RU2343502C2 - Method and system of positional analysis of object under observation by depth in aqueous medium - Google Patents

Abstract

FIELD: physics; measurement.

SUBSTANCE: invention refers to echo ranging and is aimed at positional analysis of object under observation by depth in aqueous medium. Offered method and system positional analysis of object under observation by depth in aqueous medium consist in wave sounding and receiving of sounding signals reflected from object to two or more receivers in the water spaced at preset distance considering measured radiator to object distance. Time difference of signal arrival to receivers is recoded. Depth of object is determined by inverse problem solving through comparison of observable differences at known radiator to object distance with value set for various versions of object position calculated for conditions of known measured vertical sound speed distribution within analysed aqueous site.

EFFECT: implementation of on-line positioning of object under observation (detected) by depth in aqueous medium in sound echolocation to produce applicable depth values.

5 cl, 5 dwg

Description

The invention relates to the field of sonar and is intended to determine the position of the observed object in depth in the aquatic environment.

The proposed method and system can be used when conducting underwater operations, security measures, search and rescue operations, protecting ships and structures from the aquatic environment, preventing collisions, controlling fish accumulations, conducting scientific research, including biological research, especially when it is necessary to know the depth of objects found in the aquatic environment, for example, for their classification.

The prior art solutions in the field of echolocation, allowing to determine the position of underwater objects in depth.

From the patent of the Russian Federation No. 2078353 for the invention, a solution is known that makes it possible to determine the immersion depth of an underwater object with known geometric dimensions. The invention is aimed at solving the problem of determining the immersion depth of continuous and having a periodic structure of underwater objects and their position on the line connecting the emitter to the receiver. The emitter is located near the surface, the receiver is located at the bottom, and the object is between them. An acoustic signal is emitted into the region of the possible location of the object, by transmitting and receiving signals in a wide frequency band, determine the frequency at which the effect of shadowing by the object of the emitter disappears, and from this data the depth of the object. In this case, to determine the depth of an object having a periodic structure, choose a wavelength that exceeds the distance between the component parts of the object, but commensurate with the overall dimensions of the latter.

The disadvantage of this solution is the limited scope, the ability to determine the depth of only a specific object (with known geometric dimensions), the lack of consideration when measuring the vertical distribution of the speed of sound in an aqueous medium.

In the patent of the Russian Federation No. 2208811 for the invention, a method for obtaining information about noisy in the sea objects, given the speed of sound in water in depth. The noise emitted by moving objects is received by the antenna in at least three spatial channels for observing a signal arriving at different angles due to vertical refraction of sound. The received noise signal is discretized in time and quantized into several levels, the speed of sound in water is measured depending on the depth and wave surface of the sea. From the measured data and the known characteristics of the bottom and the known characteristics of the receiving system, the object signal in each spatial channel is calculated for several distance values, solving the hydroacoustic equation in the passive mode, and as a result of comparing the measured signal values with the calculated ones, they decide on the distance and speed and on the presence of several noisy objects in one direction.

The disadvantage of this solution is also the limited scope, including due to the fact that information by the proposed method can be obtained only about noisy objects.

The invention is also known according to the patent of the Russian Federation No. 2271551, which can be used in sonar detection devices for underwater objects (submarines, small objects: mines, underwater swimmers). The physical essence of the invention consists in determining the spatial angles of sight of an acoustic beam (bearings) on a reflecting object, i.e. the direction of arrival of the sound beam reflected from the object, based on the spatial-phase and spatial-correlation processing of the reflected signals in the plane of the wave front of the received signal.

This solution, using the direction of arrival of the sound ray reflected from the object, does not allow determining the depth of the object without taking into account the refraction of sound rays in a real aqueous medium. In addition, the use of the direction of arrival of the beam, even when refraction is taken into account, does not give an exit to the depth of the object due to the weak resolution of the receiving systems at the angles of arrival of sound rays in real conditions of their operation.

Indeed, under the conditions of possible seasonal distributions of the speed of sound in depth - a negative gradient of the speed of sound in the near-surface region for summer, a positive gradient for winter and a weak positive gradient in the off-season, shown in Fig. 1, the range of angles of arrival of sound rays for practically significant depths of the object to 10-15 m from the water surface and distances to the object of a hundred or more meters does not exceed several degrees, as can be seen from figure 2 and 3, where, as an example, ranges of sound paths are presented x-ray in a vertical plane to the irradiated area of the aqueous layer.

It follows that in order to distinguish rays from objects located at different depths, a resolution in the angle of a fraction of a degree is required, which is a technically unattainable task in full-scale marine conditions, especially when working with a supply vessel experiencing pitching.

