CN114460644A

CN114460644A - Method for distinguishing near-far field of seismic waves induced by navigation of underwater target

Info

Publication number: CN114460644A
Application number: CN202210058771.0A
Authority: CN
Inventors: 程广利; 潘逊; 刘宝; 陈亚男; 庞昕
Original assignee: Naval University of Engineering PLA
Current assignee: Naval University of Engineering PLA
Priority date: 2022-01-05
Filing date: 2022-01-05
Publication date: 2022-05-10
Anticipated expiration: 2042-01-05

Abstract

The invention relates to a method for distinguishing near and far fields of seismic waves induced by navigation of an underwater target, which comprises the following steps: acquiring shallow sea seismic wave field original data; including sound pressure time domain waveform and sound pressure cloud chart; processing the sound pressure cloud picture into a sound pressure wave field snapshot set; processing the sound pressure time domain waveform into a sound pressure-distance relative change curve; performing low-precision dividing operation of the far and near fields of the seismic waves to obtain a low-precision first boundary point position and a low-precision second boundary point position; performing high-precision division operation on the near and far fields of the seismic waves to obtain a high-precision first boundary point position and a high-precision second boundary point position; and (5) carrying out boundary point checking operation to obtain a boundary point consistency evaluation result and a boundary point range. The method effectively discriminates the far field, the transition field and the near field in the seismic waves; the underwater navigation target positioning device is suitable for passively and remotely positioning an underwater navigation target; and further based on the method, a proper array arrangement topological structure of the underwater sensor can be obtained according to different measurement requirements.

Description

Method for distinguishing near-far field of seismic waves induced by navigation of underwater target

Technical Field

The invention relates to the technical field of underwater target detection, in particular to a method for distinguishing near and far fields of seismic waves induced by navigation of an underwater target.

Background

The use of seismic waves to detect underwater targets is of considerable value, since seismic waves are generated by disturbances of underwater targets during navigation; the very low frequency radiation noise field of the underwater target induces submarine seismic waves on the seabed nearby, the submarine seismic wave signals comprise a ground sound signal and an underwater sound signal, the submarine seismic wave signals are positioned in the area nearby the lower part of the target, namely a near field, and the submarine seismic wave signals are the source area of energy of the submarine seismic wave signals and gradually transit and propagate to a far field along a sea water-seabed interface and the seabed; this is an unavoidable wave propagation phenomenon; furthermore, the very low frequency band signal in the radiation noise generated by the underwater target in the navigation has the characteristics of long propagation distance, attenuation and the like, and is easy to detect; therefore, the underwater target using the existing hidden navigation technology can be effectively detected only by properly arranging the sensor array and reasonably processing the acquired seismic wave signals, and the application prospect is very wide;

however, the components of the ocean bottom seismic wave are complex, the ocean bottom seismic wave comprises a plurality of fluctuation components such as longitudinal waves, transverse waves, surface waves and side waves, and the propagation paths and the expansion modes of different fluctuation components are different, so that the original signals acquired by the receiving points are mixed and cannot be directly utilized; especially, signals of a far field, a transition field and a near field are mixed together and can be further utilized after being discriminated;

the defects of the prior art are as follows:

1. for the research of underwater acoustic signals, the method is currently limited to the far and near field discrimination method of underwater target acoustic radiation and acoustic scattering signals, but is not suitable for the discrimination of the far and near fields of submarine seismic waves induced by the navigation of underwater targets;

2. no existing literature provides an effective discrimination method for judging the far field and the near field of seismic waves;

in summary, the discrimination of the far field, the transition field and the near field of the seismic wave becomes a very valuable but not realized technology.

Disclosure of Invention

Aiming at the problems, the invention provides a method for distinguishing the near-far field and the far field of submarine seismic waves induced by navigation of an underwater target, and aims to effectively distinguish the far field, the transition field and the near field in the seismic waves; the underwater navigation target detection device is suitable for passively and remotely detecting underwater navigation targets; and further based on the method, a proper distribution topological structure of the submarine seismic wave sensor array can be obtained according to different measurement requirements.

In order to solve the problems, the technical scheme provided by the invention is as follows:

the method for distinguishing the near-far field and the far field of seismic waves induced by navigation of the underwater target comprises the following steps:

s100, acquiring shallow sea seismic wave field original data; the shallow sea seismic wave field original data comprises a sound pressure time domain waveform and a sound pressure cloud chart which are taken at the interface between sea water and the sea bottom; then processing the sound pressure cloud picture into a sound pressure wave field snapshot set; then processing the sound pressure time domain waveform into a sound pressure-distance relative change curve; the sound pressure wave field snapshot set comprises sound pressure wave field snapshots arranged in time increasing order;

s200, according to the sound pressure wave field snapshot set, performing low-precision division operation on a far-near field of seismic waves to obtain a low-precision first boundary point position and a low-precision second boundary point position;

s300, according to the sound pressure-distance relative change curve, performing high-precision division operation on the near and far fields of seismic waves to obtain a high-precision first boundary point position and a high-precision second boundary point position;

s400, performing demarcation point check operation according to the low-precision first demarcation point position, the low-precision second demarcation point position, the high-precision first demarcation point position and the high-precision second demarcation point position to obtain a demarcation point consistency evaluation result and a demarcation point range; and the dividing point consistency evaluation result and the dividing point range are the final result of the invention.

Preferably, in S100, the sound pressure time-domain waveform is acquired by a plurality of receiving points arranged on a central axis of a sea bottom surface in the established shallow sea bottom seismic wave model; the receiving points are arranged in a grid form and are equal in distance.

Preferably, the sound pressure time-domain waveform is a time-domain waveform in a two-dimensional rectangular coordinate system, where: the origin of the sound pressure time domain waveform is the sound pressure intensity received by the receiving point at time 0, the horizontal axis is time, and the vertical axis is the sound pressure intensity.

Preferably, in S100, the sound pressure cloud map is spatial data in three-dimensional coordinates, where: the original point is preset manually, the position is a place where the projection distance of the geometric center of the underwater target on the seabed surface is two grids, the horizontal axis is the horizontal coordinate of the sound pressure signal from the manually preset original point, the vertical axis is the vertical coordinate of the sound pressure signal from the original point, and the vertical axis represents the energy of the sound pressure signal.

Preferably, in S100, the processing the sound pressure cloud map into a sound pressure wave field snapshot set specifically includes the following steps:

s110, intercepting the sound pressure cloud picture in a manually preset time range according to a manually preset interception frequency, wherein each interception is to obtain one sound pressure wave field snapshot;

and S111, arranging each sound pressure wave field snapshot according to the increasing sequence of time, and then packaging to obtain the sound pressure wave field snapshot set.

Preferably, in S100, processing the sound pressure time-domain waveform into a sound pressure-distance relative variation curve specifically includes the following steps:

s120, selecting an artificially preset number from all the collected sound pressure time domain waveforms, wherein the sound pressure time domain waveforms are subjected to excitation for an excitation time length and then fluctuate up and down in fluctuation ranges on two sides of a peak value, wherein the peak value is taken as a core; the excitation time is preset manually; the fluctuation range is preset manually;

s121, extracting sound pressure peak values one by one for each sound pressure time domain waveform selected from S120;

and S122, taking logarithm of each sound pressure peak value, and then arranging the sound pressure peak values according to the sequence of the corresponding receiving points to obtain the sound pressure-distance relative change curve.

