JPH11344565A - Synthetic aperture sonar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the image of high azimuth resolution on the real time from a newest aperture position in a synthetic aperture sonar mounted on board a ship. SOLUTION: The acoustic wave is received/transmitted by an actual aperture 1 at the position (1), an image indicating the azimuth of a target object is obtained, and kept as the first azimuth information. The acoustic wave is received/transmitted by the actual aperture 1 at the position (1) and by the actual aperture 1 at the position (2) to be partly overlapped therewith, and a base line A1 passing the actual aperture 1 is set. The obtained image is synthesized through the conversion of the image of the actual aperture 1 at the position (2) and the non-overlapped part out of the kept first azimuth information to obtain the image of the azimuth by a synthetic aperture 2a on the base line A1, and the image is displayed thereby, and kept as the second azimuth information. Similarly, every time the actual aperture 1 is moved, the base line is set by the position of the actual aperture 1 to obtain the azimuth information through the aperture synthesis at the base line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underwater sonar, and more particularly to a synthetic aperture sonar capable of obtaining an azimuth resolution higher than the resolution obtained by the actual aperture by synthesizing the actual aperture.

[0002]

2. Description of the Related Art The idea of a synthetic aperture sonar for synthesizing a plurality of real apertures (an array in which a plurality of transducers are arranged in a straight line) to obtain a high azimuth resolution has existed for a long time. Was. In order to combine a plurality of actual openings, these actual openings must be arranged on one straight line called a base line. For this purpose, the ship equipped with the sonar may be moved on a straight line (base line), and the received waves of the actual aperture at each successive position on the base line may be combined. This is the basic idea of a synthetic aperture sonar.

[0003] However, at sea, a ship equipped with a sonar shakes due to the influence of waves or the like, which makes it difficult to move the ship on one straight line. It was difficult to synthesize on two baselines. For this reason, practical use of the synthetic aperture sonar did not progress easily.

[0004] In order to solve such a problem, there has been proposed a method of reducing the influence of the swing of the synthetic aperture sonar.
For example, Japanese Patent No. 2609551 and Japanese Unexamined Patent Publication No.
According to the method described in Japanese Patent No. 5082, the actual apertures at two different positions are overlapped with each other to receive waves, and the influence of the fluctuation is corrected based on the information obtained at the overlapped portions. Thus, these different positions are on one base line, and the received information of the actual aperture at each position is synthesized (that is, the actual aperture is synthesized) to obtain a high resolution.

FIG. 3 shows such a conventional synthetic aperture sonar, wherein 1 is a real aperture (shown by a thick solid line), 2 is a synthetic aperture (shown by a white frame), and A is a base line. In addition,
, Indicate the position of the actual opening 1, respectively.

Now, assuming that the actual opening 1 is located at a position, a straight line in the longitudinal direction passing through the actual opening 1 at that time is defined as a base line A. Therefore, the actual opening 1 at this position is on the base line A. Then, at that time, the actual aperture 1 transmits a sound wave (accurately, an ultrasonic wave), receives the sound wave reflected by the target object, and holds the received wave information.

At this time, the ship equipped with the actual opening 1 is moving. In this case, the ship is moved so that the actual opening 1 is on the base line A. The actual opening 1 is displaced and the base line A is shifted.

At this position deviated from the base line A, the actual aperture 1 transmits a sound wave, receives the reflected sound wave from the target object, and captures the received wave information. In this case, the position is such that when the actual opening 1 at the position is projected in a direction perpendicular to the base line A, the actual opening 1 at this time partially overlaps the actual opening 2 at the position. This is called that the actual opening 1 at the position partially overlaps. By performing arithmetic processing on the received information of the portion that does not overlap with the actual aperture 1 at the position among the received information captured from the actual aperture 1 at the position using the received information of the overlapped portion, the position is obtained. At the position on the base line A where the real aperture 1 is projected in the vertical direction.
The information is added to the received wave information of the actual aperture 1 at the position.

As a result, reception information can be obtained when there is an actual aperture having a length of a to b on the base line A.

