Ship speed measuring device and ship speed measuring method

Abstract

To provide a ship speed measuring device and a ship speed measuring method capable of more accurately measuring the counter water ship speed.SOLUTION: A ship speed measuring device 1 includes: a transducer 20 for transmitting an ultrasonic wave into water and receiving a reflected wave of the ultrasonic wave; and a signal processing circuit 110 for calculating the counter water ship speed of a ship in which the transducer 20 is installed on the basis of a reception signal outputted from the transducer 20. The signal processing circuit 110 specifies, on the basis of the reception signal, the target depth at which the vertical counter water vessel speed is substantially null, and acquires the counter water vessel speed in the traveling direction with respect to the target depth as the counter water vessel speed of the ship.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a boat speed measuring device and a boat speed measuring method that transmits a sound wave into water and measures the boat speed based on the reflected wave. [Background technology]

[0002] Conventionally, ship speed measuring devices are known that measure the speed of a ship moving on water. In this type of ship speed measuring device, for example, ultrasonic waves are transmitted in the direction of the ship's movement at a predetermined depression angle, and the ship speed is calculated based on the frequency of the reflected waves. The frequency of the reflected waves changes from the frequency at the time of transmission due to the Doppler effect, which depends on the ship's speed. Therefore, the ship's speed in water (ship speed through water) can be calculated from this change in frequency.

[0003] One method for more accurately measuring ship speed through water is to calculate the rate of change of current velocity with depth. In this method, current velocities at multiple depths are calculated based on the difference between the frequency of ultrasonic waves transmitted and the frequency of the waves reflected from the water. The rate of change of these current velocities is then calculated. The current velocity at the depth where this rate of change is equal to or less than a predetermined threshold is then calculated as the ship's speed through water.

[0004] The following Patent Document 1 describes a boat speed measurement method similar to the above. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5275486 Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, currents occur in water due to the influence of wakes and other disturbances as the ship moves forward. However, it is preferable to measure the ship's speed through water as the speed relative to a layer of water that is not affected by such disturbances. This allows for accurate calculation of the ship's fuel consumption and other factors using the ship's speed through water.

[0007] In the above measurement method, the current speed at a depth where the rate of change of current speed between depths is equal to or less than a predetermined threshold is calculated as the water speed. However, this measurement method does not determine whether this depth is affected by external disturbances such as wakes. Therefore, it is possible that this measurement method may not be able to accurately measure the ship's water speed.

[0008] In view of the above problem, an object of the present invention is to provide a ship speed measuring device and a ship speed measuring method that can measure the ship speed through water more accurately. [Means for solving the problem]

[0009] A first aspect of the present invention relates to a boat speed measuring device. The boat speed measuring device according to this aspect comprises a transducer that transmits ultrasonic waves into water and receives the reflected waves of the ultrasonic waves, and a signal processing circuit that calculates the boat speed through water of the boat on which the transducer is installed based on the received signal output from the transducer. The signal processing circuit calculates the boat speed through water based on the received signal. Calculating the vertical ship speed through water and the ship speed through water in the direction of travel for each depth, Identifying a target depth where the vertical ship speed relative to the water is substantially zero, and The aforementioned The ship's speed through water in the direction of travel is acquired as the ship's speed through water.

[0010] According to the ship speed measurement device of this aspect, the ship's speed through water in the direction of travel is obtained for a target depth where the ship's speed through water in the vertical direction is substantially zero. If a water layer is not affected by external disturbances such as wakes, the ship's speed through water in the vertical direction relative to that layer should be zero. Therefore, by obtaining the ship's speed through water in the direction of travel for a target depth where the ship's speed through water in the vertical direction is substantially zero as described above, the ship's speed through water in the water layer that is not affected by external disturbances such as wakes can be obtained. Therefore, with the above configuration, the ship's speed through water can be measured more accurately.

[0011] In the ship speed measuring device of this aspect, the signal processing circuit can be configured to calculate the average value of the ship speed relative to the water in the vertical direction for each depth over a predetermined period of time, and to identify the depth at which the calculated average value is essentially zero as the target depth.

[0012] With this configuration, even if temporary updrafts or up-and-down movement of the ship due to waves or swells occur, these are averaged out, preventing large fluctuations in the average value due to these factors. Therefore, by obtaining the ship's speed through water for a depth where this average value is essentially zero, it is possible to properly obtain the ship's speed through water for a layer of water that is not affected by disturbances such as wakes.

[0013] In this case, the signal processing circuitry may be configured to identify the depth of interest from a range around a minimum depth at which the average value is substantially zero.

