JP2023119610A - Waveform calculation system, waveform calculation method, and program for waveform calculation method - Google Patents

Abstract

To meet the demand for a waveform calculation system, a waveform calculation method, and a program for the waveform calculation method that calculate a received-wave waveform that is faithful to a change of relative distance due to the movement of a target and a sonar over time.SOLUTION: The waveform calculation system calculates a received-wave waveform that represents the sound pressure of the wave received by a sonar and the wave transmitted from a target. The waveform calculation system comprises: a control device that calculates a relative distance between the target and the sonar, for each wave transmission time at which a wave is transmitted from the target to the sonar, and calculates a received-wave waveform convoluting an impulse response that represents a sound wave propagation per wave transmission time into a transmitted-wave waveform from the target at the corresponding wave transmission time; and an impulse response calculation device that calculates an impulse response per wave transmission time on the basis of the calculated relative distance per wave transmission time.SELECTED DRAWING: Figure 2

Description

The present invention relates to a waveform calculation system, a waveform calculation method, and a waveform calculation method program for calculating a waveform, which is the sound pressure of sound waves received by a sonar.

Sonar is used to detect the presence of targets by receiving sound waves that propagate through the ocean. There are two types of sonar: passive sonar that receives sound waves emitted from targets in the ocean and detects the presence of targets; It is classified as an active sonar that detects. Conventionally, in order to evaluate the performance of such a sonar, simulating a received wave waveform, which is a time series of sound pressure received by the sonar, has been performed.

If the positional relationship between the target and the sonar is time-invariant, the acoustic wave propagation from the target to the sonar can be considered a linear time-invariant system. When simulating the waveform received by a passive sonar, the waveform received by the sonar is obtained by convolving the impulse response, which is the waveform received when an impulse is transmitted, with the transmitted waveform of the sound wave emitted from the target. be done. Impulse responses are obtained by inverse Fourier transforming frequency characteristics of sound pressure at relative distances calculated using various sound wave propagation models. At this time, for example, a normal mode model (see Non-Patent Document 1), a parabolic equation model (see Non-Patent Document 2), etc. are used as the sound wave propagation model.

When a computer such as an electronic calculator is used to simulate the received waveform, the discretized impulse response is calculated by the inverse discrete Fourier transform, and the discretized impulse response is obtained by convolving the calculation result with the discretized transmitted waveform. A converted received wave waveform is calculated.

On the other hand, in order to evaluate the sonar performance, it is necessary to simulate the received wave waveform in the state where the target and the sonar are moving together. At this time, since the impulse response changes as the relative distance between the target and the sonar changes, the acoustic wave propagation from the target to the sonar cannot be regarded as a time-invariant system.

Therefore, a method has been proposed in which the concept of a general time-varying filter is applied to the simulation of the received waveform, and the received waveform including changes in the impulse response due to changes in the relative distance between the target and the sonar is calculated by convolution. there is This calculation method calculates a received wave waveform, which is the instantaneous sound pressure at a given wave receiving time, by convolving an impulse response with respect to a relative distance into a transmitted wave waveform.

F. B. Jensen et al., “5 Normal Modes,” in Computational Ocean Acoustics (Second Edition), 2011 F. B. Jensen et al., “6 Parabolic Equations,” in Computational Ocean Acoustics (Second Edition), 2011

However, in the above calculation method, one impulse response is convoluted with respect to the relative distance at a certain reception time. Therefore, there is a problem that the phenomenon that sounds transmitted at different times propagate over different relative distances and are simultaneously received by the sonar cannot be represented. Therefore, there is a demand for a waveform calculation system, a waveform calculation method, and a waveform calculation method program for calculating a received wave waveform faithful to changes in relative distance due to movement of the target and sonar over time.

A waveform calculation system according to the present invention is a waveform calculation system for calculating a received wave waveform, which is sound pressure received by a sonar and transmitted from a target, wherein waves are transmitted from the target to the sonar. For each wave transmission time, the relative distance between the target and the sonar is calculated, and an impulse response representing sound wave propagation at each wave transmission time is converted into a wave transmission waveform from the target at the corresponding wave transmission time. and an impulse response calculation device for calculating the impulse response for each transmission time based on the calculated relative distance for each transmission time. be.

Further, a waveform calculation method according to the present invention is a waveform calculation method for calculating a received wave waveform, which is sound pressure received by a sonar and transmitted from a target, wherein the waveform is transmitted from the target to the sonar. calculating the relative distance between the target and the sonar for each wave transmission time, and calculating an impulse response for each wave transmission time based on the calculated relative distance for each wave transmission time; A received wave waveform is calculated by convolving the impulse response at each wave transmission time with the wave transmission waveform from the target at the corresponding wave transmission time.

Further, a waveform calculation method program according to the present invention is a waveform calculation method program for calculating a received wave waveform, which is sound pressure received by a sonar and transmitted from a target, wherein calculating the relative distance between the target and the sonar at each transmission time of transmitting waves to the target, and based on the calculated relative distance at each transmission time, an impulse response at each transmission time is calculated, and the impulse response for each wave transmission time is convoluted with the wave transmission waveform from the target at the corresponding wave transmission time to calculate the received wave waveform.

As described above, according to the present invention, the received waveform is calculated by convolving the impulse response at each transmission time with the transmission waveform at the corresponding transmission time. An impulse response is calculated according to the time change of the distance. As a result, it is possible to calculate a received wave waveform faithful to changes in relative distance due to movement of the target and sonar over time.

FIG. 4 is a schematic diagram for explaining creation of a sequence to be convolved with a transmission waveform; 1 is a block diagram showing an example of the configuration of a waveform calculation system according to Embodiment 1; FIG. 3 is a hardware configuration diagram showing an example of the configuration of the waveform calculation system of FIG. 2; FIG. 3 is a hardware configuration diagram showing another example of the configuration of the waveform calculation system of FIG. 2; FIG. 4 is a flowchart showing an example of the flow of waveform calculation processing by the waveform calculation system according to Embodiment 1; FIG. 10 is a block diagram showing an example of the configuration of a waveform calculation system according to Embodiment 2; FIG. 9 is a flowchart showing an example of the flow of waveform calculation processing by the waveform calculation system according to Embodiment 2; FIG. 11 is a block diagram showing an example of the configuration of a waveform calculation system according to Embodiment 3; FIG. 10 is a flow chart showing an example of the flow of waveform calculation processing by the waveform calculation system according to Embodiment 3; FIG. 11 is a block diagram showing an example of the configuration of a waveform calculation system according to Embodiment 4; FIG. 14 is a flow chart showing an example of the flow of waveform calculation processing by the waveform calculation system according to Embodiment 4;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present invention. In addition, the present invention includes all possible combinations of the configurations shown in the following embodiments. Also, in each figure, the same reference numerals denote the same or corresponding parts, which are common throughout the specification.

