JPH0119551B2 - - Google Patents

Description

Detailed Description of the Invention The present invention aims to simulate the homing performance of an underwater vehicle equipped with an underwater acoustic stationary target, especially an active sonar, without operating an actual sonar target. This invention relates to an underwater acoustic stationary target that receives a transmitted sound wave emitted by an active sonar and converts it into a sound wave that responds to the reflection characteristics of a preset sonar target, thereby emitting it just like a reflected echo from an actual sonar target.

A device that mounts an active sonar on an underwater vehicle and tracks sonar targets in the ocean, including the sea and the ocean floor, is well known as a homing vehicle.

In this homing vehicle, when the transmitted pulse sound wave transmitted from the on-board active sonar captures the sonar target and is received by the active sonar again as a reflected echo, the distance and direction information of this received signal is also acquired. It is also well known to have a homing function in which the steering system is driven so as to constantly face the sonar target and track the sonar target.

Such homing vehicles often carry out homing navigation for training, function confirmation, and other various purposes. It is clear that it is desirable to train homing operations, confirm functions, etc.

However, operating a sonar target each time such objective processing is subject to extremely strong constraints due to manpower requirements, costs, and many other related reasons, and therefore homing navigation is not recommended as a simulation of an actual sonar target. Underwater acoustic targets are often used, which receive pulsed sound waves transmitted by the body and return them with characteristics as close as possible to actual echoes.

Such underwater acoustic targets include self-propelled, towed, and fixed types, and are selectively used depending on the operational purpose such as sonar or homing vehicle training and function confirmation. The underwater acoustic stationary target is the above-mentioned fixed underwater acoustic target, and is mainly used as a target for homing vehicles. It is a watertight cylindrical structure equipped with electronic circuits including transmitters, receivers, and power sources for transmitting radio waves at predetermined positions, and utilizes self-buoyancy in either case, moored from the seabed or free-floating. It is installed at sea or underwater in an almost upright position.

The position of the underwater acoustic stationary target installed in this way is always confirmed with a predetermined accuracy by measuring the direction from land, even when it is in a free-floating state.

FIG. 1 is a block diagram showing the general configuration of a conventional underwater acoustic static target of this type.

The transmitted pulse sound wave emitted by the homing vehicle is a received pulse sound wave 1 with frequency fi and sound pressure level Pi.
01 to the receiver 1, where it is converted into an electrical signal, which is sent to the amplifier 2 as a received signal 102. Amplifier 2 is an input amplification circuit which amplifies the input to a predetermined voltage level and sends it to frequency converter 3 as amplifier output 201.

The amplifier output 201 is sent to the frequency converter 3 and undergoes frequency conversion in which a Doppler frequency f _D corresponding to the relative velocity difference between the homing vehicle and the sonar target is added. This Doppler frequency f _D usually uses a frequency with a fixed value set in advance.

The frequency f _i of the transmitted pulse sound wave emitted from the homing vehicle is reflected by the sonar target, and when it returns to the homing vehicle as a received sound wave, a Doppler wave corresponding to the speed difference between the homing vehicle and the sonar target is reflected. It is shifted by the frequency f _D.
This Doppler frequency differs depending on whether the homing vehicle and the sonar target are approaching or moving away from each other; when the homing vehicle and the sonar target are approaching, the Doppler frequency increases as the frequency f _i increases, that is, +f _D. , when they are separated, the effect is conversely as f _i decreases as −f _D . Therefore, by setting the sonar target and the speed of the homing vehicle in advance, it is possible to set the frequency f _i ±f _D to be given to the received sound wave 101.

The frequency conversion circuit 3 includes a frequency shift circuit, etc., and converts the frequency f _i of the amplifier output 201 into a Doppler frequency ±f corresponding to a relative speed difference between a preset sonar target speed V ₁ and a homing vehicle speed V ₂ . _D
Convert to . However, in this case, the Doppler frequency is set assuming that the sonar target speed V ₁ is higher than the minimum speed range value V ₀ that is normally set in advance, but this means that the sonar target to be acquired by the homing vehicle is stationary for the purpose. Since it is necessary to exclude objects from consideration, a minimum speed range value V ₀ is set, which is also the speed of the sonar target.

