Ship speedometer and method for measuring ship speed

Abstract

To determine an accurate vessel speed.SOLUTION: A vessel speed meter 1 includes: a plurality of channels 4 to 7, each transmitting sound waves of different frequencies in at least two directions into the water, receiving a reflected sound wave of the transmitted sound wave, and calculating an instantaneous Doppler frequency from the received reflected sound wave; an instantaneous vessel speed candidate calculation unit 81 that calculates a plurality of instantaneous vessel speed candidates based on the combination of instantaneous Doppler frequencies of sound waves transmitted in different directions; an instantaneous vessel speed candidate determination unit 82 that determines whether the plurality of instantaneous vessel speed candidates are normal values in order of their plausibility, and adopts a value of the instantaneous vessel speed candidate that is first determined to be a normal value as an instantaneous vessel speed; and a vessel speed calculation unit 83 that calculates a vessel speed value based on the value of the instantaneous vessel speed.SELECTED DRAWING: Figure 1

Description

[[Technical Field]]

[0001] The present invention relates to a ship speedometer and a ship speed measurement method, and relates to a technology useful when applied to ship speed measurement. [[Background Art]]

[0002] An acoustic type (also called a "Doppler type") is known as one type of ship speedometer for measuring ship speed. An acoustic ship speedometer transmits sound waves from a ship into water, and uses the difference between the frequency of the transmitted sound wave and the frequency of the sound wave reflected by suspended matter in water (specifically, plankton, etc.) (that is, the Doppler frequency corresponding to the relative speed) to calculate the relative speed of the ship with respect to water (hereinafter also referred to as speed over water or ship speed) (see Patent Document 1). In this case, where f is the frequency of the transmitted sound wave, θ is the depression angle of the transmission direction of the sound wave, C is the speed of sound in water, and Δf is the Doppler frequency of the reflected wave, the ship speed V is obtained by the following mathematical formula 1. (Formula 1) V = C·Δf / (2f·cosθ)

[0003] Acoustic ship speedometers have a method called the paired beam method. A paired-beam acoustic ship speedometer transmits sound waves forward and backward in the traveling direction of the ship (for example, toward the bow and toward the stern) respectively at the same depression angle θ, calculates the ship speed respectively from a pair of Doppler frequencies obtained from the reflected waves of each sound wave, and calculates the average value of the calculated pair of ship speeds to obtain the true ship speed (this method is also referred to as beam cancellation). According to this paired-beam acoustic ship speedometer, even when pitching or other shaking occurs to a navigating ship, the ship tilts in the fore-aft direction and the depression angle θ of the sound wave changes, the influence of the shaking can be canceled and accurate ship speed can be measured. [[Prior Art Documents]] [[Patent Documents]]

[0004] [[Patent Document 1]] Japanese Unexamined Patent Publication, Publication No. Sho 61-099868 [[Summary of Invention]] [Problems that the invention aims to solve]

[0005] Incidentally, the ship speed measured by a speedometer can sometimes show abnormal values. For example, acoustic speedometers sometimes calculate the ship speed value based on the interference wave frequency caused by interference waves or bubbles. In this case, there is a problem that calculating the ship speed using the interference wave frequency will output and display an incorrect ship speed value.

[0006] Therefore, the objective of this invention is to provide a ship speed meter and a ship speed measurement method that can accurately determine the ship's speed. [Means for solving the problem]

[0007] To solve the above problems, the invention described in claim 1 is a ship speed meter characterized by comprising: a plurality of channels that each emit sound waves of different frequencies in at least two directions in water, each receive the reflected waves of the emitted sound waves, and each calculate the instantaneous Doppler frequency from the received reflected waves; an instantaneous ship speed candidate calculation means that calculates a plurality of instantaneous ship speed candidates based on a combination of the instantaneous Doppler frequencies of sound waves emitted in different directions; an instantaneous ship speed candidate determination means that determines whether the plurality of instantaneous ship speed candidates are normal values ​​in order of increasing likelihood, and adopts the value of the instantaneous ship speed candidate that is first determined to be a normal value as the instantaneous ship speed; and a ship speed value calculation means that calculates a ship speed value based on the instantaneous ship speed value.

[0008] The invention described in claim 2 is characterized in that, in the ship speedometer described in claim 1, the plurality of channels each calculate a plurality of instantaneous Doppler frequencies from a single received reflected wave.

[0009] The invention described in claim 3 is characterized in that, in the ship speed meter described in claim 1 or 2, the instantaneous ship speed candidate calculation means generates a plurality of pairs of instantaneous Doppler frequencies by combining the instantaneous Doppler frequencies of sound waves of the same frequency transmitted in different directions, and calculates a plurality of instantaneous ship speed candidates based on each of the pairs of instantaneous Doppler frequencies.

[0010] The invention described in claim 4 is a ship speed meter according to claim 1 or 2, comprising a ship speed value conversion means for converting a plurality of instantaneous Doppler frequencies calculated in the plurality of channels into ship speed values, wherein the instantaneous ship speed candidate calculation means generates a plurality of pairs of ship speed values ​​by combining ship speed values ​​converted from the instantaneous Doppler frequencies of sound waves transmitted in different directions, and calculates a plurality of instantaneous ship speed candidates based on each of the pair of ship speed values.

[0011] The invention described in claim 5 is characterized in that, in the ship speed meter described in claim 1, the instantaneous ship speed value is stored in a buffer for a predetermined period of time, and the ship speed value is calculated using the instantaneous ship speed value stored in the buffer.

[0012] The invention described in claim 6 is characterized in that, in the ship speed meter described in claim 5, the instantaneous ship speed candidate determination means determines that an instantaneous ship speed candidate whose acceleration related to the instantaneous ship speed candidate is within a predetermined range is a normal value.

[0013] The invention described in claim 7 is characterized in that, in the ship speed meter described in claim 5, the instantaneous ship speed candidate determination means determines that an instantaneous ship speed candidate whose value is within a predetermined range based on past ship speed values ​​is a normal value.

[0014] The invention described in claim 8 is characterized in that, in the ship speed meter described in claim 6 or 7, a predetermined number of the calculated ship speed values ​​are stored in a second buffer, and the reference for the predetermined range is set using the ship speed values ​​stored in the second buffer.

[0015] The invention described in claim 9 is characterized in that, in the speedometer described in claim 8, the reference for the predetermined range is set only when the instantaneous speed stored in the buffer is updated.

[0016] The invention described in claim 10 is characterized in that, in the speedometer described in claim 9, when a predetermined condition is met while the instantaneous speed stored in the buffer is not being updated, the condition defining the predetermined range is changed.

[0017] The invention described in claim 11 is characterized in that, in the ship speed meter described in claim 1, the instantaneous ship speed candidate determination means determines the plausibility of the instantaneous ship speed candidate based on the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate.

[0018] The invention described in claim 12 is characterized in that, in the ship speed meter described in claim 2, the instantaneous ship speed candidate determination means determines the plausibility of the instantaneous ship speed candidate based on the frequency of the sound wave on which the instantaneous ship speed candidate is based and the ranking of the plausibility of the instantaneous Doppler frequencies performed in the channel when calculating the instantaneous Doppler frequency on which the instantaneous ship speed candidate is based.

[0019] The invention described in claim 13 is a ship speed measurement method characterized by transmitting sound waves of different frequencies in at least two directions in the water, receiving the reflected waves of the transmitted sound waves, calculating the instantaneous Doppler frequencies from the received reflected waves, calculating a plurality of instantaneous ship speed candidates based on the combination of instantaneous Doppler frequencies of the sound waves transmitted in different directions, determining whether the plurality of instantaneous ship speed candidates are normal values ​​in order of increasing likelihood, adopting the value of the instantaneous ship speed candidate that was first determined to be a normal value as the instantaneous ship speed, and calculating a ship speed value based on the instantaneous ship speed value. [Effects of the Invention]

[0020] According to the invention described in claims 1 and 13, sound waves of different frequencies are transmitted, and a plurality of instantaneous ship speed candidates are calculated based on the instantaneous Doppler frequency calculated from the received reflected waves. For this reason, differences arise in the attenuation amount of sound waves and the difference from the interference wave frequency, which makes the calculation less susceptible to the influence of the interference wave frequency, enabling an accurate ship speed value to be obtained. Furthermore, among the plurality of instantaneous ship speed candidates, the instantaneous ship speed candidate that is determined to be most plausible and a normal value is adopted as the normal instantaneous ship speed, and the ship speed value is calculated based on the adopted instantaneous ship speed. Therefore, when calculating the ship speed value in a paired-beam ship speedometer, instantaneous ship speed candidates based on the interference wave frequency can be eliminated, making it possible to obtain a highly accurate ship speed.

[0021] Furthermore, according to the invention described in claim 2, a plurality of instantaneous Doppler frequencies are each calculated from one received reflected wave, so that the most plausible instantaneous ship speed candidate determined to be a normal value can be selected from among a larger number of instantaneous ship speed candidates, enabling a more accurate ship speed value to be obtained.

[0022] Furthermore, according to the invention described in claim 3, a plurality of instantaneous ship speed candidates are calculated by combining instantaneous Doppler frequencies of sound waves of the same frequency. Therefore, when calculating the ship speed value in a paired-beam ship speedometer, instantaneous ship speed candidates based on the interference wave frequency can be eliminated, making it possible to obtain a highly accurate ship speed.

[0023] Furthermore, according to the invention described in claim 4, a plurality of instantaneous Doppler frequencies are converted into ship speed values, and a plurality of instantaneous ship speed candidates are calculated by combining the converted ship speed values. Therefore, instantaneous ship speed candidates can be calculated even from combinations of instantaneous Doppler frequencies of sound waves of different frequencies. For this reason, when calculating the ship speed value in a paired-beam ship speedometer, instantaneous ship speed candidates based on the interference wave frequency can be more effectively eliminated, making it possible to obtain a highly accurate ship speed.

[0024] Further, according to the invention of claim 5, the ship speed value is calculated by using the instantaneous ship speed values stored in a buffer for a predetermined period, so even if a temporary change occurs in the instantaneous ship speed due to rolling of the ship or other factors, it is possible to obtain a highly accurate ship speed.

[0025] Further, according to the invention of claim 6, since acceleration is used as a determination criterion, the tendency of ship speed can be used as the determination criterion, and it is possible to calculate a more natural ship speed value.

[0026] Further, according to the invention of claim 7, since past ship speed values are used as a determination criterion, the tendency of ship speed can be used as the determination criterion, and it is possible to calculate a more natural ship speed value.

[0027] Further, according to the invention of claim 8, the criterion for normal value determination is set based on the ship speed value calculated by using normal (in other words, within the allowable range) instantaneous ship speed values, so it is possible to obtain an accurate ship speed.

[0028] Further, according to the invention of claim 9, since the criterion for the predetermined range is set only when the instantaneous ship speed stored in the buffer has been updated, it is possible to perform accurate and stable calculation of the ship speed value in accordance with the navigation status of the ship.

[0029] Further, according to the invention of claim 10, the condition defining the predetermined range is changed when a predetermined condition is satisfied in a situation where the instantaneous ship speed stored in the buffer has not been updated. For example, when an event in which an instantaneous ship speed candidate is not determined as a normal value continues, the condition defining the predetermined range can be changed to set the criterion of the predetermined range, so it is possible to perform accurate and stable calculation of the ship speed value in accordance with the navigation status of the ship.

[0030] Furthermore, according to the invention described in claim 11, the plausibility of an instantaneous ship speed candidate is determined based on the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate. As a result, the instantaneous ship speed candidate that is determined to be the most plausible and normal value among multiple instantaneous ship speed candidates can be adopted as the regular instantaneous ship speed, making it possible to obtain a highly accurate ship speed value.

