Swimming speed measuring device and swimming speed measuring method

Abstract

A swimming speed measuring device (1) including a transducer (2), a radial velocity calculating module (13), a distance derivative calculating module (14), and a swimming speed calculating module (15) is disclosed. The transducer (2) is configured to generate echo signals based on ultrasonic pings that are periodically emitted into water and reflected by a swimming object swimming in the water. The radial velocity calculating module (13) is configured to calculate a radial velocity of the swimming object based on a phase difference between two of the echo signals. The distance derivative calculating module (14) is configured to calculate a first derivative of a distance between the swimming object and the transducer with respect to time based on the two echo signals. The swimming speed calculating module (15) is configured to calculate a swimming speed of the swimming object based on the radial velocity and the first derivative of the distance.

Description

SWIMMING SPEED MEASURING DEVICE AND SWIMMING SPEED MEASURING METHOD

[0001] The present disclosure relates to a swimming speed measuring device, a swimming speed measuring method, and a program.Background

[0002] Patent Document 1 discloses a technique for calculating a swimming speed of a fish using a single-beam transducer and utilizing the fact that a distance between the transducer and the fish changes with time according to a hyperbolic curve (see paragraphs 0085~0094).

[0003] Patent Document 1: JP2022-158950

[0004] However, with the technology disclosed in Patent Document 1, measurement accuracy of the swimming speed is not sufficient.

[0005] The present disclosure has been made in view of the above problem, and the main object thereof is to provide a swimming speed measuring device, a swimming speed measuring method, and a program capable of improving the measurement accuracy of the swimming speed.Summary

[0006] To solve the above problem, a swimming speed measuring device according to a first aspect of the present disclosure includes a transducer, a radial velocity calculating module, a distance derivative calculating module, and a swimming speed calculating module. The transducer is configured to generate echo signals based on ultrasonic pings that are periodically emitted into water and reflected by a swimming object swimming in the water. The radial velocity calculating module is configured to calculate a radial velocity of the swimming object based on a phase difference between two of the echo signals. The distance derivative calculating module is configured to calculate a first derivative of a distance between the swimming object and the transducer with respect to time based on the two echo signals. The swimming speed calculating module is configured to calculate a swimming speed of the swimming object based on the radial velocity and the first derivative of the distance. Thus, it is possible to improve the measurement accuracy of the swimming speed.

[0007] In the above embodiment, the swimming speed calculating module may be further configured to adjust the radial velocity based on a comparison of the radial velocity and the first derivative of the distance. Thus, it is possible to improve the measurement accuracy of the swimming speed.

[0008] In the above embodiment, the swimming speed calculating module may be further configured to calculate the swimming speed based on a product of the adjusted radial velocity and the distance. Thus, it is possible to improve the measurement accuracy of the swimming speed.

[0009] In the above embodiment, the swimming speed calculating module may be further configured to calculate the swimming speed based on the product being a linear function of time. Thus, it is possible to improve the measurement accuracy of the swimming speed.

[0010] In the above embodiment, the swimming speed calculating module may be further configured to calculate the swimming speed based on a slope of the linear function corresponding to a square of the swimming speed. Thus, it is possible to improve the measurement accuracy of the swimming speed.

[0011] In the above embodiment, a tracking module may further be provided. The tracking module may be configured to track echoes from the same swimming object in the echo signals. In this manner, it is possible to measure the swimming speed of the same swimming object tracked among the plurality of swimming objects.

[0012] In the above embodiment, the transducer may be a single-beam transducer. Thus, it is possible to improve the measurement accuracy of the swimming speed even with a single-beam transducer.

[0013] In the above embodiment, the transducer may generate the echo signals by forming one or more reception beams, and the two echo signals may be generated with one of the one or more reception beams. Thus, it is possible to improve the measurement accuracy of the swimming speed by using one reception beam.

[0014] A swimming speed measuring method according to a second aspect of the present disclosure includes generating echo signals with a transducer based on ultrasonic pings that are periodically emitted into water and reflected by a swimming object swimming in the water; calculating a radial velocity of the swimming object based on a phase difference between two of the echo signals; calculating a first derivative of a distance between the swimming object and the transducer with respect to time based on the two echo signals; and calculating a swimming speed of the swimming object based on the radial velocity and the first derivative of the distance. Thus, it is possible to improve the measurement accuracy of the swimming speed.

[0015] A 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 obtain echo signals generated with a transducer based on ultrasonic pings that are periodically emitted into water and reflected by a swimming object swimming in the water; calculate a radial velocity of the swimming object based on a phase difference between two of the echo signals; calculate a first derivative of a distance between the swimming object and the transducer with respect to time based on the two echo signals; and calculate a swimming speed of the swimming object based on the radial velocity and the first derivative of the distance. Thus, it is possible to improve the measurement accuracy of the swimming speed.