Preferably, in S200, the seismic wave near-far field low-precision dividing operation specifically includes the following steps:

s210, correspondingly calibrating each grid on each sound pressure wave field snapshot in the sound pressure wave field snapshot set one by one according to the following standards:

if the number of the grids occupied by the central energy ring in the area where the grids are located is the largest in all time points and the outer waveform only contains one color, calibrating the grids as low-precision first boundary points;

if the waveform of the outer side of the area where the grid is located is restored to be one color again and the wave field is in a regular circular ring shape, the grid is marked as a low-precision second boundary point;

s220, counting the number of continuously arranged grids between an origin and each low-precision first boundary point under the three-dimensional coordinates of the sound pressure cloud picture; multiplying the grid number between each low-precision first boundary point and the origin of the coordinate system by the side length of the grid to obtain the position of the low-precision first boundary point; then according to the low-precision first boundary point position, the following operations are carried out:

if the low-precision first boundary point position does not cross the middle of a grid, confirming that the low-precision first boundary point position is correct, and then outputting the low-precision first boundary point position;

if the position of the low-precision first boundary point crosses the middle of a grid, drawing a circle by taking the position of the low-precision first boundary point as a circle center and taking the side length of the grid as a radius; then, taking the range covered by the drawn circle as a new low-precision first boundary point position, and outputting the new low-precision first boundary point position;

s230, counting the number of grids between the origin of the coordinate system and each low-precision second demarcation point; multiplying the grid number between each low-precision second boundary point and the origin of the coordinate system by the side length of the grid to obtain the position of the low-precision second boundary point; then according to the low-precision second boundary point position, the following operations are carried out:

if the low-precision second boundary point position does not cross the middle of a grid, confirming that the low-precision second boundary point position is correct, and then outputting the low-precision second boundary point position;

if the position of the low-precision second boundary point crosses the middle of a grid, drawing a circle by taking the position of the low-precision second boundary point as a circle center and taking the side length of the grid as a radius; the range covered by the drawn circle is then taken as the new low-precision second demarcation point location, which is then output.

Preferably, in S300, the seismic wave near-far field high-precision dividing operation specifically includes the following steps:

s310, fitting the sound pressure-distance relative change curve to obtain a fitting curve; then dividing the sound pressure-distance relative change curve into different stages; the stages comprise a first stage, a second stage and a third stage; wherein:

the first stage is a relative change curve of the sound pressure-distance covered by a range from an original point to a first turning point; the first turning point is a first turning point which starts from an original point and runs along the positive direction of the sound pressure-distance relative change curve;

the second stage is a sound pressure-distance relative change curve covered by a range from the first turning point to a second turning point; the second turning point is a second turning point encountered by traveling along the positive direction of the sound pressure-distance relative change curve;

the third stage is a sound pressure-distance relative change curve covered by a range from the second turning point to a third turning point; the third turning point is a third turning point encountered by traveling along the positive direction of the sound pressure-distance relative change curve;

s320, judging the expansion mode of the seismic waves in each stage one by one according to the attenuation degree of the sound pressure value in each stage; the expansion mode comprises a spherical wave expansion mode and a cylindrical wave expansion mode;

then, marking the corresponding stage with a far field and a near field according to the expansion mode; wherein:

if the expansion mode is the spherical wave expansion mode, marking the corresponding stage as a near field;

if the expansion mode is the partial cylindrical wave expansion mode, marking the corresponding stage as a far field;

s330, according to the interference effect between different fluctuation components corresponding to the waveform of the sound pressure-distance relative change curve in each stage, performing near-far field confirmation on each stage; wherein:

if the coincidence degree of the sound pressure-distance relative change curve of the stage and the fitting curve is not lower than an artificially preset coincidence degree minimum threshold value, and the fluctuation degree of the sound pressure-distance relative change curve of the stage is lower than an artificially preset fluctuation index minimum threshold value and is marked as a near field in S320, determining that the stage is the near field;

if the coincidence degree of the sound pressure-distance relative change curve and the fitting curve of the stage is not lower than the coincidence degree minimum threshold and is marked as a far field in S320, the stage is confirmed to be a far field;

if the fluctuation degree of the sound pressure-distance relative change curve of the stage is lower than the fluctuation index minimum threshold, the coincidence degree of the sound pressure-distance relative change curve of the stage and the fitting curve is lower than the coincidence degree minimum threshold, and the sound pressure-distance relative change curve of the stage fluctuates up and down around the fitting curve, the stage is determined to be a transition region;

s340, obtaining the position of the high-precision first boundary point and the position of the high-precision second boundary point according to the confirmed relation between the stages; specifically, the method comprises the following steps:

in the range between the near field and the transition area, the first turning point encountered from the near field is the position of the high-precision first boundary point;

in the range between the transition area and the far field, the second turning point from the transition area is the position of the high-precision second boundary point;

then packaging all the high-precision first demarcation point positions, and packaging all the high-precision second demarcation point positions, and outputting the high-precision second demarcation point positions as a result of the step;

preferably, in S400, the obtaining of the boundary point consistency evaluation result and the boundary point range specifically includes the following steps:

and Sa410, comparing the high-precision first boundary point positions with the low-precision first boundary point positions one by one, and according to a comparison result, performing the following operations:

if the high-precision first demarcation point position is completely consistent with the low-precision first demarcation point position, or the high-precision first demarcation point position is in a range covered by a circle used as the low-precision first demarcation point position, adding a character string 'first demarcation point' in the demarcation point consistency evaluation result to obtain success; simultaneously giving the high-precision first demarcation point position to a first demarcation point; then executing Sa 430;

if the high-precision first boundary point position and the low-precision first boundary point position are not overlapped, adding a character string 'first boundary point acquisition failure' into the boundary point consistency evaluation result; then executing Sa 430;

and Sa420, comparing the high-precision second boundary point positions with the low-precision second boundary point positions one by one, and according to a comparison result, performing the following operations:

if the position of the high-precision second demarcation point is completely consistent with the position of the low-precision second demarcation point, or the position of the high-precision second demarcation point is in a range covered by a circle used as the position of the low-precision second demarcation point, adding a character string 'second demarcation point' in the demarcation point consistency evaluation result to obtain success; simultaneously endowing the high-precision second demarcation point position to a second demarcation point; then executing Sa 430;

if the high-precision second demarcation point position and the low-precision second demarcation point position are not overlapped, adding a character string 'second demarcation point acquisition failure' into the demarcation point consistency evaluation result; then executing Sa 430;

sa430, the dividing point consistency evaluation result after the character strings are added by the Sa410 and the Sa420 is the dividing point consistency evaluation result; and packing the first demarcation point and the second demarcation point as the demarcation point range.

Compared with the prior art, the invention has the following advantages:

1. according to the method, the boundary point of the far field-transition region and the boundary point of the transition region-near field are divided at low precision and high precision simultaneously based on the sound pressure-distance relative change curve and the sound pressure cloud chart, and then the division results are compared and evaluated, so that the far field, the transition field and the near field in seismic waves can be effectively discriminated;

2. the method can effectively discriminate the far field, the transition field and the near field in the seabed seismic waves induced by the navigation of the underwater target, thereby being very suitable for passively and remotely detecting the underwater navigation target;

3. because the invention can effectively discriminate far field, transition field and near field in seismic wave, a proper array arrangement topological structure of the underwater sensor can be obtained according to different measurement requirements based on the far field, the transition field and the near field.