[0031] Furthermore, according to the invention described in claim 12, the plausibility of an instantaneous ship speed candidate is determined based on the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate and the ranking of the plausibility of instantaneous Doppler frequencies performed by the channel when calculating the instantaneous Doppler frequency that formed the basis of the instantaneous ship speed candidate. As a result, the instantaneous ship speed candidate that is determined to be the most plausible and normal value among multiple instantaneous ship speed candidates can be adopted as the regular instantaneous ship speed, making it possible to obtain a highly accurate ship speed value. [Brief explanation of the drawing]

[0032] [Figure 1] This is a functional block diagram showing the schematic configuration of a ship speedometer according to Embodiment 1 of this invention. [Figure 2] This flowchart shows the processing procedure in the ship speed meter shown in Figure 1, and also outlines the processing procedure of the ship speed measurement method according to Embodiment 1 of this invention. [Figure 3] Figure 2 is a flowchart outlining the processing steps for "Calculation of Instantaneous Ship Speed". [Figure 4] This is a functional block diagram showing an overview of the process in a ship speed meter according to Embodiment 1 of the present invention, which calculates a candidate instantaneous ship speed from the instantaneous Doppler frequency and determines whether or not it is a normal value. [Figure 5] This figure illustrates the reference acceleration calculated by the ship's speedometer in Figure 1. [Figure 6] This is a functional block diagram showing an overview of the process in which a ship speed meter according to Embodiment 2 of this invention calculates a candidate instantaneous ship speed based on multiple instantaneous Doppler frequencies obtained from a single reflected wave and determines whether or not it is a normal value. [Figure 7]This is a functional block diagram showing the schematic configuration of a ship speedometer according to Embodiment 3 of the present invention. [Figure 8] This is a functional block diagram showing an overview of the process in a ship speed meter according to Embodiment 3 of the present invention, which converts the instantaneous Doppler frequency into a ship speed value, calculates a candidate instantaneous ship speed, and determines whether or not it is a normal value. [Figure 9] This is a functional block diagram showing an overview of the process in a ship speed meter according to Embodiment 4 of the present invention, which converts multiple instantaneous Doppler frequencies obtained from a single reflected wave into ship speed values, calculates instantaneous ship speed candidates, and determines whether or not they are normal values. [Figure 10] This table shows combinations for determining instantaneous ship speed candidates from multiple ship speed values ​​in a ship speed meter according to Embodiment 4 of this invention, and the ranking of the likelihood of the instantaneous ship speed candidates. [Modes for carrying out the invention]

[0033] (Embodiment 1) The present invention will be described below based on the illustrated embodiments.

[0034] Figure 1 is a functional block diagram showing the schematic configuration of a ship speed meter 1 according to an embodiment of the present invention. Figure 2 is a flowchart showing the processing procedure in the ship speed meter 1 and an overview of the processing procedure of the ship speed measurement method according to an embodiment of the present invention. Figure 3 is a flowchart showing an overview of the specific processing procedure for step S1, "Calculation of instantaneous ship speed," in the flowchart shown in Figure 2.

[0035] The ship speedometer 1 is a pair-beam acoustic (also called "Doppler") ship speedometer that is installed on a ship to measure and output the ship's speed relative to water (i.e., ship speed relative to water [kn]). It mainly comprises a control unit 2, a memory unit 3, a first channel 4, a second channel 5, a third channel 6, a fourth channel 7, a ship speed calculation unit 8, an interface unit 9, and a display unit 10.

[0036] The ship speedometer 1 according to this embodiment emits sound waves of different frequencies in at least two directions underwater using the first channel 4 to the fourth channel 7, receives the reflected waves of the emitted sound waves, and calculates the instantaneous Doppler frequency for each of the first channel 4 to the fourth channel 7 from the received reflected waves.

[0037] The speedometer 1 calculates multiple instantaneous ship speed candidates based on combinations of instantaneous Doppler frequencies of sound waves transmitted in different directions, using the instantaneous ship speed candidate calculation unit (instantaneous ship speed candidate calculation means) 81 of the ship speed calculation unit 8.

[0038] The speedometer 1 uses the instantaneous speed candidate determination unit (instantaneous speed candidate determination means) 82 of the speed calculation unit 8 to determine whether a plurality of instantaneous speed candidates are normal values ​​in order of likelihood, and adopts the value of the instantaneous speed candidate that is first determined to be a normal value as the instantaneous speed (step S1).

[0039] The speedometer 1 calculates the ship speed value based on the instantaneous ship speed value adopted by the instantaneous ship speed candidate determination unit 82, using the ship speed value calculation unit (ship speed value calculation means) 83 of the ship speed calculation unit 8 (step S3).

[0040] Furthermore, the speedometer 1, using the instantaneous speed candidate determination unit 82, determines that instantaneous speed candidates whose acceleration is within a predetermined range are normal values. The instantaneous speed candidate determination unit 82 also stores the adopted instantaneous speed value in the instantaneous speed buffer (buffer) 31 for a predetermined period of time (step S2). The speedometer 1, using the speed value calculation unit 83, calculates the ship speed value using the instantaneous speed value stored in the instantaneous speed buffer 31 (step S3).

[0041] Furthermore, the speedometer 1 stores a predetermined number of calculated ship speed values ​​in a ship speed value buffer (second buffer) 32 (step S7), and the reference acceleration calculation unit 85 of the ship speed calculation unit 8 calculates the reference acceleration for the predetermined range using the ship speed values ​​stored in the ship speed value buffer 32 (step S8). In other words, in step S8, the reference for the predetermined range is set. Also, the speedometer 1 causes the reference acceleration calculation unit 85 to calculate the reference acceleration for the predetermined range only if the instantaneous ship speed stored in the instantaneous ship speed buffer 31 has been updated by the update determination unit 84 of the ship speed calculation unit 8 (YES in step S5) (steps S7, S8).

[0042] The control unit 2 has the function of controlling the operation of each part that makes up the ship speedometer 1, and is configured as a mechanism that includes, for example, a central processing unit (CPU) that performs calculation processing related to the measurement of the ship's speed relative to water (ship speed relative to water).

[0043] The control unit 2 controls the start, content, and end of processing for each component of the ship's speedometer 1 by having the central processing unit execute a program (not shown) stored in the memory unit 3 for controlling the operation of the ship's speedometer 1, in accordance with the program.

[0044] The memory unit 3 has functions such as serving as a work area for temporarily storing data and information generated when the central processing unit performs calculations related to measuring the ship's speed over water (ship speed over water), and as a memory area for storing various information, programs, and data. For example, it is configured as a mechanism having at least one of the following: a read-only memory (ROM), a read-and-write memory (RAM), and a hard disk.

[0045] As described above, the ship speed meter 1 is a pair-beam acoustic ship speed meter and comprises multiple channels, for example, a first channel 4, a second channel 5, a third channel 6, and a fourth channel 7, which each emit sound waves of different frequencies in at least two directions in the water and each receive the reflected waves of the emitted sound waves. The first channels 4 to the fourth channels 7 each calculate the instantaneous Doppler frequency from the reflected waves (steps S1a, S1b, S1c, and S1d).

[0046] The first channel 4 comprises a first sensor 41 and a first measurement unit 42. The first sensor 41 is installed, for example, on or near the bottom of the hull and has the function of transmitting (in other words, emitting, transmitting) pulsed sound waves of a first frequency f1 [Hz] toward the water in the direction of the bow at regular time intervals, and continuously receiving (in other words, detecting) reflected sound waves reflected by floating objects in the water (specifically, plankton, etc.) between the time between the transmission of one sound wave and the transmission of the next sound wave. That is, the first sensor 41 alternately transmits pulsed sound waves and receives reflected sound waves. However, the measurement method of the first sensor 41 is not limited to the above method, and for example, it may transmit a continuous signal and receive a reflected signal of the same signal.

[0047] The first sensor 41 then outputs a received signal corresponding to the received level of the received reflected wave. The first sensor 41 may be configured, for example, by a transducer.

[0048] The constant time interval during which the first sensor 41 emits sound waves is called the "measurement time interval," and its value is denoted as Δt. The measurement time interval Δt [seconds] is not limited to a specific time length, but it can be set to any time length within the range of approximately 20 to 80 milliseconds.

[0049] In other words, the first sensor 41 outputs a received signal at each measurement time interval Δt. The first sensor 41 may also output other information / data as needed.

[0050] The first measurement unit 42 controls the operation of the first sensor 41 to perform measurements using the first sensor 41 and has the function of acquiring the measurement results output from the first sensor 41. Specifically, the first measurement unit 42 acquires the received signal at each measurement time interval Δt.

[0051] When the first measurement unit 42 acquires a received signal from the first sensor 41, it detects data of a high frequency (referred to as the "reflected wave frequency") from the waveform of the received signal. The first measurement unit 42 also associates the detected reflected wave frequency [Hz] data with the elapsed time tick [seconds] from a predetermined point in time, which is determined by the clock function (not shown) provided in the first measurement unit 42.

[0052] The first measurement unit 42 then outputs data combining the elapsed time tick [seconds] and the reflected wave frequency [Hz] for each measurement time interval Δt.

[0053] Furthermore, the predetermined time point that serves as the basis for the elapsed time tick [seconds] is not limited to a specific time point; for example, it could be the time when the ship's speedometer 1 is activated.

[0054] Furthermore, the first measurement unit 42 calculates the instantaneous Doppler frequency [Hz] based on the difference between the known frequency (referred to as the "transmission frequency") f1 of the sound wave emitted from the first sensor 41 and the combined data of the elapsed time tick [seconds] and the reflected wave frequency [Hz] (step S1a).

[0055] Here, the value of the instantaneous Doppler frequency [Hz] calculated using the combination data associated with the elapsed time tick [seconds] in the first channel 4, that is, the value of the instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] in the first channel 4, is denoted as "C1_Δf1_tick".

[0056] The second channel 5 includes a second sensor 51 and a second measuring unit 52. The second sensor 51 and the second measuring unit 52 are the same as those of the first sensor 41 and the first measuring unit 42, so a detailed explanation will be omitted. However, the second sensor 51 differs from the first sensor 41 in that it emits pulsed sound waves of a second frequency f2 [Hz] different from that of the first sensor 41, in the same direction as the first sensor 41, i.e., towards the water in the bow direction, and receives the reflected waves.

[0057] Furthermore, the relationship between the first frequency f1[Hz] and the second frequency f2[Hz] is that the first frequency f1[Hz] > the second frequency f2[Hz]. In other words, because the first frequency f1[Hz] has a higher frequency, the resolution of ship speed measurement is higher, resulting in higher accuracy compared to when ship speed measurement is performed using the second frequency f2[Hz].

[0058] Specifically, the first channel 4 calculates the instantaneous Doppler frequency [Hz] of the first frequency f1 [Hz] transmitted in the direction of the bow, while the second channel 5 calculates the instantaneous Doppler frequency [Hz] of the second frequency f2 [Hz] transmitted in the direction of the bow (step S1b). The value of the instantaneous Doppler frequency [Hz] calculated using the combination data to which the elapsed time tick [seconds] is associated in the second channel 5, that is, the value of the instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] in the second channel 5, is denoted as "C2_Δf2_tick".

[0059] The third channel 6 includes a third sensor 61 and a third measuring unit 62. The third sensor 61 and the third measuring unit 62 are the same as the first sensor 41 and the first measuring unit 42, so a detailed explanation will be omitted. However, the third sensor 61 differs from the first sensor 41 in that it emits pulsed sound waves with the same first frequency f1 [Hz] as the first sensor 41, in a different direction, namely towards the water in the stern direction, and receives reflected waves.

[0060] Specifically, the first channel 4 calculates the instantaneous Doppler frequency [Hz] of the first frequency f1 [Hz] transmitted in the bow direction, while the third channel 6 calculates the instantaneous Doppler frequency [Hz] of the first frequency f1 [Hz] transmitted in the stern direction (step S1c). The value of the instantaneous Doppler frequency [Hz] calculated using the combination data to which the elapsed time tick [seconds] is associated in the third channel 6, i.e., the value of the instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] in the third channel 6, is denoted as "C3_Δf1_tick".

[0061] The fourth channel 7 includes a fourth sensor 71 and a fourth measuring unit 72. The fourth sensor 71 and the fourth measuring unit 72 are the same as the first sensor 41 and the first measuring unit 42, so a detailed explanation will be omitted. However, the fourth sensor 71 differs from the first sensor 41 in that it emits pulsed sound waves with the same second frequency f2 [Hz] as the second sensor 51 in a different direction, namely towards the water in the stern direction, and receives reflected waves.

[0062] Specifically, the first channel 4 calculates the instantaneous Doppler frequency [Hz] of the first frequency f1 [Hz] transmitted in the bow direction, while the fourth channel 7 calculates the instantaneous Doppler frequency [Hz] of the second frequency f2 [Hz] transmitted in the stern direction (step S1d). The value of the instantaneous Doppler frequency [Hz] calculated using the combination data to which the elapsed time tick [seconds] is associated in the fourth channel 7, i.e., the value of the instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] in the fourth channel 7, is denoted as "C4_Δf2_tick".

[0063] The ship speed calculation unit 8 has the function of calculating the ship speed relative to water using data acquired by the first channel 4 to the fourth channel 7, and includes an instantaneous ship speed candidate calculation unit 81, an instantaneous ship speed candidate determination unit 82, a ship speed value calculation unit 83, an update determination unit 84, and a reference acceleration calculation unit 85.

[0064] The instantaneous ship speed candidate calculation unit 81 calculates multiple candidate values ​​(instantaneous ship speed candidate [kn]) for the ship's instantaneous speed over water (referred to as "instantaneous ship speed") using data acquired by the first channel 4 to the fourth channel 7 (step S1).

