Electromagnetic wave nondestructive detection method for gypseous soil

Abstract

The application relates to an electromagnetic wave nondestructive detection method for white clay soil barrier layer soil, and belongs to the technical field of electromagnetic wave nondestructive detection. The application is used for solving the problems of time and labor consumption and only obtaining point information in the method of detecting white clay soil by digging soil profile. The method comprises the following steps: calibration, preliminary measurement, data processing, verification and GPR detection of white clay soil. The method can not only save time and labor, but also obtain continuous distribution information of the white clay layer in the soil without destroying the original soil structure, thereby providing basis and reference for improvement of farmland quality, construction of high-standard permanent basic farmland and formulation of farmland resource protection policy.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of white clay soil barrier layer soil electromagnetic wave detection method, belong to electromagnetic wave nondestructive testing technical field. BACKGROUND

[0002] White clay is a kind of low-yield soil, white clay is extremely widely distributed in our country, only white clay area in Heilongjiang is 330 million mu, accounts for 7.47% of total land area in the province.White clay soil structure includes downward extension: plough layer, white clay layer, sedimentary layer and parent material layer.The water physical property of white clay layer and sedimentary layer is not good, which is shown in poor permeability, low effective water content, total pore, capillary pore and aeration pore are all lower, while invalid pore is higher, which determines that white clay is not drought-tolerant and not waterlogging, becomes the main obstacle factor in production, seriously restricts the growth and development of crops in the area.In the aspect of general investigation of white clay, people used to observe natural profile, dig soil profile and drill soil, etc., the method of observing natural profile is a limited method, and the two soil exploration methods of digging profile and drilling soil not only take time and effort, but also only obtain point information. SUMMARY

[0003] The purpose of the present application is to solve the technical problems of time-consuming and labor-intensive and only obtaining point information in the method of general investigation of white clay by digging soil profile, and provide a kind of white clay electromagnetic wave nondestructive detection method.

[0004] The white clay electromagnetic wave nondestructive detection method is as follows:

[0005] I. Adopting ground penetrating radar (GPR) to detect and identify white clay layer;

[0006] II. Adopting ground penetrating radar to detect and identify white clay layer needs to implement calibration, preliminary measurement, data processing, verification and ground penetrating radar detection of white clay steps;

[0007] III. Calibrating ground penetrating radar system before adopting ground penetrating radar to detect and identify white clay layer:

[0008] Dig a white clay soil profile well in the typical area of white clay distribution, take a photo and sample, use soil moisture speed detector (TDR) to obtain the water content of each layer of soil in the profile, and use vector network analyzer plus coaxial detection equipment to measure the dielectric constant of each soil layer in situ;

[0009] IV. Implementing preliminary measurement before adopting ground penetrating radar to detect and identify white clay layer:

[0010] The preliminary measurement firstly converts the dielectric constant of each soil layer obtained in step three into electromagnetic wave velocity, and then inputs into the ground penetrating radar host computer through the host computer software, and according to the center frequency of the ground penetrating radar antenna and the soil dielectric constant, firstly calculates the resolution and detection depth of the ground penetrating radar in detecting the white clay layer, and then selects several radar antennas capable of detecting and distinguishing the depth and thickness of the white clay layer, and then carries out the preliminary measurement of the ground penetrating radar in detecting the white clay layer in the area where the white clay layer is distributed.

[0011] V. Data processing after detecting and identifying the white clay layer by using the ground penetrating radar:

[0012] The data processing is carried out after the preliminary measurement, firstly, the radar data is preprocessed and denoised, then the data is processed by using the variational mode decomposition (VMD), wavelet transform, envelope extraction and Hilbert transform, and then the accurate position of the white clay layer is determined by combining the radar wave velocity of each layer of soil, so as to analyze the depth, thickness and shape information of the soil occurrence layer.

[0013] VI. Verification after detecting and identifying the white clay layer by using the ground penetrating radar after calibration, preliminary measurement and data processing:

[0014] The layered information of the white clay soil profile well obtained in step three is compared and analyzed with the white clay layer radar image obtained in steps four and five, if the two do not match, the water content and dielectric constant of each layer of soil will be re-measured by using the soil moisture TDR and vector network analyzer plus coaxial detection equipment in step three, and steps four, five and six will be re-operated, so that the parameters of the ground penetrating radar are gradually corrected, and finally the appropriate radar antenna is selected.

