Monitoring equipment for salinity in frozen soil and use method thereof

Abstract

The invention belongs to the field of salinity monitoring of frozen saline alkali soil and frozen soil engineering, and particularly relates to monitoring equipment for salinity in frozen soil and a using method thereof.The monitoring equipment for the salinity in the frozen soil comprises a time domain reflectometer and a probe, and the signal output end of the probe is connected with the time domain reflectometer through a connecting line; a heating assembly is additionally arranged at the detection end of the probe, and frozen water in soil on the periphery of the probe is melted by means of the heating assembly to form unfrozen water. According to the method, the heating assembly is used for heating the soil on the periphery of the probe and obtaining the unfrozen water, the conductivity of the unfrozen water on the periphery of the probe is obtained through the time domain reflection technology, and then the salt content of the soil is calculated, so that the time domain reflectometer can accurately capture the conductivity characteristics of the unfrozen water, and a reliable basis is provided for subsequent salt content calculation; and the accuracy and precision of measuring the salt content in the frozen soil by the time domain reflection method are improved.

Description

Technical Field

[0001] This invention belongs to the field of salt monitoring in frozen saline-alkali soil and permafrost engineering, specifically relating to a monitoring device for salt content in permafrost and its usage method. Background Technology

[0002] Soil salinity is a crucial indicator in soil salinization research and a significant factor restricting agricultural production. The ecological environment management, agricultural productivity improvement, and engineering facility safety in seasonally frozen soil regions all depend on accurate understanding of soil salinity dynamics. Conducting sensor-based measurements of soil salinity is of great importance for understanding the changing patterns of salinized soils, preventing soil degradation, promoting sustainable agricultural development, and preventing geological disasters in frozen soil engineering projects.

[0003] To achieve rapid and effective determination of soil salinity, the main methods currently used are the soil solution method based on in-situ monitoring and the soil apparent conductivity method. The soil solution conductivity method directly measures the conductivity of the soil solution, providing high accuracy in salinity measurement and requiring no calibration. However, this method requires high soil moisture content and a long response time, making it unsuitable for soils with low moisture content or for determining soil salinity in frozen soil environments below zero degrees Celsius. The soil apparent conductivity method is a rapid, efficient, and stable method for determining the spatiotemporal distribution of soil salinity. It can be used with resistance methods, electromagnetic induction methods, and time-domain reflectometry to determine soil salinity, offering advantages such as simple operation, high accuracy, no soil disturbance, rapid response, and strong data acquisition capabilities. However, this method is easily affected by factors such as soil moisture content and texture, and a universally applicable model is still lacking, thus limiting its measurement accuracy. The time-domain reflectometry (TD-SCADA) method determines electrical conductivity by analyzing the attenuation of electromagnetic waves in soil. However, it is easily affected by factors such as soil temperature and texture. Furthermore, during soil freezing, as the temperature gradually decreases below 0°C, the water phase changes, with liquid water in the soil solidifying into solid ice, creating an ice-water mixture that interferes with the transmission speed of electromagnetic signals. This leads to a non-linear and rapid decrease in soil conductivity, significantly affecting the accuracy of conductivity measurements. Soil apparent conductivity is closely related to soil moisture content, soil composition, soil salinity, and soil temperature. In permafrost regions or during soil freeze-thaw cycles, freeze-thaw devices and testing equipment are needed to accurately measure apparent conductivity under freeze-thaw conditions. Calibrating the relationship between soil salinity and apparent conductivity can also improve the accuracy of soil salinity measurements.

[0004] Traditional methods for determining soil salinity have disadvantages such as cumbersome measurement processes, long measurement times, and inability to perform in-situ measurements. More funding and effort are needed for soil salinity testing equipment, especially in the area of ​​frozen soil salinity detection, to overcome the technical challenges in developing salinity sensors and address the current difficulties and shortcomings in rapid soil salinity detection. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a device and method for monitoring salt content in permafrost. The device uses a heating element to heat the soil around a probe and obtain unfrozen water. Then, time-domain reflectometry (TDRS) is used to obtain the conductivity of the unfrozen water around the probe, thereby calculating the soil salt content. This allows the TDRS to accurately capture the conductivity characteristics of the unfrozen water, providing a reliable basis for subsequent salt content calculations and improving the accuracy and precision of determining salt content in permafrost using the TDRS method.

