GB2425595A

GB2425595A - Acoustic echo sounder for locating and quantifying a target

Info

Publication number: GB2425595A
Application number: GB0605579A
Authority: GB
Inventors: Yasushi Nishimori; Kouzo Tokuyama; Koji Tokuda; Hiromune Matsumoto
Original assignee: Furuno Electric Co Ltd
Current assignee: Furuno Electric Co Ltd
Priority date: 2005-03-29
Filing date: 2006-03-20
Publication date: 2006-11-01
Anticipated expiration: 2026-03-20
Also published as: GB0605579D0; JP4776960B2; NO20061410L; JP2006275755A; GB2425595B

Abstract

An acoustic echo sounder, particularly used as a fish finder, includes a plurality of transducer elements 41a-41n with associated circuits 4a-4n for detecting acoustic echoes reflected from a sounding area. A receiver 1 includes a first detector 10 for detecting a target region (i.e. the direction of the target) and a second detector 20 for determining quantitative data about the target (e.g. quantity of fish in a school). The first detector 10 causes the signal intensity data to saturate to a certain extent while maintaining information on directions of the target. The second detector 20 amplifies the echo signals from the individual circuits 4a-4n while maintaining a quantitative relationship between one echo signal and another, which does not cause the signal intensity data to saturate. A data synthesiser 16 outputs data to a display 2 which presents an echo sounding picture based on the signal intensity data obtained by the first detector 10 together with the quantitative data (e.g. fish quantity) obtained by the second detector 20.

Description

TITLE OF THE INVENTION

ACOUSTIC TRANSCEIVER AND ACOUSTIC DETECTION SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an acoustic transceiver of an echo sounding apparatus and an acoustic detection system for detecting a target by transmitting an acoustic sounding signal toward a sounding area and receiving an acoustic echo returning from the sounding area.

2. Description of the Related Art

A conventionally known example of an apparatus designed to detect underwater targets, such as fish schools, is a sonar which detects the underwater targets by transmitting an acoustic pulse signal underwater and receiving acoustic echoes reflected by the targets. For example, Japanese Patent Application Publication Nos. 2001- 99914 and 2004-347319 disclose this kind of apparatuses.

FIG. 21 is a block diagram generally showing the configuration of an acoustic receiver used in a typical

sonar of the prior art.

As shown in FIG. 21, the acoustic receiver includes a receiver section 101, display section 102, an interface 103 and a transducer unit including a plurality of receiving transducer circuits 104a-lQ4n (where n is a whole number) The receiving transducer circuits 104a-lO4n respectively include transducer elements 141a-l4ln, amplifiers 142a-142n and analog-to-digital (A/D) converters 104a-104n, the transducer elements l4la-l4ln being arranged in a specified geometrical pattern. The individual transducer elements l4la- l4ln receive acoustic echoes from underwater objects and convert the acoustic echoes into electrical echo signals. The amplifiers 142a-142n amplify the echo signals by a specific ratio, or gain, and the A/D converters 143a-143n convert the amplified echo signals from analog to digital form. The receiving transducer circuits 104a-lO4n constitute receiving channels CHO-CHn-l, respectively. The digitized echo signals are delivered to the receiver section 101 through the interface 103.

The receiver section 101 includes preamplifiers illa- llln, a receiving beamformer 112, a detecting circuit 113 and a plurality of post-amplifiers 114a-ll4m (where m is a whole number). The preamplifiers 111a-llln are time- varied-gain (TVG) amplifiers for amplifying the echo signals fed from the respective receiving channels CHO-CHn- 1 with specific gain which is controllably varied with time.

The receiving beamformer 112 forms a pencillike narrow receiving beam which is steered through a plurality of predefined directions around the transducer unit by using a phased array technique in which the n-channel echo signals are synthesized by controlling phases and weights thereof to produce receiving beam data Bl-Bm. The detecting circuit 113 demodulates the individual receiving beam data Bl-Bm fed from the receiving beamformer 112 to produce sounding data for the individual beam directions. The post-amplifiers 114a-114m amplify the sounding data fed from the detecting circuit 113 with specific gain in a controlled fashion to produce signal intensity data for the individual beam directions and outputs the gain-controlled signal intensity data to the display section 102.

The display section 102 generates image data from the signal intensity data entered and provides an underwater sounding image on-screen.

A conventional acoustic receiver typically produces saturated echo signals to ensure reliable detection of targets, such as fish schools. The acoustic receiver of FIG. 21 controls gain chiefly by the preamplifiers llla- llln.

FIGS. 22(A), 22(B) and 22(C) are diagrams showing how the signal intensity data for the individual beam directions vary with the gain applied to the echo signals by the preamplifiers llla-llln. As illustrated in FIGS. 22(A)-22(C), the gain applied to the echo signals successively increases in the order of (A), (B) and (C) FIGS. 22(D), 22(E) and 22(F) are schematic representations of on-screen images obtained with gain settings shown in FIGS. 22(A), 22(3) and 22(C), respectively, in which broken lines represent display threshold levels. Echoes having signal intensities not less than the threshold level are displayed on-screen as indicated by shaded speckles in FIGS. 22(D) -22 (F) The preamplifiers llla-llln adjust the gain applied to the echo signals to increase signal intensity levels of desired targets (fish schools) as discussed above while preventing an increase of the levels of side lobes or unwanted signal components. In this way, the preamplifiers illa-ilin enhance level differences between the targets (fish schools) and noise, making it possible to detect and display fish school echoes in a reliable fashion.

