Sonar system, target direction and distance correction method, and program

Abstract

To allow for reducing errors in azimuth of and distance to a target identified in data received form a line array.SOLUTION: A tilt of a line array consisting of multiple reception elements in a depth direction is detected to correct an error arising due to the tilt of a towed sonar in the depth direction relative to an azimuth to and a direction of a target identified by data received from the line array.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a sonar system, a target direction / distance correction method, and a program. [Background technology]

[0002] 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 according to the underwater sound reception conditions.

[0003] 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, the sensor unit 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 together with sonar information from underwater objects, and is superimposed on the sonar information and transmitted from a 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 07-198844 Summary of the Invention [Problem to be solved by the invention]

[0005] 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 in the receiving element row 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 (XZ plane) of the underwater towed sonar 10 as seen from the west (front side perpendicular to the paper: negative Y-axis) toward 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. FIG. 1(B) is a schematic plan view of the underwater towed sonar 10 and target 11 (underwater object) shown in FIG. 1(A) viewed from above (positive direction of the Z axis).

[0006] As shown in Fig. 1(A), when the depth (target depth 14) of target 11, which is an underwater object, differs from towed sonar depth 13, which is the depth of towed sonar 10, an error occurs between observation direction 15 and actual direction 16 of target 11, as shown in Fig. 1(B). For example, when the depth (target depth 14) of target 11 is deeper than towed sonar depth 13, the direction corresponding to the left hypotenuse of an inverted isosceles triangle (directional image 12), which is the projection of a conical receiving beam pattern onto the XY plane at towed sonar depth 13 (Z-axis coordinate = 0), is set as observation direction 15, but the actual direction 16 of target 11 is inside the direction of the left hypotenuse of the inverted isosceles triangle.

[0007] FIG. 2(A) shows a schematic diagram of a towed sonar 10 itself tilted in the depth direction due to an external force such as an ocean current. Like FIG. 1(A), FIG. 2(A) is a schematic side view showing an XZ plane of a towed sonar 10 in the sea as viewed from west to east (from the negative direction to the positive direction of the Y axis). The line array of the towed sonar 10 is tilted at a pitch angle α around the Y axis, and the cone-shaped 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 the beam becomes flattened (disk-shaped) at a 90-degree lateral angle with respect to the traveling direction (north of the positive value of the X axis) (directional image 12A). In addition, in Figure 2(A), the origin of the three-dimensional coordinate system XYZ (left-handed system) is the acoustic center of towed sonar 10 (e.g. the center of the line array), with the north side of the X-axis being positive and the south side being negative, the west side (the front side perpendicular to the paper surface) being negative and the east side (the back side perpendicular to the paper surface) being positive, and the Z-axis being positive on the sea surface side and negative on the seabed side.

[0008] FIG. 2(B) is a schematic plan view of the underwater towed sonar 10 and target 11 (underwater object) shown in FIG. 2(A) as viewed from above (positive direction of Z axis). The received beam based on the received data from the line array tilted by pitch angle α around the Y axis becomes a beam pattern spreading in a cone shape 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 YZ plane at X=0 in the three-dimensional coordinate system XYZ as shown in FIG. 2(A), in the example of FIG. 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) obtained by projecting the directional image 12 onto the X'-Y plane. 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, and an error occurs in the distance between the observed target 11A and the actual target 11. These errors have a negative effect on the measurement performance of the sonar.

[0009] The present invention has been devised in consideration of the above-mentioned problems, and has as its object to provide a sonar system, a target bearing / distance correction method, and a program that can reduce the bearing error and distance error of a target identified in data received from a line array. [Means for solving the problem]

[0010] According to the present invention, there is provided a sonar system comprising a means for detecting the inclination in the depth direction of a line array composed of a plurality of receiving elements, and further comprising an azimuth / distance correction means for correcting errors arising from the inclination in the depth direction of the line array with respect to the direction and distance of a target identified by the received data from the line array.

