GB2529063A

GB2529063A - Detecting device, detecting method and program

Info

Publication number: GB2529063A
Application number: GB1513548.6A
Authority: GB
Inventors: Akira Okunishi
Original assignee: Furuno Electric Co Ltd
Current assignee: Furuno Electric Co Ltd
Priority date: 2014-08-08
Filing date: 2015-07-31
Publication date: 2016-02-10
Anticipated expiration: 2035-07-31
Also published as: JP6339446B2; JP2016038323A; GB2529063B; GB201513548D0

Abstract

A detecting device 1 includes a transducer 10 configured to transmit detection signals and receive reflection waves from a target object as reception signals, a threshold calculator (161, figure 2C) configured to extract, from the reception signals, signals in a single detection direction as a data row, select target data from the data row in time ordering, and calculate a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data, and an amplitude limiter (162, figure 2C) configured to compare the threshold limit calculated by the threshold calculator (161, figure 2C) with an amplitude of the target data, and limit the amplitude of the target data when the amplitude of the target data exceeds the threshold. The device may also have a beam former (15, figure 2B) and a filter, with the threshold calculator and amplitude limiter placed after the beam former but before the filter. The device may also have a quadrature detector to convert the received signals into complex signals. A method and computer program of detecting a target object are also given.

Description

DETECTING DEVICE, DETECTING METHOD AND PROGRAM

Technical Field

[00011 This disclosure relates to a detecting device, detecting method and program. with which a detecting signal is transmitted and a reflection wave from a target object is received.

Background of the Invention

[0002] Conventionally, as detecting devices, ultrasonic detecting devices mounted on ships and for transmitting ultrasonic detection signals underwater and receiving reflection waves from target objects (e.g., a school of fish) are known. With these ultrasonic detecting devices, the reception signal may include an ultrasonic wave transmitted from another ship (interference signal).

[0003] For this reason, such a conventional ultrasonic detecting device calculates an amplitude ratio between a reception signal obtained in a most-recent transception operation and a reception signal obtained in a previous transception operation. and when the amplitude ratio is a predetermined value or higher, the conventional ultrasonic detecting device determines that the reception signal obtained in the most-recent transception operation is interference. For example, JP4017943B discloses such an ultrasonic detecting device.

[0004] However, in the conventional method, interference cannot he removed sufficiently when the frequency of occurrence thereof increases. For example, if interference signals are received at the same timing as each other in the most-recent transception operation and the previous transception operation, the amplitude ratio between the reception signal obtained in the most-recent transception operation and the reception signal obtained in the previous transception operation becomes small, causing difficulty in determining interference.

Summary of the Invention

[00051 This disclosure is made in view of the above situations and aims to provide a detecting device, detecting method and program, with which interference can suitably he removed even if a frequency of interference occurrence increases.

[00061 According to a first aspect of this disclosure, a detecting device is provided. The detecting device includes a transducer configured to transmit detection signals and receive reflection waves from a target object as reception signals. a threshold calculator configured to extract, from the reception signals, signals in a single detection direction as a data row, select target data from the data row in time ordering, and calculate a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data, and an amplitude limiter configured to compare the threshold calculated by the threshold calculator with an amplitude of the target data, and limit the amplitude of the target data when the amplitude of the target data exceeds the threshold.

[00071 Thus, with the detecting device of this disclosure, since the threshold is calculated in the single detection direction, even if interference signals are received at the same timing over a plurality of transception operations. the removal of interference can suitably be achieved. Moreover, for example, in a case of implementing amplification processing (TVG processing) corresponding to a detection distance, if an interference signal is inputted at a short period at the same intensity, the intensity of the interference signals may become higher than an intensity of a reflection wave from the target object as the reflection point is farther from the device. However, with the detecting device of this disclosure, since the threshold is calculated by using the plurality of data close to the target data, even in the case of implementing the TYG processing, the removal of the interference can suitably be achieved.

