Underground cavity detection method based on GNSS signal attenuation

Abstract

The invention discloses an underground cavity detection method based on GNSS signal attenuation, and relates to the field of geological exploration and satellite navigation, and the technical scheme of the invention comprises the following steps: S1, deploying a GNSS receiver array in a target area; s2, preprocessing the received signal data; s3, calculating an attenuation coefficient according to the satellite elevation angle and the model frequency; s4, generating a dielectric distribution diagram according to the attenuation coefficient; and S5, generating a cavity probability graph and geometric parameters according to the dielectric distribution graph. The GNSS satellite signal is directly used as a detection source, an expensive seismic wave emitter or radar equipment is omitted, the detection cost is reduced by about 70%, and the method is particularly suitable for wide-range area general survey. The GNSS receiver array can be deployed on the ground or an unmanned aerial vehicle platform, and the single measurement coverage area reaches several square kilometers.

Description

Technical Field

[0001] This invention relates to the fields of geological exploration and satellite navigation, and in particular to a method for detecting underground cavities based on GNSS signal attenuation. Background Technology

[0002] Traditional underground cavity detection techniques primarily rely on geophysical methods, such as ground-penetrating radar (GPR), seismic wave reflection, and electromagnetic induction. While these methods offer a certain level of accuracy, they suffer from the following significant drawbacks: 1. Reliance on artificial source equipment: Ground-penetrating radar and seismic wave methods require the artificial transmission of high-frequency electromagnetic waves or mechanical vibration signals. The equipment is complex, the operating cost is high, and the detection depth is limited by the transmission power.

[0003] 2. Limited coverage: Existing methods usually require point-by-point measurement, making it difficult to achieve large-scale continuous monitoring, especially in areas with complex terrain or dense urban areas, where deployment is extremely difficult. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for detecting underground cavities based on GNSS signal attenuation. By directly utilizing GNSS satellite signals as the detection source, it eliminates the need for expensive seismic wave transmitters or radar equipment, reducing detection costs by approximately 70%, making it particularly suitable for large-scale area surveys. The GNSS receiver array can be deployed on ground or unmanned aerial vehicle platforms, with a single measurement covering an area of ​​several square kilometers.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for detecting underground cavities based on GNSS signal attenuation, comprising the following steps: S1 deploys a GNSS receiver array in the target area; S2 preprocesses the received signal data; S3 calculates the attenuation coefficient based on the satellite elevation angle and model frequency; S4 generates a dielectric distribution diagram based on the attenuation coefficient; S5 generates a void probability map and geometric parameters based on the dielectric distribution map.

[0006] Preferably, in step S1, the GNSS receiver array spacing is 50-100 meters, L1 / L2 / L5 frequency band signals are collected, the sampling frequency is not less than 10Hz, and the continuous collection time is ≥24 hours to cover the satellite orbit cycle.

[0007] Preferably, step S2 uses a Kalman filter algorithm to preprocess the acquired raw carrier phase, RSSI, and satellite ephemeris data to generate an attenuation coefficient matrix that eliminates ionospheric interference.

[0008] Preferably, the formula for calculating the attenuation coefficient in step S3 is as follows: P rx For received power, P tx For transmission power, G t G r R is the antenna gain, and R is the penetration path length.

[0009] Preferably, in step S4, the relationship between the dielectric constant of different media and the signal attenuation coefficient is experimentally calibrated to establish the following mathematical model: ε r =f(α,θ,f) Where, ε r Where α is the relative permittivity of the medium, θ is the attenuation coefficient, θ is the satellite elevation angle, and f is the signal frequency; The void parameters are inverted using the following formula: V is the volume of the cavity, ε r0 The dielectric constant of the background medium is given.

