Swimming speed measuring apparatus, method for measuring swimming speed, and program

Abstract

To provide a swimming speed measuring apparatus capable of improving the measurement accuracy of swimming speed.SOLUTION: A swimming speed measuring apparatus includes: a transducer which is periodically fired into water and generates echo signals on the basis of ultrasonic pings reflected by a swimming object swimming in the water; a line-of-sight velocity calculation unit configured to calculate the line-of-sight velocity of the swimming object on the basis of the phase difference between two echo signals; a distance differential calculation unit configured to calculate a first-order differential of the distance between the swimming object and the transducer with respect to time on the basis of the two echo signals; and a swimming speed calculation unit configured to calculate the swimming speed of the swimming object on the basis of the line-of-sight velocity and the first-order differential of the distance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a swimming speed measurement device, a swimming speed measurement method, and a program. [Background technology]

[0002] Patent Document 1 discloses a technique for calculating the swimming speed of a fish by using a single beam transducer and utilizing the fact that the distance between the transducer and the fish changes over time according to a hyperbola (see paragraphs 0085 to 0094). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-158950 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technique disclosed in Patent Document 1 does not provide sufficient accuracy in measuring swimming speed.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its main object is to provide a swimming speed measurement device, a swimming speed measurement method, and a program that can improve the accuracy of measuring swimming speed. [Means for solving the problem]

[0006] To solve the above problems, one aspect of the present invention provides a swimming speed measuring device that includes: a transducer that periodically emits ultrasonic pings into water and generates echo signals based on the ultrasonic pings reflected by an object swimming in the water; a radial velocity calculation unit that calculates the radial velocity of the object based on the phase difference between two of the echo signals; a distance differential calculation unit that calculates a first derivative of the distance between the object and the transducer with respect to time based on the two echo signals; and a swimming speed calculation unit that calculates the swimming speed of the object based on the radial velocity and the first derivative of the distance. This makes it possible to improve the accuracy of measuring swimming speed.

[0007] In the above aspect, the swimming speed calculation unit may correct the line of sight velocity based on a comparison between the line of sight velocity and a first derivative of the distance, thereby improving the accuracy of measuring the swimming speed.

[0008] In the above aspect, the swimming speed calculation unit may calculate the swimming speed based on the product of the corrected line of sight velocity and the distance, thereby improving the accuracy of measuring the swimming speed.

[0009] In the above aspect, the swimming speed calculation unit may calculate the swimming speed based on the fact that the product is a linear function of time, thereby improving the accuracy of measuring the swimming speed.

[0010] In the above aspect, the swimming speed calculation unit may calculate the swimming speed based on the fact that the slope of the linear function corresponds to the square of the swimming speed, thereby improving the accuracy of measuring the swimming speed.

[0011] In the above aspect, the device may further include a tracking unit that tracks echoes from the same swimming object in the echo signals, thereby making it possible to measure the swimming speed of the same tracked swimming object from among a plurality of swimming objects.

[0012] In the above aspect, the transducer may be a single beam transducer. In this case, even when a single beam transducer is used, it is possible to improve the accuracy of measuring the swimming speed.

[0013] In the above aspect, the transducer may generate the echo signals by forming one or more receive beams, and the two echo signals may be generated by one of the one or more receive beams. This makes it possible to improve the accuracy of measuring swimming speed by using one receive beam.

[0014] Another aspect of the swimming speed measurement method of the present invention involves generating echo signals from a transducer based on ultrasonic pings periodically emitted into water and reflected by an object swimming in the water, calculating the radial velocity of the object based on the phase difference between two of the echo signals, calculating a first derivative of the distance between the object and the transducer with respect to time based on the two echo signals, and calculating the swimming speed of the object based on the radial velocity and the first derivative of the distance. This method makes it possible to improve the accuracy of measuring swimming speed.

