JP7102907B2 - Synthetic aperture sonar, its signal processing method, and signal processing program - Google Patents

Description

The present disclosure relates to a Synthetic Aperture Sonar (SAS) mounted on an underwater vehicle, a signal processing method thereof, and a signal processing program.

The synthetic aperture sonar is a sonar that improves the low spatial resolution, which is a problem peculiar to low-frequency acoustics, by synthetic aperture processing, and is used to acquire a precise image of the sea surface or the like. The synthetic opening treatment of the synthetic opening sonar is disclosed in, for example, Patent Document 1.

Japanese Unexamined Patent Publication No. 2007-333473

However, the synthetic aperture processing of the synthetic aperture sonar requires a relatively large amount of calculation. Therefore, the processing load of the signal processor that performs the synthetic aperture processing is large, the processing time is required, and it is an obstacle to real-time operation.

Further, if a high-speed and high-performance CPU (Central Processing Unit) is adopted for the signal processor in order to shorten the processing time of the combined aperture processing, the power consumption is increased. When the synthetic aperture treatment is performed inside the underwater vehicle, which is a closed space, the increase in power consumption leads to an increase in the internal temperature, which is a factor that cannot be overlooked from the viewpoint of stable operation of the synthetic aperture sonar. Was there.

An object of the present disclosure is a synthetic aperture sonar, a signal processing method thereof, and a signal processing program capable of solving the above-mentioned problems, reducing the processing load of a signal processor that performs synthetic aperture processing, and increasing the processing speed. Is to provide.

Synthetic aperture sonar according to one aspect
A transmitter / receiver that transmits / receives sound waves,
A signal processor that performs synthetic aperture processing on the data of the received sound wave received by the transmitter / receiver is provided.
The signal processor
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
The output of the two-dimensional Fourier is imaged.

The signal processing method of the synthetic aperture sonar according to one aspect is
It is a signal processing method of a synthetic aperture sonar that performs synthetic aperture processing on the data of the received sound waves received by the transmitter / receiver.
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
The output of the two-dimensional Fourier is imaged.

The signal processing program according to one aspect is
Computer,
A signal processing program that functions as a signal processing means that performs synthetic aperture processing on the received sound wave data received by the transmitter / receiver.
The signal processing means
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
The output of the two-dimensional Fourier is imaged.

According to the above aspect, there is an effect that a synthetic aperture sonar capable of reducing the processing load of a signal processor performing synthetic aperture processing and increasing the processing speed, a signal processing method thereof, and a signal processing program can be provided. can get.

It is a figure which shows the structural example of the synthetic opening sonar which concerns on embodiment. It is a figure which shows the example of the reference table which concerns on embodiment. It is a flow figure which shows the example of the flow of the synthetic opening processing which concerns on a related technique. It is a figure which shows the example of the multiplication process of the replica and the reference function of step S104 of FIG. It is a figure which shows the example of the total interpolation processing of steps S105 to S107 of FIG. It is a figure which shows the example of the calculation process of the index of step S105 of FIG. It is a figure which shows the example of the calculation process of the interpolation coefficient of step S105 of FIG. It is a figure which shows the example of the extraction process of the element of step S106 of FIG. It is a figure which shows the example of the multiplication process of the interpolation coefficient of step S107 of FIG. It is a figure which shows the example of the nearest neighbor method applicable to the Salt interpolation processing of steps S105 to S107 of FIG. It is a flow figure which shows the example of the flow of the synthetic opening processing by the synthetic opening sonar which concerns on embodiment. It is a figure which shows the example of the reading process of the reference table of step S203 of FIG. It is a figure which shows the example of the extraction process of the element of step S205 of FIG. It is a figure which shows the example of the multiplication process of the table coefficient of step S206 of FIG. It is a figure which shows the example of the reading method of the reference table by the synthetic opening sonar which concerns on embodiment. It is a figure which shows the structural example of the synthetic opening sonar which conceptually showed embodiment.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following descriptions and drawings have been omitted or simplified as appropriate for the purpose of clarifying the explanation. Further, in each of the following drawings, the same elements are designated by the same reference numerals, and duplicate explanations are omitted as necessary.

