Ship speedometer and method for measuring ship speed

Abstract

To find accurate ship speed.SOLUTION: An instantaneous ship speed candidate calculation part 61 calculates a plurality of instantaneous ship speed candidates from the reflected waves of the sound waves transmitted from a first channel 4 and a second channel 5 into water, and ranks the plurality of instantaneous ship speed candidates in descending order of plausibility. An instantaneous ship speed candidate determination part 62 determines whether or not the plurality of instantaneous ship speed candidates is a normal value in descending order of plausibility, and adopts a value of the instantaneous ship speed candidate which has been first determined to be the normal value as the instantaneous ship speed. A ship speed value calculation part 63 calculates a ship speed value based on the value of the instantaneous ship 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 for measuring ship speed.

Background Art

[0002] As one of the methods of a ship speedometer for measuring ship speed, an acoustic type (also called "Doppler type") is known. The acoustic ship speedometer transmits sound waves from a ship into water, and based on the difference between the frequency of the transmitted sound wave and the frequency of the reflected wave of the sound wave reflected by floating substances in water (specifically, plankton, etc.) (that is, the Doppler frequency corresponding to the relative speed), the relative speed of the ship with respect to water (hereinafter, also referred to as the speed relative to water or ship speed) is calculated (see Patent Document 1). In this case, when the frequency of the transmitted sound wave is f, the depression angle of the sound wave transmission direction is θ, the speed of sound in water is C, and the Doppler frequency of the reflected wave is Δf, the ship speed V is obtained by the following formula 1. (Equation 1) V = C·Δf / (2f·cosθ)

[0003] There is a method called pair beam in the acoustic ship speedometer. The acoustic ship speedometer of the pair beam method transmits sound waves at the same depression angle θ in the front and rear of the ship's traveling direction (for example, the bow direction and the stern direction), calculates the ship speed from each of a pair of Doppler frequencies obtained from the reflected waves of the respective sound waves, and calculates the average value of the pair of calculated ship speeds to obtain the true ship speed (this method is also called beam cancellation). According to this pair beam type acoustic ship speedometer, even when fluctuations such as pitching occur in a ship during navigation and the ship tilts in the front and rear directions and the depression angle θ of the sound wave changes, the influence of the fluctuations can be canceled and an accurate ship speed can be measured.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[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: an instantaneous ship speed candidate calculation means that calculates a plurality of instantaneous ship speed candidates from reflected sound waves transmitted into the water from a plurality of channels and ranks the plurality of instantaneous ship speed candidates in descending order of likelihood; an instantaneous ship speed candidate determination means that determines whether the value of the instantaneous ship speed candidate is a normal value, starting with the highest ranked instantaneous ship speed candidate, 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 speed meter described in claim 1, the instantaneous ship speed candidate determination means determines that an instantaneous ship speed candidate in which the acceleration related to the instantaneous ship speed candidate is within a predetermined range, or an instantaneous ship speed candidate in which the value of the instantaneous ship speed candidate is within a predetermined range based on past ship speed values, is a normal value.

[0009] The invention described in claim 3 is characterized in that, in the ship speed meter described in claim 2, the instantaneous ship speed candidate determination means stores the instantaneous ship speed value in a buffer for a predetermined period of time, and the ship speed value calculation means calculates the ship speed value using the instantaneous ship speed value stored in the buffer.

[0010] The invention described in claim 4 is characterized in that, in the ship speed meter described in claim 3, a predetermined number of the calculated ship speed values ​​are stored in a second buffer, and the acceleration or past ship speed values ​​used as a reference for the predetermined range are calculated using the ship speed values ​​stored in the second buffer.

[0011] The invention described in claim 5 is characterized in that, in the speedometer described in claim 3 or 4, the acceleration used as a reference within a predetermined range or the past speed value is calculated only when the instantaneous speed stored in the buffer is updated.

[0012] The invention described in claim 6 is characterized in that, in the speedometer described in claim 3 or 4, 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.

