Distributed monitoring system for water-ice crystal distribution of frozen soil based on neutron scattering and TDR

Abstract

The application discloses a frozen soil moisture-ice crystal distributed monitoring system based on neutron scattering and TDR combination. A synchronous trigger response module, optical fiber transmission and hierarchical sampling mode are adopted to realize accurate alignment in time dimension, and trigger delay is controlled within plus or minus 10 mu s. Through low-temperature modification, constant temperature control and lightweight shielding design, the adaptability of the system to special working conditions of frozen soil is improved, and long-term monitoring stability is ensured. The phase state of the application is clear, and the data dimension is complete. Total water is measured by neutron scattering, and unfrozen water is measured by TDR. The ice content is obtained by the difference between the two. Combined with the double calibration framework and error compensation algorithm, the quantitative measurement of the three elements of total water, unfrozen water and ice is realized. The application accurately solves the technical combination difficulty, realizes deep cooperation, solves the volume matching problem of two kinds of technical measurement through rigid positioning components, space calibration mechanism and deformation compensation design, and reduces the space correspondence error to less than 5%.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering monitoring technology in cold regions, and in particular to a distributed monitoring system for frozen soil moisture and ice crystals based on a combination of neutron scattering and TDR. Background Technology

[0002] The hydrothermal migration and phase change behavior of permafrost (permafrost or seasonally frozen soil) during freeze-thaw cycles have a significant impact on the safety and stability of engineering projects in cold regions. During freezing, liquid water migrates towards the freezing front and forms ice crystals. Upon thawing, the ice crystals revert to water. This water-ice phase change, accompanied by volume changes, often leads to engineering problems such as roadbed settlement and slope instability. To further investigate the coupled changes in the moisture and temperature fields within permafrost, real-time monitoring of the water and ice content in different parts of permafrost samples is urgently needed. However, current technologies have significant shortcomings in this regard:

[0003] On the one hand, traditional methods for measuring soil moisture content have limitations. Neutron scattering (NSD) is an advanced method that uses a radioactive neutron source and a slow neutron detector to determine soil moisture content. It obtains the volumetric water content of the soil by detecting the number of hydrogen atoms in the soil. Since hydrogen is mainly present in water and water and ice have the same molecular formula, the hydrogen content measured by NSD is not affected by whether the water is in a liquid or solid state. Therefore, NSD actually measures the total water content (liquid water + ice) in frozen soil. However, NSD alone cannot distinguish the phases of water and cannot directly obtain the liquid state. The content of water and ice respectively; the time domain reflectance method (TDR) measures the dielectric constant of soil by embedding probes, thereby estimating the water content in the soil; the dielectric constant of liquid water is very high (about 81), while the dielectric constants of ice and soil particles are relatively low (about 3-5), so the TDR method is very sensitive to changes in liquid water content; in frozen soil, the dielectric constant measured by TDR mainly reflects the unfrozen water content, but its results are significantly affected by temperature, and it is necessary to rely on dielectric mixing models and calibration experiments to infer the unfrozen water content. It is difficult to obtain information on ice content in frozen soil by using the TDR method alone;

[0004] On the other hand, existing frozen soil testing equipment often cannot achieve in-situ, continuous monitoring of the water-ice state inside the sample. Previous tests have mostly obtained water / ice content through weighing, sampling, or post-test CT / NMR scanning. These methods either cannot provide spatial distribution or have poor timeliness and cannot reflect dynamic processes. At the same time, due to the limitations of sensor size and sample size, traditional testing equipment is difficult to place sensors at multiple points inside the sample to achieve true distributed monitoring. In particular, there is a lack of technical means to synchronously and continuously measure and display the total water content, unfrozen water content, and ice content inside the sample in real time during the test.