<Structure of Embodiment>
First, a configuration example of the synthetic opening sonar 1 according to the present embodiment will be described with reference to FIG. It is assumed that the synthetic opening sonar 1 according to the present embodiment executes synthetic opening processing in real time inside an underwater vehicle that is navigating while acquiring RAW data. Further, it is assumed that the synthetic aperture sonar 1 according to the present embodiment generates SAS images on both the left and right sides by transmitting and receiving sound waves by changing the wave transmission waveform on the port side and the starboard side. Further, it is assumed that the synthetic opening sonar 1 according to the present embodiment includes a sensor for measuring the underwater sound velocity (sound velocity sensor 13 described later), and can refer to the underwater sound velocity at the time of acquiring RAW data.

As shown in FIG. 1, the synthetic aperture sonar 1 according to the present embodiment includes transmitters / receivers 11L and 11R, a transmitter / receiver 12, a sound velocity sensor 13, a signal processor 14, an external storage device 15, and the like. It has.

The transmitter / receiver 11L and 11R transmit and receive sound waves. The transmitter / receiver 11L is provided on the left side of the underwater vehicle and transmits the sound wave of the transmission waveform 1. Further, the transmitter / receiver 11R is provided on the right side of the underwater vehicle and transmits the sound wave of the transmission waveform 2.

The transmitter / receiver 12 converts the received sound wave received by the left-side transmitter / receiver 11L into RAW data, and also converts the received sound wave received by the right-side transmitter / receiver 11R into RAW data, and converts the received sound wave into RAW data. The right-side RAW data is independently output to the signal processor 14.

The sound velocity sensor 13 is a sensor that measures the underwater sound velocity, and outputs the measured underwater sound velocity to the signal processor 14.

The signal processor 14 is composed of a CPU and a memory in hardware, and a signal processing program having an algorithm described later is mounted on the memory by software. That is, the function of the signal processor 14 is realized by the CPU reading and executing the signal processing program stored in the memory.

The signal processor 14 is connected to an external storage device 15 such as an HDD (Hard Disc Drive), and has a configuration capable of inputting / outputting files to / from the external storage device 15. A plurality of reference tables generated in advance are stored in the external storage device 15 in a file format.

The contents of the reference table depend on the processing parameters such as the number of FFT (Fast Fourier Transform) points, the wave waveform, the underwater sound velocity, and the interpolation method. However, by fixing the processing parameters other than the underwater sound velocity, the total number of reference tables can be saved.

The minimum / maximum value and step of the underwater sound velocity are determined, and the signal processor 14 sets the underwater sound velocity measured by the sound velocity sensor 13, for example, C (-M), C (-M + 1), ... , C (0), C (1), ..., C (M), totaling 2M + 1 discrete values. When the processing parameters other than the underwater sound velocity are fixed, the reference table is generated in advance for each of a total of 2M + 1 underwater sound velocity and stored in the external storage device 15. In the present embodiment, since the wave transmission waveforms are different between the port side and the starboard side, the total number of reference tables is 2 × (2M + 1) as shown in FIG.

Also, as shown in FIG. 2, the reference table includes an index and table coefficients. Both the index and the table coefficient are in a matrix format having the same number of elements as the number of FFT points of the 2D-FFT (two-dimensional FFT) described later.

The signal processor 14 performs synthetic aperture processing on each of the port and starboard RAW data. At that time, the signal processor 14 selects the optimum reference table according to the processing parameters from the plurality of reference tables stored in the external storage device 15 for each synthetic aperture processing, and stores the selected reference table in the memory. Read and use in. When the processing parameters other than the underwater sound velocity are fixed, the signal processor 14 selects a reference table corresponding to the underwater sound velocity C that approximates the underwater sound velocity measured by the sound velocity sensor 13. The synthetic opening process using the reference table according to the present embodiment will be described later.

