Underwater detection device, fish school tracking method, and program

Abstract

An underwater detection device (10) is provided with a data generation module (11a) which forms a plurality of reception beams (RB1) in a scanning range based on electrical signals outputted from a pl

Description

UNDERWATER DETECTION DEVICE, FISH SCHOOL TRACKING METHOD, AND PROGRAM

[0001] The present invention relates to an underwater detection device, a fish school tracking method in the underwater detection device, and a program for making a computer execute a function for tracking a fish school.

[0002] Conventionally, underwater detection devices for detecting underwater targets have been known. Such type of underwater detection device transmits ultrasonic waves into the underwater, receives reflected waves thereof, calculates echo intensities from each position in the underwater, and displays a three-dimensional distribution (echo image) of echo intensities on a screen.

[0003] For example, the underwater detection device transmits transmitted waves from a transducer having a plurality of ultrasonic oscillators, and receives reflected waves by the transducer. A plurality of reception beams arranged in a circumferential direction on a conical surface having the position of the transducer as a vertex formed by beam forming from an electrical signal output from each ultrasonic oscillator of the transducer by receiving the reflected waves. An echo image corresponding to a scanning range of the reception beam is generated and displayed from a reception signal generated for each reception beam.

[0004] The following Patent Document 1 discloses a target image tracking device and a target image tracking method applied to a scanning sonar, a fish finder or a radar device.

[0005] Patent Document 1-Japanese Patent No. 5303284

[0006] The method described in Patent Document 1 may be applied to tracking a school of massive fish (single group) having a clear boundary. However, when an underwater detection device detects a single group near the sea surface from a distance, it detects a range where the tilt angle is around 0°. Therefore, reverberation echoes such as reflected waves from the sea surface (sea surface reflection) may be distributed over a wide range including the range of echoes from a single group (single group echo).

[0007] Under such conditions, the boundary between the single group echo and the reverberation echo may become unclear, or the reverberation echo may obscure the single group echo. In the target tracking method described in Patent Document 1, the influence of reverberation echoes such as sea surface reflection is not considered.

[0008] In view of such problems, an objective of the present invention is to provide an underwater detection device, a fish school tracking method, and a program capable of stably tracking a fish school echo even under conditions affected by reverberation echoes such as sea surface reflection.

[0009] A first aspect of the present invention relates to an underwater detection device. The underwater detection device, according to the first aspect, is provided with a transmission processing module that transmits ultrasonic waves to a plurality of ultrasonic oscillators included in a transducer installed on the bottom of a ship at transmission timings at predetermined intervals; a data generation module that forms a plurality of reception beams in a scanning range based on electrical signals output from the plurality of ultrasonic oscillators during a reception period after the transmission timings and generates data relating to echo intensities at respective positions in the scanning range; and a fish school tracking module that updates a tracking area of a fish school based on the data and navigation data relating to the movement of a ship on which the transducer is installed. The fish school tracking module determines whether to use the data based on the fish school echo in the tracking area for updating the tracking area based on a determination whether an index value indicating how large the echo intensity of the entire tracking area is relative to the echo intensity around the tracking area is equal to or greater than a predetermined threshold value.

[0010] When the index value is small, the degree to which reverberation echoes that are at least as strong as the fish school echo are distributed over a wide range including the tracking area is high. Under such situation, the fish school echo is mixed with the reverberation echo, and it is difficult to distinguish the fish school echo from the reverberation echo. Therefore, if the data based on the echo of the fish school is used for updating the tracking area in this state, then the tracking area after updating is greatly affected by the reverberation echo, and it is difficult to update the tracking area properly. On the other hand, the underwater detection device, according to this aspect, avoids using the data based on the fish school echo for updating the tracking area under such situation. Therefore, it is possible to update the tracking area properly.

[0011] In the underwater detection device, according to this aspect, the fish school tracking module may be configured such that when the index value is equal to or greater than the threshold value, the tracking area is updated based on the data based on the fish school echo and the navigation data, and when the index value is less than the threshold value, the tracking area is updated based on the navigation data without using the data based on the fish school echo.

[0012] According to this configuration, when the index value is equal to or greater than the predetermined threshold value, that is, when the influence of the reverberation echo on the fish school echo in the tracking area is small, the tracking area is updated based on the data based on the fish school echo and the navigation data. Therefore, the tracking area may be updated appropriately. On the other hand, when the index value is less than the predetermined threshold value, that is, when the influence of the reverberation echo on the fish school echo in the tracking area is large, the tracking area is updated based on the navigation data without using the data based on the fish school echo. Thus, until the influence of the reverberation echo decreases, the tracking area including the fish school to be tracked may be smoothly set based on the navigation data.

[0013] In the underwater detection device, according to this aspect, the fish school tracking module may calculate, as the index value, a reverberation contrast indicating the degree to which reverberation echo having an echo intensity equal to or greater than the echo intensity in the tracking area is distributed over a wide range including the tracking area, and perform the determination based on the reverberation contrast.

[0014] According to this configuration, the influence of the reverberation echo on the fish school echo may be evaluated by the reverberation contrast, and based on this evaluation, it may be determined whether the data based on the fish school echo should be used for updating the tracking area.

[0015] In this configuration, the reverberation contrast may be calculated from a first average value of the data in the tracking area and a second average value of the data around the tracking area.

[0016] Thus, the echo intensity of the entire tracking area may be obtained as a first average value, and the echo intensity around the tracking area may be obtained as a second average value.

[0017] In this case, the reverberation contrast may be calculated by dividing the first average value by the second average value.

[0018] Thus, it may be appropriately evaluated by the reverberation contrast whether a reverberation echo that is as strong as or stronger than a fish school echo is distributed over a wide range including the tracking area.

[0019] In the above configuration, the reverberation contrast may be calculated so as to be smaller as the degree of distribution is higher.

[0020] In this case, the fish school tracking module may set a reverberation threshold to be compared with the reverberation contrast as the threshold value, and if the reverberation contrast is equal to or greater than the reverberation threshold, the tracking area to be applied at the next transmission timing may be set based on the data based on the fish school echo and the navigation data, and if the reverberation contrast is less than the reverberation threshold, the tracking area to be applied at the next transmission timing may be set based on the navigation data without using the data based on the fish school echo.

[0021] According to this configuration, if the reverberation contrast is equal to or greater than the reverberation threshold, that is, if the degree of distribution of reverberation echoes that are at least as strong as the fish school echo over a wide range including the tracking area is low, the tracking area to be applied at the next transmission timing may be set based on the data based on the fish school echo and the navigation data. Thus, the tracking area for properly tracking the fish school echo may be set based on the amplitude data. On the other hand, if the reverberation contrast is less than the reverberation threshold, that is, if the degree of distribution of reverberation echoes that are at least as strong as the fish school echo over a wide range including the tracking area is high, the tracking area to be applied at the next transmission timing may be set based on the navigation data without using the data based on the fish school echo. Thus, it is possible to avoid that the updated tracking area is greatly affected by the reverberation echo, and the tracking area for tracking the fish school echo may be smoothly set based on the navigation data until the influence of the reverberation echo decreases.

[0022] In the underwater detection device, according to this aspect, the fish school tracking module may be configured to estimate a fish school area, which is an area of the fish school echo, based on the data in the tracking area; when the index value is equal to or greater than the threshold value, the fish school area is expanded by a predetermined magnification to constitute a new tracking area; the new tracking area is corrected to a position with reference to the position of the transducer at the next transmission timing based on the navigation data; and is set to the tracking area to be applied at the next transmission timing; and when the index value is less than the threshold value, the current tracking area is corrected to a position with reference to the position of the transducer at the next transmission timing based on the navigation data; and is to set the tracking area to be applied at the next transmission timing.

[0023] According to this configuration, the tracking area is corrected to a position based on the position of the transducer after the movement of the ship. Therefore, the tracking area may be appropriately applied at each transmission timing.

[0024] In this configuration, the fish school tracking module may be configured to change the magnification used for expanding the fish school area so that the magnification increases as the index value increases.

[0025] According to this configuration, the width of the new tracking area may be appropriately adjusted according to the distribution state of the reverberation echo.

[0026] The underwater detection device, according to this aspect, may be configured to include a fish quantity index calculation module for calculating a fish quantity index based on the data in the fish school area, and an image generation module for generating a display image including information on the fish quantity index.

[0027] According to this configuration, the fish quantity index of the fish school tracked by the fish school tracking module may be updated and displayed as needed. Thus, the user may smoothly grasp the fish quantity index of the fish school being tracked.

[0028] In the underwater detection device, according to this aspect, the fish school tracking module calculates a fish school contrast indicating the certainty that the fish school echo is included in the tracking area based on the data in the tracking area and the data around the tracking area, executes update processing of the tracking area based on the index value when the fish school contrast is not less than a predetermined fish school threshold, and sets the tracking area to be applied at the next transmission timing based on the navigation data without performing update processing of the tracking area based on the index value when the fish school contrast is less than the fish school threshold.

[0029] According to this configuration, when the fish school contrast is less than the fish school threshold, that is, when the degree of distribution of the reverberation echo that is at least as strong as the fish school echo over a wide range including the tracking area is considerably high, update processing of the tracking area based on the index value is omitted, and the tracking area to be applied at the next transmission timing is set based on the navigation data. Therefore, it is possible to properly update the tracking area while simplifying processing.

[0030] In this configuration, the fish school tracking module may calculate the fish school contrast based on the maximum value of the data in the tracking area and the median value of the data around the tracking area.

[0031] According to this configuration, it is possible to properly calculate a fish school contrast indicating the certainty that a fish school echo distinguishable from a reverberation echo is included in the tracking area.

[0032] In addition, in this configuration, when the fish school contrast is less than a predetermined fish school threshold, the image generation module may be configured to continuously display the information on the fish quantity index displayed at the previous transmission timing without updating the information on the fish quantity index.

[0033] According to this configuration, it is possible to suppress the display and presentation to the user of the information on the low-precision fish quantity index calculated in a state where the degree of distribution of a reverberation echo that is as strong as or stronger than the fish school echo over a wide range including the tracking area is considerably high. Thus, it is possible to enhance the reliability of the information on the fish quantity index visually recognized by the user.

