Nondestructive testing method for internal condition of pavement structure based on cross-frequency detection of ground penetrating radar

Abstract

The present application relates to the field of quantum radar technology, and specifically to a nondestructive detection method for the internal condition of a pavement structure based on cross-frequency detection of a ground-penetrating radar, including: obtaining the echo signal strength of multiple locations on the pavement in the target area through a detection radar; determining the signal interference degree of each location based on the change and fluctuation of the echo signal strength; determining the clutter interference degree of each location based on the change trend and discreteness of the frequency domain characteristics of the echo signal strength at each location, and then obtaining the echo signal authenticity at each location; obtaining the anti-interference evaluation value in the cross-frequency detection process based on the difference in the echo signal authenticity of adjacent locations and the average level of all echo signal authenticity, so as to calculate the step factor adjustment value, obtain the echo signal strength after filtering processing in combination with an adaptive filtering algorithm, and obtain the detection result of the internal condition of the pavement structure through ground-penetrating radar imaging technology. The present application can improve the accuracy of nondestructive detection of the internal condition of the pavement structure.

Description

Technical Field

[0001] The present application relates to the field of quantum radar technology, and in particular to a nondestructive detection method for the internal condition of a pavement structure based on cross-frequency detection of a ground penetrating radar. Background Art

[0002] With the continuous increase in traffic volume, under the repeated influence of traffic load and environmental factors, the internal structure of the road surface is prone to damage, such as settlement, voids, and hidden holes. These problems will lead to uneven road surface and poor bearing capacity, and the safety and reliability of the road surface cannot be guaranteed. With the continuous development of ground penetrating radar technology, it is widely used in non-destructive testing of the internal conditions of road structures due to its high efficiency and non-destructive characteristics.

[0003] Existing ground-penetrating radar technology can quickly detect the internal conditions of the pavement structure, and then promptly repair the abnormal internal structure of the pavement to ensure the safety and reliability of the pavement. However, since the ground-penetrating radar needs to detect the internal conditions of the pavement structure through electromagnetic waves, it is easy to be affected by various interference signals during the detection process and generate strong noise, so that the echo signal of the ground-penetrating radar cannot truly reflect the signal characteristics of the internal pavement structure, thus affecting the accuracy of the detection of the internal conditions of the pavement structure.

[0004] With the continuous development of signal processing technology, digital filtering algorithms are used to eliminate noise interference components in echo signals, so that the echo signals of ground penetrating radar can truly reflect the signal characteristics inside the pavement structure. As a common digital filtering algorithm, adaptive filtering algorithms are generally applicable to filtering echo signals. However, the step size factor in traditional adaptive filtering algorithms is single and fixed, which makes it impossible to achieve both the convergence speed and steady-state error performance of the algorithm. It is impossible to accurately eliminate the noise interference components in the echo signal, resulting in low accuracy in detecting the internal conditions of the pavement structure. Summary of the invention

[0005] In order to solve the above technical problems, the present application provides a non-destructive detection method for the internal condition of a pavement structure based on cross-frequency detection of a ground penetrating radar to solve the existing problems.

[0006] The nondestructive detection method of the internal condition of the pavement structure based on cross-frequency detection of ground penetrating radar in this application adopts the following technical solutions:

[0007] An embodiment of the present application provides a nondestructive detection method for the internal condition of a pavement structure based on cross-frequency detection of a ground penetrating radar, comprising the following steps:

[0008] The echo signal strength at multiple locations on the road surface of the target area at each acquisition time during the cross-frequency detection process is obtained by detecting radar;

[0009] Based on the fluctuation of echo signal strength at each location on the target area road surface at different acquisition times, determine the signal interference degree at each location;

[0010] Determine the clutter interference degree at each location based on the change trend and discreteness of the frequency domain characteristics of the echo signal strength at each location;

[0011] The authenticity of the echo signal at each position is obtained based on the signal interference degree and clutter interference degree at each position;

[0012] Based on the difference between the echo signal authenticity of any two adjacent positions on the road surface of the target area and the average level of the echo signal authenticity of all positions, the anti-interference evaluation value in the cross-frequency detection process is obtained;

[0013] Acquire a step factor adjustment value based on the anti-interference evaluation value and an autocorrelation matrix of echo signal strengths at each position;

[0014] The adaptive filtering algorithm is used to obtain the echo signal strength after filtering based on the step size factor adjustment value, and the detection results of the internal conditions of the pavement structure are obtained through ground penetrating radar imaging technology.