If the echo signals input into the acoustic receiver are intentionally saturated as mentioned above for precisely determining the locations of fish schools, however, relative signal intensity levels represented by the signal intensity data derived from one beam direction and another would not be in the same proportion as relative levels of the original echo signals received from the corresponding beam directions. In other words, the signal intensity levels represented by the signal intensity data would not be quantitatively correlated with the levels of the echo signals received from the individual beam directions. Thus, the conventional acoustic receiver configured as shown in FIG. 21 can not determine the exact quantities of the detected fish schools. If the gain of the preamplifiers llla-llln is lowered to determine the exact quantities of the fish schools, on the contrary, the acoustic receiver can not correctly detect the fish schools.

One previously known approach to the resolution of the aforementioned problem is to adjust the gain of the post- amplifiers 114a-ll4m. If the gain of the post-amplifiers ll4a-ll4rn is adjusted, however, not only the fish school echoes but also the unwanted signal components would be amplified to high levels and displayed on- screen as shown in FIGS. 23(A)-23(C) FIGS. 23(A), 23(B) and 23(C) are diagrams showing how the signal intensity data for the individual beam directions vary with the gain applied to the echo signals by the post- amplifiers ll4a-ll4m. As illustrated in FIGS. 23(A)-23(C), the gain applied to the echo signals successively increases in the order of (A), (B) and (C) FIGS. 23(D), 23(E) and 23(F) are schematic representations of on-screen images obtained with gain settings shown in FIGS. 23(A), 23(3) and 23(C), respectively, in which broken lines represent display threshold levels. Echoes having signal intensities not less than the threshold level are displayed on-screen as indicated by shaded speckles in FIGS. 23(D) -23 (F) StJ(ARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide an acoustic transceiver capable of reliably detecting and exactly quantifying a target from an acoustic echo received. It is another object of the invention to provide a sonar employing such an acoustic transceiver capable of locating and quantifying a target with high reliability and accuracy.

According to the invention, an acoustic transceiver includes a plurality of transducer circuits for transmitting the acoustic sounding signals toward the sounding area, receiving acoustic echoes reflected from the sounding area, and converting the acoustic echoes into electrical echo signals, a target region detector for detecting a target region within the sounding area based on the echo signals fed from the individual transducer circuits, a quantitative data detector for detecting quantitative data of the target existing within the sounding area by amplifying the echo signals fed from the individual transducer circuits while maintaining a quantitative relationship between one echo signal and another, and a quantitative data synthesizer for synthesizing the quantitative data detected by the quantitative data detector with the target region detected by the target region detector.

In the acoustic transceiver thus configured, the plurality of transducer circuits transmit acoustic sounding signals toward the sounding area and receive reflected acoustic echoes, from which electrical echo signals are generated. The target region detector detects a target region from the echo signals and the quantitative data detector detects quantitative data of the target while maintaining a relationship between intensities of one echo signal and another. The quantitative data synthesizer outputs the quantitative data allocated to the corresponding target region detected. This permits simultaneous recognition of the location of the target (e.g., a fish school) and the quantitative data thereof (e.g., target strengths) with high reliability and accuracy.

According to one aspect of the invention, the quantitative data synthesizer includes an integrator for generating integrated quantitative data by integrating the quantitative data detected within the target region, and a physical quantity calculator for estimating a specific kind of physical quantity data of the detected target from the integrated quantitative data.

In the acoustic transceiver thus configured, the integrator generates the integrated quantitative data by integrating the quantitative data of each target while the physical quantity calculator estimates the physical quantity data, such as the size (volume) of each target from the integrated quantitative data. This makes it possible to precisely determine physical quantity, such as fish quantity of each fish school.

According to another aspect of the invention, the target region detector includes a binarization circuit for binarizing the echo signals by comparing the level of each echo signal with a specific threshold, wherein the quantitative data synthesizer synthesizes results of binarization by the binarization circuit with the quantitative data output from the quantitative data detector.

In the acoustic transceiver thus configured, the binarization circuit of the target region detector outputs binary-valued data, such as a level "O representing a region where no target is detected and a level "1" representing a region where a target is detected. The quantitative data synthesizer outputs the quantitative data allocated to the corresponding target region detected.

This permits simultaneous recognition of the location of the target (e.g., a fish school) and the quantitative data thereof (e.g., target strengths) with high reliability and accuracy.

According to another aspect of the invention, the acoustic transceiver further includes a display device for displaying pieces of the data generated by the quantitative data synthesizer.

In the acoustic transceiver thus configured, the display device displays the individual pieces of the data, collectively referred to as sounding data, output from the quantitative data synthesizer. This configuration permits an operator to recognize each target region and the quantitative data thereof (e.g., target strengths) at a glance of an image presented by the display device.

According to another aspect of the invention, the acoustic detection system includes a plurality of transducer elements for transmitting acoustic search sounding signals, receiving acoustic echoes reflected from a sounding area, and converting the acoustic echoes into electrical signals, a first detector for detecting a target within the sounding area based on the echo signals fed from the transducer elements, a second detector for detecting quantitative data of the target by amplifying the echo signals while maintaining a quantitative relationship between one echo signal and another, and a signal generator for producing an output signal based on the quantitative data supplied by the second detector and the data representative of the target supplied by the first detector.