[0034] A second aspect of the present invention relates to a fish school tracking method in an underwater detection device. A fish school tracking method, according to this aspect, includes a step of transmitting ultrasonic waves to a plurality of ultrasonic oscillators included in a transducer installed on the bottom of a ship at transmission timings at predetermined intervals; a step of forming a plurality of reception beams in a scanning range based on electrical signals output from the plurality of ultrasonic oscillators during a reception period after the transmission timings and generating data on echo intensities at respective positions in the scanning range; and a step of updating a fish school tracking area based on the data and navigation data on the movement of the ship on which the transducer is installed. The step of updating the tracking area includes a step of determining whether the data based on the fish school echo in the tracking area is used for updating the tracking area based on a determination of whether an index value indicating how large the echo intensity of the entire tracking area is relative to the echo intensity around the tracking area is equal to or greater than a predetermined threshold value.

[0035] According to the fish school tracking method, according to this aspect, the same effects as those of the first aspect are exhibited.

[0036] A third aspect of the present invention is a program for causing a computer of an underwater detection device to execute a predetermined function. A program, according to this aspect, causes the computer to execute a function of transmitting ultrasonic waves to a plurality of ultrasonic oscillators included in a transducer installed on the bottom of a ship at transmission timings at predetermined intervals, a function of forming a plurality of reception beams in a scanning range based on electrical signals output from the plurality of ultrasonic oscillators during a reception period after the transmission timings and generating data on echo intensities at respective positions in the scanning range, and a function of updating a tracking area of a fish school based on the data and navigation data related to the movement of a ship on which the transducer is installed. The function of updating the tracking area includes a function of determining whether the data based on the echo of a fish school in the tracking area is used for updating the tracking area based on a determination as to whether an index value indicating how much the echo intensity of the entire tracking area is larger than the echo intensity around the tracking area is equal to or greater than a predetermined threshold value.

[0037] According to the program, according to this aspect, the same effect as in the first aspect is achieved.

[0038] As described above, according to the present invention, it is possible to provide an underwater detection device, a fish school tracking method, and a program capable of stably tracking a fish school echo even under conditions affected by reverberation echoes such as sea surface reflection.

[0039] The effect and significance of the present invention will become more clear from the following description of the embodiments. However, the embodiments shown below are merely examples for implementing the present invention, and the present invention is not limited in any way to those described in the following embodiments.

[0040] FIG. 1 is a diagram schematically showing how underwater is searched by an underwater detection device according to an embodiment.FIG. 2 is a diagram schematically showing how underwater is searched by an underwater detection device according to an embodiment.FIG. 3 is a block diagram showing a configuration of an underwater detection device according to an embodiment.FIG. 4 is a diagram for explaining a method for calculating a fish quantity index according to an embodiment.FIG. 5 is a diagram schematically showing an example of an echo image displayed on the display unit according to an embodiment.FIG. 6 is a flowchart showing generation processing of data related to echo intensity according to an embodiment.FIG. 7 is a flowchart showing tracking processing of a fish school according to an embodiment.FIG. 8 is a diagram showing a method of setting a fish school area according to an embodiment.FIG. 9 is a diagram showing an example (actual measurement) of setting a fish school area for a tracking area according to an embodiment.FIG. 10 is a diagram showing a method for calculating reverberation contrast according to an embodiment.FIG. 11 is a diagram showing a distribution state of volume scattering intensity when the reverberation contrast is relatively large according to an embodiment.FIG. 12 is a diagram showing a distribution state of volume scattering intensity when the reverberation contrast is relatively small according to an embodiment.FIG. 13 is a diagram showing an example of a display image including information on a fish quantity index according to an embodiment.FIG. 14 is a graph showing an example of a method of setting an enlargement magnification when a fish school area is enlarged to form a new tracking area according to an embodiment.FIG. 15 is a flowchart showing a fish school tracking process according to Modification 1.FIG. 16 is a flowchart showing the display processing of information related to the fish quantity index according to Modification Example 1.FIG. 17 is a flowchart showing a fish school tracking process according to Modification Example 2.FIG. 18 is a flowchart showing another fish school tracking process according to Modification 2.FIG. 19 is a diagram showing an example of a display image including information on a fish quantity index according to another modification.FIG. 20 is a diagram showing an example of a display image including information on a fish quantity index according to another modification.

[0041] Embodiments of the present invention is described with reference to the drawings. For convenience, XYZ axes orthogonal to each other are appropriately noted in the drawings. The X-axis direction and the Y-axis direction are horizontal, and the Z-axis direction is vertical. The positive X-axis direction is the direction in which the ship travels.

[0042] FIGS. 1 and 2 are diagrams schematically showing underwater search by the underwater detection device (10), according to an embodiment.

[0043] In FIGS. 1 and 2, θ is an azimuth angle about a transducer (13) installed at the bottom of the ship (S1), and φ is a tilt angle of a scanning plane (SP1) described later with respect to a horizontal plane (X-Y plane).

[0044] The underwater detection device (10) includes the transducer (13) installed at the bottom of the ship (S1) such as a fishing boat. The underwater detection device (10) transmits pulses (i.e., Transmission pulses) of acoustic waves from the transducer (13), and receives acoustic waves (i.e., echoes) reflected (i.e., backscattered) by objects such as fish existing in the underwater by the same transducer (13). The underwater detection device (10) detects objects existing in the underwater based on echoes received by the transducer (13).

[0045] The transducer (13) includes a number of ultrasonic oscillators (13a). Each ultrasonic oscillator (13a) converts an input electrical signal into a sound wave and radiates it during transmission, and converts an incident sound wave into an electrical signal and outputs it during reception. Typically, the transducer (13) has a cylindrical shape, and several hundred ultrasonic oscillators (13a) are regularly arranged on its side.

[0046] Here, the area to be detected by the underwater detection device (10) is a conical surface. The axis of the conical surface coincides with the central axis (In this case, the Z axis) of the transducer (13). The conical surface is referred to as the scanning plane (SP1), and the apex and axis of the scanning plane (SP1) are referred to as the origin and the scanning axis, respectively. The origin coincides with the position of the transducer (13), and the scanning axis extends from the origin in the direction just below. Here, the scanning axis coincides with the Z-axis. The angle formed by the scanning plane (SP1) with the horizontal plane (X-Y plane) is the tilt angle φ.

[0047] As shown in FIG. 1, during transmission, the underwater detection device (10) transmits a transmission beam (TB1) having the maximum intensity on the scanning plane (SP1) over the entire circumference. The transmission beam (TB1) has an axial intensity distribution with respect to the scanning axis (Z axis in FIG. 1), and its width in the vertical direction is relatively narrow.

[0048] As shown in FIG. 2, during reception, the underwater detection device (10) forms a number of reception beams (RB1) having the maximum sensitivity on the scanning plane (SP1). The reception beams (RB1) are formed by applying beam forming processing to electrical signals output from the plurality of ultrasonic oscillators (13a) arranged in the transducer (13).

[0049] Each reception beam (RB1) is a pencil beam having a narrow width in both the vertical and horizontal directions, and has the same directivity. A straight line passing through the origin and pointing in the direction where the sensitivity of the reception beam (RB1) is maximum is the beam axis of each reception beam (RB1). A plurality of reception beams (RB1) are formed side by side in the direction of an azimuth angle θ over the entire circumference of the scanning plane (SP1) at a constant angular interval (azimuthal resolution). The underwater detection device (10) converts the intensity of the acoustic wave received by each reception beam (RB1) into a color and displays it as an image (i.e., echo image).

[0050] FIG. 3 is a block diagram showing the configuration of the underwater detection device (10), according to an embodiment.

[0051] The underwater detection device (10) includes a control unit (11), a storage unit (12), the transducer (13), a transmission processing module (14), a reception processing module (15), a transmission / reception switching unit (16), a display unit (17), a display processing module (18), an input unit (19), and an input processing module (20). The transducer (13) is installed in the bottom of the ship (S1) as described above, and the other components such as the control unit (11) are installed in a wheelhouse of the ship (S1).

[0052] The control unit (11) includes an arithmetic processing circuit (i.e., a computer) such as a Central Processing Unit (CPU), and executes control processing described later in accordance with a program stored in the storage unit (12). The storage unit (12) includes a storage medium such as a Read Only Memory (ROM), a Random Access Memory (RAM), and a hard disk. The storage unit (12) stores a program for the control unit (11) to execute control processing.

[0053] The transducer (13) includes a plurality of ultrasonic oscillators (13a) as described above. In each transmission / reception period (i.e., ping), the transducer (13) transmits ultrasonic waves as the transmission beam (TB1) shown in FIG. 1, and the reflected waves thereof are received by the respective ultrasonic oscillators (13a).

[0054] The transmission processing module (14) outputs a transmission signal for transmitting ultrasonic waves to the transducer (13) via the transmission / reception switching unit (16) in accordance with the control from the control unit (11). As shown in FIG. 3, the transmission signal is a signal that oscillates at a predetermined amplitude for a fixed period of time. During one transmission of the transmission beam (TB1), the transmission signal is supplied to the respective ultrasonic oscillators (13a) of the transducer (13) via the transmission / reception switching unit (16). As a result, as shown in FIG. 3, ultrasonic waves corresponding to the transmission signal are transmitted from the respective ultrasonic oscillators (13a). The pulse of ultrasonic waves transmitted during one transmission is referred to as a transmission pulse.

[0055] The reception processing module (15) receives, via the transmission / reception switching unit (16), an electrical signal outputted by the ultrasonic oscillators (13a) of the transducer (13) after receiving the reflected wave of the ultrasonic wave, and applies processing of amplification and noise removal (i.e., bandpass filter) to the received electrical signal. The reception processing module (15) outputs the electrical signal subjected to the processing to the control unit (11).

[0056] The transmission / reception switching unit (16) outputs the transmission signal outputted from the transmission processing module (14) to the transducer (13) (ultrasonic oscillator (13a)) during the transmission of the transmission beam (TB1), and outputs the electrical signal outputted from the transducer (13) (ultrasonic oscillator (13a)) to the reception processing module (15) within a certain period from the timing when the transmission of the transmission beam (TB1) is completed.

[0057] Although one transmission processing module (14) and one reception processing module (15) are shown in FIG. 3, the processing described above in the transmission processing module (14) and the reception processing module (15) is performed for each ultrasonic oscillator (13a) arranged in the transducer (13). Accordingly, the electrical signal obtained by amplifying and removing noise from the electrical signal outputted from each ultrasonic oscillator (13a) is individually inputted to the control unit (11). When the electrical signal is inputted to the control unit (11), the electrical signal is converted into a digital signal having a predetermined sampling period by an A / D converter.