<Operation of the embodiment>
Hereinafter, the synthetic opening treatment by the synthetic opening sonar 1 according to the present embodiment will be described. Here, for comparison, the synthetic opening treatment according to the related technique will also be described. In the following, the synthetic aperture processing by the Wavenumber Domine algorithm will be described as an example. In addition, processing parameters other than the underwater sound velocity shall be fixed.

<Flow of synthetic aperture processing related to related technology>
First, with reference to FIG. 3, the flow of synthetic aperture processing according to the related technique will be described.
As shown in FIG. 3, first, the average of the underwater sound velocity is calculated, and this is defined as the underwater sound velocity C (step S101).
Subsequently, the replica R (i) and the reference function φ (i, j) are calculated (step S102). Here, the replica R (i) is a spectrum obtained by FFTing the transmitted waveform. Further, the reference function φ (i, j) is a spatial chirp reference function in the kr (i) -ku (j) region in which the ru-u region is 2D-FFT. Further, r is the distance in the range direction, kr (i) is the wave number in the range direction, and i ≦ _NR ( _NR = number of FFT points in the range direction). Further, u is the distance in the azimuth direction, and ku (j) is the wave number in the azimuth direction, and j ≦ _NA ( _NA = the number of FFT points in the azimuth direction).

Subsequently, the RAW data is 2D-FFT and converted from the ru-u region to the kr (i) -ku (j) region (step S103). The 2D-FFT of the RAW data gives the spectrum A0 (i, j) on the kr (i) _-ku (j) coordinates, as shown in FIG.

Subsequently, the spectrum A ₀ (i, j) is multiplied by the replica R (i), and further multiplied by the reference function φ (i, j) (step S104). By multiplying the replica R (i) and the reference function φ (i, j), the spectrum A (i, j) is finally obtained, as shown in FIG.

Subsequently, Retro interpolation, which is an unequal-interval resampling process, is performed. As shown in FIG. 5, the Salt interpolation applies the spectrum B (i, j) after applying the coordinate transformation [kr (i), ku (j)] → [kx (i), ky (j)]. This is the desired process.

Since kr (i) is not always mapped on the grid point of the kx coordinate, the spectrum B (i, j) on the grid point of the kx coordinate needs to be obtained by interpolation. There are several examples of this interpolation method, but the most common linear interpolation method will be described below as an example.

First, the index and the interpolation coefficient α are calculated (step S105). Specifically, as shown in FIG. 6, the kx'(i) index (i = 1 to _NR ) is obtained by the mapping [kr, ku] → [kx', ky'] based on the underwater sound velocity C. .. Subsequently, as shown in FIG. 7, kx'before and after kx (i) is extracted (in this example, kx'(i), kx'(i + 1)), and the interpolation coefficient α is calculated.

Subsequently, as shown in FIG. 8, the elements corresponding to the kx'index (A (i, j), A (i + 1, j) in this example) are extracted from the spectrum A (i, j) (in this example, A (i, j), A (i + 1, j)) ( Step S106).
Subsequently, as shown in FIG. 9, the interpolation coefficient α is multiplied by the elements A (i, j) and A (i + 1, j) to obtain the following spectrum B (i, j) (step S107). ..
B (i, j) = α · A (i, j) + (1-α) · A (i + 1, j)
This completes the Salt interpolation process.

Subsequently, the spectrum B (i, j) is subjected to 2D-IFFT (Inverse Fast Fourier Transform) to transform the kx (i) -ky (j) region into the xy region (step S108).
After that, the output of the 2D-IFFT is imaged into a SAS image (step S109).

The same process as described above is performed independently for the port RAW data and the starboard RAW data. However, when the wave transmission waveform is different between the port side and the starboard side as in the present embodiment, the processing parameters are different between the port side and the starboard side. Specifically, the above replica differs between port and starboard.

Examples of the interpolation method other than the linear interpolation method applied to the halt interpolation processing include the nearest neighbor method and the Nth-order interpolation method.
The nearest neighbor method replaces with the element corresponding to kx'closest to kx, as shown in FIG. In this example, kx'(i + 1) is the closest to kx (i), so B (i, j) = A (i + 1, j).