It will be appreciated from above and the following detailed description that the invention provides an acoustic transceiver configured to permit substantially simultaneous detection of a target region where a target exists and quantitative data thereof with high reliability and accuracy. For example, the acoustic transceiver thus configured can receive acoustic echoes reflected from a specific area underwater and display a target region where a fish school exists together with the density of fish within the fish school, for instance, with high accuracy.

It will also be appreciated that the invention provides an acoustic transceiver configured to determine more specific physical quantity data of a target by integrating quantitative data of the target. For example, the acoustic transceiver thus configured can receive acoustic echoes reflected from a specific area underwater and determine a target region where a fish school exists together with fish quantity contained in the detected fish school, for instance, with high accuracy.

It will be further appreciated that the invention provides an acoustic transceiver configured to present such information as a detected target region a target exists together with quantitative data (e.g., target strengths) and physical quantity data (e.g., fish quantity) of the target on a display device in a manner easily distinguishable by the operator. This configuration enables the operator to easily recognize individual pieces of the information.

These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general block diagram of an acoustic transceiver according to a first embodiment of the invention; FIG. 2 is a detailed block diagram showing part of the acoustic transceiver of the first embodiment; FIG. 3 is a block diagram generally showing the configuration of a data synthesizer shown in FIG. 2; FIG. 4 is a diagram showing an example of an on-screen image obtained by the acoustic transceiver of the first embodiment; FIG. 5 is an explanatory diagram of a first example of echo integration; FIGS. 6(a) and 6(b) are diagrams illustrating a quasi- stack method; FIG. 7 is an explanatory diagram of a second example of echo integration; FIG. 8 is an explanatory diagram of a third example of echo integration; FIG. 9 is an explanatory diagram of a fourth example of echo integration; FIG. 10 is an explanatory diagram of a fifth example of echo integration; FIG. 11 is an explanatory diagram of a sixth example of echo integration; FIG. 12 is an explanatory diagram of a seventh example of echo integration; FIG. 13 is an explanatory diagram of an eighth example of echo integration; FIG. 14 is an explanatory diagram of a ninth example of echo integration; FIG. 15 is a block diagram of a receiver of an acoustic transceiver according to a second embodiment of the invention; FIG. 16 is a block diagram generally showing the configuration of a data synthesizer shown in FIG. 15; FIGS. 17(A) and 17(B) are diagrams showing examples of on-screen images obtained when binary-valued data output from a target region detector of the receiver is presented and when quantitative data output from a quantitative data detector of the receiver is presented on a display screen of a display section, respectively; FIG. 18 is a diagram showing another example of an on- screen image presented on the display screen by the acoustic transceiver of the second embodiment; FIG. 19 is a block diagram of a receiver of an acoustic transceiver according to a third embodiment of the invention; FIG. 20 is a block diagram showing a system configuration including a data storage and a data processor which are connected to the receiver of FIG. 19 for storing and processing data output from the receiver; FIG. 21 is a block diagram generally showing the configuration of an acoustic receiver used in a typical

sonar of the prior art;

FIGS. 22(A), 22(B) and 22(C) are diagrams showing how signal intensity data for individual beam directions vary with gain applied to echo signals by preamplifiers; FIGS. 22(D), 22(E) and 22(F) are schematic representations of on-screen images obtained with gain settings shown in FIGS. 22(A), 22(B) and 22(C), respectively; FIGS. 23(A), 23(B) and 23(C) are diagrams showing how signal intensity data for individual beam directions vary with gain applied to echo signals by post-amplifiers; and FIGS. 23(D), 23(E) and 23(F) are schematic representations of on-screen images obtained with gain settings shown in FIGS. 23(A), 23(B) and 23(C), respectively.

DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS OF THE INVENTION

FIRST EMBODIMENT

An acoustic transceiver according to a first embodiment of the present invention is described with reference to the accompanying drawings, in which FIG. 1 is a general block diagram of the acoustic transceiver of the embodiment, FIG. 2 is a detailed block diagram showing part of the acoustic transceiver of the embodiment, FIG. 3 is a block diagram generally showing the configuration of a data synthesizer 16 shown in FIG. 2, and FIG. 4 is a diagram showing an example of an on-screen image obtained by the acoustic transceiver of the embodiment.

Referring to FIG. 1, the acoustic transceiver of the embodiment includes a transmitter 6, a receiver 1, an interface 3, a transducer unit including a plurality of transducer circuits 4a-4n (where n is a whole number), a display section 2, an operating section 7 and a controller for controlling the entirety of system components.

The transmitter 6 generates transmission control data in accordance with a transmit command fed from the controller 5 and outputs the transmission control data to n number of transmit/receive channels CIIl-CHn (see FIG. 2) corresponding to the individual transducer circuits 4a-4n through the interface 3 to form a transmitting beam oriented in a specified direction. The interface 3 delivers the transmission control data to the transducer circuits 4a-4n in accordance with predefined transmit timing. The individual transducer circuits 4a-4n generate acoustic pulse signals based on the transmission control data entered and emit the acoustic pulse signals underwater.

