JP5443891B2 - Synthetic aperture sonar - Google Patents

Description

  The present invention relates to a synthetic aperture sonar composed of a transmitter mounted on a traveling body and a plurality of receivers arranged at equal intervals in the moving direction, and more particularly to a synthetic aperture sonar that corrects the shaking of the traveling body. .

  Synthetic aperture sonar is a sonar that applies the technology developed in synthetic aperture radar. In order to improve the resolution of the radar, it is necessary to increase the aperture length of the receiver. That is, the synthetic aperture radar is mounted on an aircraft or an artificial satellite, and continuously receives the reflected wave of the transmitted radar wave with a receiver while moving on orbit. Thereby, the received signal of the receiver having a small aperture length is synthesized. As a result, the resolution is improved by increasing the aperture length equivalently. Synthetic aperture sonar uses acoustic waves instead of radar waves and is mounted on water or underwater vehicles to improve the resolution of the sonar based on the same principle.

  As for synthetic aperture processing, as shown in Non-Patent Document 1 and Non-Patent Document 2, a CS (Chirp Scaling) algorithm using Fast Fourier Transform and complex multiplication is known. Non-Patent Document 2 shows a method of performing shake correction by multiplying a time axis signal by a shake correction function.

  The underwater propagation speed of acoustic waves of 1,500 m / s is very slow compared to the radar wave propagation speed of 300,000 km / s. For this reason, it is necessary for the synthetic aperture sonar to take a long pulse repetition period from the start of transmission until the return of the echo wave to the start of the next transmission. Moreover, the moving distance between samples of the traveling body is extremely short, and the synthetic aperture length cannot be obtained. Further, there is a disadvantage that the speed of the traveling body is too slow and cannot be kept constant.

That is, the reciprocal of this pulse repetition period is the pulse repetition frequency PRF, the speed of the vehicle is v, the receiving aperture length of the receiver is D, the speed of sound in water is c, and the maximum search distance is Rmax. Equation 1) must be satisfied.

This problem can be solved by a DPCA (Displaced Phase-Center Antenna) system in which a plurality of receivers arranged at equal intervals in the moving direction are simultaneously received for one transmission.
Synthetic aperture and synthetic aperture methods using DPCA for shake correction are shown in Patent Document 1, Patent Document 2, and Non-Patent Document 2.

  In the DPCA method, the sum of the propagation distances from the transmitter to the target and from the target to the receiver is calculated in a plurality of arrays including one transmitter and a plurality of receivers arranged at equal intervals in the moving direction. This is based on the principle that it is approximately equal to the round-trip propagation distance from the virtual transmitter / receiver located between the transmitter and receiver to the target. The DPCA method is a method of performing synthetic aperture processing on the assumption that a signal is transmitted / received from this virtual transmitter / receiver. Hereinafter, a plurality of arrays of actual transmitters and receivers are arranged, and an array of virtual transmitters / receivers positioned between the transmitters and receivers is called a DPCA array. A transmitter / receiver in which one transmitter and one receiver are integrated is referred to as a single array.

  In the case of reception in a single array, the azimuth sampling frequency fas in the moving direction is equal to the pulse repetition frequency PRF, and there is a relationship of (Equation 2) between the traveling body speed v and the receiving aperture length D.

  When receiving with the DPCA arrangement, the azimuth sampling frequency fas can be made higher than the pulse repetition frequency PRF by arranging the interval d of the plurality of receivers in accordance with the azimuth sampling interval. At this time, there is a relationship of (Equation 3) with the number E of receivers. Here, the receiver interval d is defined differently from the receiving aperture length D of each receiver, but generally d = D.

  The pulse repetition frequency PRF is a transmission timing, and is controlled from moment to moment by an actual measurement value of the vehicle speed v based on (Equation 3). Accordingly, the azimuth sampling frequency fas is controlled.

With reference to FIG. 1, the shake correction process by a prior art is demonstrated. Here, FIG. 1 is a block diagram of a synthetic aperture sonar according to the prior art. In FIG. 1, the synthetic aperture sonar 600 includes a transmission / reception processing unit 100, a shake correction processing unit 200, a synthetic aperture processing unit 300, a display control processing unit 400, and a shake detection processing unit 500. The transmission / reception processing unit 100 includes a receiver 110, a transmitter 120, a receiver 130, a transmitter 140, and a PRF controller 150.