[0015] Furthermore, the signal interference degree of each position is the product of the information entropy and the mean square error of the echo signal strength at all acquisition moments of each position.

[0016] Furthermore, the method for determining the clutter interference degree at each position includes:

[0017] Perform fast Fourier transform on the echo intensity signals at all acquisition moments at each position, arrange the frequency domain energy in ascending order of frequency and record it as the spectrum attenuation sequence at each position, and obtain the first-order difference sequence of the spectrum attenuation sequence;

[0018] The clutter interference degree at each position is determined according to the numerical distribution of the elements in the first-order difference sequence and the discreteness of the elements in the first-order difference sequence.

[0019] Furthermore, the calculation formula of the clutter interference degree is: i =(M i ×CV i ) / (N i +∈), where C i is the clutter interference degree at the ith position, M i and N i are the number of positive and negative values ​​in the first-order difference sequence of the spectrum decay sequence at the i-th position, CV i is the coefficient of variation of the first-order difference sequence of the spectrum attenuation sequence at the i-th position, and ∈ is a value to avoid the denominator being zero.

[0020] Furthermore, the authenticity of the echo signal at each position is negatively correlated with the product of the signal disturbance degree and the clutter interference degree at each position.

[0021] Furthermore, the authenticity of the echo signal at each position is a calculation result of an exponential function with a natural constant as the base and the inverse of the product of the signal disturbance degree and the clutter interference degree at each position as the exponent.

[0022] Furthermore, obtaining the anti-interference evaluation value in the cross-frequency detection process includes:

[0023] Analyze the difference in the authenticity of the echo signals between any two adjacent positions on the road surface of the target area, record it as the signal authenticity difference, and obtain the mean value of the authenticity of the echo signals at all positions on the road surface of the target area;

[0024] An anti-interference evaluation value in the cross-frequency detection process is determined based on the signal authenticity difference and the mean, wherein the anti-interference evaluation value is positively correlated with the mean, and negatively correlated with the signal authenticity difference between any two adjacent positions.

[0025] Furthermore, the calculation formula of the anti-interference evaluation value is:

[0026] Where V is the anti-interference evaluation value in the cross-frequency detection process, is the mean value of the echo signal authenticity at all positions, n is the number of acquisition positions set on the road surface in the target area, A j and A j-1 are the echo signal authenticity of the j-th and j-1-th positions respectively.

[0027] Furthermore, the calculation formula of the step factor adjustment value is:

[0028] Where μ is the step size factor adjustment value in the adaptive filtering algorithm, λ max is the maximum eigenvalue of the autocorrelation matrix of the signal strength sequence, wherein the echo signal strengths at all acquisition moments at each position constitute each signal strength sequence, exp() is an exponential function with a natural constant as the base, and V is the anti-interference evaluation value in the cross-frequency detection process.

[0029] Further, the obtaining the echo signal strength after filtering based on the step size factor adjustment value by using the adaptive filtering algorithm includes:

[0030] The echo signal strength collected at each position is used as the input of the adaptive filtering algorithm, and the echo signal strength after filtering is output, wherein the step factor of the adaptive filtering algorithm is the step factor adjustment value.

