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WO2012133996A1 - Line array sonar and method for detecting target bearing of the same - Google Patents

Line array sonar and method for detecting target bearing of the same Download PDF

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Publication number
WO2012133996A1
WO2012133996A1 PCT/KR2011/005863 KR2011005863W WO2012133996A1 WO 2012133996 A1 WO2012133996 A1 WO 2012133996A1 KR 2011005863 W KR2011005863 W KR 2011005863W WO 2012133996 A1 WO2012133996 A1 WO 2012133996A1
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WO
WIPO (PCT)
Prior art keywords
target
bearing
arrival
angle
error
Prior art date
Application number
PCT/KR2011/005863
Other languages
French (fr)
Inventor
Joung Soo Park
Young Nam Na
Jee Woong Choi
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Agency For Defense Development
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Publication date
Application filed by Agency For Defense Development filed Critical Agency For Defense Development
Publication of WO2012133996A1 publication Critical patent/WO2012133996A1/en

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/74Systems using reradiation of acoustic waves, e.g. IFF, i.e. identification of friend or foe
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S3/00Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/80Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves
    • G01S3/802Systems for determining direction or deviation from predetermined direction
    • G01S3/808Systems for determining direction or deviation from predetermined direction using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
    • G01S3/8083Systems for determining direction or deviation from predetermined direction using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems determining direction of source
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88Sonar systems specially adapted for specific applications
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S3/00Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/80Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves
    • G01S3/8006Multi-channel systems specially adapted for direction-finding, i.e. having a single aerial system capable of giving simultaneous indications of the directions of different signals
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S3/00Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/80Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves
    • G01S3/801Details
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S3/00Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/80Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves
    • G01S3/802Systems for determining direction or deviation from predetermined direction
    • G01S3/808Systems for determining direction or deviation from predetermined direction using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
    • G01S3/8086Systems for determining direction or deviation from predetermined direction using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems determining other position line of source

Definitions

  • the present invention relates to a line array sonar for correcting an error included in a bearing of a target by applying a multi-path transmission phenomenon.
  • a sound wave is used as a means for detecting a target such as a submarine underwater.
  • a sound wave although its transmission speed is slow, can detect a long-range detection compared with a radio wave, so it is used in a sonar system using a sound wave as a means for a military purpose.
  • the sonar system may be divided into a passive sonar which detects noise radiated from a target and an active sonar which transmits a sound wave pulse and detects an echo returned upon being reflected from the target.
  • the passive sonar serves to directly detect a bearing of a target covertly.
  • a line array sonar is basically passive, in which acoustic sensors are linearly arranged in order to receive an acoustic signal of a target.
  • a beamforming technique is generally used in order to estimate the bearing from a target signal received by the linearly arranged acoustic sensors.
  • Basic information of the target detected by the passive sonar is the bearing of the target, and the bearing of the target is detected by a beamforming output on horizontal plane.
  • Plane wave beamforming is a technique of converting the difference in phase between the linearly arranged acoustic sensors into a bearing of a target on the assumption that a transmission path of a sound wave underwater is a straight line on a horizontal plane.
  • the range to the target is estimated through a target motion analysis by accumulating detected bearings.
  • a plane wave condition is included in the range estimation results of the target using the bearing estimated from the plane wave beamforming.
  • the plane wave condition is that a signal of the target reaches along a linear path on the horizontal plane having the same angle to every sensor of the line array sonar.
  • a sound wave is propagated along a reflection and refraction path, rather than along a horizontally linear path, due to the influence of the underwater sound velocity structure.
  • an acoustic signal radiated from the target reaches the line array sonar through various paths according to the underwater sound velocity structure.
  • Several transmission paths of the target signal exist and each has a different angle of arrival.
  • a path having the greatest signal strength, among several transmission paths, has the highest possibility of being selected as a bearing of the target.
  • the path according to reflection and refraction causes an error in the target bearing estimation results using beamforming.
  • the target bearing estimation results of the related art line array sonar underwater are inevitably different from the actual bearing.
  • An aspect of the present invention provides a line array sonar capable of precisely detecting a bearing of a target from a transmission path estimated by applying an actual underwater environment, without assuming that a sound wave transmission path to a target is a straight line, and a method for detecting a target bearing thereof.
  • Another aspect of the present invention provides a line array sonar detecting a bearing of a target calculating an estimated error of a target bearing from a transmission path estimated by applying an actual underwater environment and correcting an error, and a method for detecting a target bearing thereof.
  • a line array sonar including: a plurality of acoustic sensors arranged in a linear form and receiving an acoustic signal; a target detector detecting a target signal from the acoustic signal through beamforming, and outputting a target bearing and a target range; and a bearing compensator compensating for an error of the target bearing based on an angle of arrival of eigenrays according to transmission paths of the target signal.
  • the bearing compensator may search for a eigenray according to a transmission path having the strongest sound pressure among the eigenrays according to the transmission paths of the target signal and compensate for an error of the target bearing based on the angle of arrival of the eigenray according to the transmission path having the strongest sound pressure.
  • the bearing compensator may include: a transmission path calculation unit calculating the transmission paths by designated target depth; an arithmetic operation unit arithmetically operating a sound pressure and an angle of arrival of the eigenrays according to the transmission paths; an arrival angle searching unit searching for an angle of arrival consistent with the transmission path having the strongest sound pressure; and an error compensation unit removing a bearing error according to an angle of arrival searched by the arrival angle searching unit from the target bearing.
  • the bearing compensator may further include: an information input unit receiving the water depth and an underwater sound velocity structure.