[0006] The specific technical solution adopted in this invention is as follows: A device for monitoring salinity in permafrost includes a time domain reflectometer and a probe. The signal output end of the probe is connected to the time domain reflectometer via a connecting line. The detection end of the probe is equipped with a heating component, which melts the frozen water in the soil around the probe and forms unfrozen water.

[0007] The heating assembly includes an insulating resistance wire. The detection end of the probe is a hollow steel tube. The insulating resistance wire is located inside the cavity of the steel tube, and both ends of the insulating resistance wire are connected to a power supply device. The steel tube is also filled with a fixing layer for fixing the insulating resistance wire.

[0008] The fixing layer is an epoxy resin with a thermal conductivity ≥0.5 W / (m·K).

[0009] The heating component is also connected to a control device, which connects the heating component to the power supply device and allows it to be switched on and off.

[0010] The power supply device includes a solar panel and a battery, and the control device includes a solar power controller and a DC time switch. The output end of the solar panel is connected to the input end of the battery via the solar power controller, and the output end of the battery is connected to the power supply end of the heating component via the DC time switch.

[0011] The probe is provided in at least three sets, and multiple sets of the probe are fixed together on the handle. The signal output end of each set of probes is connected to the time domain reflectometer via a connecting line.

[0012] The method of using a device for monitoring salinity in permafrost includes the following steps: S1. Insert the detection end of the probe connected to the time domain reflectometer into the soil of the area to be monitored; S201. If the soil temperature in the area to be monitored is >0℃, data should be collected directly using a probe. S202. If the soil temperature in the area to be monitored is ≤0℃, first turn on the heating component to heat and melt the frozen water in the soil around the probe and form unfrozen water. Then turn off the heating component and use the probe to collect data. S3. The collected data is transferred to the terminal device using a time domain reflectometer for calculation to obtain the soil electrical conductivity. S4. Calculate soil salinity based on soil electrical conductivity.

[0013] The specific method for inserting the probe's detection end into the soil of the area to be monitored in step S1 is as follows: When the soil temperature is above 0℃, a soil profile is formed by excavating the topsoil layer, and a probe is inserted horizontally into the topsoil layer. Then the soil is backfilled, with the probe 8-15cm away from the surface.

[0014] The relationship between soil electrical conductivity and soil salinity in step S4 is f(x) = 3.92x + 1.38, where x is soil electrical conductivity and f(x) is soil salinity.

[0015] The beneficial effects of this invention are: 1. Based on the traditional time-domain reflectometry method for determining soil salinity, this invention adds a heating component. The heating component heats the soil around the probe and obtains unfrozen water. Then, the conductivity of the unfrozen water around the probe is obtained through time-domain reflectometry, and the soil salinity is calculated.

[0016] This frozen soil salinity monitoring device not only boasts advantages such as high automation, minimal impact on natural soil structure, and applicability to different bulk density and moisture content ranges in the field, but also can simultaneously obtain dynamic parameters of frozen soil electrical conductivity and moisture content, demonstrating broad application potential in the field of coupled transport processes of moisture and salinity in seasonally frozen and thawed soils.

[0017] 2. In this invention, the hollow steel tube of the probe serves as both the detection end for transmitting electromagnetic signals and the carrier of the heating component. The overall structure is compact and can reduce damage to the soil structure.

[0018] The cavity of the steel pipe is filled with a fixing layer. On the one hand, the insulating resistance wire is fixed in the center of the steel pipe to ensure that the heat is evenly radiated to the soil around the probe during heating and to avoid heating dead zones. On the other hand, it fills the gap between the resistance wire and the steel pipe to prevent soil moisture and salt from penetrating and corroding the insulating resistance wire. The fixing layer is also used to conduct heat and improve heating efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the monitoring equipment system of the present invention; Figure 2 This is a schematic diagram of the probe structure of the present invention; In the attached diagram, 1 is the connecting wire, 2 is the insulating resistance wire, 3 is the steel pipe, 4 is the fixing layer, and 5 is the handle. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: I. Specific Implementation Methods Specific implementation examples Figure 1-2 As shown, the present invention provides a device for monitoring salinity in permafrost, including a time domain reflectometer and a probe. The signal output end of the probe is connected to the time domain reflectometer via a connecting line 1. The detection end of the probe is provided with a heating component, which melts the frozen water in the soil around the probe and forms unfrozen water.

[0021] Traditional methods for determining soil salinity, such as the soil solution method and the soil apparent conductivity method, are not suitable for determining soil salinity in frozen soil environments below zero degrees Celsius. Therefore, a monitoring method for soil salinity in frozen soil environments is needed.

