10 can be suitably changed. For example, the ultrasonic transducer 10 may be configured to provide both transmission and reception by a plurality of elements.

[0049] A position of the object may be obtained based on a difference in timing at which the four receiving channels of the ultrasonic transducer 10 receive the reflection wave, i.e., a phase difference of the received reflection wave. As a result, a three-dimensional detection by the known split-beam method is realized. The position of the object is acquired by the signal processing unit 30. The signal processing unit 30 acquires the position of the object based on the phase difference of echo signals of the object outputted from each of the four receiving channels for the transmission of one transmission wave.

[0050] The transceiver unit 20 is connected to the ultrasonic transducer 10 via an electric cable. The transceiver unit 20 outputs an electric signal to the ultrasonic transducer 10 via the electric cable for the ultrasonic transducer 10 to transmit the transmission wave. Transceiver unit 20 acquires via the electric cable an electric signal acquired by the ultrasonic transducer 10 that received the reflection wave. Transceiver unit 20 converts the electric signal acquired from the ultrasonic transducer 10 into a reception signal, which is a digital signal, and transmits it to the signal processing unit 30.

[0051] The transceiver unit 20 amplifies the electric signal acquired by the four receiving channels and further performs filtering to the frequency of the transmission wave. Transceiver unit 20 converts the filtered electric signal into a reception signal, which is a digital signal, and transmits it to the signal processing unit 30.

[0052] The signal processing unit 30 may be configured as a known computer. The signal processing unit 30 may be connected to the transceiver unit 20 by a communication cable. The signal processing unit 30 communicates with the transceiver unit 20 via the communication cable. The signal processing unit 30 receives the reception signal from the transceiver unit 20 by the above communication, and sequentially stores the received reception signal. The signal processing unit 30 calculates a fish size using the received reception signal.

[0053] The signal processing unit 30 includes arithmetic processing circuitry such as a CPU (Central Processing Unit) and a storage medium such as a ROM (Read Only Memory), a RAM (Random Access Memory) and a hard disk. A program for realizing a fish size calculation process is stored in the storage medium. Functions of a fish echo extraction module 31, a fish echo tracking module 32, a fish speed calculation module 33, an ultrasound incidence angle calculation module 34, an angle adjustment module 35, and a fish size calculation module 36 are assigned to the signal processing unit 30 by this program.

[0054] The fish echo extraction module 31 extracts an echo of the fish from the echo signals outputted from the ultrasonic transducer 10, and further acquires the position of the fish in the water. After transmission, the echo signals are outputted from each of the four receiving channels, and the reception signals obtained by converting the echo signals into digital signals are inputted from the transceiver unit 20 to the signal processing unit 30. The fish echo extraction module 31 extracts an echo signal higher than a predetermined threshold value as a fish echo signal. The threshold value is set so that the fish echo signal can be extracted.

[0055] FIG. 3 is a diagram showing an example of an echo signal outputted from the ultrasonic transducer 10.

[0056] For convenience, FIG. 3 illustrates a portion of an envelope of the echo signal outputted from one receiving channel near the fish echo signal for one transmission. In the example of FIG. 3, the threshold Th1 for extracting the echo of the fish is set to -60dB.

[0057] In FIG. 3, the horizontal axis is time from a transmission timing, and the vertical axis is target strength based on the echo signal. The target strength is a parameter indicating a degree to which a part of the reflection wave scattered by the ultrasonic wave (transmission wave) hitting the object returns in the incident direction and is substantially equivalent to an intensity of the echo signal. The target strength is expressed as a decibel value. By dividing by two the time on the horizontal axis multiplied by the speed of sound in the water, distance from the ultrasonic transducer 10 can be calculated.

[0058] In the fish echo signal, there are a plurality of peaks P10 to P13 based on the reflection waves from each part of the fish, such as the back, the swim bladder, and the belly. Among these peaks, the swim bladder peak P10 is the largest. The fish echo extraction module 31 extracts the swim bladder peak P10, which is the largest peak, respectively from the echo signals of the four receiving channels. The signal processing unit 30 specifies the position of the fish's swim bladder relative to the ultrasonic transducer 10 by the split-beam method on the basis of the phase difference between the four peaks P10 of the swim bladder and the time from the transmission timing to a reception timing of these swim bladder peaks P10 (i.e., the distance from the ultrasonic transducer 10 to the swim bladder), and acquires the position of the specified swim bladder as the position of the fish relative to the ultrasonic transducer 10.

[0059] The position of the fish may not necessarily be acquired as the position of the fish's swim bladder but may be acquired as the position of other parts such as the position of the fish's back. For example, when the position of the back of the fish is used as the position of the fish, the signal processing unit 30 specifies the position of the back of the fish with respect to the ultrasonic transducer 10 by performing the above processing with respect to the peak P11, which is the peak from the back, and acquires the specified position of the back as the position of the fish with respect to the ultrasonic transducer 10. Similarly, the position of the fish may be acquired using the peak P12 from the dorsal fin or the peak P13 from the belly.

[0060] Returning to FIG. 2, the fish echo tracking module 32 tracks in time the echo of the fish from the echo signals outputted from the ultrasonic transducer 10. That is, when the position of the fish acquired by the fish echo extraction module 31 in the current transmission is almost the same as any of the positions of the fish acquired by the fish echo extraction module 31 in previous transmissions, the fish echo tracking module 32 estimates the echo signals of the fish corresponding to the positions of these two fish at almost the same position to be the echo signals from the same fish. The fish echo tracking module 32 tracks in time the echo signals from the same fish in that way.

[0061] Whether or not previous and current positions of the fish are almost the same can be determined by whether or not the positions of these two fish are included within a range that a fish can swim within a transmission period of the transmission wave. The tracking of the fish may include, for example, prediction by using a Kalman filter, and sophisticated tracking algorithms for tracking the fish may be employed.

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

[0063] The ultrasound incidence angle calculation module 34 calculates an ultrasound incidence angle of the transmission wave on the tracked fish based on the position of the fish with respect to the ultrasonic transducer 10.

[0064] FIG. 4 is a diagram schematically showing a calculation method of the ultrasound incidence angle of the transmission wave on the tracked fish.