[0011] According to the present invention, a target direction / distance correction method is provided which detects the depthwise tilt of a line array composed of a plurality of receiving elements and corrects errors caused by the depthwise tilt of the towed sonar with respect to the target direction and distance identified by the received data from the line array.

[0012] According to the present invention, there is provided a program for causing a computer of a sonar system to execute a correction process for detecting the inclination in the depth direction of a line array composed of a plurality of receiving elements, and correcting 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, there is provided a computer-readable recording medium (for example, a semiconductor storage such as a RAM (Random Access Memory), a ROM (Read Only Memory), or an EEPROM (Electrically Erasable and Programmable ROM), an HDD (Hard Disk Drive), an SSD (Solid State Drive), a CD (Compact Disc), a DVD (Digital Versatile Disc), etc.) storing the above program. Effect of the Invention

[0013] According to the present invention, it is possible to reduce errors in direction and distance of targets identified in data received from a line array. [Brief description of the drawings]

[0014] [Figure 1] 1A and 1B are diagrams for explaining the related art. [Diagram 2] 1A and 1B are diagrams for explaining the related art. [Diagram 3] FIG. 1 is a diagram illustrating an embodiment of the present invention. [Figure 4] FIG. 1 is a diagram illustrating an example of an apparatus configuration according to an embodiment of the present invention. [Diagram 5] FIG. 1 is a diagram illustrating an example of an apparatus configuration according to an embodiment of the present invention. [Figure 6] FIG. 2 is a diagram illustrating a method according to an embodiment of the present invention. [Figure 7] FIG. 1 illustrates an embodiment of the present invention. [Figure 8] FIG. 1 is a diagram illustrating a configuration of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 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), similarly to 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 XZ plane as viewed from the negative side of the Y axis. FIG. 3(B) shows the XY plane as viewed 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.

[0016] A computer device installed 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.

[0017] A sensor (e.g., an attitude sensor) is attached to the towed sonar 20 to detect attitude information (the angle (pitch angle) of the line array in the fore-and-aft direction). The computer device calculates the array pitch angle α, which is the inclination of the line array in the depth direction (the pitch angle around the Y axis in Figure 3(A)), based on the attitude information from the sensor. For example, multiple depth sensors are attached to different positions on the line array of the towed sonar 20. 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.

[0018] The computer device reduces errors in the direction and distance by correcting the direction and distance of the target (underwater object) identified by the data received from the line array of the towed sonar 20 using the search target depth 24 and the array pitch angle α. 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 position, with the acoustic center position of the towed sonar 20 as the origin, from the direction and distance of the target identified by the data received from the line array of the towed sonar 20.

[0019] The computer device outputs the direction and distance obtained by horizontally projecting the determined three-dimensional coordinates onto two-dimensional coordinates (XY plane) as the target position.

[0020] By carrying out the above processing, the computer device corrects errors that arise due to the directivity of the line array of the towed sonar 20 being a conical beam.

[0021] Fig. 4 is a diagram for explaining an embodiment of the present invention. In Fig. 4, a towed sonar 104 corresponds to the towed sonar 20 in Fig. 3, and is composed of a line array in which a plurality of receiving elements (not shown) are connected in a straight line, and each receiving element receives a sound wave reflected from an underwater object and converts it into an electric signal. In the towed sonar 104, at least two depth sensors 106A, 106B are attached at a predetermined distance (L) from each other along the longitudinal direction of the line array.

[0022] 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 electric signal from information such as the waveform of the sound wave and the 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 waveform of the sound wave and the transmission time to the reception processing device 103.

[0023] The transmission sound source 102 is a device that generates sound waves, converts the electric signal (transmission signal waveform) sent from the transmission control device 101 into an acoustic signal, and transmits the sound waves underwater.

[0024] The towed sonar 104 receives acoustic signals reflected from a target (underwater object) in response to sound waves transmitted from the transmitting sound source 102 using a receiving element row (line array), converts the signals 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).

