Quantitative processing method for ground penetrating radar image data

Abstract

The invention discloses a quantitative processing method for ground penetrating radar image data, and the method specifically comprises the following steps: S1, measuring the direct coupling waveform of a ground penetrating radar, and collecting the waveform data Sair (t) of the ground penetrating radar at the moment; s2, ground penetrating radar emission waveform calibration is carried out, a frequency spectrum difference [delta] P (f) is acquired, and waveform data of a calibrated ground penetrating radar image are acquired; s3, correcting the radar image according to the transmission attenuation of the measured object and the air interface, and obtaining a waveform after the transmission attenuation of the measured object and the air interface is corrected; s4, correcting the radar image according to the loss attenuation of the medium in the measured object, and calculating to obtain a waveform after the loss attenuation of the medium in the measured object is corrected; and S5, performing cross-medium radio wave propagation distance diffusion attenuation correction processing, converting waveform data in the ground penetrating radar image into radar scattering length, and completing quantization processing of the ground penetrating radar image data. According to the method, the consistency of different ground penetrating radar image data is improved, and then the interpretation efficiency of a manual or intelligent system is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radar and data processing, and particularly relates to a quantization processing method for ground penetrating radar image data. BACKGROUND

[0002] As an important geophysical exploration equipment, ground penetrating radar has core advantages such as non-destructive, high resolution and high efficiency, and has a wide range of applications in different fields such as urban infrastructure maintenance, geological disaster prevention, environmental and agricultural applications. With the deep integration of intelligent technology, it will play a greater role in emerging fields such as smart cities and digital twins, and provide key data support for the sustainable development of human society.

[0003] However, the interpretation of ground penetrating radar images is still mainly manual interpretation, that is, technical personnel view and analyze radar images one by one, and obtain the analysis results of the measured object based on artificial experience, which has many problems such as great subjective influence, long time consumption and low efficiency. Due to the lack of professional interpreters, it is still difficult to meet the interpretation needs of massive detection data. In recent years, domestic and foreign scholars have made progress in automatic interpretation of ground penetrating radar images, and have proposed a series of automatic interpretation methods based on machine learning, deep learning and other artificial intelligence technologies. The intelligent recognition and interpretation system developed accordingly can learn to label collapse, void, pipeline damage, crack, loose body and other diseases, and improve the recognition efficiency of typical hidden disease problems. However, the performance of the intelligent recognition and interpretation system depends on the quality of the labeled data, and it is difficult to adapt to the measurement data of different ground penetrating radars, which seriously restricts the development of ground penetrating radar intelligent interpretation technology.

[0004] Compared with the mature field of air radar measurement data processing: people perform quantization processing on radar measurement data such as target radar scattering cross section and background scattering coefficient, correlate the radar measurement results with theoretical or model values, greatly improve the extraction and utilization of information of the detected target, and improve the consistency of different radar measurement data and the interpretability of radar images. However, the current manual or intelligent system interpretation and processing method of ground penetrating radar images still stays at the qualitative analysis level of data, lacks quantization analysis of ground penetrating radar image data, and leads to large differences between different ground penetrating radar measurement data, low interpretation efficiency limited by artificial experience or intelligent system labeling learning, and low information utilization rate of measurement data due to the lack of directly corresponding quantization data model. SUMMARY

[0005] The present application aims to overcome the deficiencies in the prior art, and provides a quantitative processing method for ground penetrating radar image data, which eliminates the influence of transmission waveform, interface transmission, medium loss attenuation and propagation diffusion attenuation, improves the consistency of different ground penetrating radar image data, avoids the influence of artificial adjustment of different depth gains, enhances the similarity of underground target radar image features, and improves the efficiency of artificial or intelligent system interpretation.