[0005] Furthermore, even attempts to combine neutron scattering with TDR technology face numerous technical challenges. Spatially, the elliptical detection range of the neutron scatterer is difficult to precisely match with the local small-volume sensitive area of ​​the TDR probe, and insufficient deployment accuracy or soil deformation can easily lead to inconsistencies in the measured objects. Temporally, the acquisition cycles of the two technologies are inherently mismatched, and triggering and transmission delays can cause data timestamp deviations. In terms of environmental adaptability, the low temperature environment of permafrost can cause TDR signal attenuation and a decrease in the detection efficiency of the neutron scatterer. Moreover, neutron shielding may interfere with the soil temperature field, and soil deformation may damage the equipment or disrupt the deployment location. Therefore, there is an urgent need for an innovative monitoring system that, based on solving the above-mentioned integration difficulties, combines sensing technologies of different principles to achieve multi-point, multi-scale dynamic monitoring of moisture and ice crystal content inside permafrost. Summary of the Invention

[0006] The purpose of this invention is to provide a distributed monitoring system for permafrost moisture and ice crystals based on the combination of neutron scattering and TDR in order to solve the above-mentioned problems.

[0007] The present invention achieves the above objectives through the following technical solutions:

[0008] A distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR (Transient Reflection) includes soil units, sub-units, boundary units, a neutron scattering influence area, a TDR probe, a TDR power supply and data acquisition integration system, a neutron scattering instrument power supply and data acquisition integration system, and a computer terminal. The TDR probe and the neutron scattering instrument are deployed in pairs along the same survey line, with the effective sensitive volume of the TDR probe located within the neutron scattering influence area. The TDR power supply and data acquisition integration system is electrically connected to the TDR probe. The neutron scattering instrument power supply and data acquisition integration system is electrically connected to the neutron scattering instrument. The computer terminal is communicatively connected to both the TDR power supply and data acquisition integration system and the neutron scattering instrument power supply and data acquisition integration system. The computer terminal is used for unified triggering, synchronous data acquisition, time alignment, and data fusion, outputting the total water content, unfrozen water content, and ice content distribution along the depth direction, as well as their temporal variations. The boundary unit is adjacent to one side of the sub-unit.

[0009] Furthermore, the TDR probe and the neutron scatterer are arranged in pairs at the same depth, with a vertical spacing of 50-200mm between adjacent pairs and a horizontal spacing of 50±5mm. The measuring line is fixed inside the soil unit by a rigid positioning component. The surface of the rigid positioning component is treated with anti-corrosion and heat insulation to effectively resist the positional shift caused by soil deformation and temperature changes, ensuring that the two always maintain the same vertical projection and constant horizontal spacing.

[0010] Furthermore, the neutron scattering influence area is elliptical in shape within the soil unit, the TDR probe is positioned paraxially on the inner side of the ellipse, the neutron scatterer is positioned near the end of one side of the ellipse, and the overlap rate between the sensitive volume of the TDR probe and the neutron scattering influence area is not less than 90%, ensuring the comparability of measurement data from the two techniques within the same spatial window.

[0011] Furthermore, the TDR power supply and the data acquisition integration system are multi-channel structures, with functions of probe selection, pulse transmission, reflected waveform acquisition, and dielectric / conductivity calculation. Considering the low-temperature environment of permafrost, the TDR probe is made of low-temperature resistant titanium alloy, and the probe surface is coated with a conductive and anti-corrosion coating. The signal cable is a cold-resistant shielded cable with an operating temperature of -55℃ to 85℃ to reduce signal attenuation and equipment damage at low temperatures.

[0012] Furthermore, the neutron scatterer power supply and data acquisition integrated system includes detection counting, high-voltage power supply, forming and counting statistics, clock synchronization and data interface modules. The neutron scatterer is equipped with a lightweight shield made of boronized polyethylene with a thickness of 20-30mm, which reduces interference with the temperature field of the frozen soil sample while ensuring radiation safety. The neutron scatterer is equipped with a miniature constant temperature jacket with a temperature control accuracy of ±1℃ to avoid the decrease in counting efficiency caused by low temperature and ensure the consistency of measurement under different temperature conditions.