Embodiment 1.
A waveform calculation system according to the first embodiment will be described. The waveform calculation system according to the first embodiment simulates the waveform of the sound pressure received by a sonar from a target.

[Conventional calculation of received waveform]
First, before explaining the waveform calculation system according to the first embodiment, a conventional method for calculating a received wave waveform will be explained.

First, as explained in the background section, if the positional relationship between the target and the sonar does not change over time, the acoustic wave propagation from the target to the sonar can be considered a linear time-invariant system. Assuming a passive sonar as the sonar and simulating the received wave waveform of the sonar, the received wave waveform x(t) at time t can be expressed by Equation (1). That is, the received waveform x(t) is the convolution of the impulse response h(t, r), which is the received waveform when the impulse is transmitted, and the transmitted wave waveform s(t) of the sound wave emitted from the target. obtained by In equation (1), "r" denotes the relative distance between the target and sonar.

The impulse response h(t, r) is the frequency characteristic p(f, r) of the sound pressure at the relative distance r calculated using a sound wave propagation model such as a normal mode program, as shown by equation (2). It is obtained by inverse Fourier transform. In equation (2), "f" indicates the frequency of the sound wave.

In the simulation of the received wave waveform using a computer such as an electronic computer, the discretized impulse response h(t _k, r) (k = 0, 1, 2, ..., K-1) is expressed by the formula It is calculated by inverse discrete Fourier transform as shown in (3). In equation (3), "K" indicates the number of time samples of the impulse response, and "N" indicates the number of time samples of the transmitted and received waveforms. “t _k ” indicates the sampling time of the impulse response h(t _k , r), and “f _n ” indicates the sampling frequency of the sound pressure frequency characteristic p(f _n , r).

Then, the calculated discretized impulse response h(t _k, r) and the discretized transmitted waveform s(τ _μ ) (μ=0, 1, 2, . . . , N-1) By convolution, the discretized received waveform x(t _m ) (m=0, 1, 2, . . . , N−1) is calculated as shown in Equation (4). In Equation (4), “t _m ” indicates the received wave time, which is the sample time of the received wave waveform x(t _m ). Also, "μ" indicates the index of the transmission time, and "τ _μ " indicates the transmission time, which is the sampling time of the transmission waveform s (τ _μ ).

In equations (3) and (4), when the sampling interval at the predetermined time is "Δt", the sample time _tk of the impulse response h( _tk , r) is expressed as " _tk = kΔt". be able to. Further, the wave receiving time t _m is "t _m = mΔt", the wave transmitting time τ _μ is "τ _μ = μΔt", and the sample frequency f _n of the frequency characteristic p(f _n , r) is "f _n = n/( KΔt)”, respectively.

Here, the sample time t _k of the impulse response h(t _k ,r) is defined as having a value of 0 or greater. This is because the impulse response h(t _k , r) obtained from Equation (3) represents the frequency characteristics of sound wave propagation from the target to the sonar and is a filter representing the delay corresponding to the time required for propagation. is. Furthermore, as long as the target and the sonar exist at different positions, the time required for sound wave propagation is always greater than zero.

Here, the lower limit value μ ^(L) and the upper limit value μ ^(U) of the addition range on the right side of equation (4) will be described. When a sound wave propagates from a target to a sonar, there exist a plurality of paths other than the direct wave, such as paths reflected on the surface of the sea and the bottom of the sea. Since the propagation time in this case differs for each path, the sonar receives impulse responses at a plurality of times corresponding to each path. Therefore, the number of time samples K of the impulse response should be such that the maximum value "(K-1)Δt" of the sample time sufficiently includes the delay caused by receiving waves through a plurality of paths.

On the other hand, the number of time samples N of the transmitted waveform s(τ _μ ) and the received waveform x(t _m ) must be as large as the time desired by the user. There is usually a relationship of "K<N" between the number K of time samples of the impulse response and the number N of time samples of the transmitted waveform. In addition, as described above, the impulse response only has values in the range where the sample time _tk satisfies ' _tk ≧0'.

Therefore, when the impulse response h(t, r) is considered in the range of "-∞<t<∞", the _time t , the impulse response h(t,r) is set to "h(t,r)=0". This means that “t _m −τ _μ <0 (that is, m−μ<0)” or “t _m −τ _μ >t _K−1 (that is, m−μ>K−1) in equation (4) ] is realized by not performing the addition on the right side for m and μ.

From the above, the lower limit μ ^(L) of the range of addition on the right side of equation (4) is “μ ^(L) = max (0, m−K+1)”, and the upper limit μ ^(U) is “μ ^(U) = min(m, N-1)”. Here, the function "max(X, Y)" is a function that outputs the value of the larger of the two variables X and Y. Also, the function "min(X, Y)" is a function that outputs the value of the smaller of the two variables.

By the way, in order to evaluate the performance of a sonar, it is necessary to simulate a received wave waveform in a state in which both the target and the sonar are moving. At this time, since the impulse response h(t _k , r) changes as the relative distance r changes from moment to moment, the acoustic wave propagation from the target to the sonar cannot be regarded as a time-invariant system.

In such a case, the concept of a general time-varying filter is applied to simulate the received waveform. That is, the received wave waveform is calculated based on Equation (5). In Equation (5), "r _tm " is the relative distance corresponding to the received wave time t _m . As a result, a different impulse response h( _tk , _rtm ) is convoluted for each wave reception time _tm , and a received wave waveform including a change in impulse response due to a change in relative distance is calculated.

In this way, Equation (5) gives the transmitted waveform s(τ _μ ) (μ=μ ^(L) , _μ ^{(L) +1} , . It is a formula for calculating the received wave waveform x(tm) _, which is the instantaneous sound pressure at the received wave time _tm , by convolving the impulse response h( _tk , _rtm ) with respect to the relative distance _rtm .

Here, considering the sound wave propagation from the target to the sonar, the relative distance that the transmitted wave waveform s(τ _μ ), which is the instantaneous sound pressure transmitted from the target at each transmission time τ _μ , propagates to the sonar varies depending on the transmission time index μ. This is because the target and sonar are moving as the wave transmission time elapses.

On the other hand, the calculation formula (5) convolves one impulse response with respect to the relative distance _rtm at a given wave reception time _tm . Therefore, the phenomenon that sounds transmitted at different times propagate over different relative distances and are simultaneously received by the sonar cannot be expressed.

