CN113433547A - Ground penetrating radar hidden crack offset imaging method, system, terminal and medium - Google Patents
Ground penetrating radar hidden crack offset imaging method, system, terminal and medium Download PDFInfo
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Abstract
The invention belongs to the technical field of tunnel lining structure hidden crack detection, and particularly discloses a ground penetrating radar hidden crack migration imaging method, a system, a terminal and a medium, wherein a crack model instruction is compiled by using a time domain finite difference method, radar characteristic response images of cracks in different forms can be simulated forward, signal preprocessing is carried out on radar response signals by using methods such as static correction, direct current component removal, gain, filtering and the like, the optimal electromagnetic wave velocity determined based on a wavelet entropy theory is used as a velocity parameter of a conventional migration method, the migration imaging effect of the conventional migration algorithm is improved, echo signal interference is suppressed, diffracted waves are converged, energy is more gathered, the true form of the cracks is restored to the maximum extent, and the problem that the migration imaging of hidden cracks in a concrete structure is inaccurate by using a ground penetrating radar is solved.
Description
Technical Field
The invention belongs to the technical field of tunnel lining structure hidden crack detection, and particularly discloses a ground penetrating radar hidden crack offset imaging method, a system, a terminal and a medium.
Background
Tunnels have played an irreplaceable role in traffic engineering construction as traffic facilities with features of terrain-crossing restrictions, connection of different spaces, and rapid transit. However, due to the influence of factors such as design scheme, construction environment and cyclic load, the tunnel lining structure has different degrees of cracks, water leakage and other diseases in the construction period or service period, and because the cracks have the characteristics of small size and difficulty in identification, the tunnel operation safety can be continuously threatened if the cracks are not identified and positioned in advance and treatment measures are taken.
Cracks can be classified into surface cracks and hidden cracks according to location. The surface cracks are mainly identified by means of traditional manual visual inspection, and identification methods with visual intelligent image identification as a core appear after technical development. Nowadays, concealed crack identification mainly depends on a nondestructive testing technology, and a ground penetrating radar method is widely applied to quality detection of tunnel lining structures due to the advantages of simplicity and convenience in operation, visual images and the like. However, forward simulation and physical model experimental research for detecting blind cracks by using a ground penetrating radar are still few, and the main reason is that the blind cracks have the characteristics of small size, undefined trend, irregular shape and the like, and the minimum unit lattice and model instructions of the forward simulation cannot meet the setting of the characteristics of small size and irregular shape of the cracks. In addition, the ground penetrating radar antenna has a certain lobe width, so that diffracted waves on a ground penetrating radar spectrum are dispersed, energy is not concentrated, and crack characteristic signals are difficult to extract. Therefore, how to accurately identify and extract fracture characteristic signals by using a forward modeling and model experiment combined mode is a great technical challenge to be faced currently to maximally reduce the true morphology of the fracture.
Currently, there are various offset methods to achieve the effect of offset homing of the ground penetrating radar image, such as: shift superposition, diffraction curve superposition, reverse time shift, frequency-wavenumber shift, and Kirchhoff integral shift. No matter what kind of offset method is adopted, the offset image always has a certain difference with the real form of the target object, mainly due to the fact that the dielectric properties of the detected anisotropic media are different, the propagation speed of the electromagnetic wave is dynamically changed along with the dielectric properties of different media, and various offset algorithms are used for adjusting the offset imaging effect by establishing different speed models. Therefore, how to accurately acquire the propagation velocity of the electromagnetic wave in the anisotropic and non-uniform medium is the key to success of offset imaging.
Disclosure of Invention
The invention aims to provide a method, a system, a terminal and a medium for imaging the migration of hidden cracks of a ground penetrating radar, so as to solve the problem that the migration of hidden cracks in a concrete structure is not accurately imaged by the ground penetrating radar.
