A frequency optimization method for ground penetrating radar antennas with different detection depths

Abstract

This invention belongs to the field of non-destructive testing of road surface damage, specifically involving a method for optimizing the antenna frequency of ground-penetrating radar (GPR) at different detection depths. The method involves selecting four intermediate-frequency (IF) antennas and four high-frequency (HF) antennas; extracting single-channel wave data from radar signals acquired by the IF and HF antennas for different survey lines and calculating the average amplitude of multiple wave signals; calculating the amplitude of echo signals from layer interfaces; constructing a homogeneous model of the tested road section using electromagnetic simulation software and calculating the amplitude of echo signals from layer interfaces within the homogeneous model; and evaluating the degree of disturbance to the target echo signal caused by the non-uniform characteristics of the road surface material based on the aforementioned signal data. This invention quantitatively assesses the impact of non-uniform disturbances on radar waves excited by different antenna frequencies, thereby subdividing the overlap range within the radar detection depth at different antenna frequencies. This provides data support and prior knowledge for selecting the optimal antenna frequency in GPR field testing.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing of road surface structure damage, specifically involving a method for optimizing the frequency of ground-penetrating radar antennas at different detection depths. Background Technology

[0002] Ground-penetrating radar (GPR) utilizes the reflection of electromagnetic waves when they encounter underground media with varying dielectric properties to detect the thickness of the internal structural layers of a road surface. The timing of antenna reception and the stability of the reflection capability of the echo signal from the interface between the surface layer and the base layer are crucial factors in improving the accuracy of road structure thickness determination. According to single-channel GPR data, multiple irregular fluctuations exist between the layer interface echoes. These scattering disturbances caused by the non-uniformity of the road material lead to energy attenuation and unclear characteristics of the layer interface echoes. Radar waves excited by different antenna frequencies are disturbed to varying degrees by the non-uniform material, resulting in a discrepancy between the layer interface location information obtained from the echo signal and the actual thickness information of the road structure layers. Currently, in GPR antenna frequency selection methods that determine different detection depths based on GPR system power, the applicable detection depth ranges of different antenna frequencies overlap. To reduce the disturbance caused by the non-uniformity of the road material while meeting the effective detection depth requirements of GPR, it is necessary to optimize the radar antenna frequencies within the overlapping detection depth ranges. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for optimizing the frequency of ground-penetrating radar antennas at different detection depths, thus solving the technical problem of the disturbance caused by the non-uniform characteristics of materials and the overlap of detection depth ranges of different antenna frequencies during actual ground-penetrating radar detection on road surfaces.

[0004] To achieve the objectives of this invention, the technical solution is as follows:

[0005] The method for optimizing the frequency of a ground-penetrating radar antenna at different detection depths according to the present invention includes the following steps:

[0006] Step 1: Select an IDS-type ground-penetrating radar. The ground-penetrating radar uses four intermediate frequency antennas: 500 MHz, 600 MHz, 800 MHz, and 900 MHz; and four high frequency antennas: 1.0 GHz, 1.2 GHz, 1.5 GHz, and 2.0 GHz. These are used to collect radar signal data from the actual road surface.

[0007] Step 2: Extract single-channel radar signal data from different survey lines using radar signal data acquired by the intermediate frequency antenna and high frequency antenna, and calculate the radar wave s using the following formula:

[0008]

[0009] In the formula, Indicates the target echo. Indicates unrelated echoes. Indicates random noise;

[0010] Step 3: Extract the electric field intensity of the radar wave s at the crest and trough of the complete wave in the radar wave s calculated in Step 2, and calculate the average value of the amplitude of multiple wave signals.

[0011] Step 4: Extract the electric field intensity at the crest and trough of the echo signal from the interface between the surface layer and the base layer on each measurement line of the four intermediate frequency antennas and the four high frequency antennas, and calculate the amplitude of the echo signal at the layer interface.

[0012] Step 5: Construct a homogeneous model of the test section using the electromagnetic simulation software gprMax, extract the electric field intensity at the peaks and troughs of the echo signal at the interface between the surface layer and the base layer in the homogeneous model, and calculate the amplitude of the echo signal at the layer interface in the homogeneous model.

