JP5192983B2 - Acoustic image simulation apparatus, method, and program - Google Patents

Description

  The present invention relates to an acoustic image simulation apparatus, method, and program used for performance evaluation of an acoustic image apparatus such as a side scan sonar and a multi-beam acoustic sounding instrument.

2. Description of the Related Art Acoustic imaging devices such as side scan sonars and multi-beam acoustic sounding devices are known as devices used for searching for specific objects in seas, lakes, and the like, and for surveying seafloor topography. Such an acoustic imaging apparatus irradiates a beam, measures the azimuth intensity distribution and temporal intensity distribution of the scattered wave, and creates an acoustic image based on the measurement result.
Japanese Unexamined Patent Publication No. 63-75581

  The quality of the acoustic image acquired by the side scan sonar depends on whether the parameters of the side scan sonar, such as the frequency and width of the acoustic beam, and the parameters such as the seafloor altitude and speed of the platform on which the side scan sonar is installed, are good or bad. Is done. Conventionally, setting of such control parameters is left to the experience of the operator, and there is a problem that the quality of the acoustic image is not stable.

In addition, CAD / CAC (Computer Aided Detection / Computer Aided Classification) is a system that automatically detects and classifies a target existing on the sea floor by performing image processing on an acoustic image acquired by a side scan sonar. Are known. This performance evaluation of CAD / CAC is performed by using an acoustic image actually acquired in the sea area or the like as input data. In order to perform performance evaluation with stable accuracy, a large number of acoustic images are required when various operating conditions such as seabed conditions, target object size, and side scan sonar parameter conditions are varied. However, there is a limit to the number of acoustic images acquired in actual seafloor surveys, and there is a problem that it is difficult to stabilize the accuracy of performance evaluation due to a shortage of samples.
The quality of the seafloor topographic data acquired by the multibeam acoustic sounder depends on the quality of the seabed detection algorithm of the multibeam acoustic sounder. There are many types of algorithms that have already been put into practical use, but there is no other measurement means for error testing to identify the depth measurement error due to the seafloor detection algorithm, so it is difficult to determine whether the algorithm is good or bad was there.

  The present invention has been made to solve the above problem, and can evaluate the quality of the control parameters of the acoustic imaging apparatus and can simulate the acoustic image acquired by the acoustic imaging apparatus with sufficient accuracy. An object of the present invention is to provide an acoustic image simulation apparatus, method, and program capable of realizing quantitative performance evaluation of an acoustic image apparatus.

In order to solve the above problems, the present invention employs the following means.
The present invention provides a first storage means for storing a plurality of data required for a simulation, and a sea bottom composed of a plurality of area elements in a simulation space based on the data stored in the first storage means. Based on the wake data of the platform on which the sea bottom surface forming means to be formed and the acoustic image device stored in the first storage means are mounted, the attitude data, and the mounting position of the acoustic image device on the platform, A condition creation means for creating a condition table that associates a sound source, a reception position, and a target area element to be irradiated with an acoustic beam, and a sound source and a reception position are set in the simulation space based on the condition table In addition, when an acoustic beam is irradiated from the sound source to the target area element, the reception is performed. And simulated signal generating means for generating a scattered wave as test signal received at a position, and a second storage means for storing a simulation signal generated by said simulated signal generating means, stored in said second storage means Signal processing means for creating an acoustic image of the sea floor using a simulated signal, and the simulated signal generating means stores the sound source position and reception position set in the simulation space and the position of the target area element in the condition table. An acoustic image simulation apparatus for sequentially estimating scattered waves at different positions by updating based on the above is provided.