  • the bearing compensator may further include: an information storage unit forming a database of the water depth and the underwater sound velocity structure and storing the same.
  • the transmission path calculation unit may calculate a plurality of transmission paths according to sound transmission characteristics of the target signal by using the water depth and the underwater sound velocity structure.
  • a method for detecting a target bearing of a line array sonar including: a signal reception step of receiving a target signal radiated from a target; a target detection step of calculating a target bearing from the target signal through beamforming; and an error compensation step of compensating for an error of the target bearing based on an angle of arrival of each designated target depth according to transmission paths of the target signal.
  • the error compensation step may include: calculating the transmission paths by using a water depth and an underwater sound velocity structure; arithmetically operating a sound pressure and an angle of arrival of the eigenrays according to the transmission paths; extracting a transmission path having the strongest sound pressure; searching for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure; and removing a bearing error according to the angle of arrival searched in the searching step.
  • the error compensating step may further include: receiving the water depth and the underwater sound velocity structure.
  • the error compensating step may further include: forming a database of the water depth and the underwater sound velocity structure and storing the same.
  • an apparatus for compensating for an error of a target bearing including: an input unit receiving a target bearing and a target range with respect to a target signal; a transmission path calculation unit calculating transmission paths of the target signal by designated target depth; an arithmetic operation unit arithmetically operating a sound pressure and an angle of arrival of eigenrays according to the transmission paths; an arrival angle searching unit searching for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure, among the eigenrays according to the transmission paths of the target signal; and an error compensation unit removing a bearing error according to an angle of arrival searched by the arrival angle searching unit from the target bearing.
  • an algorithm compensating for a bearing error of a target is provided, whereby a bearing a target can be precisely detected by applying a multi-path transmission phenomenon according to the reflection and refraction of a sound wave in consideration of the underwater vertical sound velocity structure in the process of estimating a target bearing of the line array sonar, and thus, the performance of the line array sonar can be improved.
  • FIG. 1 is a schematic block diagram showing the configuration of a line array sonar according to an embodiment of the present invention
  • FIGS. 2 and 3 are schematic block diagrams of an apparatus for compensating for an error of a target bearing according to an embodiment of the present invention
  • FIGS. 4 and 5 are flow charts illustrating the process of a method for detecting a target bearing of a line array sonar according to an embodiment of the present invention
  • FIG. 6 is a view for explaining a relationship between an underwater sound velocity structure and a target signal
  • FIG. 7 is a view for explaining correlation between an angle of arrival of a target signal and a target bearing
  • FIG. 8 is a view for explaining an angle of arrival of each designated target depth of a target signal to the line array sonar.
  • FIG. 9 is a graph showing target bearing compensation values over designated target depth.
  • a line array sonar includes a plurality of acoustic sensors 100 linearly arranged to receive an acoustic signal, a target detector 200 for detecting a target signal from the acoustic signal through beamforming, and outputting a target bearing and a target range, and a bearing compensator 300 for compensating for an error of the target bearing based on an angle of arrival of eigenrays according to transmission paths of the target signal.
  • the bearing compensator 300 includes a transmission path calculation unit 310 for calculating the transmission paths by designated target depth, an arithmetic operation unit 320 for arithmetically operating a sound pressure and an angle of arrival of each of the eigenrays according to the transmission paths, an arrival angle searching unit for searching for an angle of arrival consistent with a transmission path having the strongest sound pressure; and an error compensation unit 340 for removing a bearing error according to an angle of arrival searched by the arrival angle searching unit 330 from the target bearing.
  • the bearing compensator 300 searches the eigenrays according to the transmission paths of the target signal for a eigenray according to the transmission path having the strongest sound pressure, and compensates for an error of the target bearing based on the angle of arrival of the eigenray according to the transmission path having the strongest sound pressure.
  • the bearing compensator 300 and the apparatus for compensating for an error of a standard bearing will be unified as a standard bearing error compensating apparatus 300, and the standard bearing error compensating apparatus 300 will now be described.
  • the standard bearing error compensating apparatus 300 includes an input unit 360 for receiving a target bearing and a target range with respect to a target signal, a transmission path calculation unit 310 for calculating transmission paths of the target signal by designated target depth, an arithmetic operation unit 320 for arithmetically operating a sound pressure and an angle of arrival of each of the eigenrays according to the transmission paths, an arrival angle searching unit 330 for searching for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure among eigenrays according to the transmission paths of the target signal, and an error compensation unit 340 for removing a bearing error according to an angle of arrival searched by the arrival angle searching unit from the target bearing.
  • the standard bearing error compensating apparatus 300 may further include an information input unit 351 for receiving the water depth and an underwater sound velocity structure.
  • the standard bearing error compensating apparatus 300 may further include an information storage unit 352 for forming a database of the water depth and the underwater sound velocity structure and storing the same.
  • the standard bearing error compensating apparatus 300 receives a detection bearing ( ⁇ ) of the target detected by the target detector 200, a target motion analysis, or a target range (R) given by an assumption through the input unit 360, and use them as initial conditions.
  • a user, and so on inputs sea conditions including a water depth, an underwater sound velocity structure, and the like, for calculating the angle of arrival of the target signal through the information input unit 351.
  • the standard bearing error compensating apparatus 300 may use sea conditions such as the water depth, the underwater sound velocity structure, or the like, previously stored in the information storage unit 352.
  • the sea conditions may be directly observed in situ. Namely, the standard bearing error compensating apparatus 300 may directly observe environment data including the underwater sound velocity structure, and the like, in situ, receive the environment data through the information input unit 351, or extract the environment data from the database stored in the information storage unit 352.
