RU2626068C2 - Method for calibration of parametric tract and device for its implementation - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method and the device for calibration of the parametric tract of the sonar that reduces the amplitude-frequency distortions of the matched filter response to the useful echo by optimizing the parameters emitted in aqueous medium of the pumping signals: the carrier frequency of the tone pumping signal, the carrier frequency and the frequency deviation of the frequency modulated pumping signal. The device for calibration of the parametric tract of the sonar contains a reference reflecting object, a high-frequency transmitter antenna and a low-frequency receiving antenna, a transmitting unit, a receiving unit, a digital signal processing unit, a control unit.

EFFECT: optimization of the pumping signal parameters emitted to the aqueous medium to ensure minimum amplitude-frequency distortion.

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Description

The present invention relates to the field of nonlinear sonar and can be used to calibrate the sonar parametric path.

For radiation in the parametric path of the sonar, two high-frequency pump signals are used at frequencies ω ₁ and ω ₂ , and ω ₁ > ω ₂ . As a result of the interaction of the emitted high-frequency acoustic signals with a nonlinear layer of the medium, a signal is generated at the difference frequency Ω ₁ = ω ₁ -ω ₂ , which is a copy of the emitted signal at the carrier frequency ω ₁ .

The generated signal at the difference frequency Ω ₁ undergoes amplitude-frequency distortions due to the process of its generation (nonlinear properties of the medium), propagation in the aquatic environment, and the influence of the radiating and receiving equipment of the sonar parametric path.

The neglect of the amplitude-frequency distortions of the received echo signal at the differential frequency Ω ₁ during digital processing, in particular when performing matched filtering, leads to negative consequences, which distort the response of the matched filter to the useful echo signal, which leads to its expansion (range resolution deteriorates) and an increase in the level of side lobes (the probability of missing a useful signal with a small amplitude increases), as a result, the technical characteristics of the hydra locator.

Thus, an important task is the calibration of the sonar parametric path, which consists in determining the optimal parameters of the pump signals that provide the minimum amplitude-frequency distortion of the signal at the difference frequency Ω ₁ .

The known method (patent for the invention of the Russian Federation No. 2058561 "Method for calibrating parametric emitting antennas and a device for its implementation"), comprising emitting an antenna of high-frequency acoustic pump waves at close frequencies ω ₁ and ω ₂ , receiving signals of a difference frequency Ω ₁ = ω ₁ -ω ₂ measuring hydrophone, measuring the amplitudes of the signal of the differential frequency Ω ₁ . At the location of the measuring hydrophone, simultaneously with the radiation of the pump signal, a continuous calibration high-frequency signal is additionally emitted at a frequency of ω ₃ , which is selected from the condition that the sensitivity of the hydrophone is equal at frequencies ω ₁ , ω ₂ , ω ₃ , and the signal amplitude at a frequency of ω ₃ by adjusting the radiation level set equal to the amplitude of the signals at frequencies ω ₁ and ω ₂ .

At the location of the measuring hydrophone, the amplitudes of the discrete components U (Ω ₁ ), U (Ω ₂ ), U (Ω ₃ ) are measured at frequencies Ω ₁ = ω ₁ -ω ₂ , Ω ₂ = ω ₃ -ω ₁ , Ω ₃ = ω ₃ -ω ₂ , compare the obtained values and, if U (Ω ₁ )> U (Ω ₂ ) = U (Ω ₃ ), draw a conclusion about the acoustic origin of the received signal, and for U (Ω ₁ ) = U (Ω ₂ ) = U (Ω ₃ ), conclude that a spurious signal is recorded. The signal U (Ω ₁ ) of acoustic origin is used to measure the directivity of the emitting parametric antenna and the amplitude-frequency characteristics of the emitted signal.

The disadvantages of this analogue method include the use of an additional emitter of a high-frequency calibration signal, which must have stable characteristics to perform calibration. In addition, during calibration, the measuring hydrophone is located in the far zone of the radiating antenna, which requires a large signal-to-noise ratio and prevents calibration in the case of monostatic sonar, when the radiating high-frequency and low-frequency receiving antennas are located nearby.