According to such a configuration, it is assumed that the platform such as the underwater vehicle moves along the wake data, and at this time, the scattered wave acquired by the acoustic image device such as the side scan sonar is estimated. Generate a simulated signal. Specifically, the acoustic signal generation means estimates the propagation and scattering of sound waves, which are physical phenomena, based on the momentary platform position / posture, seabed conditions and sonar specification conditions set in the simulation. A simulated signal received at is generated. Then, using the generated simulation signal, an acoustic image is created by a simulator signal processing unit having a function equivalent to that of the signal processor inside the acoustic image apparatus. In this way, the simulation is performed in a form that faithfully simulates the actual seafloor topography survey, so that the simulation accuracy can be improved.
Then, it is possible to select the most appropriate control parameter by repeatedly performing the simulation while changing the control parameter of the acoustic image apparatus and comparing the acoustic images obtained as a result of the simulation.
Furthermore, by examining such a simulation result, it is possible to quantitatively evaluate the performance of the acoustic image apparatus.

  The condition setting means, for example, sets the sound source and the reception position in the simulation space based on the platform track data, posture data, and the mounting position of the acoustic image device on the platform stored in the first storage means. The target area element is determined based on the set coordinates of the sound source and the incident angle of the acoustic beam, and the condition table in which the sound source, the reception position, and the reference area element are associated is created.

  In the acoustic image simulation apparatus, the simulation signal generating means includes a distance between the sound source and the target area element, a distance between the target area element and the reception position, and an orientation of the target area element with respect to the sound source. And the parameters including the seafloor incidence angle, and using these parameters, the amplitude, phase, waveform rise timing, and waveform fall timing of the simulation signal are calculated to simulate the scattered wave. It is good as well.

  This makes it possible to easily estimate the scattered wave.

In the acoustic image simulation apparatus, the sea bottom forming means may form a sea bottom composed of a plurality of the area elements based on a water depth and an acoustic impedance.

  As a result, it is possible to form an elaborate sea bottom reflecting the geology of the sea bottom in the simulation space. And it becomes possible to improve a simulation precision by estimating a scattered wave using such information of the sea bottom.

  In the above acoustic image simulation apparatus, the simulation signal generating means may generate a simulation signal represented by a sine wave or a cosine wave, and further beat down the simulation signal represented by the sine wave or cosine wave. A low-frequency signal (for example, quadrature modulation beat-down) may be calculated as a simulation signal. Further, the simulated signal generating means beats a simulated signal represented by the sine wave or cosine wave after the beat down (for example, quadrature modulation beat down), the amplitude, phase, waveform of the simulated signal It may be obtained directly using the rise timing and the fall timing of the waveform.

  This makes it possible to match the quality of the scattered wave used for creating the acoustic image in the simulation and the quality of the simulation signal used for creating the acoustic image during actual operation. For example, in an actual acoustic imaging apparatus, when an acoustic image is created using a beat-down low-frequency signal, the signal processing unit generates a beat-down low-frequency signal as a simulation signal in simulation. Can be made completely the same between the actual machine and the simulation, and the computation load of the simulation can be greatly reduced.

  In the acoustic image simulation apparatus, when there are a plurality of receivers that receive the simulation signal, the simulation signal generation unit simulates by setting any one of the plurality of receivers as the reception position. A simulated signal received by each of the receivers may be generated by generating a signal and correcting the phase of the simulated signal based on the arrangement position of each of the other receivers.

  By doing in this way, even if it is a case where a some receiver is provided, the scattered wave received by each receiver can be estimated easily and rapidly.

  The present invention receives a process of forming a sea bottom composed of a plurality of area elements in a simulation space, a position of a sound source that emits an acoustic beam, and a scattered wave that is a reflected wave of the acoustic beam in the simulation space. When the target area element to be irradiated with the acoustic beam is set and the acoustic beam is irradiated to the target area element from the position of the sound source, reception is performed at the position of the receiver. Generating a scattered signal as a simulation signal, generating a simulation signal for all the area elements constituting the sea floor while changing at least one of the position of the sound source and the target area element, and the generated An acoustic image simulation method including a process of creating an acoustic image of a sea floor using a simulated signal is provided.

