RU2570100C1 - Hydroacoustic determination of object spatial characteristics - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to hydroacoustics. Claimed method comprises radiation of probing signal at time t of echo signal t_echo reception. Distance D to the object is defined from time delay and known sound propagation velocity C. After radiation, measured is the level of volumetric reverberation U₀ to define the detection threshold U_thresh. Measured is the echo signal start time t_start whereat echo signal amplitude A_vol exceeds the threshold A_vol>U_thresh to define the distance D₀ = 0.5 C t_start. Measured is the time of the last amplitude t_last whereat the minimum amplitude of eco signal from the object A_vol>U_thresh to define the time of shadow start time t_shadow whereat the condition U₀≥A_shadow and t_shadow>t_last is satisfied. Defined is the shadow end time t_{shad. end} whereat U_thresh>A_vol≥U₀ to define the distance to the shadow end time D_shad = 0.5 C t_{shad. end}. Now, the depth from hydrophone to the bottom H_bot, while object height is defined by the formula $$h=\frac{(D_{shad}-D_0)H_{bot}}{D_0}.$$

EFFECT: determination of object detection height above bottom by one pulsing.

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Description

The present invention relates to the field of sonar and can be used to measure the height of an object detected at the bottom using a short-range sonar.

Known methods for detecting an object located near a mobile carrier in an aqueous medium using a sonar mounted on this carrier. Using these methods allows you to detect an object, measure the distance to it and measure the direction to the object (Yakovlev A.N., Kablov G.P. Short-range sonars. L .: Sudostroenie, 1983).

To do this, a probe signal is emitted, the delay time between the emitted signal and the received echo signal from the object is measured, the distance to the detected object is determined by the value of the time delay and the known sound propagation speed and the direction of arrival of the reflected signal in the horizontal direction is determined. These methods allow you to detect objects at the bottom, but they do not allow you to measure the height of these objects.

The well-known "Method and device for determining the depth of an underwater object", the authors of SATO KAZUO and others according to patent JP 02708109 B2 from 02/04/98. G01S 15/10 HITACYI LTD, which is based on the same principle as the previous method, but the direction is determined by scanning the directivity in the vertical plane when the probe signal is emitted by a narrow directivity. This method also does not allow to determine the height of the object above the bottom.

Methods based on the analysis of features of the shape of the shadow cast by an object when it is irradiated with a probe signal have found application in modern hydroacoustics. The effectiveness of these methods is determined by the angle of the object and its position relative to the irradiation angles (A. A. Koryakin. Ship hydroacoustic equipment. St. Petersburg: “Nauka”, 2004, p. 35-40). Difficulties in detecting the shadow parameter were repeatedly discussed in the scientific literature “On Ways of Increasing the Probability of the Shadow Image of Extended Objects” Ya.V. Moiseenko in Proceedings of the 8th international conference "Applied technologies of hydroacoustics and hydrophysics" St. Petersburg. 2006, p. 161-165. The assessment of the possibility of using a shadow image for solving classification problems is considered in relation to the display in coordinates, the course range in the work of A.N. Yakovlev, G.P. Kablov. "Short-range sonars." Shipbuilding, 1983, L., pp. 122-128).

However, none of these sources address the issues of measuring the height of a detected object above the bottom.

, где $$\Delta D=\left(D_1^2-D_2^2-V^2\Delta t^2\right)/2V\Delta t$$

, где D₁ - дистанция до объекта в момент времени t₁, D₂ - дистанция до объекта на момент времени t₁+Δt, V_соб. - скорость перемещения излучателя. Недостатком этого способа является невозможность определения высоты объекта, обнаруженного гидролокатором на дне, а также зависимость оценки глубины от числа посылок и пройденного расстояния.The closest analogue, which contains essentially similar operations, is a method for measuring the depth of immersion of an object according to the patent of the Russian Federation No. 2350983. The method comprises emitting a sounding signal, receiving an echo signal and measuring the distance D ₁ at time t ₁ , at time t ₁ + Δt repeat the procedure for measuring the distance to the object, determine the distance D ₂ to the object at time t ₁ + Δt, determine the speed carrier V _sob and the depth of immersion of the object relative to the horizon of movement of the carrier is determined by the formula $$H=\sqrt{D_2^2-\Delta D^2}$$

where $$\Delta D=\left(D_{\mathrm{one}}^2-D_2^2-V^2\Delta t^2\right)/2V\Delta t$$

where D ₁ is the distance to the object at time t ₁ , D ₂ is the distance to the object at time t ₁ + Δt, V _sob. - the speed of the emitter. The disadvantage of this method is the inability to determine the height of the object detected by the sonar at the bottom, as well as the dependence of the depth assessment on the number of parcels and the distance traveled.

This technical solution allows to eliminate this drawback and provide a measurement of the height of the object at the bottom level in one package.

The objective of the invention is to expand the functionality of the method.

