JP2012137305A - Synthetic aperture exploratory device and underwater traveling body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously and efficiently explore for unintentional deposits on the water bottom and deliberately buried objects.SOLUTION: A synthetic aperture exploratory device 1 provided with a high frequency synthetic aperture sonar 2 that is mounted on an underwater traveling body and obtains picture signals by transmitting and/or receiving a sound wave beam of a first frequency and a low frequency synthetic aperture sonar 3 that is mounted on the underwater traveling body and obtains picture signals by transmitting and/or receiving a sound wave beam of a second frequency lower than the first frequency causes the high frequency synthetic aperture sonar 2 and the low frequency synthetic aperture sonar 3 to accomplish transmission substantially in synchronism, and has the numbers of channels, physical aperture lengths and the transmission periods of the high frequency synthetic aperture sonar 2 and of the low frequency synthetic aperture sonar 3 as well as the speed of the underwater traveling body so adjusted as to substantially equalize the respective intervals of the phase centers of the high frequency synthetic aperture sonar 2 and the phase centers of the low frequency synthetic aperture sonar 3.

Description

  The present invention relates to a synthetic aperture exploration device and an underwater vehicle.

  In general, acoustic sonar is used for underwater exploration of the sea or lake. In particular, a synthetic aperture exploration device (synthetic aperture sonar) that reproduces and visualizes an exploration target on a monitor image has recently been proposed, and application of this device to underwater exploration has been studied (for example, see Patent Document 1). .

Japanese Patent Laid-Open No. 2005-9968

The synthetic aperture exploration device is widely used for exploration of submarine sediments and seafloor topography. In such a synthetic aperture exploration apparatus, generally, a high frequency band of about 100 kHz to 500 kHz is used.
By the way, in recent years, there is a demand for efficiently exploring sedimentation and buried (buried) objects simultaneously. However, when trying to explore even buried objects in the frequency band of sound waves suitable for exploring sediments, most of them are reflected on the seabed and the like, and there is a problem that objects buried under the seabed cannot be detected. there were.

  The present invention has been made in view of such circumstances, and provides a synthetic aperture exploration device and an underwater vehicle capable of exploring a sediment and an embedded object simultaneously and efficiently. For the purpose.

In order to solve the above problems, the present invention employs the following means.
The present invention is mounted on an underwater vehicle and has a first sonar that obtains an image signal by transmitting and receiving a sound beam of a first frequency, and is mounted on the underwater vehicle and the first frequency. And a second sonar that obtains an image signal by transmitting and receiving a sound beam having a second frequency lower by about one digit than the first sonar and substantially synchronously transmits the first sonar and the second sonar, and the phase of the first sonar The number of channels of the first sonar and the second sonar, the physical aperture length, the transmission period, and the speed of the underwater vehicle are adjusted so that the center of the center and the phase center of the second sonar are equally spaced. A synthetic aperture exploration device is provided.

According to the present invention, since two sonars having different frequencies are provided, it is possible to simultaneously carry out target exploration with different properties such as sediments and buried objects.
In addition, by synchronizing the transmission timings of these sound beam, it is possible to avoid the influence of mutual induced noise between the first sonar and the second sonar and obtain a clear image.
Furthermore, since various parameters are set so that the interval between the phase centers of the first and second sonars is equal between pings, fine correction of the position in the moving direction when performing image processing becomes unnecessary, and the image The burden of signal processing can be reduced, and degradation of image processing due to errors in the transmission / reception unit position can be suppressed.

  In the synthetic aperture exploration device, the position of the underwater vehicle may be corrected by overlapping channels in the first sonar, and the number of overlap channels in the second sonar may be zero.

  Since the first sonar and the second sonar are mounted on the same underwater vehicle, it is sufficient to perform position correction with one of the sonars. Therefore, only the first sonar channel is overlapped and used for position correction of the underwater vehicle, and in the second sonar, the number of channels to be overlapped is set to zero, thereby reducing the number of channels to the minimum required number. Can be squeezed. This makes it possible to reduce the size of the apparatus, save space, and reduce the weight.

  In the synthetic aperture exploration device, when the accuracy of position correction in the underwater vehicle due to channel overlap in the first sonar is less than a predetermined accuracy, the phase center of the first sonar and the phase of the second sonar The speed of the underwater vehicle may be reduced so as to satisfy the condition that the centers are equally spaced.