  The transmitter 140 generates a transmission signal based on the external setting. The transmitter 140 sends a transmission signal to the transmitter 120 in synchronization with the transmission timing signal from the PRF controller 150. The transmitter 120 performs electroacoustic conversion on the transmission signal and transmits the signal into water. The PRF controller 150 receives the speed signal 10 based on the vehicle speed v, calculates the PRF value from (Equation 4), and outputs it to the transmitter 140 as a transmission timing signal.

  The receiver 110 performs acoustoelectric conversion on the received echo. The receiver 130 frequency-converts the received signal from the receiver 110 to baseband after amplification, filtering, and analog / digital conversion. The shake correction processing unit 200 includes a shake corrector 210 and a correction amount calculator 220. The correction amount calculator 220 calculates a phase correction amount Δα based on the propagation time difference τ based on the fluctuation amount received from the fluctuation detection processing unit 500 by (Equation 5), and outputs it to the fluctuation correction device 210. Here, λ is the wavelength of the center frequency.

The fluctuation corrector 210 adds exp (Δα) to the received signal based on the correction amount from the correction amount calculator 220.
Is subjected to complex multiplication, and shake correction is performed by phase rotation.

  The synthetic aperture processing unit 300 performs synthetic aperture processing based on Non-Patent Document 1. The synthetic aperture processing unit 300 inputs a two-dimensional time signal in the range direction and the azimuth direction, and outputs a two-dimensional coordinate signal in the range direction and the azimuth direction to the display control processing unit 400. Here, the azimuth direction is the traveling direction of the traveling body, and the range direction is a direction perpendicular to the traveling direction of the traveling body in a horizontal plane.

The display control processing unit 400 is formatting, level adjustment, and a man-machine interface for displaying processing results.
The motion detection processing unit 500 receives the motion data 20 that is the output of the external motion sensor as input, and (1) rolling angle, (2) pitching angle, (3) yawing angle, and three-axis rotation angles that are three-axis rotation angles. The displacement amount (4) surging amount, (5) swaging amount, and (6) heaving amount are output as real time functions. As the external vibration sensor, there is a high-precision inertial guidance device commercially available from the French company IXSEA.

The background art described above has the following problems.
The first problem is that the shake correction is based on a single array consisting of one transmitter and one receiver, so that one transmitter as seen in Patent Document 1 and Patent Document 2 is used. It is impossible to correct an error in a plurality of arrays including a waver and a plurality of wave receivers.
The second problem is that the travel distance of the receiver varies depending on the propagation time in addition to the speed of the traveling body, but errors due to this propagation time cannot be corrected.

The third problem is that there is a limit to the detection accuracy of the amount of oscillation of the external oscillation sensor, and the wavelength becomes shorter as the frequency becomes higher, so that the accuracy required for the synthetic aperture cannot be obtained.
It is an object of the present invention to provide a synthetic aperture sonar that solves these problems and performs high-accuracy fluctuation correction.

US Pat. No. 4,244,036 JP 2004-117129 A

A. Moreira, J. Mittermayer, and R. Scheiber “Extended chirp Scaling Algorithm for Air- and Spaceborne SAR Data Processing in Stripmap and ScanSAR Imaging Modes”, IEEE Trans. Geosci. Remote Sensing, vol. 34. pp. 1123-1136 , Sept. 1996. A. Bellettini, and M. A. Pinto, “Theoretical Accuracy of Synthetic Aperture Sonar Micronavigation Using a Displaced Phase- Center Antenna”, IEEE J. Oceanic Eng., Vol. 27, pp. 780-789, Oct. 2002.

  The synthetic aperture sonar is mounted on the traveling body and is subjected to fluctuations due to rotation and movement in three axial directions during traveling. The fluctuation causes a phase rotation because it slightly changes the propagation distance, and has a significant effect on the synthetic aperture processing. The problem to be solved by the present invention is to correct the shaking with the amount of shaking detected by the external shaking sensor, and detect the remaining shaking amount that cannot be detected by the external shaking sensor with its own received signal. In addition, by performing self-stabilization correction, a highly accurate synthetic aperture sonar that is resistant to shaking is realized.