.To solve this problem, in a known method comprising emitting a sounding signal, receiving an echo signal, determining the distance to the object D from the value of the time delay of the echo signal and the known speed of sound propagation C, additional features are introduced, namely, after the radiation, the volume reverberation level U is measured₀determine the detection threshold U_sincemeasure t_beg echo start time, at which the amplitude of echo A is first_about exceeded threshold A_about> U_since, and determine the distance D₀= 0.5 C t_begmeasure the time instant of the last echo amplitude t_pic, at which the minimum amplitude of the echo from object A_about> U_since, determine the instant of the beginning of the shadow t_{the shadows}under which condition U₀≥A_ten and t_{the shadows}> t_pic, determine the time moment of the end of the shadow t_conat which U_since> A_about≥U₀, determine the distance to the end of the shadow D_{the shadows}= 0.5 C t_con, determine the depth from the sonar to the bottom of N_bottom, and the height of the object is determined by the formula

.

The technical result of the proposed method is to determine the height of the detected object above the bottom, on one premise.

Let us explain the achievement of the specified technical result.

The essence of the proposed method is as follows. An echo signal from a local object is formed on the basis of the reflection of the energy of the incident sounding signal to the object normal to the direction of arrival of the sonar probe signal. This leads to the formation of a regular wave front with a characteristic that is stable over a certain spatial interval (E.A. Stager, E . V. Chaevsky, Wave scattering on bodies of complex shape (Moscow: Sov. Radio, 1974).

.Since the object is in a far field and has limited dimensions, the echo signal from such an object represents a plane slightly distorted wave. The shape of the echo envelope will be determined by how much the individual reflecting elements of the object are illuminated or how much they will be shaded. The object itself, located at the bottom, completely screens the bottom surface behind the object, and the signal does not come to it and is not reflected from it. In this case, the echo signal intensity after reflection from the object sharply decreases even compared to the bottom reverb signal, and a signal will be received at the input of the receiving device whose amplitude is determined by the volume reverb and noise intensity, since the bottom section will be shielded by the body of the object lying at the bottom. Consequently, a peculiar dip is formed in the envelope section of the implementation of the input process, the level of which is substantially less than the echo signal from the object and from the level of the bottom reverb, and is equal to the level of volumetric reverb acting at the time of the arrival of the echo signal after reflection from the object. In fact, this level of volumetric reverberation will correspond to the noise level at the input of the receiving device (A. N. Yakovlev, G. P. Kablov. “Short-range sonars.” Shipbuilding, 1983, L., p. 50). Existing detection systems have as their goal the determination of the presence of an echo signal from an object by the magnitude of the excess of the amplitude of the echo signal from an object of a selected threshold, which is selected based on the signal / noise ratio. Thus, the criterion is the excess of the measured echo level of the measured interference level. The echo signal from the object may contain several reflectors, the amplitudes from which will be determined by the structure of the reflector and their equivalent radius. The beginning of the shadow will be determined by the beginning of the reflection, which is located at the maximum height of the object and has a minimum distance. The amplitude of the echo from the reflector with a minimum distance will not always be the largest, but this reflector will form the beginning of the shadow. Therefore, in the shadow detection task, it makes sense to consider the time of the beginning of the echo signal, the time of formation of the shadow zone and the determination of the time of the end of the shadow zone (see Fig. 2). To detect the shadow, a procedure arises for comparing the amplitude of the adopted realization A _о with the threshold U _then , which characterizes the absence of reflection from the object on the one hand. On the other hand, there should be a minimum level of U ₀ , which is determined by the level of volumetric reverb, the value of which can be measured after the radiation of the probing signal. Consider the formation of the shadow zone. There are two similar triangles, one of which is determined by the distance from the sonar to the end of the shadow zone D _shadow = 0.5 C t _end and the distance from the sonar to the bottom H of the _bottom . The second is determined by the distance {D _shadow -D ₀ (t _pos )} from the object to the end of the shadow zone and the height of the object h. To find the height of the object above the bottom, it is necessary to determine the angle at which the object is observed and which forms the length of the shadow. The sine of this angle will be defined as the ratio of the distance to the bottom under the sonar N of the _bottom to the distance of the end of the shadow length D _shadow = 0.5 C t _end . After that, the distance from the beginning of the object to the end of the shadow zone is determined (D _shadow -D ₀ ) = 0.5 C (t _end.- t _pos ) and using the estimate of the sine of the angle, the estimate of the height of the position of the object above the bottom surface is calculated

.