  • the transmission path calculation unit 310 may calculate the plurality of transmission paths according to the signal characteristics of the target signal by using the water depth and the underwater sound velocity structure.
  • the related art uses a plane wave beamforming scheme of converting the difference in phase between linearly arranged acoustic sensors into a bearing of a target on the assumption that a transmission path underwater of a sound wave is a straight line in horizontal plane. This means that a target signal arrives along a straight line path on a horizontal plane at the same angle to the acoustic sensors of the line array sonar.
  • the target signal arrives at the line array sonar through various paths according to the vertical sound velocity structure, and there are various transmission paths of the target signal and each of the transmission paths has a different angle or arrival in vertical plane.
  • the transmission path calculation unit 310 calculates a plurality of transmission paths having various angles of arrival.
  • the bearing of the target detected from beamforming output is a ⁇ bearing by the angle of arrival ( ⁇ ) of the target signal.
  • a relationship between the actual target bearing ( ⁇ ) and detected detection bearing ( ⁇ ) may be represented by a cosine function as expressed by Math Figure 1 shown below:
  • the angle of arrival ( ⁇ ) is generally greater or smaller than 0, so as shown in Math Figure 1, the detection bearing ( ⁇ ) of the target detected by the line array sonar is mostly greater than the actual target bearing ( ⁇ ).
  • the arithmetic operation unit 320 estimates multi-path eigenrays along which the target signal at a range (R) underwater is reflected and refracted so as to be propagated, by designated target depth by using a numerical value interpretation modeling scheme according to the sea conditions input through the input unit 350. Also, the arithmetic operation unit 320 calculates a sound pressure P(i,j) of each eigenray and an angle of arrival ( ⁇ (i,j)) of each eigenray. Namely, the arithmetic operation unit 320 calculates the eigenrays along which a sound wave signal is reflected, refracted and propagated underwater by applying the numeric value interpretation scheme to the target signal transmission path according to input conditions.
  • the arithmetic operation unit 320 calculates the angle of arrival ( ⁇ (i,j)) and a sound pressure P(i,j), a measure of expressing the strength of a propagated sound wave signal, of each of the multi-transmission paths (j) and designated target depth (i) within the search location (R, ⁇ ).
  • the target detector 200 includes a signal processing unit 210 for filtering and frequency analyzing the acoustic signal to receive the target signal, a beamforming unit 220 for forming a beam, and a signal detection unit 230 for detecting the target bearing of the target signal from beam output.
  • the signal detection unit 230 for detecting the target bearing of the target signal.
  • the signal processing unit 210 receives the acoustic signal through the acoustic sensor 100 and processes the received acoustic signal to receive the target signal.
  • the beamforming unit 220 forms a beam, and the signal detection unit 230 determines whether or not there is a target signal, and outputs a target bearing based on basic information of the target. Also, the signal detection unit 230 accumulates the target bearing, estimates and calculates the target range through a target motion analysis.
  • the arrival angle searching unit 330 searches for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure among the eigenrays according to the transmission paths.
  • the arrival angle searching unit 330 extracts the transmission path having the strongest sound pressure through an arithmetic operation by itself. And then, the arrival angle searching unit 330 searches for an angle of arrival consistent with the transmission path having the strongest sound pressure.
  • the arrival angle searching unit 330 searches for the angle of arrival ( ⁇ (i,j)) corresponding to the transmission paths P(i,j) existing by designated target depth and the angle arrival ( ⁇ (i)) corresponding to the selected strong eigenray transmission path P(i) by designated target depth.
  • the angle of arrival is negative (-)
  • the target signal is received from an upper side based on the horizontal plane
  • the angle of arrival is positive (+)
  • the target signal is received from a lower side based on the horizontal plane.
  • the line array sonar does not discriminate the sign of the angle of arrival, so the size of the absolute value of the angle of arrival affects the target bearing.
  • the error compensation unit 340 removes a bearing error included in the detection bearing ( ⁇ ) with the angle of arrival ( ⁇ (i)) of each designated target depth searched by the arrival angle searching unit 330.
  • the error compensation unit 340 compensates for the bearing error by removing the influence of the angle of arrival included in the detection bearing ( ⁇ ) by using Math Figure 2 induced from Math Figure 1.
  • the compensated target bearing ⁇ (i) can be calculated by substituting the angle of arrival ( ⁇ (i)) of each designated target depth illustrated in FIG. 8 to Math Figure 2.
  • the compensated target bearing can be calculated to be within the range of 45 degrees to 49 degrees according to a designated target depth. Namely, the compensated target bearing is smaller by 1 to 5 degrees than 50 degrees, the detected bearing of the target, according to a designated target depth. The difference between the detection bearing ( ⁇ ) and the compensated bearing is increased as the detection bearing is reduced as shown in Math Figure 2.
  • a method for detecting a target bearing of a line array sonar include a signal reception step S100 of receiving a target signal radiated from a certain target, a target detection step S200 of calculating a target bearing from the target signal by forming a beam, and an error compensation step S300 of compensating for an error of the target bearing based on an angle of arrival of eigenrays according to transmission paths of the target signal by designated target depth.
  • the target detection step S200 the target bearing may be accumulated and the target range can be estimated through a target motion analysis.
  • FIGS. 1 to 3 A configuration of an apparatus hereinafter is referred to FIGS. 1 to 3.
  • the error compensation step S300 includes a step S310 of calculating the transmission paths by using a water depth and an underwater sound velocity structure, a step S320 of arithmetically operating a sound pressure and an angle of arrival of the eigenrays according to the transmission paths; a step S330 of extracting a transmission path having the strongest sound pressure, a step S340 of searching for an angle of arrival of the eigenray according to the transmission path having the strongest sound pressure, and a step S350 of removing a bearing error according to the angle of arrival searched in the searching step.
