JP7639488B2 - Sonar system, target direction and distance correction method, and program - Google Patents

Description

The present invention relates to a sonar system, a method for correcting target direction and distance, and a program.

Sonar is a device that uses sound waves to pinpoint the position of underwater objects, obtaining underwater acoustic information based on signals received by an array of multiple receiving elements (transducers) that convert the received sound waves into electrical signals. Towed sonars generally use a line array in which multiple receiving elements are arranged in a straight line at the end of a cable extending from a platform such as a ship. Among towed sonars, the advantage of variable depth sonar (VDS) is that the towing depth can be changed depending on the underwater sound reception conditions.

Patent Document 1 discloses a sonar device that includes an array of multiple hydrophones suspended from a buoy monitor device and a sensor unit attached to the bottom of the hydrophones, which detects the depth, water temperature, salinity and azimuth gradient at the bottom of the hydrophones, and the detected information is transmitted to a signal processing unit along with sonar information from underwater objects, and is superimposed on the sonar information and transmitted from the transmitting antenna to the position measurement device body. The depth data and azimuth gradient data are used to improve the accuracy of position measurement of the hydrophones and underwater objects.

Japanese Patent Application Publication No. 07-198844

In a typical towed sonar in which a line array is towed by a ship or the like, the receiving directivity is conical (conical beam), as shown, for example, in directional image 12 in FIG. 1(A). That is, the receiving beam formed by performing phasing and summing on the received signals from the receiving element array that constitutes the line array of the towed sonar 10 becomes a beam pattern that spreads out in a cone shape, as shown in directional image 12. FIG. 1(A) is a schematic side view showing the side (X-Z plane) of the underwater towed sonar 10 as seen from the west (front side perpendicular to the paper: negative Y-axis) to the east (back side perpendicular to the paper: positive Y-axis). In FIG. 1(A), the north side is the positive X-axis, the south side is the negative X-axis, the sea surface side is the positive Z-axis, and the seabed side is the negative Z-axis. Figure 1(B) is a schematic plan view of the underwater towed sonar 10 and target 11 (underwater object) shown in Figure 1(A) viewed from above (positive direction of the Z axis).

As shown in Figure 1 (A), when the depth (target depth 14) of the target 11, which is an underwater object, differs from the towed sonar depth 13, which is the depth of the towed sonar 10, an error occurs between the observation direction 15 and the actual direction 16 of the target 11, as shown in Figure 1 (B). For example, when the depth (target depth 14) of the target 11 is deeper than the towed sonar depth 13, the direction corresponding to the left hypotenuse of the inverted isosceles triangle (directional image 12), which is the projection of the conical receiving beam pattern onto the X-Y plane at the towed sonar depth 13 (Z-axis coordinate = 0), is set as the observation direction 15, but the actual direction 16 of the target 11 is inside the direction of the left hypotenuse of the inverted isosceles triangle.

Figure 2(A) shows a schematic diagram of the towed sonar 10 itself tilted in the depth direction due to external forces such as ocean currents. Like Figure 1(A), Figure 2(A) is a schematic side view showing the X-Z plane of the towed sonar 10 underwater as viewed from west to east (from negative to positive Y-axis direction). The line array of the towed sonar 10 is tilted at a pitch angle α around the Y-axis, and the conical directional image 12 is also tilted at a pitch angle α. Here, the pitch angle α is positive in the counterclockwise direction around the Y-axis. Note that when angled 90 degrees to the lateral direction relative to the direction of travel (north of the positive X-axis), the beam becomes squashed (disk-shaped) (directional image 12A). In FIG. 2(A), the origin of the three-dimensional coordinate system XYZ (left-handed system) is the acoustic center of the towed sonar 10 (e.g., the center of the line array), the north side of the X axis is positive and the south side is negative, the west side (the front side perpendicular to the paper) of the Y axis is negative and the east side (the back side perpendicular to the paper) is positive, and the sea surface side of the Z axis is positive and the seabed side is negative.