[0015] Another aspect of the present invention provides a program that causes a computer to execute the following steps: acquire, with a transducer, echo signals generated based on ultrasonic pings periodically emitted into water and reflected by an object swimming in the water; calculate the radial velocity of the object based on the phase difference between two of the echo signals; calculate a first derivative of the distance between the object and the transducer with respect to time based on the two echo signals; and calculate the swimming velocity of the object based on the radial velocity and the first derivative of the distance. This allows for improved accuracy in measuring swimming velocity. [Effects of the Invention]

[0016] According to the present invention, it is possible to improve the accuracy of measuring swimming speed. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram illustrating an example of a swimming speed measuring device. [Figure 2] FIG. 2 illustrates an example of a control unit. [Figure 3] FIG. 10 is a diagram showing an example of a swimming speed measurement method. [Figure 4] FIG. 10 is a diagram for explaining swimming speed measurement. [Figure 5] FIG. 10 is a diagram for explaining swimming speed measurement. [Figure 6] FIG. 10 is a diagram showing measurement results in a reference example. [Figure 7] FIG. 1 is a diagram showing measurement results in an example. DETAILED DESCRIPTION OF THE INVENTION

[0018] The functions provided by the components described herein may be implemented in circuits or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a Central Processing Unit (CPU), conventional circuits, and / or combinations thereof, programmed to provide the described functions. A processor includes transistors and other circuitry and is considered a circuit or processing circuit. A processor may be a programmable processor that executes a program stored in a memory.

[0019] In this specification, circuits, units, and means are hardware that is programmed to realize the described functions or that performs this function, which may be any hardware disclosed herein or any hardware that is programmed to realize the described functions or that is known to perform this function.

[0020] If the hardware is a processor considered to be a type of circuit, the circuit, means, or unit is a combination of the hardware and the software used to configure the hardware and / or processor.

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification and the drawings, elements similar to those described above with reference to the previous drawings will be designated by the same reference numerals, and detailed descriptions thereof may be omitted as appropriate.

[0022] FIG. 1 shows an example of the configuration and application of a swimming speed measurement device 1. The swimming speed measurement 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 measurement device 1 is installed in, for example, a fish farm such as a fish pen. The swimming object FS is not limited to a living creature, but may be any moving object that moves in water, such as an underwater drone.

[0023] The swimming speed measuring device 1 includes a transducer 2 fixed in water and a processing unit 3 connected to the transducer 2 so as to be able to communicate with it.

[0024] The transducer 2 is a converter that converts between an electrical signal and ultrasonic vibrations. The transducer 2 periodically emits ultrasonic pings (hereinafter simply referred to as "pings") into the water, receives the pings reflected by the swimming object FS, and generates 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 receiving channel and forms a single receiving beam.

[0026] In contrast, a split beam transducer is a transducer that has multiple receiving channels and forms multiple receiving beams. It can identify the three-dimensional position of a swimming object from the phase difference between the multiple receiving channels and accurately measure the swimming speed from the time change. However, split beam transducers are more expensive than single beam transducers.

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

[0028] Therefore, in this embodiment, by using the calculation method described below, it is possible to improve the measurement accuracy of swimming speed even when using a single beam transducer, which is cheaper than a split beam transducer.

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

[0030] As shown in Figure 1, it is assumed that the swimming object FS moves at a constant speed v at a position at a distance r from the transducer 2 at time t. In this case, the angle θ at which the ping is incident on the swimming object FS has the relationship expressed by the following equation 1.

[0031]

number

[0032] t p is the time when the swimming object FS, which is moving at a constant speed in a straight line, comes closest to the transducer 2. p is the time t pThis is the distance between the swimming object FS and the transducer 2, i.e., the length of the perpendicular line drawn from the transducer 2 to the straight line of the three-dimensional trajectory of the swimming object FS.

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

[0034] 2 is a block diagram showing an example of the configuration of the control unit 3. The processing unit 3 is a computer including a CPU, and executes information processing according to a program. The program may be supplied from a non-transitory storage medium or via a communication line.