[0013] The invention described in claim 7 is characterized in that it includes frequency determination means for obtaining a plurality of instantaneous Doppler frequencies for each of the plurality of channels from the reflected sound waves transmitted from the plurality of channels toward the water, and ranking the plurality of instantaneous Doppler frequencies for each of the plurality of channels in order of plausibility, and the instantaneous ship speed candidate calculation means calculates a plurality of instantaneous ship speed candidates based on each of a plurality of pairs of instantaneous Doppler frequencies that combine the instantaneous Doppler frequencies of different channels, and ranks the plurality of instantaneous ship speed candidates based on the plausibility ranking of the instantaneous Doppler frequencies that formed the basis of the calculation.

[0014] The invention described in claim 8 is a ship speed measurement method characterized by calculating a plurality of instantaneous ship speed candidates from reflected sound waves transmitted into the water from a plurality of channels, ranking the plurality of instantaneous ship speed candidates in descending order of likelihood, determining whether the values ​​of the instantaneous ship speed candidates are normal values ​​in order from the highest ranked instantaneous ship speed candidate, adopting the value of the instantaneous ship speed candidate that is first determined to be normal as the instantaneous ship speed, and calculating a ship speed value based on the instantaneous ship speed value. [Effects of the Invention]

[0015] According to the inventions described in claims 1 and 8, a plurality of instantaneous ship speed candidates are calculated, and the instantaneous ship speed candidate that is determined to be the most plausible and normal value among the plurality of instantaneous ship speed candidates is adopted as the regular 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 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.

[0016] Furthermore, according to the invention described in claim 2, since acceleration or past ship speed values ​​are used as the determination criterion, the trend of ship speed can be used as the determination criterion, making it possible to perform a more natural calculation of ship speed values.

[0017] Furthermore, according to the invention described in claim 3, since the ship speed value is calculated using the instantaneous ship speed values ​​for a predetermined period stored in the buffer, it is possible to obtain a highly accurate ship speed even if there is a temporary change in the instantaneous ship speed due to the rocking of the ship or the like.

[0018] Furthermore, according to the invention described in claim 4, the acceleration used as the criterion for determining a normal value or the past ship speed value is calculated based on the ship speed value calculated using a normal (in other words, within the acceptable range) instantaneous ship speed value, making it possible to determine an accurate ship speed.

[0019] Furthermore, according to the invention described in claim 5, the acceleration or past ship speed values ​​used as a reference within a predetermined range are calculated only when the instantaneous ship speed stored in the buffer is updated, making it possible to calculate ship speed values ​​accurately and stably according to the ship's navigation conditions.

[0020] Further, according to the invention described in claim 6, when a predetermined condition is satisfied in a situation where the instantaneous ship speed stored in the buffer has not been updated, the condition defining the predetermined range is changed. For example, when an event where the instantaneous ship speed candidate is not determined to be a normal value continues, the condition defining the predetermined range can be changed to calculate the acceleration, and it becomes possible to accurately and stably calculate the ship speed value according to the navigation situation of the ship.

[0021] Furthermore, according to the invention described in claim 7, a plurality of instantaneous Doppler frequencies are acquired for each of a plurality of channels, the plurality of instantaneous Doppler frequencies for each of the plurality of channels are ranked in descending order of plausibility, and a plurality of instantaneous ship speed candidates are ranked based on the ranking. Therefore, it is possible to exclude the instantaneous ship speed candidates based on the interference wave frequency and obtain a highly accurate ship speed.

Brief Description of the Drawings

[0022] [Figure 1] It is a functional block diagram showing a schematic configuration of a ship speed meter according to an embodiment of this invention. [Figure 2] It is a flowchart showing the processing procedure in the ship speed meter of FIG. 1 and outlining the processing procedure of the ship speed measurement method according to an embodiment of this invention. [Figure 3] It is a flowchart showing an outline of the processing procedure of "Calculation of Instantaneous Ship Speed" in FIG. 2. [Figure 4] It is a functional block diagram showing an outline of a process of calculating a plurality of instantaneous ship speed candidates from a plurality of instantaneous Doppler frequencies and determining whether they are normal values. [Figure 5] It is a diagram for explaining the reference acceleration calculated in the ship speed meter of FIG. 1.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, this invention will be described based on the illustrated embodiments.

[0024] 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.

[0025] 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 ship speed calculation unit 6, an interface unit 7, and a display unit 8.