[0065] FIG. 4 illustrates tracked fish F1 and F1′. The fish F1 is the fish for which position P1 (position of the swim bladder) is acquired in the current transmission, and the fish F1′ is the fish for which position P1 (position of the swim bladder) was acquired in a previous transmission. The ultrasound incidence angle calculation module 34 acquires a direction from the position P1 acquired in the previous transmission to the position P1 acquired in the current transmission as a swimming direction D1 of the fish F1. The ultrasound incidence angle calculation module 34 calculates the ultrasound incidence angle θ from angle θa, formed by straight line L1 connecting the position P1 of the fish F1 and the ultrasonic transducer 10 and the swimming direction D1 of the fish F1, by the following formula.Equation 1

[0066] θ = 90° - θa

[0067] That is, the ultrasound incidence angle θ is a complementary angle of the angle θa formed by the line L1 and the swimming direction D1 of the fish F1.

[0068] Similarly, the ultrasound incidence angle θ of the transmission wave for the fish F1′ is obtained as the complementary angle of the angle θa formed by straight line L1′ connecting the position P1 of the fish F1′ and the ultrasonic transducer 10 and the swimming direction D1 of the fish F1′. Note that, the angle θa formed by a straight line connecting the position P1 of the fish and the ultrasonic transducer 10 and the swimming direction of the fish may be obtained as the ultrasound incidence angle θ.

[0069] Returning to FIG. 2, the angle adjustment module 35 adjusts the ultrasound incidence angle θ calculated by the ultrasound incidence angle calculation module 34 based on the swimming speed of the fish calculated by the fish speed calculation module 33.

[0070] That is, as described above, the ultrasound incidence angle calculation module 34 calculates the complementary angle of the angle θa formed by the straight line L1 connecting the position P1 of the fish and the ultrasonic transducer 10 and the swimming direction D1 of the fish as the ultrasound incidence angle θ of the transmission wave on 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 tilted up or down with respect to the swimming direction D1, the ultrasound incidence angle θ on the fish changes by that amount. Therefore, when the ultrasound incidence angle θ is calculated from the swimming direction D1 of the fish in the ultrasound incidence angle calculation module 34, the ultrasound incidence angle θ may be inaccurate.

[0071] FIG. 5A is a diagram showing an acquisition of the ultrasound incidence angle θ in a state when the posture of the fish F1 is parallel to the swimming direction D1, and FIG. 5B is a diagram showing an acquisition of the ultrasound incidence angle θ in a state when the posture of the fish F1 is tilted downward from the swimming direction D1 by an angle θb.

[0072] When the posture of the fish F1 is parallel to the swimming direction D1 of the fish F1 as shown in FIG. 5A, the ultrasound incidence angle θ calculated by the above Equation 1 corresponds to the actual incidence angle of the transmission wave on the fish F1, that is, the angle formed by straight line L2 extending from the position P1 in a height direction of the fish F1 and the straight line L1. On the other hand, when the posture of the fish F1 is inclined downward by the angle θb from the swimming direction D1 of the fish F1 as shown in FIG. 5B, the ultrasound incidence angle θ calculated by the above Equation 1 decreases by the angle θb from an actual incidence angle θ ′ of the transmission wave on the fish F1, that is, the angle 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. 5B, the angle adjustment module 35 acquires the angle θb as an adjustment value and adjusts the ultrasound incidence angle θ calculated by the ultrasound incidence angle calculation module 34 by the acquired adjustment value. In the example shown in FIG. 5B, the angle adjustment module 35 adds the angle θb as the adjustment value to the ultrasound incidence angle θ calculated by the ultrasound incidence angle calculation module 34 and acquires adjusted ultrasound incidence angle θ′. A method of acquiring the angle θb as the adjustment value will be described later with reference to FIG. 6A to FIG. 8B.

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

[0075] W = α・UBHβ

[0076] The coefficients α and β in Equation 2 differ for each species.

[0077] Here, even for the same fish, the time difference between the peak P10 of the swim bladder and the peak P11 of the back changes when the ultrasound incidence angle of the transmission wave changes. Therefore, the upper body height UBH of the fish calculated from the time difference between these peaks also changes with the change of the ultrasound incidence angle, and the result of calculating the size of the fish also changes. In addition, the coefficients α and β in Equation 2 are also set on the basis that the ultrasound incidence angle on the fish is a predetermined angle.

[0078] Therefore, in order to accurately calculate the size of the fish in the fish tank 2, it is preferable to obtain the upper body height UBH for the echo signal of the fish whose ultrasound incidence angle θ′ adjusted by the angle adjustment module 35 substantially matches a reference ultrasound incidence angle used as a setting criterion for the coefficients α and β, and apply the obtained upper body height UBH to the predetermined conversion formula to calculate the size (fork length, body length, body height, body weight, etc.) of the fish.

[0079] The fish size calculation module 36 may extract only the echo signals of the fish whose ultrasound incidence angle θ′ substantially matches the above reference ultrasound incidence angle among the echo signals of the fish acquired by a series of transmission. The fish size calculation module 36 calculates the upper body height UBH of the fish from the extracted echo signals of the fish and applies the calculated upper body height UBH to the conversion formula to calculate the size of the fish (fork length, body length, body height, body weight, etc.) corresponding to the extracted echo signals of the fish. The fish size calculation module 36 acquires, for example, a median of the calculated fish size (fork length, body length, body height, body weight, etc.) as the size of the fish in the fish tank 2.

[0080] Next, a method of acquiring the adjustment value in the angle adjustment module 35 of FIG. 2 is described.

[0081] As a result of research, the inventor found that the posture of a fish changes depending on the swimming speed of the fish. That is, the inventor found that the posture of a fish is not necessarily parallel to the swimming direction, but tilts from the swimming direction depending on the swimming speed. Furthermore, the inventor found that this tilt inclination varies according to the swimming speed of the fish. Thus, the ultrasound incidence angle of the transmission wave on the fish may vary according to the swimming speed of the fish. Based on this knowledge, the inventor thought that the incidence angle of the ultrasonic wave on the fish can be calculated more accurately by adding the inclination of the posture according to the swimming speed of the fish.