[0035] The processing unit 3 includes an echo signal acquisition unit 11, a tracking unit 12, a line-of-sight velocity calculation unit 13, a distance differential calculation unit 14, and a swimming speed calculation unit 15. These functional units are realized by the CPU executing information processing according to a program.

[0036] Fig. 3 is a flow diagram showing an example of the procedure of the swimming speed measuring method realized in the swimming speed measuring device 1. The control unit 3 of the swimming speed measuring device 1 executes the information processing shown in the diagram in accordance with a program. Fig. 4 and Fig. 5 are diagrams for explaining swimming speed measurement.

[0037] In S11, the processing unit 3 acquires echo signals from the transducer 2 (processing as the echo signal acquisition unit 11). As shown in Fig. 4, the processing unit 3 acquires echo signals of multiple pings 1 to 3. Although only three pings are shown in the example shown in the figure, echo signals of four or more pings may be acquired and used to measure swimming speed.

[0038] In S12, the processing unit 3 tracks echoes from the same swimming object FS in the echo signals (processing as the tracking unit 12). As shown in Fig. 4, the processing unit 3 performs tracking by extracting echoes having amplitudes equal to or greater than a predetermined value from the echo signals of multiple pings 1 to 3 and determining the continuity of the echoes between adjacent pings. Other tracking methods, such as a method using a Kalman filter, may also be used.

[0039] In S13, the processing unit 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 unit 3 calculates the distance r for each of the echo signals of multiple pings 1 to 3. The distance r is calculated based on the time from when the transducer 2 emits a ping to when the reflected ping is detected (the round-trip time of the ping) and the propagation speed of ultrasonic waves in water.

[0040] In S14, the processing unit 3 measures the phase difference ΔΦ between the echo signals. As shown in Fig. 4, the processing unit 3 measures the phase difference ΔΦ between adjacent echo signals of multiple echo signals 1 to 3. Specifically, the processing unit 3 calculates an IQ signal (in-phase / quadrature-phase signal) for each echo signal, and calculates the phase difference ΔΦ between adjacent echo signals using complex correlation or the like.

[0041] In S15, the processing unit 3 calculates the line-of-sight velocity v of the swimming object FS based on the phase difference ΔΦ. dop (Doppler velocity) is calculated (processing as the radial velocity calculation unit 13). dop is expressed by the following equation 2. λ is the wavelength of the ping. Δt is the transmission period of the ping.

[0042]

number

[0043] radial velocity v dopHowever, due to aliasing, the phase difference ΔΦ remains arbitrary and cannot be uniquely determined. Therefore, as explained below, the problem of arbitrariness is solved by using the first derivative of the distance r, −dr / dt.

[0044] In S16, the processing unit 3 calculates the first derivative -dr / dt of the distance r with respect to time t based on the echo signal (processing as the distance derivative calculation unit 14). As shown in Fig. 4, the processing unit 3 calculates the first derivative -dr / dt between adjacent pings of the echo signals of multiple pings 1 to 3.

[0045] The first derivative -dr / dt is the radial velocity v dop If there is no aliasing in the dop However, the first derivative -dr / dt does not have enough accuracy to be used alone to calculate the swimming velocity v.

[0046] In steps S17 to S20, the processing unit 3 calculates the line of sight velocity v dop and the first derivative -dr / dt, the swimming speed v is calculated (processing performed by the swimming speed calculation unit 15). Each of S17 to S20 will now be described.

[0047] In S17, the processing unit 3 calculates the line of sight velocity v dop Based on a comparison with the first derivative -dr / dt, the radial velocity v dop Specifically, the processing unit 3 calculates the nearest integer n using the following formula 3. The brackets in the formula indicate an operation to round off to the first decimal place.