[00081 Note that, the threshold may he calculated based on amplitudes of a plurality of data of the data row previous (in other words, distance closer to the device) or succeeding (in other words, distance farther from the device) to the target data in time ordering.

Furthermore, the threshold may be calculated based on amplitudes of a plurality of data of the data row including data previous and data succeeding to the target data in time ordering.

[0009] Any known method may he adopted for calculating the threshold. For example, the threshold is calculated based on an average value, a median value, or a mode value of the amplitudes.

[0010] Moreoyer, the threshold calculator preferably divides the plurality of data of the data row close to the target data into a plurality of groups, each of the plurality of groups including a predetermined number of continuous data. The threshold calculator preferably calculates the threshold based on a value obtained by using amplitudes of the predetermined number of continuous data of the respective groups. For example, the threshold calculator calculates the average value for each group and sets a minimum value among the average values to the threshold. Thus, even if the interference signal is inputted as an extremely large amplitude pulse in the single detection direction, a situation in which the threshold becomes excessively high due to an influence of the interference signal does not occur, and the removal of the interference can suitably be achieved.

[00111 Moreover, a total time width to which the plurality of data used in the calculation of the threshold corresponds is preferably longer than a time width of an interference signal and shorter than a time width of each of the detection signals. Thus, the removal of the interference signal solely can suitably be achieved without removing an echo received after reflecting on the target obiect.

[0012] Moreover, the detecting device preferably includes a beam former configured to form a beam in a predetermined detection direction by combining a plurality of the reception signals, and a filter configured to perform predetermined filtering. The threshold calculator and the amplitude limiter are preferably disposed to operate after the beam former and before the filter. The number of the reception signals after the beam formation (number of detection directions) is generally smaller than the number of the reception signals before the beam formation (number of ultrasonic transducer elements). Therefore, the operation load can be reduced by disposing the threshold calculator and the amplitude limiter to operate after the beam former. Moreover, if the filter performs a pulse compression in a case where a time width of the interference signal is short, the interference signal may he extended timewise and, thus, the effects of the interference removal may degrade. Therefore, by disposing the threshold calculator and the amplitude limiter to operate before the filter, the interference signal is not extended timewise and, thus, the removal of the interference signal can suitably be achieved.

[00131 Moreover, the detecting device preferably includes a quadrature detector configured to convert each of the reception signals into a complex signal. In this case, the threshold calculator preferably extracts, from the complex signals, signals in a single detection direction as a data row, preferably selects target data from the data row in time ordering, and preferably calculates a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data. The amplitude limiter preferably compares the threshold calculated based on the amplitudes of the data row with an amplitude of target data, and when the amplitude of the target data exceeds the threshold, the amplitude of the complex signal corresponding to the target data is preferably limited while a phase thereof is conserved. Thus, the amplitude of the complex signal corresponding to the target data solely can be limited while the phase thereof is conserved.

[0014] Moreover, according to a second aspect of this disclosure, a method of detecting a target object is provided. The method includes transmitting detection signals and receiving reflection waves from a target object as reception signals, extracting, from the reception signals, signals in a single detection direction as a data row, selecting target data from the data row in time ordering, calculating a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data, comparing the calculated threshold with an amplitude of the target data, and limiting the amplitude of the target data when the amplitude of the target data exceeds the threshold.

[0015] Moreover, according to a third aspect of this disclosure, a program of detecting a target object is provided. The program includes transmitting detection signals and receiving reflection waves from a target object as reception signals, extracting, from the reception signals, signals in a single detection direction as a data row, selecting target data from the data row in time ordering, calculating a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data, comparing the calculated threshold with an amplitude of the target data, and limiting the amplitude of the target data when the amplitude of the target data exceeds the threshold.

Effect(s) of the Invention [0016] According to this disclosure, even if a frequency of interference occurrence increases, the removal of the interference can suitably be achieved.