In the first stage of fluctuation correction, the propagation distance between a virtual single arrangement in which one transmitter and one receiver are integrated and the reference position is not added to the single arrangement. A propagation distance between the reference position and a plurality of first propagation distance calculation values to be calculated and a plurality of receivers arranged at equal intervals in the moving direction and one transmitter. From the second propagation distance calculation value calculated by artificially adding the shaking amount based on the shaking data detected by the external shaking sensor to a plurality of arrays, the shaking distance is calculated by calculating the shaking distance difference, and the shaking correction is performed. . That is,
Propagation distance between a plurality of arrays after shake correction and an arbitrary target position = Propagation distance between a plurality of arrays before shake correction and an arbitrary target position + (First propagation distance between a virtual single array to which no shake is added and a reference position -A second propagation distance between the reference position and a plurality of arrangements with shaking
As shown in (), the fluctuation amount is calculated from the propagation distance difference in parentheses, and the fluctuation is corrected.

Here, by taking the reference position at the center of the synthetic aperture processing, the difference in the amount of fluctuation between the arbitrary target position and the reference position becomes small and can be ignored, so that the fluctuation correction is effectively performed. The propagation distance can be calculated from propagation time, which is an actual measurement amount, by propagation distance = propagation time × sound speed.
As described above, as a result of the first stage of the shake correction, the positions of the plurality of arrays are corrected to the positions of the virtual single array.

  Next, in the second stage of the shake correction, a part of the position of the DPCA array corresponding to the i-th transmission and a part of the position of the DPCA array corresponding to the i + 1-th transmission are not shaken. The transmission timing is controlled so as to coincide with each other, and the amount of fluctuation is detected from the propagation distance difference between the reception signal corresponding to the i-th transmission and the target of the reception signal corresponding to the i + 1-th transmission, Further shake correction is performed on the reception signal corrected in the first stage of shake correction.

Hereinafter, the DPCA array in which the intermediate positions of the transmitter and receiver are matched is referred to as a superimposed DPCA array.
In superimposed DPCA, in order to control the transmission timing described above, the relationship of (Equation 6) is required by partially changing (Equation 3) between the number of receivers E and the number of superimposed DPCA L. .

  From this, the pulse repetition frequency PRF has a relationship of (Expression 7) by partially changing (Expression 4).

When shaking is applied, the position of the superimposed DPCA array changes, and the propagation distance from the target changes accordingly. For this reason, the amount of fluctuation can be detected from the propagation distance difference. The propagation distance difference approximately depends on only the fluctuation amount regardless of the target position within the synthetic aperture processing range. For this reason, the target need not be a specific object, and the amount of fluctuation can be detected by the rocks and the seabed forming the seafloor topography.
The same processing is performed for the i + 2nd and i + 3th times and the subsequent transmissions.

  The above-described problem is that a transmission / reception processing unit including a plurality of arrays and a PRF controller, a motion detection processing unit, and a motion compensation is performed on the output of the transmission / reception processing unit using the output of the motion detection processing unit. This can be achieved by a synthetic aperture sonar composed of a shake correction processing unit that performs further motion correction using the above, a synthetic aperture processing unit, and a display control processing unit.

Here, the shake correction processing unit includes a first propagation distance calculator, a second propagation distance calculator, a correction amount calculator, a shake correction device, a self-correction amount calculator, and a self-motion correction device. To do.
The first propagation distance calculator calculates the propagation distance between the virtual single array and the reference position without adding any fluctuation to the single array. The second propagation distance calculator calculates the propagation distance between the plurality of arrays and the reference position by artificially adding the amount of shaking from the shaking detection processing unit to the plurality of arrays. The correction amount calculator calculates the first fluctuation amount from the output of the first propagation distance calculator and the second propagation distance calculator based on the propagation distance difference. The shake corrector performs shake correction on the output of the transmission / reception processing unit based on the first shake amount. The PRF controller of the transmission / reception processing unit controls the transmission timing so that the positions of the superimposed DPCA arrays corresponding to the i-th transmission and the (i + 1) -th transmission match. The self-correction amount calculator detects the second fluctuation amount from the propagation distance difference from the target of the superimposed DPCA reception signal. The self-stabilizer corrects the fluctuation on the output of the fluctuation corrector based on the second fluctuation amount.

  According to the present invention, while performing the shake correction by the amount of shake detected by the external shake sensor, the remaining shake amount that cannot be detected by the external shake sensor is detected by its own received signal, It is possible to realize a high-precision synthetic aperture sonar that is resistant to shaking and performs self-swing correction.