The received signal converted into the frequency f _i ±f _D in this way is sent from the frequency converter circuit 3 to the frequency converter output 3.
01 to the power amplifier 4.

The power amplifier 4 amplifies the power of this to a predetermined level and sends it to the transmitter 5 as a power amplification circuit output 401, thereby increasing the frequency f _i ±f _D and the sound pressure level P _i
A response transmission sound wave 501 of +T _s is generated and radiated into the sea. The above-mentioned T _s varies depending on conditions such as the structure and material of the sonar target, and represents a coefficient that determines the magnitude of the reflection level of the sonar target, so-called target strength.

Target Strength
As is well known, it corresponds to the ratio of the sound pressure level incident on a certain reflector to the reflected echo level at a unit distance, and is similar to the pressure level P _i .
It is a quantity expressed in dB (decibels) and has a positive value for normal sonar targets. The value varies depending on the incident angle of the sound wave, and also varies depending on the size of the target with the same incident angle, the area irradiated by the incident sound wave, its shape, material, etc. However, regarding the T _s of the sonar target targeted by the homing vehicle, in addition to the basic conditions for determining T _s described above, information obtained from the known homing movement of the homing vehicle toward the actual sonar target, etc. This is set using the following, and this setting value can be arbitrarily switched within a prespecified range and with a specified switching step. This actually means that you should set T _s
This is done by switching and setting the gain of the power amplifier 4 to a desired level so as to have the desired value.

In this way, each time a received pulsed sound wave 101 is received, a response transmitted pulsed sound wave 501 corresponding to the received pulsed sound wave 101 is sent out, thereby making it possible to respond as if it were an echo reflected by an actual sonar target.

However, in the case of conventional underwater acoustic static targets of this type, as described below, it receives the transmitted pulsed sound waves emitted by the homing vehicle and amplifies them.
The waveform of the transmitted sound wave that is frequency-converted and sent back takes into account the target strength, frequency, and Doppler frequency of the sonar target.
The expansion of the pulse width of the transmitted pulsed sound wave due to the dimensions of the actual sonar target and waveform distortion due to structural characteristics are not considered, and the Doppler frequency also corresponds to the preset speed of the sonar target and homing vehicle. Since the fixed values obtained from the homing vehicle are used, the rate of change over time of these speeds, that is, the rate of approach between the sonar target and the homing vehicle, is not taken into account, so the homing ability of the homing vehicle cannot be correctly evaluated. The disadvantage is that it cannot be done.

The purpose of the present invention is to eliminate the above-mentioned drawbacks and to provide a simulated reflected echo that has characteristics equivalent to the reflected echo from an actual sonar target in an underwater acoustic stationary target for simulating the homing performance of a homing vehicle. An object of the present invention is to provide an underwater acoustic stationary target that greatly improves the homing evaluation ability of a homing vehicle by being equipped with a generating means.

The target of the present invention receives transmitted sound waves emitted from an underwater vehicle equipped with an active sonar and is homing to a sonar target in the sea, and converts the transmitted sound waves into sound waves with preset characteristics that simulate echoes reflected by the sonar target. The sonar target set in advance for the received sound wave is an underwater acoustic static target that can be sent back into the sea as a simulated reflected echo to test the homing performance of the underwater vehicle without using an actual sonar target. A Doppler frequency is given by the motion speed of the target, and an equivalent reflected energy is given by adding the target strength. Furthermore, a simulated reflected echo is generated with a waveform based on the reflected echo from the actual sonar target, and this is used as a sonar target. It is configured to include simulated reflected echo generating means that outputs after a time delay corresponding to the set relative speed between the underwater vehicles.

Next, the present invention will be explained in detail with reference to the drawings.