Figure 2 (B) is a schematic plan view of the underwater towed sonar 10 and target 11 (underwater object) shown in Figure 2 (A) viewed from above (positive Z-axis direction). The received beam based on the received data from the line array tilted by pitch angle α around the Y axis forms a cone-shaped beam pattern with the X' axis as the central axis in a three-dimensional coordinate system X'YZ' (left-handed system) in which the three-dimensional coordinate system XYZ is rotated by angle α around the Y axis, as shown as directional image 12. Although the actual target 11 is located on the Y-Z plane at X=0 in the three-dimensional coordinate system XYZ as shown in Figure 2 (A), in the example of Figure 2 (B), the target 11A observed based on the received data from the line array is the left end of an inverted isosceles triangle (height = a) projected onto the X'-Y plane of the directional image 12. That is, the observed target 11A is observed on the Y-Z' plane with the X' axis value being a, and the observation direction 15 is half the apex angle of the inverted isosceles triangle (directional image 12). Thus, an error occurs between the observation direction 15 and the actual direction 16, causing an error in the distance between the observed target 11A and the actual target 11. These errors have a negative effect on the sonar's measurement performance.

The present invention was devised in consideration of the above problems, and its purpose is to provide a sonar system, a target azimuth/distance correction method, and a program that can reduce azimuth and distance errors of targets identified by data received from a line array.

The present invention provides a sonar system that includes a means for detecting the inclination of a line array composed of multiple receiving elements in the depth direction, and further includes an azimuth/distance correction means for correcting errors caused by the inclination of the line array in the depth direction with respect to the target direction and distance identified by the received data from the line array.

The present invention provides a method for correcting target direction and distance by detecting the inclination of a line array composed of multiple receiving elements in the depth direction, and correcting errors caused by the inclination of the towed sonar in the depth direction with respect to the target direction and distance identified by the data received from the line array.

According to the present invention, a program is provided that causes a sonar system computer to detect the inclination in the depth direction of a line array composed of multiple receiving elements, and execute a correction process that corrects an error caused by the inclination in the depth direction of the towed sonar with respect to the target direction and distance specified by the received data from the line array. Furthermore, according to the present invention, a computer-readable recording medium (e.g., RAM (Random Access Memory), ROM (Read Only Memory), or semiconductor storage such as EEPROM (Electrically Erasable and Programmable ROM), HDD (Hard Disk Drive), SSD (Solid State Drive), CD (Compact Disc), DVD (Digital Versatile Disc), etc. that stores the above program is provided.

The present invention can reduce azimuth and distance errors of targets identified in data received from a line array.

1A and 1B are diagrams for explaining a related technique. 1A and 1B are diagrams for explaining a related technique. FIG. 1 is a diagram illustrating an embodiment of the present invention. FIG. 1 is a diagram illustrating an example of an apparatus configuration according to an embodiment of the present invention. FIG. 1 is a diagram illustrating an example of an apparatus configuration according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a method according to an embodiment of the present invention. FIG. 1 illustrates an embodiment of the present invention. FIG. 1 is a diagram illustrating a configuration of an embodiment of the present invention.

An embodiment of the present invention will be described. FIG. 3 is a diagram for explaining an embodiment of the present invention. In FIG. 3(A), as in FIG. 2(A), the acoustic center position of the towed sonar 20 is the origin of a three-dimensional coordinate system XYZ (left-handed system), the north side of the X axis is positive, the south side is negative, the west side (the front side perpendicular to the paper surface) is negative, the east side (the back side perpendicular to the paper surface) is positive, and the Z axis is positive on the sea surface side and negative on the seabed side. FIG. 3(A) shows the X-Z plane as seen from the negative side of the Y axis. FIG. 3(B) shows the X-Y plane as seen from the positive side of the Z axis of FIG. 3(A). Note that the three-dimensional coordinate system XYZ (left-handed system) is merely for the purpose of explanation, and it is of course possible to use a right-handed system. It is of course not intended to mean that the traveling direction of the towed sonar 20 is limited to the north side.

A computer device mounted on a ship equipped with a towed sonar 20 and a transmitting sound source and functioning as a controller for the sonar system pre-sets the search target depth 24, which is depth information of the target (underwater object) to be searched, for the towed sonar via an operation terminal (not shown) or the like.