On the other hand, in the Nth-order interpolation method, B (i, j) is calculated using kx'and A of N + 1 points including kx (i) in the interval. The illustration of the Nth-order interpolation method and the description of a specific calculation method will be omitted.

As described above, in the synthetic aperture processing according to the related technique, the amount of calculation is relatively large because the non-equidistant resampling processing such as the Salt interpolation is performed by calculation. Therefore, the processing load of the signal processor that performs the synthetic aperture processing is large, the processing time is required, and it is an obstacle to real-time operation.

<Flow of synthetic aperture processing according to the embodiment>
Subsequently, with reference to FIG. 11, the flow of the synthetic opening processing by the synthetic opening sonar 1 according to the present embodiment will be described.
As shown in FIG. 11, first, the signal processor 14 calculates the average of the underwater sound velocity measured by the sound velocity sensor 13, and the calculated average of the underwater sound velocity is one of the above-mentioned total 2M + 1 discrete values. Approximate with, and let this be the underwater sound velocity C (step S201).

Subsequently, the signal processor 14 determines whether or not to change the reference table currently being read into the memory (step S202). Here, if the reference table corresponding to the underwater sound velocity C is not currently read into the memory, it is determined that the reference table is changed.

When the signal processor 14 changes the reference table (Yes in step S202), the signal processor 14 newly reads the reference table from the external storage device 15 (step S203). The details of the reference table reading method according to the present embodiment will be described later.

Here, the reference table corresponding to the underwater sound velocity C includes a kx'index corresponding to the underwater sound velocity C and a table coefficient T (i, j) corresponding to the underwater sound velocity C instead of the interpolation coefficient. There is. Therefore, if the element corresponding to the kx'index is extracted thereafter, the interpolation calculation can be performed.

In the case of linear interpolation, two samples are required for one point interpolation calculation. Therefore, as shown in FIG. 12, two table coefficients T (i, j) are also required (in this example, a pair of T ₁ (i, j) and T ₂ (i, j) is B (i). , J) is calculated).

The table coefficient T (i, j) is a coefficient for calculating B (i, j) from A ₀ (i, j), which is the output of the 2D-FFT, and is as follows based on the flow related to the related technology. Calculate in advance by definition and save.
T ₁ (i, j) = α · A (i, j) / A ₀ (i, j) = α · R (i) · φ (i, j)
T ₂ (i, j) = (1-α) · A (i + 1, j) / A ₀ (i + 1, j)
= (1-α) ・ R (i + 1) ・ φ (i + 1, j)
As described above, the table coefficient T (i, j) is a coefficient in the form of the interpolation coefficient α multiplied in advance by the replica R (i) to be used and the reference function φ (i, j).

Subsequently, the signal processor 14 performs 2D-FFT of the RAW data obtained from the transmitter / receiver 12 to convert the ru region into the kr (i) -ku (j) region (step S204).

Subsequently, the signal processor 14 performs a process corresponding to the replica and reference function multiplication process (step S104) and the Salt interpolation process (steps S105 to S107) related to the related technique, and kx (i), ky (j). The spectrum B (i, j) of In the following, as the interpolation method, a linear interpolation method will be described as an example, as in the flow related to the related technique.

First, as shown in FIG. 13, the signal processor 14 has elements corresponding to the kx'index from A ₀ (i, j), which is the output of the 2D-FFT (in this example, A ₀ (i, j). ), A ₀ (i + 1, j)) (step S205).
Subsequently, as shown in FIG. 14, the signal processor 14 has table coefficients T ₁ (i, j), T ₂ (i, j) and elements A ₀ (i, j), A ₀ (i + 1, j). ) To obtain the following spectrum B (i, j) (step S206).
B (i, j) = T ₁ (i, j) · A ₀ (i, j) + T ₂ (i, j) · A ₀ (i + 1, j)
This completes the processing corresponding to the replica and reference function multiplication processing and the Salt interpolation processing related to the related techniques.