[0065] The instantaneous ship speed candidate calculation unit 81 calculates multiple instantaneous ship speed candidates at each time tick, based on each of multiple pairs of instantaneous Doppler frequencies, which are combinations of instantaneous Doppler frequencies of sound waves of the same frequency transmitted in different directions.

[0066] Specifically, as shown in Figure 4, the instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the first instantaneous ship speed candidate) based on the instantaneous Doppler frequency (C1_Δf1_tick) of the first channel 4 in the bow direction and the instantaneous Doppler frequency (C3_Δf1_tick) of the third channel 6 in the stern direction (step S1e).

[0067] Specifically, based on the following formula (2), the instantaneous ship speed vi1 is calculated from the instantaneous Doppler frequency (C1_Δf1_tick) of the first channel 4 in the bow direction, and similarly, based on the following formula (2), the instantaneous ship speed vi2 is calculated from the instantaneous Doppler frequency (C3_Δf1_tick) of the third channel 6 in the stern direction. Then, beam cancellation is performed to find the average of the calculated instantaneous ship speed vi1 in the bow direction and the instantaneous ship speed vi2 in the stern direction, "(vi1+vi2) / 2", and this average value is used as the first instantaneous ship speed candidate. This makes it possible to obtain an accurate instantaneous ship speed that eliminates the effects of the ship's forward and backward motion. In equation (2) below, f is the frequency of the emitted sound wave, θ is the depression angle of the direction of sound wave emission, C is the speed of sound in water, and Δf is the Doppler frequency of the reflected wave (difference between the emitted frequency and the reflected wave frequency: C1_Δf1_tick, C3_Δf1_tick). (Math 2) vi(vi1,vi2)=C·Δf / (2f·cosθ)

[0068] The value of the first instantaneous ship speed candidate calculated using the instantaneous Doppler frequency associated with the elapsed time tick [seconds], i.e., the value of the first instantaneous ship speed candidate at the elapsed time tick [seconds], will be denoted as "v1_tick".

[0069] The instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the second instantaneous ship speed candidate) based on the instantaneous Doppler frequency of the second channel 5 in the bow direction (C2_Δf2_tick) and the instantaneous Doppler frequency of the fourth channel 7 in the stern direction (C4_Δf2_tick) using the same method as for the first instantaneous ship speed candidate (v1_tick) (step S1i). The value of this second instantaneous ship speed candidate is denoted as "v2_tick".

[0070] The instantaneous speed candidate calculation unit 81 outputs the calculated first instantaneous speed candidate (v1_tick) and second instantaneous speed candidate (v2_tick) to the instantaneous speed candidate determination unit 82. However, there may be cases where the instantaneous speed candidate calculation unit 81 cannot calculate the first instantaneous speed candidate (v1_tick) or the second instantaneous speed candidate (v2_tick) for reasons such as the inability to obtain the instantaneous Doppler frequency in any of the first channels 4 to 4th channels 7. In this case, the instantaneous speed candidate that could not be calculated is not output to the instantaneous speed candidate determination unit 82. For example, if the instantaneous Doppler frequency (C2_Δf2_tick) cannot be obtained from the second channel 5, the second instantaneous speed candidate (v2_tick) cannot be calculated and is therefore not output.

[0071] It was explained that if the instantaneous Doppler frequency could not be obtained, the instantaneous ship speed candidate calculated based on that unobtained instantaneous Doppler frequency would not be output. However, the beam cancellation method may be changed to calculate and output the instantaneous ship speed candidate. Specifically, when beam cancellation is performed by calculating the average of instantaneous ship speeds vi1 and vi2, "(vi1+vi2) / 2", in order to calculate the first instantaneous ship speed candidate (v1_tick) as described above, if, for example, the instantaneous ship speed vi2 could not be calculated, the parameter for the averaging calculation could be set to "1" to calculate "vi1 / 1", and the result of that calculation could be output as the first instantaneous ship speed candidate (v1_tick).

[0072] The instantaneous ship speed candidate determination unit 82 determines whether the first instantaneous ship speed candidate (v1_tick) and the second instantaneous ship speed candidate (v2_tick) are normal values ​​if they can be calculated (YES in steps S1f and S1j) (steps S1g and S1k).

[0073] Here, the time interval in which the ship speed value V[kn] is calculated in the process of step S3 described later, and the time interval in which the reference acceleration ar[kn / sec] is calculated in the process of step S8 described later, is called the "calculation time interval," and its value is denoted as I. In the following explanation, we will use as an example the case in which the ship speed value V_T+I at the elapsed time "T+I," which is the elapsed time T from the calculation time interval I, is calculated.

[0074] The calculation time interval I is not limited to a specific time length, but is appropriately set to a suitable time length after considering the results obtained from simulations that take into account various conditions such as the type of speedometer 1, the type of ship, and the ship's speed relative to water.

[0075] The calculation time interval I can be set to a duration within a range of, for example, 0.5 to 5 seconds.

[0076] Specifically, the instantaneous ship speed candidate determination unit 82 receives inputs of the ship speed value V_T at elapsed time T output from the ship speed value calculation unit 83 and the reference acceleration ar_T for elapsed time T output from the reference acceleration calculation unit 85 (the calculation of the ship speed value V and reference acceleration ar will be described later), as well as inputs of the first instantaneous ship speed candidate (v1_tick) and the second instantaneous ship speed candidate (v2_tick) from elapsed time "T+Δt" to "T+I" output from the instantaneous ship speed candidate calculation unit 81, and determines whether the values ​​of the first instantaneous ship speed candidate (v1_tick) and the second instantaneous ship speed candidate (v2_tick) are normal values ​​based on the ship speed value V_T and reference acceleration ar_T (steps S1g, S1k).

[0077] The following section explains how to determine the normal value of the first instantaneous ship speed candidate (v1_tick). The method for determining the normal value of the second instantaneous ship speed candidate (v2_tick) is the same as for the first instantaneous ship speed candidate (v1_tick), so a detailed explanation is omitted.

[0078] For the first instantaneous ship speed candidate (v1_tick), the specific value of the first instantaneous ship speed candidate at the elapsed time "T+Δt×n" for the period from "T+Δt" to "T+I" input to the instantaneous ship speed candidate determination unit 82 is denoted as "v1_T+nΔt". Here, n=1,2,3,···,k, and in this embodiment, Δt×k=I.

[0079] For the processing of step S1g, a threshold for the upper limit of the change in acceleration from the reference acceleration ar [kN / sec] (referred to as the "acceleration upper threshold aut") and a threshold for the lower limit of the change in acceleration from the reference acceleration ar (referred to as the "acceleration lower threshold alt") are set in advance.

[0080] The acceleration upper threshold aut[kN / sec] and acceleration lower threshold alt[kN / sec] are not limited to specific values, but are set appropriately based on factors such as the type of ship, performance, and specifications, taking into account the range of acceleration changes that are normally expected (in other words, normally possible). The acceleration upper threshold aut and acceleration lower threshold alt may be set to have the same absolute value, or they may be set to have different absolute values.

[0081] Furthermore, the instantaneous ship speed candidate determination unit 82 determines, for each of the first instantaneous ship speed candidate values ​​v1_T+nΔt at the elapsed time "T+Δt×n", whether the acceleration when the ship speed changes from the ship speed value V_T at the elapsed time T to the instantaneous ship speed value v1_T+nΔt at the elapsed time "T+Δt×n" (i.e., (|v1_T+nΔt-V_T|) / (Δt×n); called "acceleration related to instantaneous ship speed") falls within the range from the lower limit of the change in acceleration from the reference acceleration "ar_T-alt" to the upper limit of the change in acceleration from the reference acceleration "ar_T+aut" (see Figure 5).

[0082] The instantaneous ship speed candidate determination unit 82 determines whether the following equation (3) holds true. (Math 3) ar_T-alt≦(|v1_T+nΔt-V_T|) / (Δt×n)≦ar_T+aut

[0083] The above formula 3 may be transformed and used as shown in formula 4 below. (Math 4) V_T+(ar_T-alt)×(Δt×n)≦v1_T+nΔt≦V_T+(ar_T+aut)×(Δt×n)

[0084] Then, if equation 3 (or equation 4) above holds true (YES in step S1g), the instantaneous ship speed candidate determination unit 82 determines that the value v1_T+nΔt of the first instantaneous ship speed candidate is a normal value (in other words, an acceptable value), and assigns a normal value flag to the first instantaneous ship speed candidate (sets it) (step S1h).

[0085] On the other hand, if equation 3 (or equation 4) above does not hold true (NO in step S1g), the instantaneous ship speed candidate determination unit 82 determines that the value v1_T+nΔt of the first instantaneous ship speed candidate is not a normal value (it is an interference frequency) and does not assign a normal value flag to the first instantaneous ship speed candidate.

[0086] The instantaneous ship speed candidate determination unit 82 performs the same determination on the second instantaneous ship speed candidate as described above for determining the normal value of the first instantaneous ship speed candidate (step S1k). If it is determined to be a normal value (YES in step S1k), it assigns a normal value flag (step S1l), and if it is determined not to be a normal value (NO in step S1k), it does not assign a normal value flag.

[0087] The first instantaneous ship speed candidate (v1_tick) and the second instantaneous ship speed candidate (v2_tick), calculated as described above, are judged to be more plausible the higher the frequency of the sound wave on which the instantaneous ship speed candidate is based. This is because, as mentioned above, the higher the frequency of the emitted sound wave, the higher the resolution of the ship speed measurement and the higher the accuracy of the ship speed measurement. In other words, in this embodiment, the first instantaneous ship speed candidate (v1_tick) based on the first frequency f1 [Hz] is judged to be more plausible than the second instantaneous ship speed candidate (v2_tick) based on the second frequency f2 [Hz].

[0088] Next, the instantaneous speed candidate determination unit 82 checks (determines) whether the normal value flag is assigned to the first instantaneous speed candidate (v1_tick) and the second instantaneous speed candidate (v2_tick) in order of likelihood (step S1m). If an instantaneous speed candidate with the normal value flag is found (YES in step S1n), that instantaneous speed candidate is adopted as the regular instantaneous speed (step S1o). Here, the value of the regular instantaneous speed at the elapsed time tick [seconds] is denoted as "v_tick".

[0089] For example, if the first instantaneous speed candidate (v1_tick) is assigned a normal value flag, then the first instantaneous speed candidate (v1_tick) is adopted as the regular instantaneous speed (v_tick). Also, if the first instantaneous speed candidate (v1_tick) is not assigned a normal value flag, but the second instantaneous speed candidate (v2_tick) is assigned a normal value flag, then the second instantaneous speed candidate (v2_tick) is adopted as the regular instantaneous speed (v_tick). If there is only one instantaneous speed candidate to check, then that instantaneous speed candidate is adopted as the regular instantaneous speed (v_tick).

[0090] Furthermore, if the instantaneous speed candidate determination unit 82 does not confirm a normal value flag from the instantaneous speed candidate with the lowest plausibility ranking in step S1p (YES in step S1p), it does not adopt the regular instantaneous speed and returns to steps S1a, S1b, S1c, and S1d.

[0091] In the above explanation, the higher the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate, the higher the plausibility ranking of the instantaneous ship speed candidate. However, it is also acceptable to assume that the lower the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate, the higher the plausibility ranking of the instantaneous ship speed candidate. This is because lower sound wave frequencies result in higher noise immunity and thus higher accuracy in ship speed measurement.

[0092] The instantaneous speed candidate determination unit 82 adds the regular instantaneous speed (v_tick) to the beginning of the instantaneous speed buffer 31 (in other words, as the most recent data in the time series) and stores it (step S2).

[0093] The instantaneous ship speed buffer 31 is configured within the storage unit 3 and has the function of storing the instantaneous ship speed value v_tick in chronological order (specifically, in descending order). The instantaneous ship speed buffer 31 stores only combination data of elapsed time tick associated with the instantaneous ship speed value v_tick stored first (in other words, the most recent in chronological order) for a predetermined period (in other words, a predetermined length of time), and combination data older than the predetermined period (in other words, older in chronological order) is discarded.

[0094] The ship speed calculation unit 83 calculates the ship speed value using the instantaneous ship speed value stored in the instantaneous ship speed buffer 31 (step S3).

[0095] The ship speed calculation unit 83 reads the instantaneous ship speed values ​​v stored in the instantaneous ship speed buffer 31 at each calculation time interval I, calculates the average value of the instantaneous ship speed values ​​v, and outputs it as the ship speed value V[kn]. For example, the ship speed calculation unit 83 calculates the average value using the instantaneous ship speed values ​​v stored in the instantaneous ship speed buffer 31 at the time of elapsed time "T+I" and sets it as the ship speed value V_T+I at the time of elapsed time "T+I". The ship speed calculation unit 83 may, for example, calculate a simple average value as the average value of the instantaneous ship speed values ​​v, or it may calculate a weighted average value that is weighted by a value n representing the progress of elapsed time so that newer instantaneous ship speed values ​​v in the time series contribute more.

