GB2540272A

GB2540272A - Method of detecting school of fish, program and fish finder

Info

Publication number: GB2540272A
Application number: GB1611570.1A
Authority: GB
Inventors: Takeuchi Hisamitsu; Misonoo Satoshi; Li Ming; Fu Gang
Original assignee: Furuno Electric Co Ltd
Current assignee: Furuno Electric Co Ltd
Priority date: 2015-07-06
Filing date: 2016-07-01
Publication date: 2017-01-11
Anticipated expiration: 2036-07-01
Also published as: JP6554345B2; JP2017015645A; GB201611570D0; CN106338734B; CN106338734A; GB2540272B

Abstract

A fish finder 1 comprises a transducer that transmits an ultrasonic wave and receives a reflected reception signal. An echo image memory 181 stores echo images generated based on the received reception signal. When in a state where at least one of the echo images is read from the echo image memory, an operation receiver 10 receives an instruction to change the read echo image. A detecting module 171 detects fish based on the received reception signal and detection information is stored in a detection result memory 172. An image processor 18 reads an echo image generated before the at least one echo image from the echo image memory, changes the echo image to output and superimposes the corresponding detection result on the changed echo image in response to the instruction. The fish finder may further comprise a display unit 19 and a positional information detector. The operation receiver may receive a specifying operation of a geographical position and the image processor can then change the echo image according to the specified geographical position.

Description

METHOD OF DETECTING SCHOOL OF FISH, PROGRAM AND FISH FINDER

Technical Field [0001] This disclosure relates to a fish finder, which transmits ultrasonic waves underwater, receives echoes, and detects a school of fish, etc.

Background [0002] Conventionally, as examples of underwater detection apparatuses, fish finders, such as those disclosed in JP3027258B and JP2567641B, are known.

[0003] For example, JP3027258B discloses the fish finder which includes a configuration which displays a histogram of various body lengths of detected fish. Further, JP2567641B discloses the fish finder which includes a configuration which stores, in a memory, previous echo images which are worth a plurality of screens, and displays on a single display screen a current echo image and one or more of the previously-displayed echo images.

[0005] However, the fish finder of JP2567641B merely displays the previous images arbitrary specified through a key (value) input, and it is difficult to display a school of fish desired by a user, at any position on the display screen upon a preference of the user. For example, when a school of fish is currently displayed at a left end of the display screen, even if the user is to look at an image thereof for a timing at which the school of fish was displayed at the center of the display screen, he/she does not know what value to input to display such an image, and thus, the school of fish may reach out of range of the display screen or be displayed at a different position from the center (e.g., right end).

Summary [0006] The purpose of this disclosure relates to providing a fish finder, which is capable of displaying a school of fish desired by a user at any position of a display screen upon a preference of the user, and displaying a detection result of the school of fish on the display screen in a superimposed manner.

[0007] According to one aspect of the present disclosure, a fish finder is provided. The fish finder includes a transducer configured to transmit an ultrasonic wave and receive a reception signal caused by the transmitted ultrasonic wave, an echo image memory configured to store echo images, each of the echo images generated based on the reception signal received by the transducer, an operation receiver configured to receive, in a state where at least one of the echo images is read from the echo image memory, a display operation to change the read echo image, a detecting module configured to detect a school of fish based on the reception signal received by the transducer, a detection result memory configured to store a detection result of the detecting module, and an image processor configured to read from the echo image memory an echo image that is generated before the at least one of the echo images, continuously change the echo image to output, and superimpose the detection result on the changed echo image to output, corresponding to the display operation.

[0008] As above, the fish finder continuously changes the echo image that is generated before the at least one of the echo images, and displays the detection result of the school of fish by superimposing it on the changed echo image, corresponding to the display operation. For example, in a case where the superimposed school of fish is currently displayed at a left end of a display screen of a display unit, when a user performs an operation to continuously shift the echo image rightward to move the display position of the school of fish toward a center of the display screen (e.g., an operation of rotating leftward a rotary knob such as a rotary switch), the display position of the school of fish shifts toward the center from the left end. Here, the detection result of the school of fish is superimposed on the echo image. Therefore, a case where the school of fish desired by the user reaches out of range of the display screen or is displayed at a different position from the center (e.g., right end) does not occur, and the user can confirm the detection result of the desired school of fish as well as the echo image simultaneously.