[0006] To achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] A quantitative processing method for ground penetrating radar image data, which specifically comprises the following steps:

[0008] S1, measuring the direct coupled waveform of the ground penetrating radar, measuring the waveform data S air (t) of the ground penetrating radar in the open area by pointing the ground penetrating radar upward; t represents the propagation time after the electromagnetic wave is transmitted;

[0009] S2, transmission waveform calibration of the ground penetrating radar, placing a metal reflector plate at R0 in front of the main beam of the ground penetrating radar antenna, collecting the waveform data S plate (t) transmitted by the ground penetrating radar, subtracting the waveform data S air (t) and S plate (t) obtained in S1, respectively performing Fourier transform on the subtracted waveform data and a specific phase unit intensity waveform, calculating and obtaining the frequency spectrum difference ΔP(f), correcting the waveform data in the measured ground penetrating radar image according to the frequency spectrum difference, and obtaining the waveform data of the calibrated ground penetrating radar image;

[0010] S3, modifying the radar image according to the transmission attenuation at the interface between the measured object and the air, calculating and obtaining the detection depth of the ground penetrating radar in the object, modifying the corrected waveform data in S2 according to the transmissivity of the interface between the measured object and the air, and obtaining the waveform modified according to the transmission attenuation at the interface between the measured object and the air;

[0011] S4, modifying the radar image according to the internal medium loss attenuation of the measured object, calculating and obtaining the waveform modified according to the internal medium loss attenuation according to the loss attenuation coefficient per unit distance of the internal medium of the object corresponding to the waveform in the ground penetrating radar image;

[0012] S5, cross-medium electric wave propagation distance diffusion correction processing, according to the characteristics that the electric wave propagation distance diffusion of the ground penetrating radar working at a short distance approximately conforms to the spherical wave attenuation rule, converting the waveform data in the ground penetrating radar image into a radar scattering length quantity, and completing the quantitative processing of the ground penetrating radar image data.

[0013] Further, R0 in S2 is greater than or equal to the wavelength of the electromagnetic wave of the ground penetrating radar, and the specific phase unit intensity waveform is S0(t-2R0 / c); the unit intensity is the envelope peak amplitude of the waveform, the amplitude value is 1, the specific phase is the waveform phase at the envelope peak of the waveform, and the specific value is 0°, 90° or -90°.

[0014] Further, the frequency spectrum difference ΔP(f) is specifically obtained as follows:

[0015] ΔP(f) = FFT[S0(t-2R0 / c)] / FFT[S plate (t)-S air (t)]

[0016] Wherein, f is the frequency of the electromagnetic wave; c is the propagation speed of the electromagnetic wave in the air, and FFT is the Fourier transform.

[0017] Further, the correction processing of the frequency spectrum difference on the waveform data in the measured ground penetrating radar image is specifically: using the frequency spectrum difference to perform transmission waveform calibration processing on the i-th channel waveform S i (t) in the measured ground penetrating radar image:

[0018] S i ′(t) = IFFT{FFT[S i (t)-S air (t)]·ΔP(f)}

[0019] Wherein, IFFT is the inverse Fourier transform; S i ′(y) is the i-th channel waveform of the ground penetrating radar image after transmission waveform calibration.

[0020] Further, the detection depth of the ground penetrating radar in the object in S3 is:

[0021] Wherein, z is the detection depth, c is the propagation speed of the electromagnetic wave in the air; t0 is the waveform time corresponding to the object surface reflection position; n is the refractive index of the medium in the object, and t is the propagation time of the electromagnetic wave.

[0022] Further, the transmission rate of the measured object and the air interface corrects the corrected waveform data, which is specifically:

[0023] Wherein, T i is the transmission rate of the measured object and the air interface, is the corrected waveform;

[0024] For the well-coupled ground penetrating radar, T i is 1, and for the air-coupled ground penetrating radar, the transmission waveform calibrated channel waveforms Si (t) the first envelope peak, denoted as V i At this time, the interface transmittance is:

[0025] T i = 1-r i ×r i

[0026]

[0027] wherein, in the formula, r i is the approximate reflection coefficient of the interface between the measured object and air; h0 is the vertical distance or height from the center of the ground penetrating radar antenna to the surface of the measured object; R0 is the distance used when calibrating the transmitted waveform.