Drawings

FIG. 1 is a schematic top view of a simulation model according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of an orthographic view of a simulation model according to an embodiment of the invention;

FIG. 3 is a schematic flow chart illustrating steps of an embodiment of the present invention;

fig. 4a to 4f are graphs showing relative variation of sound pressure-distance along the y direction of the sea bottom at different vibration source frequencies under 20m × 20m grid under non-fixed frequency according to the embodiment of the present invention, where fig. 4a corresponds to 5Hz, fig. 4b corresponds to 10Hz, fig. 4c corresponds to 20Hz, fig. 4d corresponds to 30Hz, fig. 4e corresponds to 40Hz, and fig. 4f corresponds to 50 Hz;

fig. 5a is a sound pressure-distance relative variation curve at 50Hz on a 5m × 5m grid with non-fixed frequency according to an embodiment of the present invention;

fig. 5b is a graph showing a comparison of sound pressure-distance curves at 20m × 20m grid and at 5m × 5m grid of 50Hz according to an embodiment of the present invention;

fig. 6a to 6c are schematic diagrams of sound pressure wave field snapshots at a non-fixed frequency of 50Hz, where fig. 6a corresponds to 0.07s, fig. 6b corresponds to 0.20s, and fig. 6c corresponds to 1.10s, according to an embodiment of the present invention;

FIG. 7a is a diagram illustrating a first demarcation point at a non-fixed frequency according to an embodiment of the present invention;

FIG. 7b is a diagram illustrating a second demarcation point at a non-fixed frequency according to an embodiment of the present invention;

fig. 8a to 8e are graphs showing relative variation of sound pressure-distance along the y direction of the sea bottom at different vibration source frequencies under a 20m × 20m grid with a fixed frequency according to an embodiment of the present invention, where fig. 8a corresponds to 5.607Hz, fig. 8b corresponds to 15.415Hz, fig. 8c corresponds to 25.897Hz, fig. 8d corresponds to 35.530Hz, and fig. 8e corresponds to 45.851 Hz;

FIG. 9a is a schematic diagram of a first demarcation point at different fixed frequencies according to an embodiment of the present invention;

FIG. 9b is a schematic diagram of a second demarcation point at different fixed frequencies according to an embodiment of the present invention;

FIG. 10a is a diagram illustrating a first demarcation point at each fixed frequency according to an embodiment of the present invention;

FIG. 10b is a diagram illustrating a second demarcation point at each fixed frequency in accordance with an embodiment of the present invention;

fig. 11 is a schematic diagram of a transfer relationship fitting curved surface under consideration of transfer relationships at different vibration source frequencies according to an embodiment of the present invention;

fig. 12 is a sound pressure-distance relative variation curve considering the transmission relationship when f is 50Hz according to the embodiment of the present invention;

FIG. 13 is a schematic view of underwater target surface acoustic source excitation according to an embodiment of the present invention;

FIG. 14 is a schematic representation of a seafloor surface receiver coordinate system of an embodiment of the present invention;

FIG. 15 is a schematic diagram of a seafloor surface acoustic pressure time domain waveform of an embodiment of the invention;

fig. 16a to 16f are graphs showing relative variation of sound pressure-distance along the y direction on the seabed at different vibration source frequencies according to the embodiment of the present invention, where fig. 16a corresponds to a frequency of 5Hz, fig. 16b corresponds to a frequency of 10Hz, fig. 16c corresponds to a frequency of 20Hz, fig. 16d corresponds to a frequency of 30Hz, fig. 16e corresponds to a frequency of 40Hz, and fig. 16f corresponds to a frequency of 50 Hz;

fig. 17a to 17c are schematic diagrams of sound pressure wave field snapshots at a sound source frequency f of 30Hz, where fig. 17a corresponds to 0.07s, fig. 17b corresponds to 0.20s, and fig. 17c corresponds to 1.10s, according to an embodiment of the present invention;

FIG. 18a is a schematic diagram of a first dividing point at different sound source frequencies according to an embodiment of the present invention;

FIG. 18b is a schematic diagram of a second demarcation point at different source frequencies in accordance with an embodiment of the present invention;

FIG. 19 is a fitting surface at different sound source frequencies according to an embodiment of the present invention;

fig. 20 is a sound pressure variation curve when f is 47Hz at different sound source frequencies according to an embodiment of the present invention.

Detailed Description

The present invention is further illustrated by the following examples, which are intended to be purely exemplary and are not intended to limit the scope of the invention, as various equivalent modifications of the invention will occur to those skilled in the art upon reading the present disclosure and fall within the scope of the appended claims.

It should be noted that, because the vibration frequencies generated by different devices of the target in the water are different, the influence caused by the frequency change of the vibration source needs to be considered; in addition, since the technology mainly aims at the very low frequency signals of 5Hz to 50Hz, the specific embodiment selects non-natural frequencies of 5Hz, 10Hz, 20Hz, 30Hz, 40Hz and 50Hz as main vibration sources for simulation, simultaneously selects 5.607Hz, 15.415Hz, 25.897Hz, 35.530Hz and 45.851Hz under the natural frequencies as main vibration sources for simulation, and selects simulation conditions under the conditions that the waveforms of the ship sound pressure under different frequencies are fitted by using a least square method under the consideration of the transfer relationship, and the sound source frequencies are also selected as the main vibration sources and the influence of the sound source frequencies on the far and near fields of the seismic waves is exerted, thereby explaining the technical means and the corresponding technical effects of the invention in detail.

It should be noted that although the present embodiment is exemplified by very low frequency signals, the technical solution of the present invention applied to other frequency domains also falls into the protection scope of the present invention.

It should be noted that the simulation model of the present embodiment is configured as shown in fig. 1-2, wherein the red point in fig. 2 is a receiving point arranged on the sea surface.

As shown in fig. 3, the method for determining the near-far field and the far field of seismic waves induced by the navigation of the target in water comprises the following steps:

s100, acquiring shallow sea seismic wave field original data; the shallow sea seismic wave field original data comprises a sound pressure time domain waveform and a sound pressure cloud chart; the sound pressure cloud map is then processed into a set of sound pressure wavefield snapshots.

It should be noted that when the target in the water sails in shallow sea, shallow sea seismic waves are induced; the shallow sea seismic waves carry position information of the targets in the water; therefore, the first step is to acquire the shallow sea seismic wave field raw data, and then preprocess the shallow sea seismic wave field raw data to form a sound pressure time domain waveform and a sound pressure cloud chart for the subsequent steps.

In this embodiment, the processing of the sound pressure cloud map into the sound pressure wave field snapshot set specifically includes the following steps:

and S110, intercepting the sound pressure cloud picture in the manually preset time range according to the manually preset interception frequency, wherein each interception is to obtain a sound pressure wave field snapshot.

And S111, arranging each sound pressure wave field snapshot according to the increasing sequence of time, and then packaging to obtain a sound pressure wave field snapshot set.

Then processing the sound pressure time domain waveform into a sound pressure-distance relative change curve; the set of sound pressure wavefield snapshots comprises sound pressure wavefield snapshots arranged in increasing order of time.