[0016] According to the present disclosure, it is possible to improve the measurement accuracy of the swimming speed.

[0017] FIG. 1 shows an example of a swimming speed measuring device.FIG. 2 shows an example of a processing module.FIG. 3 shows an example of a swimming speed measuring method.FIG. 4 is a diagram explaining a swimming speed measurement.FIG. 5 is a diagram explaining the swimming speed measurement.FIG. 6 is a diagram showing a measurement result of a reference example.FIG. 7 is a diagram showing a measurement result of an embodiment.DETAILED DESCRIPTION

[0018] 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.

[0019] 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.

[0020] 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.

[0021] Embodiments of the present disclosure will now be described with reference to the drawings. In the present specification and drawings, an element like a previously described element with respect to a previous drawing may be denoted by the same reference numeral and a detailed description may be omitted accordingly.

[0022] FIG. 1 is a diagram showing a configuration example and an application example of a swimming speed measuring device 1. The swimming speed measuring device 1 is a device for measuring the swimming speed of a swimming object FS swimming in water. The swimming object FS is, for example, a fish. The swimming speed measuring device 1 is, for example, installed in a fish farm such as in a fish enclosure. The swimming object FS may not only be a living creature but also any moving object moving in the water, for example, an underwater drone.

[0023] The swimming speed measuring device 1 includes a transducer 2 fixed in water and a processing module 3 communicatively connected to the transducer 2.

[0024] The transducer 2 is a transducer that converts electrical signals into ultrasonic waves and vice versa. The transducer 2 periodically transmits an ultrasonic ping (hereinafter also referred to simply as "ping") into the water and receives the ping reflected by the swimming object FS to generate an echo signal.

[0025] In this embodiment, the transducer 2 is a single-beam transducer. A single-beam transducer is a transducer that has a single reception channel and forms a single reception beam.

[0026] In contrast, a split-beam transducer has a plurality of reception channels and forms a plurality of reception beams. A three-dimensional position of a swimming object can be specified from a phase difference between the plurality of reception channels, and the swimming speed can be accurately measured from a change of the position with time. However, split-beam transducers are more expensive than single-beam transducers.

[0027] According to the technique disclosed in Patent Document 1, the swimming speed can be measured with a single-beam transducer, but the measurement accuracy is not sufficient.

[0028] In the present embodiment, by using the calculation method described below, even when a single-beam transducer, which is less expensive than a split-beam transducer, is provided, it is possible to improve the measurement accuracy of the swimming speed.

[0029] Note that the transducer 2 may be a split-beam transducer. The calculation method of the present embodiment can be applied when the split-beam transducer is used in a single-beam mode, that is, when an echo signal is generated by one of the plurality of reception beams.

[0030] As shown in FIG. 1, it is assumed that, at time t, the swimming object FS is in constant speed linear motion at a constant swimming speed v at a position that is at a distance r from the transducer 2. At this time t, an angle θ at which the ping is incident on the swimming object FS has a relationship represented by Equation 1 below.Equation 1

[0031]

[0032] tpis a time at which the swimming object FS moving at constant speed is closest to the transducer 2. rpis a distance between the swimming object FS and the transducer 2 at time tp, that is, a length of a perpendicular line lowered from the transducer 2 to a straight line corresponding to a three-dimensional trajectory of the swimming object FS.

[0033] For the swimming speed v of the swimming object FS, an acoustically detectable velocity component is vsinθ along the incident angle of the ping. Since vsinθ is a radial velocity vdop(Doppler velocity) that contributes to the Doppler effect, the calculation method of the present embodiment uses this relationship to calculate the swimming speed v.

[0034] FIG. 2 is a block diagram showing a configuration example of processing module 3. The processing module 3 is a computer including a CPU and executes signal processing according to a program. The program may be supplied from a non-temporary storage medium or from a communication line.

[0035] The processing module 3 includes an echo signal acquisition module 11, a tracking module 12, a radial velocity calculating module 13, a distance derivative calculating module 14, and a swimming speed calculating module 15. These functional modules are realized by the CPU executing signal processing according to the program.

[0036] FIG. 3 is a flow diagram showing an example of a swimming speed measuring method implemented in the swimming speed measuring device 1. The processing module 3 of the swimming speed measuring device 1 executes signal processing shown in that figure according to a program. FIGS. 4 and 5 are diagrams for explaining swimming speed measurement.

[0037] In step S11, the processing module 3 acquires an echo signal from the transducer 2 (processing of the echo signal acquisition module 11). As shown in FIG. 4, the processing module 3 acquires the echo signals of a plurality of pings 1~3. Although only 3 pings are shown in the example shown in FIG. 4, the echo signals of 4 or more pings may be acquired and used for the swimming speed measurement.