[0009] Note that, the phrase “continuously change the echo image” means changing the echo image at least pixel by pixel among display pixels of the display unit. Needless to say that changing the echo image for every plurality of pixels (e.g., two pixels) corresponding to the display operation also corresponds to the continuous change.

Effects [0010] According to this disclosure, a school of fish desired by a user can be displayed at any position of a display screen upon a preference of the user, and a detection result of the school of fish can be displayed on the display screen in a superimposed manner.

Brief Description of the Drawings [0011] The present disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which the like reference numerals indicate like elements and in which: [0011.1] Fig. 1 is a block diagram illustrating a configuration of a fish finder 1 according to one embodiment of this disclosure; [0011.2] Fig. 2 is a block diagram illustrating a configuration of a signal processor 17; [0011.3] Fig. 3 is a view illustrating reception signals; [0011.4] Figs. 4A and 4B are views illustrating generation of echo image components; [0011.5] Fig. 5 is a view illustrating echo image components stored in an echo image memory 181 and echo image components read by an image processor 18; [0011.6] Fig. 6 is a view illustrating an example of a display screen; [0011.7] Fig. 7 is a view illustrating echo image components stored in the echo image memory 181 and echo image components read by the image processor 18; [0011.8] Figs. 8A and 8B are views illustrating examples of the display screen; [0011.9] Figs. 9A and 9B are flowcharts illustrating operation of the fish finder 1; [0011.10] Fig. 10 is a block diagram illustrating a configuration of a fish finder 1A according to a modification; and [0011.11] Figs. 11A and 11B are views illustrating examples of the display screen.

Detailed Description [0012] Fig. 1 is a block diagram illustrating a fish finder 1 according to one embodiment of this disclosure. The fish finder 1 includes a user interface (may be referred to as the “operation receiver”) 10, a transducer 11, a transmission/reception switch 12, a transmission circuit 13, a controller 14, a reception circuit 15, an A/D converter 16, a signal processor 17, an image processor 18, and a display unit 19.

[0013] The controller 14 is configured using hardware, such as a microprocessor, and operates the fish finder 1 overall. The controller 14 reads a program from a built-in memory (not illustrated) to perform particular processing. For example, the controller 14 sets a transmission cycle of the transmission circuit 13, a detection range, etc. according to various operations through the user interface 10 (e.g., an instructive input for setting the detection range). Moreover, the controller 14 sets a sampling cycle of the A/D converter 16, and instructs the signal processor 17 to perform various processings, and instructs the image processor 18 to perform various processings.

[0014] The image processor 18 generates an echo image by having the vertical axis of a display screen as a depth direction and the horizontal axis thereof as a time direction. The display unit 19 displays the echo image generated by the image processor 18.

[0015] The transmission circuit 13 inputs a pulse-shaped signal to the transducer (transmitting and receiving unit) 11 via the transmission/reception switch 12 built therein with a trap circuit. An input timing, level, pulse width, etc. of the signal are controlled by the controller 14. The transducer 11 is an oscillator attached to a bottom of a ship and outputs an ultrasonic wave underwater according to the pulse-shaped signal received from the transmission circuit 13.

[0016] The ultrasonic wave outputted by the transducer 11 reflects on a target object, such as a school of fish and/or a water bottom, and is received as echo(es) (reception signal set (simply referred to as “reception signal” below)). The transducer 11 outputs the reception signal corresponding to intensity(ies) of the received echo(es), to the reception circuit 15 via the transmission/reception switch 12.

[0017] The reception circuit 15 amplifies the received reception signal and outputs it to the A/D converter 16. The A/D converter 16 converts the reception signal into a digital signal at a particular sampling cycle and outputs it to the signal processor 17.

[0018] Fig. 2 is a block diagram illustrating a functional configuration of the signal processor 17. The signal processor 17 includes a reception signal memory 170, a detecting module 171, and a detection result memory 172. The reception signal memory 170 stores the reception signal received from the A/D converter 16.

[0019] Fig. 3 is a view illustrating reception signals stored in the reception signal memory 170. The reception signal memory 170 sequentially stores data of the reception signal obtained in one measurement (one ping) in the depth direction at a particular resolution (at every particular period of time from a transmission of the ultrasonic wave). In this embodiment, the reception signal memory 170 stores data columns corresponding to a plurality of measurements. For example, in a latest (current) measurement, data with a smallest time difference from the signal transmission to the signal reception (at a shallowest depth) is stored as M(0, 0), and other data of the reception signal is stored as M(0, 1) to M(0, n) sequentially according to the resolution in the depth direction. Similarly, in a measurement of one measurement before the latest measurement (hereinafter, referred to as the “previous measurement”), data at the shallowest depth is stored as M(l, 0) and sequentially as M(l, 1) to M(l, n) according to the resolution in the depth direction. Also similarly, in a measurement of two measurements before the latest measurement (hereinafter, referred to as the “second previous measurement”), data at the shallowest depth is stored as M(2, 0) and sequentially as M(2, 1) to M(2, n) according to the resolution in the depth direction.