Subsequently, the signal processor 14 performs 2D-IFFT of the spectrum B (i, j) to convert the kx (i) -ky (j) region into the xy region (step S207).
After that, the signal processor 14 images the output of the 2D-IFFT into a SAS image (step S208), and stores the SAS image in the external storage device 15.

The same process as described above is performed independently for the port RAW data and the starboard RAW data. However, in the present embodiment, since the wave transmission waveform is different between the port side and the starboard side, the processing parameters are different between the port side and the starboard side. Specifically, the above replica differs between port and starboard.

<Method of reading the reference table according to the embodiment>
Subsequently, with reference to FIG. 15, a method of reading the reference table by the synthetic aperture sonar 1 according to the present embodiment will be described.
As shown in FIG. 15, the underwater sound velocity C may change over time (see the polygonal line in the figure). Therefore, in order to respond to the change in the underwater sound velocity C, the signal processor 14 externally stores not only the reference table selected according to the current underwater sound velocity C but also the reference tables before and / or after the reference table. It is read from the device 15 into the memory in advance and stored.

This example is an example of always holding three reference tables in memory. At the first time, the reference table selected according to the current underwater sound velocity C and the reference tables before and after it are read and held in the memory, and the selected reference table is applied to the processing. From the next time onward, if the current underwater sound velocity is within the range of the underwater sound velocity that holds the reference table, the reference table will not be newly read (the reference table applied to the processing will be changed as appropriate), and it will be out of range. When it becomes, the reference table selected according to the current underwater sound velocity is newly read into the memory and applied to the processing.

Specifically, in this example, the first (first) underwater sound velocity is C (0). Therefore, the signal processor 14 reads the reference tables of C (0) and C (-1) and C (1) before and after it into the memory, and applies the reference table of C (0) to the processing.
The second underwater sound velocity that follows is also C (0). Therefore, the signal processor 14 does not read a new reference table, and continuously applies the reference table of C (0) to the processing.

The subsequent third underwater sound velocity changes to C (-1), which is in the range of C (-1) to C (1) holding the reference table. Therefore, the signal processor 14 does not read a new reference table, but changes the reference table applied to the processing to the reference table of C (-1).
The fourth underwater sound velocity that follows is also C (-1). Therefore, the signal processor 14 does not read a new reference table, and continuously applies the reference table of C (-1) to the processing.

The subsequent fifth underwater sound velocity changes to C (-2), which is outside the range of C (-1) to C (1) holding the reference table. Therefore, the signal processor 14 newly reads the reference table of C (-2) into the memory, and deletes the reference table of C (1) from the memory. Then, the signal processor 14 changes the reference table applied to the processing to the reference table of C (-2).
The description of the sixth and subsequent processes will be omitted.

As described above, according to the present embodiment, the signal processor 14 selects the reference table, executes the 2D-FFT on the RAW data, and is included in the reference table from the output of the 2D-FFT. The element corresponding to the index is extracted, the extracted element is multiplied by the table coefficient included in the reference table, the 2D-IFFT is executed on the result of the multiplication, and the output of the 2D-IFFT is imaged. ..

As described above, according to the present embodiment, the non-equidistant resampling process such as the Salt interpolation, which has a large processing load in the related technique, is replaced with the reference of the reference table instead of the calculation. As a result, the amount of calculation for the synthetic aperture processing is reduced, so that the processing load of the signal processor 14 can be reduced and the processing speed can be increased. As a result, it can contribute to real-time operation. Further, since it is not necessary to adopt a high-speed and high-performance CPU for the signal processor 14, the power consumption of the signal processor 14 can be reduced.

Further, according to the present embodiment, as the reference table, a plurality of reference tables generated based on the processing parameters are generated in advance and stored in the external storage device 15, and the signal processor 14 performs each synthetic aperture processing. , Select the most suitable reference table according to the processing parameters, read it into the memory, and use it. As a result, it is possible to guarantee the image performance as well as the processing speed of the signal processor 14.

