Polarization field-based cavity wall displacement measurement method

Abstract

This invention discloses a method for measuring the displacement of surrounding rock in caverns based on polarization fields. Belonging to the field of cavern surrounding rock displacement measurement technology, it solves the problem that existing methods cannot simultaneously balance measurement range and accuracy. This invention introduces Skyrmions polarization field technology into cavern surrounding rock displacement measurement, utilizing its high sensitivity to propagation distance. Through full-field imaging with a polarization camera, it achieves high-precision, non-contact, full-field measurement, overcoming the limitations of existing methods such as limited single-point measurement range and complex installation and susceptibility to interference of distributed sensors. Furthermore, by calculating the local polarization distribution entropy and setting a threshold, it automatically filters out noise caused by surface roughness, water seepage, or dust, reducing computational load while ensuring data quality. Simultaneously, it introduces a reference optical path to monitor temperature and magnetic field changes in real time for differential compensation of the polarization rotation angle, effectively eliminating thermo-optical effects and stray magnetic field drift, improving the system's anti-interference capability and long-term stability.

Description

Technical Field

[0001] This invention relates to the field of cavern surrounding rock displacement measurement technology, specifically to a method for measuring cavern surrounding rock displacement based on polarization field. Background Technology

[0002] Deep caverns are subjected to the combined effects of high ground stress, high osmotic pressure, and complex geological structures, making the surrounding rock highly susceptible to deformation, fracturing, and even instability, posing a severe challenge to the safe operation of the caverns. Due to stress redistribution caused by mining operations, the surrounding rock deforms significantly, sometimes even leading to cavern collapse and endangering personnel and equipment safety. Therefore, monitoring the stability of the surrounding rock has become a critical challenge in deep cavern engineering.

[0003] Displacement and strain are key parameters reflecting changes in the mechanical state of surrounding rock in deep caverns. Accurate measurement and real-time monitoring of these parameters can provide crucial information for rock stability assessment, disaster early warning, and support design optimization. Existing measurement methods, such as total station and level instrument measurements, can only achieve single-point or local measurements, making it difficult to comprehensively obtain overall deformation information of the surrounding rock. While fiber optic grating sensing technology has distributed measurement capabilities, it has stringent installation requirements, is susceptible to interference in complex geological environments, and suffers from poor measurement accuracy and stability. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a method for measuring the displacement of surrounding rock in caverns based on polarization fields, which solves the problem that existing methods for measuring the displacement of surrounding rock in caverns cannot simultaneously consider both measurement range and measurement accuracy.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for measuring the displacement of surrounding rock in a cavern based on a polarization field is provided, including the following steps: S1. Apply Skyrmions polarization field and reference optical path for monitoring environmental changes to the cavern surrounding rock in the initial state and the moved state respectively. Based on the Skyrmions polarization field, acquire the initial optical field image and the monitoring optical field image of the cavern surrounding rock respectively. S2. Calculate the polarization state distribution entropy of the local region corresponding to each pixel in the initial light field image and the monitored light field image, and filter the local regions with polarization state distribution entropy lower than the preset threshold as high signal-to-noise ratio regions. S3. Select high signal-to-noise ratio (SNR) regions that overlap in the initial light field image and the monitored light field image and pair them up. Extract the initial polarization rotation angle and the monitored polarization rotation angle from each pair of overlapping high SNR regions. S4. Obtain the environmental changes of the cavern surrounding rock in the initial state and the state after movement relative to the preset reference environment through the reference optical path, and perform differential compensation for the environmental interference of the cavern surrounding rock for each pair of initial polarization rotation angles and monitoring polarization rotation angles based on the two environmental changes, and calculate the rotation angle change between each pair of compensated initial polarization rotation angles and monitoring polarization rotation angles. S5. Based on the mapping relationship between each rotation angle change and the propagation of the Skyrmions polarization field, the displacement of each pair of overlapping high signal-to-noise ratio regions is calculated, and all displacement outputs are integrated as a set of displacement distributions of the corresponding overlapping high signal-to-noise ratio regions on the surrounding rock of the cavern.

[0006] Furthermore, the expression for calculating the polarization state distribution entropy of the local region corresponding to each pixel is as follows: ; ; in, These are the coordinates of the pixel. For pixels The polarization state distribution entropy; For at pixel Within the corresponding local region, all pixels fall within the first... Polarization angle distribution probability density within a certain angle interval; This represents the total number of angle intervals for the polarization angle.

[0007] Furthermore, the expression for filtering high signal-to-noise ratio regions is: in, For pixels The corresponding local area, This is a high signal-to-noise ratio region; This is a preset threshold.

