RU2805137C1 - Method of noise direction finding with determination of displacement of surface ship - Google Patents

Abstract

FIELD: hydroacoustics.

SUBSTANCE: invention is intended for recognizing sea vessels of different displacements by their noise emissions. The method consists of standard noise direction finding procedures with the selection of low-frequency signal fluctuations for analysing the ship's pitch. When implementing the method, the sea state and sound speed are measured, and the signal is band-pass filtered with an adaptive choice of frequency band, depending on the measured parameters.

EFFECT: providing bandpass filtering in noise direction finding with a geometric mean frequency, optimal for further determining the displacement of a surface ship under current hydroacoustic surveillance conditions.

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Description

The invention relates to the field of hydroacoustics and is intended for recognizing sea vessels of different displacements by their noise emissions.

It is known [Boroday I.K. and others. Applied problems of ship dynamics in waves // Shipbuilding. - 1989. - T. 258. - P. 539-543, Boroday I.K., Netsvetaev Yu.A. Seaworthiness of ships // Leningrad: Shipbuilding. - 1982. - T. 288], that the process of rolling a ship under the dynamic influence of wind waves on it is, in the general case, a random process with a spectrum described by a Rayleigh curve with a pronounced maximum. This maximum corresponds to the main period of the ship's rocking, which is determined by its displacement.

In terms of hydroacoustics, the rolling of surface ships leads to the formation of low-frequency fluctuations of the noise signal received by hydroacoustic means [Kudryavtsev A.A., Luginets K.P., Mashoshin A.I. On amplitude modulation of underwater noise emission from civil ships // Acoustic Journal. - 2003. - T. 49. - No. 2. - P. 224-228]. The nature of these fluctuations in simple models is considered quasi-harmonic, similar to the spectrum of motion. Therefore, the average value of the period of fluctuations of the noise emission signal will be different for ships of different displacement under the same conditions. Methods for determining the displacement of surface ships during their noise direction finding are based on this phenomenon.

A known method and device for its implementation [Mashoshin A.I. Optimization of a device for detecting and measuring parameters of amplitude modulation of underwater noise emission from sea vessels // Acoustic Journal. - 2013. - T. 59. - No. 3. - P. 347-353]. The method processes the ship's noise signal in order to detect and analyze the spectrum of its low-frequency fluctuations, on the basis of which the ship's displacement is determined. When processing a noise signal according to this method, the full frequency band of the premium path is used, which is a disadvantage. Field studies [Konson A.D., Volkova A.A. Spectral properties of fluctuations of underwater noise emission from sea vessels // Applied technologies of hydroacoustics and hydrophysics. - 2018. - P. 427-429] showed that low-frequency fluctuations, based on the analysis of which the ship’s displacement is determined, are not present in the entire frequency band of the receiving path, but can only appear in a certain limited frequency range. In this case, isolating fluctuations using the entire frequency band leads to a weakening of the effect of signal fluctuations, and, in the limit, to the impossibility of determining the period of fluctuations and, consequently, the displacement of the ship.

A method and device for its implementation are known [Volkova A.A., Konson A.D. RF Patent No. 2694270 dated July 11, 2019. A device for determining the displacement of a surface ship during its noise direction finding. IPC G01S 3/80]. This method implements signal processing in noise direction finding, in which low-frequency fluctuations are identified for a set of frequency bands, for each of which the same type of fluctuation spectrum analysis procedures are repeated. The displacement of a surface ship is determined at the final stage of the analysis if the period of fluctuations could be determined for at least one of the frequency bands. The method partially eliminates the disadvantage of the method [Mashoshin A.I. Optimization of a device for detecting and measuring parameters of amplitude modulation of underwater noise emission from sea vessels // Acoustic Journal. - 2013. - T. 59. - No. 3. - P. 347-353], however, this significantly increases the number of arithmetic operations performed, which leads to an increase in requirements for computing resources.

The closest analogue in terms of the procedures performed to the proposed invention is the method [Konson A.D., Volkova A.A. RF Patent No. 2645013 dated February 15, 2018. A method for determining the displacement of a surface ship during its noise direction finding. IPC G01S 3/80], which can be mistaken for a prototype.