[0014] As the depth increases, the S / N ratio of the received signal decreases, which reduces the accuracy of calculating the water depth in the vertical and forward directions. In contrast, with the above configuration, the target depth is determined from the range near the minimum depth where the average value is essentially zero, so the target depth is determined within the smallest possible depth range. Therefore, the water depth in the vertical and forward directions can be calculated accurately from the received signal, which maintains a high S / N ratio.

[0015] In this case, the signal processing circuitry may be configured to identify as the depth of interest the smallest depth at which the average value is substantially zero.

[0016] With this configuration, the target depth is determined to be the minimum depth at which the average value is substantially zero, and the S / N ratio of the received signal at the target depth is maintained at the highest within the range where the average value is substantially zero, thereby enabling more accurate calculation of the water depth in the vertical and forward directions.

[0017] In the ship speed measuring device according to this aspect, the signal processing circuit may be configured to obtain the average value of the ship's speed through water in the direction of travel relative to the target depth over a predetermined period of time as the ship's speed through water.

[0018] With this configuration, the average speed of the ship through water in the ship's direction of travel over a predetermined period of time is acquired as the ship's speed through water, so that the ship's speed through water can be stably acquired even when a disturbance such as a wake from another ship occurs temporarily.

[0019] In the ship speed measuring device of this aspect, the transmitter / receiver may be equipped with a plurality of ultrasonic vibrators facing in different directions, and the signal processing circuit may be configured to determine the target depth and obtain the ship's speed through water based on the received signals output from each of the plurality of ultrasonic vibrators.

[0020] With this configuration, the forward and vertical ship speeds can be calculated from the received signals output from the multiple ultrasonic transducers. Therefore, for example, by averaging the ship speeds based on the received signals, it is possible to stably obtain the ship speed while suppressing the influence of the ship's pitching.

[0021] A second aspect of the present invention relates to a method for measuring ship speed. The method for measuring ship speed according to this aspect includes transmitting ultrasonic waves into water and receiving reflected waves of the ultrasonic waves, and calculating a speed based on the received signal of the reflected waves. Calculate the vertical ship speed through water and the ship speed through water in the direction of travel for each depth, and Identifying a target depth where the vertical ship speed relative to the water is substantially zero, and The aforementionedThe ship's speed through water in the direction of travel is acquired as the ship's speed through water.

[0022] According to the boat speed measuring method of this aspect, the same effects as those of the first aspect are achieved. [Effects of the Invention]

[0023] As described above, according to the present invention, it is possible to provide a ship speed measuring device and a ship speed measuring method that are capable of measuring the ship speed through water more accurately.

[0024] The effects and significance of the present invention will become more apparent from the following description of the embodiments, however, the embodiments shown below are merely examples of how the present invention can be implemented, and the present invention is not limited to the embodiments described below. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram schematically showing a state in which a boat speed measuring device according to an embodiment is used, as viewed from the side of a boat. [Figure 2] FIG. 2 is a diagram schematically illustrating a state in which the boat speed measuring device according to the embodiment is used, as viewed from above the boat. [Figure 3] FIG. 3 is a diagram showing the configuration of a circuit section of a boat speed measuring device according to an embodiment. [Figure 4] FIG. 4 is a graph showing the results of actual measurements of the ship's speed through water in the ship's forward direction, the ship's speed through water in the vertical direction, and the ship's speed through water in the horizontal direction for each depth, according to an embodiment. [Figure 5] FIG. 5 is a graph showing a relationship between depth and average value of vertical ship speed through water according to the embodiment. [Figure 6] FIG. 6 is a flowchart showing a process for measuring the ship's speed through water, which is executed by the signal processing circuit according to the embodiment. [Figure 7] FIG. 7 is a flowchart showing a process for measuring the vessel speed through water of a vessel executed by a signal processing circuit according to the first modification. [Figure 8] FIG. 8 is a flowchart showing a process for measuring the ship's speed through water, which is executed by the signal processing circuit, according to the second modification. [Figure 9] 9(a) and 9(b) are diagrams each showing a schematic diagram of the transmission state of a transmission beam as viewed from above the ship according to Modification Example 3. FIG. [Figure 10] FIG. 10 is a diagram schematically showing the state of transmission of a transmission beam as viewed from the side of the ship according to the third modification. [Figure 11] FIG. 11 is a flowchart showing a process for measuring the ship's speed through water, which is executed by the signal processing circuit, according to another modified example. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0027] FIG. 1 is a schematic diagram showing a state in which a boat speed measuring device according to an embodiment is used.

[0028] In Figure 1, the XY plane is a horizontal plane, and the positive direction of the Z axis is the downward vertical direction. The direction of travel of the ship S1 is the positive direction of the Y axis. For convenience, only the transducer 20 of the ship speed measuring device is shown in Figure 1.