A known solution in the field of hydroacoustics for the detection and tracking of underwater objects invading a controlled area of a natural reservoir (RF patent No. 2150123 for an invention). In this solution, using a sonar reflector located on an elliptical surface, set the controlled area of the natural reservoir. In this case, the sonar emitter and receiver are located in the foci of the elliptical surface. The emitter is made in the form of a circular hydroacoustic antenna, and the receiver connected to the indicator of all-round visibility, with a uniform directional characteristic.

Consistently in different directions, the emitter directs pulses of acoustic energy, which for the same period of time reach the receiver, reflected from hydroacoustic reflectors. A series of pulses are formed on the circular view indicator. When an underwater object invades the monitored zone, one of the pulses on the circular viewing indicator disappears, which indicates the presence of a target. Sequential processing of the output signals allows you to determine the course and speed of the target.

The disadvantage of this solution is the limited scope due to the lack of determining the position of the object relative to the bottom.

In the invention according to the RF patent No. 2272303, a method for determining the depths of the water area is proposed, according to which sonar signals are emitted by a side-scan sonar and the signal is received at two points located vertically at a given distance. The measurement of the delay time of common-mode signals vertically, including those reflected from a flat bottom surface, is carried out for each calculated direction. The directions of arrival of common-mode signals and the desired depths are determined from the data obtained and sea soil is recognized. Additionally, changes in the speed of sound directly on the horizon of the antenna are measured, the values of which introduce corrective signals. Determine the drift angle of the antenna carrier, linear and angular velocities and accelerations directly on the antenna body. A correction of the time code determined during the measurement is introduced. Recognition of sea soil is performed by clustering and numerical analysis. A device for implementing this method comprises antennas, a transmitting unit, a receiving and measuring unit, a control unit, a calculator, a recorder, a correction device, an information timing device, and a sensor unit for measuring linear and angular velocities and accelerations.

This solution, dedicated to the recognition of sea soil, cannot be applied to detect objects in the water column and determine their location.

Similar systems are also known from foreign patent sources, see Japanese application JP 2006078329, publication March 23, 2006, JP 2003215230, publication July 30, 2003, US patent No. 7006406.

For the closest analogue in terms of technical nature and the achieved result, we can take the method known in sonar for determining the spatial position of the observed object in the water column by determining the direction of arrival of the sound beam reflected from the object (see R.D. Urik. Basics of hydroacoustics. L., Shipbuilding, 1978, p. 71), the disadvantages of which were discussed above.

The problem to which the proposed invention is directed is to create a method and device with a simple implementation and an extended scope, allowing to determine the position of the observed object by depth in the aquatic environment.

To solve this problem, a method for determining the position of the observed object by depth in the aquatic environment is proposed, including wave sensing and reception of sounding signals reflected from the object. At the same time, sounding signals reflected from the object are received at two or more receivers in water, separated in space by a fixed distance, taking into account the measured distance from the emitter to the object, and the time difference between the signals arriving at the receivers is recorded.

The depth of the object is determined by solving the inverse problem by comparing the observed differences at a known distance from the emitter to the object with a set of their values for various options for the position of the object obtained by calculation for the conditions of the known measured vertical distribution of the speed of sound in the studied water area.

Also proposed is a system for implementing the method, comprising a hydroacoustic device for emitting sounding signals in an aqueous medium with the ability to determine the distance to the object, at least two receivers of sounding signals reflected from the object, spaced a fixed distance in space, and a meter for the vertical distribution of sound velocity in water layer connected to an electronic data processing complex. The electronic data processing complex provides the reception of signals from the specified sonar device and receivers, calculates the set of expected values of the difference in the arrival times of the signals reflected from the object, taking into account the measured vertical distribution of the speed of sound in the water layer for different distances from the emitter to the object and the depths of the object, determining the distance to the object and the difference in the times of arrival at the receivers of the signals reflected from the object. In this case, to quickly determine the position of the observed object by depth in the electronic data processing complex, the registered and calculated values of the differences in the time of arrival of signals to the receivers are compared for a known measured distance from the emitter to the object.

Preferably, the sonar device contains one of the receivers reflected from the object of the probing signals. It is also advisable to place at least one receiver at the bottom of the reservoir. The sonar device may be a sonar. An electronic data processing complex may consist of a series of interconnected electronic units for receiving, processing and transmitting data.

In contrast to the known solutions, the depth of the object according to the proposed method and system is determined by the difference in the time of arrival of sound signals reflected from the object to spatially spaced fixed reception points.

The essence of the claimed method and system is illustrated by drawings.

Figure 1 - graphs of the measured seasonal distribution of the speed of sound in depth.

Figure 2 - the range of trajectories of sound rays in the vertical plane for practically significant depths of the object at distances of more than 100 m in summer.