In FIG. 2, a receiver 1, an amplifier 2, a power amplifier 4, and a transmitter 5 have the same contents as those with the same symbols in FIG. 1, and a detailed explanation thereof will be omitted.

Received pulsed sound wave 1 received from the homing vehicle
A received signal 102 obtained by converting 01 into an electrical signal by a receiver 1 is input and amplified to a predetermined level by an amplifier 2 and sent to a simulated reflected echo generator 6 as an amplifier output 201.

The simulated reflection echo generator 6 is a level detector 6
1, a frequency detector 62, a simulated waveform generator 63, a variable frequency oscillator 64, and an AM modulator 65.

The amplifier output 201 is sent to a level detector 61 and a frequency detector 62, which detect an input sound pressure level P _i and an input frequency f _i and convert them into an input sound pressure level signal 611 and an input frequency signal 62, respectively.
1 to the simulated waveform generator 63 and variable frequency oscillator 64.

The level detector 61 has a preset minimum level that takes into account the output level of the active sonar mounted on the homing vehicle, the distance between the homing vehicle and the underwater acoustic stationary target, the underwater noise in the operating area of the homing vehicle, etc. Using the received input pressure level as a comparison reference voltage, this and the amplifier output 201 are compared in a level comparison circuit, and only when the input pressure level exceeds the comparison reference voltage level mentioned above, this is determined to be the input sound pressure level, and then the peak value is determined. After the level value is measured by the voltage measuring circuit, it is outputted by the A/D converter as an input pressure level signal 611 based on a binary logical value series corresponding to the input level of a predetermined number of bits.

Frequency detector 62 receives amplifier output 201, outputs a DC voltage at a level corresponding to the frequency by a frequency detection circuit using a frequency discrimination circuit, and sends this as input frequency signal 621 to variable frequency oscillator 64. Input frequency signal 621
corresponds to the frequency f _i of the received pulsed sound wave 101,
This frequency f _i is subjected to a Doppler frequency shift corresponding to the speed component of the homing vehicle in the direction of the underwater acoustic stationary target, and has a value that changes in accordance with the speed of the homing vehicle.

Now, in order to receive the received pulsed sound wave 101 and configure it to simulate a reflected echo from an actual sonar target, as in the conventional case shown in FIG.
However, it is not sufficient to simply apply the Doppler frequency based on the preset motion speed of the sonar target and apply the equivalent reflected energy by adding the target strength T _s described above.

In order to reproduce the reflected echo from an actual sonar target, it is necessary to equivalently stretch the pulse width depending on the dimensions of the sonar target, distort the reflected echo due to the difference in the reflection coefficient due to the difference in the reflection point of the sonar target, and adjust the homing direction. It is necessary to add a delay time to the response transmission pulse sound wave 501 that corresponds to the relative difference in velocity components between the moving object and the sonar target in the opposing directions. By satisfying the conditions for reflected echoes, it becomes possible to test and therefore evaluate the correct homing operation of the homing vehicle.

The simulated waveform generator 63 generates a transmission pulse waveform corresponding to the reflected echo from the actual sonar target, that is, the physical shape, dimensions, etc. of the sonar target. The operation is to provide an input delay time corresponding to the difference.

When the transmitted pulsed sound wave emitted from the homing vehicle hits the sonar target as a transmitted wave beam having a solid angle corresponding to the transmitted wave directivity specified in advance,
It is reflected by all or part of the sonar target, which is determined by the solid angle and distance to the sonar target mentioned above, and becomes a reflected echo. During homing, reflected echoes from various parts of the sonar target are received with a length that exceeds the pulse width of the transmitted pulsed sound wave, and these reflected echoes are the result of a combination of reflected waves reflected from various parts of the sonar target. Therefore, each part of the sonar target has a different level depending on the different reflection coefficient, and therefore the waveform has a corresponding amplitude distortion.

Additionally, there is usually a relative velocity difference between the sonar target and the homing vehicle, and this relative velocity difference determines the Doppler frequency for the reflected echo, which also has a time delay corresponding to this relative velocity difference. It will be given.

