Evaluation and correction method for array element time delay synchronism of three-dimensional ground penetrating radar array antenna

Abstract

The invention discloses a method for evaluating and correcting time delay synchronism of array elements of a three-dimensional ground penetrating radar array antenna, which comprises the following steps of: 1, simulating a total reflection scene in an air medium; 2, acquiring data: starting a three-dimensional ground penetrating radar, and storing data of all array elements of the array antenna for not less than 30 seconds; step 3, data recombination and interception; 4, evaluating array element time delay synchronism; and 5, calculating a time delay synchronization correction coefficient of each array element. According to the method disclosed by the invention, a three-dimensional ground penetrating radar array antenna performance evaluation system is preliminarily established, which is a supplement for general ground penetrating radar performance evaluation; the method solves the problem that an existing evaluation method cannot accurately evaluate the synchronization degree of the array elements of the three-dimensional ground penetrating radar array antenna, the time delay difference between the array elements and whether the quality and the display effect of various subsequent three-dimensional views are affected.

Description

Technical Field

[0001] The invention belongs to the field of ground penetrating radar research, and particularly relates to an evaluation and correction method for time delay synchronization of array elements of a three-dimensional ground penetrating radar array antenna in the field. Background Art

[0002] Compared with traditional two-dimensional ground penetrating radar, three-dimensional ground penetrating radar can collect high-density, seamlessly spliced ​​massive radar data without causing the loss of underground information. The spatial distribution characteristics of electromagnetic waves can be obtained through the collected three-dimensional data. The three-dimensional data body can be sliced ​​horizontally at any depth, sliced ​​vertically at any position, and displayed in an inclined profile at any angle and direction to achieve the spatial characterization of underground targets. Three-dimensional ground penetrating radar has become the mainstream product in the industry due to its high efficiency and intuitiveness. Three-dimensional ground penetrating radar array antennas can often be combined for transmission and reception, that is, the signal transmitted by any array element can be received by other array elements. When working, multiple transmitting array elements are controlled by high-speed coaxial switches to transmit electromagnetic waves to the underground in a certain sequence, and then the receiving array elements collect echo signals at the same time. The receiving characteristics of each array element will be affected by factors such as the antenna manufacturing process, crosstalk between different array elements, various RF front ends and A / D devices themselves. At the same time, the digital orthogonal demodulation after A / D sampling will further introduce fluctuations in the receiving characteristics. These factors lead to the distortion of antenna array element transmission characteristics and the inconsistency of delay synchronization characteristics between array elements, causing the time zero point of the three-dimensional data body to be inconsistent, resulting in strip-like or patchy interference or artifacts in slice and section images, reducing the imaging quality of various targets and affecting the accuracy of interpretation and evaluation.

[0003] Therefore, it is necessary to establish a 3D GPR performance evaluation system, in which the delay synchronization of the array antenna elements is an important evaluation indicator. The better the delay synchronization of the 3D GPR array antenna elements, the higher the quality of the extracted and generated profiles and 3D stereoscopic views. Only by controlling or correcting the delay synchronization of the 3D GPR array antenna elements within a certain range can subsequent target detection and recognition be guaranteed.

[0004] The patent "A method for evaluating the phase jitter of a ground-penetrating radar antenna (CN113219423B)" discloses collecting ground-penetrating radar data of a certain length, finding the number of sampling points corresponding to the direct-coupled wave or the reflected wave, and calculating the extreme value and the mean value of the sampling points to obtain the phase jitter of the ground-penetrating radar antenna. The disadvantage is that it is based on phase stability and is only applicable to the evaluation of a single antenna of a two-dimensional ground-penetrating radar or the evaluation of multiple channels of a three-dimensional ground-penetrating radar array antenna. It cannot evaluate whether the signals between the elements of a three-dimensional ground-penetrating radar array antenna are synchronized or whether the delays are consistent, and it cannot provide a quantitative correction coefficient. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for evaluating and correcting the time delay synchronization of antenna elements of a three-dimensional ground penetrating radar array.