In order to achieve the purpose, the technical scheme of the invention is as follows: a ground penetrating radar hidden crack offset imaging method comprises the following steps:
s1, pouring a hidden crack concrete model;
s2, acquiring a time-distance profile of the ground penetrating radar:
s3, preprocessing an image signal;
s4, calculating the wave velocity of the series electromagnetic waves;
s5, analyzing an entropy value of the ground penetrating radar image;
s6, solving the optimal wave velocity of the electromagnetic waves;
and S7, imaging the ground penetrating radar image in a shifting manner.
Further, in step S1, pouring the hidden crack concrete model: writing and manufacturing a concrete model containing the hidden cracks by using a Finite Difference Time Domain (FDTD) method;
in step S2, a time-distance profile of the ground penetrating radar is obtained: acquiring a time-distance profile of an original ground penetrating radar by adopting the ground penetrating radar;
in the step S3, the image signal preprocessing includes dc drift removal, static correction, direct wave removal, gain, and band-pass filtering and denoising;
in step S4, the series electromagnetic wave velocity is estimated: calculating the value range of the wave speed of the electromagnetic wave approximately according to the dielectric constant of the common medium, and setting a series of wave speeds of the electromagnetic wave as the offset parameters of the offset algorithm;
in step S5, performing ground penetrating radar image entropy analysis: extracting the frequency band energy characteristic vectors of different sub-images according to the wavelet transform decomposition coefficients, and calculating the wavelet entropy of each sub-image;
in step S6, the optimal electromagnetic wave velocity is obtained: selecting the wave velocity corresponding to the minimum value of the wavelet entropy on the offset image as the optimal wave velocity of the electromagnetic wave;
in the step S7, the ground penetrating radar image is subjected to offset imaging: and taking the optimal wave velocity of the electromagnetic wave as a deviation parameter of frequency wave number domain deviation and Kirchhoff integral deviation to perform deviation imaging processing on the ground penetrating radar image.
Further, a ground penetrating radar latent crack migration imaging system includes:
hidden crack forward modeling module: the method is used for completing the step S1 in the imaging method of the deviation of the blind crack of the ground penetrating radar, and the method is configured into a concrete geoelectric model containing the irregular blind crack, wherein the model is generated by input geoelectric parameters;
the signal acquisition module: the method is used for completing the step S2 in the imaging method of the hidden crack deviation of the ground penetrating radar, and the method is configured into the ground penetrating radar;
the image signal preprocessing module: the method for imaging the blind crack deviation of the ground penetrating radar comprises the following steps of S3, wherein the step is configured to carry out direct current drift removal, static correction, direct wave removal, gain and band-pass filtering denoising on an initial image;
an optimal electromagnetic wave velocity module: the method is used for finishing steps S4-S6 in the method for imaging the blind crack deviation of the ground penetrating radar, and is configured to adopt a series of propagation speeds as parameters of frequency wave number deviation to perform deviation processing on forward simulation images, then calculate the entropy of each forward simulation deviation image by using wavelet entropy, and select the wave velocity corresponding to the minimum value of the wavelet entropy on the deviation images as the optimal wave velocity of the electromagnetic waves;
the ground penetrating radar offset imaging module: the step S7 for completing the method for imaging the blind crack deviation of the ground penetrating radar is configured to obtain a final deviation image by utilizing two parts of frequency wave velocity domain deviation and Kirchoff integral deviation calculation.
Further, a ground penetrating radar latent crack migration imaging terminal comprises a processor, a display, a storage and computer instructions stored on the storage and run on the processor, wherein the computer instructions are executed by the processor to complete the steps of any one of the ground penetrating radar latent crack migration imaging methods in claims 1-8.
Further, a ground penetrating radar latent crack migration imaging medium for storing computer instructions, which when executed by a processor, perform the steps of any one of the methods of ground penetrating radar latent crack migration imaging of claims 1-8.
The working principle of the technical scheme is as follows:
calculating the value range of the wave velocity of the electromagnetic waves approximately according to the dielectric constant of a common medium, setting a series of wave velocities of the electromagnetic waves as offset parameters of an offset algorithm, performing wavelet decomposition on a plurality of offset images on the basis, extracting the band energy characteristic vectors of different sub-images according to the wavelet transformation decomposition coefficient, and calculating the wavelet entropy of each sub-image; and finally, selecting the wave velocity corresponding to the minimum value of the wavelet entropy on the offset image, and reusing the wave velocity as the optimal offset wave velocity in the offset imaging method.