Therefore, in the waveform calculation system according to the first embodiment, a received wave waveform is calculated that is faithful to changes in relative distance due to movement of the target and sonar over time.

[Principle of Waveform Calculation Method]
Next, the principle of the waveform calculation method according to the first embodiment will be explained. As described above, the formula (5) is used to calculate the received wave waveform x(t _m ) of the instantaneous sound pressure received at a given wave receiving time t _m . The impulse response is convolved with the transmitted waveform s(τ _μ ) for _μ .

In contrast, considering sound wave propagation from the target to the sonar, the impulse response convoluted with the transmitted waveform s(τ _μ ) should represent the change in the relative distance between the target and the sonar. . Therefore, in the first embodiment, of the two variables of the impulse response in the formula (5), the variable r _tm is replaced with the variable r _τμ as shown in formula (6). In Equation (6), "r _τμ " indicates the relative distance corresponding to the transmission time τ _μ .

When calculating the instantaneous sound pressure x(t _m ) at a given wave reception time t _m , Equation (6) is used to calculate “μ ^(U) −μ ^(L) +1” _impulse responses h A sequence created by extracting one coefficient h(t _m −τ _μ , r _τμ ) from (t _k , r τ _μ ) is convoluted with the transmitted wave waveform s(τ _μ ).

FIG. 1 is a schematic diagram for explaining the generation of a sequence to be convolved with a transmission waveform. In FIG. 1, circles arranged in the horizontal direction indicate sequences of impulse responses corresponding to "μ=μ ^(L) , μ ^(L) +1, . . . , μ ^(U) ". A sequence to be convolved with the transmitted waveform s(τ _μ ) is created by taking out the values of the black circles one by one from these “μ ^(U) −μ ^(L) +1” impulse responses. By doing so, it is possible to express the phenomenon that sounds transmitted from the target at different times propagate over different relative distances and are simultaneously received by the sonar.

Here, when performing the convolution shown in Equation (6), while changing the wave reception time t _m to "m = 0, 1, ..., N-1", the sum of the right side at each m is calculate. In this case, “μ ( ^{U )} −μ ^{( L )} +1” impulse responses h(t _k , r _τμ ) must be retained.

Next, while changing μ to “μ=1, 2, . In Equation (7), “ξ _μ (t _m )” is the instantaneous sound pressure s(τ _μ ) transmitted at the transmission time τ _μ propagates by the relative distance r _τμ and is received by the sonar. wave waveform. In the following description, this received waveform will be referred to as an "instantaneous received waveform". Then, using the obtained instantaneous received waveform ξ _μ (t _m ), it is stored in the memory area of the received waveform x(t _m ) initialized to 0 in advance as shown in Equation (8).

Here, the range of m in equation (7) is “μ≦m≦min (μ+K−1, N−1)” because the impulse response h(t, r _τμ ) is “t ₀ =0≦t This is because it has a value only at the time t that satisfies ≦t _K−1 , and is considered to have a value of “0” at other times. According to equations (7) and (8), the impulse response h( _tk , _rτμ ) held when calculating the received waveform x( _tm ) is one series for each index μ. good.

[Configuration of Waveform Calculation System 100]
FIG. 2 is a block diagram showing an example of the configuration of the waveform calculation system according to the first embodiment. As shown in FIG. 2 , the waveform calculation system 100 includes a control device 10 , an impulse response calculation device 20 and an instantaneous received wave waveform calculation device 30 . Such a waveform calculation system 100 is composed of an arithmetic unit such as a microcomputer that implements various functions by executing software, or hardware such as a circuit device that supports various functions.

The control device 10 receives the ocean environment conditions, the scenario, and the instantaneous sound pressure s(τ _μ ) of the transmitted wave waveform at the transmitted wave time τ _μ . The control device 10 exchanges various data with the impulse response calculation device 20 and the instantaneous received wave waveform calculation device 30, and calculates the received wave waveform x(t _m ). A specific operation of the control device 10 will be described later.

Marine environmental conditions are information indicating the sound velocity profile and water depth in the ocean. Also, the sound speed profile is a depth characteristic of sound speed represented by a plurality of sets of depths and sound speeds (z _l , c _l ). A scenario is information indicating the positions of the target and the sonar at each time.

The impulse response calculation device 20 receives the marine environment condition and the relative distance r _τμ from the control device 10 . The impulse response calculator 20 calculates an impulse response h(t _k , r _τμ ) based on the input marine environment condition and relative distance r _τμ . The impulse response calculation device 20 then outputs the calculated impulse response h(t _k , r _τμ ) to the control device 10 .

The instantaneous received wave waveform calculator 30 receives the impulse response h(t _k , r _τμ ) and the instantaneous sound pressure s(τ _μ ) of the transmitted waveform from the control device 10 . The instantaneous received wave waveform calculator 30 _calculates an instantaneous received wave waveform ξ μ (t _{m ) based on the input impulse response h(t k , r τ μ ) and the instantaneous sound pressure s(τ μ ) of} the transmitted waveform. do. Then, the instantaneous received wave waveform calculation device 30 outputs the calculated instantaneous received wave waveform ξ _μ (t _m ) to the control device 10 .

FIG. 3 is a hardware configuration diagram showing an example of the configuration of the waveform calculation system of FIG. When various functions performed by each device of the waveform calculation system 100 are performed by hardware, the waveform calculation system 100 of FIG. 2 is configured with a processing circuit 21 as shown in FIG. In waveform calculation system 100 of FIG. 2 , each function executed by control device 10 , impulse response calculation device 20 , and instantaneous received waveform calculation device 30 is realized by processing circuit 21 .

When each function is performed by hardware, the processing circuit 21 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination of these. The waveform calculation system 100 may realize the function of each part of the control device 10, the impulse response calculation device 20, and the instantaneous received waveform calculation device 30 by the processing circuit 21, or the functions of each part may be realized by one processing circuit 21. may be realized.

FIG. 4 is a hardware configuration diagram showing another example of the configuration of the waveform calculation system of FIG. When various functions performed by each device of the waveform calculation system 100 are performed by software, the waveform calculation system 100 of FIG. 2 is configured with a processor 22 and a memory 23 as shown in FIG. In waveform calculation system 100 , each function of control device 10 , impulse response calculation device 20 , and instantaneous received waveform calculation device 30 is implemented by processor 22 and memory 23 .