It should be further explained that, because the boundary values of the near field and the far field are different under different vibration source frequencies, the boundary point of the near field-transition region, i.e. the first boundary point, is more concentrated and has a small variation amplitude, and is easily affected by the grid precision; and the transition region-far field boundary point, namely the second boundary point, is relatively dispersed and has a large variation amplitude, so that the influence of the grid precision can be ignored.

In the specific embodiment, the sound pressure time domain waveform is acquired through a plurality of receiving points arranged on a central axis of the sea bottom surface in the built shallow sea bottom seismic wave model, wherein the sea bottom model is a cube, the sea bottom surface is a square, and the symmetry axis is a straight line which enables the square to form axial symmetry; the receiving points are arranged in a grid form and are equidistant from each other.

It should be noted that the sound pressure time domain waveform is a time domain waveform in a two-dimensional rectangular coordinate system, where: the origin of the sound pressure time domain waveform is the sound pressure intensity received by the receiving point at time 0, the horizontal axis is time, and the vertical axis is the sound pressure intensity.

It should be noted that the sound pressure cloud chart is spatial data in three-dimensional coordinates, where: the original point is preset manually, the position is the projection first grid position on the seabed surface from the right (left) end of the underwater target, if the receiving point is preset on the right side, the right end is selected, and if the receiving point is preset on the left side, the left end is selected. If the end point projection is just positioned on the grid boundary line, taking the intersection point of the grid boundary line and the symmetric axis as an origin; if the end point projection crosses a certain grid, the intersection point of the nearest grid boundary line and the symmetry axis is selected as the origin, similarly, if the receiving point is preset on the right side, the grid right boundary line is selected, and if the receiving point is preset on the left side, the grid left boundary line is selected.

The horizontal axis is the abscissa of the sound pressure signal from an artificially preset original point, the vertical axis is the ordinate of the sound pressure signal from the original point, and the vertical axis represents the energy of the sound pressure signal.

In this embodiment, the processing of the sound pressure time-domain waveform into a sound pressure-distance relative change curve specifically includes the following steps:

s120, selecting an artificially preset number from all collected sound pressure time domain waveforms, wherein the waveforms are excited for an excitation time length and then show sound pressure time domain waveforms which fluctuate up and down in fluctuation ranges on two sides of a peak value, wherein the peak value is taken as a core; the excitation time is preset manually; the fluctuation range is preset manually.

And S121, extracting sound pressure peak values one by one for each sound pressure time domain waveform selected in the S120.

S122, taking logarithm of each sound pressure peak value, and then arranging according to the sequence of the corresponding receiving points to obtain a sound pressure-distance relative change curve.

S200, according to the sound pressure wave field snapshot set, performing low-precision division operation on the far and near fields of the seismic waves to obtain a low-precision first boundary point position and a low-precision second boundary point position.

In this embodiment, the seismic wave near-far field low-precision partitioning operation specifically includes the following steps:

s210, correspondingly calibrating each grid on each sound pressure wave field snapshot in the pair-by-pair sound pressure wave field snapshot set according to the following standards:

if the number of the grids occupied by the central energy ring in the area where the grids are located is the largest in all time points, and the outer waveform only contains one color, the grids are calibrated to be the first boundary points with low precision.

If the outer waveform of the region where the grid is located is restored to one color again and the wavefield appears as a regular circular ring, the grid is scaled to a low precision second demarcation point.

S220, counting the number of continuously arranged grids between the original point and each low-precision first boundary point under the three-dimensional coordinates of the sound pressure cloud picture; multiplying the grid number between each low-precision first boundary point and the origin of the coordinate system by the side length of the grid to obtain the position of the low-precision first boundary point; then, according to the low-precision first boundary point position, the following operations are carried out:

and if the low-precision first boundary point position does not cross the middle of one grid, confirming that the low-precision first boundary point position is correct, and then outputting the low-precision first boundary point position.

If the position of the low-precision first boundary point crosses the middle of one grid, drawing a circle by taking the position of the low-precision first boundary point as the center of the circle and taking the side length of one grid as the radius; the range covered by the drawn circle is then taken as the new low-precision first demarcation point location, which is then output.

S230, counting the number of grids between the origin of the coordinate system and each low-precision second demarcation point; multiplying the grid number between each low-precision second boundary point and the origin of the coordinate system by the side length of the grid to obtain the position of the low-precision second boundary point; the following is then done according to the low-precision second demarcation point location:

and if the low-precision second boundary point position does not cross the middle of one grid, confirming that the low-precision second boundary point position is correct, and then outputting the low-precision second boundary point position.

If the position of the low-precision second boundary point crosses the middle of one grid, drawing a circle by taking the position of the low-precision second boundary point as the center of the circle and taking the side length of one grid as the radius; the range covered by the drawn circle is then taken as the new low-precision second demarcation point location, which is then output.

It should be noted that, when the seismic wave far-near field low-precision division operation is performed, a 20m × 20m grid is adopted to improve the calculation efficiency due to the complex model operation; after determining the approximate region of the near-far field, in order to improve the accuracy of near-field characteristic analysis, model reconstruction is carried out on the near-field region which is susceptible to grid precision, the model region is reduced to 200m, and the grid size is reset to 5m multiplied by 5 m.

S300, according to the sound pressure-distance relative change curve, performing high-precision division operation on the near and far fields of the seismic waves to obtain a high-precision first boundary point position and a high-precision second boundary point position.

In this embodiment, the seismic wave near-far field high-precision dividing operation specifically includes the following steps:

s310, fitting the sound pressure-distance relative change curve to obtain a fitting curve; then dividing the relative change curve of sound pressure-distance into different stages; the stages comprise a first stage, a second stage and a third stage; wherein:

the first stage is a sound pressure-distance relative change curve covered by a range from the origin to the first turning point; the first turning point is a first turning point which starts from the origin and is encountered when the sound pressure-distance relative change curve advances in the positive direction.

The second stage is a sound pressure-distance relative change curve covered by a range from the first turning point to the second turning point; the second turning point is the second turning point encountered by the forward direction of the sound pressure-distance relative change curve.

The third stage is a sound pressure-distance relative change curve covered by the range from the second turning point to the tail end of the curve; the end point is the last point encountered in traveling in the positive direction of the sound pressure-distance versus change curve.

It should be noted that, the main basis for dividing the curve into different stages is the difference between the slopes of the fitting curve or the tangent thereof, and if the fitting curve is exactly one straight line, the slope of the fitting curve itself is calculated, and if the fitting curve is not straight line, the tangent thereof is taken and the corresponding slope is calculated. The turning point refers to the intersection of two fitted curves of different slopes.

It needs to be further explained that: the fitted curve in phase 1 or the tangent slope thereof is maximum; the slope of the fitted curve in the phase 2 or the tangent line thereof is smaller than that in the phase 1; the fitted curve or its tangent slope within phase 3 is minimal.

S320, judging the expansion modes of the seabed seismic waves in different stages one by one according to the attenuation degree of the sound pressure value in each stage; the expansion mode comprises a spherical wave expansion mode, a cylindrical wave expansion mode and an expansion mode between the spherical wave and the cylindrical wave;

it should be noted that the spherical wave expansion mode and the cylindrical wave expansion mode are the prior art, and reference may be made to the "underwater sound principle" written by ulike for detailed explanation, and no further description is provided in the present invention.

if the expansion mode is a spherical wave expansion mode, the corresponding stage is marked as a near field.