[0096] Here, as mentioned above, the instantaneous ship speed buffer 31 stores only combination data of the elapsed time (Δt × n in this embodiment) and the instantaneous ship speed value v, from the elapsed time tick associated with the instantaneous ship speed value v_tick that is stored first (in other words, the most recent in the time series). The predetermined period is the time width (in other words, the averaging time) used to calculate the ship speed value V.

[0097] The time interval for averaging the instantaneous ship speed values ​​v when calculating the ship speed value V (and the time interval for the instantaneous ship speed values ​​v stored in the instantaneous ship speed buffer 31) is not limited to a specific time length. Rather, it is set to an appropriate time length after considering, for example, the results obtained from simulations that take into account the method of the ship speedometer 1, the type of ship, and various conditions related to the ship speed relative to water.

[0098] The time interval used to calculate the average of instantaneous ship speed values ​​v when determining the ship speed value V can be set to a length within a range of, for example, 1 to 60 seconds.

[0099] The ship speed calculation unit 83 outputs the ship speed value V data calculated for each calculation time interval I via the interface unit 9 (step S4).

[0100] The interface unit 9 has the function of providing an input / output interface to the ship speed calculation unit 8, and for example, it receives input of ship speed value V data calculated by the ship speed value calculation unit 83 and outputs the ship speed value V on the display unit 10.

[0101] The display unit 10 has the function of displaying various information, including the ship speed value V output from the interface unit 9, and is configured as a mechanism that includes, for example, a liquid crystal display.

[0102] The update determination unit 84 determines whether the instantaneous ship speed buffer 31 has been updated after the ship speed value V was calculated in the previous process (step S5).

[0103] The update determination unit 84 determines, for example, when the ship speed value V_T+I at elapsed time "T+I" is calculated, that the instantaneous ship speed buffer 31 has not been updated if the combination data of the elapsed time tick and the instantaneous ship speed value v_tick stored at the beginning of the instantaneous ship speed buffer 31 at elapsed time "T+I" (in other words, the most recent in the time series) is the same as the combination data of the elapsed time tick and the instantaneous ship speed value v_tick stored at the beginning of the instantaneous ship speed buffer 31 at elapsed time T (in other words, the most recent in the time series), and determines that the instantaneous ship speed buffer 31 has been updated if they are different.

[0104] If the instantaneous ship speed buffer 31 has not been updated (NO in step S5), the update determination unit 84 excludes the ship speed value calculated in the current process (in this case, the ship speed value V_T+I at the elapsed time "T+I") from subsequent processing (step S6). Then, the control unit 2 moves the processing procedure for measuring the ship's speed relative to water (ship speed relative to water) to the processing in step S1.

[0105] On the other hand, if the instantaneous ship speed buffer 31 has been updated (YES in step S5), the update determination unit 84 decides to use the ship speed value calculated in the current process (in this case, the ship speed value V_T+I at the elapsed time "T+I") as the value to be used in subsequent processes, and adds the combined data of the elapsed time "T+I" and the ship speed value V_T+I to the beginning of the ship speed value buffer 32 (in other words, as the newest data in the time series) and stores it (step S7).

[0106] The ship speed value buffer 32 (which is a second buffer in that it is a different buffer from the instantaneous ship speed buffer 31) is configured within the storage unit 3 and has the function of storing and accumulating combined data of elapsed time and ship speed value V in chronological order (specifically, in descending order).

[0107] The ship speed buffer 32 stores only a predetermined number of combination data of elapsed time and ship speed value V, and if the number exceeds the predetermined number, older combination data is discarded in chronological order.

[0108] The reference acceleration calculation unit 85 calculates the reference acceleration ar using the ship speed value stored in the ship speed value buffer 32 (step S8).

[0109] The reference acceleration calculation unit 85 reads the combined data of elapsed time and ship speed value V stored in the ship speed value buffer 32 at each calculation time interval I, calculates the acceleration based on the width of the elapsed time (in other words, the length of time) and the width of the change in the ship speed value V, and outputs it as the reference acceleration ar [kN / sec] to the instantaneous ship speed candidate determination unit 82.

[0110] The reference acceleration calculation unit 85 calculates the acceleration using the combined data of elapsed time and ship speed V stored in the ship speed buffer 32 at that time, after the ship speed value V_T+I at the elapsed time "T+I" has been calculated, and sets this as the reference acceleration ar_T+I for the elapsed time "T+I".

[0111] In the example shown in Figure 5, the ship speed value V_T-I at elapsed time "TI" and the ship speed value V_T at elapsed time T are used to calculate the reference acceleration ar_T (=(V_T-V_T-I) / I) for elapsed time T. Then, using the reference acceleration ar_T for elapsed time T, it is determined whether the first instantaneous ship speed candidate value v1_T+nΔt at elapsed time "T+Δt×n" from elapsed time "T+Δt" to "T+I" is a normal value, and then the ship speed value V_T+I at elapsed time "T+I" is calculated.

[0112] Here, as mentioned above, the ship speed buffer 32 stores only a predetermined number of data combinations of elapsed time and ship speed V. However, the predetermined number is not limited to a specific value, but is set to an appropriate value after considering that a reasonable value can be calculated as the reference acceleration.

[0113] The number of data points containing elapsed time and ship speed value V stored in the ship speed value buffer 32 can be set to a value within a range of, for example, 2 to 4.

[0114] Then, the control unit 2 moves the processing procedure for measuring the ship's speed relative to water (ship speed relative to water) to the processing of step S1.

[0115] Furthermore, the control unit 2 repeats the processes from step S1 to step S8 until it receives instructions from the user via the interface unit 9 or until a predetermined termination event occurs (for example, the ship stops), continuing to measure and output the ship speed value V.

[0116] According to the ship speed meter 1 and ship speed measurement method of Embodiment 1, at least two types of sound waves with different frequencies, such as a first frequency f1 [Hz] and a second frequency f2 [Hz], are emitted, and multiple first instantaneous ship speed candidates (v1_tick) and second instantaneous ship speed candidates (v2_tick) are calculated based on the instantaneous Doppler frequencies "C1_Δf1_tick", "C2_Δf2_tick", "C3_Δf1_tick", and "C4_Δf2_tick" calculated from the received reflected waves. For example, differences will occur in the attenuation of the sound waves and the difference with the interference wave frequency, making it less susceptible to the influence of the interference wave frequency and enabling the determination of an accurate ship speed value. Furthermore, from among multiple first instantaneous speed candidates (v1_tick) and second instantaneous speed candidates (v2_tick), the instantaneous speed candidate that is judged to be the most plausible and normal value is adopted as the regular instantaneous speed, and the speed value is calculated based on the adopted instantaneous speed (v_tick). Therefore, when calculating the speed value in a pair-beam type speedometer, instantaneous speed candidates based on interference wave frequencies can be excluded, making it possible to obtain a highly accurate speed.

[0117] Furthermore, according to the ship speed meter 1 and ship speed measurement method of Embodiment 1, multiple first instantaneous ship speed candidates (v1_tick) and second instantaneous ship speed candidates (v2_tick) are calculated by combining instantaneous Doppler frequencies of sound waves of the same frequency (for example, instantaneous Doppler frequencies "C1_Δf1_tick" and "C3_Δf1_tick", and instantaneous Doppler frequencies "C2_Δf2_tick" and "C4_Δf2_tick"). Therefore, when calculating the ship speed value in a pair-beam type ship speed meter, instantaneous ship speed candidates based on interference wave frequencies can be excluded, making it possible to obtain a highly accurate ship speed.

[0118] Furthermore, according to the ship speed meter 1 and ship speed measurement method of Embodiment 1, since acceleration is used as the criterion for determination, the trend of ship speed can be used as the criterion for determination, making it possible to calculate the ship speed value V in a more natural way.

[0119] Furthermore, according to the ship speed meter 1 and ship speed measurement method of Embodiment 1, the ship speed value V is calculated using the instantaneous ship speed value (v_tick) for a predetermined period stored in the instantaneous ship speed buffer 31. Therefore, even if there is a temporary change in the instantaneous ship speed (v_tick) due to the rocking of the ship, it is possible to obtain a highly accurate ship speed value V.

[0120] Furthermore, according to the ship speed meter 1 and ship speed measurement method of Embodiment 1, the reference acceleration ar, which is used as the criterion for determining a normal value, is calculated based on the ship speed value V, which is calculated using a normal (in other words, within the acceptable range) instantaneous ship speed value (v_tick). Therefore, even if a temporary change occurs in the instantaneous ship speed due to the rocking of the ship, it is possible to obtain a highly accurate ship speed value V.

[0121] Furthermore, according to the ship speed meter 1 and ship speed measurement method of Embodiment 1, the reference acceleration ar, which is used as a reference within a predetermined range, is calculated only when the instantaneous ship speed (v_tick) stored in the instantaneous ship speed buffer 31 is updated. Therefore, it is possible to calculate an accurate and stable ship speed value according to the ship's navigation conditions.

[0122] Furthermore, according to the ship speed meter 1 and ship speed measurement method of Embodiment 1, the plausibility of the instantaneous ship speed candidate is determined based on the frequencies of the first frequency f1 [Hz] and second frequency f2 [Hz], which are the frequencies of the sound waves that formed the basis of the first instantaneous ship speed candidate (v1_tick) and the second instantaneous ship speed candidate (v2_tick). As a result, the instantaneous ship speed candidate that is determined to be the most plausible and normal value among the multiple first instantaneous ship speed candidates (v1_tick) and second instantaneous ship speed candidates (v2_tick) can be adopted as the regular instantaneous ship speed, making it possible to obtain a highly accurate ship speed value.

[0123] (Embodiment 2) Next, a ship speed meter and ship speed measurement method according to Embodiment 2 of the present invention will be described. This Embodiment 2 differs from Embodiment 1 in that it calculates instantaneous ship speed candidates by obtaining multiple instantaneous Doppler frequencies from a single reflected wave. Otherwise, it uses the same configuration as Embodiment 1, so a detailed explanation of the same configuration will be omitted.

[0124] In this second embodiment, the first measurement unit 42 of the first channel 4, the second measurement unit 52 of the second channel 5, the third measurement unit 62 of the third channel 6, and the fourth measurement unit 72 of the fourth channel 7 each calculate multiple (e.g., two) instantaneous Doppler frequencies [Hz] from a single reflected wave.

[0125] Specifically, when the first measurement unit 42 of the first channel 4 acquires a received signal from the first sensor 41, it detects multiple, for example two, data points of reflected wave frequencies with high signal levels from the waveform of the received signal. The first measurement unit 42 also associates the two detected reflected wave frequency [Hz] data points with the elapsed time tick [seconds] from a predetermined point in time, which is determined by the clock function (not shown) of the first measurement unit 42, to form two combination data points of elapsed time tick [seconds] and reflected wave frequency [Hz]. Then, for each of the two combination data points, the first measurement unit 42 calculates the difference between it and the known transmission frequency (first frequency f1) of the sound wave emitted from the first sensor 41, and calculates two instantaneous Doppler frequencies [Hz].

[0126] The first measurement unit 42 determines the plausibility of the two instantaneous Doppler frequency [Hz] values ​​and ranks the two instantaneous Doppler frequencies [Hz] in descending order of plausibility. Here, the instantaneous Doppler frequency [Hz] with the highest plausibility among the two instantaneous Doppler frequencies [Hz] is called the first instantaneous Doppler frequency [Hz], and the instantaneous Doppler frequency [Hz] with the next highest plausibility is called the second instantaneous Doppler frequency [Hz]. In other words, the ranking of plausibility is first instantaneous Doppler frequency [Hz] > second instantaneous Doppler frequency [Hz].

[0127] The plausibility of two instantaneous Doppler frequencies [Hz] can be determined by, for example, the higher the signal level of the instantaneous Doppler frequency [Hz], the more plausible it is. Other indicators, such as orthogonality with noise, may also be used to determine the plausibility of the instantaneous Doppler frequencies [Hz].

[0128] Here, in the first channel 4, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] calculated and ranked using combination data associated with the elapsed time tick [seconds], i.e., the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] in the first channel 4, are denoted as "C1_Δf1_1_tick" and "C1_Δf1_2_tick".

[0129] The second measurement unit 52 of the second channel 5, the third measurement unit 62 of the third channel 6, and the fourth measurement unit 72 of the fourth channel 7 also calculate the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] from a single reflected wave, similar to the first measurement unit 42 of the first channel 4.