When each function is executed by software, in the waveform calculation system 100, the functions of the control device 10, the impulse response calculation device 20, and the instantaneous received waveform calculation device 30 are realized by software, firmware, or a combination of software and firmware. be done. Software and firmware are written as programs and stored in the memory 23 . The processor 22 realizes the function of each part by reading and executing the program stored in the memory 23 .

Examples of the memory 23 include nonvolatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable and Programmable ROM) and EEPROM (Electrically Erasable and Programmable ROM). is used. As the memory 23, for example, a removable recording medium such as a magnetic disk, a flexible disk, an optical disk, a CD (Compact Disc), an MD (Mini Disc), and a DVD (Digital Versatile Disc) may be used.

Thus, the waveform calculation system 100 can realize each function described above by hardware, software, firmware, or a combination thereof.

[Operation of Waveform Calculation System 100]
FIG. 5 is a flowchart showing an example of the flow of waveform calculation processing by the waveform calculation system according to the first embodiment. First, in step S1, the control device 10 initializes all the values of the received waveform x(t _m ) to zero.

In step S2, the control device 10 calculates the relative distance r _τμ corresponding to the time _τμ based on the input scenario. Here, the control device 10 calculates the relative distance r _τμ based on Equation (9). In Equation (9), P _μ ^(T) denotes a vector representing the horizontal position of the target corresponding to time τ _μ . P _μ ^(S) denotes a vector representing the horizontal position of the sonar corresponding to time τ _μ . At this time, the horizontal position P _μ ^(S) of the sonar may be the position at time τ _μ or the position at which the sound wave transmitted at time τ _μ is received.

Next, the control device 10 outputs the input marine environment conditions and the calculated relative distance r _τμ to the impulse response calculation device 20 . In step S3, the impulse response calculator 20 calculates an impulse response h( _tk , _rτμ ) based _on the marine environment condition and the relative distance rτμ input from the control device 10. FIG.

Specifically, the impulse response calculation device 20 uses the inputted marine environment conditions and calculates the frequency characteristic p(f _n , r _τμ ) of the sound pressure with respect to the relative distance r _τμ by the sound wave propagation model. Then, the impulse response calculator 20 calculates the impulse response h(t _k , r _τμ ) based on Equation (3). The impulse response calculation device 20 outputs the calculated impulse response h(t _k , r _τμ ) to the control device 10 .

When the control device 10 receives the impulse response h(t _k , r _τμ ), the instantaneous sound pressure s(τ _μ ) of the inputted transmitted waveform and the impulse response h(t _k , r _τμ ) to the instantaneous received waveform calculator 30 .

In step S4, the instantaneous received wave waveform calculator 30 calculates the instantaneous received wave waveform based on the instantaneous sound pressure s(τ _μ ) and the impulse response h(t _k , r _τμ ) of the transmitted waveform input from the control device 10. Calculate ξ _μ (t _m ). Specifically, the instantaneous received wave waveform calculating device 30 calculates an instantaneous sound pressure s(τ _μ ) of the input transmitted wave waveform and the impulse response h(t _k , r _τμ ) based on the equation (7). Received waveform ξμ(t _m ) is calculated. The instantaneous received wave waveform calculator 30 outputs the calculated instantaneous received wave waveform ξ _μ (t _m ) to the control device 10 .

In step S5, the control device 10 adds the instantaneous received wave waveform ξ _μ (t _m ) received from the instantaneous received wave waveform calculating device 30 to the storage area of the received wave waveform x(t _m ). That is, as shown in equation (10), the control device 10 adds the instantaneous received waveform ξ _μ (t _m ) to the received wave waveform x(t _m ) as the received wave waveform x(t _m ). , the storage area of the received waveform x(t _m ) is updated.

In step S6, the control device 10 determines whether or not the processes of steps S2 to S5 have been performed for all transmission time indexes μ. If the index μ of all transmission times has not been processed (step S6: No), the control device 10 increments the index μ, and the process returns to step S2. Then, the processing of steps S2 to S5 is performed for all transmission time indexes μ.

On the other hand, if the processing has been performed for the index μ of all wave transmission times (step S6: Yes), that is, if the processing of steps S2 to S5 has been performed for each time of the wave transmission time τ _μ ends a series of processes.

In this way, the addition shown in equation (10) is performed for each of the transmission time indices μ, ie, μ=0, 1, . . . , N−1. As a result, the instantaneous received wave waveform ξ _μ (t _m ) for each index μ is accumulated in the received wave waveform x(t _m ) storage area, and the calculation shown in Equation (8) is realized.

Note that the instantaneous received wave waveform ξ _μ (t _m ) in this case is a series of size N calculated by the equation (7), but the range of m in which a value other than 0 is obtained in the equation (7) is " μ≦m≦min(μ+K−1, N−1)”, and the range added by equation (10) thereafter is the same.
Therefore, the size of the storage area for the instantaneous received waveform ξ _μ (t _m ) is set to K, which is the same as the length of the impulse response, and the range of addition in Equation (10) is set to “μ≦m≦min (μ+K−1, N -1)”.

In this way, by performing the processing _shown in FIG. ). Then, the received waveform x(t _m ) is calculated by realizing the convolution shown in Equation (6).

As described above, the waveform calculation system 100 according to the first embodiment calculates the received waveform by convolving the impulse response at each transmission time with the transmission waveform at the corresponding transmission time. Thereby, an impulse response is calculated according to the time change of the relative distance between the sonar and the target. Therefore, it is possible to calculate a received wave waveform faithful to changes in relative distance due to movement of the target and sonar over time.

In addition, the waveform calculation system 100 calculates the received wave waveform according to the equations (7) and (10), and converts the convoluted impulse response to the change in the relative distance at the wave transmission time in the convolution with respect to a certain wave reception time. It can be made compatible. Therefore, it is possible to represent a phenomenon in which sounds transmitted from the target at different times propagate at different relative distances and are received by the sonar at the same time.

Embodiment 2.
Next, Embodiment 2 will be described. The second embodiment differs from the first embodiment in that the impulse response is calculated only when the change in the delay due to the change in the relative distance between the target and the sonar is large. It should be noted that, in the second embodiment, the same reference numerals are assigned to the parts that are common to the first embodiment, and detailed description thereof will be omitted.

In Embodiment 1 described above, the impulse response h(t _k , r _τμ ) is calculated for each index μ of the transmission time τ _μ . Here, when the moving speed of each of the target and the sonar is small and the change in relative distance r _τμ is small, it can be considered that the change in impulse response h(t _k , r _τμ ) is also small. Therefore, in such a case, it is not necessary to calculate impulse responses h(t _k , r _τμ ) for all indices μ.