[0028] Further, the internal medium loss attenuation correction of the radar image in S4 is specifically:

[0029] Let the loss attenuation coefficient per unit distance of the internal medium of the object corresponding to the lth waveform in the ground penetrating radar image be α i Then the corrected waveform after internal medium loss attenuation is:

[0030]

[0031] wherein, the loss attenuation coefficient α i contains absorption attenuation and scattering attenuation, and is related to the water content, porosity, granularity of the internal medium of the object, and the working electromagnetic wave frequency of the ground penetrating radar; when the initial correction is performed, α i is taken as 0 or a small initial value For working electromagnetic waves below 500 MHz, α

[0032] Further, the conversion of the waveform data in the ground penetrating radar image in S5 into the radar scattering length quantity is specifically:

[0033]

[0034] wherein, h0 is the vertical distance or height from the center of the ground penetrating radar antenna to the surface of the measured object; n i is the refractive index of the internal medium of the measured object at this position; L i (z) is the radar scattering length quantity, which has a specific meaning only at the local peak of the waveform envelope;

[0035] Two areas of stray waves with no obvious strong reflection and an amplitude higher than the bottom noise of the radar are selected at a similar depth in the converted radar scattering length image, and the root mean square of the amplitudes of the stray waves in the area is statistically analyzed to approximately estimate the equivalent attenuation coefficient of the internal medium of the object near the depth:

[0036]

[0037] In the formula, sigma (z) is the statistical amplitude root mean square value of the stray wave in a certain area, z1 and z2 are the center depths of the selected two stray wave areas, The attenuation coefficient of the selected measured object internal medium is an initial value; and the attenuation coefficient estimation value alpha i The S4 and S5 are substituted and the correction process is re-performed.

[0038] Based on the above scheme, the quantitative processing method for ground penetrating radar image data has achieved positive and beneficial effects through practice:

[0039] 1. The quantitative processing method for ground penetrating radar image data eliminates the influence of transmission waveform, interface transmission, medium loss attenuation and propagation diffusion attenuation, improves the consistency of different ground penetrating radar image data, avoids the influence of artificial adjustment of different depth gains, is beneficial to enhancing the similarity of underground target radar image features, and further improves the efficiency of artificial or intelligent system interpretation.

[0040] 2. The quantitative processing method for ground penetrating radar image data converts the waveform data in the ground penetrating radar image into a radar scattering length quantity, and the amplitude and phase of each local bright spot of the quantitative processed ground penetrating radar image can be directly associated with the electromagnetic scattering model of the target in the medium, so that the ground penetrating radar image data is given a certain physical meaning, the effective information amount is improved, and it is of great significance to promote the quantitative inversion research of ground penetrating radar.

[0041] 3. The quantitative processing method for ground penetrating radar image data provides an estimation method of the equivalent attenuation coefficient of the electromagnetic wave in the measured object internal medium based on the stray wave amplitude, which provides a new means for the research of the internal medium density, granularity and water content of the measured object. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 It is a quantitative processing flowchart of embodiment 1 in the quantitative processing method for ground penetrating radar image data.

[0043] Figure 2 It is a test ground penetrating radar direct coupling waveform chart in the quantitative processing method for ground penetrating radar image data.

[0044] Figure 3 It is a unit intensity 90° phase waveform chart used for transmission waveform calibration in the quantitative processing method for ground penetrating radar image data.

[0045] Figure 4The invention relates to a road surface reflectance distribution map measured in a quantitative processing method of ground penetrating radar image data.

[0046] Figure 5 The invention relates to a stepped frequency ground penetrating radar image after the average waveform is eliminated in a quantization processing method for ground penetrating radar image data.

[0047] Figure 6 This is a statistical comparison chart of the media stray wave amplitudes at different depths used in the quantitative processing method of ground penetrating radar image data.

[0048] Figure 7 The invention relates to a stepped-frequency ground penetrating radar scattering length distribution diagram after quantization processing in a quantization processing method for ground penetrating radar image data.

[0049] Figure 8 The invention relates to a directly coupled waveform diagram of a narrow pulse ground penetrating radar used in a quantitative processing method of ground penetrating radar image data.

[0050] Figure 9 The invention relates to a distribution map of the road surface reflection coefficient measured by a narrow-pulse ground-penetrating radar in a quantitative processing method of ground-penetrating radar image data.