1 is a block diagram of a synthetic aperture sonar according to the prior art. FIG. It is a block diagram of a synthetic aperture sonar. It is a block diagram explaining the position of a transmitter, a receiver, DPCA, and a superimposed DPCA arrangement when the number of receivers is odd. It is a block diagram explaining the position of a transmitter, a receiver, DPCA, and superposition DPCA arrangement when the receiver is an even number. It is a figure explaining the beam pattern output before and after fluctuation correction. It is a figure explaining the detection of the yawing angle by superposition DPCA.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings and mathematical formulas using examples. The same reference numerals are assigned to substantially the same parts, and the description will not be repeated.

  First, the shake correction process according to the present embodiment will be described with reference to FIG. In FIG. 2, the synthetic aperture sonar 700 includes a transmission / reception processing unit 100A, a shake correction processing unit 200A, a synthetic aperture processing unit 300, a display control processing unit 400, and a shake detection processing unit 500. The transmission / reception processing unit 100A includes a receiver 110, a transmitter 120, a receiver 130, a transmitter 140, and a PRF controller 150A.

  The transmitter 140 generates a transmission signal based on the external setting, outputs the transmission signal in synchronization with the transmission timing signal from the PRF controller 150A, and sends it to the transmitter 120. The transmitter 120 performs electroacoustic conversion on the transmission signal and transmits the signal into water. The PRF controller 150A receives the speed signal 10 based on the vehicle speed v, calculates the PRF value from (Equation 7), and outputs it to the transmitter 140 as a transmission timing signal. The receiver 110 performs acoustoelectric conversion on the received echo. The receiver 130 frequency-converts the received signal from the receiver 110 to baseband after amplification, filtering, and analog / digital conversion.

  The shake correction processing unit 200A includes a shake corrector 210A, a correction amount calculator 220A, a first propagation distance calculator 230, a second propagation distance calculator 240, a self-vibration corrector 250, and a self-correction amount calculator 260. .

  The reference position data 30 is a reference position for the synthetic aperture process, and is usually taken at the center of the synthetic aperture process.

  The first propagation distance calculator 230 calculates the propagation distance between the reference position and the virtual single array. The second propagation distance calculator 240 calculates the propagation distance between the reference position and the plurality of arrays by artificially adding the amount of movement from the movement detection processor 500. The arrangement of a plurality of transmitters and receivers will be described later with reference to FIGS.

  The correction amount calculator 220 </ b> A detects the propagation distance difference from the output of the first propagation distance calculator 230 and the output of the second propagation distance calculator 240. The correction amount calculator 220A converts this into a phase difference Δα as a shake correction amount and outputs it to the shake corrector 210A. The shake corrector 210A multiplies the received signal by exp (Δα) and performs shake correction by phase rotation. The motion corrector 210A includes a received signal 211 that forms a DPCA array excluding the superimposed DPCA array in the DPCA array, one received signal 212 that forms the superimposed DPCA array, and another received signal that forms the superimposed DPCA array. 213 is output.

  The self-correction amount calculator 260 receives the received signal 212 and the received signal 213, takes a two-dimensional cross spectrum in the range direction and the azimuth direction, the range direction corresponds to the center frequency of the transmission signal, and the azimuth direction corresponds to the Doppler zero frequency. The position phase difference Δβ is detected and sent to the self-motion correction device 250 as a motion correction amount. The self-stabilizer 250 performs complex multiplication of exp (Δβ) on the received signal 211 and performs self-stabilization by phase rotation.

  The synthetic aperture processing unit 300 performs synthetic aperture processing. The display control processing unit 400 is formatting, level adjustment, and a man-machine interface for displaying processing results. The motion detection processing unit 500 receives the motion data 20 that is the output of the external motion sensor as input, and (1) rolling angle, (2) pitching angle, (3) yawing angle, and three-axis rotation angles that are three-axis rotation angles. The displacement amount (4) surging amount, (5) swaging amount, and (6) heaving amount are output as real time functions.

  With reference to FIG. 3 and FIG. 4, each position of a transmitter and a receiver, a DPCA arrangement | sequence, and a superimposed DPCA arrangement | sequence is demonstrated. In FIG. 3 and FIG. 4, the movement of the receiver due to the propagation time from the time of transmission to the time of reception is ignored.