Therefore, in the second embodiment, the delay due to the change in the relative distance, that is, the change in the propagation time from the target to the sonar is estimated, and the impulse response h(t _k , r _τμ ) is calculated only when the change in delay is large. calculate. Then, the calculated impulse response h(t _k , r _τμ ) is stored as the stored impulse response h ⁽⁰⁾ (t _k ), and when the delay change is small, the stored stored impulse response h ⁽⁰⁾ (t _k ) as the impulse response h(t _k ,r _τμ ).

A delay change amount ΔT, which indicates a change in delay with respect to a certain index μ, is calculated based on equation (11). In Equation (11), "r _τμ " indicates the relative distance at the transmission time τ _μ . Also, "r ⁽⁰⁾ " indicates the relative distance at the wave transmission time at which the impulse response was calculated after it was determined that the change in the impulse response was large before the wave transmission time τ _μ . In the following description, “r ⁽⁰⁾ ” will be referred to as a “reference relative distance”.

In equation (11), the numerator "|r _τμ −r ⁽⁰⁾ |" on the right side represents the magnitude of change in relative distance over time, and this magnitude of change in relative distance is divided by group velocity g. is defined as the amount of delay variation ΔT. Here, the group velocity indicates the horizontal component of the speed of sound. For example, the group velocity of a path propagating at an angle θ in a medium having a constant sound speed c is expressed as c cos θ. The group velocity increases as the path propagates at an angle closer to the horizontal where θ=0, and its value approaches the speed of sound.

In the second embodiment, when the delay change amount ΔT is larger than the preset allowable amount, the impulse response h(t _k , r _τμ ) is calculated again at the transmission time τ _μ . On the other hand, when the delay change amount ΔT is smaller than the allowable amount, the stored impulse response h ⁽⁰⁾ (t _k ), which was previously calculated and held, is changed to the transmission time τ _μ instead of the impulse response h(t _k , r _τμ ) at . By doing so, it is not necessary to calculate impulse responses for all indices μ, so the amount of calculation can be reduced.

Note that the impulse response includes delays corresponding to a plurality of paths, and delay variations exist for each of the plurality of paths. Here, by using the sound velocity c as the group velocity g, the delay change amount ΔT of the path that propagates at an angle close to the horizontal, which has a large influence on the received waveform, among the plurality of paths is estimated.

[Configuration of Waveform Calculation System 200]
FIG. 6 is a block diagram showing an example of the configuration of the waveform calculation system according to the second embodiment. As shown in FIG. 6, the waveform calculation system 200 includes a control device 11, an impulse response calculation device 20, an instantaneous received waveform calculation device 30, and a delay variation calculation device 40. FIG. Such a waveform calculation system 200 is composed of an arithmetic unit such as a microcomputer that implements various functions by executing software, or hardware such as a circuit device that supports various functions.

The control device 11 receives the ocean environment conditions, the scenario, and the instantaneous sound pressure s(τ _μ ) of the transmitted wave waveform at the transmitted wave time τ _μ . The control device 11 exchanges various data with the impulse response calculator 20, the instantaneous received wave waveform calculator 30, and the delay variation calculator 40, and calculates the received wave waveform x(t _m ). A specific operation of the control device 11 will be described later.

The delay variation calculator 40 receives the reference relative distance r ⁽⁰⁾ , the group velocity g, and the relative distance r _τμ from the controller 11 . The delay change amount calculator 40 calculates the delay change amount ΔT based on the input reference relative distance r ⁽⁰⁾ , group velocity g and relative distance r _τμ . Then, the delay change amount calculation device 40 outputs the calculated delay change amount ΔT to the control device 11 .

[Operation of Waveform Calculation System 200]
FIG. 7 is a flow chart showing an example of the flow of waveform calculation processing by the waveform calculation system according to the second embodiment. It should be noted that the same reference numerals are assigned to processes that are common to the processes in the first embodiment, and detailed description thereof will be omitted.

After executing the process of step S1, the control device 11 initializes the reference relative distance r ⁽⁰⁾ to "r ⁽⁰⁾ =∞" and sets the group velocity g to "g=c" in step S11. initialize. When the process of step S11 is executed by software, a constant meaning "∞ (infinity)" is generally defined in the programming language. Therefore, the control device 11 may use a predefined constant when initializing the reference relative distance r ⁽⁰⁾ . Sound speed c is, for example, an average of sound speed values of sound speed profiles (z _l , c _l ) (l = 0, 1, 2, ..., L-1) represented by a plurality of pairs of depths and sound speeds Alternatively, it may be the maximum or minimum value of sound velocity values. For the speed of sound c, a general value of speed of sound such as “c=1500 m/s” may be used.

The initialized reference relative distance r ⁽⁰⁾ and group velocity g are used when calculating the delay change amount ΔT in step S12, which will be described later. At this time, the value of the calculated delay change amount ΔT varies depending on the value set for the speed of sound c, but the speed of sound in the ocean takes a value between approximately 1450 m/s and 1550 m/s. Therefore, the change in the delay change amount ΔT due to the set sound velocity c is at most about 10% of that value, which is sufficient for the calculation accuracy of the delay change amount ΔT.

After the process of step S2, the control device 11 outputs the reference relative distance r ⁽⁰⁾ , the group velocity g, and the relative distance r _τμ calculated in step S2 to the delay change amount calculation device 40 . In step S12, the delay change amount calculator 40 calculates the delay change amount ΔT based on the input reference relative distance r ⁽⁰⁾ , group velocity g, and relative distance r _τμ . Then, the delay change amount calculation device 40 outputs the calculated delay change amount ΔT to the control device 11 .

In step S13, the control device 11 determines whether or not the input delay change amount ΔT is large. Specifically, the control device 11 determines the magnitude of the delay change amount ΔT using equation (12) based on a preset constant α.

If the delay change amount ΔT satisfies the equation (12), that is, if the delay change amount ΔT is equal to or greater than the constant α (step S13: Yes), the control device 11 determines that the change in impulse response is large. Then, the process proceeds to step S3, and the control device 11 calculates the impulse response h( _tk , _rτμ ).

On the other hand, if the delay change amount ΔT does not satisfy the equation (12), that is, if the delay change amount ΔT is less than the constant α (step S13: No), the control device 11 determines that the change in the impulse response is small. . Then, the process moves to step S4. At this time, the controller 11 uses the stored impulse response h ⁽⁰⁾ (t _k ) already stored as the impulse response h(t _k , r _τμ ).