Figure 3 - the range of trajectories of sound rays in the vertical plane for practically significant depths of the object at distances of more than 100 m in winter conditions.

Figure 4 is a structural diagram of a system according to the proposed method.

5 is a variant of the practical implementation of the system for determining the depth of the target in the aquatic environment with receivers installed at the bottom.

Table 1. The results of a theoretical calculation of the difference in the arrival times Δt of the signal reflected from the object for two receiving points located at the same depth Z _n = 20 m and horizontally spaced 10 m and 50 m from the object.

Table 2. The results of computer calculation of the set of expected values of the difference in the times of arrival of signals reflected from the object to the receivers 2 and 3 at the bottom for different depths of the object Z _o and different distances r _{o of the} object from the emitter.

The basis of the proposed method is to take into account differences in the propagation time of sound reflected from the object over different sound rays, easily taken into account with a known vertical distribution of the speed of sound in the water column at the observation site using computer simulation, and the technical ability to resolve time intervals.

To assess the expected values of the propagation time differences of the sound signal reflected from the object for different sound rays, we consider the theoretically simplest case of a change in the speed of sound in depth according to the linear law:

C (Z) = C ₀ (1-a · Z),

where C (Z) is the speed of sound at an arbitrary depth Z;

C ₀ is the speed of sound at Z = 0;

a is a coefficient with dimension L ^-1 , for example, m ^-1 , characterizing the change in the speed of sound in depth, is set based on patterns derived empirically, based on experimental data.

This expression allows us to obtain in analytical form the dependence of the propagation time t of the sound signal from the object along the rays under the conditions of a given vertical distribution of the speed of sound in the water column depending on the values: r is the horizontal distance to the object, Z _o is the position of the object in depth, Z _n - the depth of the receiving point of the sound signal reflected from the object.

Consider the element of the ray path dS at some point where the angle of inclination of the ray from the horizontal is φ. The deflection of the beam in depth dZ is then equal to:

dZ = dSsin φ.

The expressions for r and t are then written:

To go from φ to Z, we use Snell's law:

where Z _m is the depth of the ray path at φ = 0.

We get

We introduce the notation: y = 1-a · Z,

at _m = 1-a · Z _m ,

y _o = 1-a · Z _o ,

_n = 1-a · Z _n .

As a result, we obtain for r and t expressions that allow table integration:

We exclude _m from the expression for t. To do this, we express y in _m through r, y _n and y _o .

Substituting then at _m into the expression for t, as a result we obtain the desired dependence of t on r, at _n and at ₀ :

As an example, table 1 shows the results of the calculation according to the obtained expression of the difference in the arrival times Δt of the signal reflected from the object for two receiving points located at the same depth Z _n = 20 m and horizontally spaced 10 m and 50 m from the object, for different depths object Z _o and values a = 4 · 10 ^-4 m ^-1 and C ₀ = 1430 m, close to those observed for conditions of late summer - early autumn (see figure 1).

From the data obtained, presented in table 1, it can be seen that when the depth of the object changes by 5 m, the difference in the propagation time of the signal from the object over different beams changes by 1.5-2 ms. It follows that to ensure a resolution of 1 m over the depth of the object under the considered conditions, a resolution of the propagation time along the rays of 0.3-0.4 ms is required. In turn, dividing these values by the speed of sound gives the necessary accuracy of horizontal receiver spacing of 0.45-0.6 m.

The proposed method and system are implemented in accordance with the structural diagram of the system shown in figure 4. It includes the following elements:

1 - sonar device with a probe emitter;

2, 3 - receivers of sounding signals reflected from the object;

4 - block radiation of the probing signals;

5 - block receiving signals reflected from the object;

6 is a block for calculating a set of expected values of the difference in the times of arrival at the receivers of sounding signals reflected from the object for possible depths of the object depending on the distance from the emitter to the object, taking into account the measured vertical distribution of the speed of sound in the water layer;

7 - a unit for determining the distance to the object and the difference in the arrival times of the signals reflected from the object according to the data received from the probe radiation unit 4 and the reception unit 5 for signals reflected from the object;

8 is a data processing unit in which the position of the observed object in depth is determined by comparing the distance determined from block 7 from the emitter to the object and the difference in the times of arrival of signals reflected from the object to the receivers with a set of values calculated in block 6 for possible object depths;

9 - meter vertical distribution of the speed of sound in the water layer.

In accordance with this scheme, an emitter 1 of sounding signals and at least two spatially separated receivers 2, 3 of sounding signals reflected from the object are installed in the observation zone in water, while one of the receivers can be combined with an emitter (not shown).

In the receiving part 5, the sounding signals reflected from the object are received and from them in block 7 the distance from the emitter to the object and the difference in the propagation times of the sounding signals reflected from the object to the receivers are determined.