[0058] The display unit (17) includes a display such as a liquid crystal display. The display processing module (18) causes the display unit (17) to display a predetermined image in accordance with control from the control unit (11). The input unit (19) includes input means such as operation keys and a mouse. The input processing module (20) outputs a signal corresponding to an operation performed on the input unit (19) to the control unit (11) in accordance with control from the control unit (11). The display unit (17) and the input unit (19) may comprise a liquid crystal panel in which a touch panel is superposed on the liquid crystal display.

[0059] In this embodiment, the functions of a data generation module (11a), a fish school tracking module (11b), a fish quantity index calculation module (11c), and an image generation module (11d) are imparted to the control unit (11) by a program stored in the storage unit (12).

[0060] The data generation module (11a) performs beam forming on the electrical signal (i.e., digital signal) outputted from each ultrasonic oscillator (13a) to form the reception beam (RB1) shown in FIG. 2, and generates a reception signal corresponding to a sound wave incident on the transducer (13) from the direction of the beam axis of each reception beam (RB1) (i.e., the direction of a predetermined azimuth angle θ and tilt angle φ). Further, the data generation module (11a) performs band limiting and envelope detection processing on the reception signal in each beam axis direction to acquire an envelope signal in each beam axis direction.

[0061] Here, the band limiting process is a process for extracting a frequency component of the transmission signal output from the transmission processing module (14). The process is performed when the transmission signal output from the transmission processing module (14) is a constant frequency signal (CW signal).

[0062] On the other hand, when the transmission signal output from the transmission processing module (14) is not a constant frequency signal (CW signal) but a frequency-modulated chirp signal (FM signal), the data generation module (11a) applies the matched filter process to the reception signal in each beam axis direction instead of the band limiting process. Then, the data generation module (11a) applies the envelope detection process to the signal after the matched filter process, and acquires an envelope signal in each beam axis direction.

[0063] The acquired envelope signal is a signal indicating an echo intensity (intensity of a soundwave) that changes according to the elapsed time from the transmission timing of the transmission beam (TB1) (ultrasonic waves). Here, the elapsed time from the transmission timing corresponds to the distance from the transducer (13) in each beam axis direction. By associating the elapsed time from the transmission timing with the distance, the control unit (11) acquires the echo intensity from the position of each distance in each beam axis direction from the echo signal of each reception beam (RB1). The echo intensity is acquired at a predetermined distance resolution according to the sampling period. The data generation module (11a) acquires digital data (non-negative real numbers) corresponding to the amplitude of the envelope signal at each sampling timing (distance) as amplitude data.

[0064] The data generation module (11a) generates a series of amplitude data by executing the above-described processing in a reception period after the transmission of the ultrasonic wave. The operation of transmitting the ultrasonic wave and receiving the echo generated by the transmission in a subsequent reception period is called ping. A series of amplitude data is generated for each ping.

[0065] The fish school tracking module (11b) tracks the fish school based on the amplitude data generated by the data generation module (11a). More specifically, the fish school tracking module (11b) updates the initial tracking area set by the user for each ping based on the amplitude data and the navigation data (ship speed and heading) from the navigation equipment.

[0066] If there is an echo of a fish school to be tracked (single group echo) on the echo image displayed on the display unit (17), the user specifies the area via the input unit (19). For example, the user specifies the center position of the single group echo on the echo image. Thus, an area of a predetermined size centering on this center position is set as the initial tracking area. However, the method of setting the initial tracking area is not limited to this.

[0067] The fish school tracking module (11b) updates the initial tracking area thus set so as to track the fish school based on the amplitude data and the navigation data (i.e., ship speed and heading) in the current ping, and sets the updated tracking area in the next ping. In the next ping, the updated tracking area is further updated based on the amplitude data and the navigation data (i.e., ship speed and heading) in the next ping. Thus, the fish school tracking module (11b) updates the tracking area every ping.

[0068] The fish school tracking module (11b) estimates the fish school area (A1) where the fish school exists from the amplitude data in the tracking area in each ping. Then, the fish school tracking module (11b) sets the tracking area in the next ping based on an area obtained by enlarging the estimated fish school area (A1) by a predetermined magnification. The fish school tracking process will be described later with reference to FIG. 7. A method of setting the fish school area (A1) will be described later with reference to FIG. 8.

[0069] The fish quantity index calculation module (11c) calculates a fish quantity index (Q) that may be an index of the total weight of fish included in the fish school area (A1) based on the amplitude data in the fish school area (A1). Various methods may be used as the method of calculating the fish quantity index (Q). For example, the fish quantity index (Q) may be calculated by the calculation method described in Japanese Patent Application No. 2023-116287, which the applicant has previously filed. In this case, the fish quantity index (Q) is calculated by the following equation.

[0070]

[0071] FIG. 4 is a diagram for explaining the calculation method of the fish quantity index (Q) based on the above equation (1), according to an embodiment.

[0072] Here, a rectangular coordinate system is defined in which the beam number is the horizontal axis and the sample number is the vertical axis.

[0073] The beam number is a number assigned to the reception beam (RB1). For example, 0 is assigned to the beam number (j) of the reception beam (RB1) facing the stern direction in plan view, and 1, 2, 3, ... are assigned to the beam numbers (j) of the reception beams (RB1) in order of increasing angles formed by the stern direction (reference direction) and the beam axis direction in the plan view, assuming that the clockwise direction is positive. In this case, if the total number of the reception beams (RB1) is 128, the beam numbers (j) of the reception beams (RB1) facing the port direction, the bow direction, and the starboard direction are 32, 64, and 96, respectively.

[0074] The sample number indicates the order in which the envelope signals corresponding to the reception beams (RB1) are sampled. The sample number corresponds to the distance from the origin (i.e., the position of the transducer (13)). A sample number (n) is assigned to each sampling time of the envelope signal in order of time. The transmission start time of the transmission beam (TB1), that is, the moment when the leading edge of the transmission pulse is emitted from the transducer (13), is set as the reference time, and the sample number (n) at this time is set to 0.

[0075] A(j, n) in the equation (1) is the amplitude data at the positions of the beam number (j) and the sample number (n). r0is a unit distance and is defined as 1 m. rnis the distance (unit: m) from the origin of the position corresponding to the time tnat which the n-th amplitude data is sampled. α is the absorption coefficient (i.e., Attenuation of sound waves per unit distance, unit: dB / m).

[0076] When the fish school area (A1) is set in a rectangular coordinate system as shown in Fig. 4, the calculation in parentheses of Equation (1) is performed for the group of amplitude data A(j, n) included in the fish school area (A1), and the sum of these calculation results is obtained. Then, the obtained sum is multiplied by C0, Ccor, and 1 / Vunitto calculate the fish quantity index (Q).

[0077] The coefficient Vunitis called a point spread coefficient. When there is one target on the scanning plane (SP1), in the orthogonal coordinate system of FIG. 4, normalized amplitude data A′(j, n) attributable to this target is generated behind this target (i.e., upper side in FIG. 4). The normalized amplitude data A′(j, n) is expressed by the following equation. In the following equation, I0is the intensity of the transmission pulse (unit: micropascal squared).

[0078]

[0079] Here, when a target strength (Ts) of the target is 1, the maximum value of the normalized amplitude data A′(j, n) attributable to the target is 1. The sum of squared values of the normalized amplitude data A′(j, n) is the point spread coefficient Vunit.

[0080] The coefficient C0is obtained as an approximate number of W / (2I0× k2× Ts) from the target strength (Ts) and weight (W) of the single fish, the intensity (I0)of the transmission pulse, and the reception sensitivity (k) of the device. The approximate number may be a value obtained by substituting the values of (W) and (Ts) for the representative fish and the design values of (I0) and (k) in the underwater detection device (10), or a value obtained in advance so that the catch quantity estimated by a fisherman or the actual catch quantity agrees well with the fish quantity index (Q).

[0081] The coefficient (Ccor) is a fish quantity correction coefficient. The fish quantity correction coefficient (Ccor) reflects a fish quantity correction magnification input from a user such as a fisherman. The fish quantity index calculation module (11c) calculates the fish quantity index (Q) by setting the fish quantity correction coefficient (Ccor) to an initial value of 1 until the fish quantity correction magnification is first input. Each time the fish quantity correction magnification is input, the fish quantity index calculation module (11c) updates the value of the fish quantity correction coefficient (Ccor) by the following equation.

[0082] “New Ccor” =“fish quantity correction magnification ” × “old Ccor”

[0083] That is, the fish quantity index calculation module (11c) calculates the fish quantity index (Q) by multiplying the fish quantity correction factor (Ccor) immediately before the input of the correction magnification by the fish quantity correction magnification as the new fish quantity correction factor (Ccor).

[0084] The user inputs the fish quantity correction magnification through the input unit (19) in order to suppress the difference between the displayed fish quantity index (Q) and the amount of fish actually captured. Thus, the calculation formula (1) of the fish quantity index (Q) may be corrected to approach the actual amount of fish captured based on the input fish quantity correction magnification (Ccor) by reflecting the fish quantity correction magnification input from the user to the fish quantity correction factor (Ccor). Therefore, by repeating the input of the fish quantity correction magnification, the fish quantity index (Q) may be made closer to the amount of fish estimated by the user. Thus, the fish quantity index (Q) corresponding to the fishing ground of the user, fish species, and season may be smoothly and properly displayed on the display unit (17).

[0085] The method of calculating the fish quantity index (Q) is not limited to the above and, for example, the method described in Japanese Patent Application Laid-Open Publication No. 2009-300220 may be used.

[0086] Returning to FIG. 3, the image generation module (11d) generates an echo image for displaying the echo intensity from each distance position in each beam axis direction on a predetermined color scale. The image generation module (11d) sequentially outputs the echo images generated for each ping to the display processing module (18). Thus, the echo image updated for each ping is displayed on the display unit (17). In addition, the image generation module (11d) generates a display image (110) including information on the fish quantity index (Q) as described later.

[0087] FIG. 5 is a diagram schematically showing an example of an echo image displayed on the display unit (17), according to an embodiment.

[0088] In the echo image display mode, the screen of the display unit (17) is divided into areas (A11) and (A12) in the left and right directions. An echo image (P10) is displayed in area (A11). Here, the echo image (P10) is displayed as an image when the ship (S1) is viewed from directly above. An image (P11) of the ship (S1) is arranged at the center of the echo image (P10), and a track (P12) of the ship (S1) so far is shown. A straight line (P13) indicating the direction of the bow of the ship (S1) is included in the echo image (P10).