[0082] FIG. 6A is a graph showing a measurement result of measuring a relation between the swimming speed of the fish and the posture of the fish in a fish tank for breeding amberjack.

[0083] In FIG. 6A, the horizontal axis is the average value of the swimming speed of the fish (average swimming speed), and the vertical axis is the average value of an inclination angle of the posture of the fish with respect to the swimming direction of the fish (average posture angle). The average posture angle of the vertical axis is negative when the posture of the fish (head) inclines down with respect to the swimming direction of the fish, and positive when the posture of the fish (head) inclines up with respect to the swimming direction of the fish. Measurement results of a plurality of fish tanks different from each other are integrated into the measurement result of FIG. 6A. The measurement results are plotted in the graph of FIG. 6A.

[0084] As shown in FIG. 6A, the lower the swimming speed, the lower the posture of the fish (amberjack), and the higher the swimming speed, the closer the posture becomes parallel to the swimming direction. Correlation between the average swimming speed and the average posture angle can be defined by correlation line L11 or by correlation curve L12. According to the correlation line L11, the average posture angle of fish (amberjack) can be expressed from the swimming speed v by the following formula.Equation 3

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

[0086] where v0 is a reference speed at which the posture of the fish is parallel to the swimming direction. For example, when the average posture angle is zero in the correlation line L11 of FIG. 6A, the average swimming speed can be obtained as the reference speed v0. Further, k is a correction coefficient and corresponds to the slope of the correlation line L11.

[0087] The average posture angle shown on the vertical axis in FIG. 6A corresponds to the angle θb in FIG. 5B. In Equation 3, since the average posture angle has a positive value when the fish is facing downward, a value obtained by adding a negative sign to the average posture angle calculated by Equation 3 becomes the adjustment value for the ultrasound incidence angle θ. Therefore, the adjustment value can be calculated by the following formula.Equation 4

[0088] Adjustment value = -k × (v0-v)

[0089] Therefore, the adjusted ultrasound incidence angle θ′ can be calculated by the following formula:Equation 5

[0090] θ’ = θ - k × (v0-v)

[0091] The angle adjustment module 35 in FIG. 2 may adjust the ultrasound incidence angle θ calculated by the ultrasound incidence angle calculation module 34 by using the swimming speed v of the fish calculated by the fish speed calculation module 33 according to Equation 5.

[0092] However, in the correlation line L11 shown in FIG. 6A, the average posture angle is positive in a range where the average swimming speed is higher than the reference speed v0, which is the average swimming speed when the average posture angle is zero. This indicates that the posture of the fish inclines upward with respect to the swimming direction in this range of speeds. However, the actual posture of the fish is maintained approximately parallel to the swimming direction in the range where the average swimming speed is higher than the reference speed v0. Therefore, when the swimming speed of the fish is higher than the reference speed v0, it may be preferable not to adjust the ultrasound incidence angle θ according to Equation 5.

[0093] Therefore, when the swimming speed v of the fish calculated by the fish speed calculation module 33 is less than or equal to the reference speed v0 (threshold speed), the angle adjustment module 35 in FIG. 2 may adjust the ultrasound incidence angle θ by applying Equation 5, and when the swimming speed v is higher than the reference speed v0 (threshold speed), the ultrasound incidence angle θ calculated by the ultrasound incidence angle calculation module 34 may be used as the ultrasound incidence angle of the transmission wave on the fish without performing the adjustment according to Equation 5. That is, the angle adjustment module 35 may perform the adjustment according to the following formulas.Equation 6

[0094] If v > v0 then θ’ = θEquation 7

[0095] If v ≦ v0 then θ’ = θ - k × (v0-v)

[0096] It is said that the swimming speed of fish is proportional to body length of fish. Therefore, the horizontal axis of FIG. 6A may be normalized by the body length of the fish. In this case, the graph of FIG. 6A changes as shown in FIG. 6B. In FIG. 6B, the average swimming speed in each plot of FIG. 6A is normalized by the average body length (measurement value from catch) of the fish in that plot. In the graph of FIG. 6B, the correlation between the average swimming speed and the average posture angle is higher than in the graph of FIG. 6A.

[0097] In the graph of FIG. 6B, the correlation between the average swimming speed and the average posture angle can be defined by correlation line L21 or by correlation curve L22. According to the correlation line L21, the above Equation 5 is transformed into the following equation.Equation 8

[0098] θ’ = θ - k × {v0_FL - (v / FL)}

[0099] Here, v0_FL is a reference speed at which the posture of the fish is parallel to the swimming direction and corresponds to the average swimming speed at which the average posture angle is zero in the correlation line L21. FL is the average body length of the fish in each plot.

[0100] In this case, the above Equations 6 and 7 are transformed into the following equations, respectively.Equation 9

[0101] If v / FL > v0_FL then θ’ = θEquation 10

[0102] If v / FL ≦ v0_FL then θ’ = θ - k × {v0_FL - (v / FL)}

[0103] The angle adjustment module 35 may perform the adjustment according to Equations 9 and 10. As described above, the correlation between the average swimming speed and the average posture angle is higher in the graph of FIG. 6B than in the graph of FIG. 6A. From this point of view, it is estimated that the ultrasound incidence angle θ can be adjusted more accurately by using the above Equations 9 and 10.

[0104] On the other hand, in Equations 9 and 10, it is necessary to calculate the fish body length FL from the echo signal. In this case, the fish speed calculation module 33 calculates the fish body length FL from the fish echo signal extracted by the fish echo extraction module 31. For example, the fish body length FL can be calculated by applying the upper body height of the fish calculated from the time difference between the peaks P10 and P11 in FIG. 3 to the predetermined conversion formula.

[0105] However, since the posture of the fish is not necessarily parallel to the swimming direction of the fish as described above, the calculation of the upper body height from the above time difference may include an error. Therefore, this error may affect the adjustment in Equations 9 and 10. In addition, the adjustment of the ultrasound incidence angle θ is performed to calculate the fish size such as body length and body weight of the fish. Therefore, the calculation of the fish body length FL for the adjustment of the ultrasound incidence angle θ does not follow the above calculation process.