  3 and 4, the horizontal axis represents the traveling direction of the traveling body, and the vertical axis represents the transition of the DPCA array corresponding to the i-th transmission and the i + 1-th transmission. The position of the transmitter 120 is indicated by ◯, the position of the receiver 110 is indicated by ●, and the position of the DPCA is indicated by ◎. A box surrounding the transmitter 120 and the receiver 110 is a transmitter / receiver array 160.

In FIG. 3, assuming that the coordinate of the horizontal axis of the transmitter 120 is 0 and the interval between the receivers is d, the position of the receiver 120 is −3d, −2d, −d, 0, d, 2d, 3d. It becomes. Since the position of DPCA is the center of the transmitter and receiver, they are -1.5d, -d, -0.5d, 0, 0.5d, d, and 1.5d. The positions of the superimposed DPCA in the DPCA are 0.5d, d, and 1.5d. In order to make DPCA continuous as the synthetic aperture processing, the transmission timing of the transmitter 120 is as follows.
v / PRF = (E−L) d / 2
= (7-3) d / 2
= 2d
Needs to be moved every time.

In FIG. 4, when the horizontal axis coordinate of the transmitter 120 is 0 and the receiver interval is d, as in FIG. 3, the position of the receiver 120 is −2.5d, −1.5d, − 0.5d, 0.5d, 1.5d, and 2.5d. The positions of DPCA are −1.25d, −0.75d, −0.25d, 0.25d, 0.75d, and 1.25d. The positions of the superimposed DPCA in the DPCA are 0.25d, 0.75d, and 1.25d. In order to make DPCA continuous as the synthetic aperture processing, the transmission timing of the transmitter 120 is as follows.
v / PRF = (E−L) d / 2
= (6-3) d / 2
= 1.5d
Needs to be moved every time.

  The moving direction of the vehicle is defined as an x-axis, a direction perpendicular to the moving direction is defined as a y-axis, a direction perpendicular to the moving direction is defined as a z-axis, and the y-axis is defined as a right-handed system. There are the following 6 types of shaking of the three axes: (1) The rolling angle is the amount of rotation about the x axis, (2) The pitching angle is the amount of rotation about the y axis, and (3) The yawing angle is the amount of rotation about the z axis. It is. Similarly, (4) surging displacement is the amount of movement in the x-axis direction, (5) swaging displacement is the amount of movement in the y-axis direction, and (6) heaving displacement is the amount of movement in the z-axis direction.

  In the shake correction, the yawing angle and the swaying displacement that have a great influence on the characteristics of the synthetic aperture sonar among these shake parameters will be described. Since other shaking parameters can be corrected by the same principle, the following two shaking parameters are used. ta is the azimuth time and these are functions of ta. The azimuth time ta is the reciprocal of the azimuth sampling period fas.

(1) Yawing angle Φ yaw (ta)
(2) Swing displacement Esway (ta)
For the following explanation, the navigation body position, the plural transmitter positions and the kth receiver position, the single array position, and the reference position are defined.

  First, the position of the traveling body is assumed to be (Equation 8).

  A relative position from the center of the traveling body of the plurality of transmitters is defined as (Equation 9).

  The relative position from the center of the traveling body of the k-th receivers in a plurality of arrays is defined as (Equation 10).

  Let the position of the single sequence be (Equation 11).

  The reference position taken at the center of the synthetic aperture process is defined as (Equation 12).

  The position of the transmitter at the time of transmission is the sum of the position of the traveling body and the relative position of the transmitter. When the yawing angle Φyaw and the swaying displacement Esway are shaken with the center of the running body as the rocking center, ) And (Equation 9) to (Equation 13).

  The k-th receiver position at the time of reception is the sum of the position of the traveling body and the relative position of the receiver, and considering the amount of movement of the traveling body during the propagation time Δta, ) And (Equation 10) to (Equation 14).

  The procedure for calculating the amount of shaking from the difference in the propagation distance between the single array and the reference position and the difference in propagation distance between the plurality of arrays and the reference position in the first stage of shaking correction will be described.

  The propagation distance between the reference position and the single array is given by (Equation 11) and (Equation 12) to (Equation 15).

That is, the first propagation distance calculator 230 calculates (Expression 15) and outputs it to the correction amount calculator 220A.
Here, since the error due to the propagation time Δta is also corrected at the same time, the single array does not include the propagation time Δta.

  Next, the propagation distance between the reference position and the transmitter is given by (Equation 12) and (Equation 13) to (Equation 16).

  The propagation distance between the reference position and the k-th receiver is given by (Equation 12) and (Equation 14) to (Equation 17).