[0038] In step S12, the processing module 3 tracks echoes from the same swimming object FS in the echo signals (processing of the tracking module 12). As shown in FIG. 4, the processing module 3 performs tracking by extracting echoes having at least a given intensity in the echo signals of the plurality of pings 1~3 and by determining a continuity of the echoes between adjacent pings. Other methods may be used for tracking, such as a method using a Kalman filter.

[0039] In step S13, the processing module 3 measures the distance r from the transducer 2 to the swimming object FS based on the echo signal. As shown in FIG. 4, the processing module 3 calculates the distance r for each of the echo signals of the plurality of pings 1~3. The distance r is calculated based on a time from when the transducer 2 transmits the ping to when the reflected ping is detected (round-trip time of the ping) and propagation speed of ultrasonic wave in water.

[0040] In step S14, the processing module 3 measures a phase difference ΔΦ of the echo signals. As shown in FIG. 4, the processing module 3 measures the phase difference ΔΦ between adjacent pings of the echo signals of the plurality of pings 1~3. Specifically, the processing module 3 calculates an IQ signal (in-phase / quadrature phase signal) for each echo signal and calculates the phase difference ΔΦ between adjacent pings using complex correlation or the like.

[0041] In step S15, the processing module 3 calculates the radial velocity vdop(Doppler velocity) of the swimming object FS based on the phase difference ΔΦ (processing of the radial velocity calculating module 13). The radial velocity vdopis expressed by the following Equation 2. λ is a wavelength of the ping. Δt is a transmission period of the ping.Equation 2

[0042]

[0043] Because of aliasing (wrapping), the phase difference ΔΦ remains arbitrary and cannot be uniquely determined. This problem of arbitrariness is solved by using a first derivative -dr / dt of the distance r as explained below.

[0044] In step S16, the processing module 3 calculates the first derivative -dr / dt of the distance r with respect to the time t based on the echo signal (processing of the distance derivative calculating module 14). As shown in FIG. 4, the processing module 3 calculates the first derivative -dr / dt between adjacent pings of the echo signals of the plurality of pings 1~3.

[0045] The first derivative -dr / dt should be equal to the radial velocity vdopif the radial velocity vdophas no aliasing. However, the first derivative -dr / dt is also not accurate enough to be used independently to calculate the swimming speed v.

[0046] In steps S17 to S20, the processing module 3 calculates the swimming speed v based on the radial velocity vdopand the first derivative -dr / dt (processing of the swimming speed calculating module 15). Each of steps S17 to S20 is described below.

[0047] In step S17, the processing module 3 adjusts the radial velocity vdopbased on a comparison between the radial velocity vdopand the first derivative -dr / dt. Specifically, the processing module 3 calculates the nearest integer n with the following Equation 3. Square brackets in the equation represent an operation of rounding to the nearest whole number.Equation 3

[0048]

[0049] Then, the processing module 3 adjusts the radial velocity vdopwith the following Equation 4 using the calculated integer n. As a result, the radial velocity vdopobtained by subtracting the aliasing portion is obtained. Hereinafter, the left-hand side of Equation 4 (vdopwith a hat symbol) is referred to as “adjusted radial velocity vdop”.Equation 4

[0050]

[0051] In step S18, the processing module 3 calculates a product of the adjusted radial velocity vdopand the distance r. Specifically, the following Equation 5 is obtained by substituting the above Equation 1 into sinθ of the Equation 2, and the following Equation 6 is obtained by multiplying both sides of the Equation 5 by -r.Equation 5

[0052] Equation 6

[0053]

[0054] According to Equation 6, the product of the adjusted radial velocity vdopand the distance r is a linear function with respect to time t. A slope of the linear function corresponds to a square of the swimming speed v.

[0055] In step S19, the processing module 3 performs linear regression from the calculated product and the time t to obtain the slope of the linear function. Further, in step S20, the processing module 3 calculates the swimming speed v from the slope of the linear function.

[0056] As shown in FIG. 5 and Equation 6, since the product of the adjusted radial speed vdopand the distance r is a linear function with respect to time t, and the slope of the linear function corresponds to the square of the swimming speed v, the square of the swimming speed v can be obtained by obtaining the slope of the linear function by linear regression, and the swimming speed v can be obtained by calculating the square root of the slope of the linear function.

[0057] When the slope of the linear function shown in FIG. 5 and Equation 6 is negative or when a correlation is low (for example, when a coefficient of determination is 0.8 or less), the processing module 3 may not output the swimming speed v.

[0058] The procedure of the swimming speed measuring method is completed. According to the present embodiment, it is possible to improve the measurement accuracy of the swimming speed v by adjusting the radial speed vdopusing the first derivative -dr / dt of the distance r.