The beneficial effects of this technical scheme lie in:
the wavelet entropy theory and the conventional migration algorithm are combined, the method for efficiently determining the optimal wave velocity of the electromagnetic waves is provided, the error between the estimated electromagnetic wave velocity and the true value can be controlled within 4%, the optimal wave velocity of the electromagnetic waves is used as a parameter of conventional migration imaging, the interference of adjacent signals can be reduced, the interference of echoes and diffraction waves is suppressed, the resolution of a ground penetrating radar image is remarkably improved, and therefore the migration imaging effect of the ground penetrating radar is improved.
Drawings
FIG. 1 is a schematic flow chart of a method for imaging deviation of hidden cracks of a ground penetrating radar according to the invention;
FIG. 2 is an operation diagram of a ground penetrating radar hidden crack migration imaging system according to the invention;
FIG. 3 is a diagram of a geoelectric model of different morphology cracks simulated in the embodiment;
FIG. 4 is a forward simulation image of three morphological fractures in the example;
FIG. 5 is a forward simulated image after signal preprocessing in an embodiment;
FIG. 6 is a schematic diagram of frequency-wavenumber offset imaging at different wave velocities in an example;
FIG. 7 shows Kirchhoff integral shift imaging at different wave velocities in the examples;
FIG. 8 is a graph of optimal wave velocities corresponding to minimum entropy values;
FIG. 9 is a deviation image of the optimal wave velocity of the electromagnetic wave for two deviation methods;
FIG. 10 is a concrete latent crack model design drawing of an embodiment model experiment;
FIG. 11 is a model diagram of an experimental concrete latent crack in the embodiment;
FIG. 12 is an offset imaging diagram of the model experiment in the example.
Detailed Description
The following is further detailed by way of specific embodiments:
the embodiment is basically as shown in the attached figure 1, and the method for imaging the hidden crack shift of the ground penetrating radar comprises the following specific implementation processes:
s1, pouring a hidden crack concrete model, namely compiling and manufacturing the concrete model containing hidden cracks by using a time domain finite difference method (FDTD);
s2, acquiring a time-distance profile of the ground penetrating radar: acquiring a time-distance profile of an original ground penetrating radar by adopting the ground penetrating radar;
s3, preprocessing an image signal: carrying out direct current drift removal, static correction, direct wave removal, gain and band-pass filtering denoising on the original image to obtain a preprocessed image;
s4, calculating the wave velocity of the series electromagnetic waves: the value range of the wave speed of the electromagnetic wave is roughly calculated according to the dielectric constant of the common medium, and a series of wave speeds of the electromagnetic wave are set as the offset parameters of the offset algorithm.
S5, analyzing the image entropy value of the ground penetrating radar: and extracting the frequency band energy characteristic vectors of different sub-images according to the wavelet transform decomposition coefficients, and calculating the wavelet entropy of each sub-image.
S6, obtaining the optimal wave velocity of the electromagnetic waves: and selecting the wave velocity corresponding to the minimum value of the wavelet entropy on the offset image as the optimal wave velocity of the electromagnetic wave.
S7, imaging of ground penetrating radar image shift: and taking the optimal wave velocity of the electromagnetic wave as a deviation parameter of frequency wave number domain deviation and Kirchhoff integral deviation to perform deviation imaging processing on the ground penetrating radar image.
In the scheme, as shown in fig. 2, the implementation of the ground penetrating radar hidden crack migration imaging method is based on a ground penetrating radar hidden crack migration imaging system,
the hidden crack forward modeling module is used for completing the step S1 in the ground penetrating radar hidden crack deviation imaging method: the ground penetrating radar forward simulation is the basis of image interpretation of the ground penetrating radar, electromagnetic wave propagation characteristics of radar electromagnetic waves among target object media are simulated by presetting geometric characteristics and dielectric characteristics of the target objects, then forward simulation results are compared and analyzed with actual results of field detection, understanding of interpretation personnel on radar reflection signals of the target media objects can be effectively improved, and application effects of the ground penetrating radar technology on engineering are promoted. In the scheme, a Finite Difference Time Domain (FDTD) method which occupies a small storage space and has high calculation efficiency is adopted as a forward modeling method of the ground penetrating radar.
