A method for non-destructive size measurement of subsurface targets combining frequency encoding and half-integer phase control

Abstract

The application provides a non-destructive size measurement method for underground targets by combining frequency coding and half-integer phase control, and belongs to the field of non-destructive size measurement of underground targets. The method solves the problem that the prior art cannot effectively overcome the near distance blind area and suppress the frequency domain sidelobe. The method comprises the following steps: constructing an equal-interval frequency grid; generating a transmission frequency sequence by using a step parameter coprime with the total frequency point number for coding sorting; defining the effective transmission duration of each frequency point time slot, so that the near distance blind area range is determined by meeting the half-integer period condition; in each frequency point time slot, a linear sweep signal is generated, and the cumulative phase of the signal at the end of the time slot is controlled to meet the half-integer circle constraint; the signal is transmitted in sequence, and the echo signal is received synchronously; the complex frequency response of each frequency point is extracted, and after frequency domain coherent synthesis, the phase information is differentially approximated to obtain the group time delay; and the target geometric size is calculated according to the medium propagation speed and the group time delay. The method is used in the field of pipe network detection.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive dimensional measurement of underground targets, and in particular relates to a method for non-destructive dimensional measurement of underground targets that combines frequency coding and half-integer phase control. Background Technology

[0002] Non-destructive dimensional measurement technology for underground targets refers to a class of measurement techniques that obtain geometric parameters such as the external dimensions, thickness, horizontal extension length, and spatial spacing of buried or semi-buried targets (such as pipelines, cables, and structures) without excavating the surface, damaging the overburden, contacting the target, or interrupting existing working conditions. This type of technology typically uses electromagnetic waves, ground acoustic waves, or ultrasonic waves as excitation media. By analyzing the phase, amplitude, or group time delay relationship between the excitation signal and the echo signal reflected by the underground target, the geometric parameters of the target are inferred. Compared to traditional methods that rely on excavation or contact measurement, non-destructive measurement methods have significant advantages such as minimal construction interference, strong environmental adaptability, and high measurement repeatability, making them irreplaceable in application value.

[0003] Currently, the mainstream methods in this field mostly employ multi-frequency continuous wave stepping or linear frequency sweeping methods. For example, the multi-frequency continuous wave stepping method transmits a series of single-frequency continuous wave signals sequentially at fixed frequency steps within a preset frequency band, and collects and processes the echo signal at each frequency point; while the linear frequency sweeping method transmits a signal whose frequency changes linearly and continuously with time within the same frequency band. Both methods ultimately require coherent synthesis of the echo signals collected at different frequency points in the frequency domain, and the spatial distribution and size of the target are inferred by calculating the phase change or group delay of the synthesized signal. However, in actual complex underground media environments, the above-mentioned existing methods have exposed many technical limitations, severely restricting further improvements in measurement accuracy.

[0004] First, existing systems inherently suffer from a near-range blind zone in the time domain. Because the excitation signal is typically a continuous waveform or a linear frequency sweep in the time domain, its energy cannot naturally attenuate at the boundaries of a single time slot, leading to energy leakage in the time domain. This leakage causes the weak echo signal from shallowly buried targets to superimpose with the much stronger surface reflection signal in the time domain, making them difficult to separate. This creates a blind zone within the short-range range of the detection system, resulting in detection failure or misjudgment of the size of shallowly buried targets.

[0005] Secondly, existing technologies face challenges in the frequency domain due to increased sidelobe levels and phase fluctuations. The use of continuous waves or equal-step frequency sequences results in strong correlations between adjacent transmission frequencies. This correlation can easily introduce unnecessary phase jitter and nonlinear errors during frequency domain synthesis, leading to a significant increase in the sidelobe levels of the synthesized spectrum. High sidelobes can broaden and distort the main lobe response of the target, causing unclear target boundaries and unstable size judgment results. This deficiency is particularly prominent when it is necessary to distinguish multiple adjacent targets or accurately measure target thickness.

