RU2740334C1 - Method of receiving seismic-acoustic and hydroacoustic waves at the bottom of a water reservoir and device for its implementation - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to hydroacoustics and geophysics and can be used to detect sound sources or obtain information on the structure and characteristics of the sea bottom (soil) by analyzing acoustic waves propagating in the ocean (geoacoustic inversion). Method involves directed reception of aggregate wave coaxially located inside a single rigid housing by 3-component vibration receiver and located on its surface of 3-component pressure gradient receiver of power type, equipped with acoustic pressure receiver, with subsequent joint processing of responses of coaxial components of 3-component receivers of pressure gradient and receiver of vibrations with extraction of hydroacoustic component.EFFECT: extraction of a hydroacoustic component from a set of seismic-acoustic and hydroacoustic waves affecting a receiving device, which further improves the quality of detecting a radiation source or estimating parameters of the bottom.5 cl, 1 dwg

Description

The invention relates to hydroacoustics and geophysics and can be used to detect a sound source or obtain information on the structure and characteristics of the seabed (soil) by analyzing acoustic waves propagating in the ocean (geoacoustic inversion).

When low-frequency sound sources are detected in the sea and other water areas, part of the low-frequency radiation of the source is transmitted by a hydroacoustic plane wave traveling in the aquatic environment, and part can be transmitted through various mechanisms into the sedimentary layer of the bottom and excite bottom seismoacoustic waves in it (in the form of normal waves traveling in the sedimentary layer, and / or flowing into the water, for example, Stoneley waves) [Bevans DA, Buckingham MJ Estimating the sound speed of a shallow-water marine sediment from the head wave excited by a low-flying helicopter // J. Acoust. Soc. Am. 2017.142 (4), P. 2273-2287. doi: 10.1121 / 1.5007953]. Both components of the wave - hydroacoustic and seismoacoustic - can propagate far enough and be detected by various receivers. However, when superimposed on each other, they distort the emitted signal, which prevents the source from being detected or from obtaining information about the structure and characteristics of the seabed.

An urgent task is to separate the seismoacoustic and hydroacoustic components of the wave, which makes it possible to improve the quality of source detection or the estimation of the parameters of the bottom of the reservoir.

Reception of a combination of sismoacoustic and hydroacoustic waves is usually performed as receivers of vibrations deepened into the sedimentary layer (receivers of vibrational displacement, vibrational velocity or vibrational acceleration) [Shi J., Dosso SE, Sun D., Qingyu L. Geoacoustic inversion of the acoustic-pressure vertical phase gradient from a single vector sensor // J. Acoust. Soc. Am. 2019.146 (5), P. 3159-3173. doi: 10.1121 / 1.5131235], and located in the water at the bottom of the sound pressure receivers - hydrophones [Gervaise S., Kinda BG, Bonnel J., Stephan Y., Vallez S. Passive geoacoustic inversion with a single hydrophone using broadband ship noise / / J. Acoust. Soc. Am. 2012. 131 P. 1999-2010]).

There is a known method and device in which the waves are received by receivers of vibrations (oscillatory speed) and sound pressure placed above and below the surface of the bottom of the reservoir and calculate the transfer functions between the sensors located above and below the surface of the bottom of the reservoir (Crocker SE, Miller JH, Potty GR, Osier JC, Hines P.S. Nonlinear inversion of acoustic scalar and vector field transfer function // IEEE J. Oceanic Eng. 2012.37.P. 589-607).

However, these described methods and the devices implementing them do not allow separating the seismoacoustic and hydroacoustic wave components.

The closest to the claimed device is a device for receiving a set of seismoacoustic and hydroacoustic waves, which is a mixed receiver with a single rigid body, including both a vibration receiver (geophone) and a sound pressure receiver (hydrophone), while an acceleration sensor with the inertial mass, around which the sound pressure receiver is coaxially located. A receiving seismic pin is rigidly connected to the vibration receiver. Depending on the operating conditions, the reception of a set of seismoacoustic and hydroacoustic wave components is performed either by a vibration receiver (geophone) or a non-directional sound pressure receiver (hydrophone), depending on the operating conditions, however, the sensor responses are not jointly processed in order to isolate the seismoacoustic and hydroacoustic wave components (p. FR No. 2543692).