Also a disadvantage of the analogue method under consideration is the inability to take into account the non-linear properties of the aquatic environment that vary in space and cause the generation of a useful low-frequency signal at the difference frequency Ω ₁ = ω ₁ -ω ₂ .

The closest analogue to the proposed method is a method for calibrating the sonar parametric path (Foote K., Francis T., Atkins P. Calibration sphere for low-frequency parametric sonar // JASA. 2007. Vol. 121, No. 3. P. 1482-1489 ), in which: the parametric path of the sonar is calibrated in a given area of the water area, a reference reflective object is placed at a known distance from the sonar antennas, two pump signals are used for radiation - a tone signal with a carrier frequency of ω ₂ and a frequency-modulated signal with a carrier frequency of ω ₁ and frequency deviation Δω, within the passband of the emitting high-frequency sonar antenna, emit signals at frequencies ω ₁ and ω ₂ towards the reference reflective object, receive echo signals at the difference frequency Ω ₁ = ω ₁ -ω2 using a low-frequency receive antenna, perform band pass filtering of the received echo signals, evaluate the backscatter coefficient from the reference reflective object in the reception frequency band.

A significant disadvantage of this prototype method is the inability to optimize the parameters of the pump signals, as a result, it is impossible to minimize the amplitude-frequency distortion of the echo signal at a difference frequency of Ω ₁ , which leads to a decrease in the signal-to-noise ratio during processing of echo signals and to a deterioration in the technical characteristics of the sonar (lower resolution ability in range, as well as to increase the probability of missing a useful echo signal).

The closest analogue to the proposed device is a device for calibrating the sonar parametric path (Foote K., Francis T., Atkins P. Calibration sphere for low-frequency parametric sonar // JASA. 2007. Vol. 121, No. 3. P. 1482- 1489).

The specified device contains a reference reflective object, a high-frequency emitting antenna and a low-frequency receiving antenna, a transmitting unit, a receiving unit, a digital signal processing unit, a control unit. In this case, the reference reflective object is not connected, the input of the high-frequency emitting antenna is connected to the output of the transmitting unit, the output of the low-frequency receiving antenna is connected to the input of the receiving unit, the output of which is connected to the input of the digital processing unit of the echo signals, the output of which is connected to the input of the control unit. The output of the control unit is connected to the input of the receiving unit and the transmitting unit, the digital processing unit.

The prototype device has a significant drawback consisting in the lack of control over the parameters of the pump signals emitted into the aquatic environment, as well as the parameters of the matched filter in the receiving unit to perform matched filtering, which does not allow minimizing the amplitude-frequency echo signals at the difference frequency due to propagation in the water environment with changing nonlinear properties and equipment of the parametric sonar path.

The objective of the invention is to reduce the distortion of the response of a matched filter to a useful echo signal in the parametric path of the sonar.

The technical result consists in optimizing the parameters of the pump signals emitted into the aqueous medium to ensure minimal amplitude-frequency distortions.

To ensure the indicated technical result, in a known method for calibrating the sonar parametric path, in which: the sonar parametric path is calibrated in a given area of the water area, a reference reflective object is placed at a known distance from the sonar antennas, two pump signals are used for radiation - a tone signal with a carrier frequency ω ₂ and a frequency-modulated signal with a carrier frequency ω ₁ and a frequency deviation Δω, within the passband of the radiating high-frequency antenna sonar, emit signals at frequencies ω ₁ and ω ₂ towards the reference reflective object, receive echo signals at the difference frequency Ω ₁ = ω ₁ -ω ₂ using a low-frequency receiving antenna, perform band pass filtering of the received echo signals, evaluate the backscattering coefficient from the reference reflective object in the reception frequency band, introduced new features:

- produce N sounding cycles;

, выполняют расчет коэффициентов согласованного фильтра, исходя из параметров излученных сигналов накачки, оценивают максимальное значение A(n) и ширину ΔB(n) по уровню 0.5 от значения A(n) отклика согласованного фильтра на эхосигнал от эталонного отражающего объекта;- for calibration in each probe cycle: set the parameters of the pump signals for radiation in the direction of the reference reflective object - the carrier frequency ω ₁ (n) and the frequency deviation Δω (n) of the frequency-modulated signal and the carrier frequency ω ₂ (n) of the tone signal,

calculate the coefficients of the matched filter based on the parameters of the emitted pump signals, estimate the maximum value of A (n) and the width ΔB (n) at a level of 0.5 of the value A (n) of the response of the matched filter to the echo signal from the reference reflective object;