[0048]

number

[0049] Then, the processing unit 3 uses the obtained integer n to calculate the line of sight velocity v dop This corrects for the radial velocity v after subtracting the aliasing. dop Hereafter, the left side of Equation 4 (v marked with a hat symbol)dop ) is the "corrected radial velocity v dop "

[0050]

number

[0051] In S18, the processing unit 3 calculates the corrected radial velocity v dop and the distance r are calculated. Specifically, the following formula 5 is obtained by substituting the above formula 1 for sin θ in formula 2, and the following formula 6 is obtained by multiplying both sides of formula 5 by −r.

[0052]

number

[0053]

number

[0054] According to Equation 6, the corrected radial velocity v dop The product of distance r and time t is a linear function, and the slope of the linear function corresponds to the square of swimming speed v.

[0055] In S19, the processing unit 3 performs linear regression using the calculated product and time t to determine the slope of the linear function. Furthermore, in S20, the processing unit 3 calculates the swimming speed v from the slope of the linear function.

[0056] As shown in Figure 5 and Equation 6, the corrected radial velocity v dop and the distance r is a linear function of time t, and the slope of the linear function corresponds to the square of the swimming speed v. Therefore, by determining the slope of the linear function using linear regression, the square of the swimming speed v can be found, and by further determining the square root of this, the swimming speed v can be calculated.

[0057] Note that if the slope of the linear function shown in FIG. 5 and Equation 6 is negative or if the correlation is low (for example, if the coefficient of determination is 0.8 or less), the processing unit 3 does not need to output the swimming speed v.

[0058] This completes the procedure for measuring swimming speed. According to this embodiment, the line of sight velocity v is calculated using the first derivative -dr / dt of the distance r. dop By correcting this, it is possible to improve the measurement accuracy of the swimming speed v.

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

[0060] In the experiment, yellowtails in a fish pen were tracked using echo data recorded by a split-beam fish finder. For each tracked individual, the swimming speed calculated by the split-beam, the swimming speed calculated by the Example, and the swimming speed calculated by the Reference Example were calculated.

[0061] Figure 6 is a graph plotting individual fish with the swimming speed calculated using a split beam on the horizontal axis and the swimming speed calculated in the Reference Example on the vertical axis. Figure 7 is a graph plotting individual fish with the swimming speed calculated using a split beam on the horizontal axis and the swimming speed calculated in the Example on the vertical axis.

[0062] The diagonal line in the figure is the line y=x, that is, the line when both swimming speeds are the same, and the closer it is to this line, the higher the measurement accuracy.

[0063] Comparing Figures 6 and 7, the points are more discrete in the graph of Figure 6, while the points are more clustered near a diagonal line in the graph of Figure 7, which shows that the swimming speed measurement accuracy is higher in the Example than in the Reference Example.

[0064] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made by those skilled in the art.

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

[0066] The determination of the integer n in S17 may be performed on a ping-by-ping basis, or may be performed on a tracked individual basis by dop After correcting for v dop You can also calculate the difference between -dr / dt and -dr / dt for all pings and take the average.

[0067] Representative embodiments of the present invention will be listed below.

[0068] (1) a transducer that is periodically emitted into the water and generates echo signals based on ultrasonic pings reflected by objects swimming in the water; a radial velocity calculation unit that calculates the radial velocity of the swimming object based on the phase difference between the two echo signals; a distance differential calculation unit that calculates a first derivative of the distance between the swimming object and the transducer with respect to time based on the two echo signals; a swimming speed calculation unit that calculates the swimming speed of the swimming object based on the line-of-sight velocity and a first derivative of the distance; A swimming speed measuring device comprising:

[0069] (2) the swimming speed calculation unit corrects the line of sight velocity based on a comparison between the line of sight velocity and a first derivative of the distance; The swimming speed measuring device according to (1).

[0070] (3) the swimming speed calculation unit calculates the swimming speed based on the product of the corrected line of sight speed and the distance. (2) A swimming speed measuring device according to the present invention.

[0071] (4) the swimming speed calculation unit calculates the swimming speed based on the fact that the product is a linear function with respect to time. (3) A swimming speed measuring device according to the present invention.