  The present invention receives a process of forming a sea bottom composed of a plurality of area elements in a simulation space, a position of a sound source that emits an acoustic beam, and a scattered wave that is a reflected wave of the acoustic beam in the simulation space. When the target area element to be irradiated with the acoustic beam is set and the acoustic beam is irradiated to the target area element from the position of the sound source, reception is performed at the position of the receiver. Generated as a simulation signal, changing the position of the sound source and at least one of the target area elements, generating simulation signals for all area elements constituting the sea floor, and the generated Provided is an acoustic image simulation program for causing a computer to execute processing for creating an acoustic image of a seabed using a simulated signal.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to evaluate the quality of the control parameter of an acoustic imaging device, the acoustic image acquired by an acoustic imaging device can be simulated with sufficient precision, and quantitative of an acoustic imaging device is possible. It is possible to achieve an effective performance evaluation.

  Hereinafter, embodiments of an acoustic image simulation apparatus, method, and program according to the present invention will be described with reference to the drawings.

[First Embodiment]
The acoustic image simulation apparatus according to the first embodiment of the present invention is an apparatus applied to the performance evaluation of a side scan sonar.
FIG. 1 is a diagram illustrating a schematic configuration of an acoustic image simulation apparatus according to the present embodiment. As shown in FIG. 1, an acoustic image simulation apparatus 10 according to the present embodiment is a computer system (computer system), and includes a CPU (Central Processing Unit) 11, a main storage device 12 such as a RAM (Random Access Memory), An auxiliary storage device 13 such as an HDD (Hard Disk Drive), an input device 14 such as a keyboard and a mouse, an output device 15 such as a monitor and a printer, a communication device 16 that exchanges information by communicating with external devices, and the like It consists of
Various programs (for example, an acoustic image simulation program) are stored in the auxiliary storage device 13, and the CPU 11 reads out the programs from the auxiliary storage device 13 to the main storage device 12 and executes them to implement various processes.

  FIG. 2 is a functional block diagram showing the functions provided in the acoustic image simulation apparatus 10 in an expanded manner. As shown in FIG. 2, the acoustic image simulation apparatus 10 includes a first storage unit (first storage unit) 21, a sea bottom formation unit (sea bottom formation unit) 22, and a condition creation unit (condition creation unit) 23. , A simulation signal generation unit (simulation signal generation unit) 24, a second storage unit (second storage unit) 25, and a signal processing unit (signal processing unit) 26.

The first storage unit 21 stores various data necessary for the simulation. The various data stored in the first storage unit 21 are, for example, input and registered by an operator prior to the simulation. Examples of this data include, for example, the track data of an underwater vehicle equipped with a side scan sonar, the sea floor data required to create the sea floor, the spec data of the side scan sonar, the underwater vehicle The sonar mounting coordinates and the like.
The sea bottom data is, for example, a data group in which the coordinates, the water depth of the sea bottom, the scattering intensity (for example, acoustic impedance) and the like are set for each area element obtained by dividing the sea bottom with a mesh. These data stored in the first storage unit 21 are appropriately read and used when the simulation is executed.

  The sea bottom forming unit 22 forms the sea bottom in the simulation space based on the sea bottom data stored in the first storage unit 21. Thereby, as shown in FIG. 3, the sea bottom divided into a plurality of meshes is formed in the simulation space. In FIG. 3, each mesh corresponds to an area element.

The condition creating unit 23 sets, in the simulation space, the position of a sound source that emits an acoustic beam and a receiver that receives a scattered wave generated when the acoustic beam emitted from the sound source is reflected on the sea floor. At the same time, an area element to be irradiated with the acoustic beam is set as a target area element.
In the present embodiment, it is assumed that the sound source and the receiver are attached at the same position. Therefore, by setting the position of the sound source, the position of the receiver is also set at the same time.

Specifically, the condition creating unit 23 stores the track data of the underwater vehicle stored in the first storage unit 21, the attachment position of the side scan sonar on the underwater vehicle, the emission angle of the acoustic beam of the sonar (or The incident angle at the sea bottom) is read out, the position of the sound source is set based on the position of the side scan sonar at each time from these data, and then the first storage unit 21 is set from each set sound source. When an acoustic beam is irradiated at a certain acoustic beam emission angle, an area element including the position coordinates of the sea bottom reached by the acoustic beam is obtained, and this area element is set as a target area element for observing the seabed condition. At this time, depending on the width of the acoustic beam and the positional relationship between the sound source and the sea bottom, there may be a case where the acoustic beam is applied to a plurality of area elements at one sound source position. In such a case, a plurality of area elements are calculated corresponding to the position of one sound source.
In the present embodiment, the distance and direction are calculated with the center of the target area element as the representative position, and the effect of the area element size is taken into account when calculating the amplitude, waveform rise and fall of the scattered wave. Perform a simulation.