Thus, with the help of the known geohydrophone, it is possible to work with the same device, both as a sound pressure receiver and as a vibration receiver, depending on the conditions of its operation, that is, the same as in the above analogs, without any - or joint switching on of the sensor outputs, that is, without the possibility of separating the seismoacoustic and hydroacoustic wave components.

The problem to be solved is the separation of the seismoacoustic and hydroacoustic components of the aggregate wave.

To solve it, a method is proposed for receiving a combination of seismoacoustic and hydroacoustic components of a wave at the bottom of a reservoir folded by sedimentary rocks of the soil, including directional reception of the aggregate wave simultaneously coaxially located inside a single rigid body with a 3-component vibration receiver and a 3-component receiver of pressure gradient located on its surface power type, equipped with a sound pressure receiver, joint processing of the responses of the coaxial components of the 3-component pressure gradient receivers and the vibration receiver with the extraction of the hydroacoustic component by calculating the difference in the responses of the pressure gradient receiver components and the responses of the coaxial components of the vibration receiver with presetting the amplification factor of the vibration receiver channels to the maximum suppression of model vibrations, while the vibration receiver is located in the center of mass of the housing located in the ground, and the pressure gradient receiver with the sound pressure receiver enia - on the surface of the hull in water above the ground.

If necessary, in the future, it is possible to divide the selected hydroacoustic wave into mainly flat and inhomogeneous components, using intensimetric multiplicative processing of responses. To do this, the operation of amplifying the difference in the responses of the coaxial components of the pressure gradient and vibration receivers with a predetermined gain is carried out and the mutual spectrum of the obtained difference in responses is calculated for each component with the response of the sound pressure receiver, and from the calculated mutual spectrum, the real part characterizing a plane hydroacoustic wave from the remote source, and an imaginary part characterizing an inhomogeneous hydroacoustic wave.

The problem is also solved by a device for receiving a set of seismoacoustic and hydroacoustic waves at the bottom of a reservoir composed of sedimentary rocks of the soil, consisting of a single rigid body, with an average density close to the density of the soil, in the center of mass of which there is a 3-component vibration receiver, and on the surface it is coaxial to the components of the vibration receiver, a 3-component force-type pressure gradient receiver is installed, additionally equipped with a sound pressure receiver installed to ensure a single phase center with the components of the pressure gradient receiver, while the electrical outputs of the coaxial components of the pressure gradient receiver and vibration receiver are connected through amplifiers with subtraction units, and the outputs of the subtraction units through amplifiers, together with the outputs of the sound pressure receiver, are connected to the data processing unit.

The technical result of the joint use of the proposed solutions is the separation of the hydroacoustic component from the totality of the seismoacoustic and hydroacoustic waves acting on the receiving device, which allows, if necessary, to use the obtained result for the subsequent separation from the hydroacoustic wave of a predominantly flat (traveling from a distant sound source) and inhomogeneous component, that in the future, together with the seismoacoustic component of the received aggregate signal, it can be used, inter alia, for detection / direction finding of a remote sound source or obtaining information about the structure and characteristics of the bottom of a reservoir (geoacoustic inversion) by known methods

FIG. shows the configuration of the claimed device and its placement at the bottom of the water area, where 1 - bottom sedimentary rocks of the bottom of the water area, 2 - rigid body, 3-3-component vibration receiver, 4-3-component pressure gradient receiver (PGD) of power type with built-in sound pressure receiver channel; p _wa , v _wa - sound pressure and vibrational velocity in a plane hydroacoustic wave propagating in an aqueous medium; a _sa - three components of acceleration caused by a seismoacoustic wave propagating in the ground; p _wS , v _wS - sound pressure and vibrational velocity of an inhomogeneous hydroacoustic wave re-emitted by a seismoacoustic wave from the ground into water, in particular, for example, a Stoneley wave.

The efficiency of the method and device is confirmed by the theoretical model of its functioning.