In this embodiment, the equivalent expansion of the pulse width and the amplitude distortion that the transmitted pulse sound wave emitted by the homing vehicle is subjected to by the sonar target are determined by homing the sonar vehicle to the sonar target in advance and emitting reflected echoes. A simulated signal is generated using the information of the actual reflected echo obtained by a recording device, etc., and a time delay is applied to this signal according to the approach rate δ shown by the following equation (1) to generate a simulated waveform generator. 63
It is output from

δ=(R ₁ − R ₂ )/T...(1) In equation (1), R ₁ is the distance at which the homing vehicle approaches the sonar target in unit time in the straight line direction connecting the homing vehicle and the sonar target. , _R2 indicates the distance at which the sonar target moves away from or approaches the homing vehicle per unit time, and corresponds to the speeds of the homing vehicle and the sonar target, respectively. Further, T indicates the transmission period of the transmitted pulse sound wave emitted by the homing vehicle, and therefore δ can be considered as a coefficient indicating the distance approach rate of the homing vehicle when homing to the sonar target, and δ is Obviously, it has a value corresponding to the relative speed difference between the homing vehicle and the sonar target, and therefore the Doppler frequency, and can be easily set once the Doppler frequency is determined. The target echo of the sonar caused by the transmitted pulsed sound wave is subject to a time delay proportional to the value of δ, so by giving a time delay corresponding to this δ, which can be determined in accordance with the Doppler frequency of the inputted received pulsed sound wave, the actual It is possible to set the delay time of the reflected wave echo due to the relative speed difference between the homing vehicle and the sonar target.

Now, in FIG. 2, the simulated waveform generator 63
is a ROM that stores sample values sampled at a sampling period that specifies representative reflected echo information that has been recorded in advance using an actual homing vehicle and sonar target, and also has a control program built in, and an input that is inputted. Pressure level signal 6
11 is a RAM that is read one after another under the control of the ROM program described above, an arbitrary function generation circuit, and a D/
It is equipped with an A converter, etc., reads the input sound pressure level signal 611 into the RAM, reads out the reflected echo information stored in the ROM in sample order, sends it arbitrarily to the function generation circuit, and inputs the input sound pressure level signal 611 into the RAM.
A simulated signal waveform as an arbitrary function is generated by performing weighting corresponding to the magnitude of the input level signal 611 read from the input level signal 611 .

The simulated signal generator 63 further sets in the ROM program δ of equation (1), which corresponds to the Doppler frequency f _D corresponding to the speed difference between the preset sonar target and the homing vehicle, and performs the simulation described above. The signal waveform is determined by this δ and the transmission period,
It is delayed by a delay circuit and sent to the AM modulation circuit 65 as a simulated waveform signal 631.

Meanwhile, input frequency signal 621 is sent to variable frequency oscillator 64. The variable frequency oscillator 64 includes a voltage controlled oscillator, receives the input frequency signal 621, and adjusts its level, that is, the received pulsed sound wave 10.
generate a signal with a frequency proportional to the frequency f _i of 1,
Furthermore, a frequency obtained by adding the above-mentioned Doppler frequency f _D to this frequency, f _i +f _D , is generated via a frequency shift circuit, and this is set to a predetermined level by a built-in amplifier circuit, and is sent to the AM modulator 6 as a variable frequency signal 641.
Send on 5th.

The AM modulator performs AM modulation on the variable frequency signal 641 using the simulated waveform signal 631 using the AM modulation circuit, and outputs it as a simulated reflected echo output signal 651 having a desired frequency, waveform, and delay time.
This is sent to the power amplifier 4.

The power amplifier 4 amplifies the input simulated reflected echo output signal 651 to a predetermined level, and transmits this power amplifier output 401 via the transmitter 5 to the input sound pressure level P _i of the received pulsed sound wave 101 to a target strength level T. Output sound pressure level P _i + _{T s}
This is transmitted as a response transmission pulse sound wave 501.