[0089] Further, in the echo image (P10), a range of a certain distance from the position of the own ship (S1) (i.e., image (P11)) is shown by circular boundary lines (P14), (P15), and (P16). The diameters of the circular boundary lines (P14), (P15), and (P16) are, for example, 200 m, 400 m, and 600 m. In the echo image (P10), the echo intensity described above is displayed in a predetermined color scale. In FIG. 5, hatching is applied to a range of high echo intensity for convenience. For example, the hatched range (P17) is a range of high echo intensity. The hatched range (P17) is a range where a school of fish may exist.

[0090] The area (A12) is vertically divided into a plurality of areas, and in each of the divided areas, information indicating the current position of the ship (S1) (i.e., Longitude, Latitude), the water temperature at the current position, a graph indicating the change of the water temperature with time, and the like are displayed. In any of the divided areas of the area (A12), information concerning the fish quantity index (Q) calculated by the fish quantity index calculation module (11c) is displayed. This information is updated every ping. In FIG. 5, the display of these images in the area (A12) is omitted for convenience.

[0091] FIG. 6 is a flowchart showing a process of generating data concerning the echo intensity, according to an embodiment.

[0092] The process of FIG. 6 is executed by the control unit (11) mainly by the function of the data generation module (11a). FIG. 6 shows the process of 1 ping. The control unit (11) executes the processing of FIG. 6 for each ping.

[0093] The control unit (11) causes the plurality of ultrasonic oscillators (13a) included in the transducer (13) to transmit ultrasonic waves at transmission timings at predetermined intervals (S11). The control unit (11) forms the plurality of reception beams (RB1) in a scanning range (i.e. scanning plane (SP1)) having the position of the transducer (13) as the origin based on the electrical signals output from the plurality of ultrasonic oscillators (13a) during the reception period after the transmission timing, and generates data related to the echo intensity at each position (a position defined by the azimuth angle of each reception beam (RB1) and the distance from the origin) in the scanning range (i.e., scanning plane (SP1)) (S12). Here, as data related to the echo intensity, amplitude data is generated as described above.

[0094] FIG. 7 is a flowchart showing the tracking process of the fish school, according to an embodiment.

[0095] In the flowchart of FIG. 7, the processes of steps (S102), (S103), and (S105) to (S110) are executed by the function of the fish school tracking module (11b), and the process of step (S104) is executed by the function of the fish quantity index calculation module (11c). In the following description, it is assumed that the control unit (11) performs each process by these functions.

[0096] When the user designates an area (i.e., initial tracking area (A0)) of the fish school to be tracked with respect to the echo image (P10) shown in FIG. 5 through the input unit (19) and performs an operation to start tracking, the control unit (11) determines whether the current ping is the first ping after the start of tracking (S101). If the current ping is the first ping (S101: YES), the control unit (11) sets an initial tracking area (A0) (S102), and further sets the fish school area (A1) based on the amplitude data in the set initial tracking area (A0).

[0097] FIG. 8 is a diagram showing a method of setting the fish school area (A1), according to an embodiment.

[0098] The tracking area (A0) is developed in a rectangular coordinate system shown in FIG. 8. This rectangular coordinate system is the same as the rectangular coordinate system shown in FIG. 4. The tracking area (A0) is defined by parameters of a width (W01) parallel to the horizontal axis, a width (W02) parallel to the vertical axis, and a center point (C01). The width (W01) corresponds to an angular width in the azimuthal direction, and the width (W02) corresponds to a length in the distance direction.

[0099] The control unit (11) calculates the volume scattering intensity (SV) for each amplitude data included in the tracking area (A0). Sound waves are attenuated by spherical diffusion and absorption according to distance. Due to this attenuation, the amplitude data also decreases according to distance. The volume scattering intensity (SV) is the reflectance per unit volume of the echo source (i.e., fish school or plankton group), and is obtained by correcting the amplitude data so as to compensate for the attenuation.

[0100] The control unit (11) adds the volume scattering intensities (SV) within the width (W02) to each column of beam numbers (j) included in the width (W01) to calculate the sum Sθ(j) of the volume scattering intensities (SV). In FIG. 8, an example of the sum Sθ(j) obtained for each beam number (j) is shown as a waveform below the tracking area (A0). The straight line below the waveform indicates the level at which the sum Sθ(j) is 0. Strictly speaking, the sum Sθ(j) is scattered for each beam number j, but here, for convenience, a waveform is shown in which a plot of the sum Sθ(j) is connected by a curve.

[0101] The control unit (11) adds the volume scattering intensities (SV) within the width (W01) to each row of the sample numbers n included in the width (W02) to calculates the sum Sr(n) of the volume scattering intensities SV. In FIG. 8, an example of the sum Sr(n) obtained for each sample number n is shown as a waveform on the right side of the tracking area (A0). The straight line on the right side of the waveform indicates the level at which the sum Sr(n) is 0. Strictly speaking, the sum Sr(n) is scattered for each sample number n, but here, for convenience, a waveform is shown in which a plots of the sum Sr(n) is connected by a curve.

[0102] The control unit (11) extracts a maximum value (MAX1) of the sum Sθ(j), and sets a value obtained by multiplying the maximum value (MAX1) by a predetermined magnification (For example, 0.1) as the threshold value (TH1). Similarly, the control unit (11) extracts the maximum value (MAX2) of the sum Sr(n), and sets a value obtained by multiplying the maximum value (MAX2) by a predetermined magnification (For example, 0.1) as the threshold value (TH2). Here, the magnification is set to a value extractable by distinguishing the volume scattering intensity (SV) from the fish school from noise and the like. The magnification is set to an appropriate value based on actual measurement.

[0103] Of the waveforms shown below the tracking area (A0), a portion that continuously has a value equal to or greater than the threshold value (TH1) is referred to as a crest, and of the waveforms shown to the right of the tracking area (A0), a portion that continuously has a value equal to or greater than the threshold value (TH2) is referred to as a crest.

[0104] The control unit (11) sets the range of the horizontal width of the crest waveform including the maximum value (MAX1) among the crest waveforms on the waveforms shown below the tracking area (A0) to the width (W11) in the horizontal axis direction (azimuthal direction) of the fish school area (A1). More specifically, the range between the beam number (j) closest to one boundary and the beam number (j) closest to the other boundary of this horizontal width range is set to the width (W11) in the horizontal axis direction (azimuthal direction) of the fish school area (A1). In this case, if there are crest waveforms outside the range of the crest waveform including the maximum value (MAX1), the range of the horizontal width including the crest waveform up to a predetermined number from the crest waveform including the maximum value (MAX1) may be set to the width (W11) in the horizontal axis direction (azimuthal direction) of the fish school area (A1). Also in this case, the range between the beam number (j) closest to the two boundaries of this horizontal width range is set to the width (W11) in the horizontal axis direction (azimuthal direction) of the fish school area (A1).

[0105] Similarly, the control unit (11) sets the width (W12) in the vertical axis direction (azimuthal direction) of the fish school area (A1) based on the crest waveform on the waveform shown to the right of the tracking area (A0).

[0106] Further, the control unit (11) sets a center point (C11) of the rectangular fish school area (A1) defined by the widths (W11) and (W12). This completes the setting of the fish school area (A1). The fish school area (A1) is defined by the parameters of the width (W11), the width (W12), and the center point (C11). The width (W11) corresponds to the angular width in the azimuth direction, and the width (W12) corresponds to the length in the distance direction.

[0107] FIG. 9 shows an example (actual measurement) of setting the fish school area (A1) with respect to the tracking area (A0), according to an embodiment.

[0108] FIG. 9 shows a rectangular coordinate system when the horizontal axis is set to the azimuth angle θ (corresponding to the beam number (j)) and the vertical axis is set to the distance (r) (i.e., corresponding to the sample number (n)). The volume scattering intensity (SV) at each coordinate point is indicated by the color of the scale on the right. In the original scale, the lowest value (-70dB) is black and the highest value (-30dB) is red. The middle value of the scale is green. The scale goes from the lowest value of black through blue, light blue, green, and yellow to the highest value of red. For convenience, FIG. 9 shows a grayscale version of the original figure.

[0109] In FIG. 9, a rectangular area surrounded by two outer vertical lines (V01) and (V02) and two outer horizontal lines (H01) and (H02) is the tracking area (A0), and a rectangular area surrounded by two inner vertical lines (V11) and (V12) and two inner horizontal lines (H11) and (H12) is a fish school area (A1). The fish school area (A1) is included in the tracking area (A0) and is smaller than the tracking area (A0). An area of a fish school having a high volume scattering intensity (SV) is generally included in the fish school area (A1).

[0110] Returning to FIG. 7, the control unit (11) calculates a fish quantity index (Q) based on the amplitude data included in the fish school area (A1) (S104). The method of calculating the fish quantity index (Q) is as described above.

[0111] Next, the control unit (11) calculates an index value indicating how much the echo intensity of the entire tracking area (A0) is larger than the echo intensity around the tracking area (A0) (S105). Here, the reverberation contrast is calculated as this index value.

[0112] When the underwater detection device (10) detects a school of fish near the sea surface from a distance, it detects a range where the tilt angle is around 0°. In this case, reverberation echoes such as reflected waves from the sea surface (sea surface reflection) may be distributed over a wide range including the range of echoes from fish schools (fish school echoes).

[0113] The reverberation contrast is a parameter indicating the degree to which reverberation echoes that are at least as strong as the fish school echoes are distributed over a wide range including the tracking area (A0). The reverberation contrast may be said to be a parameter indicating how large the echoes are in the tracking area (A0) compared with the surrounding area. Here, the reverberation contrast is calculated so that the higher the degree to which reverberation echoes that are at least as strong as the fish school echoes are distributed over a wide range including the tracking area (A0), the lower the reverberation contrast.

[0114] FIG. 10 is a diagram showing a method for calculating reverberation contrast, according to an embodiment.

[0115] Here, four reference areas (R1) to (R4) contacting the four sides of the tracking area (A0) are defined. The control unit (11) calculates the average value (SVa0) of the volume scattering intensity (SV) in the tracking area (A0), and further calculates the average values (SVa1) to (SVa4) of the volume scattering intensity (SV) for each of the reference areas (R1) to (R4). Then, the control unit (11) calculates a value obtained by dividing the average value (SVa0) (i.e., first average value) by the maximum value (i.e., second average value) of the average values (SVa1) to (SVa4) as the reverberation contrast.