Further, according to the present embodiment, the total number of reference tables can be saved by fixing the processing parameters other than the underwater sound velocity.
Further, according to the present embodiment, the signal processor 14 reads the reference table before and / or after the reference table selected according to the underwater sound velocity into the memory from the external storage device 15. Keep it. This makes it possible to reduce the frequency and load of reading the reference table from the external storage device 15 even when the underwater sound velocity changes with the passage of time.

<Concept of embodiment>
Subsequently, a configuration example of the synthetic aperture sonar 2 conceptually showing the above-described embodiment will be described with reference to FIG. As shown in FIG. 16, the synthetic aperture sonar 2 includes a transmitter / receiver 101 and a signal processor 102.

The transmitter / receiver 101 transmits / receives sound waves. The transmitter / receiver 101 corresponds to the transmitter / receiver 11L, 11R.
The signal processor 102 performs a synthetic aperture process on the data of the received sound wave received by the transmitter / receiver 101. The signal processor 102 corresponds to the signal processor 14. Therefore, the signal processor 102 performs the same synthetic aperture processing as the synthetic aperture processing by the signal processor 14.

That is, the signal processor 102 selects the reference table, executes the two-dimensional FFT on the data of the received sound wave received by the transmitter / receiver 101, and selects the reference table from the output of the two-dimensional FFT. The element corresponding to the index included in is extracted, the extracted element is multiplied by the table coefficient contained in the selected reference table, the result of the multiplication is subjected to the two-dimensional Fourier, and the two-dimensional Fourier is executed. Image the output.

Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the structure and details of the present disclosure within the scope of the present disclosure.

For example, the signal processing program described above can be stored and supplied to a computer using various types of non-transitory computer readable media. Non-transitory computer-readable media include various types of tangible storage media. Examples of non-temporary computer-readable media include magnetic recording media (eg flexible disks, magnetic tapes, hard disk drives), photomagnetic recording media (eg optomagnetic discs), CD-ROMs (Compact Disc-Read Only Memory), CDs. -R (CD-Recordable), CD-R / W (CD-ReWritable), semiconductor memory (for example, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory)) include. The signal processing program described above may also be supplied to the computer by various types of transient computer readable media. Examples of temporary computer-readable media include electrical, optical, and electromagnetic waves. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire and an optical fiber, or a wireless communication path.