[0020] In the example of Fig. 3, the case of storing the data columns for the three measurements of current, previous, second previous measurements is shown; however, the number of stored data columns may be set based on the volume of the reception signal memory 170. When measurements corresponding to over the set number of data columns are performed, the stored data is sequentially erased from the oldest data column and is updated by the latest data column.

[0021] Next, the image processor 18 generates the echo image to be displayed on the display unit 19, based on the reception signals stored in the reception signal memory 170. Specifically, the image processor 18 converts each of the reception signals sequentially stored in the reception signal memory 170, into echo image components in association with depth according to the time lapse from the transmission of the ultrasonic wave concerned, and outputs the echo image components to the display unit 19.

[0022] Figs. 4A and 4B are views illustrating generation of the echo image components. First, the image processor 18 converts each reception signal read from the reception signal memory 170 into components (data) of which total number corresponds to a total number of pixels in the vertical direction (vertical screen resolution) of the display unit 19. This converted data is echo image components for one measurement (one ping). For example, as illustrated in Fig. 4A, among the data obtained in the latest measurement M(0, 0) to M(0, n), M(0, 0) and M(0, 1) are averaged to be an echo image component f(0, 0) corresponding to a shallowest position.

[0023] The image processor 18 sequentially averages the plurality of data to generate echo image components f(0, 0) to f(0, m) for the respective pixels. The echo image components generated as above are the echo image components for the latest ping. Note that, the conversion manner is not limited to the example of Fig. 4A. For example, weighting may be performed according to the depth, or the data may be converted by holding a peak (highest value extraction).

[0024] The image processor 18 stores the echo image components obtained by the conversion as described above, in an echo image memory 181. The contents of the echo image memory 181 are updated in every measurement. Therefore, as illustrated in Fig. 4B, the echo image memory 181 stores echo image components for a plurality of measurements. In this example, echo image components regarding a measurement performed at an earliest timing among all the echo image components in the image memory 181 are f(l, 0) to f(l, m), and echo image components regarding a measurement performed at a latest timing among all the echo image components in the image memory 181 are f(0, 0) to f(0, m). The echo image memory 181 stores echo image components regarding the measurement performed at the earliest timing (echo image components f(l, 0) to f(l, m)) to the measurement performed at the latest timing (echo image components f(0, 0) to f(0, m)).

[0025] Further, as illustrated in Fig. 5, the image processor 18 reads echo image components for one screen of the display unit 19 (e.g., corresponding to vertical and horizontal resolutions of the display unit 19) from the echo image memory 181, and outputs them to the display unit 19. As a result, the echo images for a plurality of measurements are displayed on the display unit 19.

[0026] As illustrated in Fig. 6, the display unit 19 displays the echo images of which “ping” is assigned to the horizontal axis and “depth” is assigned to the vertical axis. In the example of Fig. 6, an echo image 201 indicating a part of a school of fish is displayed on a left side on the display screen, and an echo image 200 indicating another school of fish is displayed on a right side on the display screen. Further, an echo image of a water bottom is displayed on a bottom side of the display screen.

[0027] In the example of Fig. 6, a water bottom depth (“302m” in Fig. 6) that is a result of a water bottom detection, and school of fish information (a histogram 203 in Fig. 6) are also displayed.

[0028] The water bottom depth and the school of fish information are information outputted by the detecting module 171 of the signal processor 17. As illustrated in Fig. 2, the detecting module 171 reads the reception signal from the reception signal memory 170, analyzes it, and performs detections of the school of fish, water bottom, etc.

[0029] The school of fish detection includes at least a detection of a fish body length. The fish body length is detected, for example, by assuming that a reception signal above a particular threshold indicates a school of fish, and based on at least one of a size (the number of sampled data), an average intensity, a length in the depth direction (average length), etc. of the school of fish. The detecting module 171 may also detect a fish kind. The fish kind is distinguished based on a matching level (similarity) with a reference echo of the school of fish.