In the passive field region, the two rotations of Maxwell's equation can be expressed as:
in the formula: h is magnetic field intensity (A/m), E is electric field intensity (V/m), epsilon is dielectric constant of medium, sigma is electric conductivity (S/m), t is time (S), mu is relative magnetic permeability (H/m), sigma ismEquivalent magnetic permeability (w/m).
The finite difference method of time domain is to convert two rotation degrees in Maxwell equation from differential to differential by using central difference form of second order precision, and electric field and magnetic field are alternately sampled in time sequence and have a half time step difference. Therefore, the finite difference equation in time domain of the two-dimensional electromagnetic wave can be expressed as:
wherein
In the formula: exElectric field strength H in the direction of coordinate axis xxAnd HyThe magnetic field strength in the x direction and the y direction are respectively, the Δ x and the Δ y are respectively the space step length in the x direction and the y direction, the Δ t is the time step length, the n is the time step length, and the (i, j) is the node coordinate.
In order to ensure stable convergence of the discrete time domain finite difference equation set solution, the time step Δ t and the space steps Δ x and Δ y are required to satisfy the following relations:
assuming a semi-infinite space continuous concrete homogeneous medium in a two-dimensional plane range, electromagnetic wave reflection and refraction are performed in the plane. In order to research the reflection characteristics of the ground penetrating radar forward simulation signal of the crack inside the concrete, the geoelectric models of the cracks with different forms shown in figure 3 are designed, and various cracks in the figure are marked, such as' y1"corresponding horizontal crack", "y2"corresponding to S-shaped crack" y3"corresponding to an oblique slit with a horizontal included angle of 26.57 °. In order to meet the minimum resolution of the lowest grid step length of the FDTD method, the width of the crack is set to be 5mm, and the S-shaped crack and the oblique crack have no existing model instruction, so that a model instruction formed by combining a circle, a rectangle and a triangle is designed for simulating the irregular crack.
Setting the geoelectricity parameters of the concrete model: the area range is 2.2m multiplied by 0.3m, the thickness of the air layer is 0.01m, the lower left corner is the origin of coordinates, the horizontal coordinate is the horizontal distance of the concrete model, and the vertical coordinate is the detection depth; the target object is (a) a horizontal crack, the length of the horizontal crack is 0.2m, the width of the horizontal crack is 5mm, the distance between the left side of the crack and the left side edge of the simulation area is 0.4m, and the burial depth of the horizontal crack is 0.1 m; (b) the width of the S-shaped microcrack is 5mm, the horizontal length is 0.2m, and the burial depths of the convex top and the concave top are 0.05m and 0.15m respectively; (c) the horizontal length of the inclined crack is 0.2m, the width of the inclined crack is 5mm, an included angle of 26.57 degrees is formed between the inclined crack and the horizontal direction, and the buried depth is 0.05 m; the relative dielectric constant of the concrete is 6, the conductivity is 0.001S/m, and the magnetic permeability is 1; the medium in the crack is air.
The signal acquisition module is used for completing the step S2 in the ground penetrating radar hidden crack migration imaging method: according to the relation between the detection depth and the resolution of the ground penetrating radar, the center frequency of the antenna is 1600MHz, the boundary absorption condition is a complete matching layer, the excitation source adopts Ricker wavelets, the space step length and the sampling step length of the grid are both 0.0025m, the number of sampling channels is 880, and the total sampling time is 10 ns. In order to reduce the interference of the boundary propagation effect of the electromagnetic wave to the signal, the distance between the transmitting antenna and the receiving antenna is set to be 0.1m, so that the actual distance in the horizontal direction is 2.0m, and the obtained three-form crack forward simulation image is shown in fig. 4.