[0051] Figure 10 The invention relates to a scattering length distribution diagram of a narrow pulse ground penetrating radar after quantization processing in a quantization processing method for ground penetrating radar image data. DETAILED DESCRIPTION

[0052] To make the objectives, technical solutions, and advantages of the present invention more clearly apparent, the present invention is described below using specific examples shown in the accompanying drawings. However, it should be understood that these descriptions are merely illustrative and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0053] Example 1

[0054] like Figure 1 As shown, a method for quantizing ground penetrating radar image data includes the following steps:

[0055] S1, measure the direct-coupled waveform of the ground penetrating radar. In an open area, point the ground penetrating radar upward to measure the air and collect the waveform data S of the ground penetrating radar at this time. air (t); t represents the propagation time of the electromagnetic wave after it is emitted;

[0056] S2, GPR waveform calibration, place the metal reflector at R0 in front of the GPR antenna main beam, and collect the GPR waveform data, denoted as S plate (t), the waveform data S obtained by S1air (t) and S plate (t) are subtracted, and the subtracted waveform data are respectively subjected to Fourier transform with the specific phase unit intensity waveform, and a spectrum difference ΔP(f) is calculated and obtained, the waveform data in the measured ground penetrating radar image are corrected according to the spectrum difference, and the waveform data of the calibrated ground penetrating radar image are obtained;

[0057] S3, the detection depth of the ground penetrating radar in the object is calculated according to the transmission attenuation at the interface between the measured object and air, the corrected waveform data in S2 are corrected according to the transmission rate at the interface between the measured object and air, and the waveform corrected according to the transmission attenuation at the interface between the measured object and air is obtained;

[0058] S4, the waveform corrected according to the internal medium loss attenuation of the object is calculated according to the loss attenuation coefficient of the internal medium of the object per unit distance corresponding to the waveform in the ground penetrating radar image;

[0059] S5, the cross-medium electric wave propagation distance diffusion attenuation correction processing is performed, the waveform data in the ground penetrating radar image are converted into radar scattering length according to the characteristics that the electric wave propagation distance diffusion of the ground penetrating radar working in a short distance approximately conforms to the spherical wave attenuation rule, and the quantization processing of the ground penetrating radar image data is completed;

[0060] S6, the equivalent attenuation coefficient estimation of the internal medium of the object and the radar scattering length correction; since the approximate loss attenuation coefficient value is used in S4, the equivalent attenuation coefficient of the internal medium of the object near the depth can be approximately estimated according to the converted radar scattering length distribution based on the characteristics that the random medium self-scattering intensity distribution in the similar region is similar, two scattered wave regions with no obvious strong reflection and the amplitude higher than the radar bottom noise are selected at the similar depth in the scattering length image, the root mean square statistics of the scattered wave amplitude in the region is performed, and the equivalent attenuation coefficient of the internal medium of the object near the depth can be approximately estimated by the following formula:

[0061]

[0062] In the formula, σ(z) represents the root mean square value of the scattered wave amplitude in a certain region, z1 and z2 are the center depths of the two selected scattered wave regions, is the initial value selected in S4. The equivalent attenuation coefficient is mainly related to the water content, granularity and compactness of the internal medium of the object; in the case that the detection distance is less than or close to the size of the radar antenna, the equivalent attenuation coefficient is also related to the size of the radar antenna, resulting in that the estimated result is less than the actual loss attenuation coefficient of the medium.

[0063] The equivalent attenuation coefficient of the medium estimated by S6 is re-substituted into S4 and S5 for correction processing, and the corrected radar scattering length distribution map is obtained.

[0064] R0 in S2 is greater than or equal to the wavelength of the working electromagnetic wave of the ground penetrating radar, and the unit intensity waveform of the specific phase is S0 (t-2R0 / c); the unit intensity is the envelope peak amplitude of the waveform, the amplitude value is 1, and the specific phase is the waveform phase at the envelope peak of the waveform, which is a specific value selected, and the specific value is 0°, 90° or -90°.

[0065] The spectrum difference ΔP(f) is obtained specifically as follows:

[0066] ΔP(f)=FFT[S0(t-2R0 / c)] / FFT[S plate (t)-S air (t)]

[0067] Among them, f is the frequency of the electromagnetic wave; c is the propagation speed of the electromagnetic wave in the air, and FFT is Fourier transform.