[0026] The ship speed meter 1 according to this embodiment acquires multiple instantaneous Doppler frequencies for each channel 4 and 5 from the reflected sound waves transmitted into the water by the first channel 4 and the second channel 5. The ship speed meter 1 also uses a first frequency determination unit (frequency determination means) 43 and a second frequency determination unit (frequency determination means) 53 to determine the plausibility of the multiple instantaneous Doppler frequency values ​​for each channel 4 and 5, and ranks the multiple instantaneous Doppler frequencies in descending order of plausibility.

[0027] The speedometer 1 uses the instantaneous speed candidate calculation unit (instantaneous speed candidate calculation means) 61 of the speed calculation unit 6 to combine instantaneous Doppler frequencies of different channels to form multiple pairs of instantaneous Doppler frequencies, and calculates multiple instantaneous speed candidates based on each of the multiple pairs of instantaneous Doppler frequencies.

[0028] The speedometer 1, using the instantaneous speed candidate determination unit (instantaneous speed candidate determination means) 62 of the speed calculation unit 6, ranks a plurality of instantaneous speed candidates based on the plausibility ranking of the instantaneous Doppler frequencies on which the calculation was based. Starting with the instantaneous speed candidates with the highest rank, it determines whether the value of the instantaneous speed candidate is a normal value, and adopts the value of the instantaneous speed candidate that is first determined to be a normal value as the instantaneous speed (step S1). The speedometer 1, using the speed value calculation unit (speed value calculation means) 63 of the speed calculation unit 6, calculates the ship speed value based on the instantaneous speed value adopted by the instantaneous speed candidate determination unit 62 (step S3).

[0029] Furthermore, the speedometer 1 uses an instantaneous speed candidate determination unit 62 to determine that instantaneous speed candidates whose acceleration is within a predetermined range are normal values. The instantaneous speed candidate determination unit 62 also stores the adopted instantaneous speed value in an instantaneous speed buffer (buffer) 31 for a predetermined period of time (step S2). The speedometer 1 uses a speed value calculation unit 63 to calculate the ship speed value using the instantaneous speed value stored in the instantaneous speed buffer 31 (step S3).

[0030] 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 65 of the ship speed calculation unit 6 calculates the reference acceleration for the predetermined range using the ship speed values ​​stored in the ship speed value buffer 32 (step S8). Also, the speedometer 1 causes the reference acceleration calculation unit 65 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 64 of the ship speed calculation unit 6 (YES in step S5) (steps S7, S8).

[0031] 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).

[0032] 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.

[0033] 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.

[0034] As described above, the ship speedometer 1 is a pair-beam acoustic ship speedometer and includes multiple channels, for example, a first channel 4 and a second channel 5, that transmit sound waves into the water and receive the reflected waves. The first channel 4 and the second channel 5 each acquire multiple instantaneous Doppler frequencies, determine the plausibility of the acquired values ​​of the multiple instantaneous Doppler frequencies, and rank the multiple instantaneous Doppler frequencies in descending order of plausibility (step S1a).

[0035] The first channel 4 comprises a first sensor 41, a first measurement unit 42, and a first frequency determination unit 43. 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 at a predetermined frequency at regular time intervals toward the water in the direction of the bow, 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] When the first measurement unit 42 acquires a received signal from the first sensor 41, it detects multiple data points, for example two, with high signal levels (referred to as "reflected wave frequencies") 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) provided in the first measurement unit 42.

[0041] The first measurement unit 42 then outputs two sets of data for each measurement time interval Δt, consisting of the elapsed time tick [seconds] and the reflected wave frequency [Hz].

[0042] 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.

[0043] The first frequency determination unit 43 calculates two instantaneous Doppler frequencies [Hz] based on the difference between a known frequency of the sound wave emitted from the first sensor 41 (referred to as the "emission frequency") and a combination of two elapsed time ticks [seconds] and reflected wave frequencies [Hz].

[0044] The first frequency determination unit 43 determines the plausibility of the two instantaneous Doppler frequencies [Hz] 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 order of plausibility is first instantaneous Doppler frequency [Hz] > second instantaneous Doppler frequency [Hz].

[0045] 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].

[0046] 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], that is, 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_tick" and "C1_Δf2_tick".