[0013] Furthermore, to address the time synchronization issue, both the TDR power supply and data acquisition integrated system and the neutron scatterer power supply and data acquisition integrated system are equipped with a synchronization trigger response module. The trigger signal from the computer terminal is transmitted via optical fiber, with the trigger delay controlled within ±10μs. Both systems are controlled by a unified clock or trigger signal from the computer terminal, with a unified clock timestamp accuracy of 1μs. This achieves distributed synchronous acquisition and precise timestamp alignment. During acquisition, a mode of "neutron scattering counting period as the reference, TDR multi-period sampling averaging" is adopted, which ensures the accuracy of neutron scattering data while avoiding TDR data redundancy.

[0014] Furthermore, the computer terminal incorporates a data fusion and inversion module. Based on the neutron count-water content calibration relationship and temperature correction factor, it calculates the total water content θ_t at each depth layer, eliminating the influence of temperature on neutron detection efficiency. It calculates the unfrozen water content θ_u based on the dielectric constant inverted from the TDR reflected wave and combined with the frozen soil dielectric mixing / temperature correction model and total water content constraint term, avoiding errors in the dielectric constant caused by soil texture and conductivity interference. The ice content θ_i is obtained through θ_i = θ_t - θ_u. The data fusion and inversion module also incorporates an error compensation algorithm. Through calibration experiments, it obtains the dead time error of neutron scattering, background counting error, and the wire loss error and conductivity interference error of the TDR, establishing an error database. Before differential calculation of the ice content, it performs error cancellation processing on the total water content and unfrozen water content data.

[0015] Furthermore, the subunit is equipped with a frozen soil calibration block with standard moisture content. The frozen soil calibration block has a built-in micro TDR calibration probe and a neutron scattering calibration probe for periodic spatial registration verification. If the spacing deviation is found to exceed 3mm, it is corrected in real time through a rigid positioning component.

[0016] Furthermore, miniature displacement sensors are deployed near the measurement line to monitor the volumetric deformation of the frozen soil sample in real time. If the deformation exceeds 5%, the spatial registration parameters are corrected through the data fusion module to avoid measurement errors caused by deformation. The sub-unit is also used to deploy reference or boundary condition sensors to provide comparison data or boundary control for the parts adjacent to the soil unit, thereby improving the interpretation and calibration of the water-ice crystal migration process.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. This invention precisely addresses the challenges of technical collaboration, achieving deep synergy. Through rigid positioning components, spatial calibration mechanisms, and deformation compensation design, it solves the problem of matching the measurement volumes of the two technologies, reducing the spatial correspondence error to within 5%. By employing a synchronous trigger response module, fiber optic transmission, and a hierarchical sampling mode, it achieves precise alignment in the time dimension, controlling the trigger delay to within ±10μs. Through low-temperature modification, constant temperature control, and lightweight shielding design, it enhances the system's adaptability to the special working conditions of permafrost, ensuring long-term monitoring stability.

[0019] 2. This invention has clear phase distinction and complete data dimensions. It uses neutron scattering to measure total water and TDR to measure unfrozen water. The ice content is obtained by difference between the two. Combined with a dual calibration framework and error compensation algorithm, it realizes a three-in-one quantitative measurement of "total water - unfrozen water - ice". The accuracy of ice content calculation is improved by more than 10%, overcoming the problem that single technology cannot distinguish phases and the data is one-sided.