[0059] An example and a reference example are described below. The example is the calculation method of the embodiment described above. The reference example is the calculation method of Patent Document 1.

[0060] In an experiment, yellowtail in a fish enclosure were tracked from data from an echo recording using a split-beam type fish finder. Then, the swimming speed calculated by split beam, the swimming speed calculated according to the example, and the swimming speed calculated according to the reference example were calculated for each tracked individual.

[0061] FIG. 6 is a graph in which each individual is plotted with the horizontal axis as the swimming speed calculated by split beam and the vertical axis as the swimming speed calculated according to the reference example. FIG. 7 is a graph in which each individual is plotted with the horizontal axis as the swimming speed calculated by split beam and the vertical axis as the swimming speed calculated according to the example.

[0062] The diagonal straight line in the figures is a straight line with y=x, i.e., a straight line when both swimming speeds coincide, and the closer to the straight line, the higher the measurement accuracy is.

[0063] Comparing FIGS. 6 and 7, it can be seen that the measurement accuracy of the swimming speed is higher in the embodiment than in the reference example, because points are more discrete in the graph of FIG. 6 and points are more clustered in a vicinity of the diagonal straight line in the graph of FIG. 7.

[0064] Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are of course possible for those skilled in the art.

[0065] The swimming speed measuring method described above is typically used for a fish finder, but is not limited thereto, and may be used, for example, for sonar. Even in a fish finder or sonar that forms a plurality of reception beams, the calculation method of the present embodiment can be applied to an echo signal generated by one of the plurality of reception beams.

[0066] The determination of the integer n in step S17 may be performed in units of 1 ping, or for each tracked individual, after adjusting vdop, the difference between vdopand -dr / dt may be calculated for all the pings, and the average may be obtained. REFERENCE SIGNS LIST

[0067] 1 Swimming speed measuring device 2 Transducer 3 Processing module 11 Echo signal acquisition unit 12 Tracking module 13 Radial velocity calculating module 14 Distance derivative calculating module 15 Swimming speed calculating unit FS Swimming object

Claims

1. A swimming speed measuring device (1) comprising: a transducer (2) configured to generate echo signals based on ultrasonic pings that are periodically emitted into water and reflected by a swimming object swimming in the water; a radial velocity calculating module (13) configured to calculate a radial velocity of the swimming object based on a phase difference between two of the echo signals; a distance derivative calculating module (14) configured to calculate a first derivative of a distance between the swimming object and the transducer (2) with respect to time based on the two echo signals; and a swimming speed calculating module (15) configured to calculate a swimming speed of the swimming object based on the radial velocity and the first derivative of the distance.

2. The swimming speed measuring device (1) of claim 1, wherein: the swimming speed calculating module (15) is further configured to adjust the radial velocity based on a comparison of the radial velocity and the first derivative of the distance.

3. The swimming speed measuring device (1) of claim 2, wherein: the swimming speed calculating module (15) is further configured to calculate the swimming speed based on a product of the adjusted radial velocity and the distance.

4. The swimming speed measuring device (1) of claim 3, wherein: the swimming speed calculating module (1) is further configured to calculate the swimming speed based on the product being a linear function of time.

5. The swimming speed measuring device (1) of claim 4, wherein: the swimming speed calculating module (1) is further configured to calculate the swimming speed based on a slope of the linear function corresponding to a square of the swimming speed.

6. The swimming speed measuring device (1) of any of the preceding claims, further comprising: a tracking module (12) configured to track echoes from the same swimming object in the echo signals.

7. The swimming speed measuring device (1) of any of the preceding claims, wherein: the transducer (2) is a single-beam transducer.

8. The swimming speed measuring device (1) of any of claims 1 to 6, wherein: the transducer (2) generates the echo signals by forming one or more reception beams; and the two echo signals are generated with one of the one or more reception beams.

9. A swimming speed measuring method comprising: generating (S11) echo signals with a transducer based on ultrasonic pings that are periodically emitted into water and reflected by a swimming object swimming in the water; calculating (S15) a radial velocity of the swimming object based on a phase difference between two of the echo signals; calculating (S16) a first derivative of a distance between the swimming object and the transducer with respect to time based on the two echo signals; and calculating (S20) a swimming speed of the swimming object based on the radial velocity and the first derivative of the distance.

10. A program that causes a computer to: obtain (S11) echo signals generated with a transducer based on ultrasonic pings that are periodically emitted into water and reflected by a swimming object swimming in the water; calculate (S15) a radial velocity of the swimming object based on a phase difference between two of the echo signals; calculate (S16) a first derivative of a distance between the swimming object and the transducer with respect to time based on the two echo signals; and calculate (S20) a swimming speed of the swimming object based on the radial velocity and the first derivative of the distance.

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