[0047] The second channel 5 includes a second sensor 51, a second measurement unit 52, and a second frequency determination unit 53. The second sensor 51, second measurement unit 52, and second frequency determination unit 53 are the same as those of the first sensor 41, first measurement unit 42, and first frequency determination unit 43, so a detailed explanation will be omitted. However, the second sensor 51 differs in that, for example, it emits pulsed sound waves of the same predetermined frequency as the first sensor 41 in the opposite direction to the first sensor 41, i.e., towards the water in the stern direction, and receives the reflected waves.

[0048] Specifically, the first channel 4 calculates the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] in the bow direction, while the second channel 5 calculates the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] in the stern direction (step S1b). In the second channel 5, the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] calculated and ranked using combination data associated with elapsed time ticks [seconds], i.e., the values ​​of the first instantaneous Doppler frequency [Hz] and the second instantaneous Doppler frequency [Hz] at the elapsed time ticks [seconds] in the second channel 5, are denoted as "C2_Δf1_tick" and "C2_Δf2_tick".

[0049] The ship speed calculation unit 6 has the function of calculating the ship speed relative to water using data acquired by the first channel 4 and the second channel 5, and includes an instantaneous ship speed candidate calculation unit 61, an instantaneous ship speed candidate determination unit 62, a ship speed value calculation unit 63, an update determination unit 64, and a reference acceleration calculation unit 65.

[0050] The instantaneous ship speed candidate calculation unit 61 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 and the second channel 5 (step S1).

[0051] The instantaneous ship speed candidate calculation unit 61 combines the first instantaneous Doppler frequency (C1_Δf1_tick) and the second instantaneous Doppler frequency (C1_Δf2_tick) output from the first channel 4 with the first instantaneous Doppler frequency (C2_Δf1_tick) and the second instantaneous Doppler frequency (C2_Δf2_tick) output from the second channel 5 across different channels to form multiple pairs of instantaneous Doppler frequencies. Based on each of these multiple pairs of instantaneous Doppler frequencies, it calculates multiple instantaneous ship speed candidates for each elapsed time tick.

[0052] As shown in Figure 4, the instantaneous ship speed candidate calculation unit 61 calculates an instantaneous ship speed candidate (hereinafter referred to as the first instantaneous ship speed candidate) based on the first instantaneous Doppler frequency (C1_Δf1_tick) of the first channel 4 and the first instantaneous Doppler frequency (C2_Δf1_tick) of the second channel 5 (step S1c).

[0053] Specifically, based on the following formula (2), the instantaneous ship speed vi1 is calculated from the first instantaneous Doppler frequency (C1_Δf1_tick) of the first channel 4, and similarly, based on the following formula (2), the instantaneous ship speed vi2 is calculated from the first instantaneous Doppler frequency (C2_Δf1_tick) of the second channel 5. Then, beam cancellation is performed to find the average of the calculated instantaneous ship speeds vi1 and vi2, "(vi1+vi2) / 2", and this average value is used as the candidate for the first instantaneous ship speed. This makes it possible to obtain an accurate instantaneous ship speed that eliminates the effects of the ship's forward and backward motion. In the following formula (2), f is the frequency of the transmitted sound wave, θ is the depression angle of the direction of sound wave transmission, C is the speed of sound in water, and Δf is the Doppler frequency of the reflected wave (difference between the transmission frequency and the reflected wave frequency: C1_Δf1_tick, C2_Δf1_tick). (Math 2) vi(vi1,vi2)=C·Δf / (2f·cosθ)

[0054] 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".

[0055] The instantaneous ship speed candidate calculation unit 61 calculates an instantaneous ship speed candidate (hereinafter referred to as the second instantaneous ship speed candidate) based on the first instantaneous Doppler frequency (C1_Δf1_tick) of the first channel 4 and the second instantaneous Doppler frequency (C2_Δf2_tick) of the second channel 5, using the same method as for the first instantaneous ship speed candidate (v1_tick) (step S1g). The value of this second instantaneous ship speed candidate is denoted as "v2_tick".

[0056] The instantaneous ship speed candidate calculation unit 61 calculates an instantaneous ship speed candidate (hereinafter referred to as the third instantaneous ship speed candidate) based on the second instantaneous Doppler frequency of the first channel 4 (C1_Δf2_tick) and the first instantaneous Doppler frequency of the second channel 5 (C2_Δf1_tick) using the same method as for the first instantaneous ship speed candidate (v1_tick) (step S1k). The value of this third instantaneous ship speed candidate is denoted as "v3_tick".