[0015] VII. GPR detection of white clay:

[0016] Because the white clay distributed in different areas has different burial depth, thickness and soil shape, after steps three, four, five and six, the radar antenna used is not consistent; therefore, whether for the same region or different regions of white clay, the parameters of the ground penetrating radar need to be repeatedly corrected, and then large-scale ground penetrating radar detection experiment of white clay is carried out in this area.

[0017] The ground penetrating radar host computer in step one adopts the ProEX model system unit manufactured by MALA GeoScience of Sweden, SIR series products of the United States, EKKO series products of Canada and LTD-2100 ground penetrating radar produced in China.

[0018] The soil moisture TDR in step three adopts the TRIME-TDR moisture measurement equipment.

[0019] The method for obtaining the water content of each layer of soil in the profile can also be resistance method, drying method or neutron scattering method.

[0020] The vector network analyzer plus coaxial detection device in step three adopts KEYSIGHT vector network analyzer N5232B and its coaxial detection device N1501A.

[0021] The method for measuring the dielectric constant of each layer of soil in situ in step three can also be a resonant cavity method, a free space wave method or a waveguide method.

[0022] The center frequency of the ground penetrating radar antenna in step four is 100 MHz, 250 MHz, 500 MHz or 800 MHz.

[0023] The ground penetrating radar data based on the 500 MHz and 250 MHz ground penetrating radar antennas can accurately identify the accurate positions of the plough layer, the white clay layer and the deposit layer in the soil profile after data processing;

[0024] The ground penetrating radar data based on the 800 MHz ground penetrating radar antenna can identify the positions of multiple layers after data processing.

[0025] Although the 100 MHz ground penetrating radar antenna has a deeper detection depth, the position resolution of the white clay layer is weak.

[0026] In order to quickly and accurately obtain the thickness and distribution of the white clay layer, the application discloses a technical method for detecting the white clay layer by using a ground penetrating radar (GPR).

[0027] The application has the following beneficial effects:

[0028] Under the condition of not damaging the original soil structure, the GPR detection of the white clay layer not only saves time and labor, but also can obtain the continuous distribution information of the white clay layer in the soil.

[0029] Before GPR detection, the GPR equipment is calibrated: a white clay profile well is dug, photographed and sampled in a typical area with white clay distribution, the water content of each layer of soil in the profile is obtained by TDR, and the dielectric constant of each layer of soil is measured in situ by a vector network analyzer plus coaxial probe, so as to provide radar calibration parameters for distinguishing and identifying the white clay layer information of the GPR.

[0030] In the GPR detection process, the acquired electromagnetic parameters in different soil layers are input into the GPR device, and according to the resolution and detection depth of different center frequency antennas, the radar antenna suitable for detecting the thickness and position of the white paste layer is selected. According to the distribution information of the white paste soil in the region, the line distance and interval density of the GPR detection of the white paste soil are set, and the preliminary GPR detection experiment of the white paste soil is carried out.

[0031] In the GPR detection, when the electromagnetic wave passes through different kinds of soil layers, different degrees of reflection, refraction, scattering and other phenomena occur. For the detection of the white paste layer, the white paste layer reflection signal is the useful signal, and the others are the interference signal. Therefore, in order to remove the interference noise signal and enhance the extraction of the useful signal, the data processing steps of variational mode decomposition, wavelet transform, envelope taking and Hilbert transform are used in the GPR data processing. The positive effect of each data processing step is:

[0032] Preprocessing: GPR is mainly used for detecting underground anomalies. However, signal attenuation is the main problem faced when detecting underground features. Therefore, when processing low-energy reflections, it is often affected by noise, which can mask the signal and make it difficult to distinguish anomalies. Therefore, signal denoising is considered a prerequisite for improving the recognition rate of GPR before any data analysis.