The transducer circuits 4a-4n produce echo signals from received acoustic echoes reflected by underwater targets, such as fish schools, with predefined receive timing and output the echo signals to the receiver 1 through the interface 3. A detailed description of the transducer circuits 4a-4n is not provided here as the configuration and working of the individual transducer circuits 4a-4n are the same as described earlier with reference to the conventional acoustic receiver.

Upon receiving the echo signals from the transducer circuits 4a-4n, the receiver 1 generates a variety of predefined kinds of sounding data and outputs the same to the display section 2. The sounding data may include address data indicating addresses of detected targets (fish schools), intensity data (quantitative data) indicating target strengths of the fish schools as well as fish quantity data (physical quantity data) obtained by integrating the physical quantity data.

The display section 2 produces screen image data based on the aforementioned various kinds of sounding data fed from the receiver 1 and displays the image data thus obtained On-screen. As an example, the display section 2 performs a level conversion process to convert individual levels of the input intensity data derived from a specified sounding area into color information. The display section 2 then reads data from a color look-up table according to the color information obtained by the level conversion process and outputs color image data corresponding to individual addresses of a display screen. The display section 2 successively outputs the color image data for the individual display screen addresses by performing the aforementioned operation and eventually displays a color image of the sounding data representative of the detected target strengths.

As shown in FIG. 2, the receiver 1 includes a target region detector 10, a quantitative data detector 20 and the aforementioned data synthesizer 16.

The target region detector 10 includes the same number of preamplifiers lla-lln as the transmit/receive channels CH1-CHn, a receiving beamformer 12, a detecting circuit 13, the same number of post-amplifiers l4a-14m (where m is a whole number) as receiving beams generated and a target region extractor 15.

The preamplifiers ha-un are time-varied-gain (TVG) amplifiers which are connected to the transducer circuits 4a-4n via the interface 3, respectively. When the echo signals generated by the transducer circuits 4a-4n of the individual transmit/receive channels CH1-CHn are input, the preamplifiers lla-lln amplify the echo signals by a specific ratio, or gain, which is increased with time elapsed from a point in time when the acoustic pulse signals are emitted from transducer elements 4la-41n of the respective transducer circuits 4a- 4n. More specifically, the preamplifiers lla-lln amplify the input echo signals with the time-varied gain which would saturate to a certain extent intensity data represented by receiving beam data Bpl-Bpm picked up by the individual receiving beams generated by the later-described receiving bearnformer 12, where the expression "to a certain extent" implies a gain level (typically set to 40 dE) at which a main lobe becomes saturated.

The receiving beamformer 12 forms a pencilhike narrow receiving beam which is steered through a plurality of predefined directions around the transducer unit by using the phased array technique in which the nchannel input echo signals are synthesized by controlling phases and weights thereof to produce the receiving beam data Bpl-Bpm.

The detecting circuit 13 demodulates the individual receiving beam data Bpl-Bpm fed from the receiving beamformer 12 to produce signal intensity data for the individual beam directions.

The post-amplifiers l4a-l4m amplify the signal intensity data fed from the detecting circuit 13 with specific gain in a controlled fashion and outputs the gain- controlled signal intensity data to the target region extractor 15.

The target region extractor 15 determines addresses where the detected targets are located based on signal intensity data input for individual addresses arranged radially along each of the beam directions with reference to display threshold data used in the aforementioned level conversion process to be performed by the display section 2.

To be more specific, the target region extractor 15 detects addresses of which input signal intensity data are equal to or higher than a threshold level with reference to a minimum intensity value (threshold) preset for a target to be displayed on-screen in the level conversion process.

The target region extractor 15 outputs target region data (address data) indicating areas designated by the detected addresses to an echo integrator 161 of the data synthesizer 16 (see FIG. 3) The quantitative data detector 20 includes the same number of preamplifiers 21a-21n as the transmit/receive channels CH1-CHn, a receiving beamforiner 22, a detecting circuit 23 and as many post- amplifiers 24a-24rri as receiving beams generated.

The preamplifiers 21a-21n are time-varied-gain (TVG) amplifiers which are connected to the transducer circuits 4a-4n via the interface 3, respectively. When the echo signals generated by the transducer circuits 4a-4n of the individual transmit/receive channels CH1-CHn are input, the preamplifiers 21a-21n amplify the echo signals by a specific ratio, or gain, which is increased with time elapsed from a point in time when the acoustic pulse signals are emitted from the transducer elements 41a-41n of the respective transducer circuits 4a-4n. More specifically, the preamplifiers 21a-21n amplify the input echo signals with the time-varied gain which would not saturate intensity data represented by receiving beam data Bql-Bqrn picked up by the individual receiving beams generated by the later-described receiving beamformer 22, where the time-varied gain is typically set to 20 dE or less.

Like the receiving beamformer 12 of the target region detector 10, the receiving beamformer 22 of the quantitative data detector 20 forms a pencillilce narrow receiving beam which is steered through a plurality of predefined directions around the transducer unit by using the phased array technique in which the n-channel input echo signals are synthesized by controlling phases and weights thereof to produce the receiving beam data Bql-Bqm.

The two receiving beamformers 12, 22 work in exactly the same way.

The detecting circuit 23 demodulates the individual receiving beam data Bql-Bqm fed from the receiving beamformer 22 to produce signal intensity data for the individual beam directions. The detecting circuit 23 of the quantitative data detector 20 performs essentially the same demodulating operation as the detecting circuit 13 of the target region detector 10 except that the two detecting circuits 13, 23 are set to different demodulation levels.