[0072] (5) the swimming speed calculation unit calculates the swimming speed based on the fact that the slope of the linear function corresponds to the square of the swimming speed. (4) A swimming speed measuring device according to the present invention.

[0073] (6) Further comprising a tracking unit that tracks echoes from the same swimming object in the echo signals. A swimming speed measuring device according to any one of (1) to (5).

[0074] (7) The transducer is a single beam transducer. A swimming speed measuring device according to any one of (1) to (6).

[0075] (8) the transducer generates the echo signals by forming one or more receive beams; the two echo signals are generated in one of the one or more receive beams; A swimming speed measuring device according to any one of (1) to (6).

[0076] (9) generating echo signals based on ultrasonic pings periodically emitted into the water by a transducer and reflected by an object swimming in the water; Calculating the line-of-sight velocity of the swimming object based on the phase difference between the two echo signals; Calculating a first derivative of the distance between the swimming object and the transducer with respect to time based on the two echo signals; calculating a swimming speed of the swimming object based on the line-of-sight velocity and a first derivative of the distance; Swimming speed measurement method.

[0077] (10) acquiring, with a transducer, echo signals generated based on ultrasonic pings periodically emitted into the water and reflected by an object swimming in the water; Calculating the radial velocity of the swimming object based on the phase difference between the two echo signals; Calculating a first derivative of the 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 line-of-sight velocity and a first derivative of the distance; A program that causes a computer to execute the following. [Explanation of symbols]

[0078] 1 swimming speed measuring device, 2 transducer, 3 processing unit, 11 echo signal acquisition unit, 12 tracking unit, 13 line of sight speed calculation unit, 14 distance differential calculation unit, 15 swimming speed calculation unit, FS swimming object

Claims

1. a transducer that is periodically emitted into the water and generates echo signals based on ultrasonic pings reflected by objects swimming in the water; a radial velocity calculation unit that calculates the radial velocity of the swimming object based on the phase difference between the two echo signals; a distance differential calculation unit that calculates a first derivative of the distance between the swimming object and the transducer with respect to time based on the two echo signals; a swimming speed calculation unit that calculates the swimming speed of the swimming object based on the line-of-sight velocity and a first derivative of the distance; A swimming speed measuring device comprising:

2. the swimming speed calculation unit corrects the line of sight velocity based on a comparison between the line of sight velocity and a first derivative of the distance; The swimming speed measuring device according to claim 1 .

3. the swimming speed calculation unit calculates the swimming speed based on the product of the corrected line of sight speed and the distance. The swimming speed measuring device according to claim 2.

4. the swimming speed calculation unit calculates the swimming speed based on the fact that the product is a linear function with respect to time. The swimming speed measuring device according to claim 3.

5. the swimming speed calculation unit calculates the swimming speed based on the fact that the slope of the linear function corresponds to the square of the swimming speed. The swimming speed measuring device according to claim 4.

6. Further comprising a tracking unit that tracks echoes from the same swimming object in the echo signals. The swimming speed measuring device according to claim 1 .

7. The transducer is a single beam transducer. The swimming speed measuring device according to claim 1 .

8. the transducer generates the echo signals by forming one or more receive beams; the two echo signals are generated in one of the one or more receive beams; The swimming speed measuring device according to claim 1 .

9. generating echo signals based on ultrasonic pings periodically emitted into the water by a transducer and reflected by an object swimming in the water; Calculating the line-of-sight velocity of the swimming object based on the phase difference between the two echo signals; Calculating a first derivative of the distance between the swimming object and the transducer with respect to time based on the two echo signals; calculating a swimming speed of the swimming object based on the line-of-sight velocity and a first derivative of the distance; Swimming speed measurement method.

10. acquiring, with a transducer, echo signals generated based on ultrasonic pings periodically emitted into the water and reflected by an object swimming in the water; Calculating the radial velocity of the swimming object based on the phase difference between the two echo signals; Calculating a first derivative of the 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 line-of-sight velocity and a first derivative of the distance; A program that causes a computer to execute the following.

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