[0057] The instantaneous ship speed candidate calculation unit 61 calculates an instantaneous ship speed candidate (hereinafter referred to as the fourth instantaneous ship speed candidate) based on the second instantaneous Doppler frequency of the first channel 4 (C1_Δf2_tick) and the second instantaneous Doppler frequency of the second channel 5 (C2_Δf2_tick) using the same method as for the first instantaneous ship speed candidate (v1_tick) (step S1o). The value of this fourth instantaneous ship speed candidate is denoted as "v4_tick".

[0058] 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), calculated as described above, are already ranked based on the plausibility ranking of the instantaneous Doppler frequencies on which they were calculated. In other words, the first instantaneous ship speed candidate (v1_tick), calculated based on the first instantaneous Doppler frequency of the first channel 4 (C1_Δf1_tick) and the first instantaneous Doppler frequency of the second channel 5 (C2_Δf1_tick), which have a high plausibility ranking, is the most plausible. In contrast, the fourth instantaneous ship speed candidate (v4_tick), calculated based on the second instantaneous Doppler frequency of the first channel 4 (C1_Δf2_tick) and the second instantaneous Doppler frequency of the second channel 5 (C2_Δf2_tick), has the lowest plausibility ranking. As a result, the plausibility ranking of each instantaneous ship speed candidate is "first instantaneous ship speed candidate (v1_tick) > second instantaneous ship speed candidate (v2_tick) > third instantaneous ship speed candidate (v3_tick) > fourth instantaneous ship speed candidate (v4_tick)". Note that the ranking of the second instantaneous ship speed candidate (v2_tick) and the third instantaneous ship speed candidate (v3_tick) may be swapped.

[0059] The instantaneous speed candidate calculation unit 61 outputs the calculated 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) to the instantaneous speed candidate determination unit 62. However, there may be cases where the instantaneous speed candidate calculation unit 61 cannot calculate the first instantaneous speed candidate (v1_tick), second instantaneous speed candidate (v2_tick), third instantaneous speed candidate (v3_tick), or fourth instantaneous speed candidate (v4_tick) due to reasons such as the inability to acquire instantaneous Doppler frequencies in the first channel 4 and second channel 5. In this case, the instantaneous speed candidates that could not be calculated are not output to the instantaneous speed candidate determination unit 62. For example, if the second instantaneous Doppler frequency (C2_Δf2_tick) cannot be obtained from the second channel 5, the second instantaneous ship speed candidate (v2_tick) and the fourth instantaneous ship speed candidate (v4_tick) cannot be calculated and therefore will not be output. Although it was explained that if the instantaneous Doppler frequency cannot be obtained, the instantaneous ship speed candidate calculated based on that unobtained instantaneous Doppler frequency will not be output, 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 cannot be calculated, the parameter for the averaging calculation may be set to "1" to calculate "vi1 / 1", and the result of that calculation may be output as the first instantaneous ship speed candidate (v1_tick).

[0060] The instantaneous ship speed candidate determination unit 62 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) are normal values ​​if they can be calculated (YES in steps S1d, S1h, S1l, and S1p). (Steps S1e, S1i, S1m, and S1q)

[0061] 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.

[0062] 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.

[0063] The calculation time interval I can be set to a duration within the range of, for example, 0.5 to 5 seconds.

[0064] Specifically, the instantaneous ship speed candidate determination unit 62 receives inputs of the ship speed value V_T at elapsed time T output from the ship speed value calculation unit 63 and the reference acceleration ar_T for elapsed time T output from the reference acceleration calculation unit 65 (the calculation of the ship speed value V and reference acceleration ar will be described later), and also receives the first instantaneous ship speed candidate (v1_tick) and the second instantaneous ship speed candidate from elapsed time "T+Δt" to "T+I" output from the instantaneous ship speed candidate calculation unit 61. The system receives inputs for the supplement (v2_tick), the third instantaneous speed candidate (v3_tick), and the fourth instantaneous speed candidate (v4_tick), and determines whether the values ​​of the first instantaneous speed candidate (v1_tick), the second instantaneous speed candidate (v2_tick), the third instantaneous speed candidate (v3_tick), and the fourth instantaneous speed candidate (v4_tick) are normal values ​​based on the speed value V_T and the reference acceleration ar_T (steps S1e, S1i, S1m, and S1q).