[0106] From these points, the angle adjustment module 35 may perform the adjustment of the ultrasound incidence angle θ according to the above Equations 6 and 7. Alternatively, the angle adjustment module 35 may perform the adjustment of the ultrasound incidence angle θ according to the above Equations 9 and 10, and then the fish size calculation module 36 may calculate the body length FL of the fish again using the adjusted ultrasound incidence angle θ′.

[0107] In the case of daily measurement, the average value of the body length of the fish estimated on the previous day may be used as the body length FL in the above Equations 9 and 10 to perform the adjustment of the ultrasound incidence angle θ. Alternatively, the body length FL, etc. may be obtained once without adjusting the incidence angle θ, and then that body length FL may be used as the body length FL in the above Equations 9 and 10 to adjust the ultrasound incidence angle θ and re-estimate the body length FL, etc. with the adjusted ultrasound incidence angle θ′.

[0108] In the graph shown in FIG. 6B, 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 module 33 calculates the upper body height of the fish from the fish echo signal extracted by the fish echo extraction module 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 module 33 calculates the upper body height or fork length of the fish by applying the upper body height calculated from the fish echo signal to the predetermined conversion formula.

[0109] FIG. 7A is a graph showing a measurement result of measuring the relation between the swimming speed of the fish and the posture of the fish in a fish tank for breading yellowtail. FIG. 7B is a graph in which the horizontal axis of the graph in FIG. 7A is normalized by the average body length of the fish. In FIG. 7B, the average swimming speed in each plot of FIG. 7A is normalized by the average body length of the fish in that plot.

[0110] FIG. 8A is a graph showing a measurement result of measuring the relation between the swimming speed of the fish and the posture of the fish in a fish tank for breading mackerel. FIG. 8B is a graph in which the horizontal axis of the graph in FIG. 8A is normalized by the average body length of the fish. In FIG. 8B, the average swimming speed in each plot in FIG. 8A is normalized by the average body length of the fish in that plot.

[0111] For yellowtail and mackerel, the ultrasound incidence angle θ can also be adjusted from the above Equations 6 and 7 based on the correlation line L11 in FIG. 7A and FIG. 8A. However, as can be seen by comparing FIGS. 6A, 7A and 8A, the slope of the correlation line L11 and the reference speed v0 are different for amberjack, yellowtail, and mackerel. Therefore, when the above Equations 6 and 7 are used to adjust the ultrasound incidence angle θ, the coefficient k and the reference speed v0 may be changed according to the fish species.

[0112] Similarly, for yellowtail and mackerel, based on the correlation line L21 in FIG. 7B and FIG. 8B, the ultrasound incidence angle θ can be adjusted from the above Equations 9 and 10. Again, since the slope of the correlation line L21 and the reference speed v0_FL differ between amberjack, yellowtail, and mackerel, the coefficient k and the reference speed v0_FL may be changed according to the fish species.

[0113] Equation 4, which is the formula for calculating the adjustment value based on the correlation line L11 in FIGS. 6A, 7A, and 8A, may be modified as follows.Equation 11

[0114] Adjustment value = -k × (v0-v) = k×v - k×v0 = a1×v + b1

[0115] Therefore, Equation 7, which is the formula for calculating the adjusted ultrasound incidence angle θ′, may be modified as follows.Equation 12

[0116] If v ≦ v0 then θ’ = θ + a1×v + b1

[0117] Therefore, when the ultrasound incidence angle θ is adjusted based on the correlation line L11, coefficients a1 and b1 in Equation 12 may be changed for each fish species.

[0118] The formula for calculating the adjustment value based on the correlation line L21 in FIGS. 6B, 7B and 8B may be as follows.Equation 13

[0119] Adjustment value = -k × {v0_FL - (v / FL)} = a2×v + b2

[0120] Therefore, above Equation 10, which is the formula for calculating the adjusted ultrasound incidence angle θ′, may be modified as follows.Equation 14

[0121] If v / FL ≦ v0_FL then θ’ = θ + a2×v + b2

[0122] Therefore, when the ultrasound incidence angle θ is adjusted based on normalized correlation line L21, coefficients a2 and b2 in Equation 14 may be changed for each fish species.

[0123] The angle adjustment module 35 may calculate the adjustment value used to adjust the ultrasound incidence angle θ from Equation 11 or Equation 13. Alternatively, the angle adjustment module 35 may hold the relation between the adjustment value and the swimming speed of the fish predetermined based on these equations as a table and obtain the adjustment value from this table.

[0124] FIG. 9 is a diagram showing a structure of the table defining the relation between the adjustment value and the swimming speed of the fish.

[0125] In the table, the swimming speed of the fish is correlated with the adjustment value based on the above Equation 11 or Equation 13. The swimming speed is segmented by a predetermined speed interval. The range of the swimming speed to which the adjustment value is associated is from v1 to vn. When the above Equation 11 is used for a configuration of the table, the swimming speed vn corresponds to the reference speed v0. As shown in Equation 6, when the swimming speed exceeds the reference speed v0, the ultrasound incidence angle θ is not adjusted. Therefore, in the table, there are no adjustment values corresponding to speed ranges higher than the swimming speed vn. Similarly, when the above Equation 13 is used for the table configuration, the swimming speed vn corresponds to the swimming speed when v / FL becomes the reference speed v0_FL. Speed ranges higher than the swimming speed vn may be associated with 0 as the adjustment value.

[0126] The angle adjustment module 35 may specify the swimming speed in the table closest to the swimming speed of the fish calculated by the fish speed calculation module 33. The angle adjustment module 35 may acquire the adjustment value associated with the specified swimming speed as the adjustment value of the ultrasound incidence angle θ for the fish. The angle adjustment module 35 may add the acquired adjustment value to the ultrasound incidence angle θ calculated by the ultrasound incidence angle calculation module 34 to calculate the adjusted ultrasound incidence angle θ′.

[0127] As described above, the correlation between the swimming speed (average swimming speed) of the fish and the inclination of the posture of the fish with respect to the swimming direction (average posture angle) differs for each fish species. Therefore, the table shown in FIG. 9 may be prepared in the angle adjustment module 35 for each fish species. Depending on the fish species, it is possible that the posture of the fish inclines upward with respect to the swimming direction in a range where the swimming speed is low. For such fish species, signs of the coefficients a1, a2, b1 and b2 of the above adjustment values may be adjusted in accordance with the correlation between the average swimming speed and the average posture angle, and the table shown in FIG. 9 may be adjusted accordingly.