[0116] FIG. 11 is a diagram showing a distribution state of the volume scattering intensity (SV) when the reverberation contrast is relatively large, according to an embodiment and FIG. 12 is a diagram showing a distribution state of the volume scattering intensity (SV) when the reverberation contrast is relatively small, according to an embodiment. In FIGS. 11 and 12, the volume scattering intensity (SV) is mapped in the same orthogonal coordinate system as in FIG. 9 and on the same scale as in FIG. 9. In FIG. 12, the fish school area (A1) is approximately the same size as the tracking area (A0).

[0117] As shown in FIG. 11, when the reverberation contrast is relatively large, the degree to which reverberation echoes that are as strong as or stronger than the fish school echoes are distributed over a wide range including the tracking area (A0) is small. On the other hand, as shown in FIG. 12, when the reverberation contrast is relatively small, strong volume scattering intensities (SV) based on reverberation echoes such as sea surface reflection are widely distributed above and below and to the right of the tracking area (A0), and the degree to which reverberation echoes that are as strong as or stronger than the fish school echoes are distributed over a wide range including the tracking area (A0) is large. From these measured results, it may be confirmed that the reverberation contrast calculated by the above method is a parameter indicating the degree to which reverberation echoes that are as strong as or stronger than the fish school echoes are distributed over a wide range including the tracking area (A0).

[0118] The method of calculating the reverberation contrast is not limited to the method shown in FIG. 10. For example, a value obtained by dividing the average value (SVa0) by the average value of the average values (SVa1) to (SVa4) may be used as the reverberation contrast. Alternatively, the reference areas (R1) to (R4) may be set so that the sum of the areas of the reference areas (R1) to (R4) is equal to the area of the tracking area (A0), and a value obtained by dividing the sum of the volume scattering intensities (SV) of the tracking area (A0) by the sum of the volume scattering intensities (SV) of the reference areas (R1) to (R4) may be calculated as the reverberation contrast.

[0119] Returning to FIG. 7, the control unit (11) executes a reverberation contrast test using the reverberation contrast calculated in step S105 (S106). Specifically, the control unit (11) determines whether the reverberation contrast is equal to or greater than a predetermined reverberation threshold.

[0120] If the reverberation contrast is equal to or greater than the reverberation threshold (S107: YES), the control unit (11) enlarges the fish school area (A1) set in step (S103) by a predetermined magnification larger than 1 to constitute a new tracking area (A0) (S108). Specifically, the control unit (11) enlarges the widths (W11) and (W12) by the aforementioned magnification while maintaining the center point (C11) in FIG. 8 to constitute a new tracking area (A0). The center point of the new tracking area (A0) is the same as the center point (C11) of the fish school area (A1).

[0121] On the other hand, if the reverberation contrast is less than the reverberation threshold (S107: NO), the control unit (11) skips step (S108) and maintains the current tracking area (A0) as the tracking area (A0) for the next ping.

[0122] By constituting the new tracking area (A0) based on the fish school area (A1) in step (S108), the new tracking area (A0) may be positioned at a position shifted from the original tracking area (A0) to a position corresponding to the fish school. Further, since the new tracking area (A0) is obtained by enlarging the fish school area (A1) at a predetermined magnification greater than 1, even if the shape of the fish school itself changes or other small fish schools are integrated to enlarge and deform the fish school, the amplitude data of the expanded or deformed fish school is easily included in the new tracking area (A0). Thus, the fish school echo may be tracked smoothly.

[0123] However, if the processing of step (S108) is repeatedly performed in a state in which the reverberation echoes that are as strong as or stronger than the fish school echo is distributed over a wide range including the tracking area (A0), the tracking area (A0) may continue to be enlarged with each ping due to the influence of the surrounding reverberation echoes, and become a range that is several steps wider than the original fish school echo range. In this case, the fish school area (A1) may not be properly set.

[0124] Therefore, in the processing of FIG. 7, if the reverberation contrast is less than the reverberation threshold (S107: NO), step (S108) is skipped, and the tracking area (A0) using the current tracking area (A0) is set as the area for setting the tracking area (A0) for the next ping. Thus, in a state in which the reverberation echoes that are as strong as or stronger than the fish school echo is distributed over a wide range including the tracking area (A0), excessive enlargement of the tracking area (A0) by the processing of step (S108) is suppressed.

[0125] From this point of view, the reverberation threshold is set on the condition that the fish school area (A1) may be properly set by the volume scattering intensity (SV) in the tracking area (A0), and a new tracking area (A0) may be properly configured based on the fish school area (A1). That is, a lower limit value of the reverberation contrast that may satisfy this condition is set as the reverberation threshold. In other words, the reverberation contrast is set as the reverberation threshold value when the degree to which the reverberation echo that is as strong as or stronger than the fish school echo is distributed over a wide range including the tracking area (A0) is within the upper limit that may satisfy the condition. The reverberation threshold may be set based on actual measurement.

[0126] Thereafter, the control unit (11) determines whether an instruction to end the tracking of the fish school has been input from the user (S109). If an end instruction is input (S109: YES), the control unit (11) ends the process of FIG. 7. If no end instruction is input (S109: NO), the control unit (11) returns the process to step (S101) and executes the process for the next ping.

[0127] Since the determination in step (S101) is NO for the next and subsequent pings, step (S110) is executed. In step (S110), the position of the tracking area (A0) configured for the current ping in the previous ping is corrected based on the navigation data. That is, the position of the ship (S1) is displaced by the progress of the ship (S1) between the previous ping and the current ping, and the direction (bearing) of the ship (S1) is rotated. As a result, the origin of the scanning plane (SP1) is shifted and the scanning plane (SP1) is rotated about the central axis of the transducer (13).

[0128] In step (S110), a process of correcting (projecting) the position on the earth of the tracking area (A0) configured for the current ping in the previous ping to the position on the scanning plane (SP1) in the current ping is performed. Specifically, the control unit (11) projects the center point (C01) of the tracking area (A0) configured for the current ping in the previous ping to the closest position (Coordinate position defined by sample number and beam number) on the scanning plane (SP1) in the current ping. The control unit (11) then sets the tracking area (A0) after correction for the current ping by applying the widths (W01) and (W02) of the tracking area (A0) configured for the current ping to the center point (C01) after projection.

[0129] The tracking area (A0) corrected in step (S110) is the tracking area (A0) configured in step (S108) if the determination in step (S107) in the previous ping is YES, and is the tracking area (A0) used in the previous ping if the determination in step (S107) in the previous ping is NO.

[0130] After correcting the tracking area (A0) in this manner, the control unit (11) executes the processes from step (S103). The control unit (11) repeatedly executes the processes of steps (S110) and (S103) to (S108) until an instruction to end the tracking of the fish school is input from the user (S109: NO). Thus, for each ping, the fish school area (A1) and the fish quantity index (Q) are updated, and the tracking area (A0) is updated. Thereafter, when an instruction for ending the tracking of the fish school is input from the user (S109: YES), the control unit (11) ends the process according to the flowchart of FIG. 7.

[0131] In parallel with the process of FIG. 7, the control unit (11) executes a process for displaying information on the fish quantity index (Q) calculated in step (S104). Each time the control unit (11) calculates the fish quantity index (Q) in step (S104), it updates the fish quantity index (Q) to be displayed in the area (A12) of FIG. 5.

[0132] The control unit (11) may display a display image (110) shown in FIG. 13 on the display unit (17) as a screen for displaying information on the fish quantity index (Q).

[0133] The display image (110) includes the current fish quantity index value (111) calculated by the function of the fish quantity index calculation module (11c) in step (S104) of FIG. 7, and a graph (112) of the time series of the fish quantity index (Q) calculated so far. The current fish quantity index value (111) may be the current fish quantity index value (111) itself, or may be an average value of the current fish quantity index value (111) calculated between the present and the past fixed period. The current fish quantity index value (111) at each time in the graph (112) is the same as this.

[0134] The horizontal axis and the vertical axis of the graph (112) represent the time (unit: minutes) and the fish quantity index (Q) (unit: tons), respectively. On the horizontal axis, the current time is set at the right end, and as the time moves to the left, the time moves backward. Here, the transition of the current fish quantity index value (111) during the period from the present to 20 minutes ago is displayed as a graph (112).

[0135] The user may grasp the fish quantity at the current position from the current fish quantity index value (111) included in the display image (110), and may grasp the transition of the fish quantity in the passage of own ship (S1) so far from the graph (112). Therefore, the user may smoothly grasp the situation of the fish school and the position where the fish should be caught.

[0136] The display image (110) of FIG. 13 may be arranged in any divided area of the area (A12) on the screen of FIG. 5. Alternatively, on the screen of FIG. 5, the display image (110) of FIG. 13 may be superimposed so as not to cover the echo image (P10) as much as possible. In this case, display and erasure of the display image (110) may be switched according to an operation by the user.

[0137] Further, the magnification applied in step (S108) need not be a fixed value, and for example, the magnification may be set so that the magnification increases as the reverberation contrast increases.

[0138] FIG. 14 is a graph showing an example of a method of setting the enlargement magnification when the fish school area (A1) is enlarged to form a new tracking area (A0) in step (S108) of FIG. 7, according to an embodiment.

[0139] In this setting method, a fixed magnification is set in the range of the reverberation contrast from the reverberation threshold to the value (C1), and a fixed magnification larger than the magnification of the range up to the value (C1) is set in the range of (C2) or more in which the reverberation contrast is larger than the value (C1). The magnification is set so that the range between the value (C1) and the value (C2) linearly increases in accordance with the increase in the reverberation contrast.

[0140] By setting the magnification in this way, under a situation where the degree of distribution of the reverberation echo that is strong to the same degree as or more than the fish school echo over a wide range including the tracking area (A0) is relatively high, the expansion of the new tracking area (A0) relative to the fish school area (A1) is suppressed, and under a situation where the degree of distribution of the reverberation echo that is strong to the same degree as or more than the fish school echo over a wide range including the tracking area (A0) is low, the expansion of the new tracking area (A0) relative to the fish school area (A1) is promoted. Thus, the width of the new tracking area (A0) may be appropriately adjusted according to the distribution of the reverberation echo.