Thus, the constant α represents the allowable value of the delay change amount ΔT, and has the function of adjusting the trade-off between the amount of calculation when calculating the impulse response and the accuracy of the calculated received waveform. As the constant α increases, the chances of satisfying equation (12) decrease, so the number of impulse response calculations decreases and the amount of calculation _decreases . decreases. On the other hand, the smaller the constant α, the more the amount of calculation increases, but the lowering of the accuracy of the received wave waveform x(t _m ) with respect to changes in the impulse response can be suppressed.

Here, for example, using the time sampling interval Δt, when the constant α is set so that “α=Δt”, the delay change amount ΔT is the sampling interval Δt of the impulse response h(t _k , r _τμ ) If it is smaller, we will decide that the change in impulse response is negligible. Further, for example, when "α=1/f _max " is set for the upper limit f _max of the frequency band of the transmitted waveform, if the delay change amount ΔT is smaller than the time length of one period of oscillation of the transmitted waveform, the impulse You will decide that the change in response is negligible.

After the process of step S3, in step S14, the control device 11 converts the impulse response h(t _k , r _τμ ) calculated by the impulse response calculation device 20 in step S3 into the stored impulse response h ⁽⁰⁾ (t _k ). Next, in step S15, the control device 11 updates the reference relative distance r ⁽⁰⁾ by "r ⁽⁰⁾ =r _τμ ".

Thereafter, steps S4 to S6 are executed in the same manner as in the first embodiment. Note that at the first time (μ=0), the delay change amount ΔT output from the delay change amount calculation device 40 is calculated by Equation (11), but the reference relative distance r ⁽⁰⁾ is " ∞”, the delay change amount ΔT is also ∞, and the condition of equation (12) is always satisfied. Therefore, the impulse response h(t _k , r _τμ ) for "μ=0" is always calculated, and the result of this calculation is set as the stored impulse response h ⁽⁰⁾ (t _k ).

As described above, the waveform calculation system 200 according to the second embodiment calculates the magnitude of the change in delay using equation (11), and determines that the delay change amount ΔT is large, that is, the change in impulse response is large. Compute the impulse response h(t _k , r _τμ ) only when As a result, the number of impulse response calculations can be reduced, and the amount of calculation can be reduced.

Embodiment 3.
Next, the third embodiment will be described. The third embodiment differs from the first embodiment in that the impulse response is calculated only when the change in the delay due to the change in the relative distance between the target and the sonar is large. It differs from the second embodiment. In the third embodiment, parts common to those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the second embodiment, a value calculated from the sound speed profile is used as the group velocity g used when calculating the delay change amount ΔT. This is based on the assumption that among the multiple paths of sound wave propagation from the target to the sonar, the path that has the greatest influence on the received waveform is the path that propagates at an angle close to horizontal.

However, the path that has the greatest influence on the received waveform is not necessarily the path that propagates in a nearly horizontal angle. Therefore, in the third embodiment, based on the delay appearing in the calculated impulse response h(t _k , r _τμ ), the estimated group velocity g ⁽⁰⁾ estimated from the result of simulating propagation in water is used to determine the amount of delay change ΔT Calculate

Among the plurality of paths of sound wave propagation from the target to the sonar, one of the paths having the greatest influence on the received waveform is the path corresponding to the time when the amplitude of the impulse response becomes maximum. In the third embodiment, the group velocity is estimated based on the time when the amplitude of the impulse response is maximum, and the estimated group velocity g ⁽⁰⁾ is obtained.

[Configuration of Waveform Calculation System 300]
FIG. 8 is a block diagram showing an example of the configuration of a waveform calculation system according to the third embodiment. As shown in FIG. 8, the waveform calculation system 300 includes a control device 12, an impulse response calculation device 20, an instantaneous received waveform calculation device 30, and a delay variation calculation device 40. FIG. Such a waveform calculation system 300 is composed of an arithmetic unit such as a microcomputer that implements various functions by executing software, or hardware such as a circuit device that supports various functions.

The control device 12 receives the marine environmental conditions, the scenario, and the instantaneous sound pressure s(τ _μ ) of the transmitted wave waveform at the transmitted wave time τ _μ . The control device 12 exchanges various data with the impulse response calculation device 20, the instantaneous received wave waveform calculation device 30, and the delay variation calculation device 40, and calculates the received wave waveform x(t _m ). A specific operation of the control device 12 will be described later.

In the third embodiment, the delay variation calculation device 40 receives the reference relative distance r ⁽⁰⁾ , the estimated group velocity g ⁽⁰⁾ and the relative distance r _τμ from the control device 12 . The delay change amount calculation device 40 calculates the delay change amount ΔT based on the input reference relative distance r ⁽⁰⁾ , estimated group velocity g ⁽⁰⁾ and relative distance r _τμ and controls the calculated delay change amount ΔT. Output to device 12 .

[Operation of Waveform Calculation System 300]
FIG. 9 is a flowchart showing an example of the flow of waveform calculation processing by the waveform calculation system according to the third embodiment. It should be noted that the same reference numerals are assigned to processes that are common to the processes in Embodiments 1 and 2, and detailed description thereof will be omitted.

After executing the process of step S1, the control device 12 initializes the reference relative distance r ⁽⁰⁾ to "r ⁽⁰⁾ =∞" and executes the estimated group velocity g ⁽⁰⁾ in step S21. It is initialized with "g ⁽⁰⁾ =c" in the same way as the group velocity g in form 2 of .

After the process of step S2, the control device 12 outputs the reference relative distance r ⁽⁰⁾ , the estimated group velocity g ⁽⁰⁾ and the relative distance r _τμ calculated in step S2 to the delay variation calculation device 40. do. In step S22, the delay change amount calculator 40 calculates the delay change amount ΔT based on the input reference relative distance r ⁽⁰⁾ , estimated group velocity g ⁽⁰⁾ and relative distance r _τμ . Then, the delay change amount calculation device 40 outputs the calculated delay change amount ΔT to the control device 12 .

In the third embodiment, after the reference relative distance r ⁽⁰⁾ is updated in step S15, the control device 12 updates the estimated group velocity g ⁽⁰⁾ in step S23. Specifically, first, the control device 12 extracts an index k that maximizes "|h( _tk , _rτμ )|" from the calculated impulse response h( _tk , _rτμ ). The index k extracted at this time is assumed to be "k^".

The index k^ can be extracted by sequentially checking the magnitude of "|h(t _k ,r _τμ )|" from "k=0" to "k=K−1". Moreover, since many programming languages have a standard function for extracting the index number with the maximum value in the array, this function may be used to extract the index k^.

Once the index k^ is extracted, controller 12 updates the estimated group velocity g ⁽⁰⁾ based on equation (13). The estimated group velocity g ⁽⁰⁾ updated by equation (13) means the velocity of the sound wave propagating from the target to the sonar on the path that has the greatest influence on the received waveform in the impulse response.