Some or all of the above embodiments may also be described, but not limited to:
(Appendix 1)
A transmitter / receiver that transmits / receives sound waves,
A signal processor that performs synthetic aperture processing on the data of the received sound wave received by the transmitter / receiver is provided.
The signal processor
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
Imaging the output of the two-dimensional Fourier,
Synthetic opening sonar.
(Appendix 2)
The signal processor
Equipped with memory
A plurality of the reference tables are connected to the stored external storage device, and the reference table is connected to the storage device.
A reference table is selected from the plurality of reference tables stored in the external storage device, and the selected reference table is read into the memory and used.
The synthetic opening sonar according to Appendix 1.
(Appendix 3)
A plurality of the reference tables generated for each processing parameter are stored in the external storage device.
The signal processor selects a reference table from a plurality of the reference tables stored in the external storage device according to the processing parameters.
The synthetic opening sonar according to Appendix 2.
(Appendix 4)
Equipped with a sound velocity sensor that measures the speed of sound underwater
The processing parameters are fixed except for the underwater sound velocity.
The external storage device stores a plurality of the reference tables generated for each underwater sound velocity.
The signal processor selects a reference table from a plurality of the reference tables stored in the external storage device according to the underwater sound velocity measured by the sound velocity sensor.
The synthetic opening sonar according to Appendix 3.
(Appendix 5)
The signal processor reads and holds a reference table before and / or after the reference table in the memory together with a reference table selected according to the underwater sound velocity measured by the sound velocity sensor.
The synthetic opening sonar according to Appendix 4.
(Appendix 6)
The table coefficient is a coefficient in the form of pre-multiplying the interpolation coefficient by the replica and the reference function used for the synthetic aperture processing.
The synthetic opening sonar according to any one of Appendix 1 to 5.
(Appendix 7)
The indexes and table coefficients included in the reference table are in the form of a matrix having the same number of elements as the number of FFT points of the two-dimensional FFT.
The synthetic opening sonar according to any one of Appendix 1 to 6.
(Appendix 8)
The transmitter / receiver is provided on both the starboard and starboard sides of the underwater vehicle.
The signal processor performs the synthetic aperture processing on each of the received sound wave data received by the transmitter / receiver on both the starboard and starboard sides.
The synthetic opening sonar according to any one of Appendix 1 to 7.
(Appendix 9)
It is a signal processing method of a synthetic aperture sonar that performs synthetic aperture processing on the data of the received sound waves received by the transmitter / receiver.
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
Imaging the output of the two-dimensional Fourier,
Signal processing method for synthetic aperture sonar.
(Appendix 10)
A reference table is selected from a plurality of the reference tables stored in the external storage device, and the selected reference table is read into the memory and used.
The signal processing method for a synthetic aperture sonar according to Appendix 9.
(Appendix 11)
A plurality of the reference tables generated for each processing parameter are stored in the external storage device.
A reference table is selected from the plurality of reference tables stored in the external storage device according to the processing parameters.
The signal processing method for a synthetic aperture sonar according to Appendix 10.
(Appendix 12)
The processing parameters are fixed except for the underwater sound velocity.
The external storage device stores a plurality of the reference tables generated for each underwater sound velocity.
A reference table is selected from the plurality of reference tables stored in the external storage device according to the underwater sound velocity measured by the sound velocity sensor.
The signal processing method for a synthetic aperture sonar according to Appendix 11.
(Appendix 13)
Along with the reference table selected according to the underwater sound velocity measured by the sound velocity sensor, the reference table before and / or after the reference table is read and held in the memory.
The signal processing method for a synthetic aperture sonar according to Appendix 12.
(Appendix 14)
The table coefficient is a coefficient in the form of pre-multiplying the interpolation coefficient by the replica and the reference function used for the synthetic aperture processing.
The signal processing method for a synthetic aperture sonar according to any one of Appendix 9 to 13.
(Appendix 15)
The indexes and table coefficients included in the reference table are in the form of a matrix having the same number of elements as the number of FFT points of the two-dimensional FFT.
The signal processing method for a synthetic aperture sonar according to any one of Appendix 9 to 14.
(Appendix 16)
The transmitter / receiver is provided on both the starboard and starboard sides of the underwater vehicle.
The synthetic aperture processing is performed on each of the received sound wave data received by the transmitters and receivers on both the starboard and starboard sides.
The signal processing method for a synthetic aperture sonar according to any one of Appendix 9 to 15.
(Appendix 17)
Computer,
A signal processing program that functions as a signal processing means that performs synthetic aperture processing on the received sound wave data received by the transmitter / receiver.
The signal processing means
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
Imaging the output of the two-dimensional Fourier,
Signal processing program.
(Appendix 18)
The signal processing means selects a reference table from a plurality of the reference tables stored in the external storage device, and reads the selected reference table into the memory for use.
The signal processing program according to Appendix 17.
(Appendix 19)
A plurality of the reference tables generated for each processing parameter are stored in the external storage device.
The signal processing means selects a reference table from a plurality of the reference tables stored in the external storage device according to the processing parameters.
The signal processing program according to Appendix 18.
(Appendix 20)
The processing parameters are fixed except for the underwater sound velocity.
The external storage device stores a plurality of the reference tables generated for each underwater sound velocity.
The signal processing means selects a reference table from a plurality of the reference tables stored in the external storage device according to the underwater sound velocity measured by the sound velocity sensor.
The signal processing program according to Appendix 19.
(Appendix 21)
The signal processing means reads and holds a reference table before and / or after the reference table in the memory together with a reference table selected according to the underwater sound velocity measured by the sound velocity sensor.
The signal processing program according to Appendix 20.
(Appendix 22)
The table coefficient is a coefficient in the form of pre-multiplying the interpolation coefficient by the replica and the reference function used for the synthetic aperture processing.
The signal processing program according to any one of Appendix 17 to 21.
(Appendix 23)
The indexes and table coefficients included in the reference table are in the form of a matrix having the same number of elements as the number of FFT points of the two-dimensional FFT.
The signal processing program according to any one of Appendix 17 to 22.
(Appendix 24)
The transmitter / receiver is provided on both the starboard and starboard sides of the underwater vehicle.
The signal processing means performs the combined aperture processing on each of the received sound wave data received by the transmitters and receivers on both the starboard and starboard sides.
The signal processing program according to any one of Appendix 17 to 23.