[0141] The method of setting the magnification is not limited to this. For example, in a range where the reverberation contrast is greater than the value (C1), the magnification may be set so as to linearly increase in accordance with an increase in the reverberation contrast. Alternatively, the magnification may be set so as to linearly increase in accordance with an increase in the reverberation contrast from the reverberation threshold. The magnification which increases in accordance with an increase in the reverberation contrast may not linearly change, but may gradually increase, for example, along a predetermined curve.Effect of the Embodiment

[0142] According to the embodiment described above, the following effects may be achieved.

[0143] As shown in FIGS. 7 and 10, the control unit (11) (i.e. fish school tracking module (11b)) determines whether to use data based on the fish school echo in the tracking area (A0) for updating the tracking area (A0) (S108) based on a determination as to whether an index value (reverberation contrast) indicating how much the echo intensity (i.e. volume scattering intensity (SV)) of the entire tracking area (A0) is larger than the echo intensity (i.e. volume scattering intensity (SV)) of the surrounding area of the tracking area (A0) is equal to or larger than a predetermined threshold value (reverberation threshold) (S106 and S107).

[0144] Under a situation where the index value (reverberation contrast) is small and the degree of distribution of reverberation echoes which are as strong as or stronger than the fish school echoes over a wide range including a tracking area (A0) is high, the fish school echoes are mixed with the reverberation echoes and the fish school echoes are hardly distinguished from the reverberation echoes. Under such a situation, when the tracking area (A0) is updated (S108 and S110) using the data based on the fish school echoes (i.e., volume scattering intensity (SV)), the updated tracking area (A0) is greatly affected by the reverberation echoes and it is difficult to update the tracking area (A0) properly. On the other hand, according to the configuration described above, under such a situation, it is possible to avoid using the fish school echoes data (i.e., volume scattering intensity (SV)) for updating the tracking area (A0). Therefore, it is possible to update the tracking area (A0) properly.

[0145] As shown in FIG. 7, when the index value (reverberation contrast) is equal to or greater than the threshold value (reverberation threshold) (S107: YES), the control unit (i.e. fish school tracking module (11b)) updates the tracking area (A0) based on the data (volume scattering intensity (SV)) based on the fish school echo and the navigation data (S108 and S110), and when the index value (reverberation contrast) is less than the threshold value (reverberation threshold), the control unit (11) updates the tracking area (A0) based on the navigation data without using the data (volume scattering intensity (SV)) based on the fish school echo (S110).

[0146] According to this configuration, when the index value (reverberation contrast) is equal to or greater than a predetermined threshold value (reverberation threshold), that is, when the influence of the reverberation echo on the fish school echo in the tracking area (A0) is small, the tracking area (A0) is updated based on the data based on the fish school echo and the navigation data. Therefore, the tracking area (A0) may be updated appropriately. On the other hand, when the index value (reverberation contrast) is less than a predetermined threshold value (reverberation threshold), that is, when the influence of the reverberation echo on the fish school echo in the tracking area (A0) is large, the tracking area (A0) is updated based on the navigation data without using the data based on the fish school echo (volume scattering intensity (SV)). Therefore, until the influence of the reverberation echo decreases, the tracking area (A0) including the fish school to be tracked may be smoothly set based on the navigation data.

[0147] As shown in FIGS. 7 and 10, the control unit (11) (i.e. fish school tracking module (11b)) calculates, as the index value, a reverberation contrast indicating the degree to which the reverberation echo having an echo intensity equal to or greater than that of the echo intensity in the tracking area (A0) is distributed over a wide range including the tracking area (A0) (S105), and determines by a reverberation contrast test based on the reverberation contrast (S106 and S107).

[0148] According to this configuration, the influence of the reverberation echo on the fish school echo may be evaluated based on the reverberation contrast, and based on the evaluation, it may be determined whether the data based on the fish school echo should be used for updating the tracking area (A0).

[0149] As shown in FIG. 10, the reverberation contrast is calculated based on a first average value of the data (volume scattering intensity (SV)) in the tracking area (A0) and a second average value of the data (volume scattering intensity (SV)) in the reference areas (R1) to (R4) around the tracking area A0.

[0150] Thus, the echo intensity of the entire tracking area (A0) may be obtained as the first average value, and the echo intensity around the tracking area (A0) may be obtained as the second average value.

[0151] Here, the reverberation contrast is calculated by dividing the first average value by the second average value.

[0152] Thus, the reverberation contrast may be used to appropriately evaluate whether a reverberation echo that is as strong as or stronger than the fish school echo is distributed over a wide range including the tracking area (A0).

[0153] As described above, the reverberation contrast is calculated so that the reverberation contrast becomes smaller as the degree of distribution of the reverberation echo that is as strong or stronger than the fish school echo over a wide range including the tracking area (A0) increases.

[0154] Then, the control unit (11) (i.e., fish school tracking module (11b)) sets a reverberation threshold to be compared with the reverberation contrast, and in the process of FIG. 7, when the reverberation contrast is equal to or greater than the reverberation threshold (S107: YES), the control unit (11) sets a tracking area (A0) to be applied at the next transmission timing (next ping) based on the data (volume scattering intensity (SV)) based on the fish school echo and the navigation data (S108 and S110), and when the reverberation contrast is less than the reverberation threshold (S107: NO), the control unit (11) sets the tracking area (A0) to be applied at the next transmission timing (next ping) based on the navigation data (step 110) without using the data of the fish school echo.

[0155] According to this configuration, when the reverberation contrast is equal to or greater than the reverberation threshold, that is, when the degree of distribution of the reverberation echo that is equal to or greater than the fish school echo over a wide range including the tracking area (A0) is low, the tracking area (A0) to be applied to the next transmission timing is set based on the data based on the fish school echo and the navigation data. Thus, the tracking area (A0) to properly track the fish school echo may be set based on the amplitude data. On the other hand, when the reverberation contrast is less than the reverberation threshold, that is, when the degree of distribution of the reverberation echo that is as strong as or stronger than the fish school echo over a wide range including the tracking area is high, the tracking area (A0) to be applied to the next transmission timing is set based on the navigation data without using the data based on the fish school echo. Therefore, it is possible to avoid that the updated tracking area (A0) is greatly affected by the reverberation echo, and the tracking area (A0) to track the fish school echo may be smoothly set based on the navigation data until the influence of the reverberation echo decreases.

[0156] As shown in FIGS. 7 and 8, the control unit (11) (i.e. fish school tracking module (11b)) estimates a fish school area (A1), which is an area of a fish school echo, based on the data (volume scattering intensity (SV)) in the tracking area (A0) (S103); when the index value (reverberation contrast) is equal to or greater than the threshold value (reverberation threshold) (S107: YES), expands the fish school area (A1) by a predetermined magnification to constitute a new tracking area (A0) (S108); corrects the new tracking area (A0) to a position with reference to the origin at the next transmission timing (next ping) based on the navigation data (S110); sets the tracking area (A0) to be applied at the next transmission timing; and when the index value (reverberation contrast) is less than the threshold value (reverberation threshold) (S107: NO), the current tracking area (A0) is corrected to a position with the origin as a reference in the next transmission timing based on the navigation data (S110), and set as the tracking area (A0) to be applied in the next transmission timing.

[0157] According to this configuration, the tracking area (A0) is corrected to a position with the origin as a reference after the movement of the ship (S1). Therefore, the tracking area (A0) may be properly applied in each transmission timing.

[0158] As shown in FIG. 14, the control unit (11) (i.e., fish school tracking module (11b)) changes the magnification used to enlarge the fish school area (A1) so that the magnification increases as the index value (reverberation contrast) increases.

[0159] With this configuration, the width of the new tracking area (A0) may be appropriately adjusted according to the distribution state of the reverberation echo.

[0160] As shown in FIG. 3, the underwater detection device (10) includes the fish quantity index calculation module (11c) for calculating the fish quantity index (Q) based on data (amplitude data) in the fish school area (A1), and the image generation module (11d) for generating the display image (110) including information on the fish quantity index (Q).

[0161] Thus, the fish quantity index (Q) of the fish school tracked by the fish school tracking module (11b) may be updated and displayed as needed. Therefore, the user may smoothly grasp the fish quantity index (Q) of the fish school being tracked.Modification Example 1

[0162] FIG. 15 is a flowchart showing a fish school tracking process according to Modification Example 1, according to an embodiment.

[0163] In the flowchart of FIG. 15, steps (S111) to (S113) are added as compared with the flowchart of FIG. 7. The processes in the other steps of FIG. 15 are the same as those in the corresponding steps of FIG. 7. The processes in steps (S111) to (S113) are performed by the control unit (11) by the function of the fish school tracking module (11b).

[0164] In step (S111), the control unit (11) calculates a fish school contrast indicating the certainty (i.e., degree) that a fish school echo distinguishable from a reverberation echo is included in the tracking area (A0) based on the amplitude data in the tracking area (A0) and the amplitude data in the reference areas (R1) to (R4) of FIG. 10. More specifically, the control unit (11) calculates an average value (SVa0_max) for a range from the largest to several percent (e.g., 5%) of the volume scattering intensities (SV) included in the tracking area (A0), and calculates a median value (SVc1) to (SVc4) of the volume scattering intensities (SV) for each of the reference areas (R1) to (R4). Then, the control unit (11) calculates a value obtained by dividing the average value (SVa0_max) by the maximum value among the median values (SVc1) to (SVc4) as a fish school contrast.

[0165] The average value (SVa0_max) obtained from the tracking area (A0) corresponds to the echo intensity of the core portion of the fish school echo in the tracking area (A0). The greater the echo intensity of the core portion is than the echo intensity of the surrounding reference areas (R1) to (R4), the more clearly the fish schools in the tracking area (A0) are segmented, and the higher the certainty that the fish school echo is included in the tracking area (A0). Therefore, by calculating the fish school contrast as described above, the greater the fish school contrast, the higher the certainty that the fish school echo is included in the tracking area (A0).

[0166] In addition, by using the average value of the volume scattering intensity (SV) ranging from the largest to several percent (e.g., 5%) as the average value (SVa0_max), the representative value of the fish school echo may be properly evaluated regardless of the area width of the tracking area (A0). If the average value (SVa0_max) is the average value of all the volume scattering intensities (SV) in the tracking area (A0), the presence of the fish school echo is difficult to be reflected in the average value under a situation where weak reverberation echo (i.e., sea surface reflection) is distributed over the entire wide tracking area (A0) and strong fish school echo exists in a part of the narrow area. Note that the number percent is not limited to 5%, and may be changed to another appropriate value as long as the above evaluation may be properly performed.