[0006] Furthermore, the stratification, water content, and non-uniformity of underground media cause multipath effects and reverberation during electromagnetic wave propagation, further exacerbating the shortcomings of existing technologies. Multipath propagation leads to more complex spectral characteristics of echo signals and a decrease in the effective signal-to-noise ratio, significantly increasing the uncertainty in accurately extracting target size information from complex echoes, making it difficult to guarantee the reliability and repeatability of size inversion results.

[0007] To improve measurement accuracy, existing technologies have proposed several remedial measures, such as windowing weighting, amplitude and phase correction, or array beamforming. While windowing weighting can suppress frequency domain sidelobes to some extent, this comes at the cost of sacrificing effective signal bandwidth and expanding the main lobe width, directly leading to a decrease in range resolution. Array beamforming, while theoretically improving spatial directivity and suppressing multipath interference, places extremely high demands on the layout accuracy of physical array elements and the amplitude and phase consistency of each channel. In non-uniform and unstable underground environments, the performance of array systems is difficult to maintain, and the complexity and implementation cost of the system are significantly increased.

[0008] In summary, how to effectively overcome near-range blind zones, suppress frequency domain sidelobes, and improve the robustness of coherent signal synthesis in complex media under limited system bandwidth and actual hardware constraints has become a key technical bottleneck restricting the development and practical application of non-destructive dimensional measurement technology for underground targets. Summary of the Invention

[0009] In view of this, the present invention aims to propose a non-destructive size measurement method for underground targets that combines frequency coding and half-integer phase control, in order to solve the problem that existing technologies cannot effectively overcome near-range blind zones and suppress frequency domain sidelobes under limited system bandwidth and actual hardware constraints.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A non-destructive size measurement method for underground targets combining frequency coding and half-integer phase control, the method comprising:

[0012] Step S1: Within a preset frequency band, construct an equally spaced frequency grid containing N frequency points using a frequency step Δf, where, Indicates the step interval between adjacent frequency points;

[0013] Step S2: Select an integer s that is coprime to N as the step size parameter, and encode and sort the equally spaced frequency grids to generate the transmission frequency sequence;

[0014] Step S3: Define the effective transmission duration τ for each frequency slot. k The effective transmission duration of the time slot satisfies the half-integer period condition, and the near-range blind zone range is determined based on the half-integer period;

[0015] Step S4: At each frequency point, time slot t∈[0, τ] k Within the time slot, a narrowband linear sweep frequency signal based on the center frequency is generated, and the cumulative phase of the narrowband linear sweep frequency signal at the end of the time slot is controlled to satisfy the half-integer round constraint.

[0016] Step S5: According to the encoded and sorted transmission frequency sequence, transmit the narrowband linear sweep frequency signal processed in step S4 in sequence, and simultaneously receive the echo signal from the underground target;

[0017] Step S6: Process the echo signal to obtain the complex frequency response at each frequency point, map the complex frequency response back to the natural index, coherently synthesize it in the frequency domain, and differentially approximate the group delay based on the synthesized frequency response phase information.

[0018] Step S7: Calculate the target geometry based on the medium propagation speed and group delay.

[0019] Furthermore, a preferred embodiment is proposed, wherein the construction of an equally spaced frequency grid containing N frequency points in step S1 includes:

[0020]

[0021]

[0022] in, This represents the k-th frequency point. Indicates the starting frequency of the frequency band. N This represents the total number of frequency points. Indicates the frequency band termination frequency.

[0023] Furthermore, a preferred method is proposed, wherein the encoding and sorting of the equally spaced frequency grids in step S2 includes:

[0024]

[0025] in, This represents the frequency index after encoding and sorting.

[0026] Furthermore, a preferred embodiment is proposed, wherein the effective transmission duration of the time slot in step S3 satisfies the half-integer period condition, including:

[0027]

[0028] in, This represents the effective duration of the k-th time slot. Represents the number of half-integer periods. This represents the integer parameter used to ensure that the sine wave crosses zero at the end of the time slot. Represents an integer.

[0029] Furthermore, a preferred method is proposed, in which the start frequency and end frequency of the narrowband linear sweep frequency signal in step S4 are obtained by inverse solving of the half-integer phase boundary constraints, specifically satisfying the following relationship:

[0030]

[0031]

[0032] in, This represents the starting frequency of the k-th time slot frequency sweep. This represents the half-integer cycle parameter of the k-th time slot. This represents the sweep bandwidth of the k-th time slot. This represents the termination frequency of the k-th time slot sweep;

[0033] The center frequency after the callback is:

[0034]

[0035] in, This represents the callback center frequency obtained after phase constraint.