- after performing N sounding cycles, threshold processing of the obtained values ΔB (n) ≤ΔB _{0 is} performed, among the values ΔB lower than the threshold ΔB ₀ , the value with the largest parameter A is selected and the sounding cycle number n ₀ corresponding to the selected value is stored, the optimal signal parameters are selected pumping ω ₁ (n ₀ ), ω ₂ (n ₀ ), Δω (n ₀ ), providing the minimum amplitude-frequency distortion of the signal at the output of the matched filter, calculate the impulse response coefficients of the matched filter for optimal parameters with ignals pump and remember them;

- when the sonar parametric path is used for radiation, pump signals with the optimal parameters ω ₁ (n ₀ ), ω ₂ (n ₀ ), Δω (n ₀ ) are used, and the impulse response coefficients of the matched filter for optimal signal parameters are used to perform the coordinated processing of the received echo signals pumping.

To ensure the specified technical result in a known device for calibrating the parametric path of the sonar containing a reference reflective object, a high-frequency emitting antenna and a low-frequency receiving antenna, a transmitting unit, a receiving unit, a digital signal processing unit, a control unit, while the reference reflecting object has no connections, the input of the high-frequency emitting antenna is connected to the output of the transmitting unit, the output of the low-frequency receiving antenna is connected to the input of the receiving unit, the output which is connected to the input of the digital processing unit of the echo signals, the output of which is connected to the input of the control unit, the output of the control unit is connected to the input of the receiving unit and the transmitting unit, the digital processing unit, characterized in that

- the transmitter uses two controlled generators to generate pump signals;

- in the digital signal processing unit, a controlled coordinated filter is used;

- an additional calibration unit has been introduced, wherein the input of the calibration unit is connected to the output of the digital signal processing unit, the output of the calibration unit is connected to the input of the control unit.

Thus, the calibration of the parametric path of the parametric sonar allows you to determine the optimal values of the parameters of the pump signals taking into account the influence of the propagation medium and the amplitude-frequency characteristics of the equipment of the parametric path of the sonar to ensure minimum amplitude-frequency distortions of the response of the matched filter to the useful echo signal.

The implementation of this method is illustrated in FIG. 1-4.

In FIG. 1 shows the geometry of the parametric path calibration problem, which shows an underwater object 1, a high-frequency emitting antenna 2, a low-frequency receiving antenna 3, a nonlinear layer of the aquatic environment 4, and a reference reflecting object 5.

In FIG. 2 shows typical amplitude spectra of the emitted pump signals: 6 — amplitude spectrum of the tone signal at the carrier frequency ω ₂ , 7 — amplitude spectrum of the frequency-modulated signal at the carrier frequency ω ₁ .

In FIG. Figure 3 shows the change in optimized parameters during the calibration process.

In FIG. Figure 4 shows the response of a matched filter in the time domain to a received echo at a differential frequency.

The proposed method is implemented as follows: calibrate the sonar parametric path in a given area of the water area, in the aquatic environment (Fig. 1) set the reference reflective object 5 at a known distance from the sonar antennas 2 and 3 located on the underwater object 1.

A spherical reflector with a radius of a made of steel is used as a reference reflective object 5, and the value of a satisfies the condition a >> (λ / 2π), where λ is the length of the acoustic wave incident on object 1. Also, as a reference reflective object you can use the boundaries of the section "water-ice" or "water-air", provided that there is information about the degree of their roughness.

Within the bandwidth of the emitting high-frequency sonar antenna 2 towards the reference reflective object 5, pump signals are emitted (Fig. 2) - a tonal signal with a carrier frequency ω ₂ and a frequency-modulated signal with a carrier frequency ω ₁ and frequency deviation Δω.