[0068] The correction process of the waveform data in the measured ground penetrating radar image by using the spectrum difference is specifically as follows: i (t), use the spectrum difference to perform emission waveform calibration:

[0069] S i ′(t)=IFFT{FFT[S i (t)-S air (t)]·ΔP(f)}

[0070] Among them, IFFT is inverse Fourier transform; S i ′(t) is the waveform of the i-th GPR image after the emission waveform is calibrated.

[0071] The detection depth of the ground penetrating radar inside the object in S3 is:

[0072] Among them, z is the detection depth, c is the propagation speed of electromagnetic waves in the air; t0 is the waveform moment corresponding to the reflection position on the object surface; n is the refractive index of the medium inside the object, and t is the propagation time of the electromagnetic wave.

[0073] The transmittance of the interface between the measured object and the air is used to correct the corrected waveform data as follows:

[0074] Among them, T i is the transmittance of the interface between the object being measured and the air, is the corrected waveform;

[0075] For well-coupled ground-penetrating radar, T i The value is 1, and the waveform S of each channel after the emission waveform calibration is directly extracted for the air-coupled ground penetrating radar. i′(t) The first envelope peak, denoted as V i , at this time the interface transmittance is:

[0076] T i =1-r i ×r i

[0077]

[0078] Among them, r i is the approximate reflection coefficient of the interface between the object being measured and the air; h0 is the vertical distance or height from the center of the ground penetrating radar antenna to the surface of the object being measured; R0 is the distance used when calibrating the transmission waveform.

[0079] The radar image corrected by the medium loss attenuation inside the measured object in S4 is specifically:

[0080] Assume that the loss attenuation coefficient of the object's internal medium per unit distance corresponding to the i-th waveform in the ground penetrating radar image is α i , then the waveform after internal medium loss attenuation correction is:

[0081]

[0082] Among them, the loss attenuation coefficient α i It includes absorption attenuation and scattering attenuation, which is related to the moisture content, porosity, granularity of the medium inside the object and the working electromagnetic wave frequency of the ground penetrating radar. During the initial correction process, α i Take the initial value as 0 or smaller For working electromagnetic waves below 500MHz,

[0083] The waveform data in the ground penetrating radar image in S5 is converted into radar scattering length as follows:

[0084]

[0085] Where h0 is the vertical distance or height from the center of the ground penetrating radar antenna to the surface of the object being measured; n i is the refractive index of the medium inside the object being measured at that position; L i (z) is the radar scattering length, which has specific meaning only at the local peak of the waveform envelope.

[0086] Example 2

[0087] Take a stepped frequency sweep system ground penetrating radar as an example. The center frequency of this ground penetrating radar is 410MHz. It uses a 4-element ultra-wideband antenna array with a length of 1.06m and a width of 0.4m. The direct-coupled waveform of the ground penetrating radar measured in the air is as follows: Figure 2As shown, due to the problem of range ambiguity of the stepped-frequency radar, the range ambiguity interference waveform amplitude superimposed in the rear time period is generally large. The unit strength 90° phase waveform used for transmitting waveform calibration is as shown in Figure 3 As shown, the size of the metal plate for calibration is 1.5m*0.6m, and the measured distance R0 is 0.7m during calibration.

[0088] The ground penetrating radar is mounted on the bottom of the vehicle for road measurement, the distance from the bottom of the radar to the ground is 30cm, the total thickness of the radar is about 18cm, the height of the radar antenna to the ground is approximately h0≈0.4m, and the 1024 channel waveform data is measured at an interval of about 5cm. After the transmitting waveform calibration, the first envelope peak value of each channel waveform is extracted, and the change of the ground reflection coefficient at different positions is as shown in Figure 4 As shown, the average is about 0.51; since the road reflection wave is relatively strong, in order to highlight the internal image of the roadbed, the average of each channel waveform is subtracted, and the stepped-frequency ground penetrating radar image after the average waveform elimination is as shown in Figure 5 As shown.