[0030] The water bottom depth is detected, for example, based on a timing at which a reception signal above a certain threshold is received, or a timing at which a differential value reaches a high peak.

[0031] The detecting module 171 stores the various information detected as above (detection result) in the detection result memory 172. Here, the detection results are stored in association with information of the measurement timing of the analyzed reception signal (e.g., time point).

[0032] Further, the controller 14 instructs the detecting module 171 to output the detection result corresponding to an area specified within the display screen of the display unit 19 (e.g., an area 202 in Fig. 6). The position and size of the area 202 are specified through an operation of the user interface 10 by a user. The controller 14 outputs information indicating a timing at which the echo image within the specified area 202 is acquired (measurement timing), to the detecting module 171.

[0033] The detecting module 171 reads a detection result of which the measurement timing matches the measurement timing regarding the specified area 202 among the detection results stored in the detection result memory 172, and outputs it to the controller 14. The controller 14 outputs the detection result received from the detecting module 171, to the image processor 18. The image processor 18 superimposes the detection result received from the controller 14, on the echo image components and outputs them to the display unit 19.

[0034] Thus, within the display screen of the display unit 19, the histogram 203 illustrated in Fig. 6 is displayed as the detection result. Note that, the display mode of the detection result is not limited to displaying the histogram 203, but may also be simply displaying the fish body length as a numerical value, for example. Further, in a case where the user operates the user interface 10 to change a range of the fish body length displayed in the histogram 203, the image processor 18 changes the range of the fish body length to be displayed. Specifically, the detecting module 171 stores in the detection result memory 172 the detection result for a range wider than the actual range displayed in the histogram 203. When the user performs the operation to change (specify) the range of the fish body length, the image processor 18 extracts only the detection result for the specified range, superimposes it on the echo image components and outputs them to the display unit 19.

[0035] Further, in a case where the user operates the user interface 10 to display a previous echo image, the image processor 18 reads the previous echo image components from the image memory 181, continuously changes the echo image components to be outputted, and superimposes the detection result of the school of fish on the echo image components.

[0036] For example, in a case where the user interface 10 includes a rotary knob, when the user rotates the rotary knob, the controller 14 receives the rotation operation as an operation to display the previous echo image. The controller 14 causes the image processor 18 to continuously change the echo image to be displayed, corresponding to the display operation received through the user interface 10.

[0037] For example, a case where the user performs an operation to continuously shift, on the display screen as illustrated in Fig. 6, the echo images rightward to move the echo image 201 of the school of fish displayed at the left end toward a center of the display screen (e.g., an operation of rotating the rotary knob leftward) is described.

[0038] Once the user interface 10 receives the operation of rotating the rotary knob leftward, the controller 14 instructs the image processor 18 to read echo image components for a timing earlier than a current timing by a period of time corresponding to the rotation amount. As illustrated in Fig. 7, the image processor 18 reads from the echo image memory 181 the echo image components for the timing earlier by the instructed time period, and changes the echo image components to be outputted. Thus, the echo image displayed on the display unit 19 changes continuously as the rotary knob is rotated. In other words, as the user rotates the rotary knob leftward, as illustrated in Fig. 8A, the echo image 201 of the school of fish shifts toward the center of the display screen from the left end.

[0039] As above, the fish finder 1 displays the previous echo image while continuously changing it, corresponding to the display operation from the user. Here, the detection result of the school of fish is superimposed on the echo image. Therefore, a case where a school of fish desired by the user reaches out of range of the display screen or is not displayed at an intended position (e.g., center) does not occur, and the user can confirm the detection result of the desired school of fish as well as the echo image simultaneously.

[0040] Note that, the phrase “continuously change the echo image” means changing the echo image at least pixel by pixel among the display pixels of the display unit 19. Needless to say that changing the echo image for every plurality of pixels (e.g., two pixels) also corresponds to the continuous change.

[0041] Note that in the example of Fig. 8A, even when the user rotates the rotary knob, the area 202 does not shift from the position specified within the display screen. Since the school of fish is not detected within the area 202 in the example of Fig. 8A, nothing is displayed in the histogram 203. However for example, as illustrated in Fig. 8B, when the user rotates the rotary knob further leftward to shift the echo image 201 of the school of fish to the inside of the area 202, the detection result of the school of fish indicated as the echo image 201 is read from the detection result memory 172. Therefore, the information of the detection result of the school of fish indicated as the echo image 201 is displayed in the histogram 203.