Next, when the actual opening 1 reaches a position where a part of the actual opening 1 has an overlapping relationship as in the case of the actual opening 1, the actual opening 1 receives the sound wave again and receives the sound from the target object. A reflected sound wave is received to receive received wave information. And
Similarly to the above, using the received wave information of the overlapped portion of the actual aperture 1 at the position with respect to the actual aperture 1 at the position and the received wave information of the overlap portion of the actual aperture 1 at the position relative to the actual aperture 1 at the position, Actual aperture 1 at actual aperture position
The received wave information of the portion which does not overlap with the actual aperture 1 is converted to the received wave information when the actual aperture 1 at the position is at the position on the base line A projected in the vertical direction. 1 and the received information converted by the actual aperture 1 at the position.

As a result, reception information when the synthetic aperture 2 having a length of a to c is present on the base line A can be obtained.
That is, the synthetic aperture 2 having a length of a to c can be obtained on the base line A. Hereinafter, similarly, by repeating the above procedure, a synthetic aperture having an arbitrary length on the base line A can be obtained.

[0012]

As described above, it is possible to synthesize an actual aperture, and to display a measurement result based on received wave information as an image, thereby obtaining a measurement image with high azimuth resolution. It is.

However, in this method, the base line for synthesizing the real aperture is set so as to pass through the real aperture when the synthetic aperture method is started. For this reason, the measurement image at the synthetic aperture on the ship is a measurement image at a past position before the current position of the actual aperture, and is different from the measurement image at the current position. That is, in the conventional synthetic aperture method, a positional shift occurs between the current position of the actual aperture and the base line, and an azimuth error corresponding to the positional shift occurs.

SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem and to obtain a measurement image with high azimuth resolution in real time, that is, an azimuth of a target object measured at a position where an actual aperture is present, with high resolution. An object of the present invention is to provide a synthetic aperture sonar as described above.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is to perform aperture synthesis using actual aperture position information, wherein the position of a base line at the time of aperture synthesis is variable. It is assumed that.

Further, the present invention is to adjust the baseline for performing aperture synthesis to the current position where the actual aperture transmits and receives.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing the overall configuration of an embodiment of a synthetic aperture sonar according to the present invention, wherein 1 is a real aperture formed of a transmitting / receiving array, 3 is a waveform generator, 4 is a power amplifier, 5 Is a transmission / reception switching section, 6 is a reception amplification / filtering section, 7 is a phasing section, 8 is a signal processing / video reproduction section, 9 is an aperture synthesis section,
Reference numeral 10 denotes a control / display unit, 11 denotes an image storage unit, 12 denotes a navigation instrument unit, 13 denotes an array fluctuation correction calculation unit, 14 denotes an array coordinate movement calculation unit, and 15 denotes an array direction control unit.

In FIG. 1, an electric signal having a waveform generated by a waveform generating unit 3 is power-amplified by a power amplifying unit 4 and then supplied to a real aperture 1 via a transmission / reception switching unit 5.
A sound wave is transmitted from the actual aperture 1 in a predetermined direction (for example, a direction perpendicular to the arrangement of the transmitting and receiving antennas in the actual aperture 1).

A sound wave is reflected from the target object by this transmission, and this is received by the actual aperture 1 and converted into an electric signal. The electric signal passes through the transmission / reception switching unit 5, is amplified by the reception amplification / filtering unit 6 to remove unnecessary components, and is subjected to phasing processing by the phasing unit 7. The output signal of the phasing unit 7 is output to a signal processing / video reproducing unit 8 in a normal sonar.
Is supplied to the control / display unit 10 as a video signal, and a video display of the azimuth information is performed by the video signal. However, since this embodiment is a synthetic aperture sonar, signal processing / video Reproduction unit 8 and control / display unit 1
0, an aperture synthesizing unit 9 and an image storage unit are provided.
The video signal from the video reproduction unit 8 is processed to perform aperture synthesis. The result is displayed on the control / display unit 10 at high resolution and stored in the video storage unit 11.