[0167] In addition, by using the median value instead of the average value of the volume scattering intensity (SV) for the reference areas (R1) to (R4), the representative value of the reverberation echo (i.e., sea surface reflection) may be properly evaluated even when a relatively small fish school echo other than the tracking object exists in the reference areas (R1) to (R4).

[0168] The control unit (11) executes a fish school contrast test using the fish school contrast calculated in step (S111) (S112). Specifically, the control unit (11) determines whether the fish school contrast is equal to or greater than a predetermined fish school threshold.

[0169] If the fish school contrast is equal to or greater than the fish school threshold (S113: YES), the control unit (11) advances the process to step (S105). On the other hand, if the fish school contrast is less than the fish school threshold (S113: NO), the control unit (11) skips steps (S105) to (S108) and advances the process to step (S109).

[0170] Here, the fish school threshold is a threshold value indicating whether to display the fish quantity index (Q) calculated from the amplitude data in the fish school area (A1) in step (S104). That is, the fish school threshold defines a boundary indicating whether the fish quantity index (Q) has accuracy suitable for display. The fish school threshold may be set based on actual measurement.

[0171] Here, the acceptance criterion in step (S113) is lower than the acceptance criterion in step (S107). That is, even if the judgment in step (S107) fails, the judgment in step (S113) may pass, but if the judgment in step (S113) fails, the judgment in step (S107) usually fails. Therefore, if the judgment in step (S113) is NO, the process proceeds to step (S109) without performing the processes in steps (S105) to (S108).

[0172] FIG. 16 is a flowchart showing the display processing of information related to the fish quantity index (Q) according to the modification example 1, according to an embodiment.

[0173] The flowchart in FIG. 16 is performed by the control unit (11) using the function of the image generation module (11d). The control unit (11) executes the process in FIG. 16 for each ping.

[0174] The control unit (11) determines whether the fish school contrast test (steps (S112) and (S113) of Figure 15) in the current ping has passed (S201). If the fish school contrast test has passed (S201: YES), the control unit (11) updates the information related to the fish quantity index (Q) displayed on the display unit (17) based on the fish quantity index (Q) calculated in the current ping (step S104 in FIG. 15) (S202).

[0175] On the other hand, if the fish school contrast test has failed (S201: NO), the control unit (11) does not update the information related to the fish quantity index (Q) in the current ping but maintains the display of the information related to the previous fish quantity index (Q) (S203). The control unit (11) then determines whether the failure of the fish school contrast test has continued a predetermined number of times (for example, from a few to a dozen times) including the failure in the current ping (S204).

[0176] If the determination in step S204 is NO, the control unit (11) ends the processing in the current ping. On the other hand, if the determination in step (S204) is YES, the control unit (11) adds a predetermined reminder display to the display of the information related to the fish quantity index (Q) (S205). For example, the control unit (11) displays the information related to the fish quantity index (Q) in an unusual color (For example, red) as the reminder. Alternatively, the control unit (11) may add a mark indicating a reminder (For example, an exclamation mark) near the information related to the fish quantity index (Q). As a result, the control unit (11) terminates the processing in this ping.Effect of Modification Example 1

[0177] As shown in FIG. 15, the control unit (11) (fish school tracking module (11b)) calculates a fish school contrast indicating the certainty that a fish school echo is included in the tracking area (A0) based on the data (volume scattering intensity (SV)) in the tracking area (A0) and the data (volume scattering intensity (SV)) in the reference areas (R1) to (R4) around the tracking area (A0) (S111), executes update processing of the tracking area (A0) based on the index value (reverberation contrast) (S105 to S108) when the fish school contrast is equal to or greater than a predetermined fish school threshold (S113: YES), and sets the tracking area (A0) to be applied at the next transmission timing based on the navigation data (S110) without performing update processing of the tracking area (A0) based on the index value (reverberation contrast) (S105 to S108) when the fish school contrast is less than the fish school threshold (S113: NO),

[0178] According to this configuration, when the fish school contrast is less than the fish school threshold, that is, when the degree of distribution of the reverberation echo that is as strong as or stronger than the fish school echo over a wide range including the tracking area (A0) is considerably high, the updating process of the tracking area (A0) based on the index value (reverberation contrast) is omitted, and the tracking area (A0) to be applied at the next transmission timing is set from the navigation data. Therefore, the updating of the tracking area (A0) may be properly performed while simplifying the processing.

[0179] As described above, the control unit (11) (fish school tracking module (11b)) may be configured to calculate the fish school contrast based on the maximum value of the data (volume scattering intensity (SV)) in the tracking area (A0) and the median value of the data surrounding the tracking area (A0).

[0180] According to this configuration, it is possible to properly calculate the fish school contrast indicating the certainty of including the fish school echo distinguishable from the reverberation echo in the tracking area (A0).

[0181] As shown in FIG. 16, when the fish school contrast is less than the predetermined fish school threshold (S201: NO), the control unit (11) (i.e., image generation module (11d)) continuously displays the information on the fish quantity index (Q) displayed at the previous transmission timing without updating the information on the fish quantity index (Q) (S203).

[0182] According to this configuration, it is possible to suppress the display and presentation to the user of the information on the low-precision fish quantity index (Q) calculated in a state where the degree of distribution of the reverberation echo that is as strong as or stronger than the fish school echo over a wide range including the tracking area (A0) is considerably high. Therefore, it is possible to enhance the reliability of the information on the fish quantity index (Q) to the user.Modification Example 2

[0183] In the above embodiment, the calculation and display of the fish quantity index (Q) are performed together with the tracking processing of the fish school, but it is also possible to extract the invention only in the tracking processing.

[0184] FIG. 17 is a flowchart showing a fish school tracking process according to the modification example 2, according to an embodiment.

[0185] In the flowchart of FIG. 17, the process of step (S104) is omitted from the flowchart of FIG. 7. The process of each step in the flowchart of FIG. 17 is the same as the process of the corresponding step in the flowchart of FIG. 7. Also by this process, the echo of the fish school may be properly tracked as in the process of FIG. 7.

[0186] FIG. 18 is a flowchart showing another fish school tracking process according to the modification example 2, according to an embodiment.

[0187] In the flowchart of FIG. 18, the process of step (S104) is omitted from the flowchart of FIG. 15. The process of each step in the flowchart of FIG. 18 is the same as the process of the corresponding step in the flowchart of FIG. 15. With this processing, as with the processing of FIG. 15, the echo of the fish school may be properly tracked.Other Modification Examples

[0188] In the above embodiment, the volume scattering intensity (SV) obtained from the amplitude data is used for the processing of FIG. 7 or FIG. 15, but other data derived from the amplitude data may be used for the fish school tracking processing. For example, when the width in the distance direction of the tracking area (A0) is smaller than the distance from the transducer (13) to the tracking area (A0), the attenuation of the acoustic wave due to spherical divergence and absorption is substantially constant in the tracking area (A0), and therefore the amplitude data itself may be used for the processing of FIG. 7 or FIG. 15.

[0189] Further, in the above embodiment, a value obtained by dividing the average value (i.e. first average value) of the data (i.e. volume scattering intensity (SV)) included in the tracking area (A0) by the average value (i.e. second average value) obtained from the data (i.e. volume scattering intensity (SV)) of the reference areas (R1) to (R4) is calculated as the reverberation contrast, but a value obtained by dividing the second average value by the first average value may be calculated as the reverberation contrast. In this case, the determination in step (S107) of FIG. 7 is YES when the reverberation contrast is less than the reverberation threshold, and NO when the reverberation contrast is larger than the reverberation.

[0190] In the above embodiment, the data generation module (11a) generates amplitude data, but the data generation module (11a) may further generate the volume scattering intensity (SV) based on the amplitude data.

[0191] In the above embodiment, the display image (110) shown in FIG. 13 is exemplified as the display image (110) including the information related to the fish quantity index (Q), but the display image (110) is not limited to this.

[0192] For example, as shown in FIG. 19, in the echo image (P10), a plot (P18) may be added at regular intervals on the track (P12) of the own ship (S1), and the current fish quantity index value (111) (unit: ton) at the position (time) of each plot (P18) may be added to the right side of the plot (P18). Alternatively, as shown in FIG. 20, at regular intervals on the track (P12) of the own ship (S1), a circular mark (P19) having a diameter corresponding to the current fish quantity index value (111) at that position may be superimposed. In this case, the value of the fish quantity index (Q) at that point may be added near each circle.

[0193] Also by these display images (110), the user may grasp the transition of the fish quantity in the course of the own ship (S1). Therefore, the user may smoothly grasp the position where the fish should be caught.

[0194] Alternatively, a time series graph (112) in which the horizontal axis of FIG. 13 is corrected to the cumulative sailing distance may be displayed. The speed of the ship (S1) during the search for the fish school is not always constant. On the other hand, if the horizontal axis of the time series graph (112) is the cumulative sailing distance, when the user refers to this graph (112) and wants to return to the point where a promising current fish quantity index value (111) has occurred, the point may be easily estimated from the cumulative sailing distance on the horizontal axis of the graph (112).

[0195] In addition, only the fish quantity index (Q) itself may be displayed as the information related to the fish quantity index (Q).

[0196] The magnification shown on the vertical axis of FIG. 14 is an example, and other magnification may be assigned.

[0197] In the above embodiment, the fish quantity index calculation module (11c) and the like are implemented as the functions of the control unit (11) provided by the program stored in the storage unit (12), but these may not necessarily be implemented as the functions provided by the program stored in the storage unit (12). For example, one or more of these functions may be configured by an FPGA field-programmable gate array (FPGA) or hardware in which logic circuits are integrated.

[0198] In addition, various modifications may be made to the embodiments of the present invention as appropriate within the scope of the claims.Terminology

[0199] It is to be understood that not necessarily all objects or advantages may be achieved in accordance with any particular embodiment described herein. Thus, for example, those skilled in the art will recognize that certain embodiments may be configured to operate in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0200] All of the processes described herein may be embodied in, and fully automated via, software code modules executed by a computing system that includes one or more computers or processors. The code modules may be stored in any type of non-transitory computer-readable medium or other computer storage device. Some or all the methods may be embodied in specialized computer hardware.

[0201] Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and / or computing systems that can function together.

[0202] The various illustrative logical blocks and modules described in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a processor. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuitry configured to process computer-executable instructions. In another embodiment, a processor includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor (DSP) and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, some or all of the signal processing algorithms described herein may be implemented in analog circuitry or mixed analog and digital circuitry. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

[0203] Conditional language such as, among others, "can," "could," "might" or "may," unless specifically stated otherwise, are otherwise understood within the context as used in general to convey that certain embodiments include, while other embodiments do not include, certain features, elements and / or steps. Thus, such conditional language is not generally intended to imply that features, elements and / or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements and / or steps are included or are to be performed in any particular embodiment.