The towed sonar 20 is fitted with a sensor (e.g., an attitude sensor) that detects attitude information (the front-to-back angle (pitch angle) of the line array). Based on the attitude information from the sensor, the computer device calculates the array pitch angle α, which is the inclination of the line array in the depth direction (pitch angle around the Y axis in Figure 3 (A)). For example, multiple depth sensors are attached to different positions on the towed sonar 20 line array. The computer device is capable of obtaining the angle of inclination of the towed sonar 20 in the depth direction (array pitch angle) from the depth information at any time.

The computer device performs corrections on the direction and distance of the target (underwater object) identified by the data received from the line array of the towed sonar 20, based on the search target depth 24 and the array pitch angle α, thereby reducing errors in the direction and distance. In other words, the computer device uses the search target depth 24 and the array pitch angle α to determine the three-dimensional coordinates (XYZ coordinates) of the target's position, with the acoustic center position of the towed sonar 20 as the origin, based on the direction and distance of the target identified by the data received from the line array of the towed sonar 20.

The computer device outputs the direction and distance horizontally projected from the determined three-dimensional coordinates onto two-dimensional coordinates (X-Y plane) as the target position.

By performing the above processing, the computer device corrects errors that arise due to the directivity of the line array of the towed sonar 20 being conical (conical beam).

Figure 4 is a diagram illustrating an embodiment of the present invention. In Figure 4, the towed sonar 104 corresponds to the towed sonar 20 in Figure 3, and is composed of a line array in which multiple receiving elements (not shown) are connected in a straight line, and each receiving element receives sound waves reflected from an underwater object and converts them into an electrical signal. In the towed sonar 104, at least two depth sensors 106A, 106B are attached along the longitudinal direction of the line array, spaced a predetermined distance (L) from each other.

The transmission control device 101 controls the transmission sound source 102 and transmits the control information to the reception processing device 103. The transmission control device 101 generates an electrical signal from information such as the sound wave waveform and transmission time received from the display device 105, and outputs it to the transmission sound source 102. The transmission control device 101 also outputs information such as the sound wave waveform and transmission time to the reception processing device 103.

The transmission sound source 102 is a device that generates sound waves, converts the electrical signal (transmission signal waveform) sent from the transmission control device 101 into an acoustic signal, and transmits the sound waves underwater.

The towed sonar 104 receives acoustic signals reflected from a target (underwater object) in response to sound waves sent from the transmitting sound source 102 using a receiving element row (line array), converts them into electrical signals, and transmits them to the reception processing device 103. The towed sonar 104 also transmits depth information of two points detected by a depth sensor to the reception processing device 103, for example, at a predetermined cycle. The received signal and depth information from the towed sonar 104 are transmitted to the reception processing device 103 of the sonar system mounted on the ship via a towing cable (not shown).

The reception processing device 103 performs calculations to correct the target's direction and distance information based on the transmission information from the transmission control device 101 (e.g., transmission timing, replica signal of transmission waveform, etc.), the reception signal received by the receiving element array of the towed sonar 104, the depth information detected by the depth sensors 106A and 106B of the towed sonar 104, and the search target depth, and outputs the calculation results to the display device 105. The reception processing device 103 uses the search target depth and the inclination angle of the line array in the depth direction to determine the three-dimensional coordinates (XYZ coordinates) of the target's position, with the acoustic center position of the towed sonar 104 as the origin, from the direction and distance of the target identified by the reception data from the receiving element array (line array) of the towed sonar 104, and outputs the direction and distance projected horizontally from the three-dimensional coordinates onto a two-dimensional coordinate plane (X-Y plane) as the target's position.

The display device 105 (terminal device) converts the data output by the receiving and processing device 103 into image information and displays it. The display device 105 also has the function of setting information on the sound waves (waveform information, transmission timing, etc.) to be transmitted from the transmitting sound source 102 and transmitting it to the transmission control device 101, as well as inputting the search target depth. From an input device (not shown) of the display device 105, the person in charge inputs information such as the waveform and transmission time of the sound waves transmitted by the transmitting sound source 102, as well as the search target depth.