In the third embodiment, as described above, the estimated group velocity g ⁽⁰⁾ is used instead of the group velocity g in the second embodiment. Therefore, in step S12, the delay change amount calculation device 40 calculates the delay change amount ΔT using equation (14). The formula (14) for calculating the delay change amount ΔT is obtained by replacing the denominator group velocity g in the formula (11) with the estimated group velocity g ⁽⁰⁾ .

As described above, in the waveform calculation system 300 according to _the third embodiment, the group velocity used when calculating the delay change amount ΔT in the delay change amount calculation device ₄₀ is Let the estimated group velocity g ⁽⁰⁾ calculated by equation (13) using the delay tk _^ with the largest amplitude be used. This makes it possible to obtain the group velocity of the path with the greatest influence on the received waveform among the multiple propagation paths from the target to the sonar, even if the path with the greatest influence does not propagate at an angle close to the horizontal. Waveform x(t _m ) can be calculated with high accuracy.

Embodiment 4.
Next, the fourth embodiment will be described. The fourth embodiment differs from the first to third embodiments in that it considers the influence of the time-varying change in the sound velocity profile on the delay change amount ΔT in addition to the change in the relative distance. In the fourth embodiment, the same reference numerals are given to the parts common to the first to third embodiments, and detailed description thereof will be omitted.

In the fourth embodiment, consider a time-varying sound velocity profile with respect to the transmission time τ _μ , that is, a set of depth and sound velocity (z _l , c _l (τ _μ )). In this case, the delay change amount ΔT is calculated based on equation (15).

In Equation (15), the first and second terms in the absolute value symbol on the right side have different values of group velocity in the denominator. In Equation (15), the denominator “g ⁽⁰⁾ ” of the second term is the estimated group velocity g ⁽⁰⁾ in the third embodiment. The denominator “g _τμ ” of the first term is the corrected group velocity indicating the group velocity at the transmission time τ _μ , which is obtained by correcting the estimated group velocity g ⁽⁰⁾ based on Equation (16). In equation (16), “c ⁽⁰⁾ ” is the reference speed of sound indicating the speed of sound at the transmission time at which the estimated group velocity g ⁽⁰⁾ was calculated, and “c _τμ ” is the speed of sound at the transmission time τ _μ . be.

This corrected group velocity g _τμ is the same as the ratio of the change in sound velocity when the sound velocity at the transmission time τ _μ changes from the sound velocity at the transmission time when the estimated group velocity g ⁽⁰⁾ is calculated. calculated as a change in the ratio of This utilizes the fact that the group velocity is directly proportional to the sound velocity in the case of a medium with a constant sound velocity.

Here, the sound velocity c _τμ at the wave transmission time τ _μ is the average value of the sound velocity c _l (τ _μ ) of the sound velocity profile at the wave transmission time τ _μ with respect to the depth index l, based on, for example, Equation (17). In addition, _the sound _velocity c τ _μ at the transmission time τ μ is not limited to _this , for example, the function c (z, τ _{μ )} (0 ≦z≦z _L−1 ), and may be calculated based on equation (18).

Thus, by estimating the delay change amount ΔT using the equations (15) and (16), changes in the group velocity due to changes in the speed of sound are taken into consideration. Then, it can be expressed that the delay is changed not only by the change of the relative distance but also by the change of the group velocity.

[Configuration of Waveform Calculation System 400]
FIG. 10 is a block diagram showing an example configuration of a waveform calculation system according to the fourth embodiment. As shown in FIG. 10 , the waveform calculation system 400 includes a control device 13 , an impulse response calculation device 20 , an instantaneous received waveform calculation device 30 and a delay variation calculation device 41 . Such a waveform calculation system 400 is composed of an arithmetic unit such as a microcomputer that implements various functions by executing software, or hardware such as a circuit device that supports various functions.

The control device 13 receives the ocean environment conditions, the scenario, and the instantaneous sound pressure s(τ _μ ) of the transmitted wave waveform at the transmitted wave time τ _μ . The control device 13 exchanges various data with the impulse response calculator 20, the instantaneous received wave waveform calculator 30, and the delay variation calculator 41, and calculates the received wave waveform x(t _m ). In the fourth embodiment, the sound velocity profile input to the control device 13 is a set of a plurality of depths and sound velocities (z _l , _cl (τ _μ )) that changes with respect to the transmission time τ _μ It is the depth characteristic of the speed of sound represented.

The delay variation calculator 41 receives the reference relative distance r ⁽⁰⁾ , the estimated group velocity g ⁽⁰⁾ , the relative distance r _τμ and the corrected group velocity g _τμ from the controller 13 . The delay variation calculator 41 calculates the delay variation ΔT based on the input reference relative distance r ⁽⁰⁾ , estimated group velocity g ⁽⁰⁾ , relative distance r _τμ and corrected group velocity g _τμ . A delay change amount ΔT is output to the control device 13 .

[Operation of Waveform Calculation System 400]
FIG. 11 is a flowchart showing an example of the flow of waveform calculation processing by the waveform calculation system according to the fourth embodiment. It should be noted that the same reference numerals are assigned to processes that are common to the processes in Embodiments 1 to 3, and detailed description thereof will be omitted.

After the process of step S21, the control device 13 initializes the reference sound velocity c ⁽⁰⁾ in step S31. It is assumed that the value for initializing the reference sound velocity c ⁽⁰⁾ is the same as the value for initializing the estimated group velocity g ⁽⁰⁾ in the third embodiment.

After the process of step S2, the control device 13 calculates the sound velocity c _τμ and the corrected group velocity g _τμ based on the sound velocity profile at the wave transmission time τ _μ . The control device 13 calculates, for example, the average value of the sound velocity values c _l (τ _μ ) of the sound velocity profile at the transmission time τ _μ as the sound velocity c _τμ . Further, the control device 13 calculates a corrected group velocity g _τμ obtained by correcting the estimated group velocity g ⁽⁰⁾ using equation (16) based on the sound velocity c _τμ and the reference sound velocity c ⁽⁰⁾ .

Next, the control device 13 sends the reference relative distance r ⁽⁰⁾ , the estimated group velocity g ⁽⁰⁾ , the relative distance r _τμ , and the corrected group velocity g _τμ calculated in step S32 to the delay change amount calculating device 41. output. In step S33, the delay change amount calculator 41 calculates the delay change amount ΔT based on the input reference relative distance r ⁽⁰⁾ , estimated group velocity g ⁽⁰⁾ , relative distance r _τμ and corrected group velocity g _τμ . do. Then, the delay change amount calculation device 41 outputs the calculated delay change amount ΔT to the control device 13 .