That is, when measuring the azimuth of the target object using the synthetic aperture, in the first transmission by the actual aperture 1, the aperture synthesizing unit 9 directly controls the video signal from the signal processing / video reproducing unit 8 to control and display. 10 and stored in the video storage unit 11. In the second transmission by the real aperture 1,
The aperture synthesizing unit 9 processes the video signal from the signal processing / video reproducing unit 8 and the video signal at the time of the first transmission / reception wave stored in the video storage unit 11 to perform aperture synthesis. The video signal is supplied to the control / display unit 10 and stored in the video storage unit 11. As a result, the video signal control / display unit 10 displays the video by the synthetic aperture in the first and second transmission / reception waves. The same applies to the third and subsequent transmission / reception waves, whereby the control / display unit 10
Will display an image with high azimuth resolution.

The navigation instrument section 12 includes a roll, a pitch,
It measures the yaw and other movements of the ship and the course of the ship such as its speed and direction. The resulting swing information α is
The correction information of the direction of the actual opening 1 due to the shaking is calculated by being supplied to the array fluctuation correction calculating unit 13 and processed, and the array direction control unit 15 corrects the direction of the actual opening 1 according to the correction information. I do. Therefore, even if the ship is shaken by a wave or the like, the direction of the actual opening 1 is kept constant irrespective of the direction or inclination of the ship. Further, the course information β obtained by the measurement is supplied to the array coordinate movement calculating unit 14, where the change in the position of the actual opening 1 (that is, coordinate movement) is calculated, and the current position of the actual opening 1 is obtained. The calculation result of the array coordinate movement calculation unit 14 is supplied to the aperture synthesis unit 9 and used for correcting the position of the actual aperture 1 when performing aperture synthesis.

FIG. 1 is a view showing an aperture synthesizing method of an embodiment of a synthetic aperture sonar according to the present invention having the hardware configuration shown in FIG. 2, wherein 2a and 2b are synthetic apertures, A
Reference numerals 1 and A2 denote base lines, and portions corresponding to those in FIG.

In this figure, if it is assumed that the azimuth measurement of the target object is started when the actual aperture 1 is located at the position, the transmission and reception of the sound wave is performed at the actual aperture 1 located at this position as described above. In FIG. 2, the resulting signal processing
The video signal obtained by the video reproducing unit 8 is supplied to the control / display unit 10 through the aperture synthesizing unit 9 so that the video representing the azimuth is displayed and the video storage unit 11 also receives the first reception. It is stored as wave information.

In FIG. 1, next, when the actual aperture 1 reaches the position, a second transmission and reception of sound waves is performed. At this time, a straight line in the longitudinal direction passing through the actual aperture 1 is defined as a base line A1. I do. In this case, the array direction controller 15 (FIG. 2)
The actual apertures 1 at the position are parallel to each other, and therefore the actual apertures 1 at the position are also parallel to the base line A1. Further, as in the conventional example shown in FIG. 3, when the actual opening 1 at the position is moved on the base line A1 in the same direction, the actual opening 1 and the actual opening 1 at the position partially I try to overlap. This is called that the actual opening 1 at the position partially overlaps, and this overlapping portion is called an overlap portion.

Also in the second transmission / reception wave, in FIG. 2, a video signal resulting from the reception is obtained by the signal processing / video reproduction unit 8 and supplied to the aperture synthesis unit 9. The aperture synthesizing unit 9 reads the information from the video storage unit 11 from the portion of the reception information of the first transmission / reception stored therein that does not overlap with the actual aperture 1 at the actual aperture 1 at the location. And reads the received wave information of the
And aperture synthesis processing on the base line 1 is performed. That is, in FIG. 1, when a video signal representing the azimuth of the actual aperture 1 of the position due to transmission and reception is obtained, this video signal is added to the actual aperture of the position of the video signal representing the azimuth obtained at the actual aperture 1 of the position. A part corresponding to a part that does not overlap with 1 is converted to a part received at the base line A1 and combined. As a calculation method for this aperture synthesis, the method of the above-described conventional example can be used.