[0128] The adjustment value (average posture angle) may be obtained from the correlation curves L12 and L22 instead of the correlation lines L11 and L21. For example, the angle adjustment module 35 may hold a function representing the correlation curves L12 and L22 and apply the swimming speed of the fish to this function to calculate the adjustment value (average posture angle) of the fish. Alternatively, as in the case of FIG. 9, the angle adjustment module 35 may hold a table corresponding to the correlation curves L12 and L22 and obtain the adjustment value corresponding to the swimming speed of the fish from the table.

[0129] In these cases, the angle adjustment module 35 may add the obtained adjustment value to the ultrasound incidence angle θ calculated by the ultrasound incidence angle calculation module 34 and obtain the adjusted ultrasound incidence angle θ′. In the same manner as described above, the function or table may be held in the angle adjustment module 35 for each fish species. The angle adjustment module 35 may adjust the ultrasound incidence angle θ using the function or table corresponding to the designated fish species.

[0130] FIG. 10 is a flowchart showing a process for calculating the fish size.

[0131] Prior to the process shown in FIG. 10, the signal processing unit 30 stores in a time series a plurality of echo signals for a certain period of time (e.g., several hours) acquired by each receiving channel in a series of transmission waves. The signal processing unit 30 executes the process shown in FIG. 10 for these echo signals. Target fish species, that is, the fish species of the fish farmed in fish tank 2, is inputted through the operation display unit 40. The signal processing unit 30 executes the processing shown in FIG. 10 using the function or table corresponding to the inputted fish species.

[0132] In the flowchart shown in FIG. 10, steps S12, S13, S14, S15, S16, and S17 are executed by the functions of the fish echo extraction module 31, the fish echo tracking module 32, the fish speed calculation module 33, the ultrasound incidence angle calculation module 34, the angle adjustment module 35, and the fish size calculation module 36 shown in FIG. 2, respectively. In the following description, the signal processing unit 30 performs the processing shown in FIG. 10 by these functions. Steps S12 to S16 correspond to the processing of calculating the ultrasound incidence angle of the transmission wave on the fish.

[0133] The signal processing unit 30 sequentially sets in turns the echo signals of a certain period of time as processing target, at step S11. The signal processing unit 30 extracts the echo of the fish from the echo signal set as the processing target and obtains the position of the fish by the split-beam method described above, at step S12. The signal processing unit 30 tracks in time the echo of the fish (the position of the fish) from the obtained positions of the fish as described above, at step S13.

[0134] The signal processing unit 30 calculates the swimming speed of the fish from the tracked echoes of the fish as described above, at step S14. The signal processing unit 30 calculates the swimming direction of the fish from the tracked echoes of the fish and calculates the ultrasound incidence angle θ based on the swimming direction, at step S15. The signal processing unit 30 adjusts the calculated ultrasound incidence angle θ based on the swimming speed of the fish, at step S16. Specifically, the signal processing unit 30 obtains the adjustment value based on the swimming speed as described above and adds the obtained adjustment value to the ultrasound incidence angle θ to calculate the adjusted ultrasound incidence angle θ′.

[0135] The signal processing unit 30 calculates the fish size (Upper body height, body height, body length, fork length, body weight, etc.) only for the fish echo signals whose adjusted ultrasound incidence angle θ′ is near a predetermined angle (for example, within ± a few degrees of the predetermined angle) among the fish echo signals extracted at step S12, and stores the calculated fish size at step S17. The information processing unit 30 calculates, for example, the upper body height of the fish from the time difference between the peaks P10 and P11 in FIG. 3 and applies the calculated upper body height to the predetermined conversion formula to calculate the fish size.

[0136] Here, the predetermined angle at step S17 is the ultrasound incidence angle assumed in the formula used to calculate the upper body height and other sizes. For example, if formulas used to calculate upper body height and other sizes are specified assuming that the transmission wave is incident on the fish's back perpendicularly, the predetermined angle is set to 0°. The predetermined angle may be set to a preferred angle for each fish species.

[0137] The signal processing unit 30 determines whether or not the processing of steps S12 to S17 has been completed for all echo signals of the certain period of time, at step S18. If an unprocessed echo signal remains (S18: NO), the signal processing unit 30 sets the next echo signal as the processing target at step S11 and performs the processing of steps S12 and subsequent steps.

[0138] Thus, when the processing of steps S12 to S17 is completed for all echo signals of the certain period of time (S18: YES), the signal processing unit 30 executes the processing for displaying the fish size on the operation display unit 40, at step S19. For example, the signal processing unit 30 calculates the median value or the average value from the fish sizes (Upper body height, body height, body length, fork length, body weight, etc.) stored at step S17, and displays the calculation result on the operation display unit 40. The signal processing unit 30 terminates the processing shown in FIG. 10.

[0139] The inventor performed the following measurements in order to confirm the effectiveness of the adjustment process of step S16. The inventor performed the process shown in FIG. 10 on a plurality of days for the fish farmed in the fish tank 2 and calculated the weight of the fish. The above Equations 9 and 10 were used for the adjustment of step S16. For the fish body length FL in Equations 9 and 10, the fish body length obtained for each fish by omitting step S16 (adjustment of the ultrasound incidence angle) in FIG. 10 was used for each fish. For comparison, the inventor obtained the body weight of the fish farmed in the same fish tank 2 by actually catching and measuring the fish on multiple days. Further, as a comparative example, the inventor calculated the body weight of the fish by a process in which step S16 (adjustment of the ultrasound incidence angle) is omitted from the flowchart of FIG. 10 for the fish farmed in the same fish tank 2. The inventor confirmed the effectiveness of the adjustment process of step S16 by comparing these calculation results with measurement results from catch.

[0140] FIG. 11A and FIG. 11B are graphs showing the measurement results of the embodiment and the comparative example, and the actual measurement results from catch.