  The propagation distance between the reference position and the virtual transmitter / receiver position of the DPCA array between the transmitter and the receiver is given by (Equation 16) and (Equation 17) to (Equation 18).

  The propagation time Δta is the traveling time of the traveling body from the time of transmission to the time of reception, and is recursively (Equation 19).

  Alternatively, the propagation time Δta is approximately (Equation 20).

  The second propagation distance calculator 240 calculates (Equation 17) and outputs it to the correction amount calculator 220A. Thus, the propagation distance difference at the time of fluctuation correction is given by (Equation 15) and (Equation 18) to (Equation 21).

  Based on the above, the correction amount for fluctuation correction is multiplied by 2π / λ, which is the dimension of the distance for the k-th receiver output (Equation 21), and doubled because of reciprocation (Equation 22). The phase rotation Δαk (ta) is performed. λ is the wavelength of the center frequency. That is, the phase difference based on the propagation distance difference is (Equation 22).

  Next, since the azimuth time ta is the reciprocal of the azimuth sampling frequency fas, it is replaced with a discrete value (Equation 23) that is i times the azimuth sampling period. That is,

  Thus, the propagation distance difference of (Equation 21) is replaced with the discrete value of (Equation 24).

  From this, the phase difference of (Expression 22) is replaced with the discrete value of (Expression 25).

(Equation 25) depends on the number i indicating the position of the traveling body and the number k indicating the relative position of the receiver.

  The correction amount calculator 220A calculates the phase correction amount Δαi, k based on the propagation distance difference coming from the outputs of the first propagation distance calculator 230 and the second propagation distance calculator 240 by (Equation 25), and the shake correction device 210A. Output to. The shake corrector 210A performs complex correction by exp (Δαi, k) on the received signal based on the correction amount from the correction amount calculator 220A, and performs shake correction by phase rotation.

  In the DPCA array, as shown in FIG. 3 and FIG. 4, the virtual transmitter / receiver interval is ½ of the actual receiver interval, and the azimuth sampling period × the vehicle speed v, which is the reciprocal of the azimuth sampling frequency fas. Is made equal to 1/2 of the receiver interval d according to (Equation 3). When the vehicle speed v fluctuates, the azimuth sampling frequency fas is adjusted according to (Equation 5).

  Next, a procedure for detecting the residual fluctuation amount due to the propagation distance difference of the received signal in the second stage of the fluctuation correction will be described. In the correction up to this point, when no fluctuation is added, the intermediate position between the transmitters and receivers of the plurality of arrays matches the position of the DPCA array, and this corresponds to the i-th transmission and i + 1-th transmission. Since the positions of the superimposed DPCA arrays coincide with each other, the propagation distance difference between the superimposed DPCA reception signals corresponding to the i-th transmission and the (i + 1) -th transmission can be considered to be due to the above-described residual fluctuation amount.

For the following explanation, for (Equation 8), (Equation 9), (Equation 10), and ( Equation 12) , the discrete values of the navigation body position, the plural transmitter positions, the kth receiver position, and the reference position Define the expression. First, let the position of the navigation body be (Equation 26). Here, H is the altitude of the navigation body from the seabed.

  A relative position from the center of the traveling body of the plurality of transducers is represented by (Equation 27). Here, Yo is the distance from the center of the vehicle to the transmission surface.

  The relative position from the center of the traveling body of the k-th receivers in a plurality of arrays is represented by (Equation 28). Here, Xo is a correction term for positioning the position of the receiver symmetrically with the position of the transmitter, and Yo is the distance from the center of the traveling body to the receiving surface as in the case of the transmitter.

  The reference position is (Expression 29) as the center of the synthetic aperture process. Here, Ro is a horizontal distance from the origin of the reference position.

  As for the position of the superimposed DPCA array, Δta is approximately corrected to 0 in the first stage of the shake correction, so that (Equation 13) of the transmitter position and (Equation 14) of the receiver position are (Equation 23). ) To replace with discrete values, (Equation 30) is obtained. Here, k is the receiver position of the i-th transmission.

Thus, when (Equation 27) and (Equation 28) are substituted into the position (Equation 30) of the superimposed DPCA array, the position of the superimposed DPCA array corresponding to the i-th transmission is (Equation 31) .