  When the condition creation unit 23 determines the position of each sound source and the target area element for the sound source at each time in the above-described procedure, the condition creation unit 23 creates a condition table that associates the position of each sound source with the coordinates of the target area element. As a result, the position of the sound source and the corresponding area element along the track of the underwater vehicle are set. Thus, based on this condition table, the simulation signal generation unit 24 in the subsequent stage sequentially estimates scattered waves in the acoustic beam emitted from the position of each sound source, so that the actual seabed search can be performed as faithfully as possible. It becomes possible to simulate.

  The simulation signal generation unit 24 estimates a scattered wave received at the position of the receiver when the target area element is irradiated with the acoustic beam from the position of the sound source set by the condition generation unit 23. The details of the scattered wave estimation method performed here will be described later. The simulation signal generator 24 estimates the scattered wave at the position of each receiver set in the condition table, and stores the estimated scattered wave information in the second storage unit 25. Thereby, the information of the estimated scattered wave in all area elements of the sea bottom is stored in the second storage unit 25.

  The signal processing unit 26 processes the scattered wave stored in the second storage unit 25 to create an acoustic image of the sea bottom. The signal processing unit 26 preferably has the same function and performance as the signal processing unit included in the side scan sonar to be evaluated. By doing in this way, it becomes possible to evaluate more accurately the performance of the side scan sonar to be evaluated.

[Method of estimating scattered waves]
Next, the scattered wave estimation method performed by the simulation signal generator 24 will be described.
First, the scattered wave is determined by four elements including amplitude, phase, waveform rising edge, and waveform falling edge.
Hereinafter, calculation methods of these elements will be described respectively.

〔amplitude〕
The amplitude can be obtained from the seafloor echo level EL. The seafloor echo level EL is expressed by the following equation (1).

EL = SL-2TL + 10 log S + BS (θ _i ) +20 log | D (θ _X , θ _Y ) | (1)

  In the above equation (1), SL is the transmission level of the acoustic beam, and is determined, for example, by reading data set in advance by an operator and stored in the first storage unit 21. TL is a propagation loss that occurs until the acoustic beam reaches the target area element from the position of the sound source. Since TL is multiplied by 2, the propagation loss of the acoustic beam at the round-trip distance is obtained. This TL can be obtained by the following equation (2), for example.

  TL = 20logR × α · R (2)

  In the above equation (2), R is the distance from the sound source to the target area element, α is called the absorption coefficient, and indicates the acoustic beam attenuation per unit length in seawater.

S = RΦ · (cτ / (2sinθ _i )) (3)
Here, as the reverberation area S, the smaller one of the area of the target area element set in advance and the area represented by Expression (3) is adopted.

In the above equation (3), R is the distance from the sound source to the target area element, Φ is the equivalent beam width in the front-rear direction, τ is the pulse width of the acoustic beam, c is the speed of sound, and θ _i is the angle of incidence on the sea floor. .

In the equation (1), BS (θ _i ) is the backscattering intensity per unit area, and can be read from a table as shown in FIG. 4, for example. In FIG. 4, the horizontal axis represents the incident angle θ _i to the sea bottom, and the vertical axis represents the backscattering intensity BS (θ _i ) per unit area.

20log | D (θ _X , θ _Y ) | in the equation (1) is a directivity function of the side scan sonar and is determined based on the spec data of the side scan sonar stored in the first storage unit 21. . Here, θ _X is the side scan sonar, that is, the orientation of the target area element in the front-rear direction of the underwater vehicle with reference to the sound source, and θ _Y is the side scan sonar, that is, the sound source as a reference. It is an azimuth | direction of the object area element in the direction (lateral direction) orthogonal to the axial direction of the underwater vehicle at the time of doing.