[0029] The transducer 20 is installed on the bottom of the ship S1. In the example shown in FIG. 1, the transducer 20 is installed on the bottom of the ship S1 slightly rearward from the center. Transmission beams B1, B2, and B3 are transmitted from the transducer 20 in different directions. The transmission beams B1, B2, and B3 are ultrasonic waves. The transmission beams B1, B2, and B3 spread in a roughly conical shape within a narrow range. The depression angles φ of the transmission beams B1, B2, and B3 with respect to the horizontal plane are the same. The depression angle φ is, for example, approximately 60 degrees. However, the depression angle φ is not limited to 60 degrees. The depression angles φ of the transmission beams B1, B2, and B3 may be different from each other.

[0030] FIG. 2 is a view of the vessel S1 in use as shown in FIG. 1, viewed from above.

[0031] As shown in FIG. 2, transmit beam B1 is transmitted toward the bow in a plan view. Transmit beams B2 and B3 are transmitted toward the stern in a plan view. In a plan view, the horizontal angle θ between adjacent transmit beams is uniform. In other words, here, the horizontal angle θ between adjacent transmit beams is 120 degrees. However, the horizontal angle θ between adjacent transmit beams does not have to be the same.

[0032] Returning to Fig. 1, the transmission beams B1, B2, and B3 sent from the transducer 20 are reflected by floating objects in the water such as plankton, and the reflected waves are received by the transducer 20. A received signal for each reflected wave is output from the transducer 20. These received signals are processed by a control device 10 installed in the wheelhouse or the like of the ship S1, and the speed of the ship S1 through the water is calculated.

[0033] FIG. 3 is a diagram showing the configuration of the circuit section of the boat speed measuring device 1. As shown in FIG.

[0034] The ship speed measuring device 1 includes a control device 10 and a transducer 20. The transducer 20 includes three ultrasonic transducers 201, 202, and 203. These three ultrasonic transducers 201, 202, and 203 are oriented in different directions. As a result, transmission beams B1, B2, and B3 shown in FIG. 1 are transmitted from the ultrasonic transducers 201, 202, and 203, respectively, and the reflected waves are received by the ultrasonic transducers 201, 202, and 203.

[0035] The control device 10 includes a signal processing circuit 110, a transmission signal generating circuit 120, first to third transmission circuits 131 to 133, first to third switching circuits 141 to 143, first to third reception circuits 151 to 153, A / D conversion circuits 161 to 163, and first to third tailing signal removal circuits 171 to 173.

[0036] The signal processing circuit 110 includes a calculation processing circuit such as a CPU and a memory, and executes predetermined functions according to programs stored in the memory. The signal processing circuit 110 may also include a calculation processing circuit such as an FPGA. Under control of the signal processing circuit 110, the transmission signal generation circuit 120 generates transmission signals for driving the ultrasonic transducers 201, 202, and 203, respectively, and outputs the transmission signals to the first to third transmission circuits 131 to 133. Each transmission signal is a sine wave signal of a predetermined frequency.

[0037] The first to third transmission circuits 131 to 133 amplify the input transmission signals and output them to the first to third switching circuits 141 to 143, respectively. The first to third switching circuits 141 to 143 output the input transmission signals to the ultrasonic transducers 201 to 203, respectively. As a result, the ultrasonic transducers 201 to 203 transmit ultrasonic waves (transmission beams B1 to B3) of predetermined frequencies into the water, respectively. After that, when the ultrasonic transducers 201 to 203 receive reflected waves of these ultrasonic waves, they output reception signals based on these reflected waves to the first to third switching circuits 141 to 143.

[0038] The first to third switching circuits 141 to 143 output the reception signals input from the ultrasonic transducers 201 to 203 to the first to third reception circuits 151 to 153, respectively. The first to third reception circuits 151 to 153 amplify the input reception signals, extract reception signals of a predetermined band that includes the frequency band of the reflected waves, and output them to the A / D conversion circuits 161 to 163, respectively. The A / D conversion circuits 161 to 163 sample these input reception signals at a predetermined sampling period and convert them into digital signals.

[0039] The first to third trailing signal removal circuits 171 to 173 remove trailing signals from the received signals input from the A / D conversion circuits 161 to 163, respectively. Here, the trailing signal refers to noise superimposed on the received signal due to reverberation of the transmitted waves in the ultrasonic transducers 201 to 203. In other words, the trailing signal is an unnecessary signal that appears like ringing immediately after the ultrasonic waves are transmitted, due to factors such as reflection of the transmitted signal within the transducer 20 and the band-limited frequency characteristics of the ultrasonic transducers 201 to 203.