[0020] 3. This invention supports distributed continuous monitoring, is highly practical, and its multi-level paired deployment method combined with multi-channel modular design can adapt to the monitoring needs of permafrost at different depths and scales. The system takes into account both laboratory experiments and in-situ engineering monitoring scenarios, is safe and controllable in operation, and has high operational stability, providing accurate data support for the dynamic process of water and ice in permafrost in cold regions for scientific research and engineering. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the distributed monitoring system for frozen soil moisture and ice crystals based on the combination of neutron scattering and TDR as described in this invention;

[0022] The annotations in the attached figures are explained as follows:

[0023] 1. Soil element; 2. DR probe; 3. Neutron scatterer; 4. Neutron scattering influence area; 5. TDR power supply and data acquisition integrated system; 6. Neutron scatterer power supply and data acquisition integrated system; 7. Survey line; 8. Computer terminal; 9. Sub-unit; 10. Boundary element. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings:

[0025] like Figure 1As shown, the distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR (Transient Reflector) includes a soil unit 1, a subunit 9, a boundary unit 10, a neutron scattering influence area 4, a TDR probe 2, a TDR power supply and data acquisition integration system 5, a neutron scatterer power supply and data acquisition integration system 6, and a computer terminal 8. The TDR probe 2 and the neutron scatterer 3 are arranged in pairs along the same survey line 7, and the effective sensitive volume of the TDR probe 2 is located within the neutron scattering influence area 4. The TDR power supply and data acquisition integration system 5 is electrically connected to the TDR probe 2; the neutron scatterer power supply and data acquisition integration system 6 is electrically connected to the neutron scatterer 3; the computer terminal 8 is communicatively connected to both the TDR power supply and data acquisition integration system 5 and the neutron scatterer power supply and data acquisition integration system 6, and is used for unified triggering, synchronous data acquisition, time alignment, and data fusion. The system outputs the total water content, unfrozen water content, and ice content distribution along the depth direction, along with their temporal variations. The boundary unit 10 is located adjacent to the sub-unit 9. The boundary unit 10 can acquire comparative data from adjacent parts of the soil unit 1 based on reference or boundary condition sensors arranged in the sub-unit 9. Simultaneously, it provides clear boundary control parameters for the monitoring system, filling the data gaps in the core monitoring area of ​​soil unit 1 at the boundary, and facilitating a more comprehensive analysis of the migration process of water and ice crystals in frozen soil. Furthermore, by combining the boundary data provided by the boundary unit 10 with the core monitoring data of soil unit 1 and the calibration data of sub-unit 9, the migration patterns of water and ice crystals in different regions (core and boundary regions) during the freezing / thawing process of frozen soil can be more clearly understood, enhancing the interpretability of the migration process. Additionally, the boundary data can serve as a calibration reference, further optimizing the data calibration effect of the monitoring system and reducing monitoring errors caused by boundary effects.

[0026] In this embodiment, the TDR probe 2 and the neutron scatterer 3 are arranged in pairs at the same depth, with a vertical spacing of 50-200mm between adjacent pairs and a horizontal spacing of 50±5mm. The measuring line 7 is fixed inside the soil unit 1 by a rigid positioning component. The surface of the rigid positioning component is treated with anti-corrosion and heat insulation to effectively resist the positional shift caused by soil deformation and temperature changes, ensuring that the two always maintain the same vertical projection and constant horizontal spacing.

[0027] In this embodiment, the neutron scattering influence region 4 is elliptical in shape within the soil unit 1. The TDR probe 2 is positioned paraxially on the inner side of the ellipse, and the neutron scatterer 3 is positioned near the end of one side of the ellipse. The overlap rate between the sensitive volume of the TDR probe 2 and the neutron scattering influence region 44 is 92%, ensuring the comparability and registration of measurement data from the two techniques within the same spatial window.

[0028] In this embodiment, the TDR power supply and the data acquisition integration system are multi-channel structures, with functions of probe selection, pulse transmission, reflected waveform acquisition and dielectric / conductivity calculation. Considering the low temperature environment of permafrost, the TDR probe 2 is a low-temperature resistant titanium alloy probe with a conductive anti-corrosion coating on the probe surface. The signal cable is a cold-resistant shielded cable with an operating temperature of -55℃ to 85℃ to reduce signal attenuation and equipment damage at low temperatures.