[0013] Step 6: Based on the radar wave s from Step 2, the average amplitude of multiple wave signals from Step 3, the echo signal amplitude of the interlayer interface from Step 4, and the echo signal amplitude of the interlayer interface obtained through model calculation in Step 5, evaluate the degree of disturbance to the target echo signal caused by the non-uniform characteristics of the road surface material using the following formula:

[0014]

[0015] In the formula, This represents the j-th echo amplitude from left to right between the upper and lower interfaces of the stratigraphic level at each survey line. This represents the amplitude of the reflected wave from the lower interface in a homogeneous model. This represents the amplitude of the reflected wave from the lower interface at the i-th survey line in the heterogeneous model. This represents the number of fluctuations caused by the heterogeneity between the upper and lower interfaces. The number of test lines;

[0016] Step 7: Based on the results calculated in Step 6, when the effective detection depth ranges of four intermediate frequency antennas (500 MHz, 600 MHz, 800 MHz, and 900 MHz) and four high frequency antennas (1.0 GHz, 1.2 GHz, 1.5 GHz, and 2.0 GHz) overlap, in order to reduce the influence of the non-uniform characteristics of the road surface material, the radar antenna with the lower frequency should be selected for detection as much as possible.

[0017] Beneficial effects

[0018] The method for optimizing the antenna frequency of ground-penetrating radar at different detection depths provided by this invention compares the radar waveform of the strata interface under material heterogeneity disturbance on the actual track surface with the radar waveform of the strata interface in a homogeneous model. It proposes a disturbance index of heterogeneous materials on the strata interface radar waves, quantitatively evaluates the degree of influence of heterogeneity disturbance on radar waves excited by different antenna frequencies, and thus subdivides the overlap range in radar detection depths under different antenna frequencies. This can provide data support and prior knowledge for the selection of the optimal antenna frequency in ground-penetrating radar field testing. Attached Figure Description

[0019] Figure 1 This is a diagram of the combined ground-penetrating radar detection system of the present invention;

[0020] Figure 2 This is a schematic diagram of the ground-penetrating radar detection of different survey line layouts according to the present invention;

[0021] Figure 3 This is a schematic diagram of the measured pavement layer interface echo of the present invention;

[0022] Figure 4 This is a schematic diagram of the target echo signal behind the preferred antenna according to the present invention;

[0023] in Figure 4 (a) is the measured radar spectrum at 2.5 GHz;

[0024] Figure 4(b) shows the measured radar spectrum at a frequency of 2.0 GHz. Detailed Implementation

[0025] To make the objectives and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] This invention proposes a perturbation index for the inter-layer interface radar waves caused by heterogeneous material disturbances on the actual pavement surface, by comparing the radar waves of the inter-layer interface in a homogeneous model with those in a homogeneous model. This quantitatively assesses the degree of influence of heterogeneous disturbances on radar waves excited by different antenna frequencies, thereby subdividing the overlap range in radar detection depth under different antenna frequencies. This can provide data support and prior knowledge for selecting the optimal antenna frequency in ground penetrating radar field testing.

[0027] As attached Figure 1 The following steps illustrate the method for optimizing the frequency of a ground-penetrating radar antenna at different detection depths:

[0028] Step 1: The ground penetrating radar uses four intermediate frequency antennas: 500 MHz, 600 MHz, 800 MHz, and 900 MHz; and four high frequency antennas: 1.0 GHz, 1.2 GHz, 1.5 GHz, and 2.0 GHz; these are used to collect radar signal data from the actual road surface.

[0029] Step 2: Extract single-channel radar signal data from different survey lines using radar signal data acquired by the intermediate frequency antenna and high frequency antenna, and calculate the radar wave s using the following formula:

[0030] (1)

[0031] In the formula, Indicates the target echo. Indicates unrelated echoes. Indicates random noise;

[0032] Step 3: Extract the electric field intensity of the radar wave s at the crest and trough of the complete wave in the radar wave s calculated in Step 2, and calculate the average value of the amplitude of multiple wave signals.