[0036] Furthermore, a preferred method is proposed, wherein the half-integer cycle parameters of the k-th time slot in step S4... satisfy:

[0037]

[0038] in, Indicates center frequency deviation. This indicates the maximum permissible deviation limit.

[0039] Furthermore, a preferred embodiment is proposed, wherein step S6, based on the synthesized frequency response phase information, includes differential approximation group delay:

[0040]

[0041] in, Indicates group delay. The phase function represents the complex frequency response at the (k+1)th frequency point. The phase function representing the complex frequency response at the k-th frequency point. For the (k+1)th sampling frequency point, This represents the kth sampling frequency point.

[0042] Furthermore, a preferred embodiment is proposed, wherein step S7 includes:

[0043]

[0044] Where D represents the equivalent length or thickness of the underground target being measured. It represents the equivalent propagation speed of electromagnetic waves in underground media.

[0045] Based on the same inventive concept, the present invention also proposes a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the processor runs the computer program stored in the memory, the processor executes a non-destructive size measurement method for underground targets combining frequency encoding and half-integer phase control as described in any of the preceding claims.

[0046] Based on the same inventive concept, the present invention also proposes a computer-readable storage medium storing a computer program that, when executed by a processor, performs the steps of a method for non-destructive dimensional measurement of underground targets combining frequency encoding and half-integer phase control as described above.

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] Unlike existing technologies that transmit frequencies directly in natural order (from low to high) or through linear frequency sweeping, this invention proposes a frequency encoding mechanism based on a coprime step size. This mechanism reorders the transmitted frequency sequence using a step size parameter coprime to the total number of frequency points. This results in a pseudo-random jump in the frequency values ​​of adjacent transmissions within a preset frequency band, rather than a continuous change, at the macroscopic transmission order level. This design fundamentally breaks the inherent strong correlation between adjacent frequency points, allowing phase errors caused by medium inhomogeneities or system nonlinearities to be statistically homogenized and whitened, avoiding the accumulation of correlated phase noise as in traditional methods.

[0049] To address the problems of near-range blind zones and increased spectral sidelobes caused by time-domain energy leakage in existing technologies, this invention proposes a fundamental principle modification within the independent transmission time slots at each frequency point. Traditional methods forcibly truncate continuous waves or swept-frequency signals at time slot boundaries, inevitably resulting in abundant spectral components. This invention cleverly embeds a narrowband linear swept-frequency signal within each time slot and precisely controls the parameters of this signal through strict mathematical constraints, ensuring that its cumulative phase at the end of the time slot is exactly a half-integer cycle. This half-integer phase boundary constraint principle ensures that the time-domain waveform (sine function) naturally and smoothly crosses zero at the end of the time slot, achieving energy self-closure. This is equivalent to applying a natural time-domain window at the signal source, fundamentally avoiding spectral spread caused by truncation.

[0050] The proposed method improves the distribution characteristics of frequency samples on a global scale through a frequency coding strategy, suppressing macroscopic errors in frequency domain synthesis. Meanwhile, half-integer phase control enables fine-grained management of signal energy within each local time slot, optimizing the spectral purity of individual frequency points. These two approaches complement each other, resulting in frequency domain data points used for synthesis that possess both clean individual properties (low sidelobes) and excellent collective distribution (low cross-interference). This achieves high-resolution, high-robustness measurement results equivalent to a broadband system without extending the system's hardware bandwidth. Attached Figure Description

[0051] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0052] Figure 1 This is a flowchart of a non-destructive size measurement method for underground targets that combines frequency coding and half-integer phase control, as described in this invention.

[0053] Figure 2 This is a schematic diagram illustrating the relationship between the transmission signal frequency and the transmission sequence as described in this invention. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments.