Similarly, the position of the superimposed DPCA array corresponding to the (i + 1) th transmission is (Expression 32). Here, k ′ is the receiver position of the (i + 1) th transmission.

  The difference between the position of the superimposed DPCA array corresponding to the i-th transmission and the position of the superimposed DPCA array corresponding to the i + 1-th transmission corresponds to the propagation distance difference ΔPi, dpca. It is given by (Equation 33). Here, since the above-mentioned residual fluctuation amount is already sufficiently smaller than the azimuth sampling frequency fas in the first stage of vibration correction, the value of the yawing angle Φyaw between the i-th transmission and the i + 1-th transmission. It can be assumed that the value of the swaying displacement Esway does not change.

When shaking is not applied, the amount of shaking is 0, so the propagation distance difference (Equation 33) needs to be 0, and from this, (Equation 34) needs to hold.

  Substituting (Equation 34) into (Equation 33), the difference between the positions of the superimposed DPCA array, that is, the relationship between the propagation distance difference ΔPi, dpca and the yawing angle Φi, yaw becomes (Equation 35), and the yawing angles are compared. When the target is small, the propagation distance difference ΔPi, dpca is proportional to the yawing angle Φi, yaw regardless of the distance from the target, and the swaying displacements Ei, sway can be ignored.

On the other hand, the propagation distance difference ΔPi, dpca has a relationship of (Equation 36) with the phase difference β of the output of the superimposed DPCA. Here, the phase difference β takes a two-dimensional cross spectrum in the azimuth direction and range direction of the output of the superimposed DPCA, and the range direction detects the phase difference of the position corresponding to the center frequency of the transmission signal and the azimuth direction corresponds to the Doppler zero frequency. By seeking .

  As a result, the yawing angle φi, yaw is given by (Equation 37) by (Equation 35) and (Equation 36).

  In the second stage of the shake correction, the remaining shake amount due to the propagation distance difference is detected from its own received signal based on this principle, and the shake correction is performed.

  The self-correction amount calculator 260 detects the phase difference β from the output 212 and the output 213 of the fluctuation corrector 210 </ b> A and outputs it to the self-vibration corrector 250. The self-stabilizer 250 performs complex multiplication by expβ based on the residual amount of motion to the output 211 from the self-correction amount calculator 260 and corrects the motion by phase rotation.

  In order for (Equation 37) to hold, the propagation distance difference of (Equation 36) needs to satisfy (Equation 38) so that the amount of phase rotation does not exceed ± 45 degrees.

  From this, the constraint condition of the yawing angle Φi, yaw is given by (Equation 39).

  This constraint condition is not a problem in practical use because a large amount of shaking is already corrected in the first stage of shaking correction.

  As described above, in this embodiment, a virtual single array and a plurality of arrays are combined in the first stage, and the amount of motion based on the motion data of the external motion sensor is added to the plurality of arrays to simulate a single virtual array. Calculate the difference between the propagation distance between the array and the reference point and the propagation distance between the multiple arrays and the reference point, and use this as the amount of shaking to correct the received signal, and then use the received signal after the shaking correction in the second stage. A propagation distance difference between the superimposed DPCA array and the target is detected, and this is used as a fluctuation amount to perform fluctuation correction on the received signal.

  With reference to FIG. 5, the beam patterns before and after the shake correction according to this embodiment will be described. In FIG. 5, the horizontal axis represents the azimuth distance (m), and the vertical axis represents the reception level (dB). 5 (a) shows the case where there is no swaying in the traveling body, FIG. 5 (b) shows the case where yawing and swaying sway corresponding to 1 / 8λ are added, and FIG. 5 (c) corresponds to 1 / 8λ. This is the result of adding yawing and swaying swaying and performing sway correction. From the comparison between FIG. 5B and FIG. 5C, the effect of the shake correction is clear.

  With reference to FIG. 6, the detection result of the yawing angle of the superimposed DPCA according to the embodiment will be described. In FIG. 6, the horizontal axis represents the azimuth frequency (Hz) and the vertical axis represents the yawing angle (degrees). The given yawing angle is 0.2 degrees, and the detection results with 9 targets assuming rocks on the sea floor distributed in the synthetic aperture processing range are shown. From FIG. 6, it is clear that the yawing angle is correctly detected.