[0042] Next, the operation of the fish finder 1 is described with reference to the flowcharts of Figs. 9A and 9B. First the fish finder 1 performs the transmission and reception of the ultrasonic wave (si 1: wave transmitting and receiving step). Further, the fish finder 1 processes the reception signal (si2).

[0043] The image processor 18 generates the echo image in association with depth according to the time lapse from the transmission of the ultrasonic wave (sl3). Further, the signal processor 17 performs the school of fish detection which includes the fish body length detection (detecting step).

[0044] Then, the image processor 18 stores the generated echo image in the echo image memory 181 (updates the contents of the echo image memory 181) (echo image storing step), and the signal processor 17 stores the detection result in the detection result memory 172 (sl4: detection result storing step).

[0045] Meanwhile, the fish finder 1 determines whether the user has performed the operation to display the previous echo image through the user interface 10 (s21: operation receiving step). For example, in the case where the user interface 10 includes the rotary knob, when the user rotates the rotary knob, the controller 14 receives the rotation operation as the operation to display the previous echo image. Further, in a case where the user interface 10 includes arrow keys, the controller 14 may receive the operation to display the previous echo image when a left or right arrow key is pushed.

[0046] If the operation to display the previous echo image has not been performed, the image processor 18 reads a latest echo image for one screen of the display unit 19, which corresponds to the vertical and horizontal resolutions of the display unit 19 (s22).

[0047] On the other hand, if the user has performed through the user interface 10 the operation to display the previous echo image, the image processor 18 reads the echo image corresponding to the display operation from the echo image memory 181 (s23). Here, the image processor 18 continuously changes the echo image to be displayed, by changing the echo image read from the echo image memory 181, corresponding to the display operation received through the user interface 10 (the rotation of the rotary knob). Therefore, the echo image continuously changes corresponding to the rotation amount of the rotary knob. For example, when the user rotates the rotary knob leftward in the state of Fig. 6, the echo image 201 of the school of fish at the left end continuously shifts toward the center of the display screen to become the state illustrated in Fig. 8A. Thus, the user can shift the echo image which he/she wants to look at, to the intended position (e.g., center) while visually confirming the echo image. Further, when the user rotates the rotary knob leftward in the state of Fig. 8A, the echo image of the school of fish shifts toward the right side of the display screen as illustrated in Fig. 8B. Then, when the echo image 201 of the school of fish reaches the inside of the area 202, the detection result of the school of fish indicated as the echo image 201 is read from the detection result memory 172 (s24). Next, in response to the display operation, the image processor 18 performs display processing in which the previous echo image is read, the echo image to output is continuously changed, and the detection result is superimposed on the echo image (s25: image processing step).

[0048] Next, a modification of this disclosure is described. Fig. 10 is a block diagram illustrating a configuration of a fish finder 1A according to the modification. Common parts with Fig. 1 are denoted with the same reference characters, and the description thereof is omitted. The fish finder 1A includes a positional information detector 50 in addition to the configuration of the fish finder 1.

[0049] The positional information detector 50 includes a GPS, for example. The controller 14 receives positional information (latitude and longitude information) from the positional information detector 50 every time the transmission and reception of the ultrasonic wave is performed, and stores the positional information in a positional information memory (not illustrated) at every measurement timing. The positional information is stored along with information indicating the measurement timing (e.g., time point).

[0050] The image processor 18 reads latest positional information from the controller 14, and displays it at a particular position within the display screen of the display unit 19 as illustrated in Fig. 11 A, for example.

[0051] Further, as illustrated in Fig. 11B, the image processor 18 may acquire from the controller 14 the positional information corresponding to the measurement timing at which the echo image for the area 202 specified by the user through the user interface 10 is acquired (e.g., the measurement timing corresponding to a right end position of the area 202), and display it along with the detection result (histogram 203). Needless to say that the image processor 18 may display both of positional information corresponding to a latest measurement timing and the positional information corresponding to the measurement timing at which the echo image for the specified area 202 is acquired.

[0052] When the user operates the user interface 10 to display a previous echo image, the image processor 18 changes the positional information to acquire from the controller 14, corresponding to the display operation received through the user interface 10. For example, the image processor 18 acquires positional information corresponding to a measurement timing at which an echo image currently displayed at the right end of the display screen of the display unit 19 is acquired, and displays it. Also in a case of displaying positional information corresponding to a measurement timing at which the echo image for the specified area 202 is acquired, the image processor 18 acquires the corresponding positional information from the controller 14 and displays it.