[0031] This application has at least the following beneficial effects:

[0032] The present application realizes non-destructive detection of the internal condition of the pavement structure by using the ground penetrating radar technology. By improving the step size factor in the adaptive filtering algorithm, the noise interference component in the echo signal is eliminated more accurately, thereby improving the accuracy of detecting the internal condition of the pavement structure. Compared with the prior art that uses the adaptive filtering algorithm to filter the echo signal, since the step size factor in the traditional adaptive filtering algorithm is single and fixed, it is impossible to accurately eliminate the noise interference component in the echo signal, resulting in low accuracy in detecting the internal condition of the pavement structure. The present invention constructs the authenticity of the echo signal by analyzing the irregular interference characteristics and clutter aliasing characteristics of the echo signal when it is interfered by external noise, and then uses the echo signal authenticity to determine the anti-interference ability of the echo signal during the detection process. Based on the anti-interference ability of the echo signal during the detection process, the step size factor in the adaptive filtering algorithm is improved, so that the adaptive filtering algorithm can take into account the convergence speed and steady-state error, and more accurately eliminate the noise interference component in the echo signal, thereby improving the accuracy of non-destructive detection of the internal condition of the pavement structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 A flowchart of the steps of the non-destructive testing method for the internal condition of the pavement structure based on cross-frequency detection of ground penetrating radar provided in this application;

[0035] Figure 2 A schematic diagram of the process of determining the clutter interference degree at each location on the road surface of the target area provided in this application;

[0036] Figure 3 A schematic diagram of the process of determining the anti-interference evaluation value in the cross-frequency detection process provided in this application. DETAILED DESCRIPTION

[0037] In order to further explain the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific implementation method, structure, features and effects of the non-destructive testing method of the internal condition of the pavement structure based on cross-frequency detection of the ground penetrating radar proposed in the present application are described in detail below in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0038] Unless otherwise defined, terms such as "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a circuit structure, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such articles or devices. In the absence of further restrictions, an element defined by the statement "comprising a ..." does not exclude the presence of other identical elements in the article or device comprising the element. In addition, the term "and\or" used herein includes any and all combinations of one or more related listed items. All technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present application belongs.

[0039] The specific scheme of the non-destructive detection method of the internal condition of the pavement structure based on cross-frequency detection of the ground penetrating radar provided in the present application is described in detail below with reference to the accompanying drawings.

[0040] An embodiment of the present application provides a nondestructive detection method for the internal condition of a pavement structure based on cross-frequency detection of a ground penetrating radar. For details, please refer to Figure 1 , including the following steps:

[0041] Step 1: Use detection radar to obtain the echo signal strength at multiple locations on the road surface in the target area at each acquisition time during the cross-frequency detection process.

[0042] The purpose of this embodiment is to improve the step size factor in the adaptive filtering algorithm so that the noise interference component in the echo signal received by the detection radar can be accurately eliminated, thereby improving the accuracy of detecting the internal conditions of the road surface structure.

[0043] A detection radar system is used to perform cross-frequency detection on the road surface of the target area, wherein the detection radar system includes a transmitting antenna, a receiving antenna, a transmitter, a receiver, a data control center, and a processing center;

[0044] In the process of cross-frequency detection of the road surface in the target area by using the detection radar, the high-frequency electromagnetic wave is transmitted to the underground medium through the transmitter, and the receiver receives the reflected echo signal and transmits it to the data control center. In this embodiment, the echo signal strength in the cross-frequency detection process is sampled from the data control center. In this embodiment, the sampling frequency of the echo signal strength is 10Hz;

[0045] In order to analyze the influence of noise interference on the echo signals at different positions of the target area road surface, multiple positions are set on the target area road surface to collect the echo signal strength. In this embodiment, 50 position points are evenly set on the target area road surface, and the echo signal strength of each position is collected by the detection radar. At the same time, in order to facilitate the subsequent elimination of the noise interference component in the echo signal received by the detection radar, the echo signal strength of each position in the cross-frequency detection process is sequenced in ascending time order as a signal strength sequence.

[0046] Step 2: Based on the fluctuation of the echo signal strength at each location on the road surface in the target area at different acquisition times, determine the signal interference degree at each location.

[0047] Furthermore, since the radar echo noise is prone to generate a large amount of noise during the detection of the internal structural conditions of the road surface in the target area, the noise source is usually very complex, which will greatly reduce the signal-to-noise ratio of the reflected wave, resulting in the echo signal of the ground penetrating radar being unable to truly reflect the signal characteristics inside the road surface structure.