[0065] The following section explains how to determine the normal value of the first instantaneous speed candidate (v1_tick). The normal value determination for the second instantaneous speed candidate (v2_tick), the third instantaneous speed candidate (v3_tick), and the fourth instantaneous speed candidate (v4_tick) is the same as for the first instantaneous speed candidate (v1_tick), so a detailed explanation is omitted.

[0066] 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 62 is denoted as "v1_T+nΔt". Here, n=1,2,3,···,k, and in this embodiment, Δt×k=I.

[0067] Regarding the processing of step S1e, 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.

[0068] 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.

[0069] Furthermore, the instantaneous ship speed candidate determination unit 62 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).

[0070] The instantaneous ship speed candidate determination unit 62 determines whether the following equation (3) holds true. (Math 3) ar_T-alt≦(|v1_T+nΔt-V_T|) / (Δt×n)≦ar_T+aut

[0071] 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)

[0072] Then, if equation 3 (or equation 4) above holds true (YES in step S1e), the instantaneous ship speed candidate determination unit 62 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 S1f).

[0073] On the other hand, if equation 3 (or equation 4) above does not hold true (NO in step 1e), the instantaneous ship speed candidate determination unit 62 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.

[0074] The instantaneous ship speed candidate determination unit 62 performs the same determination as the normal value determination for the first instantaneous ship speed candidate described above for the second instantaneous ship speed candidate, the third instantaneous ship speed candidate, and the fourth instantaneous ship speed candidate (steps S1i, S1m, and S1q). If it is determined to be a normal value (YES in steps S1i, S1m, and S1q), it assigns a normal value flag (steps S1j, S1n, and S1r), and if it is determined not to be a normal value (NO in steps S1i, S1m, and S1q), it does not assign a normal value flag.

[0075] Next, the instantaneous speed candidate determination unit 62 checks (determines) whether the normal value flag is assigned to the first instantaneous speed candidate (v1_tick), the second instantaneous speed candidate (v2_tick), the third instantaneous speed candidate (v3_tick), and the fourth instantaneous speed candidate (v4_tick) in order of likelihood (step S1s). If an instantaneous speed candidate with the normal value flag is found (YES in step S1t), that instantaneous speed candidate is adopted as the normal instantaneous speed (step S1u). Here, the value of the normal instantaneous speed at the elapsed time tick [seconds] is denoted as "v_tick".

[0076] For example, if the first instantaneous speed candidate (v1_tick) is flagged as normal, then the first instantaneous speed candidate (v1_tick) is adopted as the valid instantaneous speed (v_tick). Also, if the first and second instantaneous speed candidates (v1_tick) and (v2_tick) are not flagged as normal, but the third instantaneous speed candidate (v3_tick) is flagged as normal, then the third instantaneous speed candidate (v3_tick) is adopted as the valid instantaneous speed (v_tick) without checking the fourth instantaneous speed candidate (v4_tick). If there is only one instantaneous speed candidate to check, that instantaneous speed candidate is adopted as the valid instantaneous speed (v_tick).

[0077] Furthermore, if the instantaneous speed candidate determination unit 62 does not find a normal value flag among the instantaneous speed candidates with the lowest likelihood ranking in step S1t (YES in step S1v), it does not adopt the correct instantaneous speed and returns to steps S1a and S1b.

[0078] The instantaneous speed candidate determination unit 62 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).

[0079] 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.

[0080] The ship speed calculation unit 63 calculates the ship speed value using the instantaneous ship speed value stored in the instantaneous ship speed buffer 31 (step S3).

[0081] The ship speed calculation unit 63 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 63 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 63 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] The ship speed calculation unit 63 outputs the ship speed value V data calculated for each calculation time interval I via the interface unit 7 (step S4).

[0086] The interface unit 7 has the function of providing an input / output interface to the ship speed calculation unit 6, and for example, it receives input of ship speed value V data calculated by the ship speed value calculation unit 63 and outputs the ship speed value V on the display unit 8.