In addition, in the observation zone, measurements are made in water of the sound velocity profile in the vertical plane, for example, with a profilograph probe 9 to take into account the refraction of sound rays, and in block 6, sets of values of the difference of signal propagation times to given reception points depending on the probable position are calculated in block 6 object in the water layer.

Next, in block 8, the inverse problem is solved by finding the depth of the object by comparing the differences in arrival times and distances from the emitter to the object defined in block 7 with a set of differences values calculated in block 6 corresponding to different distances from the emitter to the object and different depths of the object.

As an example, Fig. 5 shows a diagram of a practical embodiment of the system, where r _о is the distance from the probe emitter to the object, 2 and 3 are receivers laid at the bottom at a depth of Z _n at a distance of r ₁ and r ₂ from the hydroacoustic device 1 respectively. For this scheme and the conditions of the summer profile of the speed of sound shown in Fig. 1, table 2 presents in ms the results of a computer calculation of the set of expected values of the difference in the times of arrival of signals reflected from the object to receivers 2 and 3 for various object depths Z _o and different distances r _about from the emitter to the object with the given parameters: Z _n = 20 m, r ₁ = 60 m, r ₂ = 110 m.

As can be seen from the data presented in Table 2, the expected differences in the arrival of signals reflected from the object to receivers 2 and 3 clearly show a dependence on the position of the object in depth at practical distances from the emitter to the object of 50-250 m.

As can be seen from table 2, as well as from the data given in table 1 above, for a sufficiently detailed resolution of the detected objects in depth, for example, with an accuracy of 1 m, it is necessary to record the time differences of the signals reflected from the object in tenths of a ms. This, in turn, imposes requirements on the accuracy of determining the distances to which the receivers of signals reflected from the object are spaced within an error estimate of less than 1 m.

It is also necessary that these distances remain unchanged, at least within the margin of error. Possible influences, for example, from the side of the waves should be eliminated, for example, by installing receivers on the bottom or on fixed platforms.

The technical result of the present invention is the implementation of the operational determination of the position of the observed (detected) object in depth in the aquatic environment with sound echolocation to obtain the necessary resolution of depth values for practice.

Method and system for determining the position of the observed object in depth in the aquatic environment

Table 1. The results of a theoretical calculation of the difference in the arrival times Δt of the signal reflected from the object for two receiving points located at the same depth Z _n = 20 m and horizontally spaced 10 m and 50 m from the object. Z _o , m Δt, ms 5 24.02 10 25.92 fifteen 27.52

Table 2. The results of a computer calculation of the set of expected values of the difference in the arrival times of signals reflected from the object to the receivers (1) and (2) at the bottom for various object depths Z _o and different object distances r _o from the emitter. Z _o , m r _o , m fifty one hundred 150 200 250 2 28.9 16.1 33.0 33.8 33.8 four 29.9 16.7 33,4 34.0 33.9 8 31.6 18.1 34.0 34.3 34.2 fifteen 34.3 20,4 34.7 34,4 34.8

Claims (5)

1. The method of determining the position of the observed object in depth in the aquatic environment, including wave sensing and receiving sounding signals reflected from the object, characterized in that the sounding signals reflected from the object are transmitted to two or more receivers in water, separated in space by a fixed distance, taking into account the measured distance from the emitter to the object, the difference in the time of arrival of signals to the receivers is recorded, and the depth of the object is determined by solving the inverse problem by comparing yudaemyh differences at a known distance from the transducer to an object with a set of values for different position of the object obtained by calculation for the measured conditions known vertical distribution of the velocity of sound in the test aqueous portion. 2. The system for implementing the method according to claim 1, comprising a hydroacoustic device for emitting sounding signals in an aqueous medium with the ability to measure the distance to the object and at least two receivers of sounding signals reflected from the object, spaced a fixed distance in space, a vertical meter sound velocity distributions in the water layer, connected to an electronic data processing complex providing signals from said sonar apparatus and receivers, calculating a set the expected values of the difference in the times of arrival at the receivers of signals reflected from the object, taking into account the measured vertical distribution of the speed of sound in the water layer for different distances from the emitter to the object and the depths of the object, determining the distance to the object and the difference in times of arrival at the receivers of signals reflected from the object, operative determination of the position of the observed object by depth in the electronic data processing complex compares the recorded and calculated values of the time differences pr stroke signals in known receivers for the measured distance from the transducer to the object. 3. The system according to claim 2, characterized in that the hydroacoustic device provides reception of sounding signals reflected from the object. 4. The system according to claim 2, characterized in that at least one receiver is located at the bottom of the reservoir. 5. The system according to claim 2, characterized in that the electronic data processing complex consists of a series of interconnected electronic units for receiving, processing and transmitting data.

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