[0130] Here, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] of channel 2 5 are denoted as "C2_Δf1_1_tick" and "C2_Δf1_2_tick". Also, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] of channel 3 6 are denoted as "C3_Δf2_1_tick" and "C3_Δf2_2_tick". Furthermore, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] of channel 4 7 are denoted as "C4_Δf2_1_tick" and "C4_Δf2_2_tick".

[0131] The instantaneous ship speed candidate calculation unit 81 of the ship speed calculation unit 8 calculates multiple instantaneous ship speed candidates at each elapsed time tick, based on each of multiple pairs of instantaneous Doppler frequencies, which are combinations of instantaneous Doppler frequencies of sound waves of the same frequency transmitted in different directions.

[0132] Specifically, as shown in Figure 6, the instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the first instantaneous ship speed candidate of the first frequency) based on the first instantaneous Doppler frequency (C1_Δf1_1_tick) of the first channel 4 in the bow direction and the first instantaneous Doppler frequency (C3_Δf1_1_tick) of the third channel 6 in the stern direction.

[0133] Specifically, based on the following formula (5), the instantaneous ship speed vi1 is calculated from the first instantaneous Doppler frequency (C1_Δf1_1_tick) of the first channel 4 in the bow direction. Similarly, based on the following formula (5), the instantaneous ship speed vi2 is calculated from the first instantaneous Doppler frequency (C3_Δf1_1_tick) of the third channel 6 in the stern direction. Then, beam cancellation is performed to obtain the average of the calculated instantaneous ship speed vi1 in the bow direction and the instantaneous ship speed vi2 in the stern direction, "(vi1+vi2) / 2", and this average value is used as the candidate for the first instantaneous ship speed of the first frequency. This makes it possible to obtain an accurate instantaneous ship speed that eliminates the effects of the ship's forward and backward motion. Note that equation (5) below is the same as equation (2) above, where f is the frequency of the emitted sound wave, θ is the depression angle of the direction of sound wave emission, C is the speed of sound in water, and Δf is the Doppler frequency of the reflected wave (difference between the emitted frequency and the reflected wave frequency: C1_Δf1_1_tick, C3_Δf1_1_tick). (Math 2) vi(vi1,vi2)=C·Δf / (2f·cosθ)

[0134] The value of the candidate for the first instantaneous ship speed at the first frequency, calculated from the combination of the first instantaneous Doppler frequency of the first channel 4 (C1_Δf1_1_tick) and the first instantaneous Doppler frequency of the third channel 6 (C3_Δf1_1_tick), will be denoted as "v1_f1_tick".

[0135] The instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the second instantaneous ship speed candidate of the first frequency) based on the first instantaneous Doppler frequency (C1_Δf1_1_tick) of the first channel 4 in the bow direction and the second instantaneous Doppler frequency (C3_Δf1_2_tick) of the third channel 6 in the stern direction, using the same method as for the first instantaneous ship speed candidate (v1_f1_tick) of the first frequency. The value of this second instantaneous ship speed candidate of the first frequency is denoted as "v2_f1_tick".

[0136] The instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the third instantaneous ship speed candidate of the first frequency) based on the second instantaneous Doppler frequency of the first channel 4 in the bow direction (C1_Δf1_2_tick) and the first instantaneous Doppler frequency of the third channel 6 in the stern direction (C3_Δf1_1_tick), using the same method as for the first instantaneous ship speed candidate of the first frequency (v1_f1_tick). The value of this third instantaneous ship speed candidate of the first frequency is denoted as "v3_f1_tick".

[0137] The instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the fourth instantaneous ship speed candidate of the first frequency) based on the second instantaneous Doppler frequency of the first channel 4 in the bow direction (C1_Δf1_2_tick) and the second instantaneous Doppler frequency of the third channel 6 in the stern direction (C3_Δf1_2_tick), using the same method as for the first instantaneous ship speed candidate of the first frequency (v1_f1_tick). The value of this fourth instantaneous ship speed candidate of the first frequency is denoted as "v4_f1_tick".

[0138] Furthermore, the instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the first instantaneous ship speed candidate of the second frequency) based on the first instantaneous Doppler frequency of the second channel 5 in the bow direction (C2_Δf2_1_tick) and the first instantaneous Doppler frequency of the fourth channel 7 in the stern direction (C4_Δf2_1_tick), using the same method as for the first instantaneous ship speed candidate of the first frequency (v1_f1_tick). The value of this first instantaneous ship speed candidate of the second frequency is denoted as "v1_f2_tick".

[0139] The instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the second instantaneous ship speed candidate of the second frequency) based on the first instantaneous Doppler frequency (C2_Δf2_1_tick) of the second channel 5 in the bow direction and the second instantaneous Doppler frequency (C4_Δf2_2_tick) of the fourth channel 7 in the stern direction, using the same method as for the first instantaneous ship speed candidate (v1_f1_tick) of the first frequency. The value of this second instantaneous ship speed candidate of the second frequency is denoted as "v2_f2_tick".

[0140] The instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the third instantaneous ship speed candidate of the second frequency) based on the second instantaneous Doppler frequency (C2_Δf2_2_tick) of the second channel 5 in the bow direction and the first instantaneous Doppler frequency (C4_Δf2_1_tick) of the fourth channel 7 in the stern direction, using the same method as for the first instantaneous ship speed candidate of the first frequency (v1_f1_tick). The value of this third instantaneous ship speed candidate of the second frequency is denoted as "v3_f2_tick".

[0141] The instantaneous ship speed candidate calculation unit 81 calculates an instantaneous ship speed candidate (hereinafter referred to as the fourth instantaneous ship speed candidate of the second frequency) based on the second instantaneous Doppler frequency (C2_Δf2_2_tick) of the second channel 5 in the bow direction and the second instantaneous Doppler frequency (C4_Δf2_2_tick) of the fourth channel 7 in the stern direction, using the same method as for the first instantaneous ship speed candidate of the first frequency (v1_f1_tick). The value of this fourth instantaneous ship speed candidate of the second frequency is denoted as "v4_f2_tick".

[0142] The instantaneous speed candidate calculation unit 81 outputs the eight instantaneous speed candidates it has calculated, namely the first instantaneous speed candidate for the first frequency (v1_f1_tick), the second instantaneous speed candidate for the first frequency (v2_f1_tick), the third instantaneous speed candidate for the first frequency (v3_f1_tick), the fourth instantaneous speed candidate for the first frequency (v4_f1_tick), the first instantaneous speed candidate for the second frequency (v1_f2_tick), the second instantaneous speed candidate for the second frequency (v2_f2_tick), the third instantaneous speed candidate for the second frequency (v3_f2_tick), and the fourth instantaneous speed candidate for the second frequency (v4_f2_tick), to the instantaneous speed candidate determination unit 82.

[0143] The instantaneous speed candidate determination unit 82 determines whether the first instantaneous speed candidate (v1_f1_tick) of the first frequency, the second instantaneous speed candidate (v2_f1_tick) of the first frequency, the third instantaneous speed candidate (v3_f1_tick) of the first frequency, the fourth instantaneous speed candidate (v4_f1_tick) of the first frequency, the first instantaneous speed candidate (v1_f2_tick) of the second frequency, the second instantaneous speed candidate (v2_f2_tick) of the second frequency, the third instantaneous speed candidate (v3_f2_tick) of the second frequency, and the fourth instantaneous speed candidate (v4_f2_tick) of the second frequency output from the instantaneous speed candidate calculation unit 81 are normal values ​​or not, using the same method as in Embodiment 1, and assigns a normal value flag to the instantaneous speed candidates that are determined to be normal values.

[0144] Furthermore, the instantaneous ship speed candidate determination unit 82 ranks the eight instantaneous ship speed candidates output from the instantaneous ship speed candidate calculation unit 81 in descending order of plausibility. In this embodiment 2, the plausibility of instantaneous ship speed candidates is ranked based on the height of the transmission frequency and the plausibility of the instantaneous Doppler frequency, with the ranking based on the height of the transmission frequency taking precedence over the ranking based on the instantaneous Doppler frequency. That is, since the first frequency f1 is higher than the second frequency f2, the instantaneous ship speed candidate based on the first frequency f1 is ranked higher, and furthermore, the rankings assigned when calculating multiple instantaneous Doppler frequencies in each of the first channels 4 to 7 (the rankings of the first instantaneous Doppler frequency and the second instantaneous Doppler frequency) are taken into consideration. As a result, the eight instantaneous ship speed candidates calculated by the instantaneous ship speed candidate calculation unit 81 are ranked in the following order: first instantaneous ship speed candidate of the first frequency (v1_f1_tick), second instantaneous ship speed candidate of the first frequency (v2_f1_tick), third instantaneous ship speed candidate of the first frequency (v3_f1_tick), fourth instantaneous ship speed candidate of the first frequency (v4_f1_tick), first instantaneous ship speed candidate of the second frequency (v1_f2_tick), second instantaneous ship speed candidate of the second frequency (v2_f2_tick), third instantaneous ship speed candidate of the second frequency (v3_f2_tick), and fourth instantaneous ship speed candidate of the second frequency (v4_f2_tick).

[0145] In this second embodiment, as with the first embodiment described above, the lower the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate (transmission frequency), the higher the likelihood ranking of the instantaneous ship speed candidate.

[0146] The instantaneous speed candidate determination unit 82, similar to Embodiment 1, checks the normal value flags of eight instantaneous speed candidates in order of likelihood. If an instantaneous speed candidate with a normal value flag is found, that instantaneous speed candidate is adopted as the regular instantaneous speed (v_tick).

[0147] The ship speed calculation unit 8 calculates the ship speed value V from the instantaneous ship speed (v_tick) using the ship speed value calculation unit 83, similar to the first embodiment. The ship speed calculation unit 8 also checks for updates to the instantaneous ship speed stored in the instantaneous ship speed buffer 31 using the update determination unit 84, and only if an update has been made, it causes the reference acceleration calculation unit 85 to calculate the reference acceleration within the predetermined range.

[0148] According to the ship speed meter 1 and ship speed measurement method of Embodiment 2, the same effects as in Embodiment 1 can be obtained. Furthermore, since multiple instantaneous Doppler frequencies are calculated from a single received reflected wave, and a larger number of instantaneous ship speed candidates are calculated, it is possible to select the most plausible and normal instantaneous ship speed candidate from among many instantaneous ship speed candidates, thereby enabling the determination of a more accurate ship speed value.

[0149] Furthermore, according to the ship speed meter 1 and ship speed measurement method of Embodiment 2, the plausibility of an instantaneous ship speed candidate is determined based on the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate and the ranking of the plausibility of the instantaneous Doppler frequencies performed in each channel when calculating the instantaneous Doppler frequency that formed the basis of the instantaneous ship speed candidate. As a result, the instantaneous ship speed candidate that is determined to be the most plausible and normal value from among multiple instantaneous ship speed candidates can be adopted as the regular instantaneous ship speed, making it possible to obtain a highly accurate ship speed value.

[0150] (Embodiment 3) Next, a ship speed meter and ship speed measurement method according to Embodiment 3 of the present invention will be described. This Embodiment 3 differs from Embodiment 1 in that it converts multiple instantaneous Doppler frequencies calculated on multiple channels into ship speed values, generates multiple pairs of ship speed values ​​by combining ship speed values ​​converted from instantaneous Doppler frequencies of sound waves transmitted in different directions, and calculates multiple instantaneous ship speed candidates based on each of the pairs of ship speed values. Otherwise, it uses the same configuration as Embodiment 1, so a detailed explanation of the same configuration will be omitted.

[0151] Figure 7 is a functional block diagram showing the schematic configuration of the speedometer 1A according to this third embodiment. The speedometer 1A includes a speed calculation unit 8 and a speed value conversion unit (speed value conversion means) 86. As shown in Figure 8, the speed value conversion unit 86 converts the instantaneous Doppler frequency of the first channel 4 (C1_Δf1_tick), the instantaneous Doppler frequency of the second channel 5 (C2_Δf2_tick), the instantaneous Doppler frequency of the third channel 6 (C3_Δf1_tick), and the instantaneous Doppler frequency of the fourth channel 7 (C4_Δf2_tick) into a speed value [kn] based on the following formula (6). Note that the following formula (6) is the same as formula (1) above, where f is the frequency of sound wave transmission, θ is the depression angle of the direction of sound wave transmission, C is the speed of sound in water, Δf is the Doppler frequency of the reflected wave, and vd is the ship speed value converted from the Doppler frequency. (Math 6) vd = C·Δf / (2f·cosθ)

[0152] Here, the ship speed value converted from the instantaneous Doppler frequency of channel 1 (C1_Δf1_tick) is denoted as "C1_vd_tick". Similarly, the ship speed value converted from the instantaneous Doppler frequency of channel 2 (C2_Δf2_tick) is denoted as "C2_vd_tick". The ship speed value converted from the instantaneous Doppler frequency of channel 3 (C3_Δf1_tick) is denoted as "C3_vd_tick". Furthermore, the ship speed value converted from the instantaneous Doppler frequency of channel 4 (C4_Δf2_tick) is denoted as "C4_vd_tick".