[0025] The reception processing device 103 performs a calculation to correct the target's direction and distance information based on the transmission information from the transmission control device 101 (e.g., transmission timing, a replica signal of the 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 result 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 specified by the reception data from the receiving element array (line array) of the towed sonar 104, and outputs the direction and distance horizontally projected from the three-dimensional coordinates onto a two-dimensional coordinate plane (XY plane) as the target's position.

[0026] The display device 105 (terminal device) converts the data output by the reception processing device 103 into image information and displays it. The display device 105 also has a function of setting information (waveform information, transmission timing, etc.) of the sound waves transmitted from the transmission 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 transmission sound source 102, as well as the search target depth.

[0027] Fig. 5 is a functional configuration diagram explaining the processing performed by the reception processing device 103. In Fig. 5, a phasing processing unit 1032 inputs N pieces of reception data 1031 from N pieces of reception elements 1 to N that constitute the line array of the towed sonar 104, performs phasing processing, and outputs the phasing processing result to a signal processing unit 1033.

[0028] The signal processing unit 1033 extracts echoes of targets (underwater objects) using correlation processing or the like for the phasing processing results received from the phasing processing unit 1032 .

[0029] 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 geometrically calculated.

[0030] The signal processor 1033 detects the target azimuth θ T ' and distance r T ', search depth d ss From the array pitch angle α, the three-dimensional coordinates of the target position (coordinates in the three-dimensional coordinate system XYZ in FIG. 3(A)) are calculated with the acoustic center position of the towed sonar 20 as the origin.

[0031] Assume that the towed sonar 104 (line array) is equipped with at least two depth sensors 106A and 106B, and the distance between them is L [m]. When the pitch angle (array pitch angle) of the line array with respect to the acoustic center position of the towed sonar 20 is α, the depth at the depth sensor 106A is d 1 [m] (positive: toward the bottom), and the depth measured by the depth sensor 106B is d 2 [m](d 1 >d 2 ), the inclination of the depth sensors 106A and 106B with respect to the horizontal axis is α, so the depth difference is d 1 -d 2 = L sin(α), the array pitch angle α is given by the following equation (1). TIFF0007639488000001.tif9150...(1)

[0032] 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 d 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. 3(A)). ss Calculate.

[0033] The azimuth θ of the target 21 identified by N pieces of received data from the towed sonar 20 (N receiving elements of a line array) T ' and distance r T ' is a value obtained 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. In the three-dimensional coordinate system X'YZ', the position (x', y', z') of the target 21 is given by:

[0034] TIFF0007639488000002.tif6150 TIFF0007639488000003.tif6150 TIFF0007639488000004.tif6150 (2)

[0035] Here, φ is given by the following equation. TIFF0007639488000005.tif11150...(3)

[0036] In equation (2), the azimuth θ of the target 21 T θ' is the angle in the counterclockwise direction from the X' axis on the X'-Y plane. In the left-handed coordinate system, the angle in the counterclockwise direction from the X' axis on the X'-Y plane is negative, but for the sake of simplicity, the azimuth θ T In FIG. 3A, the target 21 is moved from the origin (the acoustic center position of the towed sonar 20) to a distance of length (distance) r T ' vector, and the projection value x' of the vector onto the X' axis is r T 'cos(θ T '), and the angle φ is the projection r T 'cos(θ T ') perpendicular to the component (length r T 'sin(θ T The projection of the vector y' onto the Y-Z' plane can be considered as the angle it makes with the Y-axis. Therefore, the projection value y' onto the Y-axis (negative on the west side) is -r T 'sin(θ T ') cos(φ), the projection value z' onto the Z axis is -r T 'sin(θ T ')·sin(φ).

[0037] In equation (3), the arcsine function sin -1 The numerator is the distance r of target 21. T Projection value of r onto the X-axis T 'cos(θ T The value (r T 'cos(θT ')·sin(α)>0) at search depth d ss (<0) is added. The denominator is r T 'sin(θ T The numerator is negative and the angle φ is non-negative, so a minus sign is added.