The post-amplifiers 24a-24m amplify the signal intensity data fed from the detecting circuit 23 with specific gain in a controlled fashion in a way that does not saturate the signal intensity data and outputs the gaincontroil signal intensity data as quantitative data to the echo integrator 161 of the data synthesizer 16.

Referring to FIG. 3, the data synthesizer 16 includes the aforementioned echo integrator 161 and a fish quantity calculator 162. The echo integrator 161 produces integrated quantitative data by performing threedimensional integration of the quantitative data for each of specified addresses by using a known method based on the address data obtained from the target region extractor 15 and outputs the integrated quantitative data to the fish quantity calculator 162. The fish quantity calculator 162 produces fish quantity data as well as data on the size and volume of each fish school from the integrated quantitative data input from the echo integrator 161 by using a known method and outputs such data to the display section 2. if there exists more than one target region detected within a current sounding area, the echo integrator 161 and the fish quantity calculator 162 perform such mathematical operations on each target region and generate detailed numerical data indicating the locations of individual fish schools and fish quantities thereof.

The data synthesizer 16 also outputs the signal intensity data obtained by the target region detector 10 for the individual addresses arranged radially along each of the beam directions to the display section 2.

As depicted in FIG. 4, a display screen 200 of the display section 2 is roughly divided into a sounding information display area 201 for displaying the sounding data and a digital information display area 202 for displaying digital information including the fish quantity data. When the signal intensity data for the individual addresses arranged radially along each of the beam directions is input from the data synthesizer 16 of the receiver 1, the display section 2 generates an image to be displayed on-screen by reading out data from the color look-up table according to the color information obtained by the level conversion process as discussed earlier and displays the image thus created in he sounding information display area 201. The display section 2 presents fish school echoes as illustrated in FIG. 4, for example. At the same time, the display section 2 presents the digital information, such as the fish quantity data, input from the fish quantity calculator 162 of the receiver 1 in the digital information display area 202. If there exists more than one fish school detected by the acoustic transceiver, the display section 2 presents the sounding data and digital information for the individual fish schools on the sounding information display area 201 and the digital information display area 202, respectively. If an operator specifies a particular target region by placing a target mark 210 through the operating section 7 as shown in the example of FIG. 4, the display section 2 performs operation for displaying the digital information on a fishschool tagged by the target mark 210 only or for enhancing such a fish school, for instance.

With the acoustic transceiver thus configured, the display section 2 shows a fish school of interest existing in the specified target region in a manner clearly distinguisha from targets present in the rest of the sounding area along with detailed information on that fish school. This enables the operator to distinguish the fish school of interest and recognized the detailed information on the fish school in a reliable fashion.

The aforementioned echo integration is now described in detail with reference to specific examples thereof which are pictorially shown in FIGS. 5 to 14.

FIRST EXAMPLE OF ECHO INTEGRATION

FIG. 5 is an explanatory diagram of a first example of echo integration showing a model in which acoustic sounding beams are steered to scan along an imaginary two- dimensional umbrellalike area Hi formed around a ship 80 and along an imaginary vertical plane H2 which is perpendicular to an xy-plane (horizontal plane) As shown in FIG. 5, the acoustic transceiver transmits through the transducer unit the acoustic sounding beams in multiple directions underwater. Specifically, the acoustic transceiver emits a horizontal transmitting beam directed obliquely downward in the umbreilalike area Hi around the ship 80 and scans along the umbreilalike area Hi by steering a receiving beam therein with the angular direction of the receiving beam successively varied in terms of an angle 4 from an xz-plane (vertical plane) . The acoustic transceiver also emits a vertical transmitting beam within the imaginary vertical plane H2 which is perpendicular to the xy-plane and scans along the imaginary vertical plane H2 by steering a receiving beam therein with the direction of the receiving beam successively varied in terms of a tilt angle 0 from the xyplane.

If equivalent input sound intensities PM2 is obtained with the receiving beam steered along the imaginary two- dimensional umbrellaljke area Hi and the imaginary vertical plane H2, it is possible to calculate an approximate number of individual fish in each fish school by a known principle of fish counting and a quasi-stack method. The quasi-stack method is described in detail with reference to FIGS. 6(a) and 6(b).

FIG. 6(a) is a diagram showing cross sections of a fish school FS taken along the imaginary two-dimensional umbrellalike area Hi formed around the ship 80 and along the imaginary vertical plane H2 which is perpendicular to the xy-plane. Acoustic waves are transmitted and received by the transmitting and receiving beams formed within the umbrellalike area Hi and the vertical plane H2. FIG. 6(b) is a conceptual illustration of the quasi-stack method.