Figure 5 is a functional block diagram explaining the processing performed by the reception processing device 103. In Figure 5, the phasing processing unit 1032 inputs N pieces of reception data 1031 from N pieces of reception elements 1 to N that make up the line array of the towed sonar 104, performs phasing processing, and outputs the phasing processing results to the signal processing unit 1033.

The signal processing unit 1033 extracts the reverberation (echo) of the target (underwater object) using correlation processing or the like from the phasing processing result received from the phasing processing unit 1032.

Since the transmission time and position of the transmitting sound source 102 and the position of the towed sonar 104 are known, the direction and distance of the reflected sound (echo) are calculated geometrically.

The signal processing unit 1033 determines the three-dimensional coordinates of _the target position (coordinates in the three-dimensional coordinate system _XYZ in Figure 3(A)) with the acoustic center position of the towed sonar 20 as the origin, from _the target's azimuth θ T ' and distance r T ', search depth d ss, and array pitch angle α.

・・・(1) Assume that the towed sonar 104 (line array) is equipped with at least two depth sensors 106A, 106B, with a distance between them of L [m]. If the pitch angle (array pitch angle) of the line array relative to the acoustic center position of the towed sonar 20 is α, and the depth at the depth sensor 106A is d ₁ [m] (positive: toward the seabed) and the depth at the depth sensor 106B is d ₂ [m] (d ₁ > d ₂ ), then since the inclination of the depth sensors 106A and 106B with respect to the horizontal axis is α, the difference in depth = d ₁ - _{d 2} = L sin(α), the array pitch angle α is given by the following equation (1).

...(1)

The azimuth/distance correction unit 1034 calculates the array pitch angle α from equation (1). The azimuth/distance correction unit 1034 calculates the search target depth _dss based on the acoustic center position of the towed sonar as the reference (0 m) from the information from the depth sensors 106A and 106B and the search target depth 24 (FIG. 3A).

The azimuth θ _T ' and distance r _T ' of the target 21 identified by N pieces of received data from the towed sonar 20 (N receiving elements of a line array) are values determined in the three-dimensional coordinate system X'YZ' in Figure 3(A). The three-dimensional coordinate system X'YZ' is obtained by rotating the three-dimensional coordinate system XYZ by a pitch angle α around the Y axis. The position (x', y', z') of the target 21 in the three-dimensional coordinate system X'YZ' is given by:

・・・(2)

...(2)

・・・(3) Here, φ is given by the following equation.

...(3)

In equation (2), the azimuth θ _T ' of the target 21 is the angle counterclockwise from the X' axis on the X'-Y plane. In left-handed coordinates, the angle counterclockwise from the X' axis on the X'-Y plane is negative, but for simplicity, the azimuth θ _T ' is taken to be a positive value. In FIG. 3(A), the target 21 is considered to be a vector of length (distance) r _T ' from the origin (the acoustic center position of the towed sonar 20), and the projection value x' of this vector onto the X' axis is given by r _T 'cos(θ _T '), and the angle φ can be considered to be the angle formed by the projection onto the Y-Z' plane of the component (vector of length r _T 'sin(θ _T ')) perpendicular to the projection r _T 'cos(θ _T ') onto the X' axis, with the Y axis. Therefore, the projection value y' onto the Y axis (west is negative) is given by -r _T ' sin(θ _T ') · cos(φ), and the projection value z' onto the Z axis is given by -r _T ' sin(θ _T ') · sin(φ).

In equation (3), the numerator in the arcsine function sin ^-1 is the sum of the search target depth _dss (<0) and the value ( _rT'cos ( _θT ')·sin(α)>0) obtained by projecting the distance _rT ' of the target 21 onto the X' axis, _rT'cos ( _θT '), onto the Z axis (negative side). The denominator is the product of _rT'sin ( _θT ') multiplied by cos(α), and a minus sign is added because the numerator is negative and the angle φ is non-negative.

・・・(4)
を施してＸＹＺ座標系での座標値に変換する。 The azimuth/distance correction unit 1034 calculates a transformation matrix R(-α) that rotates the target 21 by -α degrees around the Y axis with respect to the position (x', y', z') of the target 21 in the three-dimensional coordinate system X'YZ':

...(4)
is applied to convert the result into coordinate values in the XYZ coordinate system.