  When the seafloor echo level EL is obtained by inputting each parameter to the above (1), the seafloor echo level EL expressed in logarithm is expressed as a true number by using the following equation (4), thereby scattering. The effective amplitude value A of the wave can be obtained.

A = 10 ^{(EL / 20)} (4)

〔phase〕
Next, a method for calculating the phase will be described.
The phase θ can be calculated by the following equation (5).

  θ = 2R / λ × 2π (5)

[Wave rise and fall of waveform]
As shown in FIG. 5, the rising and falling edges of the waveform are R as the distance from the sound source to the target area element, Δy as the width of the target area element, and a direction orthogonal to the axial direction of the underwater vehicle as viewed from the reference position. When the orientation of the target area element in the (lateral direction) is θ _Y , the sound speed is c, and the pulse width is τ, the following expression (6) and (7) are used.

Rise of waveform = 2R / c− (Δy · sin θ _Y ) / c (6)
Fall of waveform = 2R / c + τ + (Δy · sinθ _Y ) / c (7)

  When the simulation signal generation unit 24 calculates the four elements for specifying the scattered wave, the simulated signal generation unit 24 obtains a sine wave scattered wave having the amplitude, waveform rising and falling, and having the calculated phase. The information on the scattered wave is stored in the second storage unit 25.

  Next, processing contents executed in each unit included in the above-described acoustic image simulation apparatus according to the present embodiment will be described with reference to FIG. Various processes described later realized by the respective units illustrated in FIG. 6 are realized by the CPU 11 reading out and executing the acoustic image simulation program stored in the auxiliary storage device 13 to the main storage device 12. is there.

  First, as a pre-stage for carrying out the simulation, an operation of inputting various data necessary for the simulation is performed. This input work is performed by, for example, an operator operating the input device 14 (see FIG. 1) of the acoustic image simulation device. Various types of data to be input are as described above.

When the simulation is executed, first, the bottom surface data is read from the first storage unit 21, and the bottom surface is formed in the simulation space based on the bottom surface data (step SA1). The sea bottom is composed of a plurality of area elements (see FIG. 3).
Next, there is a condition table in which sound sources and target area elements are associated with each other based on the track data of the underwater vehicle stored in the first storage unit 21, the attachment position of the side scan sonar, the emission angle of the acoustic beam, and the like. It is created (step SA2).
Subsequently, when the target area element is irradiated with an acoustic beam from the position of each sound source based on the created condition table, the scattered wave received at the position of the receiver (sound source) is estimated, and a simulated signal A simulation signal generation process is performed to generate (step SA3).

Hereinafter, the processing procedure of the simulation signal generation process performed in step SA3 will be described with reference to FIG.
First, referring to the condition table, the position of one sound source is set (step SB1), and the target area element associated with the position of this sound source is read (step SB2). Next, it is determined whether or not there are a plurality of read target area elements. If there are a plurality of target area elements, one of them is set, and if it is one, one is set (step SB3). ). In this way, when the position of the sound source and the target area element are set, estimation of the scattered wave is performed when the acoustic beam is irradiated to the target area element set from the set position of the sound source, A simulation signal is generated (step SB4). The procedure for estimating the scattered wave is as described above.

Subsequently, hidden surface processing is performed on the estimated scattered wave to adjust the amplitude and the like of the scattered wave (step SB5), and the adjusted scattered wave information is added to the position of the sound source and the position of the target area element. It is associated and stored in the second storage unit 25 (step SB6).
Subsequently, in the condition table, it is determined whether or not a simulation signal has been generated for all the target area elements associated with the position of the sound source set this time (step SB7), and all the processing must be completed. For example, in step SB3, an unprocessed target area element is newly set, thereby generating a simulation signal in the relationship between the position of the sound source and the newly set target area element.