  As described above, even when the speed is lowered because the accuracy of the position correction is less than the predetermined accuracy, the condition that the phase center of the first sonar and the phase center of the second sonar are equally spaced is satisfied. Since the speed of the underwater vehicle is reduced, fine correction of the position in the moving direction when performing image processing can be eliminated. As a result, it is possible to reduce the burden of image signal processing, and it is possible to maintain the effect that it is possible to suppress deterioration in image processing due to an error in the position of the transmission / reception unit.

  In the synthetic aperture exploration device, the second sonar transmits and receives a plurality of sound beams having different beam main pole directions, and creates images using received signals having the same beam main pole direction. Also good.

  Thereby, in the second sonar, it is possible to efficiently search even a target having a directivity such as a cylindrical shape by oscillating a sound beam in a plurality of main pole directions.

  In the above synthetic aperture exploration device, the second sonar includes a transmission array in which a plurality of transmission elements are arranged and a reception array in which a plurality of reception elements are arranged, and the transmission array is about 90 in one direction. A plurality of sound beams having different directions of the beam main poles may be transmitted and received by transmitting a sound beam having a width of about 50 degrees and directing the beam main pole of the receiving array in a plurality of directions.

  As described above, the transmitting array transmits the sound beam only in one direction and directs the beam main pole of the receiving array in a plurality of directions, so that the phase shift of the transmitting array can be made unnecessary. The configuration can be simplified.

  In the synthetic aperture exploration device, the second sonar has a receiving array in which a plurality of receiving elements are arranged, and supports a plurality of beam main poles by changing a combination of receiving elements constituting the receiving array. A receiving array may be formed.

  According to such a configuration, the spatial sampling in the moving direction can be made denser, and the image quality can be improved.

  The present invention provides an underwater vehicle equipped with any of the synthetic aperture exploration devices described above.

  According to the present invention, there is an effect that the sediment and the buried object can be explored simultaneously and efficiently.

It is the figure which showed schematic structure of the synthetic aperture exploration apparatus which concerns on 1st Embodiment of this invention. It is a figure for demonstrating the transmission timing of a sound beam. It is the schematic diagram which showed the state by which the synthetic aperture exploration apparatus is mounted in the underwater vehicle. It is the model which showed the state in which the sound beam is transmitted from the synthetic aperture exploration device mounted in the underwater vehicle, and (a) shows the underwater vehicle from the z-axis direction in FIG. FIG. 3B is a view of the underwater vehicle as viewed from the x-axis direction of FIG. 3, that is, the moving direction. FIG. 9C is a view of the underwater vehicle as viewed from the y-axis direction of FIG. It is. It is the figure which showed the example of arrangement | positioning of the 1st transmission part and 1st receiving part of a high frequency synthetic aperture sonar, and the 2nd transmission part and 2nd receiving part of a low frequency synthetic aperture sonar. It is a figure for demonstrating the design of the transmission / reception part for making a phase center into an equal interval. It is a figure for demonstrating the design of the transmission / reception part for making a phase center into an equal interval. It is a figure for demonstrating the design of the transmission / reception part which considered overlapping. It is a figure for demonstrating the design of the transmission / reception part which considered overlapping. It is a figure for demonstrating the synthetic aperture exploration apparatus and underwater vehicle which concern on 2nd Embodiment of this invention. It is a figure for demonstrating the general navigation method of a high frequency synthetic aperture sonar. It is a figure for demonstrating the synthetic aperture exploration apparatus and underwater vehicle which concern on 2nd Embodiment of this invention.

[First Embodiment]
Hereinafter, a synthetic aperture exploration device and an underwater vehicle according to a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of the synthetic aperture exploration device 1. As shown in FIG. 1, the synthetic aperture exploration apparatus 1 includes a high frequency synthetic aperture sonar (first sonar) 2 that obtains an image signal by transmitting and receiving a sound beam of a first frequency, and a second lower than the first frequency. A low-frequency synthetic aperture sonar (second sonar) 3 that obtains an image signal by transmitting and receiving a sound wave beam of a frequency, and a control unit 4 that controls transmission / reception timing of the high-frequency synthetic aperture sonar and the low-frequency synthetic aperture sonar are provided.

  The high frequency synthetic aperture sonar 2 is, for example, a sonar for bottom sediment search, and the first transmission unit HF_Tx that transmits a high frequency sound wave beam and the sound beam transmitted from the first transmission unit HF_Tx is reflected on the search target. The first receiving unit HF_Rx that receives the sound wave that has returned and the first image processing unit 6 that creates an image based on the sound wave signal received by the first receiving unit HF_Rx.