The prototype method contains the following operations:

reception of a noise signal from a surface ship by a hydroacoustic antenna from fixed directions horizontally and vertically in the frequency range of the receiving path,

analog-to-digital signal conversion,

detection,

low-pass filtering,

calculation of the spectrum of fluctuations caused by rolling,

fluctuation spectrum analysis,

determination of the displacement of a surface ship.

The disadvantage of this method is similar to the disadvantage of the method [Mashoshin A.I. Optimization of a device for detecting and measuring parameters of amplitude modulation of underwater noise emission from sea vessels // Acoustic Journal. - 2013. - T. 59. - No. 3. - P. 347-353], and lies in the fact that processing during noise direction finding in the full frequency band of the pre-receiver path is not optimal for further highlighting low-frequency signal fluctuations, and can lead to the impossibility of determining the displacement of a surface ship.

The objective of the proposed method is to create optimal signal processing in noise direction finding for determining the displacement of surface ships.

To solve the problem, a method of noise direction finding with determination of the displacement of a surface ship, which contains the reception of a noise signal of a surface ship by a hydroacoustic antenna from the horizontal direction α and the vertical direction β in the frequency range from f _min to f _max , analog-to-digital signal conversion, detection, low-frequency filtering , calculation of the spectrum of fluctuations caused by rolling, analysis of the spectrum of fluctuations, determination of the displacement of a surface ship,

new features have been introduced, namely:

measure sea waves σ in meters,

measure the speed of sound C at the antenna installation location,

determine a set of coefficients K(f)=4πfσsinβ/C for a set of frequencies f in the range from f _min to f _max , with fixed parameters σ, β, C, where σ is the measured sea state, β is the signal reception angle in the vertical plane, C - measured speed of sound, π - number pi,

select one frequency f _opt from the set for which the coefficient K(f) takes the greatest value of those that are not more than one f _opt =argmax{K(f)≤1},

and bandpass filtering of the signal with the average frequency of the passband equal to the selected frequency f _opt is carried out before detection.

The technical result of the invention is to provide bandpass filtering in noise direction finding with a geometric mean frequency, optimal for further determining the displacement of a surface ship in the current conditions of hydroacoustic surveillance.

We will show the possibility of achieving the specified technical result using the proposed method.

In the work [Konson A.D., Volkova A.A. Modulation of the noise signal when the ship rolls due to fluctuating interference of rays // Fundamental and Applied Hydrophysics. - 2023. T. 15. - No. 4. - P. 74-81] a large complex of analytical, simulation and experimental studies was carried out on the phenomenon of the formation of low-frequency fluctuations of the noise signal during the rolling of a surface ship. Research has shown that the phenomenon of signal fluctuations when the ship rocks can be explained by the formation of fluctuating interference of rays propagating from a vertically rocking source. In this case, the spectral and energy characteristics of the signal fluctuations depend on the overall conditions, which are characterized by the value of the coefficient K. According to this work, the coefficient K is written as K=2kσsinβ, where - wave number, f - signal frequency, C - sound speed, σ - sea state in meters, β - signal reception angle in the vertical plane, π - pi number. In terms more convenient for this application, the expression for K can be rewritten as: K=4πfσsinβ/C. The work shows that the value of the coefficient K divides the physical process of the formation of low-frequency fluctuations into two types. For values of K≤1, the results of observing the process of signal fluctuations can be identified with the process of ship rocking. In this case, the period of fluctuations corresponds to the rolling period of the ship, which makes it possible to determine the displacement. In this case, the maximum fluctuation power is achieved at K=1. For values of K>1, the spectrum of low-frequency signal fluctuations no longer corresponds to the spectrum of the pumping process, which makes determining the displacement impossible.