If the expansion mode is a partial cylindrical wave expansion mode, the corresponding stage is marked as a far field.

It should be further noted that there is a transition region between the spherical wave expansion mode and the cylindrical wave expansion mode, specifically: when the distance is doubled and the sound pressure is 3.0dB, the spherical wave is just the spherical wave, and when the distance is doubled and the sound pressure is 6.0dB, the cylindrical wave is just the cylindrical wave; thus for the interval (3.0dB,6.0dB), in this particular embodiment, the midpoint of the interval is defined, i.e. 4.5dB is the demarcation point of the spherical wave and the cylindrical wave; such an average division of the transition intervals has proved to be very suitable in practice; therefore, the basis for determining the extension mode is as follows:

if the distance is doubled and the variation range of the sound pressure is [3.0dB,4.5dB ], judging that the expansion mode is a spherical wave expansion mode;

it should be noted that 3.0dB at the left end is a theoretical value, and in practical application, due to the existence of various errors including but not limited to instrument error, measurement degree error, and environmental noise, this value will oscillate around 3.0dB according to the practical environment, so this value is not suitable or may not be completely 3.0dB in the practical application process, but may be less than 3.0dB, for example, 2.6 dB;

if the distance is doubled, if the variation range of the sound pressure is [4.5dB,6.0dB ], judging that the extension mode is a cylindrical wave extension mode;

it should be noted that 6.0dB at the right end is a theoretical value, and in practical application, due to the existence of various errors including but not limited to instrument errors, measurement degree errors, and environmental noise, this value may oscillate around 6.0dB according to the practical environment, so this value is not suitable or may not be completely 6.0dB in the practical application process, but may be greater than 6.0dB, for example, 7.5 dB;

s330, according to the corresponding interference effect of the waveform of the sound pressure-distance relative change curve in each stage, performing near-far field confirmation on each stage; wherein:

and if the coincidence degree of the sound pressure-distance relative change curve and the fitting curve of the stage is not lower than the artificially preset coincidence degree minimum threshold, and the fluctuation degree of the sound pressure-distance relative change curve of the stage is lower than the artificially preset fluctuation index minimum threshold and is marked as a near field in S320, determining that the stage is the near field.

If the coincidence degree of the sound pressure-distance relative change curve of the stage with the fitting curve is not lower than the coincidence degree minimum threshold value and is marked as a far field in S320, the stage is confirmed to be a far field.

And if the fluctuation degree of the sound pressure-distance relative change curve of the stage is lower than the minimum threshold of the fluctuation index, the coincidence degree of the sound pressure-distance relative change curve of the stage and the fitting curve is lower than the minimum threshold of the coincidence degree, and the sound pressure-distance relative change curve of the stage fluctuates up and down around the fitting curve, the stage is determined to be a transition region.

S340, obtaining a high-precision first boundary point position and a high-precision second boundary point position according to the relation between the confirmed stages; specifically, the method comprises the following steps:

in the range between the near field and the transition zone, the first turning point encountered from the near field is the position of the high-precision first demarcation point.

In the range between the transition zone and the far field, the second transition encountered from the transition zone is the high-precision second demarcation point position.

And then packaging all the high-precision first boundary point positions, and packaging all the high-precision second boundary point positions, and outputting the high-precision second boundary point positions as a result of the step.

S400, carrying out demarcation point check operation according to the low-precision first demarcation point position, the low-precision second demarcation point position, the high-precision first demarcation point position and the high-precision second demarcation point position to obtain a demarcation point consistency evaluation result and a demarcation point range; the evaluation result of the consistency of the demarcation points and the scope of the demarcation points are the final results of the invention.

In this specific embodiment, obtaining the boundary point consistency evaluation result and the boundary point range specifically includes the following steps:

and Sa410, comparing the high-precision first boundary point positions with the low-precision first boundary point positions one by one, and according to the comparison result, performing the following operations:

if the position of the high-precision first demarcation point is completely consistent with the position of the low-precision first demarcation point, or the position of the high-precision first demarcation point is in a range covered by a circle used as the position of the low-precision first demarcation point, adding a character string 'first demarcation point acquisition success' in the demarcation point consistency evaluation result; simultaneously endowing the high-precision first demarcation point position to a first demarcation point; and then executes Sa430.

If the high-precision first demarcation point position and the low-precision first demarcation point position are not overlapped, adding a character string 'first demarcation point acquisition failure' into the demarcation point consistency evaluation result; and then executes Sa430.

It should be noted that, if a failure occurs, the model is rechecked and the calculation is performed again; there are many reasons for failure, mainly from objective data noise, such as collecting objects, collecting equipment, etc.; therefore, multiple acquisition, calculation and verification are necessary.

if the position of the high-precision second demarcation point is completely consistent with the position of the low-precision second demarcation point, or the position of the high-precision second demarcation point is in a range covered by a circle used as the position of the low-precision second demarcation point, adding a character string into the demarcation point consistency evaluation result, wherein the second demarcation point is successfully obtained; simultaneously endowing the high-precision second demarcation point position to a second demarcation point; and then executes Sa430.

If the high-precision second demarcation point position and the low-precision second demarcation point position are not overlapped, adding a character string 'second demarcation point acquisition failure' into the demarcation point consistency evaluation result; and then executes Sa430.

It should be noted that, when a failure occurs, the model needs to be checked again and recalculated, which is not described in detail.

Sa430, outputting the consistency evaluation result of the boundary points after the character strings are added by the Sa410 and the Sa 420; and meanwhile, packaging the first demarcation point and the second demarcation point to be used as a demarcation point range for outputting.

In order to verify the reliability of the method, the embodiment further provides a simulation result and a corresponding description of the seismic wave far-near field low-precision dividing operation under 3 conditions that the non-fixed frequency of the underwater target is considered, the natural frequency of the underwater target is considered, and the influence of the sound source frequency on the seismic wave far-near field is considered;

as will be described in detail below:

considering the non-fixed frequency of the underwater target:

as shown in fig. 4a to 4f, the curves are the relative variation curve of sound pressure-distance along the y direction of the sea bottom under the excitation of the vibration sources with frequencies of 5Hz, 10Hz, 20Hz, 30Hz, 40Hz, and 50 Hz.

As can be seen from fig. 4a to 4f, each sound pressure-distance relative change curve can be divided into three regions along with the change of distance, and a boundary point is formed between two adjacent regions; the first boundary point is closer to the origin, and the second boundary point is farther from the origin; wherein: wherein the first demarcation point is mainly concentrated near 102m, and the second demarcation point is mainly concentrated after 103 m; the sound pressure-distance relative variation curve is in the first region between the origin and the first boundary point, i.e. the concept "first stage" described above, and it can be seen from the curve that the sound pressure decays rapidly; in the second region from the first boundary point to the second boundary point, i.e. the above-mentioned concept "second stage", the sound pressure amplitude attenuation speed is reduced and fluctuates up and down; in the third region of the sound pressure-distance relative change curve from the second dividing point, i.e. the concept "third stage", the waveform gradually becomes gentle and has a linear change trend.