The low-frequency synthetic aperture sonar 3 is, for example, a sonar for exploring an embedded object, a second transmission unit LF_Tx that outputs a sound beam having a frequency lower than that of the first transmission unit HF_Tx that transmits a high-frequency sound beam, A second receiving unit LF_Rx that receives a sound wave reflected and returned by the sound beam transmitted from the transmitting unit LF_Tx, and a second that creates an image based on the sound wave signal received by the second receiving unit LF_Rx An image processing unit 7 is provided.
For example, the sound beam transmitted and received by the high frequency synthetic aperture sonar 2 is a sound beam having a frequency of about 100 kHz to 500 kHz, and the sound beam transmitted and received by the low frequency synthetic aperture sonar 3 is about 10 kHz to 50 kHz. A sound beam of any frequency.

  The control unit 3 synchronously controls the first transmission unit HF_Tx, the second transmission unit LF_Tx, the first reception unit HF_Rx, and the second reception unit LF_Rx. As described above, the first transmission unit HF_Tx, the second transmission unit LF_Tx, the first reception unit HF_Rx, and the second reception unit LF_Rx are synchronously controlled, so that the timing at which the sound beam is transmitted from the first transmission unit HF_Tx and the first The timing at which the sound beam is transmitted from the two transmission units LF_Tx can be matched. Thereby, for example, it is possible to avoid the possibility that induced noise or acoustic noise at the time of transmitting a sound wave beam is mixed into the other receiving system. Note that the timing at which the sound beam is transmitted from the first transmission unit HF_Tx and the timing at which the sound beam is transmitted from the second transmission unit LF_Tx may not completely match.

  For example, as illustrated in FIG. 2, the time may be shifted sufficiently shorter than the transmission period T. For example, the synthetic aperture exploration device 1 according to this embodiment is for exploring sedimentation and buried objects. Therefore, in the area before the sound wave reaches the seabed, that is, in the vicinity of the underwater vehicle, it is not so important for the exploration. Therefore, there is no problem in exploration accuracy even if noise is included in this area. Therefore, as shown in FIG. 2, the transmission timing of the acoustic beam may be shifted by a time corresponding to a region having no problem in search accuracy. Also, for example, when the first transmitter HF_Tx and the second transmitter LF_Tx are operated in synchronization, the operating currents for two transmitters flow in the device, but as shown in FIG. By shifting the timing, the operating current can be dispersed, and the capacity of the power supply device used in the apparatus can be set small.

As shown in FIG. 3, the synthetic aperture exploration device 1 is mounted on each side surface of the underwater vehicle 10, and as shown in FIG. 4, the sound wave beam is transmitted obliquely downward and the return wave is received. To do.
FIG. 5 is a diagram illustrating an arrangement example of the first transmission unit HF_Tx and the first reception unit HF_Rx of the high frequency synthetic aperture sonar 2 and the second transmission unit LF_Tx and the second reception unit LF_Rx of the low frequency synthetic aperture sonar 3. As shown in FIG. 5, the first receiving unit HF_Rx and the second receiving unit LF_Rx are arranged side by side in the vertical direction, the first receiving unit HF_Rx is disposed above them, and the second transmitting unit LF_Tx is disposed below them. Has been. This arrangement is an example and is not necessarily limited to this arrangement.

  Here, the physical aperture length and the number of channels of the transmission / reception unit of the high frequency synthetic aperture sonar 2, the physical aperture length and the number of channels of the transmission / reception unit of the low frequency synthetic aperture sonar 3, the transmission cycle of the sound beam of both synthetic aperture sonars, underwater navigation It is preferable that the speed relationship of the running body 10 is set so as to satisfy the following relational expression (1).

  D * (MN) = d (mn) = ΔX = 2 * V * T (1)

  Here, D is the physical aperture length of the low frequency synthetic aperture sonar 3, M is the number of channels of the low frequency synthetic aperture sonar 3, N is the number of overlapping channels of the low frequency synthetic aperture sonar 3, and d is the frequency of the high frequency synthetic aperture sonar 2. Physical aperture length, m is the number of channels of the high frequency synthetic aperture sonar 2, n is the number of overlapping channels of the high frequency synthetic aperture sonar 2, V is the speed of the underwater vehicle, and T is the transmission period (repetition period) of the acoustic beam . Here, the number of channels corresponds to the number of receiving units.