[0055] Implementation Method 1: This implementation method addresses the limitations of existing technologies in effectively overcoming near-range blind zones and suppressing frequency domain sidelobes under conditions of limited system bandwidth and practical hardware constraints. It proposes a non-destructive dimensional measurement method for underground targets that combines frequency coding and half-integer phase control. The method includes:

[0056] Step S1: Within a preset frequency band, construct an equally spaced frequency grid containing N frequency points with a frequency step Δf;

[0057] Step S2: Select an integer s that is coprime to N as the step size parameter, and encode and sort the equally spaced frequency grids to generate the transmission frequency sequence;

[0058] Step S3: Define the effective transmission duration τ for each frequency slot. k The effective transmission duration of the time slot satisfies the half-integer period condition, and the near-range blind zone range is determined based on the half-integer period;

[0059] Step S4: At each frequency point, time slot t∈[0, τ] k Within the time slot, a narrowband linear sweep frequency signal based on the center frequency is generated, and the cumulative phase of the narrowband linear sweep frequency signal at the end of the time slot is controlled to satisfy the half-integer round constraint.

[0060] Step S5: According to the encoded and sorted transmission frequency sequence, transmit the narrowband linear sweep frequency signal processed in step S4 in sequence, and simultaneously receive the echo signal from the underground target;

[0061] Step S6: Process the echo signal to obtain the complex frequency response at each frequency point, map the complex frequency response back to the natural index, coherently synthesize it in the frequency domain, and differentially approximate the group delay based on the synthesized frequency response phase information.

[0062] Step S7: Calculate the target geometry based on the medium propagation speed and group delay.

[0063] This implementation proposes a non-destructive dimensional measurement method for underground targets that combines frequency coding and half-integer phase control. This method addresses the problem of increased measurement errors caused by multipath reflection, phase perturbation, and near-range blind zones in underground media. It achieves smooth energy distribution in the time domain and effective suppression of sidelobes by designing a stepped-frequency pulse train signal within a fixed frequency band and introducing narrow-band linear frequency sweeping within each frequency slot. A half-integer phase constraint is applied to the transmitted signal at the end of the time slot, ensuring the excitation waveform naturally crosses zero at the boundary, thus preventing energy leakage to adjacent time slots. Simultaneously, a frequency coding strategy with coprime step sizes keeps the difference between adjacent frequencies nearly constant and uniformly distributed across the frequency sequence, improving the robustness and noise immunity of spectral synthesis. The receiver uses coherent synthesis and group delay estimation to obtain the geometric dimensional parameters of the target, achieving high-precision non-destructive measurement of the length, thickness, or spatial dimensions of underground targets without increasing the system bandwidth. This method balances hardware feasibility with signal processing stability, is suitable for high-resolution non-contact measurement in complex underground media environments, and significantly improves the accuracy and repeatability of target size inversion.

[0064] Implementation Method 2, see below Figure 1 and Figure 2 This embodiment describes a complete implementation of the non-destructive dimensional measurement method for underground targets combining frequency coding and half-integer phase control described in Embodiment 1, including:

[0065] Step S1: In the preset frequency band [f start ,f end Within the range, an equally spaced frequency grid containing N frequency points is constructed using a frequency step Δf, including;

[0066] (1)

[0067]

[0068] in, This represents the k-th frequency point. Indicates the starting frequency of the frequency band. Indicates the step interval between adjacent frequency points. N This represents the total number of frequency points. Indicates the frequency band termination frequency.

[0069] Step S2: Select an integer s that is coprime to N as the step size parameter, and encode and sort the equally spaced frequency grids to generate a transmission frequency sequence;

[0070] To reduce inter-frequency interference and improve the robustness of frequency synthesis, an integer s coprime to N and close to N / 2 is selected, and the equally spaced frequency grids are encoded and sorted.

[0071] (2)

[0072] in, Let represent the frequency index after encoding and sorting, and s represent the step size parameter, which is coprime to N. The encoded emission sequence is {f}. π In the sequence (k), the frequency difference between adjacent frequencies is statistically approximately constant and remains relatively large, which helps to reduce phase coupling between adjacent frequency components. Figure 2 The diagram shows the relationship between the transmission signal frequency and the transmission sequence in this embodiment.