[0053] Note that, when the user operates the user interface 10 to input the positional information, the image processor 18 may read the echo image corresponding to the inputted positional information from the echo image memory 181 and causes the display unit 19 to display it. Thus, in a case where, for example, the user has passed through a fishing ground and knows the position thereof, the user can review the underwater situation when he/she passed through the fishing ground.

[0054] Further, in a case where the fish finder 1 is connected to a plotter via a communication function, such as a LAN, the fish finder 1 may display an echo image of a position specified by the user on the plotter. In this case, the positional information detector 50 may separately be provided to the plotter so that the plotter acquires positional information, or the fish finder 1A and the plotter may use the same positional information detector 50 to share the positional information. Thus, the user can, by simply specifying on the plotter the position of the fishing ground which he/she has passed through, review the underwater situation when he/she passed through the fishing ground.

Claims

1. A fish finder (1, 1 A), comprising: a transducer (11) configured to transmit an ultrasonic wave and receive a reception signal caused by the transmitted ultrasonic wave; an echo image memory (181) configured to store echo images, each of the echo images generated based on the reception signal received by the transducer (11); an operation receiver (10) configured to receive, in a state where at least one of the echo images is read from the echo image memory (181), a display operation to change the read echo image; a detecting module (171) configured to detect a school of fish based on the reception signal received by the transducer (11); a detection result memory (172) configured to store a detection result of the detecting module (171); and an image processor (18) configured to read from the echo image memory (181) an echo image that is generated before the at least one of the echo images, continuously change the echo image to output, and superimpose the detection result on the changed echo image to output, corresponding to the display operation.

2. The fish finder (1, 1A) of claim 1, wherein the detecting module (171) detects information including a fish body length of the school of fish.

3. The fish finder (1, 1A) of claim 1 or 2, further comprising a display unit (19) configured to display at least one of the echo images read from the echo image memory (181), wherein the operation receiver (10) receives a specifying operation of an area for which the school of fish is detected, within the echo image displayed on the display unit (19), and wherein the detection result superimposed on the echo image is acquired by reading, from the detection result memory (172), a detection result corresponding to the area specified through the operation receiver (10).

4. The fish finder (1, 1A) of claim 3, wherein the area is fixed at a position specified within a display screen of the display unit (19) even when the echo image is continuously changed corresponding to the display operation.

5. The fish finder (1, 1A) of any one of claims 1 to 4, further comprising a positional information detector (50) configured to detect geographical position information, wherein each of the echo images stored in the echo image memory (181) is associated with the geographical position information.

6. The fish finder (1, 1A) of claim 5, wherein the operation receiver (10) receives a specifying operation of a geographical position, and wherein the image processor (18) changes the echo image according to the specified geographical position.

7. A program configured to execute: a wave transmitting and receiving step of transmitting an ultrasonic wave and receiving a reception signal caused by the transmitted ultrasonic wave; an echo image memory storing step of storing echo images, each of the echo images generated based on the reception signal received in the wave transmitting and receiving step; an operation receiving step of receiving, in a state where at least one of the echo images stored in the echo image memory storing step is read, a display operation to change the read echo image; a detecting step of detecting a school of fish based on the reception signal received in the wave transmitting and receiving step; a detection result storing step of storing a detection result obtained in the detecting step; and an image processing step of reading one of the echo images stored in the echo image memory storing step, continuously changing the echo image to output, and superimposing the detection result on the changed echo image to output, corresponding to the display operation, the one of the echo images being generated before the at least one of the echo images.

8. A method of detecting a school of fish, comprising: a wave transmitting and receiving step of transmitting an ultrasonic wave and receiving a reception signal caused by the transmitted ultrasonic wave; an echo image memory storing step of storing echo images, each of the echo images generated based on the reception signal received in the wave transmitting and receiving step; an operation receiving step of receiving, in a state where at least one of the echo images stored in the echo image memory storing step is read, a display operation to change the read echo image; a detecting step of detecting the school of fish based on the reception signal received in the wave transmitting and receiving step; a detection result storing step of storing a detection result obtained in the detecting step; and an image processing step of reading one of the echo images stored in the echo image memory storing step, continuously changing the echo image to output, and superimposing the detection result on the changed echo image to output, corresponding to the display operation, the one of the echo images being generated before the at least one of the echo images.

9. A fish finder substantially as described herein with reference to and as illustrated in the accompanying drawings.

10. A method of detecting fish substantially as described herein with reference to the accompanying drawings.