[0040] In this way, the trailing signal appears like a ringing immediately after the ultrasonic wave is transmitted, and therefore overlaps with the period during which the reflected ultrasonic wave is received, i.e., near the beginning of the period during which the received signal based on the reflected wave appears. The first to third trailing signal removal circuits 171 to 173 remove the trailing signal thus superimposed on the received signal from the received signal.

[0041] The first to third tailing signal removal circuits 171 to 173 include low-pass filters 171a to 173a and adders 171b to 173b, respectively. The low-pass filters 171a to 173a extract the frequency components of the tailing signals from the received signals, invert the polarity of the extracted frequency components, and input them to the adders 171b to 173b. The adders 171b to 173b add the frequency components input from the low-pass filters 171a to 173a to the received signals. This removes the frequency components from the received signals, thereby obtaining received signals from which the tailing signals have been removed. The received signals from which the tailing signals have been removed are output sequentially to the signal processing circuit 110 and stored in a memory within the signal processing circuit 110.

[0042] For more detailed configurations and operations of the first to third tailing signal removal circuits 171 to 173, the description in Japanese Patent No. 4828120 can be incorporated by reference.

[0043] The signal processing circuit 110 calculates the vessel speed through water of the vessel S1 for a plurality of depths based on the received signals input from the first to third tailing signal removal circuits 171 to 173. More specifically, for each of these three received signals, the signal processing circuit 110 calculates the vessel speed through water in the direction of travel of the vessel S1 and the vessel speed through water in the up-down direction (vertical direction) of the vessel S1, for each depth. The depth can be identified by the time of the received signal on the time axis (the time required from the transmission of the wave to that time).

[0044] These ship speeds through the water are calculated based on the Doppler effect from the frequency difference between the transmitted signal and the received signal at each depth.

[0045] For example, for the received signal input from the first trailing signal removal circuit 171, i.e., the received signal based on the transmitted beam B1 in Fig. 1, the ship speed through water in the direction of the transmitted beam B1 is calculated based on the Doppler effect from the frequency difference between the transmitted signal and the received signal at each depth. Then, from this ship speed through water, the ship speed through water at each depth in the traveling direction of the ship S1 and the ship speed through water at each depth in the vertical direction of the ship S1 are calculated based on the horizontal angle θ and the depression angle φ.

[0046] For the received signals based on the transmitted beams B2 and B3 in Figure 1, the ship speed through water at each depth in the direction of the transmitted beams B2 and B3 is calculated as described above, and from this ship speed through water, the ship speed through water at each depth in the direction of ship S1's travel and the ship speed through water at each depth in the vertical direction of ship S1 are calculated based on the horizontal angle θ and the depression angle φ.

[0047] Then, the signal processing circuit 110 averages the three ship speeds through water in the direction of travel based on the transmitted beams B1 to B3 for each depth to calculate the ship speed through water in the direction of travel for each depth, and averages the three ship speeds through water in the vertical direction based on the transmitted beams B1 to B3 for each depth to calculate the ship speed through water in the vertical direction for each depth.

[0048] In addition, the ship speed relative to the water in the left-right direction (X-axis direction) of ship S1, which will be described later, is also calculated, as described above, from the ship speed relative to the water at each depth in the direction of each transmitted beam based on the horizontal angle θ and depression angle φ, and then calculated by averaging these for each depth.

[0049] The signal processing circuit 110 determines the water speed of the ship S1 from the water speeds in the forward direction and vertical direction at each depth calculated in this way. More specifically, the signal processing circuit 110 identifies a target depth where the water speed in the vertical direction is substantially zero, and determines the water speed of the ship S1 in the forward direction for this target depth as the water speed of the ship.

[0050] In other words, if a water layer is not affected by disturbances such as wakes, the ship's vertical speed through water relative to that layer should be substantially zero. Therefore, as described above, by obtaining the ship's speed through water in the direction of travel for a target depth where the vertical speed through water is substantially zero, the ship's speed through water relative to a water layer that is not affected by disturbances such as wakes can be obtained. This allows the ship S1's speed through water in the direction of travel to be accurately measured.

[0051] The signal processing circuit 110 displays the measured ship speed through water in the traveling direction of the ship S1 on the display device 30. The display device 30 is installed, for example, in the wheelhouse of the ship S1.

[0052] Figure 4 is a graph showing the results of actual measurements of the ship's speed through water in the ship's direction of travel (hereinafter referred to as "Y ship speed"), the ship's speed through water in the ship's vertical direction (hereinafter referred to as "Z ship speed"), and the ship's speed through water in the ship's left-right direction (hereinafter referred to as "X ship speed") for each depth in the above configuration.