[0087] The display unit 8 has the function of displaying various information, including the ship speed value V output from the interface unit 7, and is configured as a mechanism that includes, for example, a liquid crystal display.

[0088] The update determination unit 64 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).

[0089] The update determination unit 64 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.

[0090] If the instantaneous ship speed buffer 31 has not been updated (NO in step S5), the update determination unit 64 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.

[0091] On the other hand, if the instantaneous ship speed buffer 31 has been updated (YES in step S5), the update determination unit 64 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).

[0092] 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).

[0093] 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.

[0094] The reference acceleration calculation unit 65 calculates the reference acceleration ar using the ship speed value stored in the ship speed value buffer 32 (step S8).

[0095] The reference acceleration calculation unit 65 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 62.

[0096] The reference acceleration calculation unit 65 calculates the acceleration using the combined data of elapsed time and ship speed V stored in the ship speed buffer 32 at the time after the ship speed value V_T+I has been calculated, for example, and sets this as the reference acceleration ar_T+I for the elapsed time T+I.

[0097] 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.

[0098] 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.

[0099] The number of data points stored in the ship speed buffer 32, which are combinations of elapsed time and ship speed value V, can be set to a value within a range of, for example, 2 to 4.

[0100] 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.

[0101] 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 7 or until a predetermined termination event occurs (for example, the ship stops), continuing to measure and output the ship speed value V.

[0102] According to the ship speed meter 1 and ship speed measurement method of the embodiment, a first instantaneous ship speed candidate (v1_tick), a second instantaneous ship speed candidate (v2_tick), a third instantaneous ship speed candidate (v3_tick), and a fourth instantaneous ship speed candidate (v4_tick) are calculated as multiple instantaneous ship speed candidates. From among these multiple instantaneous ship speed candidates, the instantaneous ship speed candidate that is judged to be the most plausible and normal value is adopted as the regular instantaneous ship speed (v_tick), and the ship speed value V is calculated based on this instantaneous ship speed (v_tick). Therefore, when calculating the ship speed value V in a pair-beam type ship speed meter, instantaneous ship speed candidates based on interference wave frequencies can be excluded, and it becomes possible to obtain a ship speed value V with high accuracy.

[0103] Furthermore, according to the ship speed meter 1 and ship speed measurement method of the embodiment, acceleration is used as the criterion for determination, so 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.

[0104] Furthermore, according to the ship speed meter 1 and ship speed measurement method of the embodiment, 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.

[0105] Furthermore, according to the ship speed meter 1 and ship speed measurement method of the embodiment, 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 there is a temporary change in the instantaneous ship speed due to the rocking of the ship, it is possible to obtain a highly accurate ship speed value V.

[0106] Furthermore, according to the ship speed meter 1 and ship speed measurement method of the embodiment, 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.

[0107] Furthermore, according to the ship speed meter 1 and ship speed measurement method of the embodiment, multiple instantaneous Doppler frequencies are acquired for each of the first channel 4 and the second channel 5, and these multiple instantaneous Doppler frequencies are ranked in descending order of likelihood for each of the first channel 4 and the second channel 5. Based on this ranking, multiple instantaneous ship speed candidates are ranked, thereby eliminating instantaneous ship speed candidates based on interference wave frequencies, and enabling the determination of a highly accurate ship speed.

[0108] Although embodiments of this invention have been described above, the specific configuration is not limited to the embodiments described above, and any design changes, etc., that do not depart from the spirit of this invention are also included.

[0109] For example, in the above embodiment, the first Doppler frequency and the second Doppler frequency are acquired for each of the first channel 4 in the bow direction and the second channel in the stern direction. However, it is also possible to acquire even more Doppler frequencies for even more channels, or to acquire multiple Doppler frequencies for each of the multiple channels in the width direction. In that case, an even larger number of instantaneous speed candidates may be calculated according to the number of Doppler frequencies acquired, and the normal instantaneous speed may be determined from these instantaneous speed candidates.

[0110] Furthermore, although the above-described embodiment uses the speedometer 1 to measure the ship's speed relative to water, this invention can also be applied to measuring the ship's speed relative to land (i.e., the ship's speed relative to the ground).