The image signal preprocessing module is used for completing the step S3 in the ground penetrating radar hidden crack migration imaging method: configured to perform dc drift removal, static correction, direct wave removal, gain and band-pass filtering denoising on the initial image, and the preprocessed image is shown in fig. 5.
The optimal electromagnetic wave velocity module is used for completing steps S4-S6 in the ground penetrating radar hidden crack migration imaging method: the two migration methods are adopted to carry out migration imaging processing on three forms of cracks after conventional signal processing, as the wave velocity of electromagnetic waves in a migration algorithm cannot be directly known, different velocity parameters are set for reference, the dielectric constant of common concrete is 6, and the wave velocity of the calculated electromagnetic waves is 0.1225m/ns, 5 groups of wave velocity values are set: 0.1, 0.11, 0.12, 0.13, 0.14m/ns, offset images are shown in fig. 6 and 7. The three cracks are in different forms after different electromagnetic wave speed migration imaging processing is adopted, signal denoising and energy gathering are achieved to a certain extent, particularly, the migration imaging effect of the horizontal cracks and the oblique cracks is obvious, and for S-shaped cracks, the migration effect is poor due to the fact that the wave speed is smaller than or larger than the optimal wave speed, and the real form of the S-shaped cracks cannot be completely restored. Therefore, according to the wavelet energy entropy principle, 40 velocity values are selected in a 0.1-0.14 m/ns electromagnetic wave velocity interval, the electromagnetic wave velocity corresponding to the minimum energy entropy value is obtained by combining frequency wave velocity domain migration and a Kirchhoff integral migration method, as shown in fig. 8, when the image entropy value is the lowest, the electromagnetic wave velocity V corresponding to the frequency wave velocity domain migration and the Kirchhoff integral migration is 0.126m/ns and 0.127m/ns respectively, the relative errors of the electromagnetic wave propagation velocity and the true value determined according to the wavelet entropy theory are 2.86% and 3.67% respectively, and the optimal electromagnetic wave velocity is selected as a velocity parameter.
The ground penetrating radar offset imaging module is used for completing the step S7 in the ground penetrating radar hidden crack offset imaging method, the optimal electromagnetic wave speed is used as a speed parameter, the final offset imaging is obtained through calculation of frequency wave speed domain offset and Kirchhoff integral offset, and the offset imaging result is shown in fig. 9. After the two migration methods adopt respective optimal electromagnetic wave velocity migration imaging, the fracture is enabled to have better effect of restoring the real form of the fracture, especially for S-shaped fractures, the upper convex hyperbola and the lower convex hyperbola are separated, and radians are kept relatively consistent, which shows that the electromagnetic wave velocity selected based on the wavelet entropy can be used as the optimal migration velocity parameter of the conventional migration algorithm.
In the scheme, a ground penetrating radar offset imaging module writes a program on an MATLAB language computing platform, and the program comprises two parts of frequency wave velocity domain offset computation and Kirchhoff integral offset computation, wherein the frequency wave velocity domain offset principle is that Fourier transformation of a two-dimensional signal or image F (x, z ═ 0, t) is set to F (k ═ 0, t)x0, w), then
Where x is the horizontal coordinate, z is the vertical coordinate, downward is positive, and t is time. In the frequency-wavenumber domain, the wavefield at depth z may be represented as
Let the two-dimensional signal F (x, Z, t) { continuation of F (x, t) in Z-direction } be F (k)xZ, w) with respect to kxTwo-dimensional inverse Fourier transform of w, then
Then, according to the dispersion relation
At the same time, let t equal to 0, through derivation
The Kirchhoff integral offset method is based on the principle that a certain closed curved surface S exists around a field source, the displacement function u (x, y, z, t) and the derivative thereof exist on the curved surface S, and the displacement u caused by the field source on any point N (x, y, z, t) outside the curved surface S can be calculated according to the Wheatstone-Fresnel principle. Kirchhoff derives a Kirchhoff integral formula from the wave equation, which can be written as:
where R is the ray distance, representing point N1(x1,y1,z1T) distance to each point u (x, y, z, t) on the curved surface S; r represents a delay bit. If for a plane diffracted wave, the Kirchhoff diffraction formula is:
where a denotes the amplitude, θ denotes the propagation angle, and ω denotes the frequency of the wave. From Kirchhoff's diffraction formula, it is seen that the magnitude of the diffracted wave amplitude is related to the direction of wave propagation.