  • the error compensation step S300 may further include a step of receiving the water depth and the underwater sound velocity structure, or may further include a step S301 of forming a database of the water depth and the underwater sound velocity structure in advance and storing the same.
  • the line array sonar receives an acoustic signal from a target by using a plurality of acoustic sensors (S100), and processes the acoustic signal to determine whether or not it is a target signal, and outputs a target bearing as basic information of the target (S200). Also, the line array sonar accumulates the target bearing, and the target range is estimated through a target motion analysis.
  • the line array sonar uses the detected target bearing ( ⁇ ) and a target range (R) given by the target motion analysis or an assumption, as initial conditions.
  • the line array sonar may directly observe environment data including the underwater sound velocity structure, or the like, in situ, receive the environment data from a user, and so on, or extract the environment data from previously stored database and use it (S301).
  • the line array sonar calculates the plurality of transmission paths according to sound transmission characteristics of the target signal by using the water depth and the underwater sound velocity structure.
  • the related art uses the plane wave beamforming scheme of converting the difference in phase between the linearly arranged acoustic sensors into a target bearing on the assumption that the transmission path of the underwater sound wave is a straight line. This means that the target signal arrives at a straight line path on the horizontal plane having the same angle to the acoustic sensors of the line array sonar.
  • the target signal arrives at the line array sonar through various paths along the vertical sound velocity structure, and there are several transmission paths of the target signal and each of the transmission paths has a different angle of arrival.
  • the line array sonar calculates a plurality of transmission paths having various angles of arrival (step S310).
  • the bearing of the target detected from a beamforming output is bearing ⁇ by the angle of arrival ( ⁇ ).
  • a relationship between the actual target bearing ( ⁇ ) of the target and the detected bearing q is as shown Math Figure 1.
  • the angle of arrival ( ⁇ ) underwater is generally greater than or smaller than 0, so as shown in Math Figure 1, the detection bearing ⁇ of the target detected by the line array sonar is mostly greater than the actual target bearing ⁇ .
  • the line array sonar calculates the angle of arrival ( ⁇ (i,j)) of the eigenrays along which a sound wave signal is reflected, refracted and propagated underwater according to multi-transmissions paths (j) and designated target depth (i) within a search location (R, ⁇ ) and a sound pressure P(i,j), a measure of expressing the strength of a propagated sound wave signal, by applying the numeric value interpretation scheme to the target signal transmission path according to input conditions (step S320).
  • the line array sonar extracts a transmission path having the strongest sound pressure among the eigenrays according to the transmission paths of the target signal (step S330), and searches for an angle of arrival of the eigenray according to the transmission path having the strongest sound pressure (step S340).
  • steps S330 several transmission paths of a target signal exist between the line array sonar and the target, and there is an angle of arrival ( ⁇ (i,j)) corresponding to the several transmission paths P(i,j) different by designated target depth (i).
  • the line array sonar searches for the angle of arrival ( ⁇ (i,j)) corresponding to the transmission paths P(i,j) existing by designated target depth and the angle arrival ( ⁇ (i)) corresponding to the selected strong transmission path P(i) by designated target depth.
  • the line array sonar does not discriminate the sign of the angle of arrival, so the size of the absolute value of the angle of arrival affects the target bearing.
  • the line array sonar removes a bearing error included in the detection bearing ( ⁇ ) with the angle of arrival ( ⁇ (i)) of each designated target depth searched by the arrival angle searching unit 330. Namely, the line array sonar compensates for the bearing error by removing the influence of the angle of arrival included in the detection bearing ( ⁇ ) by using Math Figure 2 induced from Math Figure 1 (step S350).
  • the bearing of the target can be precisely detected.
  • the present invention have industrial applicability by the line array sonar capable of detecting a bearing of a target and a method for detecting a target bearing thereof.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

A line array sonar and a method for detecting a target bearing thereof are disclosed. A bearing error of a target is compensated for by applying a multi-path transmission phenomenon according to reflection and refraction of a sound wave in consideration of an underwater vertical sound velocity structure in a process of detecting a target bearing of the line array sonar, thus accurately detecting a bearing of the target.

Description

LINE ARRAY SONAR AND METHOD FOR DETECTING TARGET BEARING OF THE SAME
The present invention relates to a line array sonar for correcting an error included in a bearing of a target by applying a multi-path transmission phenomenon.
A sound wave is used as a means for detecting a target such as a submarine underwater. A sound wave, although its transmission speed is slow, can detect a long-range detection compared with a radio wave, so it is used in a sonar system using a sound wave as a means for a military purpose. The sonar system may be divided into a passive sonar which detects noise radiated from a target and an active sonar which transmits a sound wave pulse and detects an echo returned upon being reflected from the target. The passive sonar serves to directly detect a bearing of a target covertly. A line array sonar is basically passive, in which acoustic sensors are linearly arranged in order to receive an acoustic signal of a target. A beamforming technique is generally used in order to estimate the bearing from a target signal received by the linearly arranged acoustic sensors. Basic information of the target detected by the passive sonar is the bearing of the target, and the bearing of the target is detected by a beamforming output on horizontal plane. Plane wave beamforming is a technique of converting the difference in phase between the linearly arranged acoustic sensors into a bearing of a target on the assumption that a transmission path of a sound wave underwater is a straight line on a horizontal plane. The range to the target is estimated through a target motion analysis by accumulating detected bearings. Thus, a plane wave condition is included in the range estimation results of the target using the bearing estimated from the plane wave beamforming. The plane wave condition is that a signal of the target reaches along a linear path on the horizontal plane having the same angle to every sensor of the line array sonar.