[0008] Furthermore, the environmental interference differential compensation methods for the initial polarization rotation angle and the monitored polarization rotation angle are the same. The expression for differential compensation of the cavern surrounding rock environmental interference for the initial polarization rotation angle is as follows: in, The initial polarization rotation angle after compensation; The initial polarization rotation angle; and These are the changes in ambient temperature and ambient magnetic field relative to the reference environment, obtained when monitoring the surrounding rock of the cavern in its initial state using a reference optical path. and These are the temperature compensation coefficient and the magnetic field compensation coefficient, respectively.

[0009] Furthermore, the change in rotation angle between the initial polarization rotation angle and the monitored polarization rotation angle after compensation is calculated using an angle unwinding algorithm.

[0010] Furthermore, the expression for calculating the displacement of each pair of overlapping high signal-to-noise ratio regions is as follows: in, The displacement of the overlapping high signal-to-noise ratio region; Rayleigh distance; This represents the change in rotation angle; and These are the modulus orders of the amplitude envelopes of the left-hand circularly polarized Gaussian beam and the right-hand circularly polarized Gaussian beam, respectively, in the Skyrmions polarization field. The initial phase constant; The reference refractive index is at standard atmospheric pressure. For real-time temperature With air pressure The air refractive index correction function under environmental conditions.

[0011] Furthermore, the expression for the total electric field vector of the Skyrmions polarization field is: in, For cylindrical coordinates The total electric field vector, These are the radial distance, azimuth angle, and distance along the beam propagation direction, respectively. and These are the amplitude envelopes of a left-handed circularly polarized Gaussian beam and a right-handed circularly polarized Gaussian beam in the Skyrmions polarization field, respectively. The imaginary unit; and These are the Gouy phase shifts accumulated during the propagation of a left-handed circularly polarized Gaussian beam and a right-handed circularly polarized Gaussian beam, respectively. and These are the unit vectors for the left-hand circularly polarized Gaussian beam and the right-hand circularly polarized Gaussian beam, respectively.

[0012] Compared with the prior art, the present invention has the following significant advantages: 1. Considering that the Skyrmions polarization field has topological protection characteristics, and its polarization direction rotates with the propagation distance according to strict physical laws, even a small displacement will cause a measurable change in the polarization angle when the light field propagates. Therefore, applying the Skyrmions polarization field to the displacement measurement of the surrounding rock of the cavern improves the sensitivity and accuracy of the displacement measurement. Moreover, by using a polarization camera to capture the Skyrmions polarization field of the entire field of view at once, the displacement of the surface area can be measured in its entirety without scanning point by point. This overcomes the shortcomings of single-point measurement methods such as total stations and levels, and also avoids the dependence on complex installation processes and sensitivity to environmental interference of distributed measurement methods such as fiber optic grating sensing.

[0013] 2. Considering the enormous computational burden faced by existing distributed measurement methods such as fiber optic grating sensing when performing full-field calculations, this invention calculates the polarization state distribution entropy of the local region of each pixel and automatically filters out high signal-to-noise ratio regions through a preset threshold. This filters out polarization state distortion data caused by rough surrounding rock surfaces, water seepage, or dust coverage. Not only can the polarization angles of all feature points in the light field be obtained in a single imaging, enabling the reconstruction of the displacement distribution of the entire field, but invalid data is also pre-filtered, significantly reducing the amount of full-field matrix operations, alleviating the contradiction between computational complexity and real-time performance, and ensuring data quality.

[0014] 3. Considering that temperature drift and stray magnetic fields in the surrounding rock of the cavern can cause undesirable drift in the optical signal and reduce the accuracy of the measurement, in order to introduce a reference optical path to sense the optical signal deviation caused by the current environmental disturbance to the measurement optical system, differential compensation is performed on the extracted polarization rotation angle by real-time monitoring of changes in ambient temperature and magnetic field. This ensures that the polarization rotation angle of each measurement is normalized to the same environmental reference, effectively eliminating the system reference drift caused by thermo-optical effects and stray magnetic fields, overcoming the interference of strong magnetic fields and thermo-optical effects in the surrounding rock of deep caverns on the optical sensitive field, and further improving the measurement accuracy. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the measurement system structure used in the method of measuring displacement of surrounding rock in caverns.

[0016] Figure 2 This is a schematic diagram illustrating the principle of polarization field formation in Skyrmions.

[0017] Figure 3 This is a flowchart of a method for measuring displacement of surrounding rock in a cavern based on polarization field.