[0053] This graph shows the measurement results when the ship S1 was proceeding in a straight line. The graph also plots the average values ​​of the Y, Z, and X ship speeds calculated for each depth from the time of this measurement up to a predetermined time before. In this measurement, the predetermined time for averaging was set to 15 minutes.

[0054] Referring to the graph in Figure 4, as the depth increases, the Z ship speed gradually approaches 0, and the Y ship speed gradually converges to 17 kiloknots. Therefore, it can be inferred that as the depth increases, the effect of disturbances on the water layer decreases, and once the depth reaches a certain depth, the effect of disturbances is almost eliminated and the water layer becomes almost stationary. Furthermore, in the range where the Z ship speed is essentially 0, it can be inferred that the Y ship speed converges to 17 kiloknots, which is the natural ship speed through water in a water layer that is not affected by disturbances.

[0055] FIG. 5 is a graph showing a schematic relationship between depth and Z ship speed (average value).

[0056] In the graph of Figure 5, the depth range of 0 to 17 m reflects the graph of Figure 4, and the depth range of 17 m and above reflects a decreasing trend similar to the decreasing trend in the range of 5 to 17 m in the graph of Figure 4.

[0057] Here, whether or not the Z vessel speed is substantially zero can be determined by comparing the Z vessel speed with a threshold value Vth. This threshold value Vth may be set to a value close to zero. For example, the threshold value Vth may be set to approximately ±0.1 to ±0.3 relative to 0. If the Z vessel speed falls within the range of this threshold value Vth, the Z vessel speed is determined to be substantially zero. In the example of FIG. 5, the minimum depth D0 at which the Z vessel speed falls within the threshold value Vth is approximately 41.5 m. Therefore, in the range W0 above this depth D0, the Z vessel speed is substantially zero across the board.

[0058] Therefore, by selecting the Y vessel speed calculated for any depth included in this range W0 as the Y vessel speed of the vessel S1, the vessel speed relative to the water layer that is not affected by external disturbances can be obtained.

[0059] However, the greater the depth, the lower the S / N ratio of the received signal. Therefore, at depths within range W0 that are far removed from depth D0, the S / N ratio of the received signal decreases, making it difficult to accurately calculate the Y and Z ship speeds. Therefore, the depth range for calculating the Y and Z ship speeds is preferably set to range W1 near the minimum depth D0 where the Z ship speed is essentially zero, and more preferably to depth D0. Range W1 can be set, for example, from several meters to approximately 10 meters.

[0060] 4, the X vessel speed also converges to zero as the depth increases. Therefore, a method may be considered in which the Y vessel speed calculated for a depth included in the range where the X vessel speed is substantially zero is acquired as the vessel speed through water of the vessel S1.

[0061] However, the reason why the X vessel speed converges to zero in the graph of Figure 4 is because the vessel S1 is proceeding straight, and if the vessel S1 turns left or right or if this causes the vessel S1 to drift, the X vessel speed at each depth will deviate from 0. In this way, the X vessel speed at each depth can change dynamically depending on the progress of the vessel S1, so it can be estimated that it would be difficult to use the Y vessel speed calculated for a depth included in the range of depths where the X vessel speed is substantially zero as the vessel speed through water of the vessel S1.

[0062] FIG. 6 is a flowchart showing the process of measuring the speed of the ship S1 through water, which is executed by the signal processing circuit 110.

[0063] When ultrasonic waves (transmission beams B1-B3) are transmitted from the transducer 20, the signal processing circuit 110 calculates the Y and Z vessel speeds for each depth as described above based on the received signals input from the first to third trailing signal removal circuits 171-173, respectively, and stores the calculated Y and Z vessel speeds for each depth in memory (S101). Next, the signal processing circuit 110 sets the variable n to 1 (S102), and calculates the average value of the Z vessel speed at depth Dn over a predetermined period of time (S103).

[0064] Here, depth Dn increases by a predetermined distance (for example, 0.5 m) as variable n increases. The initial value of depth Dn (variable n = 1) does not necessarily have to be a value obtained by adding a predetermined distance (for example, 0.5 m) to zero, but may be a fixed value such as 3 m or 5 m. In step S103, the average Z ship speed is calculated by averaging the Z ship speeds for that depth Dn calculated over the period from the current measurement time to a predetermined time ago, as in the case of Figure 4.

[0065] Next, the signal processing circuit 110 determines whether the calculated average value of the Z vessel speed is substantially zero (S104). Here, as in the case of FIG. 5, it is determined whether the Z vessel speed is within the range from zero to the threshold value Vth. If the calculated average value of the Z vessel speed is not substantially zero (S104: NO), the signal processing circuit 110 adds 1 to the variable n (S107) and returns the process to step S103. This causes the process from step S103 onwards to be carried out for the next depth Dn. In this way, the process of steps S103 and S104 is repeatedly carried out while the depth Dn to be processed is changed in the increasing direction until the average value of the Z vessel speed becomes substantially zero.