・・・(5)

...(5)

・・・(6) From equation (5),

...(6)

The azimuth and distance correction unit 1034 calculates the coordinates (x, y, z) of the target 21 in the three-dimensional coordinate system XYZ using the above formula (6).

Next, the orientation/distance correction unit 1034 calculates the orientation θ t (25 in FIG. 3B) and distance r _{t (} 26 in FIG. 3B), which are the coordinates (x, y) projected onto the two-dimensional coordinate plane, the XY plane, from the position coordinates (x, y, z) of the target 21 in the three-dimensional coordinate system _XYZ , using the following equations (7) and (8).

・・・(7)

...(7)

・・・(8)

...(8)

In addition, in equation (7), since the direction _θt is a non-negative value, in the calculation of tan ⁻¹ , the Y coordinate value: y (negative value) of the position of the target 21 is set to −y. However, if the direction _θt shown by 25 in FIG. 3B is set to a negative value, (−y/x) in equation (7) becomes (y/x).

The direction and distance correction unit 1034 outputs the direction θ _t and distance r _t of the target 21A projected onto the two-dimensional XY plane as the final processing results.

According to this embodiment, by using the search target depth 24 and the array pitch angle α of the towed sonar 20, the direction and distance of the target 21 (underwater object) identified by the towed sonar 104 can be corrected, thereby reducing errors.

Figure 6 is a diagram explaining the method of this embodiment. The reception processing device 103 calculates the azimuth and distance of the target from the received data of the line array (step S11).

The reception processing device 103 calculates the array pitch angle α, which is the pitch angle (tilt in the depth direction) of the line array, from the line array attitude information (sensing information from the depth sensor and attitude sensor) (step S12). Note that either step S11 or S12 may be performed first.

The reception processing device 103 uses the input search depth 24 and array pitch angle α to calculate the three-dimensional coordinates (XYZ coordinates) of the target position, with the acoustic center position of the towed sonar 20 as the origin, from the target direction and distance identified from the line array reception data (step S13).

The reception processing device 103 outputs the direction 25 and distance 26 projected onto two-dimensional coordinates (X-Y plane) from the three-dimensional coordinates obtained in step S13 as the position of the target 21 (step S14).

Figure 7 is a diagram explaining one embodiment. It shows the effect of applying the embodiment to towed sonar detection information (azimuth, distance) obtained when the search target depth 24 is 100 m (based on the towed sonar depth) and the array pitch angle is 10°. In Figure 7, the graph has the acoustic center position of the towed sonar as the origin, and the detection azimuth and distance obtained by the towed sonar, as well as the detection azimuth and distance corrected by applying the present invention, are expanded into plane coordinates.

When there is a depth difference between the towed sonar and the target, the actual direction will be closer to the origin than the observed direction due to the directionality (conical beam) of the towed sonar, but it can be seen that this property is corrected. The search target depth can be determined not only by an operating terminal, but also by a method in which it can be stored in a memory device in advance and read out at will.

FIG. 8 is a diagram for explaining an embodiment of the present invention, and is a diagram for explaining a configuration in the case where the reception processing device 103 is implemented in a computer device 110. Referring to FIG. 8, the computer device 110 includes a processor 111, a storage device 112 such as a semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or an HDD (Hard Disk Drive), a display device 105, and an interface 114 for communicating with the towed sonar 104 and the display device 105. The processor 111 may be a DSP (Digital Signal Processor). By reading and executing a program 113 stored in the storage device 112, the processor 111 executes the processes of the phasing processing device 1032, the signal processing device 1033, and the azimuth/distance correction device 1034 of the reception processing device 103 in FIG. 5. The computer device 110 may be configured to implement the functions of the transmission control device 101 in FIG. 4.

In the above embodiment, the inclination of the towed sonar in the depth direction is an example using two depth sensors, but it can also be calculated by installing multiple depth sensors. Any sensor that can obtain attitude information, such as an acceleration sensor, can be used. Also, while Figure 4 shows an example of a line array towed from a ship, the present invention can be widely used in cases where the receiving directivity is a conical line array.