[0033] Variational mode decomposition and wavelet transform: GPR signal is a wideband signal, and each frequency band signal affects each other. Direct time-frequency analysis of wideband signal is easily disturbed by high-frequency signal, which is not conducive to the interpretation of the results. Variational mode decomposition and wavelet transform can decompose the signal into each frequency band, which can see the overall information of the signal and also see the detailed information.

[0034] Envelope taking: the GPR signal reconstructed by variational mode decomposition and wavelet transform can better reflect the detail changes of GPR signal at different scales, but it also contains noise. The envelope signal performs well in preserving the waveform characteristics of the signal, can demodulate the low-frequency signal containing soil layering information in the high-frequency signal, and has lower requirements for signal-to-noise ratio.

[0035] Hilbert transform: instantaneous frequency is the time rate of change of phase. When the electromagnetic wave passes through the interface between different media, the instantaneous frequency of the electromagnetic wave will change significantly, which reflects the changes between different layers of soil and helps to identify the soil layering boundary. Hilbert transform is an important tool for analyzing and processing signals. After the signal is subjected to Hilbert transform, the instantaneous parameters of the signal can be obtained.

[0036] After the above processing steps, the accurate position of the white paste soil layer is determined by combining the dielectric properties of the soil layering, so as to analyze the depth, thickness and shape information of the soil layering.

[0037] The above steps are sequentially advanced, mutually contrasted, mutually verified, finally, the soil profile well picture is compared and analyzed with the GPR obtained white clay layer radar image, so that the GPR radar parameter is further corrected, and finally the physical and mathematical preparation for carrying out large-scale GPR detection experiment is good.

[0038] The present application can not only detect white clay soil under the condition of not destroying the original soil structure, saving time and labor, but also obtain continuous distribution information of the white clay layer in the soil. Before GPR detection, the equipment is calibrated, thereby providing electromagnetic parameters for GPR to distinguish and identify the white clay layer information in the region, and providing a physical basis for selecting a radar antenna suitable for detecting the thickness and position of the white clay layer. The white clay layer reflection signal is a useful signal, and the others are interference signals. In the GPR data processing, the radar data are subjected to the data processing steps of variation mode decomposition (VMD), wavelet transform, envelope extraction, Hilbert transform, etc., thereby eliminating the noise interference phenomenon occurring when the electromagnetic wave penetrates through different types of soil layers, and providing an effective processing method for identifying the white clay layer reflection signal.

[0039] The present application provides a technical method for detecting white clay layer by using ground penetrating radar (GPR), which can quickly, non-destructively, continuously and accurately obtain the depth and thickness information of white clay soil. Therefore, it provides basis and reference for improving the quality of cultivated land, constructing high-standard permanent basic farmland, and formulating cultivated land resource protection policy. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a white clay soil electromagnetic wave nondestructive detection method of the present application, in which 1 represents a ground penetrating radar host, 2 represents a ground penetrating radar transmitting antenna, 3 represents a ground penetrating radar receiving antenna, 4 represents a ploughing layer, 5 represents a white clay layer, 6 represents a deposition layer, and 7 represents a parent material layer.

[0041] Figure 2 It is a step block diagram of the white clay soil electromagnetic wave nondestructive detection method of the present application.

[0042] Figure 3 It is a soil profile well picture dug for calibration in experiment one, in which AP represents a ploughing layer, E represents a white clay layer, Bt and Btr represent deposition layers.

[0043] Figure 4 It is a white clay soil radar soil layering profile diagram of a 500MHz center frequency radar antenna in experiment one.

[0044] Figure 5 It is a white clay soil radar soil layering profile diagram of a 250MHz center frequency radar antenna in experiment one.

[0045] Figure 6The radar soil layered profile graph of the white clay soil with the radar antenna center frequency of 100MHz in experiment one;

[0046] Figure 7 The radar soil layered profile graph of the white clay soil with the radar antenna center frequency of 800MHz in experiment one;

[0047] Figure 8 The radar soil layered profile graph of the white clay soil with the radar antenna center frequency of 800MHz in experiment one;

[0048] Figure 9 The radar soil layered profile graph of the white clay soil with the radar antenna center frequency of 800MHz in experiment one. DETAILED DESCRIPTION

[0049] The technical scheme of the present application is not limited to the following specific embodiments, and any combination of the specific embodiments is also included.