Brief Descriptiofi of the Drawings

[0017] 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: [0017.1] Fig. 1 A is a perspective view for describing underwater detection performed by a scanning sonar which is one example of a detecting device of this disclosure, and Fig. lB is an external view of a plurality of ultrasonic transducer elements; [0017.2] Fig. 2A to Fig. 2C are block diagrams illustrating a configuration of the scanning sonar; [0017.3] Figs. 3A and 3B show views illustrating examples of an image (detecting image) displayed on a display unit, respectively; [0017.4] Figs. 4A to 4C show charts for describing a calculating method of a threshold; [0017.5] Figs. 5A to SC show charts for describing application examples of the calculating method of the threshold; and [0017.6] Figs. 6A and 6B show charts for describing effects of interference removal.

Detailed Description

[0018] Fig. 1A is a perspective view for describing underwater detection performed by a scanning sonar I which is one example of a detecting device of this disclosure, and Fig. 1 B is an external view of a plurality of ultrasonic iransducer elements 100.

[0019] The scanning sonar I is mounted on a ship (hereinafter, may he referred to as "the ship concerned" or simply "the ship"). A transducer 10 of the scanning sonar 1 is attached to a bottom of the ship, for example. The scanning sonar 1 detects underwater by using ultrasonic waves. The ultrasonic waves are transmitted to spread radially by the plurality of ultrasonic transducer elements 100 as illustrated in Fig. lB. The ultrasonic waves transmitted underwater reflect on target object(s) (e.g., a school of fish) and are received as reception signals by the plurality of ultrasonic transducer elements 100. As illustrated in Fig. IA, the scanning sonar 1 combines the reception signals of the plurality of ultrasonic transducer elements 100 to compose a beam 60 having a directivity of a predetermined angle 0 on a horizontal plane. The scanning sonar 1 generates a plurality of beams 60 by switching the ultrasonic transducer elements 100 to be used in the combining. Then, the scanning sonar 1 generates an image signal based on an amplitude of each beam 60, and displays an echo image on a display unit 30.

[0020] Moreover, a fish finder 2 is mounted on the ship. A transducer of the fish finder 2 is attached to the bottom of the ship. The fish finder 2 is also one example of the detecting device. The fish finder 2 transmits an ultrasonic wave directly below the ship and receives an ultrasonic wave therefrom. The scanning sonar 1 and the fish finder 2 are disposed close to each other. Therefore, the ultrasonic wave radiated from the fish finder 2 is received as an interference signal by the scanning sonar I. Thus, the scanning sonar 1 removes the interference signal included in the reception signals.

[0021] Fig. 2A is a block diagram illustrating a configuration of the scanning sonar 1.

The scanning sonar 1 includes the transducer 10, a transception switch 11, a transmission unit 12, a reception unit 20, and the display unit 30. Fig. 2B is a block diagram illustrating a configuration of the reception unit 20. The reception unit 20 includes an AID converter 13, a quadrature detector 14, a beam former 15, an interference remover 16, a filter 17, and an image signal generator 18.

[0022] The transducer 10 includes a cylindrical housing ISO as illustrated in Fig. lB. The transducer 10 includes the plurality of ultrasonic transducer elements 100 arrayed in a predetermined pattern, in a circumferential side face of the cylindrical housing 150.

[0023] The transmission unit 12 outputs a pulse-shaped transmission signal. The transmission signal is outputted to the transducer 10 via the tnmsception switch 11. The transducer 10 converts the inputted transmission signal into an ultrasonic pulse which is a detection signal, and radiates the ultrasonic pulse underwater from the plurality of ultrasonic transducer elements 100. Each ultrasonic transducer elements 100 receives, as the reception signal, a reflection wave from the target object. The operation of transmitting a single ultrasonic pulse from the plurality of ultrasonic transducer elements 100 and receiving the reflection waves before the next transmission of an ultrasonic pulse is referred to as a single transception operation.