The disclosure of Patent Document 1 is incorporated herein by reference. Modifications and adjustments of the embodiments and examples are possible within the framework of the entire disclosure of the present invention (including the scope of the claims), and further based on the basic technical ideas. Furthermore, various combinations and selections of the various disclosed elements (including each element of each claim, each element of each example, each element of each drawing, etc.) are possible within the framework of the scope of the claims of the present invention. In other words, the present invention naturally includes various modifications and alterations that a person skilled in the art would be able to make in accordance with the entire disclosure, including the scope of the claims, and the technical ideas.

10, 20 Towed sonar 11, 11A, 21, 21A Target 12, 12A, 22 Directional image 13, 23 Towed sonar depth 14 Target depth 15 Observation direction 16 Actual direction 24 Search target depth 25 Direction 26 Distance 101 Transmission control device 102 Transmission sound source 103 Reception processing device 104 Towed sonar 105 Display device 110 Computer device 111 Processor 112 Storage device 113 Program 114 Interface 106A, 106B Depth sensor 1031 Received data 1032 Phase adjustment processing unit 1033 Signal processing unit 1034 Direction and distance correction unit

Claims (6)

A means for detecting a tilt in a depth direction of a line array composed of a plurality of receiving elements is provided,
the line array being a line array of a towed sonar, and further comprising: an azimuth/distance correction means for correcting an error caused by a tilt of the line array in a depth direction with respect to the azimuth and distance of a target identified by data received from the line array;
means for inputting a search depth of the target;
Equipped with
a search target depth inputted in advance for the target's azimuth and distance specified by the received data from the line array, thereby correcting an error caused by a difference between the depth of the acoustic center position of the towed sonar and the depth of the target . The towed sonar includes at least two depth sensors spaced apart from one another;
The azimuth and distance correction means
Calculating an array pitch angle, which is a tilt in the depth direction, from the depth information detected by the depth sensor;
using the search depth and the array pitch angle, determining three-dimensional coordinates of the position of the target with the acoustic center position of the towed sonar as the origin from the azimuth and distance of the target identified by the reception data from the line array;
The sonar system according to claim 1 , which outputs a direction and a distance projected from the three-dimensional coordinates onto a two-dimensional coordinate. A line array is configured with a plurality of receiving elements, and a tilt in the depth direction of the line array of the towed sonar is detected;
Enter the target search depth setting,
A target bearing/distance correction method in which an error occurring due to a difference between the depth of the acoustic center position of the towed sonar and the depth of the target is corrected for the target bearing and distance specified by the received data from the line array, by using the search target depth that is set and input in advance . At least two depth sensors are mounted on the towed sonar at the same height and spaced apart from each other;
Calculating an array pitch angle, which is a tilt in the depth direction, from the depth information detected by the depth sensor;
using the search depth and the array pitch angle, determining three-dimensional coordinates of the position of the target with the acoustic center position of the towed sonar as the origin from the azimuth and distance of the target identified by the reception data from the line array;
4. The target direction/distance correction method according to claim 3, further comprising the steps of: outputting the direction and distance projected from the three-dimensional coordinates onto two-dimensional coordinates as the position of the target. The sonar system computer
A process of detecting the inclination in the depth direction of a line array composed of multiple receiving elements;
a correction process for correcting an error caused by a tilt of the line array in the depth direction with respect to a target direction and distance specified by the received data from the line array;
A program for executing
the line array is a towed sonar line array,
The correction process is a program that corrects errors caused by the difference between the depth of the acoustic center position of the towed sonar and the depth of the target, relative to the azimuth and distance of the target identified by the received data from the line array, by using a previously input search depth of the target . The correction process uses an array pitch angle, which is a tilt in the depth direction, from depth information detected by at least two depth sensors attached to the towed sonar at a distance from each other, and the search target depth, to calculate three-dimensional coordinates of the position of the target, with the acoustic center position of the towed sonar as the origin, from the azimuth and distance of the target specified by the received data from the line array;
6. The program according to claim 5 , further comprising: outputting, as the position of the target, a direction and a distance projected from the three-dimensional coordinates onto a two-dimensional coordinates.

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