The central difference in binding to FDTD can be found:
in the grid rule of forward modeling, if Δ t is a sampling time interval, Δ x is a sampling interval, and Δ z is a sampling interval in the depth direction, then x may be madep＝mΔx，zp＝lΔz，x＝αΔx，
Wherein m, alpha and l are positive integers. The above formula can be converted into discrete form
In the scheme, model experiment research is also carried out on a ground penetrating radar concealed crack offset imaging method, the thickness of a lining structure in tunnel engineering is generally 0.3 m-0.4 m, the relation between the depth and the vertical resolution of concealed cracks detected by the ground penetrating radar is comprehensively considered, and the length multiplied by the width multiplied by the height of the model is set to be 2.2m multiplied by 0.3m multiplied by 0.5 m. The risk class of the width (W) of the crack in the tunnel lining structure is divided into three categories: low risk (0< W <0.2 mm); medium risk (W is more than or equal to 0.2 and less than 0.5 mm); high risk (W is less than or equal to 0.5mm), low risk and medium risk can be monitored and observed, and the high risk needs to be treated by adopting corresponding measures. The width of the designed seam is 0.5mm by taking the high-risk seam as a reference in the model test. The model crack is made by inserting and pulling out a thin steel sheet with the thickness of 0.5mm into a concrete test block, the width of the crack is easy to expand due to the self adsorption force and viscous force of the concrete during pouring, and the actual crack width is 0.5mm-0.8mm after measurement and calculation. Three types of cracks are set in the test: horizontal type, S type, inclined type, the schematic diagram of the model is shown in figure 10, the model test block is cast by C30 concrete, and the main materials comprise P.O 32.5.5 grade cement, fine sand, gravel, water reducing agent and the like. Fixing the three thin steel sheets with different shapes to the position with the depth of 0.2m of the mould by using a wood plate mould, then pouring and forming at one time, eliminating air by using a vibrating rod to enable the interior of concrete to be vibrated compactly, troweling the surface of the concrete after vibrating is finished, pulling out the thin steel sheets after standard maintenance is carried out for 3 days, and then continuing to maintain for 28 days, wherein the model test piece is shown in figure 11. The method comprises the steps of considering the relation between the antenna frequency and the vertical resolution, adopting Italian RIS-K2 type ground penetrating radar with main frequency of 1600MHz, enabling the sampling step length to be 0.0025m, enabling the time window and the stacking times to be 12ns and 384 times respectively, enabling a measuring line to be arranged in a mode that the side wall of the model moves from left to right at a constant speed to obtain a time-distance profile of the original ground penetrating radar, preprocessing signals, carrying out entropy analysis on ground penetrating radar images after signal preprocessing based on the wavelet entropy image estimation principle, and selecting a speed value corresponding to the minimum entropy. According to the method for obtaining the optimal wave velocity of the electromagnetic waves, the optimal wave velocity of the electromagnetic waves of the wavelet entropy theory combined frequency wave number domain deviation and the Kirchhoff integral deviation is respectively 0.118m/ns and 0.116m/ns, the optimal wave velocity of the electromagnetic waves is used as a deviation parameter to perform deviation processing again, and as shown in fig. 12, the result shows that the boundary of the concrete model at the position with the thickness of 0.3m is obvious, the ground penetrating radar diffracted waves after deviation are effectively converged, the original form of the ground penetrating radar diffracted waves is well restored by the horizontal cracks and the oblique cracks, the top energy of the raised hyperbolic curves on the S-shaped cracks can be well gathered to reduce the interference of adjacent signals, suppress the interference of echoes and diffracted waves, and remarkably improve the resolution of ground penetrating radar images, so that the deviation imaging effect of the ground penetrating radar is improved, and the feasibility of the method is further explained.