[0024] The transception switch 11 outputs the reception signals received by the plurality of ultrasonic transducer elements 100 of the transducer 10, to the AID converter 13 of the reception unit 20.

[0025] The A/D converter 13 converts each of inputted reception signals in analog format into digital format at a predetermined sampling period, and outputs them to the quadrature detector 14.

[0026] The quadrature detector 14 perfoims a quadrature detection on each of the reception signals received by the plurality of ultrasonic transducer elements 100, so as to extract an I (In-phase) signal component and a Q (Quadrature-phase) signal component. When the extracted number of pairs of the I and Q signal components is N, they are expressed as complex signals comprised of a row of N-pieces of data: I10]-i-jQ[01, I[11-i-jQ[1] l[N-11+jQ[N-11. An absolute value of each complex signal corresponds to an amplitude of the corresponding reception signal received by one of the plurality of ultrasonic transducer elements 100, and an argument of the complex signal corresponds to a phase of the reception signal. The reception signal converted into the complex signal is outputted to the beam former 15.

[0027] The beam former 15 forms a beam having a directivity in a predetermined detection direction by combining the reception signals received by the plurality of ultrasonic transducer elements 100 in the predetermined detection direction. Moreover, the beam former 15 can form beams in a plurality of detection directions by switching the plurality of ultrasonic transducer elements 100 to be used in the combining.

[0028] The reception signals combined as a single beam signal of the corresponding detection direction are inputted into the interference remover 16. The interference remover 16 removes the interference signal component (the interference signal described above) included in the inputted beam signal of the detection direction. The beam signal, after the interference signal component is removed therefrom, is inputted into the filter 17.

[0029] The filter 17 performs various kinds of filtering on the inputted beam signal. For example, the filter 17 performs a correlation between a reference signal (e.g., transmission signal) and the beam signal, and pulse-compresses the beam signal. Moreover, the filter 17 limits a frequency band of the beam signal. for example.

[0030] The image signal generator 18 generates an image signal based on the filtered beam signal, and outputs it to the display unit 30. For example. the image signal generator 18 generates an image signal of a tone corresponding to the amplitude of the beam signal of each detection direction, and causes the display unit 30 to display the echo image.

Moreover, the image signal generator 18 matches the number of data in the beam signal with the number of display pixels of the display unit 30.

[0031] Further, the image signal generator 18 is built therein with a memory (not illustrated) configured to temporally store the image signals obtained by a single or a plurality of transmissions immediately previous to a latest transmission. Thus, the image signal generator 18 can correlate between a previous image signal and a latest image signal.

For example, the image signal generator 18 compares the image signals obtained from continuous two (latest and immediately previous) transmissions, so as to select an image signal with lower intensity with respect to each pixel and output it. Thus, the interference signal component with relatively high intensity can be removed without lowering the intensity of the echo image. Note that, the image correlation by the image signal generator

18 is not essential processing in this disclosure.

[0032] In this manner, the display unit 30 displays the images as illustrated in Figs. 3A and 3B. Figs. 3A and 3B show views illustrating examples of the image (detection image) displayed on the display unit 30, respectively, in which Fig. 3A illustrates a detection image in a case where the interference remover 16 does not perform the interference removal (conventional configuration) and Fig. 3B illustrates a detection image in a case where the interference remover 16 performs the interference removal (configuration of this embodiment). The display unit 30 displays the detection image corresponding to azimuth and distance centering on a position of the ship. In the example of Fig.3A, a noise image component corresponding to a water surface reflection is displayed around the ship.

Moreover, an image component corresponding to screw noise is displayed in the rear of the ship. Furthermore, an echo image component indicating the school of fish is displayed at the upper right of the detection image.

[0033] In the case where the transducer of the fish finder 2 is disposed closely to the transducer 10 of the scanning sonar 1, the interference signal component is received periodically, corresponding to a transmission period of the fish finder 2. In this example, the transmission period of the scanning sonar 1 is longer than that of the fish finder 2.