[0141] In FIGS. 11A and 11B, the body weight of the fish calculated by the processing shown in FIG. 10 is indicated by a white circle, and the actual measurement results from catch of the fish are indicated by a white square. The body weight of the fish in the comparative example is indicated by a black triangle. The body weight of these fish is the median weight of multiple fish obtained on the day. The graph of FIG. 11A shows the measurement results when fish (target fish for measurement) farmed in the fish tank 2 are amberjack, and the graph of FIG. 11B shows the measurement results when fish (target fish for measurement) farmed in the fish tank 2 are yellowtail.

[0142] As shown in FIGS. 11A and 11B, when the target fish is amberjack or yellowtail, the body weight of the fish calculated by the processing of FIG. 10 is closer to the actual measurement result from catch of the fish than the body weight of the fish calculated by omitting step S16 according to the comparative example. Thus, the effectiveness of the adjustment process of step S16 of FIG. 10 can be confirmed.

[0143] According to the embodiments, the following effects can be achieved.

[0144] As shown in FIG. 2, the ultrasonic device 1 includes: an ultrasonic transducer 10 configured to sequentially transmit a plurality of transmission waves toward a fish and generate an echo signal for each of the plurality of transmission waves; a fish echo tracking module 32 configured to track in time an echo of the fish from the echo signals; a fish speed calculation module 33 configured to calculate a swimming speed of the tracked fish from the tracked echoes of tracked fish; an ultrasound incidence angle calculation module 34 configured to calculate an ultrasound incidence angle θ of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer 10; and an angle adjustment module 35 configured to adjust the ultrasound incidence angle θ based on the swimming speed of the fish.

[0145] According to this configuration, as described above, the ultrasound incidence angle θ calculated based on the position of the fish relative to the ultrasonic transducer 10 is adjusted based on the swimming speed of the fish. Specifically, the angle θb shown in FIG. 5B is obtained as the adjustment value based on the swimming speed of the fish, and the ultrasound incidence angle θ is adjusted with this adjustment value. Therefore, the ultrasound incidence angle on the fish can be calculated more accurately.

[0146] As described with reference to FIGS. 6A and 6B, 7A and 7B, and 8A and 8B, the angle adjustment module 35 may be configured to adjust the ultrasound incidence angle θ with an adjustment value (average posture angle) that changes as a function of the swimming speed (average swimming speed).

[0147] As described above, the inclination of the posture of the fish with respect to the swimming direction may change with a predetermined function according to the change of the swimming speed. Therefore, according to this configuration, the ultrasound incidence angle can be properly adjusted with the adjustment value, which changes as a function of the swimming speed.

[0148] As shown in FIG. 9, the adjustment value for adjusting the ultrasound incidence angle θ may be obtained from a predetermined relation (e.g., a table) between adjustment value and swimming speed of the fish.

[0149] According to this configuration, the adjustment value of the ultrasound incidence angle θ can be smoothly obtained from the table defining the predetermined relation between adjustment value and swimming speed of the fish.

[0150] As described with reference to FIGS. 6A and 6B, 7A and 7B, and 8A and 8B, the angle adjustment module 35 may be configured to adjust the ultrasound incidence angle θ with an adjustment value (average posture angle) that changes linearly with the swimming speed (average swimming speed).

[0151] As described above, the relation between the swimming speed of the fish and the adjustment value (the inclination of the posture of the fish with respect to the swimming direction) can be approximated by the predetermined correlation lines L11 and L21. Therefore, according to this configuration, the ultrasound incidence angle θ can be properly adjusted with the adjustment value that changes linearly with the swimming speed according to the correlation lines L11 and L21.

[0152] As shown in Equations 11 and 13 above, the angle adjustment module 35 may be configured to adjust the ultrasound incidence angle θ with an adjustment value according to equation a×v+b, where v is the swimming speed, and a and b are coefficients predetermined by fish species.

[0153] As shown in FIGS. 6A and 6B, 7A and 7B, and 8A and 8B, the correlation lines L11 and L21 are different for each fish species. Therefore, when the correlation lines L11 and L21 are expressed as a×v+b from the coefficients a (slope) and b (intercept) and the swimming speed v of the fish, the coefficients a and b are different for each fish species. Therefore, according to this configuration, since the adjustment value is obtained from the coefficients a and b predetermined for each fish species by the equation a×v+b, the ultrasound incidence angle θ on the fish can be adjusted appropriately for each fish species.

[0154] As shown in Equations 6 and 7 and Equations 9 and 10 above, the angle adjustment module 35 may be configured to adjust the ultrasound incidence angle θ when the swimming speed is below a threshold speed (reference speed v0, v0_FL), and not adjust the ultrasound incidence angle θ when the swimming speed is above the threshold speed (reference speed v0, v0_FL ).

[0155] As described above, the posture of the fish is inclined with respect to the swimming direction D1 of the fish in the range where the swimming speed is low but is almost parallel to the swimming direction D1 of the fish in the range where the swimming speed is high. Therefore, according to this configuration, since the ultrasound incidence angle θ is only adjusted when the swimming speed is lower than the threshold speed, the ultrasound incidence angle θ can be smoothly adjusted according to the swimming speed of the fish.

[0156] As described with reference to FIGS. 6B, 7B and 8B, the fish speed calculation module 33 may further be configured to normalize the swimming speed with a fish size of the fish.

[0157] The swimming speed of fish is said to be proportional to body length of the fish. The body length of the fish has a predetermined correlation with various sizes such as upper body height and body height. Therefore, according to this configuration, the adjustment value of the ultrasound incidence angle θ is obtained from the relation between the swimming speed of the fish and the adjustment value when the swimming speed is normalized by the fish size of the fish, so that the adjustment value can be properly obtained.

[0158] In this case, the fish size used for normalization may be the size of the fish in a height direction of the fish (upper body height, body height, etc.) as described above.

[0159] Alternatively, the fish size used for normalization may be the size of the fish in a longitudinal direction of the fish (body length, fork length, etc.) as described above.

[0160] Further, as described above, the adjustment of the ultrasound incidence angle θ may depend on fish species.