The specified new knowledge obtained in the work [Konson A.D., Volkova A.A. Modulation of the noise signal when the ship rolls due to fluctuating interference of rays // Fundamental and Applied Hydrophysics. - 2023. T. 15. - No. 4. - P. 74-81], allows you to create a method of noise direction finding that will adaptively adapt to the current conditions of hydroacoustic observation to determine the displacement in the best possible way. To do this, it is necessary that the set of parameter values included in the expression for the coefficient K allows for the value of the coefficient K to be optimal for the subsequent determination of displacement, that is, close to unity, but not exceeding it. The expression K includes the following parameters: signal frequency, sea state, signal reception angle and sound speed. The signal reception angle parameter is measured in the procedure of the restrictive part of the claims. The parameters sea waves and sound speed represent the current conditions of hydroacoustic observation, and can be measured, for which appropriate procedures are introduced into the method. Thus, the parameters reception angle, sea state and sound speed become fixed numbers that cannot be changed. Then, to ensure the optimality of the coefficient K, it is necessary to select and then use in noise direction finding the last parameter included in the expression for K, namely the signal frequency. For this purpose, the method includes a procedure for determining a set of coefficients K for different signal frequencies and a procedure for selecting one frequency f _opt at which the coefficient K becomes optimal. The selected frequency is the signal frequency that is optimal for further determining the displacement of a surface ship under current hydroacoustic surveillance conditions. Due to the fact that in noise direction finding processing is carried out not for a tonal signal, but for a noise signal, a band-pass filtering procedure with an average passband frequency equal to the selected frequency f _opt is introduced into the method. Thus, the noise direction finding method is adjusted to the optimal determination of the surface ship’s displacement.

The essence of the invention is illustrated in Fig. 1, which shows a block diagram of a device that implements the proposed method.

The method is technically implemented in hardware and software according to the block diagram shown in Fig. 1. To implement the method, the following are connected in series: antenna 1, analog-to-digital conversion (ADC) unit 2, bandpass filter 3, amplitude detector 4, low-frequency filter 5, spectrum analyzer 6, displacement determination unit 7. In addition, the circuit contains a wave measurement unit 8, a sound speed measurement unit 9, and a frequency selection unit 10. The outputs of blocks 8 and 9 are connected to the first and second inputs of block 10. The second output of block 1 is connected to the third input of block 10, and the output of block 10 is connected to the second input of block 3.

In operational dynamics, the proposed method is implemented as follows. Previously, in block 8, the sea state is measured, and in block 9, the speed of sound is measured at the antenna installation site. Measurement of waves σ can be carried out using technical means, for example weather buoys. Excitement is measured either in meters, which is required to implement the method, or in points. Conversion from points to meters is carried out on a nine-point scale of excitement [Directory of the watch officer / Ed. Ph.D. Naval Sciences Rear Admiral A.P. Pronichkina. M: Military Publishing House of the USSR Ministry of Defense, 1975]. To measure the speed of sound C, one of the instruments described in [Komlyakov V.A. Shipborne means of measuring the speed of sound and modeling acoustic fields in the ocean. SPb.: Science. - 2003. - 357 p.]. The measured values of the wave magnitude σ and the speed of sound C are sent to block 10 for use in further work. When the waves or the installation location of the antenna change, a new measurement of the waves or speed of sound is carried out, and in block 10 the updated values replace the previous ones.

The noise signal of the object, received by antenna 1, enters block 2, where its analog-to-digital conversion is carried out [Rabiner L., Gould B. Theory and application of digital signal processing. - Ripol Classic, 1978]. The angle of arrival of the signal in the horizontal α and vertical β planes is determined either by mechanical rotation of the antenna in space, or by electrical compensation of the directivity characteristics [Kolchedantsev A.S. Hydroacoustic stations // Leningrad: Shipbuilding. - 1982. - T. 237]. In any case, the angle of arrival of the signal in the vertical plane β enters the frequency selection block 10. And the signal in digitized form from block 2 enters bandpass filter 3.

In block 10, the set of coefficients K(f)=4πfσsinβ/C is calculated for a set of frequencies f in the range from the minimum possible to the maximum possible values determined by the antenna parameters. It is known [Balyan R.Kh., Batanogov E.V., Bogorodsky A.V. Terminological dictionary - reference book on hydroacoustics // Leningrad: Shipbuilding. - 1989, Smaryshev M.D. Directivity of hydroacoustic antennas // Leningrad: Shipbuilding. - 1973. - T. 278], that the minimum frequency of the received signal is determined by the size of the aperture of the entire antenna, and the maximum frequency by the distance between the individual receiving elements. The number of frequencies in a set is determined empirically, taking into account the frequency range and computing resources. When calculating the set of coefficients K(f), in addition to the mathematical constant π=3.14, the following are used:

- wave magnitude σ, measured in block 8;

- speed of sound C, measured in block 9;

- angle of arrival of the signal in the vertical plane β from block 1.