[0033] Step 4: Extract the electric field intensity at the crest and trough of the echo signal from the interface between the surface layer and the base layer on each measurement line of the four intermediate frequency antennas and the four high frequency antennas, and calculate the amplitude of the echo signal at the layer interface.

[0034] In this step: the surface layer is the top layer of the entire road structure, directly in contact with passing vehicles and the atmosphere; the base layer is the load-bearing structural layer below the surface layer, paved with high-quality materials.

[0035] Step 5: Construct a homogeneous model of the test section using the electromagnetic simulation software gprMax, extract the electric field intensity at the peaks and troughs of the echo signal at the interface between the surface layer and the base layer in the homogeneous model, and calculate the amplitude of the echo signal at the layer interface in the homogeneous model.

[0036] Step 6: Based on the radar wave s from Step 2, the average amplitude of multiple wave signals from Step 3, the echo signal amplitude of the interlayer interface from Step 4, and the echo signal amplitude of the interlayer interface obtained through model calculation in Step 5, evaluate the degree of disturbance to the target echo signal caused by the non-uniform characteristics of the road surface material using the following formula:

[0037] (2)

[0038] In the formula, This represents the j-th echo amplitude from left to right between the upper and lower interfaces of the stratigraphic level at each survey line. This represents the amplitude of the reflected wave from the lower interface in a homogeneous model. This represents the amplitude of the reflected wave from the lower interface at the i-th survey line in the heterogeneous model. This represents the number of fluctuations caused by the heterogeneity between the upper and lower interfaces. The number of test lines;

[0039] Step 7: Based on the results calculated in Step 6, when the effective detection depth ranges of four intermediate frequency antennas (500 MHz, 600 MHz, 800 MHz, and 900 MHz) and four high frequency antennas (1.0 GHz, 1.2 GHz, 1.5 GHz, and 2.0 GHz) overlap, to reduce the influence of the non-uniform characteristics of the road surface material, radar antennas with lower frequencies should be selected for detection as much as possible. As shown in Table 1, the higher the antenna frequency, the greater the influence of non-uniform disturbances on the radar wave propagation in the structural layer.

[0040] Table 1. Indices of Heterogeneity (HI)

[0041] Layer 0.5 GHz 0.6 GHz 0.8 GHz 0.9 GHz 1.0 GHz 1.2 GHz 1.5 GHz 2.0 GHz cement panel 15.425 15.829 17.824 18.623 24.296 41.088 88.090 168.662 Water-stabilized base course 10.619 13.161 40.570 53.719 70.055 94.790 141.458 200.781

[0042] The maximum detection depth of ground-penetrating radar mainly depends on factors such as the performance of the radar system, the attenuation of the underground medium, and the reflection characteristics of the interface, and can be expressed by equation (3):

[0043] (3)

[0044] In the formula, Indicates the received power. Indicates the transmission power. Indicates antenna gain. Indicates the wavelength of radar waves, This represents the area of ​​the target's scattering interface. This represents the relative permittivity of the medium. Indicates the maximum detection depth. This represents the attenuation coefficient of radar waves.

[0045] The detection depth of existing ground-penetrating radars at different antenna frequencies is divided according to equation (3), as shown in Table (2). It can be seen that the detection depth ranges overlap for different antenna frequencies. Based on the conclusions drawn from the non-homogeneous disturbance index, the overlapping range of depth detection is further subdivided, as shown in Table 3.

[0046] Table 2 Detection depth at different antenna frequencies

[0047] Antenna center frequency (GHz) Detection depth (m) Antenna center frequency (GHz) Detection depth (m) 2.5 0.3~0.6 1.0 0.6~1.0 2.0 0.4~0.7 0.9 0.75~1.5 1.5 0.5~0.8 0.5 1.5~3 1.2 - 0.4 1.5~3

[0048] Table 3. Optimal detection depths for different antenna frequencies after correction.