However, in actuality, a sound wave is propagated along a reflection and refraction path, rather than along a horizontally linear path, due to the influence of the underwater sound velocity structure. As shown in FIG. 6, an acoustic signal radiated from the target reaches the line array sonar through various paths according to the underwater sound velocity structure. Several transmission paths of the target signal exist and each has a different angle of arrival. A path having the greatest signal strength, among several transmission paths, has the highest possibility of being selected as a bearing of the target. The path according to reflection and refraction causes an error in the target bearing estimation results using beamforming. Thus, the target bearing estimation results of the related art line array sonar underwater are inevitably different from the actual bearing.
An aspect of the present invention provides a line array sonar capable of precisely detecting a bearing of a target from a transmission path estimated by applying an actual underwater environment, without assuming that a sound wave transmission path to a target is a straight line, and a method for detecting a target bearing thereof.
Another aspect of the present invention provides a line array sonar detecting a bearing of a target calculating an estimated error of a target bearing from a transmission path estimated by applying an actual underwater environment and correcting an error, and a method for detecting a target bearing thereof.
According to an aspect of the present invention, there is provided a line array sonar including: a plurality of acoustic sensors arranged in a linear form and receiving an acoustic signal; a target detector detecting a target signal from the acoustic signal through beamforming, and outputting a target bearing and a target range; and a bearing compensator compensating for an error of the target bearing based on an angle of arrival of eigenrays according to transmission paths of the target signal.
The bearing compensator may search for a eigenray according to a transmission path having the strongest sound pressure among the eigenrays according to the transmission paths of the target signal and compensate for an error of the target bearing based on the angle of arrival of the eigenray according to the transmission path having the strongest sound pressure.
The bearing compensator may include: a transmission path calculation unit calculating the transmission paths by designated target depth; an arithmetic operation unit arithmetically operating a sound pressure and an angle of arrival of the eigenrays according to the transmission paths; an arrival angle searching unit searching for an angle of arrival consistent with the transmission path having the strongest sound pressure; and an error compensation unit removing a bearing error according to an angle of arrival searched by the arrival angle searching unit from the target bearing.
The bearing compensator may further include: an information input unit receiving the water depth and an underwater sound velocity structure.
The bearing compensator may further include: an information storage unit forming a database of the water depth and the underwater sound velocity structure and storing the same.
The transmission path calculation unit may calculate a plurality of transmission paths according to sound transmission characteristics of the target signal by using the water depth and the underwater sound velocity structure.
According to another aspect of the present invention, there is provided a method for detecting a target bearing of a line array sonar, including: a signal reception step of receiving a target signal radiated from a target; a target detection step of calculating a target bearing from the target signal through beamforming; and an error compensation step of compensating for an error of the target bearing based on an angle of arrival of each designated target depth according to transmission paths of the target signal.
The error compensation step may include: calculating the transmission paths by using a water depth and an underwater sound velocity structure; arithmetically operating a sound pressure and an angle of arrival of the eigenrays according to the transmission paths; extracting a transmission path having the strongest sound pressure; searching for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure; and removing a bearing error according to the angle of arrival searched in the searching step.
The error compensating step may further include: receiving the water depth and the underwater sound velocity structure.
The error compensating step may further include: forming a database of the water depth and the underwater sound velocity structure and storing the same.
According to another aspect of the present invention, there is provided an apparatus for compensating for an error of a target bearing, including: an input unit receiving a target bearing and a target range with respect to a target signal; a transmission path calculation unit calculating transmission paths of the target signal by designated target depth; an arithmetic operation unit arithmetically operating a sound pressure and an angle of arrival of eigenrays according to the transmission paths; an arrival angle searching unit searching for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure, among the eigenrays according to the transmission paths of the target signal; and an error compensation unit removing a bearing error according to an angle of arrival searched by the arrival angle searching unit from the target bearing.
In the line array sonar and the method for detecting a target bearing thereof according to embodiments of the present invention, an algorithm compensating for a bearing error of a target is provided, whereby a bearing a target can be precisely detected by applying a multi-path transmission phenomenon according to the reflection and refraction of a sound wave in consideration of the underwater vertical sound velocity structure in the process of estimating a target bearing of the line array sonar, and thus, the performance of the line array sonar can be improved.
FIG. 1 is a schematic block diagram showing the configuration of a line array sonar according to an embodiment of the present invention;
FIGS. 2 and 3 are schematic block diagrams of an apparatus for compensating for an error of a target bearing according to an embodiment of the present invention;
FIGS. 4 and 5 are flow charts illustrating the process of a method for detecting a target bearing of a line array sonar according to an embodiment of the present invention;
FIG. 6 is a view for explaining a relationship between an underwater sound velocity structure and a target signal;
FIG. 7 is a view for explaining correlation between an angle of arrival of a target signal and a target bearing;
FIG. 8 is a view for explaining an angle of arrival of each designated target depth of a target signal to the line array sonar; and
FIG. 9 is a graph showing target bearing compensation values over designated target depth.
A line array sonar and a method for detecting a target bearing thereof according to embodiments of the present invention will now be described with reference to the accompanying drawings.
With reference to FIG. 1, a line array sonar according to an embodiment of the present invention includes a plurality of acoustic sensors 100 linearly arranged to receive an acoustic signal, a target detector 200 for detecting a target signal from the acoustic signal through beamforming, and outputting a target bearing and a target range, and a bearing compensator 300 for compensating for an error of the target bearing based on an angle of arrival of eigenrays according to transmission paths of the target signal.
