RU2830066C1 - Method of determining coordinates and parameters of movement of underwater objects during multistatic sonar - Google Patents

Abstract

FIELD: hydroacoustics.

SUBSTANCE: invention relates to hydroacoustics, namely to methods and devices for detecting underwater objects in a multistatic sonar system. Bearing and distance to detected target are determined based on measurement by directional spatially non-oriented by angle receiver of differences of time and direction of detection of probing and echo signals taking into account known coordinates of emitter and receiver; target course and speed are determined based on the time distance measurement between the maxima in the echo signal caused by the probing signal reflection from the characteristic target bright points (reflectors), and determining the Doppler parameter of the echo signal relative to the probing signal.

EFFECT: determination of coordinates and motion parameters of a target with one receiver of a multistatic sonar system in one cycle of emitting a probing signal with an unknown angular orientation of the receiver in space.

1 cl, 3 dwg

Description

The invention relates to the field of hydroacoustics, namely to methods and devices for detecting underwater objects using multistatic sonar.

As is known [1,2], multistatic (multi-position) hydrolocation differs from monostatic in that the hydroacoustic emitters and hydroacoustic receivers are spaced apart, which increases the detection distance of underwater objects. When using one emitter and one receiver spaced apart, hydrolocation is called bistatic.

The use of multistatic sonar is especially relevant when searching for submarines (PL) using aviation radio-hydroacoustic systems [3]. This search consists of an anti-submarine aircraft placing a field of radio-hydroacoustic buoys (RHB), which should detect the PL when it passes through the RHB field and the fact of detection, together with coordinates and, preferably, movement parameters, should be reported to the aircraft via radio channel.

Until recently, passive RGB were used mainly to solve the problem. However, due to the steady decrease in submarine noise, the detection distance using RGB is constantly decreasing, which requires increasing the density of the buoy field and leads to an increase in the cost of the search operation. In view of this, in recent years there has been a steady trend towards switching to submarine search in an active multistatic mode, in which non-directional (omnidirectional) emitting RGB and directional receiving RGB are used.

When switching to multistatic search, it became necessary to continuously determine the orientation of the receiving antenna relative to the direction to the geographic north, since the receiving antennas of the RGB, supported by buoyancy at a given depth, freely rotate around the vertical axis. Given the requirements for low cost and limited volume for placing equipment inside the RGB case, the simplest magnetic compass is used as orientation equipment, which has a low accuracy of determining the direction, and significantly depends on the geographic latitude. At high latitudes, the accuracy provided by the magnetic compass becomes unacceptable, which is a problem when solving problems in the multistatic mode.

When searching for a submarine in multistatic sonar mode, when the emitting and receiving RGB are separated by a large distance, significant errors in determining the bearing of the detected submarine do not allow determining the distance to it and the direction of its movement.

When searching in passive mode, this problem existed, but was not decisive, since when detecting a submarine by a specific RGB with a small detection range, it was clear that the submarine was in the small vicinity of the buoy and a specific direction to it was not necessary, due to the fact that the submarine's trajectory was successfully restored by the sequence of operation of individual RGB, the coordinates of which could be determined using satellite navigation system (SNS) receivers installed on the RGB, or by direction finding the RGB using an extended antenna installed on the aircraft [3].

When searching for a submarine in multistatic sonar mode, when the emitting and receiving RGB are separated by a large distance, significant errors in determining the bearing of the detected submarine do not allow determining the distance to it and the direction of its movement.

Taking into account the above, the problem of how to determine the coordinates and motion parameters of a detected underwater object with high accuracy in the multistatic sonar mode without equipment for determining the orientation in space of the receiving RGB antennas (active RGB, being non-directional, do not require orientation) is relevant.