Therefore, as illustrated in Fig. 3A, an interference image component with high intensity which is caused by the interference signal component is displayed at every predetermined distance within the detection image of the scanning sonar 1. The interference remover 16 removes the interference signal component obtained at the every predetermined distance.

[0034] Fig. 2C is a block diagram illustrating a configuration of the interference remover 16. The interference remover 16 includes a threshold calculator 161 and an amplitude limiter 162.

[0035] The threshold calculator 161 receives the beam signal of each detection direction outputted from the beam former 15. The threshold calculator 161 calculates a threshold for determining whether the beam signal includes interference based on the amplitude of the beam signal of the detection direction.

[0036] Figs. 4A 10 4C show charts for describing a calculating method of the threshold, in which the lateral axis indicates distance and the vertical axis indicates amplitude. When a beam signal of a certain detection direction is comprised of a row of N-pieces of data expressed in complex numbers (complex data): I[0]+jQ[0], IF l]-i-jQ[ 1] I[N-1]+jQ[N-11, the threshold calculator 161 calculates the amplitudes of the complex data, in other words, absolute values of the complex data (r[0]. r[1] r[N-1I). respectively. Further, for each of the complex data (hereinafter, referred to as the "target data"), the threshold calculator 161 sequentially calculates the threshold Th based on the amplitudes of a plurality of pieces (M-pieces: McN) of complex data among which the latest data is obtained immediately previous to the target data. Specifically, for the (n+M)-th target data, an average value among M-pieces of amplitude data configuring the amplitude data row (r[n], r[n÷ II, r[n+M-1I) is obtained. The threshold Th may be either one of the average value itself and a value obtained by multiplying the average value by a predetermined coefficient C (e.g., C=3). Alternatively, a predetermined constant may he added to the average value, or a predetermined constant may be added to the value obtained by multiplying the average value by the predetermined coefficient. Moreover, the calculating method of the threshold Th is not limited to be based on the average value, and may be based on a median value, a mode value, etc. [0037] The threshold calculator 161 outputs the calculated threshold Th of each target data, to the amplitude limiter 162. The threshold calculator 161 repeats the above calculation of the threshold Th while changing the value of "n" from 0 (zero) to N-M. In other words, the threshold Th is calculated for each of M-th to (N-1)-th target data. For (0)-th to (M-1)-th target data, a predetermined constant is outputted as the threshold Th.

[0038] The amplitude limiter 162 receives the beam signal of each detection direction outputted from the beam former 15. Further, the amplitude limiter 162 compares the threshold Th with the amplitude of the target data, sequentially for each of the target data.

When the amplitude Z (absolute value) of the target data is higher than the threshold Th, the -10-ampHtude limiter 162 limits the ampHtude Z (absolitte value) of the target data to the thresh&d Th or lower. In other words, the values of the I signal I[n+M] and the Q signal Q[n+M] of the (n÷M)-th target data are replaced with Th/ZxI[n+M] and Th/ZXQ[n÷MI, respectively.

[00391 Thus, the phase of the complex signal is conserved as it is, while only the amplitude (absolute value) is limited to the threshold Th or lower. As a result, the interference remover 16 can remove the interference signal component without influencing the pulse compression performed by the following filter 17. Note that, the interference remover 16 maybe disposed to operate after the filter 17. However, if the filter 17 performs the pulse compression in a case where the pulse width of the interference signa' component is shorter than that of the transmission signal, the interference signa' component may be extended timewise and, thus, the effects of the interference remova' may degrade. Therefore, the interference remover 16 is preferably disposed to operate before the filter 17. Moreover, the interference remover 16 may be disposed to operate before the beam former 15.

However, the number of the beam signals after the beam formation (number of detection directions) is generally smaller than the number of the reception signals before the beam formation (number of ultrasonic transducer elements 100). Therefore, the interference remover 16 is preferably disposed to operate after the beam former 15, so as to reduce the operation load.