[0006] The present invention adopts the following technical solution:

[0007] A method for evaluating and correcting the time delay synchronization of antenna elements of a three-dimensional ground penetrating radar array is improved in that it comprises the following steps:

[0008] Step 1: Simulation of total reflection scene in air medium:

[0009] Copper foil is laid flat on the ground, a cubic foam is placed in the center of the copper foil, and a three-dimensional ground penetrating radar array antenna is horizontally placed on the top of the cubic foam, with the radiation surface of the array antenna facing downward, and the center point of the array antenna is aligned with the center point of the copper foil;

[0010] Step 2, data collection:

[0011] Turn on the 3D ground penetrating radar and save data of all elements of the array antenna for no less than 30 seconds;

[0012] Step 3, data reorganization and interception:

[0013] Arrange the data in the order of array antenna elements, and remove the data of the first 10 seconds and the last 10 seconds of each element, and only keep the middle data, so as to obtain the valid data set of each element: {S 1 , S 2 , …, S i , …, S N}, where S i S represents the valid data set of the ith array element, N is the total number of array antenna elements, and the valid data set of a single array element contains the received echo signals at several moments: i ={s i1 ,s i2 ,…,s ij ,…,s im}, where s ij represents the received echo signal of the i-th array element at the j-th moment;

[0014] Step 4: Array delay synchronization evaluation:

[0015] The valid data set S of the i-th array element is i The received echo signal s at a single moment in ij Through analysis, the delay corresponding to the sub-wave reflected by the ground copper foil of the array element at each moment is obtained: i1 ,tt i2 ,…,tt ij ,…,tt im}, where tt ijMeanTT represents the ground copper foil reflection delay in the echo signal received by the i-th array element at the j-th time. The average delay of the ground copper foil reflection wavelet of the array element is obtained by averaging: i =mean(tt i1 ,tt i2 ,…,tt ij ,…,tt im );

[0016] Then, the mean delay of the sub-waves reflected by the ground copper foil of all array elements is obtained: [MeanTT 1 , MeanTT 2 , …, MeanTT i , …, MeanTT N ], the maximum value of the time delay of the sub-wave reflected by the ground copper foil of all array elements is MeanTT max , the minimum value is MeanTT min , the average value is MeanTT mean ;

[0017] The delay synchronization of each element of the three-dimensional ground penetrating radar array antenna is expressed as:

[0018]

[0019] Step 5: Calculate the delay synchronization correction coefficient of each array element:

[0020] The correction coefficient corresponding to the i-th element of the three-dimensional ground penetrating radar array antenna is: CoefTim i =MeanTT mean -MeanTT i , after reverse compensation, delay synchronization correction is performed.

[0021] Further, in step 1, the cross-section of the top of the cubic foam is larger than the bottom surface of the array antenna.

[0022] Further, in step 1, the height of the cubic foam is 2λ, where λ is the wavelength of the center frequency of the array antenna corresponding to the air medium.

[0023] Furthermore, in step 1, in the length and width directions, the paving range of the copper foil exceeds the bottom edge of the cubic foam by 4λ.

[0024] Furthermore, in step 2, the corresponding array antenna default parameters are selected, and the antenna is preheated for ten minutes to check and confirm that all array elements are in working state, time-triggered mode, and can send and receive signals normally.

[0025] The beneficial effects of the present invention are:

[0026] The method disclosed in the present invention preliminarily establishes a three-dimensional ground-penetrating radar array antenna performance evaluation system, which is a supplement to the general ground-penetrating radar performance evaluation. It makes up for the fact that the existing evaluation methods cannot accurately evaluate the degree of synchronization of the elements of the three-dimensional ground-penetrating radar array antenna, the difference in time delay between the elements, and whether it will affect the quality and display effect of various subsequent three-dimensional stereoscopic views. At the same time, it provides a correction coefficient calculation method that has not been involved before, which can be used for reverse compensation.