The use of multistatic sonar [1,2] and radar [4,5] to solve various problems is widely known. The paper [6] considers the problem of underwater situation illumination using a submarine hydroacoustic complex as a transmitter and a RGB field as receivers. The paper [7] proposes to eliminate the ambiguity of the detected target bearing, which is typical for linear towed antennas, by using 2 ships equipped with hydroacoustic stations with flexible extended towed antennas and detecting targets in the bistatic sonar mode. The paper [8] considers a system consisting of a directional transmitter-emitter and a directional receiver spaced apart in space, provided that the target is outside the receiver's visibility zone. Due to this, the receiver detects an echo signal reflected not from the target, but from the transmitter-emitter. In all of the listed analogs, the receivers are considered to be oriented in space, i.e. the above problem is not a concern.

The method for determining target coordinates described in [4, pp. 33-34] was chosen as the prototype method. The prototype method is illustrated in Fig. 1, in which:

1 – non-directional emitter (hereinafter referred to as the emitter);

2 – directional receiver, oriented in space;

3 – goal;

– distance between the emitter and the receiver;

– distance between the emitter and the target;

– distance between the target and the receiver;

– the angle with its vertex at the location of the receiver between the bearings to the emitter and the target.

The prototype method is as follows. There are a non-directional emitter 1 and a receiver 2 with a directional antenna, which are spaced apart and stationary with known coordinates. Moreover, the receiver is spatially oriented, i.e., it is equipped with inertial navigation devices that ensure control of the current direction to the geographic north.

Emitter 1 emits a probing signal (PS), which is reflected from target 3. Receiver 2 receives the PS, measures and stores the bearing. and time its reception. Then it receives an echo signal (ES), measures and remembers the bearing and time his reception.

Using the measured data, a system of equations is formed

Where

- the difference in reception times of the echo signal and the probing signal;

- the difference in bearings between the reception of the echo signal and the probing signal;

– the speed of sound in water.

The first equation in (1) relates the distances traveled by the echo signal and the probing signal with the difference in their detection times. The second equation relates the lengths of the sides of the triangle 1-2-3 with the angle according to the law of cosines.

Substituting the 1st equation into the 2nd, we get:

Considering that And defined, and is calculated based on the known geographic coordinates of the emitter and receiver, from (2) the distance (range) between the target and the receiver is determined :

As a result, the target bearing was obtained. and the distance to it relative to the receiver.

The disadvantages of the prototype method are:

- for its implementation the receiver must be oriented in space;

- the method does not allow determining the course and speed of the target.

The technical problem being solved is improving the search for underwater objects using a multistatic underwater surveillance system.

The technical result is the determination of coordinates (bearing and distance) and movement parameters (course and speed) of a target by one receiver of a multistatic sonar system in one cycle of emission of a probing signal with an unknown angular orientation of the receiver in space.

The claimed method is illustrated in Fig. 2, in which:

4 – a directional receiver, not oriented in space and determining the direction in a local coordinate system, the center of which is aligned with the center of the receiving antenna (hereinafter referred to as the receiver);

– the course angle of the target relative to the receiver;

– the course angle of the target relative to the emitter;

d – the difference in the target course angles relative to the directions of the emitter and receiver.

The implementation of the claimed method is as follows:

- Non-directional (omnidirectional) emitter 1 emits a probing signal (PS).

- Directional receiver 4 receives the ZS, measures the direction and time reception of the ZS, and also remembers the ZS itself .

- Then the directional receiver 4 receives the echo signal (ES) reflected from the target 3, measures the direction and time reception of ES, and also remembers the ES itself

- Using the received data, the current coordinates of the target in space are determined. This is achieved as follows:

- the difference in the directions of arrival of the ES and ZS is calculated

- the difference between the reception times of the ES and ZS is calculated

It is assumed that the receiver has not changed its angular orientation during the interval between the reception of the ES and the ES, which is true, since the interval between the reception of the ES and the ES does not exceed units of seconds, and it has been experimentally established that when adopting appropriate hardware solutions (equipping the RGB with a damper in the form of a sail made of fabric and micromechanical accelerometers), the maximum unaccounted rotation speed of the RGB around its vertical axis does not exceed units of degrees per minute;

- bearings are calculated and distance emitter relative to receiver:

Where

– known (calculated using signals from a satellite navigation system) geographic coordinates of the receiver in some local Cartesian coordinate system in which the axis is directed to the north, and the axis - to the east;

– known (calculated using signals from a satellite navigation system) geographic coordinates of the emitter in the same coordinate system;

- the target bearing relative to the receiver is calculated

The sign on the right side of formula (7) is determined based on the fact that in practice it is known from which side the target approaches the RGB barrier;

- using formula (3), the distance to the target relative to the receiver is calculated.