Given the variable nature of the nonlinear properties of the portion of the aqueous medium that generates a useful signal at the difference frequency as a result of the interaction of the pump signals, as well as the frequency-dependent nature of the processes of noise generation and propagation of acoustic waves in the aqueous medium, the following parameters of the pump signals must be optimized: carrier frequency ω ₁ and deviation frequency Δω of the frequency-modulated signal, and the carrier frequency ω _{2 of the} tone signal.

Calibrate the sonar parametric path for N sounding cycles.

For calibration, in each n-th sensing cycle, the parameters of the pump signals are set (Fig. 3) for radiation in the direction of the reference reflecting object 5 - the carrier frequency ω ₁ (n) and the frequency deviation Δω (n) of the frequency-modulated signal and the carrier frequency ω ₂ (n) tone, which is determined by the formulas:

Where

N ₂ - the number of gradations of the carrier frequency ω ₁ tone signal;

N ₃ is the number of gradations of the difference frequency ω ₁ -ω ₂ ;

N ₄ - the number of gradations of the frequency deviation of the frequency-modulated pump signal with a carrier frequency ω ₂ ;

int [.] - operator that extracts the integer part of a number;

mod (x, y) - an operator that calculates the number x modulo the number y;

ω ₀₂ - the initial value of the carrier frequency ω ₂ tone pump signal;

Δω ₀ is the initial value of the frequency deviation;

Δω ₂ - frequency change step ω ₁ ;

Δω ₁ is the step of changing the difference frequency ω ₁ -ω ₂ ;

Δω ₀₁ is the step of changing the frequency deviation.

The parameters N ₂ , N ₃ , N ₄ , ω ₀₂ , Δω ₀ , Δω ₂ , Δω ₁ , Δω ₀₁ are set before calibration.

The set values of N ₂ , N ₃ , N ₄ must be a multiple of 2 and satisfy the conditions:

Based on conditions (4), the number N is determined by the number of gradations N ₂ , N ₃ , N _{4 of the} optimized parameters of the pump signals.

There are also restrictions on the values of ω ₀₂ and ω ₁ (N):

Where

Δω ₀₂ - the spectrum width of the pump tone 6 (Fig. 2);

ω _n and ω _{in the} left and right borders of the passband of the high-frequency radiating antenna 2, respectively.

As a result of the interaction of the emitted pump signals with a nonlinear layer of the aqueous medium 4, a frequency-modulated signal is generated with a carrier frequency of Ω ₁ (n) = ω ₁ (n) -ω ₂ (n) and a frequency deviation Δω (n), which is reflected from the reference reflective object 5, receive echo signals at a frequency of Ω ₁ (n) = ω ₁ (n) -ω ₂ (n) using a low-frequency receiving antenna 3.

Band-pass filtering of the received echo signals at a frequency of Ω ₁ (n) = ω ₁ (n) -ω ₂ (n) is performed.

Based on the known range R to the reference reflective object 5, the strobe boundaries are calculated to highlight the useful echo signal according to the formula:

Where

τ _u - the duration of the emitted frequency-modulated pulse,

- частота дискретизации АЦП.

- sampling frequency of the ADC.

являются техническими характеристиками гидролокатора.The values of τ _u and

are the technical characteristics of sonar.

The well-known procedure for calculating the coefficients of the impulse response of a matched filter for a frequency-modulated signal with a carrier frequency of Ω ₁ (n) = ω ₁ (n) -ω ₂ (n) and frequency deviation Δω (n) is performed (S.I. Baskakov, Radio Engineering Circuits and signals. - M.: Higher School, 1988.S. 105, S. 420).

Perform consistent filtering:

Where

z is the amplitude of the echo signals received by the low-frequency receiving antenna 3,

h is the impulse response of the matched filter,

m is the ADC sample number.

To estimate the amplitude-frequency distortions, the maximum value A (n) and the width ΔB (n) are estimated at a level of 0.5 from the value A (n) of the response of the matched filter B to the echo signal (Fig. 4) from the reference reflective object 5.

The value of A (n) makes it possible to evaluate the efficiency of converting the emitted pump signals into a signal at the difference frequency, and the value ΔB (n) - the frequency-selective properties of the aqueous medium, taking into account the influence of the equipment of the sonar parametric path.