[0161] As shown in FIGS. 6A and 6B, 7A and 7B, and 8A and 8B, the relation between the swimming speed (average swimming speed) of the fish and the adjustment value (average posture angle) differs for each fish species. Therefore, by changing the adjustment of the ultrasound incidence angle θ according to the fish species in this way, the ultrasound incidence angle θ can be properly adjusted.

[0162] As shown in FIG. 10, an ultrasound incidence angle calculation method executed by a signal processing unit 30 (computer) by a program held in the signal processing unit 30 includes tracking in time at step S13 an echo of a fish from echo signals generated by receiving with an ultrasonic transducer 10 reflection wave of each transmission wave of a plurality of transmission waves sequentially transmitted toward the fish with the ultrasonic transducer 10, calculating at step S14 a swimming speed of the tracked fish from the tracked echo of the fish, calculating at step S15 an ultrasound incidence angle θ of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer 10, and adjusting at step S16 the ultrasound incidence angle θ based on the swimming speed of the fish.

[0163] According to this ultrasound incidence angle calculation method, the ultrasound incidence angle on the fish can be accurately calculated as described above.

[0164] The present disclosure is not limited to the above embodiments. In addition, the embodiments of the present disclosure can be modified in various ways other than the above configurations.

[0165] For example, in the above embodiments, as shown in Equations 6 and 7, the reference speed v0 at which the average posture angle becomes 0 on the correlation line L11 is set as the threshold speed for the execution or not of the adjustment. However, the method for setting the threshold speed is not limited thereto. The threshold speed may be set near an upper limit of a range of the swimming speed (average swimming speed) that can be assumed to be appropriate to use the correlation line L11 for obtaining the adjustment value (average posture angle). Similarly, when the correlation line L21 is used for adjustment, the threshold speed may be set near an upper limit of a range of the normalized swimming speed (average swimming speed) that can be assumed to be appropriate to use the correlation line L21 for obtaining the adjustment value (average posture angle).

[0166] In the above embodiments, as a method of using the correlation curves L12 and L22 for adjusting the ultrasound incidence angle θ, a method of using a correlation function representing the correlation curves L12 and L22 or a table corresponding to the correlation curves L12 and L22 has been described. However, the method of using the correlation curves L12 and L22 for adjusting is not limited thereto. For example, as in the case of using Equations 6 and 7 and Equations 9 and 10, when the swimming speed of the fish is higher than a predetermined threshold speed, adjustment based on the correlation curves L12 and L22 may not be performed. In this case, for example, the threshold speed may be set near a lower limit of a range of the swimming speed (average swimming speed) in which the adjustment value (average posture angle) of the correlation curves L12 and L22 is assumed to have substantially converged to 0°.

[0167] In the flowchart of FIG. 10, the fish size calculation processing (S17) and the display processing (S19) are performed as a series of processing together with the ultrasound incidence angle calculation processing (S12 to S16), but the fish size calculation processing (S17) and the display processing (S19) may be performed separately from the ultrasound incidence angle calculation processing (S12 to S16).

[0168] In this case, the signal processing unit 30 stores the adjusted ultrasound incidence angle θ′ obtained in steps S12 to S16 in connection with the corresponding fish echo signal for each echo signal. Then, when the signal processing unit 30 calculates and displays the size of fish, the signal processing unit 30 reads the echo signal of a predetermined period including the fish echo signal and the adjusted ultrasound incidence angle θ′ associated with the fish echo signal, and calculates the size of the fish with the same processing as in step S17. Then, the signal processing unit 30 causes the operation display unit 40 to display the calculated size of the fish.

[0169] The size of the fish may be calculated and displayed by an external computer separate from the signal processing unit 30. In this case, the signal processing unit 30 stores the adjusted ultrasound incidence angle θ′ obtained in steps S12 to S16 for each echo signal in the same manner as described above, in connection with the corresponding fish echo signal. The external computer acquires the echo signal of a predetermined period including the fish echo signal and the adjusted ultrasound incidence angle θ′ associated with the fish echo signal from the signal processing unit 30. Then, the external computer calculates the size of the fish with the same processing as in step S17 and displays the calculated size of the fish on its display unit.

[0170] The receiving channels of the ultrasonic transducer 10 are not limited to 4 but 5 or more may be provided. Again, the position of the fish relative to the ultrasonic transducer 10 can be calculated by the processing based on the split beam method. To the extent that the position of the fish relative to the ultrasonic transducer 10 can be calculated, the number of receiving channels of the ultrasonic transducer 10 can be appropriately changed. Furthermore, the position of the fish relative to the ultrasonic transducer 10 may be calculated based on the echo signal by a method other than the split beam method. For example, the single-beam method disclosed in JP2022-158950 can also estimate speed and incidence angle to calculate the position of the fish.

[0171] In the above embodiments, the ultrasonic transducer 10 is provided vertically downward so that the transmission wave (ultrasonic wave) is transmitted downward from the water surface side toward the water, but the ultrasonic transducer 10 may be arranged at the bottom of the net 5 to transmit the transmission wave (ultrasonic wave) vertically upward toward the water surface above.

[0172] In addition, the fish to be the object of data acquisition is not limited to fish farmed in an aquaculture farm (e.g., fish tank 2). For example, if the fish species of a fish school can be inferred by a fisherman or identified by a conventional fish finder capable of identifying the fish species, the ultrasonic transducer 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 fish size of fish in the fish school.

[0173] In addition, the embodiments of the present disclosure may be suitably modified within the scope of the appended claims.

[0174] It is to be understood that not necessarily all objects or advantages may be achieved in accordance with any particular embodiment described herein. Thus, for example, those skilled in the art will recognize that certain embodiments may be configured to operate in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0175] All of the processes described herein may be embodied in, and fully automated via, software code modules executed by a computing system that includes one or more computers or processors. The code modules may be stored in any type of non-transitory computer-readable medium or other computer storage device. Some or all the methods may be embodied in specialized computer hardware.

[0176] Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and / or computing systems that can function together.

