RU2797161C1 - Methods for determining coordinates of a sea target emitting noise - Google Patents

Abstract

FIELD: hydroacoustics.

SUBSTANCE: invention is related to methods and devices for detecting marine targets by their noise emission, and more specifically to methods for determining the coordinates of targets using interference maxima in the autocorrelation function of target noise. In the method, a broadband target signal is detected at the output of the noise direction finder, its autocorrelation function (ACF) is measured, in which narrow-band interference maxima (IM) are detected, from which the IM with the highest level is selected and its abscissa is stored (i.e., the position on the delay axis). With a known distance to the target, for it and a plurality of depths in the range of possible depths of the target, the ray structure of the target signal is calculated using the ray program for calculating the acoustic field of the source with which the abscissas of one to three MIs with the highest level in the ACF are calculated. As the target depth, the depth from the plurality of depths for which the MI abscissa with the highest level in the measured ACF turned out to be closest to one of the calculated MI abscissa is chosen.

EFFECT: improved accuracy of determining the coordinates of a target emitting noise.

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Description

The invention relates to the field of hydroacoustics, and in particular to methods and devices for detecting marine targets by their noise emission.

One of the topical practical problems of hydroacoustics is the determination of the coordinates of a noisy marine target (hereinafter referred to as the target) according to the data of the noise direction finding station (hereinafter referred to as the NSS). To solve this problem, a large number of methods are known, a review of which is given in [1].

One of the methods is based on the use of the measured autocorrelation function (hereinafter - ACF) of a broadband acoustic signal (hereinafter - signal) to determine the coordinates (distance and depth) of the signal source [1-8]. Information about the coordinates of the signal source (target) in the measured ACF is contained in the location on the abscissa (time) axis of narrow-band interference maxima (hereinafter referred to as MI), due to the interference of correlated source signals that came to the input of the receiving hydroacoustic antenna (hereinafter referred to as the antenna) of the NPS along different beams . Each pair of rays in the ACF (with a sufficient signal-to-noise ratio - SIR) corresponds to one MI with a width equal to the reciprocal of the effective bandwidth of the signal at the antenna input, and a position on the abscissa axis equal to the absolute value of the difference in the signal propagation times along the interfering rays [9 ]. In FIG. As an illustration, Figure 1 shows the ACF of the source signal that arrived at the antenna via four acoustic beams.

Determining the coordinates of the signal source by the considered method consists in finding such a position of the signal source in terms of distance and depth, for which the calculation of the parameters of acoustic rays using the ray program [10] shows the presence in the ACF at the output of the MI antenna, the number of which and the location on the abscissa axis is as close as possible to the number and location of IM in the measured ACF.

The main disadvantage of the described method is the ambiguity of the result of determining the coordinates of the signal source. Inventions [7, 8] are devoted to eliminating this disadvantage. However, they cope with the problem only in certain limited conditions.

The conducted studies have shown that the ambiguity of the result manifests itself much less often if one of the two coordinates of the source is known - the range or the depth. This fact is illustrated in Fig. 3, where for conditions of continuous acoustic illumination in the deep sea with the vertical sound velocity distribution shown in FIG. Figure 2 shows the dependences on the distance between the source and receiver (abscissa axis) and the source depth (graph parameter in meters) of the abscissa of the highest level maximum in the ACF, due to the relative delay (delay) of the two most powerful beams arriving at the antenna. With rare exceptions, the highest level maximum in the ACF is formed due to the interference of the direct beam and the beam that is singly reflected from the surface.

From a consideration of FIG. 3 follows:

- with a known depth of the source, there is a one-to-one correspondence between the distance to the source and the abscissa of the highest level maximum in the ACF;

- at a known distance to the source, there is a one-to-one correspondence between the depth of the source and the abscissa of the highest maximum in the ACF;

This fact makes it possible to determine the depth of the source if the distance to it is known and, conversely, to determine the distance to the source if its depth is known.

As a prototype method, we choose the invention [7]. In FIG. 4 shows its block diagram. The processing of incoming information is carried out on a computing device connected to the NSS, along two parallel branches simultaneously.

The first (left) branch includes sequentially performed operations for detecting a broadband target signal at the antenna output (block 1.1); measuring the ACF set of the detected broadband target signal at time intervals that make up the analysis interval (block 1.2); detection in each measured ACF from the ACF set of narrow-band MIs and measurement of their abscissas (block 1.3); combining the MI abscissas found in all measured ACFs of the analysis interval into a single array (block 1.4). Performing the above operations ensures the formation of an array of all MIs measured over the analysis interval and ready for comparison with the calculated data generated by the blocks of the second branch.