[0027] The method disclosed in the present invention provides a basis for three-dimensional ground penetrating radar manufacturers to self-test performance indicators, provides guidance for three-dimensional ground penetrating radar users to purchase equipment, and provides a reference for three-dimensional ground penetrating radar users to conduct secondary development. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the transverse profile of the 3D GPR array antenna element when the delay synchronization is poor;

[0029] Figure 2 It is the horizontal profile of the 3D GPR array antenna element when the delay synchronization is poor;

[0030] Figure 3 It is a schematic flow diagram of the method of the present invention;

[0031] Figure 4 It is a schematic diagram of the total reflection simulation scene in the air medium;

[0032] Figure 5 It is a data set of ten elements of a three-dimensional ground penetrating radar array antenna;

[0033] Figure 6 It is the received echo signal diagram of a certain array element at a single moment. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] Figure 1 It is the transverse profile of the 3D GPR array antenna element when the delay synchronization is poor; Figure 2 It is a horizontal profile diagram when the time delay synchronization of the antenna elements of the three-dimensional ground penetrating radar array is poor.

[0036] Embodiment 1. This embodiment discloses a method for evaluating and correcting the time delay synchronization of array elements of a three-dimensional ground penetrating radar array antenna. Under static conditions, the reflected waves of each array element of the three-dimensional ground penetrating radar array antenna to the same surface target are collected at the same time, and the time delay of the reflected waves of each array element is statistically analyzed respectively, and its synchronization is calculated, and the synchronization correction coefficient of each array element of the array antenna is obtained.

[0037] like Figure 3 As shown, the specific steps are as follows:

[0038] Step 1: Simulation of total reflection scene in air medium:

[0039] like Figure 4 As shown, the 3D ground penetrating radar 400M array antenna is horizontally placed on a cubic foam with a cross-section larger than the bottom of the array antenna. The height of the foam is 150cm. The wavelength of the array antenna with a center frequency of 400M corresponds to 75cm in the air medium. The radiation surface of the array antenna faces downward, and the ground is flat and paved with copper foil. In the length and width directions, the paving range of the copper foil exceeds the edge of the bottom surface of the antenna by 300cm. The center point of the array antenna is aligned with the center point of the paved copper foil;

[0040] Step 2, data collection:

[0041] Turn on the 3D ground penetrating radar, select the corresponding array antenna default parameters, preheat for ten minutes, check that all 10 array elements are in working condition, time trigger mode, and can send and receive signals normally. At the same time, save the data of 10 array elements for no less than 30 seconds;

[0042] Step 3, data reorganization and interception:

[0043] Arrange the data in the order of the array antenna elements, and remove the data of the first 10 seconds and the last 10 seconds of each element, and only keep the data of the middle 10 seconds, so as to obtain the following Figure 5 The 10-element valid data set is shown in Figure 1. Figure 6 As shown, the effective data set of a single array element includes the received echo signals at several moments;

[0044] Step 4: Array delay synchronization evaluation:

[0045] The effective data sets of each array element are counted in turn. For the effective data set of each array element, the received echo signal at a single moment is analyzed in turn. The ground copper foil reflection sub-wave delay of the array element at each moment is obtained, and the average delay of the ground copper foil reflection sub-wave of the array element is obtained. Thus, the average delays of the ground copper foil reflection sub-waves of 10 array elements are obtained respectively [2.84ns, 3ns, 3.02ns, 2.84ns, 2.88ns, 2.84ns, 3.02ns, 3.02ns, 2.9ns, 2.88ns], the maximum value of the average delay of the ground copper foil reflection sub-wave of 10 array elements is 3.02ns, the minimum value is 2.84ns, and the average value is 2.924ns. The delay synchronization of the three-dimensional ground penetrating radar array antenna elements is about 0.534dB;

[0046] Step 5: Calculate the delay synchronization correction coefficient of each array element:

[0047] The synchronization correction coefficients corresponding to the 10 array elements of the three-dimensional ground penetrating radar array antenna are [0.084ns, -0.076ns, -0.096ns, 0.084ns, 0.044ns, 0.084ns, -0.096ns, -0.096ns, 0.024ns, 0.044ns], and the delay synchronization correction can be performed by performing reverse compensation.