[0177] The various illustrative logical blocks and modules described in connection with the embodiment disclosed herein can be implemented or performed by a machine, such as a processor. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuitry configured to process computer-executable instructions. In another embodiment, a processor includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor (DSP) and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, some or all of the signal processing algorithms described herein may be implemented in analog circuitry or mixed analog and digital circuitry. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

[0178] Conditional language such as, among others, “can,” “could,” “might” or “may,” unless specifically stated otherwise, are otherwise understood within the context as used in general to convey that certain embodiments include, while other embodiments do not include, certain features, elements and / or steps. Thus, such conditional language is not generally intended to imply that features, elements and / or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and / or steps are included or are to be performed in any particular embodiment.

[0179] Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and / or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present.

[0180] Any process descriptions, elements or blocks in the flow diagrams described herein and / or depicted in the attached figures should be understood as potentially representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or elements in the process. Alternate implementations are included within the scope of the embodiments described herein in which elements or functions may be deleted, executed out of order from that shown, or discussed, including substantially concurrently or in reverse order, depending on the functionality involved as would be understood by those skilled in the art.

[0181] Unless otherwise explicitly stated, articles such as “a” or “an” should generally be interpreted to include one or more described items. Accordingly, phrases such as “a device configured to” are intended to include one or more recited devices. Such one or more recited devices can also be collectively configured to carry out the stated recitations. For example, “a processor configured to carry out recitations A, B and C” can include a first processor configured to carry out recitation A working in conjunction with a second processor configured to carry out recitations B and C. The same holds true for the use of definite articles used to introduce embodiment recitations. In addition, even if a specific number of an introduced embodiment recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations).

[0182] It will be understood by those within the art that, in general, terms used herein, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.).

[0183] For expository purposes, the term “horizontal” as used herein is defined as a plane parallel to the plane or surface of the floor of the area in which the system being described is used or the method being described is performed, regardless of its orientation. The term “floor” can be interchanged with the term “ground” or “water surface”. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms such as “above,” “below,” “bottom,” “top,” “side,” “higher,” “lower,” “upper,” “over,” and “under,” are defined with respect to the horizontal plane.

[0184] As used herein, the terms “attached,” “connected,” “mated,” and other such relational terms should be construed, unless otherwise noted, to include removable, movable, fixed, adjustable, and / or releasable connections or attachments. The connections / attachments can include direct connections and / or connections having intermediate structure between the two components discussed.

[0185] Unless otherwise explicitly stated, numbers preceded by a term such as “approximately”, “about”, and “substantially” as used herein include the recited numbers, and also represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, unless otherwise explicitly stated, the terms “approximately”, “about”, and “substantially” may refer to an amount that is within less than 10% of the stated amount. Features of embodiments disclosed herein preceded by a term such as “approximately”, “about”, and “substantially” as used herein represent the feature with some variability that still performs a desired function or achieves a desired result for that feature.

[0186] It should be emphasized that many variations and modifications may be made to the above-described embodiments, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. REFERENCE SIGNS LIST

[0187] 1 Ultrasonic device 10 Ultrasonic transducer 32 Fish echo tracking module 33 Fish speed calculation module 34 Ultrasound incidence angle calculation module 35 Angle adjustment module

Claims

1. An ultrasonic device (1) for fish detection, comprising: an ultrasonic transducer (10) configured to sequentially transmit a plurality of transmission waves toward a fish and generate an echo signal for each of the plurality of transmission waves; a fish echo tracking module (32) configured to track in time an echo of the fish from the echo signals; a fish speed calculation module (33) configured to calculate a swimming speed of the tracked fish from the tracked echoes of the fish; an ultrasound incidence angle calculation module (34) configured to calculate an ultrasound incidence angle of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer (10); and an angle adjustment module (35) configured to adjust the ultrasound incidence angle based on the swimming speed of the fish.

2. The ultrasonic device (1) of claim 1, wherein the angle adjustment module (35) is configured to adjust the ultrasound incidence angle with an adjustment value that changes as a function of the swimming speed.

3. The ultrasonic device (1) of claim 2, wherein the adjustment value is obtained from a predetermined relation between adjustment value and swimming speed of the fish.

4. The ultrasonic device (1) of any of the preceding claims, wherein the angle adjustment module (35) is configured to adjust the ultrasound incidence angle with an adjustment value that changes linearly with the swimming speed.

5. The ultrasonic device (1) of any of the preceding claims, wherein the angle adjustment module (35) is configured to adjust the ultrasound incidence angle with an adjustment value according to equation a×v+b, where (v) is the swimming speed, and (a) and (b) are coefficients predetermined by fish species.

6. The ultrasonic device (1) of any of the preceding claims, wherein the angle adjustment module (35) is configured to: adjust the ultrasound incidence angle when the swimming speed is below a threshold speed; and not adjust the ultrasound incidence angle when the swimming speed is above the threshold speed.

7. The ultrasonic device (1) of any of the preceding claims, wherein the fish speed calculation module (33) is further configured to normalize the swimming speed with a fish size of the fish.

8. The ultrasonic device (1) of claim 7, wherein the fish size is a size of the fish in a height direction of the fish.

9. The ultrasonic device (1) of claim 7, wherein the fish size is a size of the fish in a longitudinal direction of the fish.

10. The ultrasonic device (1) of any of the preceding claims, wherein the adjustment of the ultrasound incidence angle depends on fish species.

11. An ultrasound incidence angle calculation method, comprising: tracking (S13) in time an echo of a fish from echo signals generated by receiving with an ultrasonic transducer reflection wave of each transmission wave of a plurality of transmission waves sequentially transmitted toward the fish with the ultrasonic transducer; calculating (S14) a swimming speed of the tracked fish from the tracked echoes of the fish; calculating (S15) an ultrasound incidence angle of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer; and adjusting (S16) the ultrasound incidence angle based on the swimming speed of the fish.

12. A program that causes a computer to: track (S13) in time an echo of a fish from echo signals generated by receiving with an ultrasonic transducer reflection wave of each transmission wave of a plurality of transmission waves sequentially transmitted toward the fish with the ultrasonic transducer; calculate (S14) a swimming speed of the tracked fish from the tracked echoes of the fish; calculate (S15) an ultrasound incidence angle of the plurality of transmission waves on the tracked fish based on a position of the fish relative to the ultrasonic transducer; and adjust (S16) the ultrasound incidence angle based on the swimming speed of the fish.

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