[0048] Generally, the source of external noise is very complex. At this time, the external noise interference signal often has irregular characteristics, which will cause the echo signal strength to change irregularly when detecting each position. At the same time, the greater the irregular change characteristics of the echo signal strength, the greater the impact of the external irregular interference signal to a certain extent.

[0049] In order to analyze the degree to which the echo signal at each position is affected by the external irregular interference, the signal strength characteristic sequence at each position of the road surface in the target area is used as the input of the extreme point detection algorithm, and the output of the extreme point detection algorithm is used as all the extreme points in the signal strength characteristic sequence, wherein the extreme point detection algorithm is a well-known technology, and the specific process is not repeated here;

[0050] In order to analyze the irregular change characteristics of echo signal strength, the sequence of echo signal strengths at all extreme points in the signal strength feature sequence in ascending time order is taken as the signal strength extreme value sequence at each position, and the first-order difference sequence of the signal strength extreme value sequence at each position is taken as the signal strength change sequence at each position;

[0051] Based on the above analysis, the signal interference degree at each location is calculated:

[0052] D i =α i ×σ i , where D i is the signal interference degree at the i-th position, α i is the information entropy of the signal strength change sequence at the ith position, σ iis the mean square error of the signal strength change sequence at the i-th position. Information entropy α i The larger the mean square error σ i The larger it is, the greater the chaos and irregularity of the echo signal intensity change when measuring at that position on the target road surface. At this time, the greater the influence of external irregular interference signals, the greater the signal disturbance degree.

[0053] Step 3: Determine the clutter interference degree at each location based on the change trend and discreteness of the frequency domain characteristics of the echo signal strength obtained at each location.

[0054] Furthermore, when detecting underground media at a certain location, due to the high complexity of external noise sources, clutter aliasing is likely to occur in the echo signal, that is, clutter generated by different noise sources will alias, thereby affecting the authenticity of the echo signal. Generally, when clutter aliasing occurs in the echo signal, the spectrum attenuation characteristics of the echo signal will change abnormally, and the stronger the clutter aliasing characteristics in the echo signal, the greater the abnormal change in the spectrum attenuation.

[0055] In order to analyze the clutter and aliasing characteristics in the echo signal, the signal strength characteristic sequence at each position of the road surface in the target area is used as the input of the FFT fast Fourier transform (Fast Fourier Transform), and the output of the FFT fast Fourier transform is used as the right frequency domain data of the signal strength characteristic sequence, wherein the right frequency domain data includes the frequency and the frequency domain energy corresponding to the frequency, wherein the FFT fast Fourier transform is a well-known technology, and the specific process is not repeated here.

[0056] In order to reflect the abnormal changes in the spectral attenuation of the echo signal, the sequence of frequency domain energy in ascending order of frequency is taken as the spectral attenuation sequence of each position, and the first-order difference sequence of the spectral attenuation sequence of each position is calculated, and the number of positive values ​​and negative values ​​in the first-order difference sequence are counted respectively. The calculation of the first-order difference sequence is a well-known technology, and the specific process will not be repeated here.

[0057] Under normal circumstances, the change of data in the spectrum attenuation sequence shows a downward trend, but under the influence of clutter superposition, the change of data in the spectrum attenuation sequence will show a local upward feature. At this time, the spectrum attenuation feature is broken. Therefore, the larger the proportion of positive values ​​in the first-order difference sequence of the spectrum attenuation sequence, and the higher the discreteness of the data in the first-order difference sequence, the more it can be explained that the echo signal is affected by the clutter superposition.

[0058] Based on the above analysis, the clutter interference degree at each position is calculated:

[0059] C i =(M i ×CVi ) / (N i +∈), where C i is the clutter interference degree at the ith position, M i and N i are the number of positive and negative values ​​in the first-order difference sequence of the spectrum decay sequence at the i-th position, CV i is the coefficient of variation of the first-order difference sequence of the spectrum attenuation sequence at the ith position, ∈ is a value to avoid the denominator being zero, and in this embodiment is taken as 1, wherein the calculation of the coefficient of variation is a well-known technology and the specific process will not be repeated here.