Next, in block 10, one frequency f _opt is selected from the set for which the coefficient K(f) takes the largest value of those that are not more than one f _opt =argmax{K(f)≤1}. The selected frequency value goes to bandpass filter 3.

The table shows an example of the values of the coefficient K(f) for a set of frequencies f at fixed values σ=1 m, β=3°, С=1500 m/s.

In this case, the frequency of 2000 Hz will be chosen as f _opt , since it is for this frequency that the coefficient K takes its maximum value, but not exceeding one.

Bandpass filter 3 adjusts its passband based on the value of the average frequency f _opt received from block 10. The bandwidth can be selected equal to one octave when the final frequency of the band is twice the initial frequency, which provides good noise immunity [Volkova A.A. ., Konson A.D., Nikulin M.N. Estimating the distance to the source of a noise signal using the “optimal frequencies” method using bandpass filters // Hydroacoustics. - 2015. - No. 22. - P. 43-52]. Then the initial frequency of the passband is determined as , and the final frequency is as . After setting the bandwidth in block 3, bandpass filtering of the signal received from block 2 is carried out.

After bandpass filtering, the signal sequentially enters the amplitude detector 4, low-pass filter 5 and spectrum analyzer 6. Both a quadratic and a linear detector can act as a detector for isolating low-frequency signal fluctuations [Kharkevich A.A. Spectra and analysis. - 1962]. With low-frequency filtering, an analysis band must be achieved in which low-frequency signal fluctuations caused by heaving during sea surface waves are observed. The parameters of such a band are known from [Mashoshin A.I. Optimization of a device for detecting and measuring parameters of amplitude modulation of underwater noise emission from sea vessels // Acoustic Journal. - 2013. - T. 59. - No. 3. - P. 347-353]. In the spectrum analyzer, to optimize the calculation, the fast Fourier transform procedure is used, with a number of samples equal to the nearest power of two [Rabiner L., Gould B. Theory and application of digital signal processing. - Ripol Classic, 1978]. The resulting spectrum of low-frequency signal fluctuations is sent from block 6 to block 7 to determine the displacement.

In block 7, the resulting spectrum is analyzed according to the prototype method, as a result of which the frequency of low-frequency signal fluctuations and its period are determined. Next, using the tabular dependence of the displacement on the period of low-frequency signal fluctuations, the displacement of the surface ship is determined. The method for determining the relationship between the displacement of a surface ship and the period of its rolling is known, for example, from [Sizov V.G. Theory of the ship // Odessa: Phoenix. - 2003. - T. 5] (section 7.2.2 and, in particular, table 7.2 - Periods of rolling of ships of various types). The rolling period, in turn, is the reciprocal of the frequency of signal fluctuations [Balyan R.Kh., Batanogov E.V., Bogorodsky A.V. Terminological dictionary - reference book on hydroacoustics // Leningrad: Shipbuilding. - 1989].

All of the above allows us to consider the problem of the invention solved. A method for noise direction finding is proposed, which quickly adjusts the signal filtering frequency band in such a way that further processing makes it possible to best determine the displacement of a surface ship under the current conditions of hydroacoustic surveillance.

Claims (1)

A method for noise direction finding with determination of the displacement of a surface ship, containing the reception of a noise signal of a surface ship by a hydroacoustic antenna from the horizontal direction α and the vertical direction β in the frequency range from f _min to f _max , analog-to-digital signal conversion, detection, low-frequency filtering, calculation of the spectrum of fluctuations caused by pitching, analysis of the spectrum of fluctuations, determination of the displacement of a surface ship, characterized in that they measure the sea state σ in meters, measure the speed of sound C at the antenna installation site, determine the set of coefficients K(f) = 4πfσsinβ/C for a set of frequencies f in the range from f _min to f _max , with fixed parameters σ, β, C, where σ is the measured sea state, β is the signal reception angle in the vertical plane, C is the measured speed of sound, π is the number pi, select one frequency f _opt from the set, for in which the coefficient K(f) takes the largest value of those that are not more than one f _opt =argmax{K(f)≤1}, and bandpass filtering of the signal with the average frequency of the passband equal to the selected frequency f _opt is carried out before detection.

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