The foregoing is merely an example of the present invention and common general knowledge of known specific structures and features of the embodiments is not described herein in any greater detail. It should be noted that, for those skilled in the art, without departing from the structure of the present invention, several changes and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent.
Claims (5)
1. A ground penetrating radar hidden crack offset imaging method is characterized by comprising the following steps:
s1, pouring a hidden crack concrete model;
s2, acquiring a time-distance profile of the ground penetrating radar;
s3, preprocessing an image signal;
s4, calculating the wave velocity of the series electromagnetic waves;
s5, analyzing an entropy value of the ground penetrating radar image;
s6, solving the optimal wave velocity of the electromagnetic waves;
and S7, imaging the ground penetrating radar image in a shifting manner.
2. The method for imaging the blind crack deviation of the ground penetrating radar as claimed in claim 1, wherein in the step S1, the concrete model of the blind crack is poured: writing and manufacturing a concrete model containing the hidden cracks by using a time domain finite difference method;
in step S2, a time-distance profile of the ground penetrating radar is obtained: acquiring a time-distance profile of an original ground penetrating radar by adopting the ground penetrating radar;
in the step S3, the image signal preprocessing includes dc drift removal, static correction, direct wave removal, gain, and band-pass filtering and denoising;
in step S4, the series electromagnetic wave velocity is estimated: calculating the value range of the wave speed of the electromagnetic wave approximately according to the dielectric constant of the common medium, and setting a series of wave speeds of the electromagnetic wave as the offset parameters of the offset algorithm;
in step S5, performing ground penetrating radar image entropy analysis: extracting the frequency band energy characteristic vectors of different sub-images according to the wavelet transform decomposition coefficients, and calculating the wavelet entropy of each sub-image;
in step S6, the optimal electromagnetic wave velocity is obtained: selecting the wave velocity corresponding to the minimum value of the wavelet entropy on the offset image as the optimal wave velocity of the electromagnetic wave;
in the step S7, the ground penetrating radar image is subjected to offset imaging: and taking the optimal wave velocity of the electromagnetic wave as a deviation parameter of frequency wave number domain deviation and Kirchhoff integral deviation to perform deviation imaging processing on the ground penetrating radar image.
3. The ground penetrating radar latent crack migration imaging system of claim 1, comprising:
hidden crack forward modeling module: the method is used for completing the step S1 in the imaging method of the deviation of the blind crack of the ground penetrating radar, and the method is configured into a concrete geoelectric model containing the irregular blind crack, wherein the model is generated by input geoelectric parameters;
the signal acquisition module: the method is used for completing the step S2 in the imaging method of the hidden crack deviation of the ground penetrating radar, and the method is configured into the ground penetrating radar;
the image signal preprocessing module: the method for imaging the blind crack deviation of the ground penetrating radar comprises the following steps of S3, wherein the step is configured to carry out direct current drift removal, static correction, direct wave removal, gain and band-pass filtering denoising on an initial image;
an optimal electromagnetic wave velocity module: the method is used for finishing steps S4-S6 in the method for imaging the blind crack deviation of the ground penetrating radar, and is configured to adopt a series of propagation speeds as parameters of frequency wave number deviation to perform deviation processing on forward simulation images, then calculate the entropy of each forward simulation deviation image by using wavelet entropy, and select the wave velocity corresponding to the minimum value of the wavelet entropy on the deviation images as the optimal wave velocity of the electromagnetic waves;
the ground penetrating radar offset imaging module: the step S7 for completing the method for imaging the blind crack deviation of the ground penetrating radar is configured to obtain a final deviation image by utilizing two parts of frequency wave velocity domain deviation and Kirchoff integral deviation calculation.
4. A ground penetrating radar latent fracture migration imaging terminal, comprising a processor, a display, a storage and computer instructions stored on the storage and run on the processor, wherein the computer instructions, when executed by the processor, perform the steps of any one of the methods of claim 1 to 8.
5. A ground penetrating radar latent crack migration imaging medium storing computer instructions which, when executed by a processor, perform the steps of any one of the methods of ground penetrating radar latent crack migration imaging of claims 1-8.
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