[0153] The ship speed value conversion unit 86 outputs the ship speed values ​​for the first channel 4 (C1_vd_tick), the second channel 5 (C2_vd_tick), the third channel 6 (C3_vd_tick), and the fourth channel 7 (C4_vd_tick), which are converted from the Doppler frequency, to the instantaneous ship speed candidate calculation unit 81.

[0154] The instantaneous ship speed candidate calculation unit 81 generates multiple pairs of ship speed values ​​by combining ship speed values ​​converted from the instantaneous Doppler frequencies of sound waves transmitted in different directions, and calculates multiple instantaneous ship speed candidates based on each of the pairs of ship speed values. Specifically, the instantaneous ship speed candidate calculation unit 81 calculates the instantaneous ship speed candidate by calculating the average of the ship speed value of the first channel 4 in the bow direction (C1_vd_tick) and the ship speed value of the third channel 6 in the stern direction (C3_vd_tick) "(C1_vd_tick+C3_vd_tick) / 2" and performing beam cancellation. Here, the instantaneous ship speed candidate obtained from the ship speed value of the first channel 4 (C1_vd_tick) and the ship speed value of the third channel 6 (C3_vd_tick) is called the first instantaneous ship speed candidate and is denoted as "v1_tick".

[0155] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the speed value of the first channel 4 in the bow direction (C1_vd_tick) and the speed value of the fourth channel 7 in the stern direction (C4_vd_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the speed value of the first channel 4 (C1_vd_tick) and the speed value of the fourth channel 7 (C4_vd_tick) is called the second instantaneous speed candidate and is denoted as "v2_tick".

[0156] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the speed value of the second channel 5 in the bow direction (C2_vd_tick) and the speed value of the third channel 6 in the stern direction (C3_vd_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the speed value of the second channel 5 (C2_vd_tick) and the speed value of the third channel 6 (C6_vd_tick) is called the third instantaneous speed candidate and is denoted as "v3_tick".

[0157] Furthermore, the instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the speed value of the second channel 5 in the bow direction (C2_vd_tick) and the speed value of the fourth channel 7 in the stern direction (C4_vd_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the speed value of the second channel 5 (C2_vd_tick) and the speed value of the fourth channel 7 (C7_vd_tick) is called the fourth instantaneous speed candidate and is denoted as "v4_tick".

[0158] The instantaneous ship speed candidate determination unit 82 determines whether the first instantaneous ship speed candidate (v1_tick), second instantaneous ship speed candidate (v2_tick), third instantaneous ship speed candidate (v3_tick), and fourth instantaneous ship speed candidate (v4_tick) output from the instantaneous ship speed candidate calculation unit 81 are normal values ​​using the same method as in Embodiment 1, and assigns a normal value flag to the instantaneous ship speed candidates that are determined to be normal values.

[0159] Furthermore, the instantaneous speed candidate determination unit 82 ranks the four instantaneous speed candidates output from the instantaneous speed candidate calculation unit 81 in order of plausibility. In this embodiment 3, the plausibility of the instantaneous speed candidates is ranked based on the height of the transmission frequency. That is, since the first frequency f1 is higher than the second frequency f2, the instantaneous speed candidate based on the first frequency f1 is ranked higher. As a result, the four instantaneous speed candidates calculated by the instantaneous speed candidate calculation unit 81 are ranked in the order of first instantaneous speed candidate (v1_tick), second instantaneous speed candidate (v2_tick), third instantaneous speed candidate (v3_tick), and fourth instantaneous speed candidate (v4_tick).

[0160] In this third embodiment, as with the first embodiment described above, the lower the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate (launch frequency), the higher the likelihood ranking of the instantaneous ship speed candidate.

[0161] The instantaneous speed candidate determination unit 82, similar to Embodiment 1, checks the normal value flags of four instantaneous speed candidates in order of likelihood. If an instantaneous speed candidate with a normal value flag is found, that instantaneous speed candidate is adopted as the regular instantaneous speed (v_tick).

[0162] The ship speed calculation unit 8 calculates the ship speed value V from the instantaneous ship speed (v_tick) using the ship speed value calculation unit 83, similar to the first embodiment. The ship speed calculation unit 8 also checks for updates to the instantaneous ship speed stored in the instantaneous ship speed buffer 31 using the update determination unit 84, and only if an update has been made, it causes the reference acceleration calculation unit 85 to calculate the reference acceleration within the predetermined range.

[0163] According to the ship speed meter 1A and ship speed measurement method of Embodiment 3, the same effects as in Embodiment 1 can be obtained. Furthermore, since multiple instantaneous Doppler frequencies are converted into ship speed values ​​and multiple instantaneous ship speed candidates are calculated by combining the converted ship speed values, instantaneous ship speed candidates can be calculated even for combinations of instantaneous Doppler frequencies of sound waves with different frequencies. Therefore, when calculating ship speed values ​​in a pair-beam type ship speed meter, instantaneous ship speed candidates based on interference wave frequencies can be more effectively excluded, making it possible to obtain a highly accurate ship speed.

[0164] (Embodiment 4) Next, a ship speed meter and ship speed measurement method according to Embodiment 4 of the present invention will be described. This Embodiment 4 differs from Embodiment 1 in that it obtains multiple instantaneous Doppler frequencies from a single reflected wave, converts these instantaneous Doppler frequencies into ship speed values, generates multiple pairs of ship speed values ​​by combining ship speed values ​​converted from the instantaneous Doppler frequencies of sound waves transmitted in different directions, and calculates multiple instantaneous ship speed candidates based on each of the pairs of ship speed values. Otherwise, it uses the same configuration as Embodiment 1, so a detailed explanation of the same configuration will be omitted.

[0165] The speedometer according to this fourth embodiment, like the speedometer 1A of the third embodiment shown in Figure 7, is equipped with a speed value conversion unit (speed value conversion means) 86 in the speed calculation unit 8. In the speedometer according to this fourth embodiment, similar to the second embodiment, the first measurement unit 42 of the first channel 4, the second measurement unit 52 of the second channel 5, the third measurement unit 62 of the third channel 6, and the fourth measurement unit 72 of the fourth channel 7 each calculate multiple (for example, two) instantaneous Doppler frequencies [Hz] from a single reflected wave.

[0166] Specifically, when the first measurement unit 42 of the first channel 4 acquires a received signal from the first sensor 41, it detects multiple data points, for example two, of reflected wave frequencies with high signal levels from the waveform of the received signal, similar to the second embodiment. The first measurement unit 42 also associates the two detected reflected wave frequency [Hz] data points with the elapsed time tick [seconds] from a predetermined point in time, which is determined by the clock function (not shown) of the first measurement unit 42, to form two combination data points of elapsed time tick [seconds] and reflected wave frequency [Hz]. Then, for each of the two combination data points, the first measurement unit 42 calculates the difference between it and the known transmission frequency (first frequency f1) of the sound wave transmitted from the first sensor 41, and calculates two instantaneous Doppler frequencies [Hz].

[0167] The first measurement unit 42 determines the plausibility of the two instantaneous Doppler frequency [Hz] values ​​and ranks the two instantaneous Doppler frequencies [Hz] in descending order of plausibility. Here, the instantaneous Doppler frequency [Hz] with the highest plausibility among the two instantaneous Doppler frequencies [Hz] is called the first instantaneous Doppler frequency [Hz], and the instantaneous Doppler frequency [Hz] with the next highest plausibility is called the second instantaneous Doppler frequency [Hz]. In other words, the ranking of plausibility is first instantaneous Doppler frequency [Hz] > second instantaneous Doppler frequency [Hz].

[0168] The plausibility of two instantaneous Doppler frequencies [Hz] can be determined by, for example, the higher the signal level of the instantaneous Doppler frequency [Hz], the more plausible it is. Other indicators, such as orthogonality with noise, may also be used to determine the plausibility of the instantaneous Doppler frequencies [Hz].

[0169] Here, in the first channel 4, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] calculated and ranked using combination data associated with the elapsed time tick [seconds], i.e., the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] in the first channel 4, are denoted as "C1_Δf1_1_tick" and "C1_Δf1_2_tick".

[0170] The second measurement unit 52 of the second channel 5, the third measurement unit 62 of the third channel 6, and the fourth measurement unit 72 of the fourth channel 7 also calculate the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] from a single reflected wave, similar to the first measurement unit 42 of the first channel 4.

[0171] Here, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] of channel 2 5 are denoted as "C2_Δf1_1_tick" and "C2_Δf1_2_tick". Also, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] of channel 3 6 are denoted as "C3_Δf2_1_tick" and "C3_Δf2_2_tick". Furthermore, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time tick [seconds] of channel 4 7 are denoted as "C4_Δf2_1_tick" and "C4_Δf2_2_tick".

[0172] As shown in Figure 9, the ship speed value conversion unit 86 converts the first instantaneous Doppler frequency (C1_Δf1_1_tick) and second instantaneous Doppler frequency (C1_Δf1_2_tick) of the first channel 4, the first instantaneous Doppler frequency (C2_Δf2_1_tick) and second instantaneous Doppler frequency (C2_Δf2_2_tick) of the second channel 5, the first instantaneous Doppler frequency (C3_Δf1_1_tick) and second instantaneous Doppler frequency (C3_Δf1_2_tick) of the third channel 6, and the first instantaneous Doppler frequency (C4_Δf2_1_tick) and second instantaneous Doppler frequency (C4_Δf2_2_tick) of the fourth channel 7 into ship speed values ​​[kn] based on the following formula (7). Note that formula (7) below is identical to formula (6) above. (Math 7) vd = C·Δf / (2f·cosθ)

[0173] Here, the first ship speed value converted from the first instantaneous Doppler frequency (C1_Δf1_1_tick) of the first channel 4 is denoted as "C1_vd1_tick", and the second ship speed value converted from the second instantaneous Doppler frequency (C1_Δf1_2_tick) is denoted as "C1_vd2_tick". Similarly, the first ship speed value converted from the first instantaneous Doppler frequency (C2_Δf2_1_tick) of the second channel 5 is denoted as "C2_vd1_tick", and the second ship speed value converted from the second instantaneous Doppler frequency (C2_Δf2_2_tick) is denoted as "C2_vd2_tick". The first ship speed value converted from the first instantaneous Doppler frequency (C3_Δf1_1_tick) of channel 36 is denoted as "C3_vd1_tick", and the second ship speed value converted from the second instantaneous Doppler frequency (C3_Δf1_2_tick) is denoted as "C3_vd2_tick". Furthermore, the first ship speed value converted from the first instantaneous Doppler frequency (C4_Δf2_1_tick) of channel 47 is denoted as "C4_vd1_tick", and the second ship speed value converted from the second instantaneous Doppler frequency (C4_Δf2_2_tick) is denoted as "C4_vd2_tick".

[0174] The ship speed value conversion unit 86 outputs the first ship speed value (C1_vd1_tick) and second ship speed value (C1_vd2_tick) of the first channel 4, converted from the Doppler frequency, the first ship speed value (C2_vd1_tick) and second ship speed value (C2_vd2_tick) of the second channel 5, the first ship speed value (C3_vd1_tick) and second ship speed value (C3_vd2_tick) of the third channel 6, and the first ship speed value (C4_vd1_tick) and second ship speed value (C4_vd2_tick) of the fourth channel 7 to the instantaneous ship speed candidate calculation unit 81.

[0175] The instantaneous ship speed candidate calculation unit 81 generates multiple pairs of ship speed values ​​by combining ship speed values ​​converted from the instantaneous Doppler frequencies of sound waves transmitted in different directions, and calculates multiple instantaneous ship speed candidates based on each of the pairs of ship speed values. In this embodiment 4, the instantaneous ship speed candidate calculation unit 81 calculates 16 instantaneous ship speed candidates based on combinations of 8 ship speed values. Figure 10 shows the 16 instantaneous ship speed candidates calculated based on combinations of 8 ship speed values.

[0176] As shown in Figure 10, the instantaneous ship speed candidate calculation unit 81 calculates the instantaneous ship speed candidate by calculating the average of the first ship speed value (C1_vd1_tick) of the first channel 4 in the bow direction and the first ship speed value (C3_vd1_tick) of the third channel 6 in the stern direction, "(C1_vd1_tick+C3_vd1_tick) / 2", performing beam cancellation. Here, the instantaneous ship speed candidate obtained from the first ship speed value (C1_vd1_tick) of the first channel 4 and the first ship speed value (C3_vd1_tick) of the third channel 6 is called the first instantaneous ship speed candidate and is denoted as "v1_tick".