First, the cross sections of the fish school FS taken along the imaginary urnbrellalike area Hl and the imaginary vertical plane H2 are traced to obtain nonelliptical models SH and Sv of the fish school FS, respectively, as depicted in FIG. 6(a). Then, the noneiliptical model Sv formed on the imaginary vertical plane H2 is copied onto the imaginary umbrellalike area Hi at an enlarged or reduced size to produce nonelliptical models Svl, Sv2, ... to construct quasi-three-dimensj data. Referring to FIG. 6(b), a scale factor applied in copying operation is determined by the ratio of an integral value of equivalent input sound intensities PM2 along a line L of intersection of the nonelliptical models SH and Sv to an integral value of equivalent input sound intensities PM2 along a line Li (L2, ...) on the nonelliptical model SH obtained by moving the line L on the uinbrellaljke area Hi in a direction in which the angle 4' varies (or in a j direction) around an origin 0 (see FIG. 5). More particularly, a nonelliptical model Svj. shown in FIG. 6(b) is a model obtained by reducing the nonelliptical model Sv in such a way that when the nonelliptical model Sv is moved around the origin 0 along the nonelliptical model SH, the integral value of the equivalent input sound intensities PM2 along the line L of intersection of the nonelliptical model SH and the shifted nonelliptical models SH becomes equal to the integral value of the equivalent input sound intensities PM2 along the line Li. A nonelliptjcaj. model Sv2 shown in FIG. 6(b) is also generated in a similar way.

SECOND EXAMPLE OF ECHO INTEGRATION

A second example of echo integration is now described with reference to FIG. 7 which is a diagram showing a model using a cylindrical coordinate system with a vertical scanning plane which is perpendicular to an x-axis. As depicted in FIG. 7, the ship 80 is supposed to be moving in a positive direction of the x-axis while scanning along a yz-plane with transmitting and receiving beams formed therewjthjn.

In this model, equivalent input sound intensity PM2 is obtained from each point at coordinates (r, x) in each beam direction 0. As the receiving beam is steered, equivalent input sound intensities PM2 successively acquired from coordinates in r, 0 and x directions are integrated by using preset constants to accomplish the echo integration with this normal cylinder model.

THIRD EXAMPLE OF ECHO INTEGRATION

A third example of echo integration is described with reference to FIG. 8 which is a diagram showing a model using a cylindrical coordinate system with a vertically inclined scanning plane. As depicted in FIG. 8, the ship is supposed to be moving in the positive direction of the x-axis while scanning along a slant plane Hl with transmitting and receiving beams formed therewithin. The "slant plane Hl" is an imaginary plane containing a y-axis and a w-axis (directed obliquely downward) which exists in an xz-plane, the w-axis being inclined at a specific angle q with respect to a z-axis toward the positive direction of the x-axis as illustrated. This model can be regarded as a variation of the normal cylinder model of the aforementioned second example obtained by vertically inclining the cylinder model thereof. Thus, it is possible to perform the echo integration using a cylinder model by applying the coordinate system of the normal cylinder model of the second example to the coordinate system of the model of the third example.

FOURTH EXAMPLE OF ECHO INTEGRATION

A fourth example of echo integration is described with reference to FIG. 9 which is a diagram showing a model using a cylindrical coordinate system with a horizontally inclined scanning plane. As depicted in FIG. 9, the ship is supposed to be moving in the positive direction of the x- axis while scanning along a horizontally oblique vertical plane H2 with transmitting and receiving beams formed therewithin. This model can be regarded as another variation of the normal cylinder model of the aforementioned second example obtained by horizontally inclining the cylinder model thereof. Thus, it is possible to perform the echo integration using a cylinder model by applying the coordinate system of the normal cylinder model of the second example to the coordinate system of the model of the fourth example.

FIFTH EXAMPLE OF ECHO INTEGRATION

A fifth example of echo integration is described with reference to FIG. 10 which is a diagram showing a model using a cylindrical coordinate system with a vertically and horizontally inclined scanning plane. As depicted in FIG. 10, the ship 80 is supposed to be moving in the positive direction of the x-axis while scanning along a horizontally oblique slant plane H3 with transmitting and receiving beams formed therewithin. This model can also be regarded as a variation of the normal cylinder model of the aforementioned second example obtained by vertically and horizontally inclining the cylinder model thereof. Thus, as in the third and fourth examples, it is possible to perform the echo integration using a cylinder model by applying the coordinate system of the normal cylinder model of the second example to the coordinate system of the model of the fifth example.

SIXTH EXAMPLE OF ECHO INTEGRATION

A sixth example of echo integration is described with reference to FIG. 11 which is a diagram showing a model using a coordinate system with a horizontally moving umbrellaljke scan area. As depicted in FIG. 11, the ship is supposed to be moving in the positive direction of the x-axis while scanning along an imaginary umbrellalike area H4 formed around the ship 80 with transmitting and receiving beams formed therewithin. As in the aforementioned third, fourth and fifth examples, it is possible to perform the echo integration using a cylinder model by applying the coordinate system of the normal cylinder model of the second example to the coordinate system of the model of the sixth example.

SEVENTH TO NINTH EXAMPLES OF ECHO INTEGRATION

While the echo integration of the present invention has been discussed with reference to the nonelliptical and cylinder models in the foregoing first to sixth examples, it is also possible to perform the echo integration using models of seventh, eighth and ninth examples illustrated in FIGS. 12, 13 and 14, respectively.

FIG. 12 is a diagram showing a model of the seventh example of echo integration in which acoustic sounding (transmitting and receiving) beams are once formed within an imaginary vertical plane H5 containing the x-axis and the y-axis, and the angular direction of the acoustic sounding beams is altered by rotating a scanning plane represented by the imaginary vertical plane H5 counterclockwise about the z-axjs. As depicted in FIG. 12, the acoustic sounding beams are formed in a sector scan area shown by the imaginary vertical plane H5 to scan this sector area while successively varying the tilt angle 0 from the x-axjs, or from the xy-plane (horizontal plane), within the imaginary vertical plane H5. On the other hand, the angle of the imaginary vertical plane H5 with respect to the xz-plane is successively varied to rotate the sector scan area counterclockwise about the z-axis so that the angular direction of the acoustic sounding beams is successively altered.