1 Synthetic aperture sonar 11L, 11R Transmitter / receiver 12 Transmitter / receiver 13 Sound speed sensor 14 Signal processor 15 External storage device 2 Synthetic aperture sonar 101 Transmitter / receiver 102 Signal processor

Claims (9)

A transmitter / receiver that transmits / receives sound waves,
A signal processor that performs synthetic aperture processing on the data of the received sound wave received by the transmitter / receiver is provided.
The signal processor
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
The output of the two-dimensional Fourier is imaged and
The table coefficient is a coefficient in the form of pre-multiplying the interpolation coefficient by the replica and the reference function used for the synthetic aperture processing.
Synthetic opening sonar. The signal processor
Equipped with memory
A plurality of the reference tables are connected to the stored external storage device, and the reference table is connected to the storage device.
A reference table is selected from the plurality of reference tables stored in the external storage device, and the selected reference table is read into the memory and used.
The synthetic aperture sonar according to claim 1. A plurality of the reference tables generated for each processing parameter are stored in the external storage device.
The signal processor selects a reference table from a plurality of the reference tables stored in the external storage device according to the processing parameters.
The synthetic aperture sonar according to claim 2. Equipped with a sound velocity sensor that measures the speed of sound underwater
The processing parameters are fixed except for the underwater sound velocity.
The external storage device stores a plurality of the reference tables generated for each underwater sound velocity.
The signal processor selects a reference table from a plurality of the reference tables stored in the external storage device according to the underwater sound velocity measured by the sound velocity sensor.
The synthetic aperture sonar according to claim 3. The signal processor reads and holds a reference table before and / or after the reference table in the memory together with a reference table selected according to the underwater sound velocity measured by the sound velocity sensor.
The synthetic aperture sonar according to claim 4. The indexes and table coefficients included in the reference table are in the form of a matrix having the same number of elements as the number of FFT points of the two-dimensional FFT.
The synthetic opening sonar according to any one of claims 1 to 5 . The transmitter / receiver is provided on both the starboard and starboard sides of the underwater vehicle.
The signal processor performs the synthetic aperture processing on each of the received sound wave data received by the transmitter / receiver on both the starboard and starboard sides.
The synthetic opening sonar according to any one of claims 1 to 6 . It is a signal processing method of a synthetic aperture sonar that performs synthetic aperture processing on the data of the received sound waves received by the transmitter / receiver.
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
The output of the two-dimensional Fourier is imaged and
The table coefficient is a coefficient in the form of pre-multiplying the interpolation coefficient by the replica and the reference function used for the synthetic aperture processing.
Signal processing method for synthetic aperture sonar. Computer,
A signal processing program that functions as a signal processing means that performs synthetic aperture processing on the received sound wave data received by the transmitter / receiver.
The signal processing means
Select a lookup table and
A two-dimensional FFT is executed on the data,
From the output of the two-dimensional FFT, the element corresponding to the index included in the selected reference table is extracted.
Multiply the extracted elements by the table coefficients contained in the selected reference table.
A two-dimensional Fourier is executed on the result of the multiplication,
The output of the two-dimensional Fourier is imaged and
The table coefficient is a coefficient in the form of pre-multiplying the interpolation coefficient by the replica and the reference function used for the synthetic aperture processing.
Signal processing program.

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