  Now, it is assumed that the underwater vehicle 10 is moving at a constant linear velocity in the x-axis direction without being shaken. In this state, the sound beam transmitted from the second transmitter LF_Tx with a repetition period T is searched. When receiving a sound beam reflected back from the object, the received signal can be represented as shown in FIG. Here, black dots 1 to 5 shown in FIG. 7 are phase centers. The phase center means that when the sound wave transmitted from the transmitting unit is reflected by the search target and received by the receiving unit, the sound beam is actually transmitted at that position. The pseudo sound beam transmission / reception position which can be performed is shown. This phase center is set corresponding to each receiving unit. 6 and 7 exemplify the case where there are five receiving units, there are also five phase centers. The distance between the phase centers is D / 2.

Here, considering the image creation processing in the subsequent image processing unit, it is preferable that the phase centers are arranged at equal intervals. That is, as shown in FIGS. 6 and 7, it is preferable that the phase centers are always arranged at regular intervals even between pings. This is because setting the phase centers at equal intervals eliminates the need for fine correction of the position in the moving direction when performing image processing, thereby reducing the burden of signal processing.
In the high frequency synthetic aperture sonar 2 and the low frequency synthetic aperture sonar 3, in order for the phase centers to be arranged at equal intervals, the following equation (2) needs to be satisfied.

  Δx = D / 2 × (MN) = d / 2 × (mn) = V × T (2)

In the above equation (2), Δx is the moving distance of the underwater vehicle during one ping. The above equation (1) is derived from the above equation (2).
In other words, by determining each parameter so as to satisfy the above equation (1), it is possible to always arrange the phase centers at regular intervals regardless of whether or not they are between pings as shown in FIGS. It becomes. 6 and 7, the channels are not overlapped, but the channels may be overlapped as shown in FIGS. 8 and 9.

  By creating an overlap channel, it is possible to estimate the motion of the underwater vehicle 10. In the examples shown in FIGS. 8 and 9, the overlap rate is 40%. In this way, if the overlap ratio is 40% when five reception units are provided, two reception channels (phase centers) are used for fluctuation estimation for one ping, and three reception channels (phase centers) are used. It will be used for exploration.

  Examples of the design of the low-frequency synthetic aperture sonar 3 and the high-frequency synthetic aperture sonar 2 for satisfying the above expression (1) include the following examples.

Low frequency synthetic aperture sonar: D = 240 mm, M = 5, N = 1, L _L = D × M = 1200 mm
High-frequency synthetic aperture sonar: d = 40 mm, m = 32, n = 8, L _H = d × m = 1280 mm

  In the above design example, both the low-frequency synthetic aperture sonar 3 and the high-frequency synthetic aperture sonar 2 are provided with overlap channels, and are used for motion estimation. Exploration efficiency is high because the number of receivers (channels) used increases, but the accuracy of fluctuation estimation decreases. Moreover, since the low frequency synthetic aperture sonar 3 and the high frequency synthetic aperture sonar 2 are mounted on the same underwater vehicle 10, if the motion estimation by either one is performed, the motion estimation by the other synthetic aperture sonar is performed. Is no longer necessary.

  Therefore, the motion estimation is performed using only the overlap channel in the high frequency synthetic aperture sonar 2 with a large number of channels, and the channel used for the motion estimation is set to zero for the low frequency synthetic aperture sonar 3 with a small number of channels. Set the number of overlapping channels to zero. By setting the number of overlaps to zero, unnecessary channels can be deleted to minimize the number of channels, and space saving and cost reduction can be achieved.

  In this case, in the above equation (1), N = 0 may be set. Thereby, the following (3) Formula is derived | led-out from the said (1) Formula.

  M = d (mn) / D (3)

  That is, in the case of the above example, M = 4, and the number of channels can be reduced by one.

  Further, as described above, the fluctuation estimation is performed by the high-frequency synthetic aperture sonar 2, but if sufficient fluctuation estimation accuracy cannot be obtained, it is necessary to lower the speed V and further increase the number of overlapping channels. At this time, in both the high frequency synthetic aperture sonar 3 and the low frequency synthetic aperture sonar 2, the speed V is determined so that the phase centers are arranged at an equal pitch. That is, even when the speed is lowered, by adjusting the speed so as to satisfy the above expression (1), the interval between the phase centers can always be set to D / 2, and the processing load in image generation can be reduced. it can.

  Whether or not sufficient fluctuation estimation accuracy is obtained depends on, for example, calculating a correlation value of received signals of overlapping channels in real time and whether the correlation value is less than a preset threshold value. Done.