1) If a search is carried out for a submarine of a known design and if the range resolution of the surface-to-surface system does not exceed a few meters, the target's course and speed are determined. This is implemented as follows:

- the target's course angle relative to the receiver is determined , for which the cross-correlation function (CCF) of the ZS and ES is calculated :

Where

– duration of the ZS;

– argument of the cross-correlation function;

– argument of the probing and echo signals.

In the VCF (shown in red in Fig. 3), narrow-band maxima caused by reflections from characteristic bright points of the target are identified, and the differences in their abscissas are measured. (i.e. the delay in the arrival of the ES reflected from the receiver -th and -th of bright points - reflectors). In the case of a submarine, the characteristic bright points (reflectors) are the bow, conning tower and stern empennage [9]. With a known submarine design, the distances between the characteristic -th and -th shiny points (reflectors) along the diametrical plane are known. Since the relative delays of the arrival of echo signals from the reflectors in the cross-correlation function depend on the course angle of the target relative to the receiver (which is shown in Fig. 3 in red), this allows us to determine the course angle of the target relative to the receiver using the formula:

Where And - numbers of the reflectors most distant from each other.

To improve accuracy, the difference is used between the most distant from each other bright points. The sign on the right side of formula (9) is determined by the side of the change in the bearing of the target when several ES are radiating;

- the target course is determined :

-

- the target speed is determined , which is achieved as follows:

o in multistatic location, the Doppler transformation of the ZS spectrum into the ES spectrum has the form

Where

– complex spectrum of the echo signal;

– the transfer characteristic of the transmission channel of the ground station from the emitter to the receiver, the value of which does not affect the problem being solved;

– complex spectrum of the ZS, transformed under the influence of the Doppler effect;

- the course angle of the target relative to the emitter and receiver, respectively;

- Doppler parameter, defined as

Formula (12) shows that the ZS is subject to the Doppler effect twice: first when falling on the target at an angle , and then when reflected from it at an angle .

The value of the Doppler parameter can be determined from the following condition: the correlation of the ES and the ZS is maximum if the ZS is transformed using the Doppler parameter determined by formula (12). To do this, we calculate the correlation of the ES and the ZS transformed using different values of the Doppler parameter , iterated from 1 to the value with a step :

Where

– boundary frequencies of the frequency band of the ZS;

– frequency and duration of the ES;

- maximum possible target speed;

– conjugate complex spectrum of the echo signal;

– complex spectrum of the ZS, transformed in accordance with the value of the Doppler parameter ;

- frequency.

Let's determine the value of the Doppler parameter as corresponding to the maximum of the function .

Having determined the Doppler parameter , we find the target speed from (12), taking into account that :

The only unknown parameter in (14) is d , which is the angle with the vertex at the target location between the directions to the emitter and receiver, and is determined from the triangle 1-2-3 in Fig. 2 using the law of sines, and the distance between the emitter and the target is is calculated from the first equation of system (1):

Thus, without taking into account the angular orientation of the receiver, the target bearing was determined based on the data of one cycle of the ZS radiation. , distance to it , target course and its speed .

The significant differences between the claimed method and the prototype method are the additional determination in the absence of the angular orientation of the receiver:

1) target coordinates;

2) target course;

3) target speed.

To assess the accuracy of determining the coordinates and parameters of the target's movement using the claimed method, mathematical modeling of the solution to the problem was carried out, which made it possible to establish the following:

The accuracy of determining the coordinates and parameters of target movement is affected by the root mean square errors (RMS) of the determination:

current coordinates of the emitter and receiver;

moments of arrival of the ZS and ES;

directions of arrival of ZS and ES;

distances between the maxima in the VCF of the ZS and ES;

Doppler parameter;

the speed of sound at the depth of the receiver.