[0089] After the radar measurement image is corrected and processed by transmission attenuation, medium loss attenuation, and range diffusion, the lateral 60th to 160th channel waveforms in the radar scattering length image are selected, and the root mean square statistics of the stray wave amplitude are performed on the two stray wave regions at the depths of 1.26m to 1.66m and 1.67m to 2.07m in the longitudinal direction, and the comparison curve is as shown in Figure 6 As shown, the average is 1.30cm and 1.02cm respectively, and the equivalent attenuation amount α of the object internal medium calculated by the method of step 6 is i ≈0.296; the ground penetrating radar scattering length distribution after the re-correction of S4 and S5 in embodiment 1 is as shown in Figure 7 As shown.

[0090] Embodiment 3

[0091] Taking a certain narrow pulse ground penetrating radar as an example, the half width of the transmitting pulse of the ground penetrating radar is about 800ps, the center frequency of the electromagnetic wave of the radar is about 370MHz, and the real-time sampling rate of the radar waveform is 2.5Gs; the detection antenna adopts a 4-unit ultra-wideband antenna array, and the length of the linear array is 1.06m; the direct coupling waveform of the ground penetrating radar for skyward measurement is as shown in Figure 8 As shown.

[0092] The ground penetrating radar is mounted on the bottom of the vehicle for road measurement, the distance from the bottom of the radar to the ground is 15cm, the thickness of the radar is about 18cm, the height of the radar antenna to the ground is approximately h0≈0.25m, the measurement data is calibrated by the transmitting waveform, and the first envelope peak value of each channel waveform is extracted, and the change of the ground reflection coefficient at different positions is as shown in Figure 9 As shown, the average is about 0.42.

[0093] After the S3 to S5 in the example 1 are corrected, the 300th to 500th wave number of the radar image is selected respectively, the depth range of the two stray wave regions is 1.55m to 1.85m, 2.55m to 2.85m, the mean square root statistics of the stray wave amplitude is about 0.30cm and 0.27cm respectively; the equivalent attenuation amount α of the object internal medium estimated according to the method of step 6 is about 0.053; the scattering length distribution of the ground penetrating radar after the S4 and S5 are re-corrected is shown as follows: i Figure 10 It can be seen that the amplitude of the quantized ground penetrating radar image is consistent at different depths, the numerical physical meaning of the ground penetrating image is given, and the display degree of the image is increased.

[0094] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it; although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that; the specific embodiments of the present application can still be modified or some technical features can be replaced by equivalent; without departing from the spirit of the technical solutions of the present application, they should be covered in the technical solution range of the present application claimed.​

Claims

1. A method for quantizing ground penetrating radar image data, characterized in that: The method specifically comprises the following steps: S1, measure the direct-coupled waveform of the ground penetrating radar. In an open area, point the ground penetrating radar upward to measure the air and collect the waveform data S of the ground penetrating radar at this time. air (t); t represents the propagation time of the electromagnetic wave after it is emitted; S2, GPR waveform calibration, place the metal reflector at R0 in front of the GPR antenna main beam, and collect the GPR waveform data, denoted as S plate (t), the waveform data S obtained by S1 air (t) and S plate (t) performing subtraction, performing Fourier transform on the subtracted waveform data and the specific phase unit intensity waveform, respectively, and then calculating to obtain a spectrum difference ΔP(f), and correcting the waveform data in the measured ground penetrating radar image according to the spectrum difference to obtain waveform data of a calibrated ground penetrating radar image; S3, correcting the radar image based on the transmission attenuation at the interface between the object and the air, calculating and obtaining the detection depth of the ground penetrating radar inside the object, and correcting the waveform data corrected in S2 based on the transmittance of the interface between the object and the air, to obtain a waveform corrected for the transmission attenuation at the interface between the object and the air; S4, correcting the radar image according to the loss attenuation of the internal medium of the measured object, and calculating and obtaining a waveform corrected for the internal medium loss attenuation according to the loss attenuation coefficient of the internal medium of the object per unit distance corresponding to the waveform in the ground penetrating radar image; S5, cross-media radio wave propagation distance diffusion attenuation correction processing, based on the characteristic that the radio wave propagation distance diffusion of the ground penetrating radar working at close range approximately conforms to the spherical wave attenuation law, the waveform data in the ground penetrating radar image is converted into radar scattering length quantity, completing the quantization processing of the ground penetrating radar image data.