As described above, according to the synthetic aperture exploration device and the underwater vehicle according to the present embodiment, two synthetic aperture sonars having different frequencies are provided, so that simultaneous exploration of sediments and buried objects is possible. It can be.
Further, by synchronizing the transmission timing of these sound wave beams, it is possible to avoid the influence of induced noise and the like, and it is possible to obtain a clear image.
Further, since various parameters are set so that the phase center intervals in the high frequency synthetic aperture sonar 2 and the low frequency synthetic aperture sonar 3 are equal to each other between pings, the position in the moving direction when performing image processing is finely corrected. Can be reduced, and the burden of image signal processing can be reduced, and deterioration of image processing due to an error in the position of the transmission / reception unit can be suppressed.
In addition, only the channel of the high frequency synthetic aperture sonar 2 is overlapped to be used for estimating the underwater vehicle's motion, and in the low frequency synthetic aperture sonar 3, the number of channels to be overlapped is set to zero, thereby minimizing the number of channels. It is possible to reduce the number to the required number, and it is possible to reduce the size, space and weight of the device.

[Second Embodiment]
Next, the synthetic aperture exploration device and the underwater vehicle according to the second embodiment of the present invention will be described.
When searching for a target using synthetic aperture sonar, if the target has no directivity, the normal resolution of the synthetic aperture search device can be obtained. Even if transmission / reception is repeatedly performed while moving to, the ping that can obtain an effective echo is limited.

  For example, when the sound beam width (the angle range of the beam) of the synthetic aperture sonar is narrow, the probability that the target enters the beam width is low, making it difficult to find the target, and in front of the target where it is easy to find the target. Even when the transmission / reception unit arrives, a significant echo cannot be obtained due to the aspect characteristic of the reflection of the target, and as a result, it may be overlooked.

  On the other hand, when the sound beam width of the synthetic aperture sonar is widened, the probability of overlooking the target is lowered, but since a wide range of noise is also picked up, the signal to reverberation ratio (S / N ratio) is deteriorated. Therefore, the sound beam width cannot be expanded to the dark clouds. Here, by the synthetic aperture processing, the reverberation level can be suppressed normally, but in order to obtain a sufficient suppression effect, it is necessary to increase the synthetic aperture length in proportion to the beam width. However, if the required synthetic aperture length becomes long, it becomes difficult to accurately characterize the position of the underwater vehicle, and other problems will arise.

  In general, in the high frequency synthetic aperture sonar that searches for sediments, as shown in FIG. 11, in the first exploration, it scans in one direction, and in the second exploration, it intersects perpendicularly with the scanning direction in the first exploration. Target exploration is often performed by two 90-degree crossings that scan in the direction. This is because, for example, even if the reflection characteristic of the target has directivity, in the high frequency synthetic aperture sonar 2, the intensity of the reflected wave from the seabed portion hidden in the shadow of the target is the intensity of the reflected wave from the surrounding seabed part. Therefore, even if the intensity of the target echo is not enough, the presence of the target can be identified by the shadow called shadow, and the target can be found with considerable accuracy by exploring in two directions. Because. On the other hand, in the low-frequency synthetic aperture sonar 3, the intensity of the reflected wave from the surrounding portion compared with the shadow of the buried target is also weak and a clear shadow is not formed, so that the presence of the target is specified by the target echo intensity. There is a need.

Therefore, in the synthetic aperture exploration device and the underwater vehicle according to the present embodiment, the low frequency synthetic aperture sonar 3 transmits and receives a plurality of sound beams having different beam main pole directions, and the beam main pole directions are the same. Images were created using the received signals.
For example, as shown in FIG. 10, a 30-degree beam width acoustic wave beam is swung so that the beam main pole is 30 degrees, 0 degrees, and -30 degrees, and the beam main pole is 30 degrees, 0 degrees, and -30 degrees. Images are created with the received signals at the time of. Thereby, an image when the beam main pole is 30 degrees, an image when it is 0 degrees, and an image when it is -30 degrees are created.
Note that the present invention is not limited to the above example, and a sound beam having a constant beam width of 90 degrees or less may be distributed to a plurality of main poles, and an image may be created for each main pole using the received signal obtained at that time.

In this way, the low-frequency synthetic aperture sonar 3 mounted on the underwater vehicle 10 common to the high-frequency synthetic aperture sonar 2 also searches for the target by two 90-degree crossings as with the high-frequency synthetic aperture sonar 2. By making it possible, overall search efficiency can be maintained without reducing search efficiency.
Therefore, as described above, in the low-frequency synthetic aperture sonar 3, the main pole of the sound wave beam is swung over three angles, so that scanning is actually performed in three directions in one go. Similar effects can be obtained. Thereby, the frequency | count of a voyage can be match | combined with the high frequency synthetic aperture sonar 2, and a target can be searched efficiently.