[0029] In this embodiment, the neutron scatterer power supply and data acquisition integrated system 6 includes a detection counting module, a high-voltage power supply module, a forming and counting statistics module, a clock synchronization module, and a data interface module. The neutron scatterer 3 is equipped with a lightweight shield made of boronized polyethylene with a thickness of 20-30mm, which reduces interference with the temperature field of the frozen soil sample while ensuring radiation safety. The neutron scatterer 3 is externally equipped with a miniature constant temperature jacket with a temperature control accuracy of ±1℃, which avoids the decrease in counting efficiency caused by low temperature and ensures the consistency of measurements under different temperature conditions.

[0030] In this embodiment, to solve the time synchronization problem, both the TDR power supply and data acquisition integrated system 5 and the neutron scatterer power supply and data acquisition integrated system 6 are equipped with a synchronization trigger response module. The trigger signal of the computer terminal 8 is transmitted by optical fiber, and the trigger delay is controlled within ±8μs. The two systems are controlled by a unified clock of the computer terminal 8, and the timestamp accuracy is 1μs. During acquisition, the neutron scattering counting accumulation time is set to 10 seconds. The TDR collects 100 sets of data within these 10 seconds (sampling period 100ms), and the average value is taken as the unfrozen water content data for this period. This achieves distributed synchronous acquisition and precise timestamp alignment. The acquisition adopts the mode of "neutron scattering counting period as the benchmark, TDR multi-period sampling averaging", which ensures the accuracy of neutron scattering data and avoids TDR data redundancy.

[0031] In this embodiment, the computer terminal 8 has a built-in data fusion and inversion module. Based on the neutron count-water content calibration relationship and temperature correction factor, it calculates the total water content θ_t at each depth layer, eliminating the influence of temperature on neutron detection efficiency. It calculates the unfrozen water content θ_u based on the dielectric constant inverted from the TDR reflected wave and combined with the frozen soil dielectric mixing / temperature correction model and total water content constraint term, avoiding errors in the dielectric constant caused by soil texture and conductivity interference. The ice content θ_i is obtained through θ_i = θ_t - θ_u. The data fusion and inversion module also incorporates an error compensation algorithm. Through calibration experiments, it obtains the dead time error of neutron scattering, background counting error, and the wire loss error and conductivity interference error of the TDR, establishing an error database. Before differential calculation of the ice content, it performs error cancellation processing on the total water content and unfrozen water content data.

[0032] In this embodiment, a frozen soil calibration block with standard moisture content is arranged in the subunit 9. The frozen soil calibration block has a built-in micro TDR calibration probe and a neutron scattering calibration probe for periodic spatial registration verification. If the spacing offset is found to exceed 3mm, it is corrected in real time by a rigid positioning component.

[0033] In this embodiment, a miniature displacement sensor is deployed near the measuring line 7 to monitor the volumetric deformation of the frozen soil sample in real time. If the deformation exceeds 5%, the spatial registration parameters are corrected through the data fusion module to avoid measurement errors caused by deformation. The subunit 9 is also used to deploy reference or boundary condition sensors to provide comparison data or boundary control for the adjacent parts of the soil unit 1, thereby improving the interpretation and calibration of the water-ice crystal migration process.