[0050] Specific embodiment one: the white clay soil electromagnetic wave nondestructive detection method in the embodiment is as follows:

[0051] I. Adopting the ground penetrating radar to detect and identify the white clay soil layer;

[0052] II. Adopting the ground penetrating radar to detect and identify the white clay soil layer needs to implement the steps of calibration, preliminary measurement, data processing, verification and ground penetrating radar detection of the white clay soil;

[0053] III. Calibrating the ground penetrating radar system before adopting the ground penetrating radar to detect and identify the white clay soil layer:

[0054] Digging a white clay soil profile well in a typical area where the white clay soil is distributed, taking photos and samples, using the soil moisture speed detector (TDR) to obtain the water content of each soil layer on the profile, and using the vector network analyzer plus coaxial detection equipment to measure the dielectric constant of each soil layer in situ;

[0055] IV. Implementing preliminary measurement before adopting the ground penetrating radar to detect and identify the white clay soil layer:

[0056] The preliminary measurement firstly converts the dielectric constant of each soil layer obtained in step III into electromagnetic wave speed, and then inputs the electromagnetic wave speed into the ground penetrating radar host computer through the host software, and according to the center frequency of the ground penetrating radar antenna and the soil dielectric constant, firstly calculates the resolution and detection depth of the ground penetrating radar in detecting the white clay layer in theory, and then selects several radar antennas capable of detecting and resolving the depth and thickness of the white clay layer, and then carries out preliminary measurement of the ground penetrating radar in detecting the white clay soil in the area where the white clay soil is distributed;

[0057] V. Implementing data processing after adopting the ground penetrating radar to detect and identify the white clay soil layer:

[0058] Data processing is first to preprocess and denoise radar data after preliminary measurement, then to process data by using variational mode decomposition, wavelet transform, envelope taking and Hilbert transform, and to determine the accurate position of the white clay layer by combining the soil radar wave velocity of each layer, so as to analyze the depth, thickness and shape of the soil occurrence layer;

[0059] Six, the verification of the white clay layer detected and identified by ground penetrating radar is carried out after the implementation of calibration, preliminary measurement and data processing:

[0060] The layered information of the white clay soil profile well obtained in step three is compared and analyzed with the white clay layer radar image obtained through steps four and five. If the two do not match, the soil moisture speed tester and the vector network analyzer in step three and the coaxial detection equipment are used to re-measure the water content and dielectric constant of each layer of soil, and steps four, five and six are re-operated, so that the parameters of the ground penetrating radar are gradually corrected, and the appropriate radar antenna is finally selected;

[0061] Seven, GPR detection of white clay:

[0062] Because the white clay in different regions has different burial depths, thicknesses and soil shapes, after steps three, four, five and six, the radar antenna used is not consistent. Therefore, whether for the same region or different regions of white clay, the ground penetrating radar parameters need to be repeatedly corrected before carrying out large-scale ground penetrating radar detection of white clay in this region.

[0063] Specific implementation method two: the difference between this implementation method and specific implementation method one is that the ground penetrating radar host in step one uses the ProEX model system unit manufactured by MALA GeoScience of Sweden, the SIR series products of the United States, the EKKO series products of Canada and the LTD-2100 ground penetrating radar produced in China. The others are the same as specific implementation method one.

[0064] Specific implementation method three: the difference between this implementation method and specific implementation method one or two is that the soil moisture speed tester in step three uses TRIME-TDR moisture measurement equipment. The others are the same as specific implementation method one or two.

[0065] Specific implementation method four: the difference between this implementation method and one of specific implementation methods one to three is that the method for obtaining the water content of each layer of soil on the profile in step three can also be resistance method, drying method or neutron scattering method. The others are the same as one of specific implementation methods one to three.

[0066] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the vector network analyzer and the coaxial probe device in step three use KEYSIGHT vector network analyzer N5232B and its coaxial probe device N1501A. The others are the same as one of the specific embodiments one to four.

[0067] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that the method for measuring the dielectric constant of each soil layer in situ in step three can also be the resonant cavity method, the free space wave method or the waveguide method. The others are the same as one of the specific embodiments one to five.