[0177] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the first speed value (C1_vd1tick) of the first channel 4 in the bow direction and the second speed value (C3_vd2_tick) of the third channel 6 in the stern direction, similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the first speed value (C1_vd1_tick) of the first channel 4 and the second speed value (C3_vd2_tick) of the third channel 6 is called the second instantaneous speed candidate and is denoted as "v2_tick".

[0178] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the second speed value (C1_vd2_tick) of the first channel 4 in the bow direction and the first speed value (C3_vd1_tick) of the third channel 6 in the stern direction, similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the second speed value (C1_vd2_tick) of the first channel 4 and the first speed value (C3_vd1_tick) of the third channel 6 is called the third instantaneous speed candidate and is denoted as "v3_tick".

[0179] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the second speed value of the first channel 4 in the bow direction (C1_vd2_tick) and the second speed value of the third channel 6 in the stern direction (C3_vd2_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the second speed value of the first channel 4 (C1_vd2_tick) and the second speed value of the third channel 6 (C3_vd2_tick) is called the fourth instantaneous speed candidate and is denoted as "v4_tick".

[0180] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the first speed value of the first channel 4 in the bow direction (C1_vd1_tick) and the first speed value of the fourth channel 7 in the stern direction (C4_vd1_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the first speed value of the first channel 4 (C1_vd1_tick) and the first speed value of the fourth channel 7 (C4_vd1_tick) is called the fifth instantaneous speed candidate and is denoted as "v5_tick".

[0181] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the first speed value of the second channel 5 in the bow direction (C2_vd1_tick) and the first speed value of the third channel 6 in the stern direction (C3_vd1_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the first speed value of the second channel 5 (C2_vd1_tick) and the first speed value of the third channel 6 (C3_vd1_tick) is called the sixth instantaneous speed candidate and is denoted as "v6_tick".

[0182] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the second speed value of the first channel 4 in the bow direction (C1_vd2_tick) and the first speed value of the fourth channel 7 in the stern direction (C4_vd1_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the second speed value of the first channel 4 (C1_vd2_tick) and the first speed value of the fourth channel 7 (C4_vd1_tick) is called the seventh instantaneous speed candidate and is denoted as "v7_tick".

[0183] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the first speed value (C2_vd1_tick) of the second channel 5 in the bow direction and the second speed value (C3_vd2_tick) of the third channel 6 in the stern direction, similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the first speed value (C2_vd1_tick) of the second channel 5 and the second speed value (C3_vd2_tick) of the third channel 6 is called the eighth instantaneous speed candidate and is denoted as "v8_tick".

[0184] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the first speed value of the second channel 5 in the bow direction (C2_vd1_tick) and the first speed value of the fourth channel 7 in the stern direction (C4_vd1_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the first speed value of the second channel 5 (C2_vd1_tick) and the first speed value of the fourth channel 7 (C4_vd1_tick) is called the ninth instantaneous speed candidate and is denoted as "v9_tick".

[0185] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the first speed value (C1_vd1_tick) of the first channel 4 in the bow direction and the second speed value (C4_vd2_tick) of the fourth channel 7 in the stern direction, similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the first speed value (C1_vd1_tick) of the first channel 4 and the second speed value (C4_vd2_tick) of the fourth channel 7 is called the 10th instantaneous speed candidate and is denoted as "v10_tick".

[0186] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the second speed value (C2_vd2_tick) of the second channel 5 in the bow direction and the first speed value (C3_vd1_tick) of the third channel 6 in the stern direction, similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the second speed value (C2_vd2_tick) of the second channel 5 and the first speed value (C3_vd1_tick) of the third channel 6 is called the 11th instantaneous speed candidate and is denoted as "v11_tick".

[0187] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the second speed value of the first channel 4 in the bow direction (C1_vd2_tick) and the second speed value of the fourth channel 7 in the stern direction (C4_vd2_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the second speed value of the first channel 4 (C1_vd2_tick) and the second speed value of the fourth channel 7 (C4_vd2_tick) is called the 12th instantaneous speed candidate and is denoted as "v12_tick".

[0188] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the second speed value (C2_vd2_tick) of the second channel 5 in the bow direction and the first speed value (C3_vd1_tick) of the third channel 6 in the stern direction, similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the second speed value (C2_vd2_tick) of the second channel 5 and the first speed value (C3_vd1_tick) of the third channel 6 is called the 13th instantaneous speed candidate and is denoted as "v13_tick".

[0189] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the first speed value (C2_vd1_tick) of the second channel 5 in the bow direction and the second speed value (C4_vd2_tick) of the fourth channel 7 in the stern direction, similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the first speed value (C2_vd1_tick) of the second channel 5 and the second speed value (C4_vd2_tick) of the fourth channel 7 is called the 14th instantaneous speed candidate and is denoted as "v14_tick".

[0190] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the second speed value (C2_vd2_tick) of the second channel 5 in the bow direction and the first speed value (C4_vd1_tick) of the fourth channel 7 in the stern direction, similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the second speed value (C2_vd2_tick) of the second channel 5 and the first speed value (C4_vd1_tick) of the fourth channel 7 is called the 15th instantaneous speed candidate and is denoted as "v15_tick".

[0191] The instantaneous speed candidate calculation unit 81 calculates an instantaneous speed candidate based on the second speed value of the second channel 5 in the bow direction (C2_vd2_tick) and the second speed value of the fourth channel 7 in the stern direction (C4_vd2_tick), similar to the first instantaneous speed candidate (v1_tick). Here, the instantaneous speed candidate obtained from the second speed value of the second channel 5 (C2_vd2_tick) and the second speed value of the fourth channel 7 (C4_vd2_tick) is called the 16th instantaneous speed candidate and is denoted as "v16_tick".

[0192] The instantaneous speed candidate determination unit 82 determines the first instantaneous speed candidate (v1_tick), second instantaneous speed candidate (v2_tick), third instantaneous speed candidate (v3_tick), fourth instantaneous speed candidate (v4_tick), fifth instantaneous speed candidate (v5_tick), sixth instantaneous speed candidate (v6_tick), seventh instantaneous speed candidate (v7_tick), eighth instantaneous speed candidate (v8_tick), ninth instantaneous speed candidate (v9_tick), and tenth instantaneous speed candidate output from the instantaneous speed candidate calculation unit 81. For candidate (v10_tick), candidate 11th instantaneous ship speed (v11_tick), candidate 12th instantaneous ship speed (v12_tick), candidate 13th instantaneous ship speed (v13_tick), candidate 14th instantaneous ship speed (v14_tick), candidate 15th instantaneous ship speed (v15_tick), and candidate 16th instantaneous ship speed (v16_tick), it is determined whether or not they are normal values ​​using the same method as in Embodiment 1, and a normal value flag is assigned to instantaneous ship speed candidates that are determined to be normal values.

[0193] Furthermore, the instantaneous ship speed candidate determination unit 82 ranks the 16 instantaneous ship speed candidates output from the instantaneous ship speed candidate calculation unit 81 in descending order of plausibility. In this embodiment 4, the plausibility of instantaneous ship speed candidates is ranked based on the height of the transmission frequency and the plausibility of the instantaneous Doppler frequency, with the ranking based on the height of the transmission frequency taking precedence over the ranking based on the instantaneous Doppler frequency. That is, since the first frequency f1 is higher than the second frequency f2, instantaneous ship speed candidates based on the first frequency f1 are ranked higher, and furthermore, the rankings assigned when calculating multiple instantaneous Doppler frequencies in each of the first channels 4 to 7 (the rankings of the first instantaneous Doppler frequency and the second instantaneous Doppler frequency) are taken into consideration.

[0194] As a result, the 16 instantaneous ship speed candidates calculated by the instantaneous ship speed candidate calculation unit 81 are: 1st instantaneous ship speed candidate (v1_tick), 2nd instantaneous ship speed candidate (v2_tick), 3rd instantaneous ship speed candidate (v3_tick), 4th instantaneous ship speed candidate (v4_tick), 5th instantaneous ship speed candidate (v5_tick), 6th instantaneous ship speed candidate (v6_tick), 7th instantaneous ship speed candidate (v7_tick), 8th instantaneous ship speed candidate (v8_ The candidates are ranked in the following order: (tick), 9th instantaneous speed candidate (v9_tick), 10th instantaneous speed candidate (v10_tick), 11th instantaneous speed candidate (v11_tick), 12th instantaneous speed candidate (v12_tick), 13th instantaneous speed candidate (v13_tick), 14th instantaneous speed candidate (v14_tick), 15th instantaneous speed candidate (v15_tick), and 16th instantaneous speed candidate (v16_tick). In the table shown in Figure 10, the instantaneous speed candidate in the upper left has the highest probability, and the instantaneous speed candidate in the lower right has the lowest probability. Furthermore, some of these instantaneous speed candidates have equal plausibility. For example, the second instantaneous speed candidate (v2_tick) and the third instantaneous speed candidate (v3_tick), and the seventh instantaneous speed candidate (v7_tick) and the tenth instantaneous speed candidate (v10_tick) have equal plausibility, so their rankings can be swapped.

[0195] The instantaneous speed candidate determination unit 82, similar to Embodiment 1, checks the normal value flags of 16 instantaneous speed candidates in order of likelihood. If an instantaneous speed candidate with a normal value flag is found, that instantaneous speed candidate is adopted as the regular instantaneous speed (v_tick).

[0196] In this embodiment 4, as with embodiment 1 described above, the lower the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate (launch frequency), the higher the likelihood ranking of the instantaneous ship speed candidate.

[0197] The ship speed calculation unit 8 calculates the ship speed value V from the instantaneous ship speed (v_tick) using the ship speed value calculation unit 83, similar to the first embodiment. The ship speed calculation unit 8 also checks for updates to the instantaneous ship speed stored in the instantaneous ship speed buffer 31 using the update determination unit 84, and only if an update has been made, it causes the reference acceleration calculation unit 85 to calculate the reference acceleration within the predetermined range.

[0198] According to the ship speed meter 1 and ship speed measurement method of Embodiment 4, the same effects as in Embodiment 1 can be obtained. Furthermore, since multiple instantaneous Doppler frequencies are calculated from a single received reflected wave, and a larger number of instantaneous ship speed candidates are calculated, it is possible to select the most plausible and normal instantaneous ship speed candidate from among many instantaneous ship speed candidates, thereby enabling the determination of a more accurate ship speed value.

[0199] Furthermore, by converting multiple instantaneous Doppler frequencies into ship speed values ​​and combining these converted ship speed values ​​to calculate multiple instantaneous ship speed candidates, it is possible to calculate instantaneous ship speed candidates even for combinations of instantaneous Doppler frequencies of sound waves with different frequencies. Therefore, when calculating ship speed values ​​in a pair-beam type ship speed meter, instantaneous ship speed candidates based on interference wave frequencies can be more effectively eliminated, making it possible to obtain a more accurate ship speed.

[0200] Furthermore, according to the ship speed meter 1 and ship speed measurement method of Embodiment 4, the plausibility of an instantaneous ship speed candidate is determined based on the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate and the ranking of the plausibility of the instantaneous Doppler frequencies performed in each channel when calculating the instantaneous Doppler frequency that formed the basis of the instantaneous ship speed candidate. As a result, the instantaneous ship speed candidate that is determined to be the most plausible and normal value from among multiple instantaneous ship speed candidates can be adopted as the regular instantaneous ship speed, making it possible to obtain a highly accurate ship speed value.

[0201] Although embodiments 1 to 4 of this invention have been described above, the specific configuration is not limited to embodiments 1 to 4 described above, and any design changes, etc., that do not depart from the spirit of this invention are also included.

[0202] For example, in embodiments 1 to 4 described above, a sound wave with a first frequency f1 [Hz] and a sound wave with a second frequency f2 [Hz] were transmitted in the bow direction and the stern direction, respectively. However, for example, one of the sound waves with the first frequency f1 [Hz] or the second frequency f2 [Hz] may be transmitted in the bow direction, and the other sound wave may be transmitted in the stern direction. In this case, since the transmission frequencies of the sound waves are different in the bow direction and the stern direction, the instantaneous Doppler frequency is converted to a ship speed value before determining the instantaneous ship speed candidate. This results in differences in the attenuation of the sound waves and the difference with the interference wave frequency between the bow direction and the stern direction, making it less susceptible to the influence of the interference wave frequency and enabling the determination of an accurate ship speed value.