With reference to FIG. 2, the bearing compensator 300 includes a transmission path calculation unit 310 for calculating the transmission paths by designated target depth, an arithmetic operation unit 320 for arithmetically operating a sound pressure and an angle of arrival of each of the eigenrays according to the transmission paths, an arrival angle searching unit for searching for an angle of arrival consistent with a transmission path having the strongest sound pressure; and an error compensation unit 340 for removing a bearing error according to an angle of arrival searched by the arrival angle searching unit 330 from the target bearing.
The bearing compensator 300 searches the eigenrays according to the transmission paths of the target signal for a eigenray according to the transmission path having the strongest sound pressure, and compensates for an error of the target bearing based on the angle of arrival of the eigenray according to the transmission path having the strongest sound pressure.
Hereinafter, the bearing compensator 300 and the apparatus for compensating for an error of a standard bearing will be unified as a standard bearing error compensating apparatus 300, and the standard bearing error compensating apparatus 300 will now be described.
Namely, with reference to FIGS. 2 and 3, the standard bearing error compensating apparatus 300 includes an input unit 360 for receiving a target bearing and a target range with respect to a target signal, a transmission path calculation unit 310 for calculating transmission paths of the target signal by designated target depth, an arithmetic operation unit 320 for arithmetically operating a sound pressure and an angle of arrival of each of the eigenrays according to the transmission paths, an arrival angle searching unit 330 for searching for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure among eigenrays according to the transmission paths of the target signal, and an error compensation unit 340 for removing a bearing error according to an angle of arrival searched by the arrival angle searching unit from the target bearing.
With reference to FIG. 2, for example, the standard bearing error compensating apparatus 300 may further include an information input unit 351 for receiving the water depth and an underwater sound velocity structure. In another example, with reference to FIG. 3, the standard bearing error compensating apparatus 300 may further include an information storage unit 352 for forming a database of the water depth and the underwater sound velocity structure and storing the same.
The standard bearing error compensating apparatus 300 receives a detection bearing (θ) of the target detected by the target detector 200, a target motion analysis, or a target range (R) given by an assumption through the input unit 360, and use them as initial conditions. A user, and so on, inputs sea conditions including a water depth, an underwater sound velocity structure, and the like, for calculating the angle of arrival of the target signal through the information input unit 351. Also, the standard bearing error compensating apparatus 300 may use sea conditions such as the water depth, the underwater sound velocity structure, or the like, previously stored in the information storage unit 352. Also, the sea conditions may be directly observed in situ. Namely, the standard bearing error compensating apparatus 300 may directly observe environment data including the underwater sound velocity structure, and the like, in situ, receive the environment data through the information input unit 351, or extract the environment data from the database stored in the information storage unit 352.
The transmission path calculation unit 310 may calculate the plurality of transmission paths according to the signal characteristics of the target signal by using the water depth and the underwater sound velocity structure. The related art uses a plane wave beamforming scheme of converting the difference in phase between linearly arranged acoustic sensors into a bearing of a target on the assumption that a transmission path underwater of a sound wave is a straight line in horizontal plane. This means that a target signal arrives along a straight line path on a horizontal plane at the same angle to the acoustic sensors of the line array sonar. However, with reference to FIG. 6, the target signal arrives at the line array sonar through various paths according to the vertical sound velocity structure, and there are various transmission paths of the target signal and each of the transmission paths has a different angle or arrival in vertical plane. The transmission path calculation unit 310 calculates a plurality of transmission paths having various angles of arrival.
With reference to FIG. 7, when the acoustic sensors of the line array sonar are at the y axis and the target is in a φ bearing at the center of the line array sonar, the bearing of the target detected from beamforming output is a θ bearing by the angle of arrival (μ) of the target signal. A relationship between the actual target bearing (φ) and detected detection bearing (θ) may be represented by a cosine function as expressed by Math Figure 1 shown below:
MathFigure 1
Figure PCTKR2011005863-appb-M000001
In the sea, the angle of arrival (μ) is generally greater or smaller than 0, so as shown in Math Figure 1, the detection bearing (θ) of the target detected by the line array sonar is mostly greater than the actual target bearing (φ).
The arithmetic operation unit 320 estimates multi-path eigenrays along which the target signal at a range (R) underwater is reflected and refracted so as to be propagated, by designated target depth by using a numerical value interpretation modeling scheme according to the sea conditions input through the input unit 350. Also, the arithmetic operation unit 320 calculates a sound pressure P(i,j) of each eigenray and an angle of arrival (μ(i,j)) of each eigenray. Namely, the arithmetic operation unit 320 calculates the eigenrays along which a sound wave signal is reflected, refracted and propagated underwater by applying the numeric value interpretation scheme to the target signal transmission path according to input conditions. And then, the arithmetic operation unit 320 calculates the angle of arrival (μ(i,j)) and a sound pressure P(i,j), a measure of expressing the strength of a propagated sound wave signal, of each of the multi-transmission paths (j) and designated target depth (i) within the search location (R, θ).
With reference to FIG. 1, the target detector 200 includes a signal processing unit 210 for filtering and frequency analyzing the acoustic signal to receive the target signal, a beamforming unit 220 for forming a beam, and a signal detection unit 230 for detecting the target bearing of the target signal from beam output. The signal detection unit 230 for detecting the target bearing of the target signal. The signal processing unit 210 receives the acoustic signal through the acoustic sensor 100 and processes the received acoustic signal to receive the target signal. The beamforming unit 220 forms a beam, and the signal detection unit 230 determines whether or not there is a target signal, and outputs a target bearing based on basic information of the target. Also, the signal detection unit 230 accumulates the target bearing, estimates and calculates the target range through a target motion analysis.