The response transmitted pulse sound wave 501 obtained in this way has a waveform that is almost the same as the echo reflected by the actual sonar target, and has a level that corresponds to the target strength and therefore the reflection coefficient of the actual sonar target. The content was sent to the homing vehicle with a delay time that corresponded to the speed difference with the homing vehicle, that is, the Doppler frequency, and took into account the approach rate, and it was able to almost completely simulate the echo reflected by the actual sonar target. It can be used as a pseudo reflected echo, and the accuracy of evaluating the homing performance of a homing vehicle can be greatly improved.

The present invention is an underwater acoustic stationary target whose purpose is to generate a pseudo reflected echo instead of an actual sonar target in order to evaluate and confirm the homing performance of a homing vehicle. The basic feature is that a pseudo reflected echo is generated and transmitted, and various modifications of the embodiment of the present invention shown in FIG. 2 can be considered.

For example, the response transmitted pulse sound wave 501 obtained by the embodiment of FIG. We consider both amplitude distortion and add this to the Doppler frequency and target strength conditions for conventional hydroacoustic stationary targets, but this does not apply to either approach rate alone or pulse width stretching and waveform amplitude distortion alone. There is no problem in using the conditions alone or in combination, or in combination with the above-mentioned conventional conditions alone or in combination, and this is done by changing the control program built in the ROM of the simulated waveform generator 63. It is clear that it can be easily implemented by

In addition, the receiver 1 and the transmitter 5 in FIG.
may be replaced with a transmitting/receiving transducer having substantially equivalent characteristics, and the input sound pressure level signal 611 output from the level detector 61 is a digital signal corresponding to the input level. This input sound pressure level signal 611 can be sent as an analog signal and converted into a digital quantity via an A/D converter or the like in the simulated waveform generator, or the arbitrary function generating circuit of the simulated waveform generating circuit can be configured as an analog circuit. It is clear that weighting can also be carried out easily.

Furthermore, it is clear that the variable frequency oscillator 64 can be easily implemented as a variable frequency generation type using a frequency synthesis circuit instead of the voltage controlled oscillator in this embodiment, and all of the above can be easily implemented without detracting from the gist of the present invention. It can be implemented in

As explained above, according to the present invention, an underwater acoustic static target whose purpose is to generate a simulated reflected echo instead of an actual sonar target in order to evaluate and confirm the homing performance of a homing vehicle, etc. By using the reflected echo from the sonar target of By making the approximation possible, the accuracy of evaluating and confirming the homing performance of a homing vehicle can be greatly improved, and the time required for evaluation and confirmation can be significantly reduced. This has the effect of realizing an underwater acoustic stationary target. .

[Brief explanation of drawings]

1 and 2 are block diagrams of underwater acoustic static targets according to the prior art and the present invention. 1... Receiver, 2... Amplifier, 3... Frequency converter, 4... Power amplifier, 5... Transmitter, 6...
Simulated reflected echo generation circuit, 61... Level detector, 62... Frequency detector, 63... Simulated waveform generator, 64... Variable frequency oscillator, 65... AM modulator.

Claims (1)

[Claims] 1 A simulated reflected echo that receives a transmitted sound wave emitted from an underwater vehicle equipped with an active sonar and is homing to a sonar target in the sea, and converts it into a sound wave with preset characteristics that simulates the sound reflected by the sonar target. In an underwater acoustic stationary target, it is possible to simulate the homing performance of the underwater vehicle without using an actual sonar target by sending it into the sea again as a sonar target. In addition to adding a Doppler frequency and adding target strength to give equivalent reflected energy, a simulated reflected echo is generated with a waveform based on the echo reflected by the actual sonar target, and this is used to identify the sonar target and the underwater vehicle. An underwater acoustic stationary target characterized in that the underwater acoustic stationary target is equipped with a simulated reflected echo generating means that outputs the simulated reflected echo after a time delay corresponding to a set relative velocity between the underwater vehicle and the simulated reflected echo in response to the transmitted sound wave of the underwater vehicle.