[0049] Antenna center frequency (GHz) Detection depth (m) Antenna center frequency (GHz) Detection depth (m) 2.5 0.3~0.4 1.0 0.6~0.75 2.0 0.4~0.5 0.9 0.75~1.5 1.5 0.5~0.8 0.5 1.5~3 1.2 - 0.4 1.5~3

[0050] A combined ground-penetrating radar (GPR) detection system was used to inspect the concrete pavement of an airport. The investigation revealed that the rigid pavement consists of a 0.4 m thick concrete slab and a 0.2 m thick cement-stabilized crushed stone upper base. The effective depth of reflection from the interface between the detection layers must be at least 0.4 m. Referring to Table 2 (uncorrected detection depths for different antenna frequencies), the selectable antenna frequencies are 2.0 GHz and 2.5 GHz. Referring to Table 3 (corrected detection depths for different antenna frequencies), the preferred antenna frequency is 2.0 GHz. Radar signal acquisition was performed on a test section of the airport pavement using both antenna frequencies, as shown in the attached table. Figure 4 As shown. (Attached) Figure 4 (a) is the measured radar spectrum at 2.5 GHz, with appended... Figure 4 (b) is the measured radar spectrum at 2.0 GHz. (From the attached...) Figure 4 It is evident that at 2.5 GHz, the reflection at the stratigraphic interface in the radar spectrum fluctuates frequently, resulting in a larger error in the thickness calculation; while at 2.0 GHz, the reflection at the stratigraphic interface is more uniform with smaller fluctuations, leading to a smaller error in the thickness calculation. Therefore, the antenna frequency selected based on the corrected detection depths of different antenna frequencies offers better detection accuracy and is 2.0 GHz.

[0051] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for optimizing the frequency of a ground-penetrating radar antenna at different detection depths, characterized in that: Includes the following steps: Step 1: Select an IDS-type ground-penetrating radar. The ground-penetrating radar uses four intermediate frequency antennas: 500 MHz, 600 MHz, 800 MHz, and 900 MHz; and four high frequency antennas: 1.0 GHz, 1.2 GHz, 1.5 GHz, and 2.0 GHz. These are used to collect radar signal data from the actual road surface. Step 2: Extract single-channel radar signal data from different survey lines using radar signal data acquired by the intermediate frequency antenna and high frequency antenna, and calculate the radar wave s using the following formula: In the formula, Indicates the target echo. Indicates unrelated echoes. Indicates random noise; Step 3: Extract the electric field intensity of the radar wave s at the crest and trough of the complete wave in the radar wave s calculated in Step 2, and calculate the average value of the amplitude of multiple wave signals. Step 4: Extract the electric field intensity at the crest and trough of the echo signal from the interface between the surface layer and the base layer on each measurement line of the four intermediate frequency antennas and the four high frequency antennas, and calculate the amplitude of the echo signal at the layer interface. Step 5: Construct a homogeneous model of the test section using the electromagnetic simulation software gprMax, extract the electric field intensity at the peaks and troughs of the echo signal at the interface between the surface layer and the base layer in the homogeneous model, and calculate the amplitude of the echo signal at the layer interface in the homogeneous model. Step 6: Based on the radar wave s from Step 2, the average amplitude of multiple wave signals from Step 3, the echo signal amplitude of the layer interface from Step 4, and the echo signal amplitude of the layer interface obtained through model calculation in Step 5, evaluate the degree of disturbance to the target echo signal caused by the non-uniform characteristics of the road surface material using the following formula: In the formula, This represents the j-th echo amplitude from left to right between the upper and lower interfaces of the stratigraphic level at each survey line. This represents the amplitude of the reflected wave from the lower interface in a homogeneous model. This represents the amplitude of the reflected wave from the lower interface at the i-th survey line in the heterogeneous model. This represents the number of fluctuations caused by the heterogeneity between the upper and lower interfaces. The number of test lines; Step 7: Based on the results calculated in Step 6, when the effective detection depth ranges of four intermediate frequency antennas (500 MHz, 600 MHz, 800 MHz, and 900 MHz) and four high frequency antennas (1.0 GHz, 1.2 GHz, 1.5 GHz, and 2.0 GHz) overlap, in order to reduce the influence of the non-uniform characteristics of the road surface material, the radar antenna with the lower frequency should be selected for detection.

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