[0111] Furthermore, in the above embodiment, if the 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) cannot be calculated (NO in steps S1d, S1h, S1l, and S1p), or if they are not determined to be normal values ​​(NO in steps S1e, S1i, S1m, and S1q), the instantaneous speed buffer 31 will not be updated (NO in step S5). Therefore, as long as the instantaneous speed buffer 31 is not updated, the 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].

[0112] In this case, for example, 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 if 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 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.

[0113] Furthermore, in the above embodiment, 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.

[0114] Furthermore, in the above embodiment, in the normal value determination (steps S1e, S1i, S1m, and S1q) of 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), 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] Furthermore, the process of calculating the reference ship speed value from multiple ship speed values ​​stored in the ship speed value buffer 32 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 the ship speed value accurately and stably according to the ship's navigation conditions.

[0119] Furthermore, if the 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) 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 a predetermined range based on the reference speed value may be set to 0 [kn], or the upper limit of a 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 a predetermined range based on the reference speed value may be removed (i.e., no lower limit), or the upper limit of a predetermined range based on the reference speed value may be set to 0 [kn].

[0120] 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]

[0121] 1 Speedometer 2 Control Unit 3 Storage section 31 Instantaneous ship speed buffer (buffer) 32. Ship speed value buffer (second buffer) 4. Channel 1 43 First frequency determination unit (frequency determination means) 5. Channel 2 53 Second frequency determination unit (frequency determination means) 6 Ship speed calculation section 61 Instantaneous ship speed candidate calculation unit (instantaneous ship speed candidate calculation means) 62 Instantaneous ship speed candidate determination unit (instantaneous ship speed candidate determination means) 63 Ship Speed ​​Value Calculation Unit 64 Update determination section 65 Reference acceleration calculation section 7 Interface section 8 Display

Claims

1. An instantaneous ship speed candidate calculation means calculates multiple instantaneous ship speed candidates from reflected sound waves transmitted into the water from multiple channels, and ranks the multiple instantaneous ship speed candidates in order of plausibility, An instantaneous ship speed candidate determination means determines whether the value of the instantaneous ship speed candidate is a normal value, starting with the highest-ranked instantaneous ship speed candidate, and adopts the value of the instantaneous ship speed candidate that is first determined to be a normal value 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 instantaneous ship speed candidate determination means is Instantaneous ship speed candidates whose acceleration is within a predetermined range, or instantaneous ship speed candidates whose value is within a predetermined range based on past ship speed values, are determined to be normal values. The ship speedometer according to feature 1.

3. The instantaneous ship speed candidate determination means stores the instantaneous ship speed value in a buffer for a predetermined period of time, The ship speed value calculation means calculates the ship speed value using the instantaneous ship speed value stored in the buffer. The ship speedometer according to feature 2.

4. The calculated ship speed values ​​are stored in a second buffer in a predetermined number of values, and the acceleration or past ship speed values ​​used as a reference for the predetermined range are calculated using the ship speed values ​​stored in the second buffer. The ship speedometer according to feature 3.

5. Only when the instantaneous ship speed stored in the buffer is updated, the acceleration or past ship speed value used as a reference within the predetermined range is calculated. The ship speedometer according to feature 3 or 4.

6. 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 3 or 4.

7. The system includes a frequency determination means that obtains multiple instantaneous Doppler frequencies for each of the multiple channels from the reflected sound waves transmitted from the multiple channels toward the water, and ranks the multiple instantaneous Doppler frequencies for each of the multiple channels in order of likelihood, The instantaneous ship speed candidate calculation means calculates a plurality of instantaneous ship speed candidates based on each of a plurality of pairs of instantaneous Doppler frequencies formed by combining the instantaneous Doppler frequencies of different channels, and ranks the plurality of instantaneous ship speed candidates based on the ranking of the plausibility of the instantaneous Doppler frequencies on which the calculation was based. A ship speedometer according to feature 1 or 2.

8. Multiple instantaneous ship speed candidates are calculated from the reflected sound waves transmitted into the water from multiple channels, and these multiple instantaneous ship speed candidates are ranked in order of plausibility. Starting with the highest-ranking instantaneous ship speed candidates, the system determines whether the value of each instantaneous ship speed candidate is a normal value, and the first instantaneous ship speed candidate determined to be a normal value 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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