[0073] Step S3: Define the effective transmission duration τ for each frequency slot. k The effective transmission duration of the time slot satisfies the half-integer period condition, and the near-range blind zone range is determined based on the half-integer period, including:

[0074] To suppress near-range blind zones and facilitate subsequent phase boundary control, the effective transmit duration τ for each time slot is defined. k And satisfy:

[0075] (3)

[0076] in, This represents the effective duration of the k-th time slot. Represents the number of half-integer periods. This represents the integer parameter used to ensure that the sine wave crosses zero at the end of the time slot. Represents an integer. The resulting near-field blind zone range is:

[0077] (4)

[0078] in, c represents the near-field dead zone length corresponding to the k-th frequency point. eff It represents the equivalent propagation speed of electromagnetic waves in underground media.

[0079] Step S4: At each frequency point, time slot t∈[0, τ] k Within the specified time slot, a narrowband linear sweep frequency signal based on the center frequency is generated, and the cumulative phase of the narrowband linear sweep frequency signal at the end of the time slot is controlled to satisfy the half-integer round constraint, including:

[0080] Around the center frequency f k In the time slot interval t∈[0, τ] k The applied bandwidth is B k Linear frequency sweep:

[0081] (5)

[0082] in, This represents the sweep bandwidth of the k-th time slot. This represents the bandwidth scaling factor. This represents the sweep slope. The corresponding instantaneous frequency and phase are as follows:

[0083] (6)

[0084] (7)

[0085] in, This indicates the starting frequency of the frequency sweep within that time slot. This represents the instantaneous phase function of the signal within the time slot. This represents the instantaneous frequency of the k-th time slot. To eliminate cross-time slot energy leakage and suppress frequency domain sidelobes, this implementation applies a half-integer round-phase boundary constraint at the end of the time slot:

[0086] (8)

[0087] in, This represents the instantaneous phase value at the end of the k-th time slot. This represents the half-integer cycle parameter of the k-th time slot. Let represent the set of non-negative integers. Substituting equation (6) into equation (7) yields:

[0088] (9)

[0089] in, This represents the cumulative phase revolutions. The sweep start and end frequencies can be deduced from equation (8):

[0090] (10)

[0091] (11)

[0092] in, This represents the starting frequency of the k-th time slot frequency sweep. This represents the termination frequency of the k-th time slot frequency sweep. The center frequency after the callback is:

[0093] (12)

[0094] in, This represents the callback center frequency obtained after phase constraint. To ensure the center frequency deviation is minimized, the following is selected:

[0095] (13)

[0096] in, Indicates center frequency deviation. This indicates the maximum permissible deviation limit. If the deviation exceeds the limit, [the following applies]. Make a ±1 adjustment to minimize the error.

[0097] Step S5: Based on the encoded and sorted transmission frequency sequence, transmit the narrowband linear sweep frequency signal processed in step S4 sequentially, and simultaneously receive the echo signal from the underground target; this also includes discrete implementation and frequency quantization correction steps.

[0098] The sampling rate of the transmitted frequency sequence in this embodiment f s Choosing a sample that satisfies the Nyquist sampling theorem, the number of discrete sampling points in the time slot is:

[0099] (14)

[0100] in, f s Indicates the sampling frequency. This represents the number of sampling points in the k-th time slot. This represents the nth sampling time. The discrete expression of the excitation signal is:

[0101] (15)

[0102] in, Indicates a real-value excitation signal. Indicate its complex analytic form, j Represents the imaginary unit. This represents the instantaneous phase value at the end of the nth time slot. If the frequency synthesizer has a quantization step size Δf... DDS , need to and K is recalculated after quantization to this raster. k With M k This ensures that the half-integer phase condition of equation (7) is still satisfied.

[0103] Step S6: Process the echo signal to obtain the complex frequency response at each frequency point. Map the complex frequency response back to the natural index and coherently synthesize it in the frequency domain. Then, based on the synthesized frequency response phase information, perform differential approximation of the group delay, including:

[0104] The receiver synchronously samples the echo signal and forms an analytical signal, obtaining the complex frequency response H(f) arranged in the coding order. π (k)) After mapping the complex frequency response back to the natural index, it is coherently synthesized in the frequency domain, and the group delay is approximated by the phase difference:

[0105] (16)

[0106] in, Indicates group delay. The phase function represents the complex frequency response at the (k+1)th frequency point. The phase function representing the complex frequency response at the k-th frequency point. For the (k+1)th sampling frequency point, This represents the kth sampling frequency point.