After performing N sounding cycles, threshold processing of the obtained values is performed:

Where

- пороговое значение.

- threshold value.

Among the values ΔB lower than the threshold ΔB ₀ (9), a value with the largest parameter A is selected and the probe cycle number n ₀ corresponding to the selected value is stored.

As a result of the calibration, the optimal parameters of the pump signals ω ₁ (n ₀ ), ω ₂ (n ₀ ), Δω (n ₀ ), which provide the minimum amplitude-frequency distortion of the signal at the output of the matched filter, are selected, and the corresponding pulse characteristics of the matched filter are calculated to perform processing of received echoes.

When the sonar parametric path is used for radiation, pump signals with the optimal parameters ω ₁ (n ₀ ), ω ₂ (n ₀ ), Δω (n ₀ ) are used, and the impulse response coefficients of the matched filter are used for the optimal parameters of the pump signals to perform coordinated processing of the received echo signals .

An implementation of a device that implements the proposed method is illustrated in FIG. 5-9.

In FIG. 5 is a structural block diagram of a device for calibrating a sonar parametric path.

In FIG. 6 is a structural block diagram of a receiving unit.

In FIG. 7 is a structural block diagram of a transmitting unit.

In FIG. 8 is a structural block diagram of a digital signal processing unit.

Figure 9. presents a structural block diagram of a calibration unit.

The device (Fig. 5) consists of a high-frequency emitting antenna 2, a low-frequency receiving antenna 3, a reference reflective object 5, a transmitting unit 8, a receiving unit 9, a digital signal processing unit 10, a calibration unit 11, and a control unit 12.

The reference reflective object 5 is not connected, the input of the high-frequency emitting antenna 2 is connected to the output of the transmitting unit 8, the output of the low-frequency receiving antenna 3 is connected to the input of the receiving unit 9, the output of which is connected to the input of the block 10 for digital processing of echo signals, the output of block 10 is connected to the input of the block 11 calibration, the output of unit 11 is connected to the input of the control unit 12. The output of the control unit 12 is connected to the input of the receiving unit 9 and the transmitting unit 8, the digital processing unit 10.

The transmitting unit 5 (Fig. 6) consists of a controlled tone signal generator 13, a controlled frequency-modulated signal generator 14, a two-channel power amplifier 16, a two-channel load balancing device 17, a supply voltage converter 15, and a control device 18.

The controlled tone generator 13 and the controlled frequency-modulated signal generator 14 are made on the basis of microcircuits for direct digital synthesis of the AD9912 IC.

The receiving unit 9 (Fig. 7) consists of a band-pass filter 19, an amplifier 20, an analog-to-digital converter 21, and a control device 22.

Block 10 digital signal processing (Fig. 8) consists of an interface unit 23, managed matched filter 24, block 25 calculating the distance to the target. The digital processing unit 10, including the controlled matched filter 24, is implemented on the basis of the ALTERA EP3C16Q240C8 programmable logic integrated circuit and the ADSP 21368 signal processor.

The calibration block 11 (Fig. 9) consists of a block 26 for evaluating the response parameters of a matched filter, an accumulation block 27, a resolver 28. The calibration block 11 is implemented on an ADSP 21368 signal processor.

The control unit 12 consists of a processor device, random access memory and a crystal oscillator.

The device operates as follows. When calibrating the sonar parametric path in each sensing cycle by command pulses generated by the control unit, in the transmitting unit 8 (Fig. 6), two controlled generators 13 and 14 generate two electrical signals (tone and frequency-modulated) with the set parameters (carriers frequency and frequency deviation of the frequency-modulated signal), which are converted into acoustic pulses of a high-frequency radiating antenna 2 and radiated towards the reference reflection 5. Admission guide object and conversion into electrical signals are performed the receiving low-frequency antenna 3. The received electrical signals from the low frequency receiving antenna 32 are input to the receiving unit 9 (FIG. 7), which is performed bandpass filtering, amplification, and analog-to-digital conversion.

Next, the control unit 12 issues to the block 10 a command to set the coefficients of the matched filter corresponding to the parameters of the emitted pump signals. Then, the digitized data enters the block 10 of digital signal processing (Fig. 8), where the coordinated filtering and calculation of the range to the target are performed. From the output of block 10, the echo signal processing data enters the calibration block 11 (Fig. 9).