[0066] Thereafter, when the average value of the Z vessel speed becomes substantially zero (S104: YES), the signal processing circuit 110 determines the Y vessel speed corresponding to the current depth Dn, among the Y vessel speeds for each depth stored in memory in step S101, as the vessel speed through water in the traveling direction of the vessel S1 (S105).Then, the signal processing circuit 110 determines whether or not the measurement of the vessel speed through water has been completed (S106), and if not completed (S106: NO), the process returns to step S101 and performs the same process on the next transmitted ultrasonic wave (transmission beams B1 to B3).

[0067] In this way, the signal processing circuit 110 repeatedly executes the processes of steps S101 to S105 and S107 each time it transmits ultrasonic waves (transmission beams B1 to B3), and acquires the vessel speed through water in the traveling direction of the vessel S1. The signal processing circuit 110 causes the display device 30 to display the vessel speed through water of the vessel S1 acquired at each measurement point as needed. Thereafter, when the operation of measuring the vessel speed through water is completed (S106: YES), the signal processing circuit 110 ends the process of FIG. 6.

[0068] In the processing of Figure 6, the depth Dn when the determination in step S104 is YES is the depth in the depth direction at which the Z vessel speed first falls within the range of the threshold value Vth, and corresponds to the depth D0 in Figure 5. In other words, in the processing of Figure 6, the smallest depth at which the average value of the Z vessel speed is substantially zero is identified as the target depth for calculating the vessel speed through water in the direction of travel of the vessel S1.

[0069] <Effects of the embodiment> According to this embodiment, the following effects can be achieved.

[0070] As shown in FIG. 6, for a depth Dn (target depth) where the vertical ship speed through water (Z ship speed) is substantially zero (S104: YES), the ship speed through water in the ship's direction of travel is acquired (S105). If a water layer is not affected by external disturbances such as wakes, the ship speed through water in the vertical direction relative to that layer should be zero. Therefore, by acquiring the ship speed through water in the ship's direction of travel for a depth Dn (target depth) where the vertical ship speed through water (Z ship speed) is substantially zero as described above, the ship speed through water for a water layer that is not affected by external disturbances such as wakes can be acquired. This allows for more accurate measurement of the ship speed through water.

[0071] As shown in Figure 6, the signal processing circuit 110 calculates the average value of the ship's vertical speed through water (ship's speed Z) for each depth over a predetermined time period (S103), and identifies the depth at which the calculated average value is substantially zero as the target depth (S104, S105). This averages out temporary updrafts and vertical movement of the ship S1 due to waves or swells, thereby preventing large fluctuations in the average value due to these factors. Therefore, by obtaining the ship's speed through water (ship's speed Y) for a depth at which this average value is substantially zero, it is possible to properly obtain the ship's speed through water for a layer of water that is not affected by disturbances such as wakes.

[0072] As shown in Figure 5, it is preferable for the signal processing circuit 110 to specify the target depth for obtaining the Y vessel speed from a range W1 near the minimum depth D0 where the average value of the Z vessel speed is substantially zero. This specifies the target depth within as small a range as possible, making it possible to accurately calculate the water depth in the vertical and forward directions (Z vessel speed, Y vessel speed) from received signals that maintain a high S / N ratio.

[0073] In the above embodiment, as shown in Figure 6, the signal processing circuit 110 specifies the minimum depth at which the average value of the Z boat speed is substantially zero as the target depth for obtaining the Y boat speed (S104, S105). This maintains the highest S / N ratio of the received signal at the target depth within the range W0 where the average value is substantially zero. This allows for more accurate calculation of the water depth in the vertical and forward directions (Z boat speed, Y boat speed).

[0074] As shown in Figures 1 to 3, the transducer 20 includes a plurality of ultrasonic transducers 201 to 203 oriented in different directions. The signal processing circuit 110 performs the processing shown in Figure 6 based on the received signals output from the ultrasonic transducers 201 to 203, to identify the target depth and acquire the vessel's speed through the water. With this configuration, the vessel speeds (Y vessel speed, Z vessel speed) can be calculated from the received signals output from the ultrasonic transducers 201 to 203. Therefore, by averaging these vessel speeds as described above, the vessel speed can be stably acquired while suppressing the influence of vessel pitching.

[0075] <Change example 1> In the above embodiment, both the Z vessel speed and the Y vessel speed are calculated for each depth in step S101 of Fig. 6. In contrast, in Modification Example 1, only the Z vessel speed is calculated for each depth, and the Y vessel speed is calculated only for the target depth.