The arrival angle searching unit 330 searches for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure among the eigenrays according to the transmission paths. The arrival angle searching unit 330 extracts the transmission path having the strongest sound pressure through an arithmetic operation by itself. And then, the arrival angle searching unit 330 searches for an angle of arrival consistent with the transmission path having the strongest sound pressure.
With reference to FIG. 8, several transmission paths of a target signal exist between the line array sonar and the target, and there is an angle of arrival (μ(i,j)) corresponding to the several transmission paths P(i,j) different by designated target depth (i). The arrival angle searching unit 330 searches for the angle of arrival (μ(i,j)) corresponding to the transmission paths P(i,j) existing by designated target depth and the angle arrival (μ(i)) corresponding to the selected strong eigenray transmission path P(i) by designated target depth. Here, when the angle of arrival is negative (-), the target signal is received from an upper side based on the horizontal plane, and when the angle of arrival is positive (+), the target signal is received from a lower side based on the horizontal plane. In general, the line array sonar does not discriminate the sign of the angle of arrival, so the size of the absolute value of the angle of arrival affects the target bearing.
The error compensation unit 340 removes a bearing error included in the detection bearing (θ) with the angle of arrival (μ(i)) of each designated target depth searched by the arrival angle searching unit 330. The error compensation unit 340 compensates for the bearing error by removing the influence of the angle of arrival included in the detection bearing (θ) by using Math Figure 2 induced from Math Figure 1.
MathFigure 2
Figure PCTKR2011005863-appb-M000002
With reference to FIG. 9, when it is assumed that the a detection bearing of the target detected by the line array sonar is 50 degrees, regardless of a depth of the target, the compensated target bearing φ(i) can be calculated by substituting the angle of arrival (μ(i)) of each designated target depth illustrated in FIG. 8 to Math Figure 2. The compensated target bearing can be calculated to be within the range of 45 degrees to 49 degrees according to a designated target depth. Namely, the compensated target bearing is smaller by 1 to 5 degrees than 50 degrees, the detected bearing of the target, according to a designated target depth. The difference between the detection bearing (θ) and the compensated bearing is increased as the detection bearing is reduced as shown in Math Figure 2.
With reference to FIG. 4, a method for detecting a target bearing of a line array sonar according to an embodiment of the present invention include a signal reception step S100 of receiving a target signal radiated from a certain target, a target detection step S200 of calculating a target bearing from the target signal by forming a beam, and an error compensation step S300 of compensating for an error of the target bearing based on an angle of arrival of eigenrays according to transmission paths of the target signal by designated target depth. Here, in the target detection step S200, the target bearing may be accumulated and the target range can be estimated through a target motion analysis. A configuration of an apparatus hereinafter is referred to FIGS. 1 to 3.
With reference to FIG. 5, the error compensation step S300 includes a step S310 of calculating the transmission paths by using a water depth and an underwater sound velocity structure, a step S320 of arithmetically operating a sound pressure and an angle of arrival of the eigenrays according to the transmission paths; a step S330 of extracting a transmission path having the strongest sound pressure, a step S340 of searching for an angle of arrival of the eigenray according to the transmission path having the strongest sound pressure, and a step S350 of removing a bearing error according to the angle of arrival searched in the searching step. With reference to FIG. 5, the error compensation step S300 may further include a step of receiving the water depth and the underwater sound velocity structure, or may further include a step S301 of forming a database of the water depth and the underwater sound velocity structure in advance and storing the same.
First, the line array sonar receives an acoustic signal from a target by using a plurality of acoustic sensors (S100), and processes the acoustic signal to determine whether or not it is a target signal, and outputs a target bearing as basic information of the target (S200). Also, the line array sonar accumulates the target bearing, and the target range is estimated through a target motion analysis.
The line array sonar uses the detected target bearing (θ) and a target range (R) given by the target motion analysis or an assumption, as initial conditions. The line array sonar may directly observe environment data including the underwater sound velocity structure, or the like, in situ, receive the environment data from a user, and so on, or extract the environment data from previously stored database and use it (S301).
The line array sonar calculates the plurality of transmission paths according to sound transmission characteristics of the target signal by using the water depth and the underwater sound velocity structure. The related art uses the plane wave beamforming scheme of converting the difference in phase between the linearly arranged acoustic sensors into a target bearing on the assumption that the transmission path of the underwater sound wave is a straight line. This means that the target signal arrives at a straight line path on the horizontal plane having the same angle to the acoustic sensors of the line array sonar. However, with reference to FIG. 6, the target signal arrives at the line array sonar through various paths along the vertical sound velocity structure, and there are several transmission paths of the target signal and each of the transmission paths has a different angle of arrival. The line array sonar calculates a plurality of transmission paths having various angles of arrival (step S310).
With reference to FIG. 7, when the acoustic sensors of the line array sonar are at the y axis and the target is at a φ bearing at the center of the line array sonar, the bearing of the target detected from a beamforming output is bearing θ by the angle of arrival (μ). A relationship between the actual target bearing (φ) of the target and the detected bearing q is as shown Math Figure 1. The angle of arrival (μ) underwater is generally greater than or smaller than 0, so as shown in Math Figure 1, the detection bearing θ of the target detected by the line array sonar is mostly greater than the actual target bearing φ.