The second branch (right) includes determining the source class, measuring the pressure of its signal at the output of the NLS receiving path and using them to determine the area of the possible location of the target in the “distance - depth” space (block 2.1); calculations for each point of this area, taking into account the current hydroacoustic conditions of the beam structure of the signal at the input of the NLS antenna (block 2.2); calculation for each point of this area and for each pair of rays from the calculated ray structure of the abscissa and SRF values of the calculated MIs generated by this pair of rays (block 2.3) and the operation of forming for each point of the area of the array of calculated MIs for which the calculated SFRs exceed the specified threshold value for their detection in the ACF (block 2.4). The operations of the second branch can be performed once for the current state of hydrological conditions, which determines the beam structure of the signals at the antenna input. The execution of operations of the second branch ensures the formation of an array of calculated data ready for comparison with the measurement results generated by the first branch.

The comparison is performed by sequentially located blocks 3 and 4, performing the operations of determining in the arrays of calculated IMs formed for each point in space, the number of IMs, the abscissas of which, taking into account the accuracy of their measurement, are equal to the abscissas of the IMs in the combined array of IMs found in the entire set of ACFs measured over the interval analysis (block 3) and, finally, the operation of determining the coordinates of the target by selecting the coordinates of that point of the possible location of the target in the “distance - depth” space, which corresponds to the largest number of calculated MIs, the abscissas of which are equal to the abscissas of the MIs in the combined array of MIs found in the entire set measured ACFs (block 4).

The disadvantage of the prototype method, despite the measures taken, is the high probability of obtaining a multivalued solution.

The technical problem to be solved is to increase the operational characteristics of the direction-finding station.

The technical result provided by the invention is an increase in the accuracy of determining the coordinates of a noisy marine target.

The specified technical result is achieved in cases where one of the two coordinates of the target is known - distance or depth. These cases are quite common in practice. For example, the distance to a detected target can be determined in the sonar mode or by mutual positioning using hydroacoustic communication signals [11]. The target depth, as a rule, is known when several marine objects interact in a group [12].

As a result, 2 independent methods are declared:

- a method for determining the depth of a sea noisy target, the block diagram of which is shown in FIG. 5;

- a method for determining the distance to a sea noisy target, the block diagram of which is shown in Fig. 6.

In both methods, as in the prototype method, the processing of the input signal is carried out in two parallel branches. The first (left) branch, identical for both methods, includes sequentially performed operations:

- detection of a broadband target signal at the output of the NLS receiving path (block 1.1);

- measurement of the ACF of the detected broadband target signal (block 1.2);

- detection of narrow-band MIs in the measured ACF and measurement of their abscissas and amplitudes (block 1.3);

- selection from the array of detected MIs, MIs with the highest amplitude, determination and memorization of its abscissa (block 1.4).

The second branch (right) for the method for determining the depth of a sea noisy target includes the following operations (Fig. 5):

- determination of the distance to the target by one of the known [1, 11] methods (block 2.1);

- calculation for the measured distance of the beam structure of the signal for each of the set of depths in the range of possible target depths (block 2.2);

- calculation of the ACF for each depth from a set of target depths, detection of one or three MIs with the highest amplitude in the calculated ACFs and determination of their abscissas (block 2.3).

In block 3 in Fig. 5, the abscissa of the highest MI in the measured ACF is compared with the abscissa of MI in the calculated ACF for each depth from the set of depths. The depth for which the MI abscissa with the highest amplitude in the measured ACF is closest to one of the MI abscissas in the calculated ACF is selected as the target depth.

The second branch (right) for the method of determining the distance to the target includes the following operations (Fig. 6):

- calculation for the known depth of the target of the beam structure of the signal for each of the set of distances in the range of possible distances to the target (block 2.1);

- calculation of the ACF for each distance from a set of distances, detection of one or three MIs with the highest amplitude in the calculated ACFs and determination of their abscissas (block 2.2).

In block 3 in Fig. 6, the abscissa of the largest MI in the measured ACF is compared with the abscissa of the MI in the calculated ACF for each distance from the set of distances. The distance to the target is chosen as the distance for which the MI abscissa with the highest level in the measured ACF is closest to one of the MI abscissas in the calculated ACF.