On the assumption that body 2 is significantly less than the wavelength and is almost completely in the ground, only seismic acoustic waves (both longitudinal and transverse) act on it, but a plane hydroacoustic wave traveling from a distant source does not act. In this system (Fig), we have the following sensor responses.

The electrical response of a 3-component vibration receiver 3 in the form of an acceleration accelerometer can be written in the form:

U _acsa = ν _acsa a _sa , where ν _acsa is the accelerometer acceleration sensitivity, and

a _sa - acceleration, vectors with components ( _ax , _y , a _z ), x, y, z - Cartesian coordinates.

In the case of harmonic signals, this electrical response of the accelerometer can be converted to the form

where i is the imaginary unit, ω is the circular frequency of the signal.

When the longitudinal seismoacoustic component of the wave propagates in sedimentary rocks, information on the direction of its arrival can be obtained in a known manner by the value of the ratios of the obtained components (ν _acsax a _x , ν _acsay a _y , ν _acsaz a _z ), i.e. direction to the signal source. However, when a transverse seismoacoustic wave propagates in sedimentary rocks, all information about the direction of its arrival is lost.

On the other hand, the electrical response of a 3-component PGD of power type 4 consists of several components

where ν _pgsa is the acceleration sensitivity of PGD, ν _pgsv is the oscillatory velocity sensitivity of PGD,

a _sa / iω vector that corresponds to the vibrational velocity in the seismoacoustic wave,

v _wa vector, which corresponds to the vibrational velocity in a plane hydroacoustic wave,

v _wS is a vector that corresponds to the vibrational velocity of an inhomogeneous hydroacoustic wave flowing from the ground into the water.

_By constructing the difference of responses U _pgsv - U _acsv , we obtain:

If the equality ν _pgsa = ν _acsa (for each of the 3 components of both receivers is _fulfilled , which is achieved by presetting the accelerometer gain ν _acsa to the maximum suppression of model vibrations when the device is suspended on a vibration table above water in each direction of the components of the pressure gradient receivers and vibration, for example, as suggested in p. RF No. 2624791, the term in parentheses (3) is reset to zero, and expression (3) itself is reduced to the form

Thus, the obtained difference (4) describes the response only to the hydroacoustic component of the total wave incident on the device.

At the same time, it is known that there are two waves in the hydroacoustic component - plane (first term) and inhomogeneous, flowing from the bottom (second term). In this case, the sound pressure channel, combined with the PGD, being insensitive to vibrations, registers the response of scalar quantities:

To separate the plane hydroacoustic wave, described by the parameters p _wa , v _wa, and the inhomogeneous flowing hydroacoustic wave, described by the parameters p _wS , v _{wS, we} use the _{intensimetric} multiplicative processing of the responses. It is known that the separation of the real part of the mutual spectrum (power flow) through the fast Fourier transform (FFT) allows suppressing inhomogeneous hydroacoustic waves (Korenbaum VI, Tagiltsev AA. Flow noise of an underwater vector sensor embedded in a flexible towed array // J. Acoust. Soc. Am. 2012. 131 (5): 3755-3762. DOI: 10.1121 / 1.3693647) and calculate the spectra of the spatial components of the vector of the active part of the power flux (intensity) of a plane hydroacoustic wave. Thus, we get

Accordingly, on the contrary, the calculation of the imaginary part of the mutual spectrum makes it possible to single out the spectra of the spatial components of the reactive part of the power flow:

Thus, using expression (1), the predominantly seismoacoustic component of the aggregate wave can be recorded, using expressions (3, 4), the predominantly hydroacoustic component of the aggregate wave, using expression (6), a predominantly plane hydroacoustic wave, and using the expression ( 7) - predominantly inhomogeneous hydroacoustic wave.

Thus, all hydroacoustic and seismoacoustic components of the received aggregate signal can be separated. And this can be used to detect / find a distant sound source or obtain information about the structure and characteristics of the bottom of a reservoir (geoacoustic inversion) using known methods.