The line array sonar calculates the angle of arrival (μ(i,j)) of the eigenrays along which a sound wave signal is reflected, refracted and propagated underwater according to multi-transmissions paths (j) and designated target depth (i) within a search location (R, θ) and a sound pressure P(i,j), a measure of expressing the strength of a propagated sound wave signal, by applying the numeric value interpretation scheme to the target signal transmission path according to input conditions (step S320).
The line array sonar extracts a transmission path having the strongest sound pressure among the eigenrays according to the transmission paths of the target signal (step S330), and searches for an angle of arrival of the eigenray according to the transmission path having the strongest sound pressure (step S340). With reference to FIG. 8, several transmission paths of a target signal exist between the line array sonar and the target, and there is an angle of arrival (μ(i,j)) corresponding to the several transmission paths P(i,j) different by designated target depth (i). The line array sonar searches for the angle of arrival (μ(i,j)) corresponding to the transmission paths P(i,j) existing by designated target depth and the angle arrival (μ(i)) corresponding to the selected strong transmission path P(i) by designated target depth. Here, when the angle of arrival is negative (-), the target signal is received from an upper side based on the horizontal plane, and when the angle of arrival is positive (+), the target signal is received from a lower side based on the horizontal plane. In general, the line array sonar does not discriminate the sign of the angle of arrival, so the size of the absolute value of the angle of arrival affects the target bearing.
The line array sonar removes a bearing error included in the detection bearing (θ) with the angle of arrival (μ(i)) of each designated target depth searched by the arrival angle searching unit 330. Namely, the line array sonar compensates for the bearing error by removing the influence of the angle of arrival included in the detection bearing (θ) by using Math Figure 2 induced from Math Figure 1 (step S350).
As described above, in the line array sonar and the method for detecting a target bearing thereof according to embodiments of the present invention, since a bearing error of a target is compensated for by applying a multi-path transmission phenomenon according to the reflection and refraction of a sound wave in consideration of the underwater vertical sound velocity structure in the process of detecting a target bearing of the line array sonar, the bearing of the target can be precisely detected.
The present invention have industrial applicability by the line array sonar capable of detecting a bearing of a target and a method for detecting a target bearing thereof.

Claims (13)

  1. A line array sonar comprising:
    a plurality of acoustic sensors arranged in a linear form and receiving an acoustic signal;
    a target detector detecting a target signal from the acoustic signal through beamforming, and outputting a target bearing and a target range; and
    a bearing compensator compensating for an error of the target bearing based on an angle of arrival of eigenrays according to transmission paths of the target signal.
  2. The line array sonar of claim 1, wherein the bearing compensator searches for a eigenray according to a transmission path having the strongest sound pressure among the eigenrays according to the transmission paths of the target signal and compensates for an error of the target bearing based on the angle of arrival of the eigenray according to the transmission path having the strongest sound pressure.
  3. The line array sonar of claim 2, wherein the bearing compensator comprises:
    a transmission path calculation unit calculating the transmission paths by designated target depth;
    an arithmetic operation unit arithmetically operating a sound pressure and an angle of arrival of the eigenrays according to the transmission paths;
    an arrival angle searching unit searching for an angle of arrival consistent with the transmission path having the strongest sound pressure; and
    an error compensation unit removing a bearing error according to an angle of arrival searched by the arrival angle searching unit from the target bearing.
  4. The line array sonar of claim 3, wherein the bearing compensator further comprises:
    an information input unit receiving the water depth and an underwater sound velocity structure.
  5. The line array sonar of claim 3, wherein the bearing compensator further comprises:
    an information storage unit forming a database of the water depth and the underwater sound velocity structure and storing the same.
  6. The line array sonar of claim 4 or claim 5, wherein the transmission path calculation unit calculates a plurality of transmission paths according to sound transmission characteristics of the target signal by using the water depth and the underwater sound velocity structure.
  7. A method for detecting a target bearing of a line array sonar, the method comprising:
    a signal reception step of receiving a target signal radiated from a certain target; a target detection step of calculating a target bearing from the target signal through beamforming; and
    an error compensation step of compensating for an error of the target bearing based on an angle of arrival of each designated target depth of eigenrays according to transmission paths of the target signal.
  8. The method of claim 7, the error compensation step comprises:
    calculating the transmission paths by using a water depth and an underwater sound velocity structure;
    arithmetically operating a sound pressure and an angle of arrival of the eigenrays according to the transmission paths;
    extracting a transmission path having the strongest sound pressure;
    searching for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure; and
    removing a bearing error according to the angle of arrival searched in the searching step.
  9. The method of claim 8, wherein the error compensating step further comprises:
    receiving the water depth and the underwater sound velocity structure.
  10. The method of claim 8, wherein the error compensating step further comprises:
    forming a database of the water depth and the underwater sound velocity structure and storing the same.
  11. An apparatus for compensating for an error of a target bearing, the apparatus comprising:
    an input unit receiving a target bearing and a target range with respect to a target signal;
    a transmission path calculation unit calculating transmission paths of the target signal by designated target depth;
    an arithmetic operation unit arithmetically operating a sound pressure and an angle of arrival of eigenrays according to the transmission paths;
    an arrival angle searching unit searching for an angle of arrival of a eigenray according to the transmission path having the strongest sound pressure, among the eigenrays according to the transmission paths of the target signal; and
    an error compensation unit removing a bearing error according to an angle of arrival searched by the arrival angle searching unit from the target bearing.
  12. The apparatus of claim 11, further comprising:
    an information input unit receiving the water depth and an underwater sound velocity structure.
  13. The apparatus of claim 11, further comprising:
    an information storage unit forming a database of the water depth and the underwater sound velocity structure and storing the same.
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