[0038] The azimuth / distance correction unit 1034 calculates a transformation matrix R(-α) that rotates the position (x', y', z') of the target 21 in the three-dimensional coordinate system X'YZ' by -α degrees around the Y axis: TIFF0007639488000006.tif14150...(4) This is applied to convert the values ​​into coordinates in the XYZ coordinate system.

[0039] TIFF0007639488000007.tif13150 (5)

[0040] From equation (5), TIFF0007639488000008.tif6150 TIFF0007639488000009.tif6150 TIFF0007639488000010.tif6150...(6)

[0041] The azimuth / distance correction unit 1034 calculates the coordinates (x, y, z) of the target 21 in the three-dimensional coordinate system XYZ using the above equation (6).

[0042] Next, the azimuth / distance correction unit 1034 calculates an azimuth θ , which is a coordinate (x, y) projected onto a two-dimensional coordinate plane, XY, 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). t (25 in Fig. 3(B)) and the distance r t (26 in Figure 3(B)) is calculated.

[0043] TIFF0007639488000011.tif8150...(7)

[0044] TIFF0007639488000012.tif21153...(8)

[0045] In addition, in equation (7), the direction θ t Since is a non-negative value, tan -1 In the calculation, the Y coordinate value of the position of the target 21: y (negative value) is set to -y, but the direction θ t If is set to a negative value, (-y / x) in equation (7) becomes (y / x).

[0046] The direction / distance correction unit 1034 corrects the direction θ of the target 21A projected on the two-dimensional XY plane. t and distance r t is output as the final processing result.

[0047] 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.

[0048] 6 is a diagram for explaining the method of this embodiment. The reception processing device 103 calculates the azimuth and distance of the target from the reception data of the line array (step S11).

[0049] 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.

[0050] The reception processing device 103 uses the input search target 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).

[0051] The reception processing device 103 outputs the direction 25 and distance 26 projected onto two-dimensional coordinates (XY plane) from the three-dimensional coordinates found in step S13 as the position of the target 21 (step S14).

[0052] Fig. 7 is a diagram for explaining one embodiment. It shows the effect when the embodiment is applied to the towed sonar detection information (azimuth, distance) obtained when the search target depth 24 is 100m (based on the towed sonar depth) and the array pitch angle is 10°. In Fig. 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, and the detection azimuth and distance corrected by applying the present invention are expanded onto plane coordinates.

[0053] 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 directivity (conical beam) of the towed sonar, but it can be seen that this property is corrected. The search 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.

[0054] 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 each process of the phasing processing unit 1032, the signal processing unit 1033, and the azimuth / distance correction unit 1034 of the reception processing device 103 of FIG. 5. The computer device 110 may be configured to implement the functions of the transmission control device 101 of FIG. 4.

[0055] In the above embodiment, the inclination of the towed sonar in the depth direction is an example in which two depth sensors are used, but it is also possible to use a method in which multiple depth sensors are mounted and calculated. Also, any sensor that can obtain attitude information, such as an acceleration sensor, can be used. Also, while Fig. 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 line array with a conical shape.

[0056] The disclosure of the above-mentioned Patent Document 1 is incorporated herein by reference. Modifications and adjustments of the embodiments and examples are possible within the scope of the entire disclosure of the present invention (including the scope of 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 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 claims and the technical ideas. [Explanation of symbols]

[0057] 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 depth 25 directions 26 distance 101 Transmission control device 102 Transmission source 103 Receiving processing device 104 Towed Sonar 105 Display device 110 Computer equipment 111 Processor 112 Storage device 113 Programs 114 Interface 106A, 106B Depth Sensor 1031 Received Data 1032 Phase adjustment processing section 1033 Signal Processing Unit 1034 Direction / distance correction section

Claims

1. 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 is a towed sonar line array; and 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 specified by the 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.

2. The towed sonar includes at least two depth sensors spaced apart from each other; 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 target 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.

3. 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, with respect to the target bearing and distance specified by the received data from the line array, is corrected by using the search target depth that is set and input in advance.

4. 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 target 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.

5. 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.

6. 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.

Images