Claims

1. A method for evaluating and correcting the time delay synchronization of antenna elements of a three-dimensional ground penetrating radar array, characterized in that: The steps include: Step 1: Simulation of total reflection scene in air medium: Copper foil is laid flat on the ground, a cubic foam is placed in the center of the copper foil, and a three-dimensional ground penetrating radar array antenna is horizontally placed on the top of the cubic foam, with the radiation surface of the array antenna facing downward, and the center point of the array antenna is aligned with the center point of the copper foil; Step 2, data collection: Turn on the 3D ground penetrating radar and save data of all elements of the array antenna for no less than 30 seconds; Step 3, data reorganization and interception: Arrange the data in the order of array antenna elements, and remove the data of the first 10 seconds and the last 10 seconds of each element, and only keep the middle data, so as to obtain the valid data set of each element: {S1, S2, ..., S i , …, S N }, where S i S represents the valid data set of the ith array element, N is the total number of array antenna elements, and the valid data set of a single array element contains the received echo signals at several moments: i ={s i1 ,s i2 ,…,s ij ,…,s im }, where s ij represents the received echo signal of the i-th array element at the j-th moment; Step 4: Array delay synchronization evaluation: The effective data set S of the i-th array element is i The received echo signal s at a single moment in ij Through analysis, the delay corresponding to the sub-wave reflected by the ground copper foil of the array element at each moment is obtained: i1 ,tt i2 ,…,tt ij ,…,tt im }, where tt ij MeanTT represents the ground copper foil reflection delay in the echo signal received by the i-th array element at the j-th time. The average delay of the ground copper foil reflection wavelet of the array element is obtained by averaging: i =mean(tt i1 ,tt i2 ,…,tt ij ,…,tt im ); Then, the mean delay of the wavelet reflected by the ground copper foil of all array elements is obtained: [MeanTT1, MeanTT2, …, MeanTT i , …, MeanTT N ], the maximum value of the time delay of the sub-wave reflected by the ground copper foil of all array elements is MeanTT max , the minimum value is MeanTT min , the average value is MeanTT mean ; The delay synchronization of each element of the three-dimensional ground penetrating radar array antenna is expressed as: Step 5: Calculate the delay synchronization correction coefficient of each array element: The correction coefficient corresponding to the i-th element of the three-dimensional ground penetrating radar array antenna is: CoefTim i =MeanTT mean -MeanTT i , after reverse compensation, delay synchronization correction is performed.

2. The method for evaluating and correcting the time delay synchronization of antenna elements of a three-dimensional ground penetrating radar array according to claim 1, characterized in that: In step 1, the top cross-section of the cubic foam is larger than the bottom surface of the array antenna.

3. The method for evaluating and correcting the time delay synchronization of antenna elements of a three-dimensional ground penetrating radar array according to claim 1, characterized in that: In step 1, the height of the cubic foam is 2λ, where λ is the wavelength of the center frequency of the array antenna corresponding to the air medium.

4. The method for evaluating and correcting the time delay synchronization of the three-dimensional ground penetrating radar array antenna elements according to claim 3, characterized in that: In step 1, in the length and width directions, the paving range of the copper foil exceeds the bottom edge of the cubic foam by 4λ.

5. The method for evaluating and correcting the delay synchronization of antenna elements of a three-dimensional ground penetrating radar array according to claim 1, characterized in that: In step 2, select the corresponding default parameters of the array antenna, preheat for ten minutes, check and confirm that all array elements are in working state, time-triggered mode, and can send and receive signals normally.

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