[0203] Furthermore, in embodiments 1 to 4 described above, instantaneous Doppler frequencies are calculated for each of the first channel 4 and second channel 5 in the bow direction, and for each of the third channel 6 and fourth channel 7 in the stern direction. However, it is also possible to obtain even more Doppler frequencies for each of many more channels, or to obtain multiple Doppler frequencies for each of the multiple channels in the width direction. In that case, an even larger number of instantaneous ship speed candidates may be calculated according to the number of Doppler frequencies obtained, and the normal instantaneous ship speed may be determined from these instantaneous ship speed candidates.

[0204] Furthermore, while the speedometer 1 in embodiments 1 to 4 above measures the ship's speed relative to the water, this invention can also be applied to measuring the ship's speed relative to the ground (i.e., the ship's speed relative to the ground). In addition, in embodiments 1 to 4 above, the first channel 4 and the second channel 5 transmit sound waves of different frequencies in the bow direction, and the third channel 6 and the fourth channel 7 transmit sound waves of different frequencies in the stern direction. However, one channel may be provided for both the bow and stern directions, and the frequencies of the sound waves transmitted may be switched using these channels.

[0205] Furthermore, in embodiments 1 to 4 described above, if the first instantaneous ship speed candidate (v1_tick) and the second instantaneous ship speed candidate (v2_tick) cannot be calculated (NO in steps S1f and S1j), or if they are not determined to be normal values ​​(NO in steps S1g and S1k), the instantaneous ship speed buffer 31 will not be updated (NO in step S5). Therefore, as long as the instantaneous ship speed buffer 31 is not updated, the ship speed value V calculated in the process of step S3 will not change. Therefore, as a countermeasure when the instantaneous ship speed buffer 31 is not updated for a certain period of time, (for example, when the ship is moving forward) the lower limit of the change in acceleration from the reference acceleration ar, "ar_T-alt", may be set to 0 [kn / sec], or the upper limit of the change in acceleration from the reference acceleration ar, "ar_T+aut", may be removed (i.e., set to no upper limit), or (for example, when the ship is moving backward) the lower limit of the change in acceleration from the reference acceleration ar, "ar_T-alt", may be removed (i.e., set to no lower limit), or the upper limit of the change in acceleration from the reference acceleration ar, "ar_T+aut", may be set to 0 [kn / sec].

[0206] In this case, for example, when assuming that the ship is sailing at the last calculated reference acceleration ar, measures may be taken to address the case where the instantaneous ship speed buffer 31 is not updated when a predetermined ship speed is reached (note that this is not limited to a specific speed, but could be set to, for example, the maximum speed based on the ship's performance and specifications, or to 0). Alternatively, the above measures may be taken when the instantaneous ship speed buffer 31 is not updated for a predetermined period of time (note that this is not limited to a specific period of time, but could be set to, for example, any period of time within the range of 5 to 15 seconds). In other words, when the instantaneous ship speed value v stored in the instantaneous ship speed buffer 31 is not updated and predetermined conditions are met, the conditions defining the range of acceleration related to instantaneous ship speed (specifically, the lower limit of the change in acceleration from the reference acceleration ar, "ar_T-alt", and the upper limit of the change in acceleration from the reference acceleration, "ar_T+aut") may be changed. This makes it possible to calculate ship speed values ​​accurately and stably according to the ship's sailing conditions.

[0207] Furthermore, in embodiments 1 to 4 described above, all instantaneous ship speed values ​​v selected from among multiple instantaneous ship speed candidates are added to and stored in the instantaneous ship speed buffer 31 (step S2). However, the addition and storage to the instantaneous ship speed buffer 31 is not limited to this embodiment. For example, the data of the average value of the instantaneous ship speed values ​​v selected in the calculation time interval I (specifically, for example, from the elapsed time "T+Δt" to "T+I") and a representative value of the elapsed time (e.g., T+I / 2) may be added to the beginning of the instantaneous ship speed buffer 31 and stored. Alternatively, the data of the instantaneous ship speed value v whose acceleration related to the instantaneous ship speed is closest to the reference acceleration ar among the instantaneous ship speed values ​​v selected in the calculation time interval I (specifically, for example, from the elapsed time "T+Δt" to "T+I") and a representative value of the elapsed time (e.g., T+I / 2) may be added to the beginning of the instantaneous ship speed buffer 31 and stored.

[0208] Furthermore, in the above embodiments 1 to 4, in the normal value determination (steps S1g, S1k) of the first instantaneous ship speed candidate (v1_tick) and the second instantaneous ship speed candidate (v2_tick), instantaneous ship speed candidates whose acceleration related to the instantaneous ship speed candidate is within a predetermined range were determined to be normal values. However, it is also possible to determine that instantaneous ship speed candidates whose values ​​are within a predetermined range based on past ship speed values ​​are normal values.

[0209] The past ship speed value used as a reference may be the ship speed value calculated immediately before, or the average value of ship speed values ​​within a predetermined period. For example, in the example shown in Figure 5, when determining the normal value of an instantaneous ship speed candidate between elapsed time "T" and "T+I", if the ship speed value calculated immediately before is used as the reference ship speed value, the ship speed value V_T at elapsed time "T" becomes the reference ship speed value. This allows the trend of ship speed to be used as the judgment criterion, making it possible to calculate ship speed values ​​in a more natural way.

[0210] Furthermore, when determining the normal value of an instantaneous ship speed candidate between the elapsed time "T" and "T+I", if the average value of the ship speed values ​​within a predetermined period is used as the reference ship speed value, the average value of the ship speed value V_T-I at the elapsed time "TI" and the ship speed value V_T at the elapsed time "T" may be used as the reference ship speed value. Note that the predetermined period for determining the reference ship speed value using the average value is not limited to a specific time length, but is set appropriately after considering various conditions such as the type of ship and the ship speed relative to the water. In addition, as the average value of the ship speed values ​​within the predetermined period, for example, the average value of multiple ship speed values ​​stored in the ship speed value buffer 32 may be used.

[0211] Furthermore, the predetermined range based on past ship speed values ​​is not limited to a specific time length, but is set appropriately to a suitable time length (for example, ±1 to 5 [Kn] relative to the reference ship speed value) after considering various conditions related to the ship type and ship speed relative to water. In addition, the predetermined range relative to the reference ship speed value may be set so that the absolute values ​​of the upper and lower limits are the same, or it may be set so that the absolute values ​​are different from each other.

[0212] Furthermore, the process of calculating a reference ship speed value from multiple ship speed values ​​stored in the ship speed value buffer 32 (the process of setting a reference within a predetermined range) may be performed only when the instantaneous ship speed stored in the instantaneous ship speed buffer 31 is updated, similar to the calculation of the reference acceleration described above. This makes it possible to calculate ship speed values ​​accurately and stably according to the ship's navigation conditions.

[0213] Furthermore, if the first instantaneous speed candidate (v1_tick) and the second instantaneous speed candidate (v2_tick) cannot be calculated or are not determined to be normal values ​​for a series of events, the instantaneous speed buffer 31 will not be updated, and the speed value V will not change while the instantaneous speed buffer 31 is not updated. For this reason, as a countermeasure when the instantaneous speed buffer 31 is not updated for a certain period of time, (for example, when the ship is moving forward) the lower limit of the predetermined range based on the reference speed value may be set to 0 [kn], or the upper limit of the predetermined range based on the reference speed value may be removed (i.e., no upper limit), or (for example, when the ship is moving backward) the lower limit of the predetermined range based on the reference speed value may be removed (i.e., no lower limit), or the upper limit of the predetermined range based on the reference speed value may be set to 0 [kn].

[0214] In this case, for example, a countermeasure may be implemented if the instantaneous speed buffer 31 is not updated when a predetermined speed (which is not limited to a specific speed, but could be set to the maximum speed based on the ship's performance and specifications, or to 0) is reached, assuming that the ship is sailing at the last calculated reference speed value. Alternatively, the above countermeasure may be implemented if the instantaneous speed buffer 31 is not updated for a predetermined period of time (which is not limited to a specific period of time, but could be set to any period of time within a range of approximately 5 to 15 seconds). In other words, if a predetermined condition is met while the instantaneous speed value v stored in the instantaneous speed buffer 31 is not updated, the conditions defining a predetermined range based on the reference speed value (specifically, the lower and upper limits based on the reference speed value) may be changed. This makes it possible to calculate the ship speed value accurately and stably according to the ship's sailing conditions. [Explanation of Symbols]

[0215] 1, 1A speedometer 2 Control Unit 3 Storage section 31 Instantaneous ship speed buffer (buffer) 32. Ship speed value buffer (second buffer) 4. Channel 1 5. Channel 2 6. Channel 3 7 Channel 4 8 Ship speed calculation section 81 Instantaneous ship speed candidate calculation unit (instantaneous ship speed candidate calculation means) 82 Instantaneous ship speed candidate determination unit (instantaneous ship speed candidate determination means) 83. Ship speed value calculation unit (ship speed value calculation means) 84 Update determination section 85 Reference acceleration calculation section 86 Ship speed value conversion unit (ship speed value conversion means) 9 Interface section 10 Display section

Claims

1. Multiple channels that emit sound waves of different frequencies in at least two directions underwater, receive the reflected waves of the emitted sound waves, and calculate the instantaneous Doppler frequency from the received reflected waves, An instantaneous ship speed candidate calculation means calculates multiple instantaneous ship speed candidates based on combinations of instantaneous Doppler frequencies of sound waves transmitted in different directions, An instantaneous ship speed candidate determination means that determines whether the multiple instantaneous ship speed candidates are normal values ​​in order of increasing likelihood, and adopts the value of the instantaneous ship speed candidate that is first determined to be normal as the instantaneous ship speed, A ship speed value calculation means that calculates a ship speed value based on the instantaneous ship speed value, A ship speedometer characterized by being equipped with the following features.

2. The ship speedometer according to claim 1, characterized in that the plurality of channels each calculate a plurality of instantaneous Doppler frequencies from a single reflected wave received.

3. The instantaneous ship speed candidate calculation means generates multiple pairs of instantaneous Doppler frequencies by combining the instantaneous Doppler frequencies of sound waves of the same frequency transmitted in different directions, and calculates multiple instantaneous ship speed candidates based on each of the pairs of instantaneous Doppler frequencies. A ship speedometer according to feature 1 or 2.

4. The system includes a ship speed value conversion means that converts multiple instantaneous Doppler frequencies calculated in the aforementioned multiple channels into ship speed values. The instantaneous ship speed candidate calculation means generates multiple pairs of ship speed values ​​by combining ship speed values ​​converted from the instantaneous Doppler frequencies of sound waves transmitted in different directions, and calculates multiple instantaneous ship speed candidates based on each of the pair of ship speed values. A ship speedometer according to feature 1 or 2.

5. The instantaneous ship speed value is stored in a buffer for a predetermined period of time, and the ship speed value is calculated using the instantaneous ship speed value stored in the buffer. The ship speedometer according to feature 1.

6. The instantaneous ship speed candidate determination means determines that an instantaneous ship speed candidate whose acceleration is within a predetermined range is a normal value. The ship speedometer according to feature 5.

7. The instantaneous ship speed candidate determination means determines that an instantaneous ship speed candidate whose value falls within a predetermined range based on past ship speed values ​​is a normal value. The ship speedometer according to feature 5.

8. The calculated ship speed values ​​are stored in a predetermined number of second buffers, and the predetermined range reference is set using the ship speed values ​​stored in the second buffer. The ship speedometer according to claim 6 or 7.

9. The predetermined range reference is set only when the instantaneous ship speed stored in the buffer is updated. The ship speedometer according to feature 8.

10. When the instantaneous ship speed stored in the buffer has not been updated and a predetermined condition is met, the condition defining the predetermined range is changed. The ship speedometer according to feature 9.

11. The instantaneous ship speed candidate determination means determines the likelihood of the instantaneous ship speed candidate based on the frequency of the sound wave that formed the basis of the instantaneous ship speed candidate. The ship speedometer according to feature 1.

12. The instantaneous ship speed candidate determination means determines the plausibility of the instantaneous ship speed candidate based on the frequency of the sound wave on which the instantaneous ship speed candidate is based and the ranking of the plausibility of the instantaneous Doppler frequencies performed on the channel when calculating the instantaneous Doppler frequency on which the instantaneous ship speed candidate is based. The ship speedometer according to feature 2.

13. Sound waves of different frequencies are emitted in at least two directions underwater, the reflected waves of the emitted sound waves are received, and the instantaneous Doppler frequencies are calculated from the received reflected waves. Based on combinations of instantaneous Doppler frequencies of sound waves emitted in different directions, multiple instantaneous ship speed candidates are calculated. The aforementioned multiple instantaneous ship speed candidates are judged to be normal values ​​in order of plausibility, and the value of the instantaneous ship speed candidate that is first judged to be normal is adopted as the instantaneous ship speed. The ship speed value is calculated based on the aforementioned instantaneous ship speed value. A method for measuring ship speed characterized by the following features.

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