  According to the above-described embodiment, in the first stage of the shake correction, the propagation distance between the virtual single array that does not add the shake and the reference position and the external shake sensor are detected in the shake correction of the synthetic aperture sonar. The synthetic aperture sonar is used to calculate the propagation distance between the reference position and the multiple arrays with simulated fluctuations added, and the fluctuation correction amount is calculated from the propagation distance difference and the received signal is corrected. It is corrected to an ideal form with no single array, and high-precision shake correction can be performed without increasing side lobes.

  In addition, in the second stage of the shake correction, since the residual shake amount is detected based on the propagation time difference of the superimposed DPCA array for the received signal corrected in the first stage, the small shake that cannot be detected by the external shake sensor. Can be detected, and shake correction can be performed with high accuracy.

  DESCRIPTION OF SYMBOLS 10 ... Speed signal, 20 ... Reference position data, 30 ... Shaking data, 100 ... Transmission / reception processing part, 110 ... Receiver, 120 ... Transmitter, 130 ... Receiver, 140 ... Transmitter, 150 ... PRF controller, DESCRIPTION OF SYMBOLS 160 ... Transmitter-receiver array, 200 ... Shake correction process part, 210 ... Shake corrector, 211 ... DPCA received signal, 212 ... Superimposed DPCA received signal, 213 ... Superposed DPCA received signal, 220 ... Correction amount calculator, 230 ... First DESCRIPTION OF SYMBOLS 1 propagation distance calculator, 240 ... 2nd propagation distance calculator, 250 ... Self-stabilization corrector, 260 ... Self-correction amount calculator, 300 ... Synthetic aperture processing part, 400 ... Display control processing part, 500 ... Shaking detection processing part 600 ... Synthetic aperture sonar, 700 ... Synthetic aperture sonar.

Claims (4)

A plurality of transmission / reception processing units;
A motion detection processing unit;
A first propagation distance calculator that calculates a propagation distance between a virtual single array in which one transmitter and one receiver are integrated and a reference position without adding fluctuation to the single array. And a propagation distance between the reference position and a plurality of arrays including a single transmitter and a plurality of receivers arranged at equal intervals in the moving direction, A second propagation distance calculator that calculates the amount by pseudo-addition, and a correction that calculates the first fluctuation amount from the propagation distance difference between the output of the first propagation distance calculator and the output of the second propagation distance calculator A quantity calculator, a fluctuation corrector that performs fluctuation correction on a received signal based on the first fluctuation amount, a part of an intermediate position between a transmitter and a receiver corresponding to an arbitrary i-th transmission, , Transmit so that a part of the intermediate position between the transmitter and receiver corresponding to the (i + 1) -th transmission coincides with no shaking. The second fluctuation amount is detected from the propagation distance difference between the PRF controller that controls the imming and the reception signal corresponding to the i-th transmission and the target of the reception signal corresponding to the i + 1-th transmission. A self-correction amount calculator; and a self-motion correction device that performs motion correction on the output of the received signal of the motion correction device based on the second motion amount, and using the output of the motion detection processing unit A shake correction processing unit that performs shake correction on the output of the transmission / reception processing unit and performs further shake correction using its own received signal after the shake correction,
A synthetic aperture processing section;
A display control processing unit ;
A synthetic aperture sonar characterized by comprising: The synthetic aperture sonar of claim 1 ,
In the propagation distance calculation, the first propagation distance calculator does not include the moving distance of the traveling body caused by the propagation time between the virtual single array and the reference position.
The synthetic propagation sonar characterized in that the second propagation distance calculator calculates a traveling distance including a moving distance of the traveling body caused by a propagation time between the plurality of arrays and the reference position. The synthetic aperture sonar of claim 1 ,
The self-correction amount calculator takes a two-dimensional cross spectrum in the range direction and the azimuth direction for the received signal corresponding to the i-th transmission and the received signal corresponding to the i + 1-th transmission, and the range direction is transmitted. A synthetic aperture sonar characterized by detecting a phase difference at a position corresponding to a Doppler zero frequency in the center frequency and azimuth direction of a signal and converting the detected phase difference into a propagation distance difference to obtain the second fluctuation amount. The synthetic aperture sonar of claim 1 ,
The self-correction amount calculator calculates a two-dimensional cross-correlation in the range direction and the azimuth direction for the reception signal corresponding to the i-th transmission and the reception signal corresponding to the i + 1-th transmission, and the position of the peak value A synthetic aperture sonar characterized in that a propagation time difference is detected and converted into a propagation distance difference to obtain the second fluctuation amount.

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