[0068] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the center frequency of the ground penetrating radar antenna in step four is 100 MHz, 250 MHz, 500 MHz or 800 MHz.

[0069] The ground penetrating radar data based on 500 MHz and 250 MHz ground penetrating radar antennas can accurately identify the accurate positions of the white clay soil plough layer, the white clay layer and the deposition layer in the soil profile after data processing;

[0070] The ground penetrating radar data based on 800 MHz ground penetrating radar antennas can identify the positions of multiple layers after data processing;

[0071] Although the detection depth based on 100 MHz ground penetrating radar antennas is deeper, the position resolution of the white clay soil layer is weaker. The others are the same as one of the specific embodiments one to six.

[0072] The following experiment is used to verify the effect of the present application:

[0073] Experiment one:

[0074] In combination Figure 1 , the white clay soil electromagnetic wave nondestructive detection method is as follows:

[0075] I. Using ground penetrating radar to detect and identify white clay soil layer;

[0076] II. The steps of calibration, preliminary measurement, data processing, verification and ground penetrating radar detection of white clay soil are needed for using ground penetrating radar to detect and identify white clay soil layer.

[0077] III. Calibrating the ground penetrating radar system before using the ground penetrating radar to detect and identify the white clay soil layer:

[0078] The calibration method is: digging a soil profile well of albic soil in a typical area where albic soil is distributed, the digging depth is 1.2m, and taking photos and samples. The soil moisture content of each layer of the profile is obtained by using a soil moisture rapid tester (TDR) 8, the moisture content of the plough layer 4 is 34.9%, the albic layer 5 is 45.0%, and the accumulation layer 6 is 43.0%, and the dielectric constant of each soil layer is measured in situ by using a vector network analyzer plus coaxial probe device 9, the dielectric constant of the plough layer 4 is 12.8, the dielectric constant of the albic layer 5 is 21.6, and the dielectric constant of the accumulation layer 6 is 24.9;

[0079] Four, preliminary measurement before using ground penetrating radar to detect and identify albic soil layer:

[0080] The preliminary measurement first converts the dielectric constant of each soil layer into electromagnetic wave speed, the electromagnetic wave speed of the plough layer 4 is 0.0839m / ns, the electromagnetic wave speed of the albic layer 5 is 0.0734m / ns, and the electromagnetic wave speed of the accumulation layer 6 is 0.0720m / ns, then the data is input into the software GroundVision2 of the ground penetrating radar host (GPR) 1, and according to the center frequency (100MHz, 250MHz, 500MHz or 800MHz) of the ground penetrating radar (GPR) antenna and the soil dielectric constant obtained in the calibration step, the resolution and detection depth of the GPR in detecting the albic soil layer are first calculated theoretically, and then several radar antennas capable of detecting and resolving the depth and thickness of the albic layer are selected, among which the resolution and detection depth of the 100MHz antenna are 16.12cm and 25m respectively, the resolution and detection depth of the 250MHz antenna are 6.44cm and 8m respectively, the resolution and detection depth of the 500MHz antenna are 3.4cm and 6m respectively, and the resolution and detection depth of the 800MHz antenna are 2.18cm and 2.5m respectively. Secondly, in this area where albic soil is distributed, according to the actual situation of the thickness and position of the albic layer of the profile well, the preliminary measurement of ground penetrating radar (GPR) in detecting albic soil is carried out;

[0081] Five, data processing after using ground penetrating radar to detect and identify albic soil layer:

[0082] Data processing is first to preprocess and denoise the radar data after preliminary measurement, that is: (A) the direct current component or direct current offset in the radar signal needs to be eliminated, and the subsequent delay oscillation or low frequency signal tailing is also needed to be eliminated; (B) the starting time is removed to obtain a unified time zero point, so as to facilitate the comparison and analysis of subsequent signal processing; (C) energy attenuation gain, mainly to overcome the influence of small amplitude of the later time signal caused by energy attenuation of electromagnetic wave in the propagation process, and the energy attenuation gain can ensure the relative amplitude information of the radar signal; secondly, the data is processed by using variational mode decomposition (VMD), wavelet transform, envelope extraction and Hilbert transform, and then the accurate position of the white clay layer is determined combined with the soil radar wave velocity of each layer, so as to analyze the depth, thickness and shape information of the soil occurrence layer.