[0204] Disjunctive language such as the phrase "at least one of X, Y, or Z," unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and / or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present.

[0205] Any process descriptions, elements or blocks in the flow diagrams described herein and / or depicted in the attached figures should be understood as potentially representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or elements in the process. Alternate implementations are included within the scope of the embodiments described herein in which elements or functions may be deleted, executed out of order from that shown, or discussed, including substantially concurrently or in reverse order, depending on the functionality involved as would be understood by those skilled in the art.

[0206] Unless otherwise explicitly stated, articles such as "a" or "an" should generally be interpreted to include one or more described items. Accordingly, phrases such as "a device configured to" are intended to include one or more recited devices. Such one or more recited devices can also be collectively configured to carry out the stated recitations. For example, "a processor configured to carry out recitations A, B and C" can include a first processor configured to carry out recitation A working in conjunction with a second processor configured to carry out recitations B and C. The same holds true for the use of definite articles used to introduce embodiment recitations. In addition, even if a specific number of an introduced embodiment recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations).

[0207] It will be understood by those within the art that, in general, terms used herein, are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.).

[0208] For expository purposes, the term "horizontal" as used herein is defined as a plane parallel to the plane or surface of the floor of the area in which the system being described is used or the method being described is performed, regardless of its orientation. The term "floor" can be interchanged with the term "ground" or "water surface." The term "vertical" refers to a direction perpendicular to the horizontal as just defined. Terms such as "above," "below," "bottom," "top," "side," "higher," "lower," "upper," "over," and "under," are defined with respect to the horizontal plane.

[0209] As used herein, the terms "attached," "connected," "mated" and other such relational terms should be construed, unless otherwise noted, to include removable, moveable, fixed, adjustable, and / or releasable connections or attachments. The connections / attachments can include direct connections and / or connections having intermediate structure between the two components discussed.

[0210] Numbers preceded by a term such as "approximately," "about," and "substantially" as used herein include the recited numbers, and also represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms "approximately," "about," and "substantially" may refer to an amount that is within less than 10% of the stated amount. Features of embodiments disclosed herein preceded by a term such as "approximately," "about," and "substantially" as used herein represent the feature with some variability that still performs a desired function or achieves a desired result for that feature.

[0211] It should be emphasized that many variations and modifications may be made to the above-described embodiments, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.List of Reference Numerals

[0212] 10 Underwater detection device 11 Control unit 11a Data generation module 11b Fish school tracking module 11c Fish quantity index calculation module 11d Image generation module 12 Storage unit 13 Transducer 13a Ultrasonic Oscillator 14 Transmission processing module 15 Reception processing module 16 Transmission / reception switching unit 17 Display unit 18 Display processing module 19 Input unit 20 Input processing module 110 Display image 111 Current fish quantity index value 112 Graph S1 Ship SP1 Scanning plane TB1 Transmission beam RB1 Reception beams Q Fish quantity index A1 Fish school area A11, A12 Area P10 Echo image P11 Image P12 Track P13 Straight line P14, P15, P16 Circular boundary line P17 Hatched Range P18 Plot P19 Circular mark A0 Tracking area W01, W02, W11, W12 Width C01, C11 Center point SV Volume scattering intensity V01, V02 Outer vertical lines V11, V12 Inner vertical lines H01, H02 Outer horizontal lines H11, H12 Inner horizontal lines R1, R2, R3, R4 Reference area

Claims

1. An underwater detection device (10) comprising: 　a transmission processing module (14) configured to transmit ultrasonic waves to a plurality of ultrasonic oscillators (13a) included in a transducer (13) installed on a bottom of a ship (S1) at transmission timings at predetermined intervals; 　a data generation module (11a) configured to form a plurality of reception beams (RB1) in a scanning range based on electrical signals output from the plurality of ultrasonic oscillators (13a) during a reception period after the transmission timings, and generate data on echo intensities at respective positions in the scanning range; and 　a fish school tracking module (11b) configured to update a tracking area (A0) of a fish school based on the data and navigation data related to a movement of the ship (S1) on which the transducer (13) is installed, wherein 　the fish school tracking module (11b) determines whether to use the data based on the fish school echo in the tracking area (A0) for updating the tracking area (A0) based on a determination as to whether an index value indicating how large the echo intensity of the entire tracking area (A0) is relative to the echo intensity around the tracking area (A0) is equal to or greater than a predetermined threshold value.

2. The underwater detection device (10) according to claim 1, wherein 　the fish school tracking module (11b) 　　updates the tracking area (A0) based on the data based on the fish school echo and the navigation data when the index value is equal to or greater than the predetermined threshold value, and 　　updates the tracking area (A0) based on the navigation data without using the data based on the fish school echo when the index value is less than the predetermined threshold value.

3. The underwater detection device (10) according to claim 1, wherein 　the fish school tracking module (11b) calculates, as the index value, a reverberation contrast indicating a degree to which reverberation echoes having the echo intensity equal to or greater than that in the tracking area (A0) are distributed over a wide range including the tracking area (A0), and performs a determination based on the reverberation contrast.

4. The underwater detection device (10) according to claim 3, wherein 　the reverberation contrast is calculated from a first average value of the data in the tracking area (A0) and a second average value of the data around the tracking area (A0).

5. The underwater detection device (10) according to claim 4, wherein 　the reverberation contrast is calculated by dividing the first average value by the second average value.

6. The underwater detection device (10) according to claim 3, wherein 　the reverberation contrast is calculated so that the higher the degree of distribution, the smaller the reverberation contrast.

7. The underwater detection device (10) according to claim 6, wherein 　the fish school tracking module (11b) 　　sets a reverberation threshold to be compared with the reverberation contrast as the threshold value; 　　when the reverberation contrast is equal to or greater than the reverberation threshold, sets the tracking area (A0) to be applied at a next transmission timing based on the data based on the fish school echo and the navigation data; and 　　when the reverberation contrast is less than the reverberation threshold, sets the tracking area (A0) to be applied at the next transmission timing based on the navigation data without using the data based on the fish school echo.

8. The underwater detection device (10) according to claim 1, wherein 　the fish school tracking module (11b) 　　estimates a fish school area (A1) that is an area of the fish school echo based on the data in the tracking area (A0); 　　when the index value is equal to or greater than the threshold value, expands the fish school area (A1) by a predetermined magnification to constitute a new tracking area (A0); corrects the new tracking area (A0) to a position with reference to the position of the transducer (13) at the next transmission timing based on the navigation data and sets to the tracking area (A0) to be applied at the next transmission timing; and 　　when the index value is less than the threshold value, corrects the current tracking area (A0) to a position with reference to the position of the transducer (13) at the next transmission timing based on the navigation data and sets to the tracking area (A0) to be applied at the next transmission timing.

9. The underwater detection device (10) according to claim 8, wherein 　the fish school tracking module (11b) changes the predetermined magnification used for enlarging the fish school area (A1) so that the predetermined magnification increases as the index value increases.

10. The underwater detection device (10) according to claim 8, further comprising: 　a fish quantity index calculation module (11c) configured to calculate a fish quantity index (Q) based on the data in the fish school area (A1); and 　an image generation module (11d) configured to generate a display image (110) including information on the fish quantity index (Q).

11. The underwater detection device (10) according to claim 1, wherein 　the fish school tracking module (11b) 　　calculates a fish school contrast indicating a certainty that the fish school echo is included in the tracking area (A0) based on the data in the tracking area (A0) and the data around the tracking area (A0); 　　when the fish school contrast is equal to or greater than a predetermined fish school threshold, executes the update process of the tracking area (A0) based on the index value; and 　　when the fish school contrast is less than the fish school threshold, sets the tracking area (A0) to be applied at the next transmission timing based on the navigation data without performing the update process of the tracking area (A0) based on the index value.

12. The underwater detection device (10) according to claim 11, wherein 　the fish school tracking module (11b) calculates the fish school contrast based on a maximum value of the data in the tracking area (A0) and a median value of the data around the tracking area (A0).

13. The underwater detection device (10) according to claim 11, wherein 　the image generation module (11d) continuously displays an information related to the fish quantity index (Q) displayed at the previous transmission timing without updating the information related to the fish quantity index (Q) when the fish school contrast is less than a predetermined fish school threshold.

14. A method for tracking fish school in an underwater detection device (10), comprising: 　transmitting, by a transmission processing module (14), ultrasonic waves to a plurality of ultrasonic oscillators (13a) included in a transducer (13) installed on a bottom of a ship (S1) at transmission timings at predetermined intervals; 　forming, by a data generation module (11a), a plurality of reception beams (RB1) in a scanning range based on electrical signals output from the plurality of ultrasonic oscillators (13a) during a reception period after the transmission timing, and generating data on echo intensities at respective positions in the scanning range; and 　updating, by a fish school tracking module (11b), a tracking area (A0) of the fish school based on the data and navigation data related to a movement of the ship (S1) on which the transducer (13) is installed, wherein 　the fish school tracking module (11b) determines whether to use the data based on the fish school echo in the tracking area (A0) for updating the tracking area (A0) based on a determination as to whether an index value indicating how large the echo intensity of the entire tracking area (A0) is relative to the echo intensity around the tracking area (A0) is equal to or greater than a predetermined threshold value.

15. A program that makes perform to a computer of an underwater detection device (10): 　a function of transmitting ultrasonic waves to a plurality of ultrasonic oscillators (13a) included in a transducer (13) installed on a bottom of a ship (S1) at transmission timings at predetermined intervals; 　a function of forming a plurality of reception beams (RB1) in a scanning range based on electrical signals output from the plurality of ultrasonic oscillators (13a) during a reception period after the transmission timings, and generating data on echo intensities at respective positions in the scanning range; and 　a function of updating a tracking area (A0) of a fish school based on the data and navigation data on the movement of the ship (S1) on which the transducer (13) is installed, wherein 　the function of updating the tracking area (A0) comprising a function of determining whether to use the data based on the fish school echo in the tracking area (A0) for updating the tracking area (A0) based on a determination as to whether an index value indicating how large the echo intensity of the entire tracking area (A0) is relative to the echo intensity around the tracking area (A0) is equal to or greater than a predetermined threshold value.

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