[0018] The components include: 1. Laser; 2. Optical objective lens; 3. Polarizing beam splitter; 4. Mirror; 5. Quarter wave plate; 6. Zero-order vortex wave plate; 7. Attenuating lens; 8. Unpolarizing beam splitter; 9. Polarizing camera; 10. Host computer. Detailed Implementation

[0019] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0020] This embodiment provides a method for measuring the displacement of surrounding rock in a cavern based on a polarization field, referencing... Figure 3 The steps include: S1. Apply Skyrmions polarization field and reference light path to the cavern surrounding rock in the initial state and the moved state respectively through the measurement system. Based on the Skyrmions polarization field, acquire the initial light field image and monitoring light field image of the cavern surrounding rock respectively. The reference light is used to monitor the environmental changes of the cavern surrounding rock relative to the reference environment. The environmental changes include temperature and magnetic field changes.

[0021] S2. Calculate the polarization state distribution entropy of the local region corresponding to each pixel in the initial light field image and the monitoring light field image, and select the local regions with polarization state distribution entropy lower than the preset threshold as high signal-to-noise ratio regions.

[0022] Specifically, the expression for calculating the polarization state distribution entropy of the local region corresponding to each pixel is: ; ; in, These are the coordinates of the pixel. For pixels The polarization state distribution entropy; For at pixel Within the corresponding local region, all pixels fall within the first... The probability density of polarization angle distribution within a certain angle range, and the size of the local region can be changed; This represents the total number of angle intervals for polarization angles. For better understanding, let's assume the angle interval size is 36°. The size is 10.

[0023] The expression for filtering high signal-to-noise ratio regions is: in, For pixels The corresponding local area, This is a high signal-to-noise ratio region; This is a preset threshold.

[0024] S3. Select overlapping high signal-to-noise ratio regions from the high signal-to-noise ratio regions of the initial light field image and the monitoring light field image and pair them. Extract the initial polarization rotation angle and the monitoring polarization rotation angle from each pair of overlapping high signal-to-noise ratio regions.

[0025] S4. Obtain the environmental changes of the cavern surrounding rock in the initial state and the state after movement relative to the preset reference environment through the reference optical path, and perform differential compensation for the environmental interference of the cavern surrounding rock for each pair of initial polarization rotation angles and monitoring polarization rotation angles based on the two environmental changes, and calculate the rotation angle change between the compensated initial polarization rotation angle and monitoring polarization rotation angle for each pair.

[0026] In this embodiment, the rotation angle change between the initial polarization rotation angle and the monitored polarization rotation angle after compensation is calculated by the angle unwinding algorithm, which solves the problem of the periodic jump of ±180° between the initial polarization rotation angle and the monitored polarization rotation angle after compensation.

[0027] Specifically, the environmental interference differential compensation methods for the initial polarization rotation angle and the monitored polarization rotation angle are the same. Taking the initial polarization rotation angle as an example, the expression for differential compensation of the surrounding rock environment interference of the cavern for the initial polarization rotation angle is as follows: in, The initial polarization rotation angle after compensation; The initial polarization rotation angle; and These are the changes in ambient temperature and ambient magnetic field relative to the reference environment, obtained when monitoring the surrounding rock of the cavern in its initial state using a reference optical path. and These are the temperature compensation coefficient and the magnetic field compensation coefficient, respectively.

[0028] In this embodiment, the reference optical path is formed by introducing a set of environmentally modulated interferometric branches on top of a conventional measurement optical path. Using the same optical elements but without carrying displacement information of the surrounding rock, it provides a reference environmental quantity for differential compensation in the measurement algorithm. Specifically, a small portion of the beam emitted from the laser is split off by a beam splitter to form an independent reference beam. This reference beam is guided to a fixed, stable reference surface (such as a fixed mirror or directly into the detector) without illuminating the changing surface of the surrounding rock. By monitoring the changes in optical path, polarization state, or phase on this fixed optical path, the optical system drift caused purely by environmental factors (temperature, magnetism) can be directly inferred. Since the reference optical path is existing technology, its specific working principle and connection relationships will not be elaborated upon in this embodiment.

[0029] S5. Based on the mapping relationship between each rotation angle change and the propagation of the Skyrmions polarization field, the displacement of each pair of overlapping high signal-to-noise ratio regions is calculated, and all displacement outputs are integrated as a set of displacement distributions of the corresponding overlapping high signal-to-noise ratio regions on the surrounding rock of the cavern.

[0030] Specifically, the expression for calculating the displacement of each pair of overlapping high signal-to-noise ratio regions is as follows: in, The displacement of the overlapping high signal-to-noise ratio region; Rayleigh distance; This represents the change in rotation angle; and These are the modulus orders of the amplitude envelopes of the left-hand circularly polarized Gaussian beam and the right-hand circularly polarized Gaussian beam, respectively, in the Skyrmions polarization field. The initial phase constant; The reference refractive index is at standard atmospheric pressure. For real-time temperature With air pressure The air refractive index correction function in the environment is a classical empirical formula, such as the Edlén formula or the Ciddor formula.