  In this way, when the processing is completed for all target area elements associated with the set sound source positions (“YES” in step SB7), the processing is performed for all sound source positions set in the condition table. It is determined whether or not the processing has been completed (step SB8). As a result, when the process is not completed (“NO” in step SB8), the process returns to step SB1, the position of the unprocessed sound source is set, and the target area element associated with the position of the sound source is set. Simulated signals are sequentially generated. When simulation signals are generated at the positions of all the sound sources or the corresponding target area elements (“YES” in step SB8), this process is terminated.

  When the simulation signal generation process ends, the second storage unit 25 stores information on scattered waves obtained when the underwater vehicle moves based on the wake data stored in the first storage unit 21. Is stored as a simulation signal.

  Subsequently, an acoustic image is created by performing image processing using the scattered wave information stored in the second storage unit 25 (step SA4 in FIG. 6), and this acoustic image is displayed or printed. (Step SA5 in FIG. 6).

As described above, according to the acoustic image simulation apparatus, method, and program according to the present embodiment, it is assumed that the underwater vehicle moves along the wake data, and at this time, by the side scan sonar. Each of the acquired scattered waves is estimated to generate a simulation signal, and an acoustic image is created using the simulation signal. In this way, the simulation is performed in a form that faithfully simulates the actual seafloor topography survey, so that the simulation accuracy can be improved.
Then, it is possible to select the most appropriate control parameter by repeating the simulation while changing the control parameters of the side scan sonar and comparing the acoustic images obtained as a result of the simulation.
Further, by examining such simulation results, it is possible to quantitatively evaluate the performance of the side scan sonar.

  In the above embodiment, the case where the seafloor topography survey is performed by the side scan sonar has been described as an example. For example, when the side scan sonar is used for the purpose of detecting the target object existing on the seabed. There is. In such a case, it is important to discriminate between the target object and the seabed and how to accurately detect the target object.

  In this case, the worker inputs the sea bottom data as in the above-described embodiment, and also inputs the object data related to the target object to be placed on the sea bottom. For example, as the object data, set coordinates, size, shape, acoustic impedance, and the like of the target object are set.

  By doing in this way, in the formation process of the sea bottom, the sea bottom is formed in the simulation space, and the target object is formed at a predetermined position on the sea bottom. Thereafter, the same processing as described above is performed, so that an acoustic image in which the target object is finally arranged on the sea bottom is created.

  By performing such acoustic image simulation while changing the control parameters of the side scan sonar such as the incident angle, beam width, and frequency of the acoustic beam, it is possible to acquire acoustic images acquired under different control parameter conditions. Can do. Then, by comparing the obtained acoustic images, the acoustic image that most clearly and most accurately reflects the target object is specified, and the parameters when the acoustic images are obtained are used as the optimum parameters. It may be used for detecting the target object.

[Second Embodiment]
Next, an acoustic image simulation apparatus, method, and program according to the second embodiment of the present invention will be described.
In the first embodiment described above, the side scan sonar is targeted. In the present embodiment, a case where the multi-beam acoustic sounder is targeted will be described.
The multi-beam acoustic sounder is provided with a plurality of receivers that receive scattered waves, and differs from the above-described side scan sonar in that these receivers are arranged in an array.

Thus, when there are a plurality of receivers, one of them is set as a representative receiver, an acoustic beam is emitted from the position of the sound source, and the scattered wave is received by the representative receiver. Estimate scattered waves. At this time, the position of the representative receiver may be the same as the position of the sound source, or a different position may be set.
Then, when the scattered wave in the representative receiver is estimated, the phase of the estimated scattered wave is corrected based on the arrangement position of each receiver and the representative receiver, for example, the arrangement interval, etc. Estimate scattered waves in the machine.
In this way, the scattered waves at the representative receiver when the position of the sound source is moved are estimated, and further, the scattered waves at the other receivers are estimated using this estimation result. After the estimation of the scattered wave in the receiver is completed, an acoustic image is created by performing signal processing on the simulation signal obtained as the estimation result.

  As described above, when a multi-beam acoustic detector or the like in which a plurality of receivers are arranged in an array is targeted, any one of the receivers arranged in an array is representatively received. The simulated signal is generated in the representative receiver, and the simulated signal is generated by correcting the phase of the signal received by the representative receiver for the signal received by the other receiver. By doing in this way, compared with the case where the scattered wave in each receiver is each estimated, it becomes possible to reduce the processing burden significantly.