[0060] It is understandable that the positive number M i The more negative values ​​N i The smaller the number, the more obvious the abnormal characteristics of local rise in the data change in the spectrum attenuation sequence, and the coefficient of variation CV i The larger it is, the stronger the discrete characteristics of the echo signal's spectrum attenuation change are. At this time, it can be said that the echo signal is affected by the superposition interference of external clutter, and the greater the clutter interference degree is.

[0061] See also Figure 2 , Figure 2 A schematic diagram of the process of determining the clutter interference degree at each position on the road surface of the target area in this embodiment is shown.

[0062] Step 4: Obtain the echo signal authenticity at each location based on the signal interference degree and clutter interference degree at each location.

[0063] Furthermore, when the ground-penetrating radar transmits electromagnetic waves at each location on the target road surface for ground-penetrating measurement, the stronger the echo signal is affected by the external irregular interference and the stronger the effect of the superposition of clutter on the echo signal, the greater the impact on the authenticity of the echo signal, making it impossible for the echo signal to truly reflect the signal characteristics inside the road surface structure at that location.

[0064] Based on the above analysis, the echo signal authenticity of each position is calculated. The echo signal authenticity of each position is negatively correlated with the product of the signal disturbance degree and the clutter interference degree of each position. It should be noted that the negative correlation indicates that the change trends between the two variables are opposite, and the dependent variable decreases (increases) as the independent variable increases (decreases). Preferably, in this embodiment, the calculation formula of the echo signal authenticity is:

[0065] A i =exp[-(D i ×C i )], where A i is the authenticity of the echo signal at the ith position, exp() is an exponential function with a natural constant as the base, D iis the signal interference degree at the ith position, C i is the clutter interference degree at the ith position.

[0066] In actual application, the implementer can also obtain the echo signal authenticity at each position through the inverse of the product of the signal interference degree and the clutter interference degree at each position.

[0067] It can be understood that the authenticity of the echo signal reflects whether the echo signal can truly reflect the signal characteristics inside the pavement structure at that location. The smaller the authenticity of the echo signal, the greater the impact of external interference signals, and the less able it is to truly reflect the signal characteristics inside the pavement structure at that location.

[0068] Step 5: Based on the difference between the echo signal authenticity of any two adjacent positions on the road surface in the target area and the average level of the echo signal authenticity of all positions, obtain the anti-interference evaluation value in the cross-frequency detection process.

[0069] Furthermore, in order to improve the step size factor in the adaptive filtering algorithm, it is necessary to evaluate the anti-interference characteristics of the echo signal during cross-frequency detection using the ground penetrating radar. The greater the fluctuation of the echo signal's authenticity during cross-frequency detection of the target road surface, and the lower the average level of authenticity, to a certain extent, it shows that the anti-interference ability of the echo signal is poorer.

[0070] According to the difference between the echo signal authenticity of all positions on the target area road surface and the echo signal authenticity of adjacent positions, the difference in the echo signal authenticity between any two adjacent positions on the target area road surface is analyzed and recorded as the signal authenticity difference, and the mean of the echo signal authenticity of all positions on the target area road surface is obtained; based on the signal authenticity difference and the mean, the anti-interference evaluation value in the cross-frequency detection process is determined, wherein the anti-interference evaluation value is positively correlated with the mean, and negatively correlated with the signal authenticity difference between all any two adjacent positions.

[0071] Preferably, in this embodiment, the anti-interference evaluation value in the cross-frequency detection process is calculated:

[0072] Where V is the anti-interference evaluation value in the cross-frequency detection process, is the mean value of the echo signal authenticity at all positions, n is the number of acquisition positions set on the road surface in the target area, A j and A j-1 are the echo signal authenticity of the jth and j-1th positions, respectively. ∈ is a value to avoid the denominator being zero. In this embodiment, it is taken as 1. j -A j-1 |Recorded as the difference in signal authenticity between the jth and j-1th positions. Mean The smaller the signal authenticity difference |A j -A j-1 The larger the value is, the worse the anti-interference ability of the echo signal is, and the higher the degree of influence of external noise is, the smaller the anti-interference evaluation value is.