[0031] As a further aspect of this embodiment, to facilitate understanding of the formation of the Skyrmions polarization field and the principle between the rotation angle and propagation distance in the Skyrmions polarization field, this embodiment also provides a measurement system applied to the displacement measurement method of cavern surrounding rock, referencing... Figure 1 It includes: laser 1, Mach-Zehnder interferometer, polarization camera 9, and host computer 10.

[0032] Laser 1 is used to generate a highly stable laser as a source for generating Skyrmions polarization fields.

[0033] A Mach-Zehnder interferometer is used to form the Skyrmions polarization field and reference optical path. It includes an optical objective lens 2, a polarizing beam splitter 3, a mirror 4, a quarter-wave plate 5, a zero-order vortex waveplate 6, an attenuating mirror 7, and a non-polarizing beam splitter 8. Since the Mach-Zehnder interferometer is existing technology, its specific working principle and connection relationships will not be described in detail in this embodiment.

[0034] Polarization camera 9 is used to measure the polarization distribution of the Skyrmions polarization field generated after beam combining.

[0035] The host computer 10 is used to read the polarization distribution of the Skyrmions polarization field in real time and analyze the displacement distribution.

[0036] The working principle of the measurement system is as follows: (reference) Figure 2 After the laser beam is emitted, it is shaped by an optical objective lens 2 and then passes through a Mach-Zehnder interferometer. The beam with p-polarization is converted into a left-handed circularly polarized Gaussian beam by a quarter-wave plate 5, while the beam with s-polarization is converted into a right-handed circularly polarized first-order vortex beam by a quarter-wave plate 5 and a zero-order vortex plate 6. Finally, a non-polarizing beam splitter 8 combines the left-handed circularly polarized Gaussian beam and the right-handed circularly polarized first-order vortex beam. A polarization camera 9 measures the polarization distribution of the Skyrmions polarization field generated after beam combining and transmits the data to a host computer 10. Because these two transverse modes are different, they have different Gouy phase shifts, which change with the transmission distance. An additional phase shift occurs during propagation within the Rayleigh range. Therefore, the dual-ion beam composed of the Gaussian beam and the vortex beam with different polarizations will experience a propagation-related phase difference between the two polarization components, thus inducing a longitudinally varying vector mode.

[0037] The total electric field vector expression for the Skyrmions polarization field is: in, For cylindrical coordinates The total electric field vector, These are the radial distance, azimuth angle, and distance along the beam propagation direction, respectively. and These are the amplitude envelopes of a left-handed circularly polarized Gaussian beam and a right-handed circularly polarized Gaussian beam in the Skyrmions polarization field, respectively. The imaginary unit; and These are the Gouy phase shifts accumulated during the propagation of a left-handed circularly polarized Gaussian beam and a right-handed circularly polarized Gaussian beam, respectively. and These are the unit vectors of the left-hand circularly polarized Gaussian beam and the right-hand circularly polarized Gaussian beam, respectively. Based on the expression for the total electric field vector of the Skyrmions polarization field, the expression for the displacement of each pair of overlapping high signal-to-noise ratio regions is obtained.

[0038] In summary, the beneficial effects of this plan are as follows: By introducing the Skyrmions polarization field, which possesses topological protection characteristics, into the displacement measurement of the surrounding rock in caverns, and leveraging its extremely high sensitivity to propagation distance via polarization direction, combined with one-time full-field imaging by a polarization camera, high-precision, non-contact, and full-field distributed displacement measurement is achieved. This overcomes the limitations of existing single-point measurement methods (such as total stations and levels) with their limited range, and the complex installation and susceptibility to interference inherent in distributed sensing technologies (such as fiber optic gratings). By calculating the polarization state distribution entropy of local areas and setting thresholds to filter high signal-to-noise ratio regions, this method can automatically filter out noise data caused by rough rock surfaces, water seepage, or dust cover. While ensuring data quality, it significantly reduces subsequent computational load and alleviates the real-time contradiction of full-field calculations. Furthermore, this scheme effectively eliminates system reference drift caused by thermal-optical effects and stray magnetic fields in deep cavern environments by introducing a reference optical path to monitor changes in ambient temperature and magnetic field in real time, and performs differential compensation on the extracted polarization rotation angle. This significantly improves the anti-interference capability and long-term stability of the measurement system.