  As described above, according to the synthetic aperture exploration device and the underwater vehicle according to the present embodiment, the low frequency synthetic aperture sonar 3 has directivity by oscillating a sound beam in a plurality of main pole directions. Even a target can be efficiently searched. Further, the search can be performed in accordance with the scanning method of the high frequency synthetic aperture sonar 2 that is normally performed, and the search efficiency by the high frequency synthetic aperture sonar 2 can be maintained.

[Third Embodiment]
Next, a synthetic aperture exploration device and an underwater vehicle according to a third embodiment of the present invention will be described. In the present embodiment, the receiving portion of the low frequency synthetic aperture sonar 3 is configured as a receiving array in which a plurality of receiving elements are arranged, and by changing the combination of receiving elements, the phase center is made more dense in a pseudo manner. Is. For example, as shown in FIG. 12, the signals received by the elements 1 to 4, 2 to 5, 3 to 6, 5 to 8, 7 to 10, and 9 to 12 are combined into one piece of data to synthesize a beam. To create an image. As a result, although the amount of computation increases, spatial sampling in the moving direction can be made dense, and the generation of grating lobes that are likely to occur when sampling in the moving direction is coarse in the image creation process can be suppressed. Image quality can be improved. Note that the arrangement interval of the receiving elements is λ / 2 or less. Here, λ is the wavelength of the sound wave.

As described above, according to the synthetic aperture exploration device and the underwater vehicle according to the present embodiment, spatial sampling in the moving direction can be made denser and image quality can be improved.
Also in the second embodiment described above, as in this embodiment, the transmitter and receiver of the low-frequency synthetic aperture sonar 3 are configured by an array of a plurality of elements, and each combination is changed to change the sound wave. If the beam is transmitted and the sound wave beam is received, the phase shift of the transmission array can be eliminated, and the configuration of the transmission unit can be simplified.

DESCRIPTION OF SYMBOLS 1 Synthetic aperture exploration device 2 High frequency synthetic aperture sonar 3 Low frequency synthetic aperture sonar 4 Control part 6 1st image processing part 7 2nd image processing part 10 Underwater vehicle HF_Tx 1st transmission part HF_Rx 1st reception part LF_Tx 2nd transmission Part LF_Rx second receiving part

Claims (7)

A first sonar mounted on the underwater vehicle and transmitting and receiving a sound beam of a first frequency to obtain an image signal;
A second sonar mounted on the underwater vehicle and transmitting and receiving a sound beam having a second frequency lower than the first frequency to obtain an image signal;
The first sonar and the second sonar are transmitted substantially synchronously, and the first sonar and the second sonar are arranged so that the phase centers of the first sonar and the second sonar are equally spaced from each other. A synthetic aperture exploration device in which the number of channels, physical aperture length, transmission cycle, and speed of the underwater vehicle are adjusted.   The synthetic aperture exploration device according to claim 1, wherein the position of the underwater vehicle is corrected by overlapping channels in the first sonar and the number of overlap channels in the second sonar is zero.   When the accuracy of position correction in the underwater vehicle due to channel overlap in the first sonar is less than a predetermined accuracy, the phase center of the first sonar and the phase center of the second sonar are equally spaced from each other. The synthetic aperture exploration device according to claim 1 or 2, wherein a speed of the underwater vehicle is decreased so as to satisfy the following condition.   The second sonar transmits and receives a plurality of sound beams having different beam main pole directions, and creates images using reception signals having the same beam main pole direction, respectively. Synthetic aperture exploration device according to the above. The second sonar has a transmitting array in which a plurality of transmitting elements are arranged and a receiving array in which a plurality of receiving elements are arranged,
The transmission array transmits a sound beam having a width of about 90 degrees with respect to one direction, and directs the beam main pole of the reception array in a plurality of directions, whereby a plurality of sound waves having different directions of the beam main pole are respectively provided. The synthetic aperture exploration device according to claim 4 which transmits and receives a beam. The second sonar has a receiving array in which a plurality of receiving elements are arranged,
The synthetic aperture exploration device according to claim 4 or 5, wherein a receiving array corresponding to a plurality of beam main poles is formed by changing a combination of receiving elements constituting the receiving array.   An underwater vehicle equipped with the synthetic aperture exploration device according to any one of claims 1 to 6.

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