[00401 Note that, in this embodiment, the thresh&d calculator 161 cacuFates each threshold based on continuous M-pieces of data among which the atest data is obtained immediately previous to the target data; however, the threshold may be calculated based on a row of M-pieces of amplitude data which does not include the data obtained immediately previous to the target data (r[n-11, r[nl r[n+M-21), for example. Moreover, it is not essential to use the eniire row of M-pieces of amplitude daui o calculate the threshold. For example, in a row of eight-pieces of amplitude data (r[nI. r[n+1] r[n+7]), a row of amplitude data obtained by decimating every other data (r[nI, r[n-i-21 r[n-i-6]), in other words four-pieces of data, may be used to calculate the threshold.

[00411 Moreover, the threshold calculation may he performed by using M-pieces of amplitude data succeeding to the target data in time ordering (corresponding to the distance farther from the scanning sonar), as illustrated in Fig. 4B. Alternatively, as illustrated in Fig. 4C, both of a plurality of data previous and a plurality of data succeeding to the target data in time ordering may be used. Note that, to use the data succeeding to the target data in time ordering, a memory is provided to store reception signals in a single transception operation and the threshold is calculated in the state where all the reception signals are stored.

[0042] Note that, a total time width to which the M-pieces of data correspond may be any time width; however, it is preferably longer than a time width of the interference signal component and shorter than the time width of the detection signal. In other words, the total time width to which the M-pieces of data correspond is preferably longer than the pulse width of the transmission signal of the fish finder 2 and shorter than the pulse width of the transmission signal of the scanning sonar 1. If the total time width to which the M-pieces of data correspond is shorter than the pulse width of the transmission signal of the fish finder 2, the interference signal component may not be removed, and if the total time width to which the M-pieces of data correspond is longer than the pulse width of the transmission signal of the scanning sonar 1, the echo caused by the ultrasonic wave outputted from the scanning sonar 1 may be removed. Therefore, by designing the total time width to which the M-pieces of data correspond to he longer than the pulse width of the transmission signal of the fish finder 2 and shorter than the pulse width of the transmission signal of the scanning sonar 1, the interference can suitably be removed without removing the echo received after reflecting on the target object (e.g., the school of fish).

[0043] As described above, the scanning sonar I calculates the threshold based on the plurality of data close to the target data, sequentially for each of the target data in the data rows of the respective detection directions in the beam signal. Thus, even if the interference signal components are received at the same timing as each other over a plurality -12-of transception operations, the suitable removal of the interference signal components solely can he achieved.

[0044] Moreover, in a case of implementing TVG processing, if an interference signal component is inputted at a short period at the substantially same intensity, the intensity of interference may become higher than the intensity of the reflection wave from the target object as the reflection point is farther from the scanning sonar 1. However, since the scanning sonar 1 calculates the threshold by using the plurality of data close to the target data sequentially for each target data, even in the case of implementing the TVG processing, the suitable removal of the interference signal component solely can be achieved.

[0045] Next, Figs.5A to 5C show charts for describing application examples of the calculating method of the threshold. The threshold calculator 161 of the application example divides the M-pieces of data immediately previous to the target data (amplitude data row) into a plurality of groups and calculates the threshold based on amplitudes (absolute values) of each group. Each group includes a plurality of pieces of continuous data. In this example, for the amplitude r[n+ 121 of the target data, the threshold calculator 161 divides the amplitude data row into a first group of four pieces of data (r[n], r[n+1I r[n+31). a second group of four pieces of data (r[n+4]. r[n-i-5] r[n+71). and a third group of four pieces of data (r[n+81, r[n+9]. ..., r[n+11I). Further, the threshold calculator 161 obtains an average value of the amplitude data row of the first group, an average value of the amplitude data row of the second group, and an average value of the amplitude data row of the third group. The threshold calculator 161 selects the minimum value among the average values obtained in the respective groups. Finally, the threshold calculator 161 calculates the threshold Th by multiplying the selected minimum value by the predetermined coefficient C (e.g., C=3). Note that, the minimum value may be adopted as the threshold as it is, a predetermined constant may he added to the minimum value, or a predetermined constant may be added to the value obtained by multiplying the minimum value by the predetermined coefficient. Moreover, the threshold Th may be calculated based on, for example, median values or mode values obtained in the respectively groups, -13-without limiting to the average values.