[0107] Step S7: Calculate the target geometry based on the medium propagation speed and group delay, including:

[0108] (17)

[0109] Where D represents the equivalent length or thickness of the underground target being measured. This represents the equivalent propagation speed of electromagnetic waves in underground media. When the total bandwidth is B = f... end -f startB At that time, the distance resolution and the unambiguous distance are respectively:

[0110] (18)

[0111] (19)

[0112] in, ΔR Indicates the minimum resolvable distance. R max This indicates an unambiguous distance range. Through the synergistic effect of half-integer phase control and frequency coding strategies, frequency domain sidelobes can be significantly reduced, and signal-to-noise ratio and dimensional measurement accuracy can be improved without extending bandwidth and sampling rate.

[0113] Traditional non-destructive measurement of underground targets often employs linear frequency sweeping or equal-step continuous wave systems. With fixed frequency point sequences and small adjacent frequency differences, this easily leads to increased spectral sidelobes and energy coupling between frequencies. The method proposed in this implementation introduces an encoding step size coprime to the number of frequency points and close to half a period within a fixed frequency band. This reorders the frequency sequence, ensuring that the statistical difference between adjacent transmission frequencies remains nearly constant and large, thereby significantly reducing frequency interference and phase nonlinearity errors. This strategy guarantees the uniformity of phase distribution during frequency domain synthesis, improves the coherent superposition accuracy of the signal and the system's anti-frequency drift performance, and provides a foundation for stable group delay estimation.

[0114] Existing multi-frequency excitation signals often exhibit energy tailing and near-range blind spots at time slot boundaries due to insufficient phase continuity. The method proposed in this embodiment introduces a narrowband linear sweep signal within each frequency time slot. By adjusting the start and end frequencies of the sweep and the time slot length, the signal satisfies the condition of a cumulative phase of half-integer cycles at the end of the time slot, allowing the sine term to naturally cross zero at the time domain boundary, thus achieving energy closure of the excitation waveform. This half-integer phase control mechanism effectively eliminates cross-time slot energy leakage, significantly reduces the sidelobe level of the synthesized spectrum, and improves the detection resolution and signal-to-noise ratio of near-range targets.

[0115] The method proposed in this embodiment superimposes a narrowband swept frequency signal with a bandwidth proportional to the step frequency within an independent time slot at each step frequency point. This results in a signal that exhibits both local smoothness in the frequency domain and a broadband equivalent response after synthesis. Through the coordinated design of half-integer phase boundary conditions and frequency coding, the method achieves characteristics such as narrow main lobe maintenance, effective sidelobe suppression, and robust coherent synthesis in the frequency domain. Furthermore, the designed signal format is compatible with common analog-to-digital or direct digital synthesizers, and can be implemented without increasing the sampling rate or total bandwidth.

[0116] Implementation Method 3: A computer device according to this implementation method includes a memory and a processor. The memory stores a computer program. When the processor runs the computer program stored in the memory, the processor executes a non-destructive size measurement method for underground targets that combines frequency encoding and half-integer phase control, as described in any one of Implementation Methods 1 to 2.

[0117] Implementation Method 4: A computer-readable storage medium according to this implementation method stores a computer program, which, when executed by a processor, performs the steps of a non-destructive size measurement method for underground targets combining frequency encoding and half-integer phase control as described in any one of Implementation Methods 1 to 2.

[0118] Those skilled in the art will understand that embodiments of this disclosure can be provided as methods, systems, or computer program products. Therefore, this disclosure can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this disclosure can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0119] This disclosure is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 The computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0120] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure and not to limit its protection scope. Although this disclosure has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading this disclosure, they can still make various changes, modifications or equivalent substitutions to the specific implementation of the invention, but these changes, modifications or equivalent substitutions are all within the protection scope of the published pending claims.