[0083] The obtained white clay layer radar image information is compared with the white clay soil profile well layering information, specifically:

[0084] For the GPR data obtained by the three center frequency antennas (500MHz / 250MHz / 100MHz), the envelope extraction of the high frequency information reconstruction signal of the white clay soil is carried out based on the wavelet transform reconstruction result, the instantaneous frequency is obtained, and finally the ground penetrating radar (GPR) soil layered profile diagram is obtained combined with the radar wave velocity. Figures 4-6 For the GPR data generated by the 800MHz center frequency antenna, the envelope extraction of the signal is carried out based on the result after VMD decomposition, the instantaneous frequency is obtained, and the ground penetrating radar (GPR) soil layered profile diagram shown in Figures 7-9 is drawn combined with the radar wave propagation velocity of different soil occurrence layers.

[0085] From the Figure 3 soil profile well picture, the actual layering position is at 32cm, 43cm and 74cm, the layering position based on the data obtained by the 500MHz antenna is more accurate, which is about 37cm Figure 4 , the layering position based on the data obtained by the 250MHz antenna has low accuracy, which is about 58cm Figure 5 . But the 100MHz antenna cannot identify the layering position of the deposition layer 6 (Bt layer and Btr layer), which is mainly caused by the insufficient resolution of the 100MHz antenna. From the GPR data result Figures 7-9 obtained by the 800MHz antenna, the typical white clay layering position is about 30cm, 40cm and 79cm, and the layering result is more accurate compared with the processing results based on the data obtained by the other three types of antennas.

[0086] Through the above data processing and comparative analysis, if the two do not match, the soil moisture TDR 8 and vector network analyzer plus coaxial detection equipment 9 will be re-measured each layer of soil moisture and dielectric constant, and repeat the above steps, so that the ground penetrating radar (GPR) each parameter is gradually corrected, and finally select the appropriate radar antenna, and carry out large-scale ground penetrating radar (GPR) detection of white clay soil experiment in this area.

[0087] The experimental ground penetrating radar (GPR) is a ProEx model system unit manufactured by Sweden MALA GeoScience, the antenna frequency is 800MHz, 500MHz, 250MHz and 100MHz, and the radar software GroundVision2 is used;

[0088] The soil moisture TDR 8 uses TRIME-TDR moisture measuring equipment; the soil dielectric constant uses KEYSIGHT vector network analyzer N5232B and its coaxial detection equipment N1501A9.

[0089] Through comparative experiments, although the 100MHz antenna has a deeper detection depth, it has weaker position resolution ability for white clay soil layer, while the ground penetrating radar (GPR) data based on 500MHz and 250MHz antennas can accurately identify the accurate position of white clay soil plough layer, white clay layer and deposition layer in the soil profile after data processing. The ground penetrating radar (GPR) data based on 800MHz antenna can identify multiple hierarchical layer positions after data processing.