In the calibration block 11, the response parameters of the matched filter to the useful echo signal and the accumulation of the obtained data are estimated, as well as the selection of the optimal parameters of the pump signals from the data set for the totality of the sounding cycles performed. After that, the calculated optimal values of the pump signal parameters are sent to the control unit 12 for further operation of the sonar.

Let us explain the operation of block 11.

In block 26 for evaluating the response parameters of the matched filter, the maximum value of A and width ΔB are estimated at a level of 0.5 from the maximum value of the response of the matched filter. In block 27 of the accumulation is the accumulation of values of A and ΔB obtained for N sensing cycles. In the solving device 28, the accumulated values of A and ΔB are analyzed to select the optimal values of the pump signals for further operation of the sonar.

A method and device for calibrating the parametric path of a sonar is proposed, which allows to reduce the amplitude-frequency distortions of the response of the matched filter to a useful echo signal by optimizing the parameters of the pump signals emitted into the aquatic environment: carrier frequency of the pump tone, carrier frequency and frequency deviation of the frequency modulated pump signal.

Thus, the technical result of the invention is achieved.

Claims (2)

1. The method of calibrating the parametric path, in which: calibrate the parametric path of the sonar in a given area of the water area, place a reference reflective object at a known distance from the sonar antennas, use two pump signals for a radiation - a tone signal with a carrier frequency of ω ₂ and a frequency-modulated signal with a carrier frequency ω ₁ and a frequency deviation Δω, within the passband of the emitting high-frequency sonar antenna, they emit signals at frequencies ω ₁ and ω ₂ in the direction of the reference signal pressing object, receive echo signals at the differential frequency

using a low-frequency receiving antenna, they perform band-pass filtering of the received echo signals, evaluate the backscattering coefficient from the reference reflective object in the reception frequency band, characterized in that N sounding cycles are performed, for calibration in each sounding cycle, set the pump signal parameters for radiation in the direction of the reference reflective object - the carrier frequency ω ₁ (n) and the frequency deviation Δω (n) of the frequency-modulated signal and the carrier frequency ω ₂ (n) of the tone signal,

, calculate the coefficients of the matched filter based on the parameters of the emitted pump signals; estimate the maximum value of A (n) and the width ΔB (n) at a level of 0.5 of the value A (n) of the response of the matched filter to the echo signal from the reference reflective object, after performing N sounding cycles, the threshold processing of the obtained values ΔB (n) ≤ΔB ₀ , among the values ΔB lower than the threshold ΔB ₀ , the value with the largest parameter A is selected and the probe cycle number n ₀ corresponding to the selected value is stored, the optimal parameters of the pump signals ω ₁ (n ₀ ), ω ₂ (n ₀ ), Δω ( n _0), providing minimum amplitude-frequency IC CONTROL signal at the output of the matched filter, calculate the coefficients of the impulse response of the matched filter for optimal pump signal parameters and storing them at work parametric tract sonar radiation using pump signals with optimal parameters ω ₁ (n _0), ω ₂ (n _0), Δω (n ₀ ), to perform consistent processing of the received echo signals, the impulse response coefficients of the matched filter are used for the optimal parameters of the pump signals. 2. Device for calibrating the parametric path, containing a reference reflective object, a high-frequency emitting antenna and a low-frequency receiving antenna, a transmitting unit, a receiving unit, a digital signal processing unit, a control unit, while the reference reflective object is not connected, the input of the high-frequency radiating antenna is connected to the output of the transmitting unit, the output of the low-frequency receiving antenna is connected to the input of the receiving unit, the output of which is connected to the input of the digital processing unit of the echo signals, the output of which ohm is connected to the input of the control unit, the output of the control unit is connected to the input of the receiving unit and the transmitting unit, the digital processing unit, characterized in that the transmitting device uses two controlled oscillators to generate pump signals, the digital signal processing unit uses a controlled coordinated filter, in addition a calibration unit is introduced, the input of the calibration unit being connected to the output of the digital signal processing unit, the output of the calibration unit being connected to the input of the control unit.

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