[0034] The specific monitoring method of the system is as follows: Before the test, several pairs of TDR probes 2 and neutron scatterers 3 are arranged along the depth direction in the soil unit 1 using rigid positioning components to form the measurement line 7, ensuring that the sensitive volume of the TDR probe 2 is located within the neutron scattering influence area 4 and the overlap rate is not less than 90%. A standard moisture content frozen soil calibration block and a reference or boundary condition sensor are arranged in the subunit 9, and a miniature displacement sensor is arranged near the measurement line 7. Then, the TDR power supply and data acquisition integration system 5, the neutron scatterer 3 power supply, and the data acquisition integration system are connected to the computer terminal 8, and a unified sampling period is set, where the cumulative counting time of neutron scattering is used as a reference, and the TDR performs multi-cycle sampling within this reference time. During the test, the computer terminal 8 sends a trigger signal, and the synchronous acquisition of the two acquisition systems is achieved through the synchronous trigger response module. The scatterer 3 is powered by the data acquisition and integration system, which collects slow neutron counts at various depths. The TDR power supply and the data acquisition and integration system 5 synchronously acquire TDR reflected waves. The computer terminal 8 performs time alignment on the collected data and performs dead time correction, background subtraction, temperature correction, and error compensation through the data fusion and inversion module to calculate the total water content θ_t, unfrozen water content θ_u, and ice content θ_i. Spatial registration is periodically verified using frozen soil calibration blocks. If the spacing deviation exceeds 3mm, it is corrected in real time using rigid positioning components. Based on the soil deformation monitored by the micro displacement sensor, if the deformation exceeds 5%, the spatial registration parameters are corrected through the data fusion module. The computer terminal 8 generates a "depth-content" distribution curve and time series change results, displays and stores them in real time, and executes the steps cyclically to achieve continuous distributed monitoring of water-ice migration during the freezing / thawing process.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A distributed monitoring system for permafrost moisture and ice crystals based on a combination of neutron scattering and TDR, characterized in that: It includes soil unit (1), sub-unit (9), boundary unit (10), neutron scattering influence area (4), TDR probe (2), TDR power supply and data acquisition integrated system (5), neutron scatterer power supply and data acquisition integrated system (6), and computer terminal (8); The TDR probe (2) and the neutron scatterer (3) are arranged in pairs along the same measuring line (7), and the effective sensitive volume of the TDR probe (2) is located within the neutron scattering influence area (4); the TDR power supply and data acquisition integrated system (5) is electrically connected to the TDR probe (2); The neutron scatterer power supply and data acquisition integrated system (6) is electrically connected to the neutron scatterer (3); The computer terminal (8) is connected to the TDR power supply and data acquisition integration system (5) and the neutron scatterer power supply and data acquisition integration system (6) respectively. The computer terminal (8) is used for unified triggering, synchronous data acquisition, time alignment and data fusion, and outputs the total water content, unfrozen water content and ice content distribution and their temporal changes along the depth direction. The boundary unit (10) is adjacent to the subunit (9) on one side.

2. The distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR as described in claim 1, characterized in that: The TDR probe (2) and the neutron scatterer (3) are arranged in pairs at the same depth. The vertical distance between adjacent pairs is 50-200mm, and the horizontal distance between them is controlled at 50±5mm. The measuring line (7) is fixed inside the soil unit (1) by a rigid positioning component. The surface of the rigid positioning component is treated with anti-corrosion and heat insulation to ensure that the TDR probe (2) and the neutron scatterer (3) maintain the same vertical projection and constant horizontal distance.

3. The distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR as described in claim 1, characterized in that: The neutron scattering influence area (4) is elliptical in the soil unit (1). The TDR probe (2) is located at the paraxial position inside the ellipse. The neutron scatterer (3) is located at the near end of one side of the ellipse. The overlap rate between the sensitive volume of the TDR probe (2) and the neutron scattering influence area (4) is not less than 90%.

4. The distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR as described in claim 1, characterized in that: The TDR power supply and data acquisition integrated system (5) is a multi-channel structure with probe selection, pulse transmission, reflection waveform acquisition and dielectric / conductivity calculation functions. The TDR probe (2) is a low-temperature resistant titanium alloy probe with a conductive anti-corrosion coating on the probe surface. The signal cable is a cold-resistant shielded cable with a working temperature of -55℃ to 85℃.