Already isolated from the hydroacoustic component - a plane sound wave (6) - in each direction of the components of the pressure gradient receiver according to the ratio of the amplitudes of the responses in these components, using the additional channel of the sound pressure receiver to eliminate the ambiguity of direction finding, it is possible to determine the direction to the signal source by a known vector phase method. Thus, having performed the operation of calculating the real part of the mutual spectrum in the directions of each of the coaxial components of the receivers of the pressure gradient and vibrations, the bearing to the source of the hydroacoustic wave is determined in relation to the amplitudes of the components of the real part of the mutual spectrum.

Similarly, to increase the noise immunity of receiving the hydroacoustic part of the signal from a remote source or scanning through space in search of a signal source, using the already identified difference in responses characterizing the components of the hydroacoustic signal, unidirectional radiation patterns such as a cardioid or a product of a cosine and a cardioid can be formed, for example, as in p. RF 2687301. For this, the operation of amplifying the difference in responses with a predetermined gain of the difference is carried out, and together with the response of the sound pressure receiver, unidirectional radiation patterns of the cardioid type or the product of the cosine wave and the cardioid are formed in the direction of each of the components of the pressure gradient and vibration receivers.

You can also try to sum up in phased all the selected wave components with an adjustable time delay to improve the efficiency of detecting a remote signal source. In this case, time delays can be determined by one of the known criteria for optimal signal detection against the background of interference.

For the tasks of geoacoustic inversion, information on the inhomogeneous flowing hydroacoustic wave obtained in accordance with expression (7) may be useful. By the ratio of signal amplitudes in the channels of the x, y, z components, one can obtain information about the vertical angle of the outflow of this wave from the bottom, which determines the seismoacoustic properties of the sedimentary layer of the soil.

During seismoacoustic sounding of the bottom from inclined directions close to vertical, as a rule, there are three acoustic waves: hydroacoustic incident, reflected and seismoacoustic transmitted. The transmitted seismoacoustic wave causes vibrations of the device body; therefore, to separate the incident and reflected waves, it is necessary to use the differences in the responses of the components of the pressure gradient receivers and the vibration receiver. Only to isolate the incident wave, it follows from the indicated difference in the responses of the vertical components of the PGD and the vibration receiver, as well as the response of the sound pressure channel, to form a cardioid directivity characteristic oriented with its maximum upward, and zero - downward. Thus, the reflected hydroacoustic wave is largely suppressed.

Whereas, in order to isolate the hydroacoustic wave reflected from the bottom, it is necessary to form an oppositely oriented cardioid directivity characteristic from the same responses. In this case, on the contrary, the incident hydroacoustic wave is suppressed.

The seismoacoustic wave that has passed into the bottom, if it is longitudinal, is determined from the response of the vertical component of the vibration receiver, and if it is transverse, then from the responses of the horizontal components of the vibration receiver. By providing appropriate gains that equalize the sensitivities of the sensors, you can now accurately determine the reflection and transmission coefficients of the probe wave. Moreover, in this case, sounding can be performed not only by impulse, but also by continuous, including noise, signal.

The claimed invention will be illustrated by the following example.

In case 2, (made, for example, of sea concrete), having an average density corresponding to the density of the soil 1 of bottom sedimentary rocks, a three-component accelerometer 3 is installed in the center of mass as a vibration receiver, and on top of the symmetry axis, a three-component power-type PGD is coaxial to the accelerometer components with a sound pressure channel, for example, in the form of a cruciform device 4 described in RF patent No. 2679931. In this case, the body 2 is installed with its bottom in the sedimentary rocks of the soil 1 with a depression, but so that the PGD remains in the aquatic environment (Fig).

Accelerometer 3 components are used to receive seismoacoustic waves propagating in sedimentary rocks of the bottom, while for receiving hydroacoustic waves propagating in an aquatic environment, the difference in responses of the components of PGD 4 and accelerometer 3 is used, formed in the subtraction unit (made, for example, on an operational amplifier located in the processing unit, according to expressions (3, 4), having previously adjusted the equality of their vibration acceleration sensitivities ν _pgsa = ν _acsa for each of the 3 components of both sensors.This is achieved, for example, by presetting the accelerometer gain ν _acsa to the maximum suppression of model vibrations when the device is suspended on a vibrating vibration table above the water with orientation in each direction of the components of the pressure gradient and vibration receivers (for example, p. RF No. 2624791. This inclusion provides compensation for the responses of the PGD components to the vibrations of a single rigid body caused by a seismoacoustic wave.