It should be noted that, regarding the three stages, at the non-natural frequency, the following further needs to be explained:

for the first stage, the change rule of the sound pressure under different vibration source frequencies shows that when the receiving distance is doubled, the sound pressure attenuation range of the sound pressure-distance relative change curve in the first stage is between 4.0dB and 6.5dB, the propagation rule of the sound pressure-distance relative change curve is between the spherical wave attenuation rule and the cylindrical wave attenuation rule, but is closer to the spherical wave; at the moment, the main action in the seismic wave field is direct wave, and the interference action of each wave component in the seismic wave field is relatively weak; moreover, because the frequency of the vibration source is very low, the wavelength of the vibration source is far larger than the geometric scale of the target, and the near-field interference effect is relatively weak; in addition, the calculation efficiency is considered, the space grid is divided greatly, and the near field effect recognition is also influenced to a certain extent.

For the second stage, when the sound pressure-distance relative change curve doubles the receiving distance of the sound pressure in the second stage, the attenuation range is between 3.3dB and 5.0dB, the propagation rule is also between the spherical wave attenuation rule and the cylindrical wave attenuation rule, but the curve is slightly biased to the cylindrical wave compared with the curve in the first stage; the reason for this phenomenon is that as the reception distance increases, the influence of the reflected wave, Scholte wave, and other components in the wave component on the seismic wave field gradually increases, the complexity of the seismic wave field interference increases, and the fluctuation of the waveform is accelerated. The propagation rule at the stage is complex, the propagation rule is mainly in an oscillation propagation state and cannot be judged as a far field or a near field, so that the region is judged as a seismic wave far-near field transition region.

For the third stage, when the receiving distance is doubled in the sound pressure-distance relative change curve in the third stage, the sound pressure attenuation range is 2.8 dB-3.4 dB, and the propagation law is very close to the propagation law of cylindrical waves; at the moment, the propagation distance is longer, the influence of the underwater sound waves on the seismic wave field is reduced, the main component is Scholte waves, the interference is more stable, and the waveform is smoother; accordingly, the stage is determined to be the seismic far field.

It should be noted that the above description of the three phases is a theoretical basis for determining the near field, the transition field, and the far field according to the present invention.

As shown in fig. 5a to 5b, the relative change curve of sound pressure-distance calculated when f is 50Hz is shown; the near field region can be more accurately judged through the graph; because the waveform of the transition region is incomplete, the difference of the change rule of the near field and the transition region can not be directly and specifically read through human observation, which is one of the technical problems to be solved by the invention; it can be seen from figures 5a to 5b that there is a more pronounced demarcation point near the general area identified above; furthermore, it can also be seen that the near field region does have wavefield undulations due to interference; thus FIGS. 5 a-5 b demonstrate that the method of the present invention is effective.

It should be further noted that the physical meaning of the above waveform change is detailed as follows: taking the sound pressure-distance relative change curve when f is 50Hz as an example, for convenience of description, the sound pressure wave field snapshots shown in fig. 6a to 6c are derived, and in this specific embodiment, the sound pressure wave field snapshots at three time points of 0.07s, 0.20s and 1.10s are captured and displayed, because these three sound pressure wave field snapshots are typical and representative; here a 20m x 20m grid is used; when the time is 0.07s, the range of the red area is maximum, and the peripheral waveform of the red area is not obviously diffused; since the origin of coordinates is taken at a distance of 40m from the center of the circle, the sound pressure waveform forms a near field in the vicinity of 160m from the center of the circle, i.e., 120m from the origin of coordinates; then, with the continuous excitation of the continuous vibration source, when the time is 0.2s, the waveform has uneven color blocks near the center of the circle at 340m, namely the intersection of the light blue block and the dark blue block, which is the far-near field transition; when the sound pressure is transmitted to 1.1s, a far field with uniform color blocks appears, and the integral waveform tends to be stable at the moment, namely the range of the far field; as can be seen from the three graphs of fig. 6a to 6c, the range of the red central region is gradually reduced in the sound pressure diffusion process, and then is increased due to the continuous superposition of the vibration source, which corresponds to the fluctuation of the waveform in the sound pressure-distance relative change curve, thereby further verifying the effectiveness of the method of the present invention.

As shown in table 1, through the seismic wave near-far field low-precision dividing operation of S200, the near-far field dividing points under different vibration source frequencies can be obtained:

TABLE 1. low precision division of boundary point list of near and far fields (non-natural frequency) under different vibration source frequencies

Frequency (Hz)	First demarcation point (m)	Second demarcation point (m)
			5	70	1660
10	80	1620
			20	90	1580
30	95	1660
			40	100	1720
50	110	1640

It should be further noted that, the near-field and far-field threshold values at different vibration source frequencies shown in table 1 are plotted into curves, and fig. 7a to 7b can be seen, as the vibration source frequency increases, the near-field threshold value gradually increases, and the overall value is linear, while the far-field threshold value fluctuates, but the overall value remains unchanged.

Fig. 7a to 7b should be understood in this way: when the frequency of the vibration source is reduced, the wavelength is increased, the size of the underwater target is reduced relative to the wavelength, and the size of the underwater target has larger influence on a near field because the main effect in the near field region is direct waves; therefore, the lower the frequency is, the smaller the target size is, the closer the target size approaches a point source, the weaker the interference generated by each fluctuation component in the induced seabed seismic waves is, so that a near field is difficult to form, and the boundary value of the near field is reduced; and the far field is reached, the propagation distance is relatively far, the main component is Scholte wave, the influence of the size of the underwater target on the interference is reduced, the interference is relatively stable, and therefore the boundary value of the far field is kept unchanged.

Consider the case of natural frequencies of underwater targets:

5.607Hz, 15.415Hz, 25.897Hz, 35.530Hz and 45.851Hz are selected as main vibration sources for simulation under the natural frequency.

In the simulation process, the change conditions of the far and near fields of the seismic waves under the consideration of the natural frequency of the mode of the underwater target are shown in fig. 8a to 8 e.

Obviously, compared with the common situation, the integral amplitude of the excitation sound pressure considering the natural frequency is slightly larger than the non-natural frequency; the fundamental reason for this difference is due to the resonance of underwater targets; in contrast, the sound pressure-distance relative change curve is still divided into a first stage, a second stage and a third stage, which are as follows:

for the first stage, the change law of the sound pressure under different vibration source frequencies shows that when the receiving distance is doubled, the sound pressure attenuation range of a sound pressure-distance relative change curve in the first stage is 3.9-6.6dB, the propagation law of the sound pressure-distance relative change curve is between the spherical wave attenuation law and the cylindrical wave attenuation law, but is closer to the spherical wave; in this case, the main wave in the seismic wavefield is the direct wave, and the interference effect of each wave component in the seismic wavefield is relatively weak.

For the second stage, when the receiving distance of the sound pressure is doubled in the second stage, the attenuation range is 3.3 dB-5.1 dB, the propagation rule is also between the spherical wave attenuation rule and the cylindrical wave attenuation rule, but compared with the curve in the first stage, the curve is slightly biased to the cylindrical wave, the complexity of the seismic wave field interference is increased, and the fluctuation of the waveform is accelerated. The propagation rule at the stage is complex, the propagation rule is mainly in an oscillation propagation state and cannot be judged as a far field or a near field, so that the region is judged as a seismic wave far-near field transition region.