5. The distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR as described in claim 1, characterized in that: The neutron scatterer power supply and data acquisition integrated system (6) includes a detection counting, high voltage power supply, forming and counting statistics, clock synchronization and data interface module. The neutron scatterer (3) is equipped with a lightweight shield made of boronized polyethylene material with a shield thickness of 20-30mm. The neutron scatterer (3) is also equipped with a miniature constant temperature jacket with a temperature control accuracy of ±1℃.

6. The distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR as described in claim 1, characterized in that: Both the TDR power supply and data acquisition integrated system (5) and the neutron scatterer power supply and data acquisition integrated system (6) are equipped with a synchronous trigger response module. The trigger signal of the computer terminal (8) is transmitted by optical fiber. The trigger delay is controlled within ±10μs. Both systems are controlled by the unified clock or trigger signal of the computer terminal (8). The timestamp accuracy of the unified clock is 1μs.

7. The distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR as described in claim 1, characterized in that: The computer terminal (8) has a built-in data fusion and inversion module, which is used to calculate the total water content θ_t of each depth layer based on the neutron count-water content calibration relationship and temperature correction factor, calculate the unfrozen water content θ_u based on the dielectric constant inversion of TDR reflection wave and combined with the frozen soil dielectric mixing / temperature correction model and total water content constraint term, and obtain the ice content θ_i through θ_i=θ_t-θ_u. The data fusion and inversion module also incorporates an error compensation algorithm, which is used to perform error cancellation processing on the total water content and unfrozen water content data.

8. The distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR as described in claim 1, characterized in that: The subunit (9) is equipped with a frozen soil calibration block with standard moisture content. The frozen soil calibration block has a built-in micro TDR calibration probe and a neutron scattering calibration probe for periodic spatial registration verification.

9. The distributed monitoring system for frozen soil moisture and ice crystals based on neutron scattering and TDR as described in claim 1, characterized in that: Miniature displacement sensors are installed near the measuring line (7) to monitor the volume deformation of the frozen soil sample in real time.

10. The monitoring method of the distributed monitoring system for frozen soil moisture-ice crystals based on neutron scattering and TDR as described in any one of claims 1-9, characterized in that: Before the test, several pairs of TDR probes (2) and neutron scatterers (3) are arranged in the soil unit (1) along the depth direction using rigid positioning components to form the measurement line (7). It is ensured that the sensitive volume of the TDR probe (2) is located within the neutron scattering influence area (4) and the overlap rate is not less than 90%. A standard moisture content frozen soil calibration block and a reference or boundary condition sensor are arranged in the subunit (9). A miniature displacement sensor is arranged near the measurement line (7). Then, the TDR power supply and data acquisition integration system (5), the neutron scatterer power supply and the data acquisition integration system (6) are connected to the computer terminal (8). A unified sampling period is set, with the neutron scattering counting accumulation time as the benchmark. The TDR performs multiple sampling cycles within this benchmark time. During the test, the computer terminal (8) sends a trigger signal to achieve synchronous acquisition of the two acquisition systems through the synchronous trigger response module. The neutron scatterer power supply and the data acquisition integration system (6) acquire slow neutron counts at each depth position. The TDR power supply and the data acquisition integration system (5) synchronously acquire TDR reflected waves. The computer terminal (8) performs time alignment on the acquired data and performs dead time correction, background subtraction, temperature correction and error compensation through the data fusion and inversion module to calculate the total water content θ_t, unfrozen water content θ_u and ice content θ_i. Spatial registration verification is performed periodically through frozen soil calibration blocks. If the spacing offset is found to exceed 3mm, it is corrected in real time through rigid positioning components. According to the soil deformation monitored by the micro displacement sensor, if the deformation exceeds 5%, the spatial registration parameters are corrected through the data fusion module. The computer terminal (8) generates the "depth-content" distribution curve and the time sequence change results and displays and stores them in real time. By cyclically executing the steps, continuous distributed monitoring of water-ice migration during the freezing / thawing process can be achieved.

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