[0046] Thus, even if the interference remover 16 receives an interference signal component with extremely high amplitude regarding a certain detection direction, the threshold does not become excessively high. and the interference remover 16 can suitably remove interference. For example, in a case where the target data is a part of an interference signal component, the interference signal component may also be included in the third group closest thereto in time ordering, causing the average value of the third group to be high.

Even in such a case, the average values of the other groups do not become excessively high.

and therefore, the threshold calculated finally does not become excessively high.

[0047] Note that, also in the case of dividing into the plurality of groups, for example, as illustrated in Fig. SB, the M-pieces of data succeeding to the target data in time ordering (corresponding to the distance farther from he scanning sonar) may he divided into the plurality of groups. Alternatively, as illustrated in Fig. SC, the M-pieces of data may be divided into a plurality of groups by using both of a plurality of data previous and a plurality of data succeeding to the target data in time ordering. Note that, in the example of Fig. SC, the target data r[n-i-6] of the data row of the second group is excluded from the target of the threshold calculation.

[0048] Moreover, in this embodiment, the example in which the number of data to be used for the threshold calculation is twelve and the threshold calculator 161 divides the twelve-pieces of data into three groups each including four pieces of data is described; however, the number of data to he used for the threshold calculation is not limited to this.

The number of data forming each group is also not limited to four. For example, twenty-four pieces of data may be divided into three groups each including eight pieces of data. Moreover, the number of groups is not limited to three, and it may be divided into two groups or a larger number of groups (e.g., five). Further, the value selected from the average values of the respective groups is not limited to the minimum value. For example, a median value among the average values of the respective groups may be selected or the second largest value among the average values of the respective groups may be selected. -14-

[0049] Figs. 6A and 6B show charts for describing effects of the interference removal, in which Fig. 6A is a chart illustrating a data row in a case where the TVG processing is performed without the interference removal and Fig. 6B is a chart illustrating a data row in a case where the TYG processing is performed after the interference removal. In both charts of Figs. 6A and 6B, the lateral axis indicates distance and the vertical axis indicates amplitude (absolute value). The data rows in Figs. 6A and 6B correspond to the data rows in the detection direction of the straight lines in Figs. 3A and 3B (straight line passing through the echo image component of the school of fish displayed at the upper right of the detection image).

[0050] As illustrated in Figs. 6A and 6B, with the interference removal by the interference remover 16, the intensity of data corresponding to interference can solely he reduced without lowing the intensities of the data corresponding to the echoes of the school of fish.

[0051] Note that, in this embodiment, the example in which the scanning sonar 1 is applied as the detecting device and the interference signal component is the transmission signal of the fish finder 2 is described. However, the interference remover 16 is not limited to he provided to the scanning sonar 1. For example, when a solid-state radar using a semiconductor device is compared with a radar using a magnetron, a pulse width of a transmission signal of the radar using the magnetron is shorter than a pulse width of a transmission signal of the solid-state radar. Moreover, an amplitude of the transmission signal of the radar using the magnetron is higher than an amplitude of the transmission signal of the solid-state radar. Therefore, also with the solid-state radar configured to transmit an electromagnetic wave as the detection signal. by applying the interference removal by the interference remover 16 described in the embodiment, an interference signal component from the radar using the magnetron can suitably be removed. Moreover, in a case where transducers of a plurality of fish finders are attached to, for example, the bottom of the ship, even if transmission signals of the respective fish finders have different pulse widths, the interference removal of the interference remover 16 can be applied.