Claims

1. A method for measuring displacement of surrounding rock of a cavity based on a polarization field, characterized in that, Including the following steps: S1. Apply Skyrmions polarization field and reference optical path for monitoring environmental changes to the cavern surrounding rock in the initial state and the moved state respectively. Based on the Skyrmions polarization field, acquire the initial optical field image and the monitoring optical field image of the cavern surrounding rock respectively. S2. Calculate the polarization state distribution entropy of the local region corresponding to each pixel in the initial light field image and the monitored light field image, and filter the local regions with polarization state distribution entropy lower than the preset threshold as high signal-to-noise ratio regions. S3. Select high signal-to-noise ratio regions with overlapping positions from the high signal-to-noise ratio regions of the initial light field image and the monitoring light field image and pair them. Extract the initial polarization rotation angle and the monitoring polarization rotation angle from the two overlapping high signal-to-noise ratio regions of each pair, respectively. S4. Obtain the environmental changes of the cavern surrounding rock in the initial state and the state after movement relative to the preset reference environment through the reference optical path, and perform differential compensation for the environmental interference of the cavern surrounding rock for each pair of initial polarization rotation angles and monitoring polarization rotation angles based on the two environmental changes, and calculate the rotation angle change between each pair of compensated initial polarization rotation angles and monitoring polarization rotation angles. S5. Based on the mapping relationship between each rotation angle change and the propagation of the Skyrmions polarization field, the displacement of each pair of overlapping high signal-to-noise ratio regions is calculated, and all displacement outputs are integrated as a set of displacement distributions of the corresponding overlapping high signal-to-noise ratio regions on the surrounding rock of the cavern.

2. The polarization field based cavity wall displacement measurement method of claim 1, wherein, The expression for calculating the polarization state distribution entropy of the local region corresponding to each pixel is: ； ； wherein, is the coordinate of the pixel point; is the polarization state distribution entropy of the pixel point ; is the polarization angle distribution probability density of all pixel points in the local region corresponding to the pixel point ; is the polarization angle distribution probability density of all pixel points in the local region corresponding to the pixel point ; is the total number of angle intervals of the polarization angle.

3. The Polarization Field Based Cavity Displacement Measurement Method of claim 2, wherein, The expression for filtering high signal-to-noise ratio regions is: wherein, is a pixel point a corresponding local region, is a high signal-to-noise region; is a preset threshold.

4. The polarization field based cavity wall displacement measurement method of claim 2, wherein, The environmental disturbance differential compensation methods for the initial polarization rotation angle and the monitored polarization rotation angle are the same. The expression for differential compensation of the surrounding rock environment disturbance of the cavern for the initial polarization rotation angle is as follows: in, The initial polarization rotation angle after compensation; The initial polarization rotation angle; and These are the changes in ambient temperature and ambient magnetic field relative to the reference environment, obtained when monitoring the surrounding rock of the cavern in its initial state using a reference optical path. and These are the temperature compensation coefficient and the magnetic field compensation coefficient, respectively.

5. The method for measuring the displacement of surrounding rock in a cavern based on a polarization field according to claim 4, characterized in that, The change in rotation angle between the initial polarization rotation angle and the monitored polarization rotation angle after compensation is calculated using an angle unwinding algorithm.

6. The method for measuring the displacement of surrounding rock in a cavern based on a polarization field according to claim 4, characterized in that, The expression for calculating the displacement of each pair of overlapping high signal-to-noise ratio regions is as follows: in, The displacement of the overlapping high signal-to-noise ratio region; Rayleigh distance; This represents the change in rotation angle; and These are the modulus orders of the amplitude envelopes of the left-hand circularly polarized Gaussian beam and the right-hand circularly polarized Gaussian beam, respectively, in the Skyrmions polarization field. The initial phase constant; The reference refractive index is at standard atmospheric pressure. For information about real-time temperature With air pressure The air refractive index correction function under environmental conditions.

7. The method for measuring the displacement of surrounding rock in a cavern based on a polarization field according to claim 1, characterized in that, The expression for the total electric field vector of the Skyrmions polarization field is: in, For cylindrical coordinates The total electric field vector, These are the radial distance, azimuth angle, and distance along the beam propagation direction, respectively. and These are the amplitude envelopes of a left-handed circularly polarized Gaussian beam and a right-handed circularly polarized Gaussian beam in the Skyrmions polarization field, respectively. The imaginary unit; and These are the Gouy phase shifts accumulated during the propagation of a left-handed circularly polarized Gaussian beam and a right-handed circularly polarized Gaussian beam, respectively. and These are the unit vectors for the left-hand circularly polarized Gaussian beam and the right-hand circularly polarized Gaussian beam, respectively.

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