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

In FIG. 1 antenna 1 through a transmission receiving switch 2 is connected to a special processor 5, in which through the first output of the receiver 6, through the first output of the reverb level measuring unit 8, through the first input of the block 11 is connected by two-way communication with the indicator 12. The second output of the receiver 6 through the first input of the block 7, the threshold measurement, through the first output unit 9 measuring the distance to the object, through the block 10 measuring the distance to the shadow is connected with the second input of the block 10 calculating the height of the object. The second output of the reverb level measuring unit 8 is connected to the second input of the threshold measuring unit. The second output of the unit for measuring the distance to the object is connected to the third input of the unit 11 for calculating the height of the object, the fourth input of which is connected to the depth gauge 4, the second input of the switch is connected to the generator 3, the third output of the receiver 6 is connected to the second input of the indicator 12.

Using the proposed device, the method of measuring the height of the object above the bottom works as follows.

Generator 3 generates a probing signal, which, through the transmission reception switch, enters the antenna and is radiated into the aquatic environment. Antenna 1 receives the echo signals reflected from the object, which are transmitted through the transfer reception switch 2 to a special processor 5, which includes a receiver 6. Antenna 1, generator 3, transmission reception switch 2 and receiver are known devices that are used in the prototype and are described in sufficient detail in the literature (Yakovlev A.N., Kablov G.P. Short-range sonars. L .: Shipbuilding, 1983). Special processor 5 is a well-known device that is widely used in modern electronic technology for processing echo signals. For a high-quality solution to the problems of processing sonar information in modern ship sonar equipment (stations), special processors based on a digital computer system are used, which have high performance, functional reliability and small dimensions. Using special algorithmic and software, special processors can solve all the problems of generating and processing received hydroacoustic signals, including for automatically measuring the height of an object above the bottom (Yu.A. Koryakin, SA Smirnov, GV Yakovlev. “Ship sonar technology ", St. Petersburg: publishing house" Science ", 2004, p. 281).

The proposed method using the device (Fig. 1) is as follows. Accepted by the hydroacoustic antenna 1, the temporary implementation arrives at the receiver 6, where the optimal processing of the received signals occurs, which is transmitted to the threshold measurement unit 7. In parallel, the input information enters block 8 for measuring the volume of the volume reverberation, the value of which is also used to select the detection threshold in block 7. Echo signals that exceed the threshold are transmitted to block 9 for measuring the distance to the object, the times of the formation of the echo signal to the object are used to measure distances to the shadow zone, which is determined by the implementation, transmitted through blocks 7 and 9 to block 10, where, according to the selected characteristics, the end time of the shadow zone. The distance to the beginning of the object and the distance to the final border of the shadow zone are received in the block 11 for calculating the height of the object. The volume reverberation level, threshold level, and from the depth gauge 4, the depth estimate from the sonar antenna to the bottom also comes from block 8. As a meter 4 of the depth to the bottom, for example, a multi-beam echo sounder can be used, which is a separate special sonar considered in the book of A.V. Bogorodsky, D.B. Ostrovsky. "Hydroacoustic navigation and search and survey means." St. Petersburg, 2009, p. 122. The fish finder contains a transmitting and receiving antenna, preprocessing equipment, the main processor of the system, a secondary processing unit, and a sound velocity meter. The accuracy of measuring the depth to the bottom of modern echo sounders can be several centimeters depending on the depth to the bottom and the accuracy of the estimate of the speed of sound. In block 11, the height of the object at the bottom is calculated. All input information from the output of the receiver goes to indicator 12, where the obtained estimate of the height of the object above the bottom is also output. Block 11 and block 12 are connected by two-way communication, which allows you to control the correct measurement of the height of the object by the operator and, if necessary, make adjustments. Almost all of these procedures can be implemented on modern computers and laptops that use the computer programs Matlab, Matsard, etc. (A.B. Sergienko. Digital signal processing. St. Petersburg. "BHV - Petersburg", 2011).

Thus, the proposed method allows one parcel to determine the height of the location object above the bottom. This allows us to consider the claimed technical result achieved.

Claims (1)

The hydroacoustic method for determining the spatial characteristics of an object, containing the radiation of a sounding signal at time t, receiving an echo t _echo , determines the distance D to the object from the value of the time delay and the known sound propagation speed C, characterized in that after the radiation, the volume reverberation level U ₀ is measured, U is determined detection threshold _then, the measured time t _nach echo start, wherein the first echo amplitude A _{of an} exceeded threshold A> U _pores, and determining a distance D = ₀ t _nach 0.5C measure the time instant of the last echo amplitude t _pos , at which the minimum amplitude of the echo from the object And _about > U _then. , determine the time moment of the beginning of the shadow t of the _shadow , at which the condition U ₀ ≥A _ten and t _shadow > t _pos are satisfied, determine the time of the end of the shadow t _end , at which U _then > A _about ≥U ₀ , determine the distance to the moment the end of the shadow D _shadow = 0.5 C t _con.t , determine the depth from the sonar to the bottom H of the _bottom , and the height of the object is determined by the formula $$h=\frac{(D_{ten\mathrm{and}}-D_0)H_{dn\mathrm{but}}}{D_0}$$

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