In this case, to separate a plane hydroacoustic wave from the outgoing part of an inhomogeneous wave, for example, a Stoneley wave, the real part of the mutual spectrum (power flux) is calculated from the difference between the responses of the PGD components and the components of the accelerometer (after integration) and the sound pressure channel according to expression (6).

On the contrary, to isolate the inhomogeneous part of the hydroacoustic wave, in particular the flowing out, for example, Stoneley wave, the imaginary part of the mutual spectrum is calculated from the difference in responses of the PGD components and the components of the accelerometer (after integration) and the sound pressure channel, according to expression (7).

Cross-spectrum calculations are performed in a processing unit using a program, for example, SpectraPLUS (Pioneer Hill Software), located either next to the device, or on the water surface in a special buoy, or on the shore. The real and imaginary parts of the mutual spectrum are calculated, for example, by transferring the module and phase calculated in the SpectraPLUS (Pioneer Hill Software) package in the form of columns to any spreadsheet, for example, Excel (Microsoft), by multiplying the modulus by the cosine or sine of the phase, respectively.

Thus, the proposed solution allows us to solve the posed problem of separating the hydroacoustic and seismoacoustic components from the aggregate wave acting on the receiving device, and significantly expand the functionality of the proposed solution, allowing then to solve many problems facing hydroacoustics and geophysics, including can be used for detecting a distant sound source or obtaining information about the structure and characteristics of the seabed

Claims (5)

1. A method of receiving seismoacoustic and hydroacoustic components of a wave at the bottom of a reservoir folded by sedimentary rocks, including a directional reception of the aggregate wave simultaneously coaxially located in a single rigid body with a 3-component force-type pressure gradient receiver equipped with a sound pressure receiver and a 3-component vibration receiver, joint processing the response of the coaxial components of the 3-component receivers and the vibration receiver, followed by the extraction of the hydroacoustic component by calculating the difference in the responses of the pressure gradient receiver components and the responses of the coaxial components of the vibration receiver with preliminary adjustment of the amplification factor of the vibration receiver channels to the maximum suppression of model vibrations, while the vibration receiver is placed in the center of mass of the housing located in the ground, and the pressure gradient receiver with the sound pressure receiver is on the surface of the housing in the water. 2. The method according to claim 1, characterized in that the operation of amplifying the difference between the responses of the components of the pressure gradient receiver and the coaxial components of the vibration receiver with a predetermined gain is performed, and the result is summed and / or subtracted with the response of the sound pressure receiver, forming unidirectional radiation patterns of the type cardioids in the direction of each of the components. 3. The method according to claim 1, characterized in that the operation of amplifying the difference in responses of the coaxial components of the pressure gradient and vibration receivers with a predetermined gain is carried out and the mutual spectrum of the obtained difference in responses is calculated for each component with the response of the sound pressure receiver, from which the real part is extracted , characterizing a plane hydroacoustic wave from a distant source, and an imaginary part characterizing an inhomogeneous hydroacoustic wave. 4. The method according to claim 3, characterized in that the ratio of the amplitudes of the components of the real part of the mutual spectrum is calculated and the bearing to the source of the hydroacoustic wave is determined. 5. A device for receiving seismoacoustic and hydroacoustic waves at the bottom of a reservoir composed of sedimentary rocks, consisting of a single rigid body with an average density close to the density of the soil, in the center of mass of which there is a 3-component vibration receiver, and on the surface, coaxially with the components of the vibration receiver, 3 - a power-type component pressure gradient receiver, additionally equipped with a sound pressure receiver installed to ensure a single phase center with the components of the pressure gradient receiver, while the electrical outputs of the coaxial components of the pressure gradient receiver and vibration receiver are connected through amplifiers with subtraction units, and the outputs of the subtraction units through the amplifiers together with the outputs of the sound pressure receiver are connected to the data processing unit.

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