[0052] Note that, the configuration of the interference remover 16 of this embodiment can he achieved in detecting devices configured to transmit detection signals and receive, as reception signals, reflection waves from target objects, by software (program) executed by the detecting devices. -16-

Claims

CLAIMS1. A detecting device (:1), comprising: a transducer (10) configured to transmit detection signals and receive reflection waves from a target object as reception signals; a threshold calculator (161) configured to extract, from the reception signals, signals in a single detection direction as a data row, select target data from the data row in time ordering, and calculate a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data; and an amplitude limiter 062) configured to compare the threshold calculated by the threshold calculator (161) with an amplitude of the target data, and limit the amplitude of the target data when the amplitude of the target data exceeds the threshold.
2. The detecting device (1) of claim 1, wherein the threshold calculator (161) calculates the threshold based on amplitudes of a plurality of data of the data row previous or succeeding to the target data in time ordering.
3. The detecting device (1) of claim 1, wherein the threshold calculator (161) calculates the threshold based on amplitudes of a plurality of data of the data row including data previous and data succeeding to the target data in time ordering.
4. The detecting device (1) of any one of claims 1 to 3. wherein the threshold calculator (161) calculates the threshold based on an average value of the amplitudes of the plurality of data of the data row close to the target data in time ordering.
5. The detecting device (1) of any one of claims 1 to 4. wherein the threshold calculator (161) divides the plurality of data of the data row close to the target data into a plurality of groups, each of the plurality of groups including a predetermined number of -17-continuous data, and wherein the threshold calculator (161) calculates the threshold based on a value obtained by using amplitudes of the predetermined number of continuous data of the respective groups.
6. The detecting device (1) of any one of claims 1 to 5, wherein a total time width to which the plurality of data used in the calculation of the threshold corresponds is longer than a time width of an interference signal and shorter than a time width of each of the detection signals.
7. The detecting device (1) of any one of claims I to 6, Further comprising: a beam former (I 5) conFigured to form a beam in a predetermined detection direction by combining a plurality of the reception signals; and a filter (17) configured to perform predetermined filtering, wherein the threshold calculator (161) and the amplitude limiter (162) are disposed to operate after the beam former (15) and before the filter (17).
8. The detecting device (1) of any one of claims 1 to 7. further comprising a quadrature detector (14) configured to convert each of the reception signals into a complex signal, wherein the threshold calculator (161) extracts, from the complex signals, signals in a single detection direction as a data row, select target data from the data row in time ordering, and calculates a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data, and wherein the amplitude limiter (162) compares the threshold calculated based on the amplitudes of the data row with an amplitude of target data, and when the amplitude of the target data exceeds the threshold, the amplitude of the complex signal corresponding to the target data is limited while a phase thereof is conserved.
9. A method of detecting a target object, comprising: transmitting detection signals and receiving reflection waves from a target object as reception signals; extracting, from the reception signals, signals in a single detection direction as a data row, selecting target data from the data row in time ordering, and calculating a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data; and comparing the calculated threshold with an amplitude of the target data, and limiting the amplitude of the target data when the amplitude of the target data exceeds the threshold.
10. A program of detecting a target object, comprising: transmitting detection signals and receiving reflection waves from a target object as reception signals; extracting, from the reception signals, signals in a single detection direction as a data row, selecting target data from the data row in time ordering, and calculating a threshold for the target data based on amplitudes of a plurality of data of the data row close to the target data; and comparing the calculated threshold with an amplitude of the target data, and limiting the amplitude of the target data when the amplitude of the target data exceeds the threshold.
11. A detecting device substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.
12. A method of detecting a target object substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.
13. A program of detecting a target object substantially as hereinbefore -19-described with reference to andlor as shown in the accompanying drawings.-20 -