[Third Embodiment]
Next, an acoustic image simulation apparatus, method, and program according to the third embodiment of the present invention will be described.
In the first embodiment described above, four elements consisting of amplitude, phase, waveform rising edge, and waveform falling edge are calculated, and these elements are used as a sine wave (or cosine wave) having the phase. I was dealing with scattered waves. FIG. 8 shows an example of the scattered wave estimated in the first embodiment. On the other hand, in this embodiment, as shown in FIG. 9, a low frequency signal obtained by beat-down of the analog signal shown in FIG. 8 is estimated as a scattered wave.

In an actual acoustic image apparatus, a scattered wave, which is an analog signal, is converted into a low-frequency signal by quadrature modulation beat-down, and the low-frequency signal is sampled to generate an acoustic image by digital signal processing.
For example, as shown in FIG. 10, the original signal X (t) of frequency f is multiplied by cos (2πf _c t) and sin (2πf _c t), respectively, and then passed through a low-pass filter (LPF). By obtaining a difference frequency component between the original signal frequency f and the local frequency fc, and converting the cos component a (t) and sin component b (t) of the difference frequency signal into a digital signal by an analog / digital converter, Convert the original signal to a low frequency signal. Thus, by performing quadrature modulation beat-down, it is possible to sample the received signal at a low speed while retaining the phase information of the received signal, and the number of data points can be greatly reduced.

  In this way, when simulating an acoustic image, the simulated signal is not generated once at the original signal frequency of the sonar acoustic signal and then beat-down by quadrature modulation, but the simulated signal is generated as a low-frequency signal after the beatdown from the beginning. Thus, the processing load can be significantly reduced, and the simulation signal processing unit can be made the same as the processing content of the signal processor of the acoustic image apparatus.

  Specifically, the simulation signal generation unit 25 calculates the amplitude, the rise of the waveform, and the fall of the waveform by the same method as in the first embodiment described above, and matches the local frequency to the original signal frequency. The phase θ is obtained by the following equation (8).

  θ = arg [b (n) / a (n)] = 2π × (2R / λ) (8)

In the above equation (8), a (n) is the cos component of the difference frequency signal, b (n) is the cos component of the difference frequency signal, R is the distance from the position of the sound source to the target area element, and λ is the wavelength of the acoustic beam. It is.
The sampling frequency fs is preferably fs = c / (2 × Δr) where the distance direction resolution is Δr. Here, c is the speed of sound.

  In the above description, the local oscillation frequency is matched with the original signal frequency, but it is not always necessary to match. However, the sampling frequency can be roughened by matching.

  In the above embodiment, the beat-down low-frequency signal is directly calculated using four elements, but instead of this, the analog signal obtained in the above-described first embodiment is calculated. A low frequency signal may be obtained by performing beat-down processing on the scattered wave, and an acoustic image may be created using the low frequency signal.

1 is a block diagram illustrating an overall configuration of an acoustic image simulation apparatus according to a first embodiment of the present invention. It is the functional block diagram which expand | deployed and showed the function with which the acoustic image simulation apparatus which concerns on the 1st Embodiment of this invention is provided. It is a figure for demonstrating an example of the sea bottom formed in simulation space. It is a figure for demonstrating backscattering intensity | strength BS ((theta) _i ) per unit area. It is a figure for demonstrating the calculation method of the rising / falling of the waveform of a scattered wave. It is the flowchart explaining the effect | action of the acoustic image simulation apparatus which concerns on the 1st Embodiment of this invention. It is the flowchart which showed the process sequence of the scattered wave estimation process shown in FIG. It is the figure which showed an example of the scattered wave estimated in the 1st Embodiment of this invention. It is the figure which showed an example of the scattered wave estimated in the 3rd Embodiment of this invention. It is the figure which showed an example of the circuit structure which implement | achieves a beatdown process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Acoustic image simulation apparatus 21 1st memory | storage part 22 Sea bottom formation part 23 Condition preparation part 24 Simulation signal generation part 25 2nd memory | storage part 26 Signal processing part