Claims

1. A non-destructive size measurement method for underground targets combining frequency coding and half-integer phase control, characterized in that, The method includes: Step S1: Within a preset frequency band, construct an equally spaced frequency grid containing N frequency points using a frequency step Δf, where, Indicates the step interval between adjacent frequency points; Step S2: Select an integer s that is coprime to N as the step size parameter, and encode and sort the equally spaced frequency grids to generate the transmission frequency sequence; Step S3: Define the effective transmission duration τ for each frequency slot. k The effective transmission duration of the time slot satisfies the half-integer period condition, and the near-range blind zone range is determined based on the half-integer period; Step S4: At each frequency point, time slot t∈[0, τ] k Within the time slot, a narrowband linear sweep frequency signal based on the center frequency is generated, and the cumulative phase of the narrowband linear sweep frequency signal at the end of the time slot is controlled to satisfy the half-integer round constraint. Step S5: According to the encoded and sorted transmission frequency sequence, transmit the narrowband linear sweep frequency signal processed in step S4 in sequence, and simultaneously receive the echo signal from the underground target; Step S6: Process the echo signal to obtain the complex frequency response at each frequency point, map the complex frequency response back to the natural index, coherently synthesize it in the frequency domain, and differentially approximate the group delay based on the synthesized frequency response phase information. Step S7: Calculate the target geometry based on the medium propagation speed and group delay.

2. The method for non-destructive measurement of underground targets combining frequency coding and half-integer phase control according to claim 1, characterized in that, The step S1 of constructing an equally spaced frequency grid containing N frequency points includes: in, This represents the k-th frequency point. Indicates the starting frequency of the frequency band. N This represents the total number of frequency points. Indicates the frequency band termination frequency.

3. The method for non-destructive measurement of underground targets combining frequency coding and half-integer phase control according to claim 2, characterized in that, Step S2, which involves encoding and sorting the equally spaced frequency grids, includes: in, This represents the frequency index after encoding and sorting.

4. The method for non-destructive measurement of underground targets combining frequency coding and half-integer phase control according to claim 2, characterized in that, In step S3, the effective transmission duration of the time slot satisfies the half-integer period condition, including: in, This represents the effective duration of the k-th time slot. Represents the number of half-integer periods. This represents the integer parameter used to ensure that the sine wave crosses zero at the end of the time slot. Represents an integer.

5. The method for non-destructive measurement of underground targets combining frequency coding and half-integer phase control according to claim 4, characterized in that, In step S4, the start and end frequencies of the narrowband linear sweep signal are obtained by inverse solving of the half-integer phase boundary constraints, specifically satisfying the following relationship: in, This represents the starting frequency of the k-th time slot frequency sweep. This represents the half-integer cycle parameter of the k-th time slot. This represents the sweep bandwidth of the k-th time slot. This represents the termination frequency of the k-th time slot sweep; The center frequency after the callback is: in, This represents the callback center frequency obtained after phase constraint.

6. The method for non-destructive measurement of underground targets combining frequency coding and half-integer phase control according to claim 5, characterized in that, The half-integer cycle parameters of the k-th time slot in step S4 satisfy: in, Indicates center frequency deviation. This indicates the maximum permissible deviation limit.

7. The method for non-destructive measurement of underground targets combining frequency coding and half-integer phase control according to claim 1, characterized in that, Step S6, based on the synthesized frequency response phase information, includes the differential approximation group delay: in, Indicates group delay. The phase function represents the complex frequency response at the (k+1)th frequency point. The phase function representing the complex frequency response at the k-th frequency point. For the (k+1)th sampling frequency point, This represents the kth sampling frequency point.

8. The method for non-destructive measurement of underground targets combining frequency coding and half-integer phase control according to claim 7, characterized in that, Step S7 includes: Where D represents the equivalent length or thickness of the underground target being measured. It represents the equivalent propagation speed of electromagnetic waves in underground media.

9. A computer device, characterized in that: It includes a memory and a processor, wherein the memory stores a computer program, and when the processor runs the computer program stored in the memory, the processor executes a non-destructive size measurement method for underground targets combining frequency coding and half-integer phase control as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, performs the steps of a non-destructive dimensional measurement method for underground targets combining frequency encoding and half-integer phase control as described in any one of claims 1-8.

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