Claims

1. A non-destructive electromagnetic wave detection method for alkaline soil, characterized in that... The white clay electromagnetic wave nondestructive detection method is as follows: I. Adopting ground penetrating radar to detect and identify white clay layer; II. Adopting ground penetrating radar to detect and identify white clay layer needs to implement calibration, preliminary measurement, data processing, verification and ground penetrating radar detection of white clay steps; III. Before adopting ground penetrating radar to detect and identify white clay layer, calibrating ground penetrating radar system: Dig a white clay soil profile well in a typical area where white clay is distributed, take photos and samples, use soil moisture speed meter to obtain the water content of each layer of soil in the profile, and use vector network analyzer plus coaxial detection equipment to measure the dielectric constant of each soil layer in situ; IV. Before adopting ground penetrating radar to detect and identify white clay layer, implementing preliminary measurement: The preliminary measurement first converts the dielectric constant of each soil layer obtained in step III into electromagnetic wave speed, then inputs it into the ground penetrating radar host computer through the host software, and according to the center frequency of the ground penetrating radar antenna and the soil dielectric constant, first calculates the resolution and detection depth of the ground penetrating radar in detecting white clay layer in theory, and then selects several radar antennas that can detect and distinguish the depth and thickness of white clay layer, and then carries out preliminary measurement of ground penetrating radar detection of white clay in the area where white clay is distributed; V. After adopting ground penetrating radar to detect and identify white clay layer, implement data processing: Data processing is after preliminary measurement, first pre-process and denoise the radar data, then use variational mode decomposition, wavelet transform, envelope extraction and Hilbert transform for data processing, and then combine the radar wave speed of each layer to determine the accurate position of white clay layer, so as to analyze the depth, thickness and shape information of the soil occurrence layer; Compare the obtained white clay layer radar image information with the layered information of white clay soil profile well, specifically: For the GPR data obtained by three center frequency antennas 500MHz, 250MHz and 100MHz, based on the wavelet transform reconstruction result, the envelope of the white clay high frequency information reconstruction signal is extracted to obtain its instantaneous frequency, and finally the ground penetrating radar soil layering profile is obtained by combining the radar wave speed. For the GPR data generated by the 800MHz center frequency antenna, based on the result after VMD decomposition, the envelope of the signal is extracted to obtain the instantaneous frequency, and the ground penetrating radar soil layering profile is drawn by combining the radar wave propagation speed of different soil occurrence layers; VI. After adopting ground penetrating radar to detect and identify white clay layer, implement calibration, preliminary measurement and data processing, verification: Compare the layered information of white clay soil profile well obtained in step III with the white clay layer radar image obtained in steps IV and V, if they do not match, re-measure the water content and dielectric constant of each layer of soil by using the soil moisture speed meter and vector network analyzer plus coaxial detection equipment in step III, and re-operate steps IV, V and VI, so as to gradually correct the parameters of ground penetrating radar, and finally select the appropriate radar antenna; VII. GPR detection of white clay: Because of the different depth, thickness and the soil morphology of the different regions of the white clay, the used radar antenna is not consistent after the step three, step four, step five and step six; therefore, whether for the same region or different regions of the white clay, the ground penetrating radar parameters need to be repeatedly corrected before carrying out large-scale ground penetrating radar detection experiment of the white clay in this area.

2. The method for non-destructive detection of electromagnetic waves in kaolin according to claim 1, characterized in that The ground penetrating radar host of step one adopts the ProEX model system unit manufactured by MALA GeoScience of Sweden, the SIR series products of the United States, the EKKO series products of Canada and the LTD-2100 ground penetrating radar produced in China.

3. The method for non-destructive detection of electromagnetic waves in kaolin according to claim 1, characterized in that The soil moisture rapid tester of step three adopts the TRIME-TDR moisture measuring equipment.

4. The method of claim 1, wherein the kaolin is characterized by The method for obtaining the water content of each layer of soil on the profile of step three is resistance method, drying method or neutron scattering method.

5. The method of claim 1, wherein the kaolin is selected from the group consisting of Georgia kaolin, Alabama kaolin, and mixtures thereof. The vector network analyzer plus coaxial detection equipment of step three adopts KEYSIGHT vector network analyzer N5232B and its coaxial detection equipment N1501A.

6. The method of claim 1, wherein the kaolin is selected from the group consisting of Georgia kaolin, Alabama kaolin, and mixtures thereof. The method for measuring the dielectric constant of each soil layer in situ of step three is resonant cavity method, free space wave method or waveguide method.

7. The method of claim 1, wherein the kaolin is selected from the group consisting of Georgia kaolin, Alabama kaolin, and mixtures thereof. The center frequency of the ground penetrating radar antenna of step four is 100MHz, 250MHz, 500MHz or 800MHz; The ground penetrating radar data based on 500MHz and 250MHz ground penetrating radar antenna can accurately identify the accurate position of the white clay plough layer, white clay layer and deposition layer in the soil profile after data processing; The ground penetrating radar data based on 800MHz ground penetrating radar antenna can identify the position of multiple levels of layering after data processing; Although the detection depth of 100MHz ground penetrating radar antenna is deeper, the position resolution of the white clay layer is weaker.

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