2. The method for quantizing ground penetrating radar image data according to claim 1, wherein: R0 in S2 is greater than or equal to the wavelength of the working electromagnetic wave of the ground penetrating radar, and the unit intensity waveform of the specific phase is S0 (t-2R0 / c); the unit intensity is the envelope peak amplitude of the waveform, the amplitude value is 1, and the specific phase is the waveform phase at the envelope peak of the waveform, which is a specific value selected, and the specific value is 0°, 90° or -90°.

3. The method for quantizing ground penetrating radar image data according to claim 2, wherein: The spectrum difference ΔP(f) is obtained specifically as follows: ΔP(f)=FFT[S0(t-2R0 / c)] / FFT[S plate (t)-S air (t)] Among them, f is the frequency of the electromagnetic wave; c is the propagation speed of the electromagnetic wave in the air, and FFT is Fourier transform.

4. The method for quantizing ground penetrating radar image data according to claim 3, wherein: The correction process of the waveform data in the measured ground penetrating radar image by using the spectrum difference is specifically as follows: i (t), use the spectrum difference to perform emission waveform calibration: S i ′(t)=IFFT{FFT[S i (t)-S air (t)]·ΔP(f)} Among them, IFFT is inverse Fourier transform; S i ′(t) is the waveform of the i-th GPR image after the emission waveform is calibrated.

5. The method for quantizing ground penetrating radar image data according to claim 1, wherein: The detection depth of the ground penetrating radar inside the object in S3 is: Among them, z is the detection depth, c is the propagation speed of electromagnetic waves in the air; t0 is the waveform moment corresponding to the reflection position on the object surface; n is the refractive index of the medium inside the object, and t is the propagation time of the electromagnetic wave.

6. The method for quantizing ground penetrating radar image data according to claim 5, characterized in that: The transmittance of the interface between the measured object and the air is used to correct the corrected waveform data as follows: Among them, T i is the transmittance of the interface between the object being measured and the air, is the corrected waveform; For well-coupled ground-penetrating radar, T i The value is 1, and the waveform S of each channel after the emission waveform calibration is directly extracted for the air-coupled ground penetrating radar. i ′(t) The first envelope peak, denoted as V i , at this time the interface transmittance is: T i ＝1-r i ×r i Among them, r i is the approximate reflection coefficient of the interface between the object being measured and the air; h0 is the vertical distance or height from the center of the ground penetrating radar antenna to the surface of the object being measured; R0 is the distance used when calibrating the transmission waveform.

7. The method for quantizing ground penetrating radar image data according to claim 1, characterized in that: The radar image corrected by the medium loss attenuation inside the measured object in S4 is specifically: Assume that the loss attenuation coefficient of the object's internal medium per unit distance corresponding to the i-th waveform in the ground penetrating radar image is α i , then the waveform after internal medium loss attenuation correction is: Among them, the loss attenuation coefficient α i It includes absorption attenuation and scattering attenuation, which is related to the moisture content, porosity, granularity of the medium inside the object and the working electromagnetic wave frequency of the ground penetrating radar. During the initial correction process, α i Take the initial value as 0 or smaller For working electromagnetic waves below 500MHz, 8. The method for quantizing ground penetrating radar image data according to claim 1, wherein: The waveform data in the ground penetrating radar image in S5 is converted into radar scattering length as follows: Where h0 is the vertical distance or height from the center of the ground penetrating radar antenna to the surface of the object being measured; n i is the refractive index of the medium inside the object being measured at that position; L i (z) is the radar scattering length, which has a specific meaning only at the local peak of the waveform envelope; At similar depths in the converted radar scattering length image, two spurious wave regions with no obvious strong reflection and amplitudes higher than the radar's own noise floor are selected. The root mean square statistics of the spurious wave amplitudes in these regions are performed to approximately estimate the equivalent attenuation coefficient of the medium inside the object near this depth: Where σ(z) is the root mean square value of the stray wave amplitude in a certain area obtained by statistics, z1 and z2 are the center depths of the two selected stray wave areas, The initial value of the internal medium loss attenuation coefficient of the measured object selected by S4; and then using the attenuation coefficient to estimate the value α i Substitute the above S4 and S5 and perform the correction process again.

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