[0010] Advantages of this invention: This invention directly utilizes GNSS satellite signals as the detection source, eliminating the need for expensive seismic wave transmitters or radar equipment, reducing detection costs by approximately 70%, and making it particularly suitable for large-scale area surveys. The GNSS receiver array can be deployed on ground or UAV platforms, covering an area of ​​several square kilometers in a single measurement, and supports long-term dynamic monitoring, significantly improving detection efficiency. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only one of the drawings of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a flowchart illustrating the steps of an embodiment of the present invention; Detailed Implementation

[0013] To enhance understanding of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. These embodiments are only used to explain the invention and do not limit the scope of protection of the invention. Example

[0014] like Figure 1 As shown, the method for detecting underground cavities based on GNSS signal attenuation includes the following steps: S1 deploys a GNSS receiver array in the target area; the spacing between the GNSS receiver arrays is 50-100 meters, and signals in the L1 / L2 / L5 bands are collected at a sampling frequency of not less than 10Hz, with a continuous collection time of ≥24 hours to cover the satellite orbital period.

[0015] S2 preprocesses the received signal data; it uses a Kalman filter algorithm to preprocess the acquired raw carrier phase, RSSI, and satellite ephemeris data to generate an attenuation coefficient matrix to eliminate ionospheric interference.

[0016] S3 calculates the attenuation coefficient based on the satellite elevation angle and model frequency; the formula for calculating the attenuation coefficient in step S3 is as follows: P rx For received power, P tx For transmission power, G t G r R is the antenna gain, and R is the penetration path length.

[0017] S4 generates a dielectric distribution map based on the attenuation coefficient; through experiments, the correspondence between the dielectric constant of different media and the signal attenuation coefficient is calibrated, and the following mathematical model is established: ε r =f(α,θ,f) Where, ε r Where α is the relative permittivity of the medium, θ is the attenuation coefficient, θ is the satellite elevation angle, and f is the signal frequency; The void parameters are inverted using the following formula: V is the volume of the cavity, ε r0 The dielectric constant of the background medium is given.

[0018] S5 generates a void probability map and geometric parameters (depth error ≤ 0.5m, volume error ≤ 5%) based on the dielectric distribution map.

[0019] Finally, the model's hyperparameters were optimized by comparing the CNN output results with local verification through borehole sampling or ground-penetrating radar. An automated report generation module was deployed on the server side to output a PDF detection report, including 3D visualization results and risk level assessment.

[0020] Advantages of this invention: This invention directly utilizes GNSS satellite signals as the detection source, eliminating the need for expensive seismic wave transmitters or radar equipment, reducing detection costs by approximately 70%, and making it particularly suitable for large-scale area surveys. The GNSS receiver array can be deployed on ground or UAV platforms, covering an area of ​​several square kilometers in a single measurement, and supports long-term dynamic monitoring, significantly improving detection efficiency.

[0021] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0022] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for detecting underground cavities based on GNSS signal attenuation, characterized in that, Comprising the following steps: S1 deploying a GNSS receiver array in the target area; S2 preprocessing the received signal data; S3 calculating the attenuation coefficient according to the satellite elevation angle and model frequency; S4 generating a dielectric distribution map according to the attenuation coefficient; S5 generating a cavity probability map and geometric parameters according to the dielectric distribution map. 2.The GNSS signal attenuation based underground cavity detection method according to claim 1, characterized in that: The step S1, the GNSS receiver array spacing is 50-100 meters, the L1 / L2 / L5 frequency band signal is collected, the sampling frequency is not less than 10Hz, and the continuous collection time is greater than or equal to 24 hours to cover the satellite orbit period. 3.The GNSS signal attenuation based underground void detection method of claim 1, wherein: Step S2 adopts Kalman filtering algorithm to preprocess the collected original carrier phase, RSSI and satellite ephemeris data, and generates an attenuation coefficient matrix eliminating ionospheric interference. 4.The GNSS signal attenuation based underground void detection method of claim 1, wherein: The attenuation coefficient is calculated according to the following formula in step S3: Prx is the received power, Ptx is the transmitted power, Gt and Gr are the antenna gains, and R is the penetration path length.

5. The GNSS signal attenuation based subsurface void detection method of claim 1, wherein: Step S4 calibrates the corresponding relationship between the dielectric constant of different media and the signal attenuation coefficient through experiment, and establishes the following mathematical model: e r = f(a, 0, f) where ε r is the relative permittivity of the medium, a is the attenuation coefficient, θ is the satellite elevation angle, and f is the signal frequency. The cavity parameters are inverted by the following equation: V is the cavity volume and εr0is the background medium dielectric constant.

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