For the third stage, when the receiving distance is doubled in the sound pressure-distance relative change curve in the third stage, the sound pressure attenuation range is 2.7 dB-3.4 dB, and the propagation law is very close to the propagation law of cylindrical waves; at the moment, the propagation distance is longer, the influence of the underwater sound waves on the seismic wave field is reduced, the main component is Scholte waves, the interference is more stable, and the waveform is smoother; accordingly, the stage is determined to be the seismic far field.

After the fixed frequency is considered, in order to improve the accuracy of near field characteristic analysis, model reconstruction is carried out on a near field region which is easily affected by grid precision, the model region is reduced to 200m, and the size of a grid is reset to 5m multiplied by 5 m; then, the sound pressure-distance relative change curves excited by different modal natural frequencies are processed again according to the mode of S200, so as to obtain the far-near field boundary points under each modal natural frequency, as shown in table 2:

TABLE 2. low-precision division of boundary point list of near and far fields under different vibration source frequencies (under natural frequency)

Frequency (Hz)	First demarcation point (m)	Second demarcation point (m)
			5.6071	70	1640
15.415	85	1580
			25.897	95	1540
35.530	100	1600
			45.851	110	1640

As shown in fig. 9a to 9b, the distance-near field boundary values at different modal natural frequencies are plotted into a curve according to the method of S200; obviously, as the natural frequency increases, the near-field critical value gradually increases and has a linear trend overall, while the far-field critical value fluctuates up and down but remains the same overall; this is consistent with the results at non-natural frequencies.

As shown in fig. 10a to 10b, then, according to the method of S200, the distance-field boundary values of all the frequencies are plotted into a curve; comparing fig. 7a to 7b with fig. 10a to 10b, it is clear that no matter the natural frequency or the non-natural frequency, the variation trend of the far and near field critical value does not have obvious mutation with the increase of the frequency; this may indicate that in the very low frequency range, the natural frequency has a limited effect on the far and near field boundaries of the ocean bottom seismic waves.

It can thus be concluded that the method of the invention is effective even if the natural frequency is considered.

It should be noted that the transfer relationship should also be considered:

the transmission relationship here is to examine the transmission relationship between the input and the output with the vibration source frequency as the input and the sound pressure as the output.

As shown in fig. 11, the sound pressure waveforms at different frequencies are fitted using the least square method, resulting in a fitted surface.

From fig. 12, the sound pressure-distance relative variation curves at different frequencies can be intercepted; here, taking f as 18Hz as an example, it can be read: at 18Hz, the near-field transition zone demarcation point, i.e. the first demarcation point, is approximately 90 m; the transition-far field demarcation point, the second demarcation point, is about 1580 m.

Under the consideration of the influence of the sound source frequency on the far and near fields of seismic waves

Considering that the underwater target has different navigation speeds, different propeller rotating speeds and different radiation noise frequencies, the influence of the sound source frequency on the far and near fields needs to be considered, so that a sedimentary deposit-free simulation model is adopted, a single-frequency sound source is loaded at the tail part of the propeller of the underwater target, the load type is set to be concentration force, and the magnitude is 10⁶N, the position of which is shown in fig. 13.

In the present embodiment, 5Hz, 10Hz, 20Hz, 30Hz, 40Hz, and 50Hz are still selected as the sound source frequencies; the underwater target is fixed 50m away from the seabed, the tail sound source frequency of the propeller is changed, and the method is verified to be still effective under the condition of analyzing the influence of the sound source frequency change on the far and near fields of the seabed seismic waves.

As shown in fig. 14, since the sound source is loaded on the central axis of the underwater target, the influence of different directions does not need to be considered, and therefore, the length direction, i.e., the y direction, of the underwater target only needs to be verified, the construction method of the coordinate system is the same as that described above, and only the position of the sound source is changed.

In order to improve the calculation efficiency, firstly, the interval of each receiving point is set to be 20m, and as the target is arranged at the center of the model, the receiving distance is set to be L/2, namely 4000m, and the stable sound pressure time domain waveform is obtained by operation; taking f as 40Hz as an example, the stable sound pressure time domain waveforms received by the receiving points with the target distances of 200m, 400m, 600m, 800m and 1000m at the sound source frequency are normalized to obtain fig. 15.

As is apparent from fig. 15, the sound pressure time-domain waveform under the sound source condition also generates a certain interference phenomenon.

Then, the variation of the far and near fields of the seismic waves of 5Hz, 10Hz, 20Hz, 30Hz, 40Hz and 50Hz is shown in FIGS. 16a to 16f according to the method of S200.

It is obvious that the sound pressure-distance relative change curve is still divided into a first stage, a second stage and a third stage, which are as follows:

for the first stage, the sound pressure attenuation range of the sound pressure-distance relative change curve in the first stage is between 5.6dB and 6.4dB when the receiving distance is doubled according to the change rule of the sound pressure under different vibration source frequencies, and the interference effect of each fluctuation component in the seismic wave field is relatively weak and still in the near field.

For the second stage, when the receiving distance of the sound pressure is doubled in the second stage, the attenuation range is 3.7 dB-5.5 dB, the complexity of the seismic wave field interference is increased, and the fluctuation of the waveform is accelerated. Still a transition region.

For the third stage, when the receiving distance is doubled in the sound pressure-distance relative change curve in the third stage, the sound pressure attenuation range is 2.7 dB-3.5 dB, no interference occurs basically, and the waveform is smooth; accordingly, the stage is determined to be the seismic far field.

Then, still following the step of S200, a sound pressure wavefield snapshot is obtained.

As shown in fig. 17a to 17c, a 20m × 20m grid is used, taking the sound pressure wavefield snapshot when f is 30Hz as an example.

Still selecting sound pressure wave field snapshots at three moments of time 0.07s, 0.20s and 1.10s, wherein the origin of coordinates is 40m away from the center of the circle, so that near fields are formed nearby when the sound pressure is 140m away from the center of the circle at 0.07s, namely 100m away from the origin of coordinates; then, with the continuous excitation of a continuous sound source, the phenomenon that uneven color blocks with yellow-green intervals appear near the distance of 340m from the center of a circle when the waveform is 0.20s can be seen, and a far field transition region and a near field transition region are formed preliminarily; when the sound pressure is transmitted to 1.10s, a far field with uniform color blocks appears, and the overall waveform tends to be stable.

In order to improve the accuracy of verification, model reconstruction is carried out on a near field region which is easily affected by grid precision, the model region is reduced to 200m, and the size of a grid is reset to 5m multiplied by 5 m. Then, using the step of S200 again, the far-near field demarcation point considering transmissibility can be obtained, as shown in table 3:

TABLE 3 boundary point list of near and far fields under different vibration source frequencies divided by low precision (considering transmissibility)

As shown in fig. 18a to 18b, the distance-near field boundary values at different modal natural frequencies are plotted into a curve according to the method of S200; obviously, as the natural frequency increases, the near-field critical value gradually increases and generally has a linear trend, while the far-field critical value fluctuates up and down but generally remains unchanged; this is consistent with the results at the non-natural frequency, the natural frequency.

As shown in fig. 19, fitting curved surfaces can be obtained by summarizing sound pressure waveforms at different sound source frequencies, using the sound source frequencies as input and the sound pressures as output, analyzing the transfer relationship between the input and the output, and fitting the sound pressure waveforms at the different frequencies by using the least square method.