FIG. 13 is a diagram showing a model of the eighth example of echo integration in which acoustic sounding (transmitting and receiving) beams are formed around the ship 80 within a scan area represented by an umbrellalike area 116 of which tilt angle 0 from the xy-plane (horizontal plane) is successively varied to scan both horizontally and vertically.

FIG. 14 is a diagram showing a model of the ninth example of echo integration in which acoustic sounding (transmitting and receiving) beams are formed within a scan area represented by a slant plane H7 of which tilt angle q is varied so that the scan area is swung about the y-axis.

The "slant plane H7" is an imaginary plane containing the y-axis and a waxis (directed obliquely downward) which exists in the xz-plane, the waxis being inclined at the specific angle q with respect to the z-axis toward the positive direction of the x-axis as illustrated. Thus, the slant plane H7 is equivalent to the slant plane I-Il described earlier with reference to the third example of echo integration. As the tilt angle q is successively varied so that the scan area (slant plane H7) is swung about the y-axis, the acoustic sounding beams are steered to scan both horizontally and vertically.

While the foregoing discussion of the first to ninth examples of echo integration has dealt mainly with three- dimensional integration, it is possible apply these examples by performing not only three-dimensional echo integration but also two- dimensional echo integration along horizontal and vertical planes to calculate fish quantities,

for example.

The shaped of the transducer unit on which the transducer elements 4la4ln are arranged used for performing the echo integration of the aforementioned examples may be spherical or cylindrical.

SECOND EMBODIMENT

An acoustic transceiver according to a second embodiment of the invention is now described with reference to FIGS. 15 to 18, in which FIG. 15 is a block diagram of a receiver 1 of the acoustic transceiver of the second embodiment, and FIG. 16 is a block diagram generally showing the configuration of a data synthesizer 16 shown in FIG. 15.

FIG. 17(A) is a diagram showing an example of an on- screen image obtained when binary-valued data output from a target region detector 10 of the receiver 1 is presented on a display screen 200 of a display section 2, FIG. 17(3) is a diagram showing an example of an on- screen image obtained when quantitative data output from a quantitative data detector 20 of the receiver 1 is presented on the display screen 200 of the display section 2, and FIG. 18 is a diagram showing another example of an on-screen image presented on the display screen 200 of the display section 2 of the present embodiment.

The acoustic transceiver of the second embodiment is identical to that of the first embodiment except for the configuration of the target region detector 10 and the data synthesizer 16 of the receiver 1 and the display section 2, so that the rest of the acoustic transceiver is not specifically described below.

Referring to FIG. 15, the target region detector 10 includes the same number of preamplifiers lla-lln (where n is a whole number) as the number of channels, a receiving beamformer 12, a detecting circuit 13, the same number of post-amplifiers 14a-l4m (where m is a whole number) as receiving beams generated, and a binarization circuit 17.

The configuration and working of the preamplifiers lia-lin, the receiving beamformer 12, the detecting circuit 13 and the post-amplifiers l4a-l4m corresponding to the number of the receiving beams generated are the same as described earlier with reference to the first embodiment, so that these circuits are not specifically described here.

A minimum intensity value (threshold) is preset for use as a criterion in making a judgment on the presence of a true target in a level conversion process performed by the display section 2. The binarizatjon circuit 17 compares input signal intensity data of each echo signal with the threshold. If the input signal intensity data is equal to or higher than the threshold, the binarization circuit 17 outputs a high level "1" indicating that a target is present. If the input signal intensity data is lower than the threshold, on the contrary, the binarjzatjon circuit 17 outputs a low level "0" indicating that no target is present. When such level data is directly displayed, the display section 2 presents an image containing a target region 211, for instance, on the display screen 200 as depicted in FIG. 17(A), in which the target region 211 is clearly distinguished from other regions. it is to be noted however that this image does not enable the operator to recognize quantitative data (target strengths) and physical quantity data (e.g., fish quantity) of each target (fish school).

When the quantitative data output from the quantitative data detector 20 is displayed, on the other hand, the display section 2 presents an image containing a target region 212, for instance, on the display screen 200 as depicted in FIG. 17(3), in which a target echo is shown with varying target strengths (represented by gradations) within a fish school. This image does not permit the operator to clearly recognize a boundary of the target (fish school), however.

Referring to FIG. 16, the data synthesizer 16 of this embodiment includes the same number of multipliers l63a- l63m as the receiving beams.

These multipliers l63a-163rn multiply the level data output from the binarizatjon circuit 17 of the target region detector 10 by the quantitative data fed from the quantitative data detector 20. The data synthesizer 16 controls signal flow in such a way that values of the level data and the quantitative data derived from the same address would be multiplied together. As a result of this operation, quantitative data (target strengths) are allocated to addresses where the high level "1" (equal to or higher than the threshold) is detected, whereas no quantitative data (target strengths) are allocated to addresses where the low level "0" (lower than the threshold) is detected. In other words, the quantitative data (target strengths) are allocated only to such addresses where targets have been detected. The data synthesizer 16 outputs sounding data obtained by such mathematical operation to the display section 2.