Claims (9)

First storage means for storing a plurality of data necessary for the simulation;
Based on the data stored in the first storage means, a sea bottom forming means for forming a sea bottom composed of a plurality of area elements in the simulation space;
The sound source and reception position set in the simulation space based on the wake data, attitude data of the platform on which the acoustic image device stored in the first storage means is mounted, and the mounting position of the acoustic image device on the platform And a condition creating means for creating a condition table in which target area elements to be irradiated with an acoustic beam are associated with each other;
Based on the condition table, the sound source and the reception position are set in the simulation space, and when the acoustic beam is irradiated from the sound source to the target area element, the scattered wave received at the reception position is simulated. Simulated signal generation means for generating a signal;
Second storage means for storing the simulation signal generated by the simulation signal generation means;
Signal processing means for creating an acoustic image of the sea floor using the simulation signal stored in the second storage means,
The simulation signal generation unit sequentially estimates scattered waves at different positions by updating the sound source position and reception position set in the simulation space and the position of the target area element based on the condition table. .   The simulation signal generating means includes a distance between the sound source and the target area element, a distance between the target area element and the reception position, an orientation of the target area element with respect to the sound source, and a seafloor incident angle. The acoustic according to claim 1, wherein the scattered wave is simulated by obtaining parameters and calculating the amplitude, phase, waveform rise timing, and waveform fall timing of the simulated signal using these parameters. Image simulation device. The acoustic image simulation apparatus according to claim 1, wherein the sea bottom surface forming unit forms a sea bottom surface including a plurality of the area elements based on a water depth and an acoustic impedance.   The acoustic image simulation apparatus according to claim 1, wherein the simulation signal generation unit estimates a simulation signal represented by a sine wave or a cosine wave.   The acoustic image simulation apparatus according to any one of claims 1 to 3, wherein the simulation signal generation unit calculates a low-frequency signal obtained by further beat-downing the simulation signal represented by the sine wave or cosine wave as a simulation signal. .   The simulated signal generating means uses the simulated signal represented by the sine wave or the cosine wave to beat down the low frequency signal, the simulated signal amplitude, phase, waveform rising timing, and waveform falling timing. The acoustic image simulation apparatus according to any one of claims 1 to 3, wherein the acoustic image simulation apparatus is obtained directly using a computer. When there are a plurality of receivers that receive the simulated signal,
The simulation signal generating means generates a simulation signal by setting any one position of a plurality of receivers as the reception position, and sets the phase of the simulation signal to the arrangement position of each of the other receivers. The acoustic image simulation apparatus according to any one of claims 1 to 6, wherein a simulation signal received by each of the receivers is estimated by performing correction based on the correction. In the simulation space, a process of forming a sea bottom composed of a plurality of area elements,
In the simulation space, setting the position of the sound source that emits the acoustic beam, the position of the receiver that receives the scattered wave that is the reflected wave of the acoustic beam, and setting the target area element to irradiate the acoustic beam, When a target area element is irradiated with an acoustic beam from the position of the sound source, a scattered wave received at the position of the receiver is generated as a simulation signal, and at least one of the position of the sound source and the target area element The process of generating simulated signals for all area elements constituting the sea floor while changing
And a process of creating an acoustic image of the sea floor using the generated simulation signal. In the simulation space, a process of forming a sea bottom composed of a plurality of area elements;
In the simulation space, setting the position of the sound source that emits the acoustic beam, the position of the receiver that receives the scattered wave that is the reflected wave of the acoustic beam, and setting the target area element to irradiate the acoustic beam, When a target area element is irradiated with an acoustic beam from the position of the sound source, a scattered wave received at the position of the receiver is generated as a simulation signal, and at least one of the position of the sound source and the target area element Processing to generate simulated signals for all area elements constituting the sea floor,
An acoustic image simulation program for causing a computer to execute a process of creating an acoustic image of the sea floor using the generated simulation signal.

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