[0073] See also Figure 3 , Figure 3 A schematic diagram of the process of determining the anti-interference evaluation value during the cross-frequency detection process of this embodiment is shown.

[0074] Step 6: Obtain a step factor adjustment value based on the anti-interference evaluation value and the autocorrelation matrix of the signal strength at each position.

[0075] Furthermore, if the anti-interference evaluation value in the cross-frequency detection process is smaller, it means that the detection process is more susceptible to external interference noise. At this time, a larger step size factor should be selected using the adaptive filtering algorithm in order to effectively perform filtering processing; and if the anti-interference evaluation value in the cross-frequency detection process is larger, it means that the detection process is less susceptible to external interference noise. At this time, a smaller step size factor should be selected using the adaptive filtering algorithm in order to ensure steady-state accuracy during filtering processing.

[0076] Based on the above analysis, the step size factor adjustment value in the adaptive filtering algorithm is calculated:

[0077] Where μ is the step size factor adjustment value in the adaptive filtering algorithm, λ max is the maximum eigenvalue of the autocorrelation matrix of the signal strength sequence, exp() is an exponential function with a natural constant as the base, and V is the anti-interference evaluation value in the cross-frequency detection process. max The calculation of is a well-known technique in the adaptive filtering algorithm, and the specific calculation process will not be described in detail in this embodiment.

[0078] Step 7: Use the adaptive filtering algorithm to obtain the echo signal strength after filtering based on the step size factor adjustment value, and obtain the detection result of the internal condition of the pavement structure through ground penetrating radar imaging technology.

[0079] In order to make the echo signal of the ground penetrating radar reflect the signal characteristics inside the pavement structure more realistically, thereby improving the accuracy of detecting the internal conditions of the pavement structure.

[0080] The signal strength sequence of each position is used as the input of the adaptive filtering algorithm. In this embodiment, the preset number of iterations is 10, and the step factor adjustment value is used as the step factor in the adaptive filtering algorithm. The adaptive filtering algorithm outputs the echo signal strength after filtering. The adaptive filtering algorithm is a well-known technology and the specific process will not be repeated here.

[0081] The echo signal intensity after filtering is transmitted to the processing center, and the echo signal is processed in the processing center through ground penetrating radar imaging technology to obtain the underground image of the road surface. The underground image of the road surface is used as the detection result of the internal condition of the road surface structure, so that the target road surface can be repaired in time based on the detection result of the internal condition of the road surface structure.

[0082] It is understood that references to "one embodiment" or "some embodiments" etc. described in the specification of the present application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, if "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. appear in different places in this specification, they do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0083] It should be noted that the sequence of the above-mentioned embodiments of the present application is only for description and does not represent the advantages and disadvantages of the embodiments. And the above-mentioned specific embodiments of this specification are described. In addition, the process depicted in the accompanying drawings does not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multi-tasking and parallel processing are also possible or may be advantageous. At the same time, the size of the sequence number of each step in the embodiment does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments in this specification.

[0084] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A nondestructive testing method for the internal condition of a pavement structure based on cross-frequency detection of a ground penetrating radar, characterized in that: The following steps are involved: The echo signal strength at multiple locations on the road surface of the target area at each acquisition time during the cross-frequency detection process is obtained by detecting radar; Based on the fluctuation of echo signal strength at each location on the target area road surface at different acquisition times, determine the signal interference degree at each location; Determine the clutter interference degree at each location based on the change trend and discreteness of the frequency domain characteristics of the echo signal strength at each location; The authenticity of the echo signal at each position is obtained based on the signal interference degree and clutter interference degree at each position; Based on the difference between the echo signal authenticity of any two adjacent positions on the road surface of the target area and the average level of the echo signal authenticity of all positions, the anti-interference evaluation value in the cross-frequency detection process is obtained; Acquire a step factor adjustment value based on the anti-interference evaluation value and an autocorrelation matrix of echo signal strengths at each position; The adaptive filtering algorithm is used to obtain the echo signal strength after filtering based on the step size factor adjustment value, and the detection results of the internal conditions of the pavement structure are obtained through ground penetrating radar imaging technology.