[0076] FIG. 7 is a flowchart showing the process of measuring the vessel speed through water of the vessel S1 executed by the signal processing circuit 110 according to the first modification.

[0077] In the flowchart of Fig. 7, steps S101 and S105 in the flowchart of Fig. 6 are changed to steps S111 and S112, respectively. The processing of the other steps in Fig. 7 is the same as the corresponding steps in Fig. 6.

[0078] In step S111, the signal processing circuit 110 calculates only the Z vessel speed for each depth from the received signal and stores it in memory. The signal processing circuit 110 executes the processes of steps S102 to S104 and S107 in the same manner as described above, using the Z vessel speed for each depth stored in memory. As a result, if the determination in step S104 is YES, the signal processing circuit 110 calculates the Y vessel speed for the current depth Dn from the received signal acquired by the current transmission, and acquires the calculated Y vessel speed as the vessel speed through water of the vessel S1 (S112). The signal processing circuit 110 repeatedly executes the processes from step S111 onwards for each ultrasonic transmission until measurement is completed (S106: NO).

[0079] According to the first modification, the Y vessel speed is calculated only for the depth Dn (target depth) when the determination in step S104 is YES. Therefore, compared to the processing in Fig. 6, the processing load for calculating the Y vessel speed can be reduced, and the vessel speed through water of the vessel S1 can be calculated more efficiently.

[0080] <Change example 2> In the above embodiment, the Y vessel speed for the target depth is acquired as the vessel speed through water of the vessel S1 in step S105 of Fig. 6. In contrast, in Modification 2, the average value of the Y vessel speed for the target depth over a predetermined time period is acquired as the vessel speed through water of the vessel S1.

[0081] FIG. 8 is a flowchart showing a process for measuring the vessel speed through water of the vessel S1 executed by the signal processing circuit 110 according to the second modification.

[0082] In the flowchart of Fig. 8, step S105 in the flowchart of Fig. 6 is changed to step S121. The processing of the other steps in Fig. 7 is the same as the corresponding steps in Fig. 6.

[0083] In step S111, the signal processing circuit 110 calculates the average value of the Y vessel speed for the depth Dn when the determination in step S104 is YES. More specifically, the signal processing circuit 110 extracts from memory the Y vessel speed for that depth Dn from the current measurement point up to a predetermined time (predetermined number of times) ago, and calculates the average value of the extracted Y vessel speeds. The signal processing circuit 110 then obtains the calculated average value of the Y vessel speed as the vessel speed through water of the vessel S1.

[0084] Here, the predetermined time for averaging in step S121 may be the same as or different from the predetermined time used to calculate the average Z boat speed in step S103. For example, the predetermined time for averaging in step S121 may be a period corresponding to the measurement points up to several dozen points prior to the current measurement point.

[0085] 8, the average value of the Y vessel speed over a predetermined time period is acquired as the vessel speed through water of the vessel S1. Therefore, even if a disturbance such as a wake from another vessel temporarily occurs, the vessel speed through water of the vessel S1 can be acquired stably.

[0086] <Change example 3> 1 and 2, in the above embodiment, three transmission beams B1 to B3 are transmitted in predetermined directions from the transducer 20. However, the number and directions of the transmission beams B1 transmitted from the transducer 20 are not limited to this.

[0087] For example, as shown in Fig. 9(a), transmission beams B1 and B4 may be transmitted at a predetermined depression angle in the fore-and-aft direction of the ship S1, or as shown in Fig. 9(b), in addition to transmission beams B1 to B3, transmission beam B4 may also be transmitted at a predetermined depression angle in the stern direction of the ship S1. Also, as shown in Fig. 10, in addition to transmission beams B1 to B3, transmission beam B5 may also be transmitted directly below the ship S1, or only transmission beam B1 may be transmitted.

[0088] In these modified examples, the number of ultrasonic transducers arranged in the transducer 20 is changed according to the number of transmission beams. Each ultrasonic transducer is arranged facing the transmission direction of the corresponding transmission beam. In these modified examples, as in the above embodiment, the Y vessel speed and Z vessel speed are calculated for each depth from the received signals corresponding to each transmission beam, and further, the Y vessel speed and Z vessel speed are averaged for each depth over a predetermined time period to calculate the average Y vessel speed and Z vessel speed for each depth.

[0089] Therefore, even with the configuration of the third modified example, the ship speed through water with respect to a layer of water that is not affected by external disturbances can be obtained by the processes of FIGS. 6 to 8, and the ship speed through water can be accurately measured.