Typical values of the listed SCPs are:

current coordinates of the emitter and receiver when using a satellite navigation system 5...8 m;

moments of arrival time of the ZS and ES 0.5...1.0 ms;

directions of arrival of the West Siberian Branch and the Eastern Siberian Branch 2°…3°;

distances between the maxima in the VCF ZS and ES 2...3 ms;

Doppler parameter 0.03…0.05;

speed of sound 0.5…1.0 m/s.

With typical error values, the coordinates and parameters of the target's movement are determined with the SCP:

bearing 2°…3°;

distances 7…10%;

course 7°…9°;

speeds of 0.8…1.2 m/s.

The provided justification and results of modeling the claimed method allow us to assert that the claimed technical result – determination of coordinates and parameters of target movement by one receiver of a multistatic sonar system in one cycle of emission of a probing signal with an unknown angular orientation of the receiver in space – can be considered achieved.

Sources of information

1. Urick R. J. Fundamentals of hydroacoustics // L.: Shipbuilding. 1978.

2. Cox H. of bistatic active sonar. In "Undewater acoustic data processing" by Y.T.Chan (editor). Springer.1989.

3. Borodavkin A.N., Bogomolov A.P., Durnev I.N., Titkov I.V. Radiohydroacoustic systems of naval aviation // Military Scientific Center of the Navy "Naval Academy". St. Petersburg. 2022. 287 p.

4. Averyanov V.E. Separated radar stations and systems // Minsk: Science and Technology. 1978.

5. Chernyak V.S. Multi-position radar // M.: Radio and communication. 1993.

6. Patent of the Russian Federation No. 2555192.

7. Patent of the Russian Federation No. 2715409.

8. Patent of the Russian Federation No. 2751999.

9. Chernov V.P. Characteristics of sonar reflection of complex underwater objects based on the results of physical modeling // Hydroacoustics. 2022. Issue 51 (3). P.50-60.

Claims (23)

A method for determining the coordinates and parameters of movement of underwater objects during multistatic hydrolocation, including the emission of a probing signal by a non-directional emitter, the reception of a probing signal by a directional receiver with measurement of the time of arrival of the probing signal, the reception by the same directional receiver of an echo signal reflected from a target with measurement of the time of arrival of the echo signal, and the calculation of the difference in the arrival times of the echo signal and the probing signal , determination of target coordinates using measured parameters and known coordinates of the emitter and receiver, characterized in that the directions of arrival of the probing signal and the echo signal are measured by a directional receiver that is not oriented in space, and the difference is calculated directions of arrival of the echo signal and the probing signal, using the known geographic coordinates of the emitter and receiver, the bearing of the emitter relative to the receiver is calculated and the distance between the emitter and the receiver , calculate the bearing of the target relative to the receiver according to the formula , calculate the distance to the target relative to the receiver according to the formula Where – the speed of sound in water, calculate the cross-correlation function between the probing and echo signals, identifying the maxima in it caused by reflections from characteristic shiny points - target reflectors, and measuring the delays between the most distant pair of bright dots, determine the course angle of the target relative to the receiver according to the formula , Where – known distances along the target's diametrical plane between -th and - with characteristic shiny dots (reflectors), calculate the target's course according to the formula , calculate the dependence of the correlation value of the echo signal and the probing signal on the value of the Doppler parameter according to the formula , Where – frequency; – boundary frequencies of the frequency band of the probing signal; – conjugate complex spectrum of the echo signal; – complex spectrum of the probing signal, transformed in accordance with the value of the Doppler parameter , determine the value of the Doppler parameter , corresponding to the maximum dependence of the correlation value of the echo signal and the probing signal on the value of the Doppler parameter , calculate the target's speed according to the formula , Where – the angle with the vertex at the target location between the directions to the emitter and receiver, determined by the formula .