Examples of the implementation of the proposed methods:

1) in the group use of autonomous uninhabited underwater vehicles (for example, in the problem of searching for hydrocarbon deposits on the seabed [12]), it is necessary to constantly control the mutual distance between the vehicles. Since the depths of the devices in this are known (given), the inventive method allows to determine the distance to the device from the measured abscissa of the largest amplitude maximum in the noise ACF;

2) if it is necessary to determine the immersion depth of the detected underwater noise source, measure the distance to it in the active mode, and then determine its depth using the inventive method.

The inventive method for determining the depth of an object has been experimentally tested. The experiment was carried out under conditions of continuous acoustic illumination with a vertical sound velocity distribution shown in Fig. 2. The source of the broadband (in the band 1-5 kHz) acoustic signal was at a depth of 200 m. The SNR at the output of the receiving path of the NSS was 15 dB.

The source signal at the output of the NLS receiving path was subjected to autocorrelation analysis. The measured ACF is shown in the graph of Fig. 7, along the abscissa axis of which time is plotted in ms, along the ordinate axis - the ACF level in relative units. In the measured ACF, the largest MI was distinguished in terms of amplitude, the abscissa of which is equal to 13.4 ms.

For the experimental conditions, the calculation of the ray structure of the signal field was performed and, based on its results, the abscissa of the largest MI in the ACF depending on the depth of the source was calculated, which is shown in Fig. 8.

Entering the graph in Fig. 8 with an MI abscissa of 13.4 ms in the measured ACF, we obtain an estimate of the source depth of 200 m, which corresponds to the experimental conditions.

Thus, the claimed technical result - improving the accuracy of determining the coordinates of a noisy target - can be considered achieved.

Information sources:

1. Mashoshin A.I. Synthesis of the optimal algorithm for passive determination of the distance to the target // Marine Radioelectronics. 2012. No. 2 (40). pp. 30-34.

2. Hassab I. C. Contact Localization and Motion Analysis in the Ocean Environment: a Perspective // IEEE Journal of Oceanic Engineering. 1983 Vol. OE-8, #3. P.136-147.

3. Quazi A.H., Lerro D.T. Passive localization using time-delay estimates with sensor positional errors // JASA. 1985 Vol. 78, No. 5. P.1664-1670.

4. Worthmann B.M., Song H.C., Dowling D.R. High frequency source localization in a shallow ocean sound channel using frequency difference matched field processing // Journal Acoust. soc. Am. 2015. Vol. 138. P.3549.

5. Orlov E.F., Fokin V.N., Sharonov G.A. Investigation of the parameters of interference modulation of broadband sound in the deep ocean // Acoustic journal. 1988. Vol. 34, no. 5. S. 902-907.

6. Lazarev V.A., Orlov E.F., Fokin V.N., Sharonov G.A. Frequency dependence of the parameters of interference modulation of broadband sound in a shallow sea // Acoustic journal. 1989. Volume 35, no. 4. S. 685-688.

7. RF patent No. 2690223.

8. RF patent No. 2724962.

9. Mashoshin A.I. Noise immunity of the selection of maxima in the correlation function of a broadband noise signal of a marine object, due to multipath signal propagation in the aquatic environment // Acoustic journal. 2001. Volume 47, No. 6. S. 823-829.

10. Hydroacoustic calculations for a noise direction finding station. Authors Marasev S.V., Mashoshin A.I. Registration certificate No. 2021617661 dated April 26, 2021 Application No. 2021615792 dated April 22, 2021. State date. registration on April 26, 2021. The copyright holder is the Joint Stock Company Concern Central Research Institute Elektropribor.

11. Koryakin Yu.A., Smirnov S.A., Yakovlev G.V. Ship hydroacoustic equipment. Status and current problems // St. Petersburg: Nauka, 2004.

12. Sakharov V.V., Chertkov A.A., Tormashev D.S. Algorithm for optimal planning of group interaction of robots // Morskoy vestnik. 2014. No. 4 (52). pp. 119-122.

Claims (1)

A method for determining the depth of a noisy sea target, which includes detecting a broadband target signal at the output of a direction-finding station, measuring its autocorrelation function (ACF), detecting narrow-band interference maxima (MI) in the measured ACF, determining the abscissa of the MI with the highest amplitude, characterized in that the distance to target using one of the known methods, for the measured distance and the set of depths in the range of possible depths of the target, using the ray program for calculating the acoustic field of the source, the ray structure of the target signal is calculated, using which the ACF of the source signal is calculated, in which one to three IMs with the highest amplitude are detected, their abscissas are determined, from the set of target depths the depth is selected for which the MI abscissa with the highest amplitude in the measured ACF is closest to one of the MI abscissas in the calculated ACF.

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