[0090] <Other change examples> In the above embodiment and its modified examples, the minimum depth at which the average value of the Z vessel speed is substantially zero is specified as the target depth for obtaining the vessel speed through water (Y vessel speed) of the vessel S1, but the method for specifying the target depth is not limited to this. For example, as shown in step S131 of Figure 11, a depth (a depth deeper than the depth Dn by the predetermined distance ΔD) obtained by adding a predetermined distance ΔD (for example, several meters) to the depth Dn (corresponding to the depth D0 in Figure 5) when the determination in step S104 is YES may be specified as the target depth, and the Y vessel speed for this depth may be obtained as the vessel speed through water of the vessel S1.

[0091] 6 to 8 and 11, the depth Dn at which the average Z vessel speed first became substantially zero was identified as the target depth, but even if the depth Dn at which the average Z vessel speed first became substantially zero is the depth Dn, if the average Z vessel speeds of the subsequent depths are not substantially zero, this depth Dn does not have to be identified as the target depth. In this case, when a depth Dn at which the average Z vessel speed becomes substantially zero subsequently occurs, this depth Dn may be identified as the target depth provided that the average Z vessel speeds of a predetermined number of depths subsequent to this depth Dn also become substantially zero.

[0092] Furthermore, the processing for obtaining the vessel speed through water of the vessel S1 is not limited to the processing of Figures 6 to 8 and Figure 11, but may be performed by processing steps other than those of Figures 6 to 8 and Figure 11, as long as the processing involves identifying a target depth where the Z vessel speed is substantially zero based on the received signal and obtaining the Y vessel speed for the identified target depth as the vessel speed through water of the vessel S1.

[0093] Furthermore, the configuration of the boat speed measuring device 1 is not limited to the configuration shown in Fig. 3 and can be modified as appropriate. For example, the first to third trailing signal removal circuits 171 to 173 may be omitted from the configuration of Fig. 3. In this case, the signal processing circuit 110 may perform the processes of Figs. 6 to 8 and 11 for a depth range deeper than the depth range in which the trailing signal is superimposed.

[0094] In the above embodiment and its modified examples, the boat speed measuring device 1 only has a function of measuring boat speed, but the boat speed measuring device 1 may have other functions such as a target detection function in addition to the boat speed measuring function. The boat speed measuring device 1 may also be mounted on a device having other functions such as sonar, and may be included in this device as one of the functions executed by this device.

[0095] The embodiments of the present invention can be modified in various ways as appropriate within the scope of the claims. [Explanation of symbols]

[0096] 1 Ship speed measuring device 20 Transmitter / Receiver 110 Signal Processing Circuit 201, 202, 203 Ultrasonic transducers

Claims

1. a transducer that transmits ultrasonic waves into water and receives reflected waves of the ultrasonic waves; a signal processing circuit that calculates the water speed of the vessel on which the transducer is installed based on the received signal output from the transducer; The signal processing circuit calculates the vertical ship speed through water and the ship speed through water in the forward direction of the ship for each depth based on the received signal, identifies a target depth at which the calculated vertical ship speed through water is substantially zero, and acquires the ship speed through water in the forward direction for the target depth as the ship speed through water. A ship speed measuring device characterized by:

2. 2. The boat speed measuring device according to claim 1, The signal processing circuit calculates an average value of the vertical ship speed relative to water for a predetermined time for each depth, and identifies the depth at which the calculated average value is substantially zero as the target depth. A ship speed measuring device characterized by:

3. The boat speed measuring device according to claim 1 or 2, the signal processing circuit identifies the target depth from a range around a minimum depth at which the average value is substantially zero; A ship speed measuring device characterized by:

4. 4. The boat speed measuring device according to claim 3, the signal processing circuit identifies the target depth as the minimum depth at which the average value is substantially zero; A ship speed measuring device characterized by:

5. The boat speed measuring device according to any one of claims 1 to 4, The signal processing circuit acquires an average value of the ship's speed through water in the traveling direction relative to the target depth over a predetermined time period as the ship's speed through water. A ship speed measuring device characterized by:

6. The boat speed measuring device according to any one of claims 1 to 5, The transducer includes a plurality of ultrasonic transducers oriented in different directions; The signal processing circuit determines the target depth and acquires the ship's speed through water based on the received signals output from the plurality of ultrasonic transducers. A ship speed measuring device characterized by:

7. Transmitting ultrasonic waves into water and receiving reflected waves of the ultrasonic waves; Based on the received signal of the reflected wave, the vertical ship speed through water and the ship speed through water in the direction of travel of the ship are calculated for each depth; Identifying a target depth at which the calculated vertical ship speed through water is substantially zero; The vessel speed through water in the direction of travel relative to the target depth is acquired as the vessel speed through water of the vessel. A method for measuring ship speed.

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