Further, in step S13, if the delay change amount ΔT satisfies the equation (12) and is equal to or greater than the constant α (step S13: Yes), the control device 13, in step S34, controls the impulse response h(t _k , r _τμ ). At this time, the sound velocity profile among the marine environment conditions input to the impulse response calculator 20 is the sound velocity profile (z _l , c _l (τ _μ )) at the wave transmission time τ _μ .

Furthermore, after the process of step S23, the control device 13 updates the reference sound velocity c ⁽⁰⁾ by "c ⁽⁰⁾ =c _τμ " in step S35.

As described above, the waveform calculation system 400 according to the fourth embodiment responds to changes in the group velocity for calculating the delay change amount ΔT with respect to the transmission time _τμ , so that only the relative distance It can be expressed that the delay changes not only by the time change of the sound speed profile but also by the time change. Then, even when the sound velocity profile changes with time, the received waveform x(t _m ) can be calculated with high accuracy.

As described above, Embodiments 1 to 4 of the present invention have been described, but the present invention is not limited to the above-described Embodiments 1 to 4, and various modifications or Application is possible. In the prior art and Embodiments 1 to 4, simulation of a received wave waveform when a passive sonar receives a sound wave emitted from a target has been described, but this is not limited to this example. For example, this waveform calculation system can be applied to any combination of any underwater sound source and any wave receiver that receives sound waves emitted from the underwater sound source. Specifically, for example, when the waveform calculation system is used to simulate a received wave waveform when evaluating the performance of underwater acoustic communication, the target in the passive sonar becomes the transmitter and the sonar becomes the receiver.

In the first to fourth embodiments, a passive sonar is assumed as a sonar, but the waveform calculation systems 100, 200, 300, and 400 are not limited to this, and can be applied to, for example, an active sonar. be able to. In active sonar, sound waves propagate from a sonar source to a target, and after being scattered by the target, the scattered sound waves propagate from the target to a sonar receiver. Therefore, the frequency characteristic p(f _n , r) of the sound pressure to be inverse Fourier transformed in Equation (3) is represented by Equation (19) in the case of active sonar. In equation (19), “r ^S→T ” denotes the distance from the sonar source to the target, and “r ^T→R ” denotes the distance from the target to the sonar receiver. Also, “S(f _n )” indicates the scattering properties at the target.

At this time, the relative distance r _τμ used in the calculation of the delay change amount ΔT is the sum of the distance r ^{S → T} from the sonar sound source to the target and the distance r ^{T → R} from the target to the sonar receiver, It is shown by Formula (20).

In the prior art and Embodiments 1 to 4, for ease of explanation, the impulse response h(t _k , r _τμ ) does not depend on the respective positions of the target and the sonar, but only the relative distance r It is supposed to depend on This holds true if the sound velocity profile and water depth are position independent.

For example, if the sound velocity profile and water depth depend on the position, it is preferable to use the sound velocity profile and water depth on a two-dimensional cross section that shows the relationship between the distance and depth connecting the target position and the sonar position. Specifically, for example, the frequency characteristic p(f _n , r) of the sound pressure is calculated using a distance-dependent propagation model as shown in Non-Patent Document 2, and the impulse response is calculated from the result. .

This makes it possible to represent a phenomenon in which sounds transmitted at different transmission times propagate at different relative distances in different marine environments and are simultaneously received by the sonar. However, in the calculation of the delay change amount ΔT in Embodiments 2 to 4, the influence of the relative distance change is included in the delay change, but the influence of the position change is ignored.

10, 11, 12, 13 control device, 20 impulse response calculation device, 21 processing circuit, 22 processor, 23 memory, 30 instantaneous received waveform calculation device, 40, 41 delay variation calculation device, 100, 200, 300, 400 Waveform calculation system.

Claims (7)

A waveform calculation system for calculating a received wave waveform, which is sound pressure received by a sonar and transmitted from a target,
A relative distance between the target and the sonar is calculated for each wave transmission time at which waves are transmitted from the target to the sonar, and an impulse response representing sound wave propagation at each wave transmission time is converted to the corresponding a control device for calculating a received wave waveform by convoluting the transmitted wave waveform from the target at the wave transmission time;
A waveform calculation system comprising: an impulse response calculation device that calculates the impulse response for each wave transmission time based on the calculated relative distance for each wave transmission time. further comprising an instantaneous received wave waveform calculating device that calculates an instantaneous received wave waveform by multiplying the impulse response at each of the transmitted wave times by the transmitted wave waveform at the corresponding transmitted wave time,
The control device is
2. A waveform calculation system according to claim 1, wherein said instantaneous received wave waveform is accumulated in said received wave waveform to calculate a new received wave waveform. further comprising a delay change amount calculation device that calculates a delay change amount determined based on the change in the relative distance over time and the group velocity,
The control device is
determining that the change in the impulse response is large when the amount of delay change is greater than or equal to a set value;
The impulse response calculator,
3. The waveform calculation system according to claim 1, wherein the impulse response is calculated when it is determined that the change in the impulse response is large. The delay change amount calculation device includes:
4. The waveform calculation system according to claim 3, wherein the amount of change in delay is calculated by dividing the amount of change in the relative distance by the group velocity. The delay change amount calculation device includes:
4. The waveform calculation system according to claim 3, wherein the change amount of the delay is calculated by dividing the change amount of the relative distance by an estimated group velocity, which is a group velocity at a time when the calculated impulse response has a maximum amplitude. A waveform calculation method for calculating a received wave waveform, which is sound pressure received by a sonar and transmitted from a target, comprising:
calculating a relative distance between the target and the sonar at each transmission time of transmitting waves from the target to the sonar;
calculating an impulse response for each wave transmission time based on the calculated relative distance for each wave transmission time;
A waveform calculation method for calculating a received waveform by convolving the impulse response for each of the wave transmission times with the waveform of the wave transmitted from the target at the corresponding wave transmission time. A waveform calculation method program for calculating a received wave waveform, which is sound pressure received by a sonar and transmitted from a target, comprising:
calculating a relative distance between the target and the sonar at each transmission time of transmitting waves from the target to the sonar;
calculating an impulse response for each wave transmission time based on the calculated relative distance for each wave transmission time;
A waveform calculation method program for causing a computer to perform a process of calculating a received waveform by convolving the impulse response at each of the wave transmission times with the waveform of the wave transmitted from the target at the corresponding wave transmission time.

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