As shown in fig. 20, taking f-47 Hz as an example, a corresponding curve is taken from a propagation distance-sound pressure plane; it is clear that the first demarcation point is about 110m and the second demarcation point is about 1720m at 47 Hz.

The above simulation results again prove that the method of the invention is still effective under the consideration of the influence of the sound source frequency on the far and near fields of the seismic waves.

In the foregoing detailed description, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, invention lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. To those skilled in the art; various modifications to these embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the embodiments described herein are intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent that the term "includes" is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term "comprising" as "comprising" is interpreted when employed as a transitional word in a claim. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or".

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Finally, it should be noted that the above embodiments are merely representative examples of the present invention. It is obvious that the invention is not limited to the above-described embodiments, but that many variations are possible. Any simple modification, equivalent change and modification made to the above embodiments in accordance with the technical spirit of the present invention should be considered to be within the scope of the present invention.

Here, it should be noted that the description of the above technical solutions is exemplary, the present specification may be embodied in different forms, and should not be construed as being limited to the technical solutions set forth herein. Rather, these descriptions are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Furthermore, the technical solution of the present invention is limited only by the scope of the claims.

The shapes, sizes, ratios, angles, and numbers disclosed to describe aspects of the specification and claims are examples only, and thus, the specification and claims are not limited to the details shown. In the following description, when a detailed description of related known functions or configurations is determined to unnecessarily obscure the focus of the present specification and claims, the detailed description will be omitted.

Where the terms "comprising", "having" and "including" are used in this specification, there may be another part or parts unless otherwise stated, and the terms used may generally be in the singular but may also be in the plural.

It should be noted that although the terms "first," "second," "top," "bottom," "side," "other," "end," "other end," and the like may be used and used in this specification to describe various components, these components and parts should not be limited by these terms. These terms are only used to distinguish one element or section from another element or section. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, with the top and bottom elements being interchangeable or switchable with one another, where appropriate, without departing from the scope of the present description; the components at one end and the other end may be of the same or different properties to each other.

Further, in constituting the component, although it is not explicitly described, it is understood that a certain error region is necessarily included.

In describing positional relationships, for example, when positional sequences are described as being "on.. above", "over.. below", "below", and "next", unless such words or terms are used as "exactly" or "directly", they may include cases where there is no contact or contact therebetween. If a first element is referred to as being "on" a second element, that does not mean that the first element must be above the second element in the figures. The upper and lower portions of the member will change depending on the angle of view and the change in orientation. Thus, in the drawings or in actual construction, if a first element is referred to as being "on" a second element, it can be said that the first element is "under" the second element and the first element is "over" the second element. In describing temporal relationships, unless "exactly" or "directly" is used, the description of "after", "subsequently", and "before" may include instances where there is no discontinuity between steps. The features of the various embodiments of the present invention may be partially or fully combined or spliced with each other and performed in a variety of different configurations as would be well understood by those skilled in the art. Embodiments of the invention may be performed independently of each other or may be performed together in an interdependent relationship.

Claims

1. A method for distinguishing near and far fields of seismic waves induced by navigation of an underwater target is characterized by comprising the following steps: comprises the following steps:

s100, acquiring shallow sea seismic wave field original data; the shallow sea seismic wave field original data comprises a sound pressure time domain waveform and a sound pressure cloud chart which are taken at the interface between sea water and the sea bottom; then processing the sound pressure cloud picture into a sound pressure wave field snapshot set; then processing the sound pressure time domain waveform into a sound pressure-distance relative change curve; the sound pressure wave field snapshot set comprises sound pressure wave field snapshots arranged in a time increasing order;

s200, according to the sound pressure wave field snapshot set, performing seismic wave far-near field low-precision division operation to obtain a low-precision first boundary point position and a low-precision second boundary point position;

2. The method for discriminating near and far fields of seismic waves induced by navigation of an underwater target according to claim 1, wherein: in S100, the sound pressure time-domain waveform is acquired through a plurality of receiving points arranged on a central axis of the sea bottom surface in the established shallow sea bottom seismic wave model; the receiving points are arranged in a grid form and are equal in distance.

3. The method for discriminating near and far fields of seismic waves induced by navigation of an underwater target according to claim 1, wherein: the sound pressure time domain waveform is a time domain waveform under a two-dimensional rectangular coordinate system, wherein: the origin of the sound pressure time domain waveform is the sound pressure intensity received by the receiving point at time 0, the horizontal axis is time, and the vertical axis is the sound pressure intensity.

4. The method for discriminating near and far fields of seismic waves induced by navigation of an underwater target according to claim 1, wherein: in S100, the sound pressure cloud map is spatial data in a three-dimensional coordinate, where: the original point is manually preset, the position is a place where the projection distance of the geometric center of the underwater target on the seabed surface is two grids, the horizontal axis is the horizontal coordinate of the distance between the sound pressure signal and the manually preset original point, the vertical axis is the vertical coordinate of the distance between the sound pressure signal and the original point, and the vertical axis represents the energy of the sound pressure signal.

5. The method for discriminating near and far fields of seismic waves induced by navigation of an underwater target according to claim 1, wherein: in S100, processing the sound pressure cloud image into a sound pressure wave field snapshot set, which specifically includes the following steps:

6. The method for discriminating near and far fields of seismic waves induced by navigation of an underwater target according to claim 1, wherein: in S100, processing the sound pressure time-domain waveform into a sound pressure-distance relative variation curve specifically includes the following steps:

7. The method for discriminating near and far fields of seismic waves induced by navigation of an underwater target according to claim 1, wherein: in S200, the seismic wave near-far field low-precision dividing operation specifically includes the following steps:

s230, counting the number of grids between the origin of the coordinate system and each low-precision second demarcation point; multiplying the grid number between each low-precision second boundary point and the origin of the coordinate system by the side length of the grid to obtain the position of the low-precision second boundary point; and then according to the low-precision second boundary point position, the following operations are carried out:

8. The method for discriminating near and far fields of seismic waves induced by navigation of an underwater target according to claim 1, wherein: in S300, the seismic wave near-far field high-precision dividing operation specifically includes the following steps:

the second stage is a sound pressure-distance relative change curve covered by a range from the first turning point to a second turning point; the second turning point is a second turning point encountered by advancing along the positive direction of the sound pressure-distance relative change curve;

s330, according to the interference effect corresponding to the waveform of the sound pressure-distance relative change curve in each stage, performing near-far field confirmation on each stage; wherein:

and then packaging all the high-precision first boundary point positions, and packaging all the high-precision second boundary point positions as a result of the step for output.

9. The method of discriminating near and far fields of seismic waves induced by the navigation of an underwater target according to claim 8, wherein: in S400, the obtaining of the demarcation point consistency evaluation result and the demarcation point range specifically includes the following steps:

if the position of the high-precision second demarcation point is completely consistent with the position of the low-precision second demarcation point, or the position of the high-precision second demarcation point is in a range covered by a circle used as the position of the low-precision second demarcation point, adding a character string 'second demarcation point' in the demarcation point consistency evaluation result to obtain success; simultaneously endowing the high-precision second dividing point position with a second dividing point; then executing Sa 430;