2. The nondestructive detection method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 1, characterized in that: The signal disturbance degree of each position is as follows: the sequence composed of all echo signal intensities at each position is used as the input of the extreme point detection algorithm, and the sequence composed of echo signal intensities corresponding to all extreme points of the output is used as the signal strength extreme value sequence of each position; the first-order difference sequence of each signal strength extreme value sequence is used as each signal strength change sequence; the product of the information entropy and the mean square error of the signal strength change sequence at each position is used as the signal disturbance degree of each position.

3. The nondestructive detection method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 1, characterized in that: The method for determining the clutter interference degree at each position includes: Perform fast Fourier transform on the echo intensity signals at all acquisition moments at each position, arrange the frequency domain energy in ascending order of frequency and record it as the spectrum attenuation sequence at each position, and obtain the first-order difference sequence of the spectrum attenuation sequence; The clutter interference degree at each position is determined according to the numerical distribution of the elements in the first-order difference sequence and the discreteness of the elements in the first-order difference sequence.

4. The nondestructive detection method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 3, characterized in that: The calculation formula of the clutter interference degree is: C i =(M i ×CV i ) / (N i +∈), where C i is the clutter interference degree at the ith position, M i and N i are the number of positive and negative values ​​in the first-order difference sequence of the spectrum decay sequence at the i-th position, CV i is the coefficient of variation of the first-order difference sequence of the spectrum attenuation sequence at the i-th position, and ∈ is a value to avoid the denominator being zero.

5. The nondestructive testing method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 1, characterized in that: The authenticity of the echo signal at each position is negatively correlated to the product of the signal disturbance degree and the clutter interference degree at each position.

6. The nondestructive detection method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 5, characterized in that: The authenticity of the echo signal at each position is a calculation result of an exponential function with a natural constant as the base and the inverse of the product of the signal disturbance degree and the clutter interference degree at each position as the exponent.

7. The nondestructive detection method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 1, characterized in that: Acquisition of the anti-interference evaluation value during the cross-frequency detection process includes: Analyze the difference in the authenticity of the echo signals between any two adjacent positions on the road surface of the target area, record it as the signal authenticity difference, and obtain the mean value of the authenticity of the echo signals at all positions on the road surface of the target area; An anti-interference evaluation value in the cross-frequency detection process is determined based on the signal authenticity difference and the mean, wherein the anti-interference evaluation value is positively correlated with the mean, and negatively correlated with the signal authenticity difference between any two adjacent positions.

8. The nondestructive detection method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 4, characterized in that: The calculation formula of the anti-interference evaluation value is: Where V is the anti-interference evaluation value in the cross-frequency detection process, is the mean value of the echo signal authenticity at all positions, n is the number of acquisition positions set on the road surface in the target area, A j and A j-1 are the echo signal authenticity of the j-th and j-1-th positions respectively.

9. The nondestructive testing method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 1, characterized in that: The calculation formula of the step factor adjustment value is: Where μ is the step size factor adjustment value in the adaptive filtering algorithm, λ max is the maximum eigenvalue of the autocorrelation matrix of the signal strength sequence, wherein the echo signal strengths at all acquisition moments at each position constitute each signal strength sequence, exp() is an exponential function with a natural constant as the base, and V is the anti-interference evaluation value in the cross-frequency detection process.

10. The nondestructive testing method for internal conditions of pavement structure based on cross-frequency detection of ground penetrating radar according to claim 1, characterized in that: The method of obtaining the echo signal strength after filtering based on the step size factor adjustment value by using the adaptive filtering algorithm includes: The echo signal strength collected at each position is used as the input of the adaptive filtering algorithm, and the echo signal strength after filtering is output, wherein the step factor of the adaptive filtering algorithm is the step factor adjustment value.

Images