As shown in FIG. 1, when the actual aperture 1 on the base line A1 is transmitted and received by the synthetic aperture 2a which is extended to a position opposed to the portion of the actual aperture 1 which does not overlap with the aperture, as shown in FIG. 2 is supplied to the control / display unit 10 in FIG. 2 to display an image of the azimuth by the second transmission / reception wave and to receive the second reception information as the second reception information. It is stored in the video storage unit 11.

As described above, in the second transmitted / received wave, the image of the actual aperture 1 at the position and the synthetic aperture 2a is displayed, so that the image displayed according to the first transmitted / received wave is displayed. In comparison with the azimuth resolution being higher, this image shows the azimuth of the target object when the actual aperture 1 is at the position, and thus from the current position of the ship.

When the actual aperture 1 reaches a position where the actual aperture 1 partially overlaps with the actual aperture 1 at the position, the third transmission / reception is performed. The image of the azimuth measured by the synthetic aperture 2b on the base line A2 obtained by synthesizing the actual apertures 1 of the set positions,.
The information is stored in the video storage unit 11 as third reception information.
In this case, in the aperture synthesizing unit 9 shown in FIG. 2, the video signal obtained by the transmission / reception of the actual aperture 1 at the position is added to the video of the measurement direction obtained by the synthetic real aperture 2a on the base line A1 set immediately before. A signal corresponding to a portion that does not overlap with the actual aperture 1 at the position is converted into a signal when received on the base line A2 and synthesized.

Similarly, for the fourth and subsequent transmission / reception waves, a baseline is set at the current position of the actual aperture 1 at that time, and aperture synthesis is performed on this baseline. That is, the base line also moves sequentially along with the movement of the actual aperture 1, and the aperture synthesis is always performed on this baseline, and the image by the synthetic aperture on this baseline is displayed in real time. In this case, it goes without saying that as the number of times of transmission / reception is increased and the number of times of aperture synthesis is increased, the resolution of the obtained measurement direction is higher.

As described above, in this embodiment, by repeating the aperture synthesis, it is possible to obtain the measurement azimuth at the current position of the actual aperture with high resolution and in real time. It is possible to prevent the occurrence of measurement errors caused by displaying the measurement azimuth at a time point far from the present, as in the above-described conventional technique.

Before performing the azimuth measurement described with reference to FIG. 1, transmission / reception is performed with the actual aperture 1 kept in an arbitrary direction, and based on the measurement result, the actual aperture 1 is set to a target whose longitudinal direction is measured. Preliminary settings are made so as to be perpendicular to the direction of the object. In this case, the measurement azimuth has a low resolution, but the transmission / reception directional characteristics of the actual aperture 1 can be almost accurately directed to the direction of the target object. Therefore, FIG.
By performing the measurement shown in (1), the measurement sensitivity can be set to almost the maximum, and the measurement accuracy is improved.

[0033]

As described above, according to the present invention,
Since the base line is set so as to pass through the actual aperture at the position where the wave is currently being received, and synthesis of the actual aperture is performed at that position, a high azimuth resolution image can be obtained in real time, that is, the current high azimuth resolution. Video can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a main part of an embodiment of a synthetic aperture sonar according to the present invention.

FIG. 2 is a block diagram of a flow of an acoustic signal and opening posture information.

FIG. 3 is a diagram showing a main part of a conventional synthetic aperture sonar.

[Explanation of symbols]

 Reference Signs List 1 real aperture 2a, 2b synthetic aperture 8 signal processing / video reproduction section 9 aperture synthesis section 10 control / display section 11 video storage section A1, A2 base line

Claims (2)

[Claims] 1. A synthetic aperture sonar in which a transmitting wave and a receiving wave are repeated at least twice or more, and the respective received signals are synthesized to obtain an image having a resolution higher than the resolution obtained by an actual aperture. A synthetic aperture sonar characterized in that the position of a base line when performing is performed. 2. A synthetic aperture sonar in which transmission and reception are repeated at least twice or more, and the respective received signals are combined to obtain an image having a resolution higher than the resolution obtained by an actual aperture. A synthetic aperture sonar characterized in that a base line for performing synthesis is set on an extension of the latest actual aperture that has received waves.