The display section 2 performs the aforementioned level conversion process to convert the input sounding data into color information. The display section 2 then reads data from a color look-up table according to the color information and outputs color image data. Since the data synthesizer 16 outputs the quantitative data (target strengths) for addresses of only such a region that contains targets, the display section 2 presents an image containing a target region 213, for instance, on the display screen 200 as depicted in FIG. 18, in which a target echo is shown with varying gradations within a fish school based on the quantitative data (target strengths) in a manner that permits the operator to clearly distinguish the target region 213 from other regions. This enables the operator to simultaneously recognize from a single on- screen image a target region (e.g., a fish school) where any target exists and the quantity of targets (e.g., fish quantity).

While FIG. 18 shows an example in which only one fish school is detected, the display section 2 shows the locations of individual fish schools and fish quantities thereof if a plurality of fish schools are detected in the sounding area. This arrangement permits the operator to recognize the locations of the multiple fish schools and relative sizes thereof in a reliable fashion at a glance of the single on-screen image representing target distribution within the sounding area.

The foregoing discussion of the first and second embodiments has been based on examples in which the sounding area is directed obliquely downward or horizontally, the above-described configurations of the embodiments are applicable to an acoustic transceiver designed to also provide an echo-sounding picture covering a sounding area directed vertically downward or an echo- sounding picture simultaneously covering sounding areas directed horizontally and vertically.

THIRD EMBODIMENT

An acoustic transceiver according to a third embodiment of the invention is now described with reference to FIGS. 19 and 20, in which FIG. 19 is a block diagram of a receiver 1 of the acoustic transceiver of the third embodiment, and FIG. 20 is a block diagram showing a system configuration including a data storage 8 and a data processor 9 which are connected to the receiver 1 of FIG. 19 for storing and processing data output from the receiver 1.

The receiver 1 of this embodiment differs from that of the first embodiment in that the former includes a data communications controller 18 instead of the target region extractor 15 and the data synthesizer 16 of the first embodiment. The receiver 1 of the third embodiment is otherwise the same as that of the first embodiment. Signal intensity data (quantitative data) output from the post- amplifiers l4a-14m of the target region detector 10 and physical quantity data (e.g., fish quantity) output from the post-amplifiers 24a-24m are fed into the data communications controller 18 and output to external equipment.

The data output from the data communications controller 18 of the receiver 1 are once stored in the data storage 8 which is, for example, a hard disk. Individual pieces of the data stored in the data storage 8 are read out by the data processor 9 which is, for example, a personal computer. The data processor 9 performs various kinds of data processing on the data read from the data storage 8. Typical examples of information produced by the data processing operation performed by the data processor 9 are bottom features and fish quantities which are obtainable from acoustic sounding signals.

The aforementioned system configuration of the third embodiment makes it possible to temporarily store a great deal of signal intensity data and physical quantity data and obtain various kinds of sounding information by processing the data.

While the invention has thus far been described with reference to the acoustic transceivers according to the preferred embodiments thereof, the above-described configuratjon of the invention are also applicable to other types of apparatuses which are designed to detect targets within a search area by use of a sounding signal.

Claims

WHAT IS CLAIMED IS: 1. An acoustic transceiver comprising: a plurality of

transducer circuits for transmitting the acoustic sounding signals toward the sounding area, receiving acoustic echoes reflected from the sounding area, and converting the acoustic echoes into electrical echo signals; a target region detector for detecting a target region within the sounding area based on the echo signals fed from said individual transducer circuits; a quantitative data detector for detecting quantitative data of the target existing within the sounding area by amplifying the echo signals fed from said individual transducer circuits while maintaining a quantitative relationship between one echo signal and another; and a quantitative data synthesizer for synthesizing the quantitative data detected by said quantitative data detector with the target region detected by said target region detector.
2. The acoustic transceiver according to claim 1, said quantitative data synthesizer including: an integrator for generating integrated quantitative data by integrating the quantitative data detected within the target region; and a physical quantity calculator for estimating a specific kind of physical quantity data of the detected target from the integrated quantitative data.
3. The acoustic transceiver according to claim 1, said target region detector including: a binarizatjon circuit for binarizing the echo signals by comparing the level of each echo signal with a specific threshold; wherein said quantitative data synthesizer synthesizes results of binarization by said binarization circuit with the quantitative data output from said quantitative data detector.
4. The acoustic transceiver according to claim 1, 2 or 3 further comprising a display device for displaying pieces of the data generated by said quantitative data synthesizer.
5. An acoustic detection system comprising: a plurality of transducer elements for transmitting acoustic search sounding signals, receiving acoustic echoes reflected from a sounding area, and converting the acoustic echoes into electrical signals; a first detector for detecting a target within the sounding area based on the echo signals fed from said transducer elements; a second detector for detecting quantitative data of the target by amplifying the echo signals while maintaining a quantitative relationship between one echo signal and another; and a signal generator for producing an output signal based on the quantitative data supplied by said second detector and the data representative of the target supplied by said first detector.
6. An acoustic transceiver substantially as hereinbefore described with reference to Figures 1 to 14, Figures 15 to 18, or Figures 19 and 20 of the accompanying drawings,
7. An acoustic detection system substantially as hereinbefore described with reference to Figures 1 to 14, Figures 15 to 18, or Figures 19 and 20 of the accompanying drawings.