[0022] Therefore, based on the traditional time-domain reflectometry method for determining soil salinity, this invention adds a heating component. The heating component heats the soil around the probe and obtains unfrozen water. Then, the conductivity of the unfrozen water around the probe is obtained through time-domain reflectometry, and the soil salinity is calculated.

[0023] The aforementioned monitoring equipment addresses the issue of the significant impact of water phase changes on conductivity measurement accuracy during soil freezing. The time-domain reflectometry (TDDR) relies on the transmission of electromagnetic signals by liquid water in the soil. The presence of unfrozen water eliminates the interference of the ice-water mixture on the transmission speed of electromagnetic signals, enabling the TDDR to accurately capture the conductivity characteristics of unfrozen water. This provides a reliable basis for subsequent salt content calculations, improving the accuracy and precision of TDDR in determining salt content in frozen soil. Furthermore, this method offers advantages such as in-situ measurement, minimal soil disturbance, speed, and high automation.

[0024] like Figure 2 As shown, the heating assembly includes an insulating resistance wire 2, the detection end of the probe is a hollow steel tube 3, the insulating resistance wire 2 is located inside the cavity of the steel tube 3, and both ends of the insulating resistance wire 2 are respectively connected to the power supply device. The steel tube 3 is also filled with a fixing layer 4 for fixing the insulating resistance wire 2.

[0025] The hollow steel pipe 3 serves as both the detection end of the probe for transmitting electromagnetic signals and the carrier of the heating component. Its compact structure minimizes damage to the soil structure. The fixing layer 4 fills the cavity of the steel pipe 3, which serves two purposes: firstly, it fixes the insulating resistance wire 2 at the center of the steel pipe 3, ensuring that heat is evenly radiated to the soil around the probe during heating and avoiding heating dead zones; secondly, it fills the gap between the resistance wire and the steel pipe 3, preventing soil moisture and salt from penetrating and corroding the insulating resistance wire 2, and the fixing layer 4 also facilitates heat conduction and improves heating efficiency.

[0026] The fixing layer 4 is an epoxy resin with a thermal conductivity ≥0.5 W / (m·K).

[0027] High thermal conductivity epoxy resin can quickly transfer the heat generated by the insulating resistance wire 2, so that the heat is conducted from the insulating resistance wire 2 through the epoxy resin to the wall of the steel pipe 3, and then efficiently radiated to the surrounding frozen soil.

[0028] The heating component is also connected to a control device, which connects the heating component to the power supply device and allows it to be switched on and off.

[0029] The heating component is connected to the power supply device through a control device to achieve on-demand switching. The control device can determine whether heating is needed based on soil temperature data. For example, heating is turned on when the soil temperature is ≤0℃ and turned off when it is >0℃, avoiding ineffective heating, saving power supply energy, and preventing problems such as excessive unfrozen water and salt migration caused by excessively high soil temperature, ensuring that the test data reflects the true salinity of the soil.

[0030] like Figure 1 As shown, the power supply device includes a solar panel and a battery, and the control device includes a solar power controller and a DC time switch. The output end of the solar panel is connected to the input end of the battery through the solar power controller, and the output end of the battery is connected to the power supply end of the heating component through the DC time switch.

[0031] The battery is a 12V battery, which is charged by a solar panel. The insulating resistance wire 2 is connected to the 12V battery through a DC time control switch. Under the set conditions, the 12V battery is turned on and heated by the insulating resistance wire 2.

[0032] The probe is provided in at least three sets, and multiple sets of the probe are fixed together on the handle 5. The signal output end of each set of probes is connected to the time domain reflectometer via the connecting line 1.

[0033] like Figure 2 As shown, the diameter of the insulating resistance wire 2 is 75 μm, the material of the resistance wire is nickel-chromium resistance alloy, and the specification of the insulating resistance wire 2 is 221.9 Ω m. -1 During fabrication, resistance wires are placed into each stainless steel tube 3, and insulated resistance wires 2 are folded in half according to the length of the probe's steel tube 3 (total length 80mm). The two ends of the insulated resistance wires 2 in the probe are connected in parallel to form the positive and negative terminals of the power supply. Then, high thermal conductivity epoxy resin is poured into the steel tube 3 of each probe to fix it.

[0034] In the time-domain reflectometry section, the central copper wire of a 75 Ω coaxial cable is soldered to the upper end of the steel tube 3 of the intermediate probe. Then, the outer mesh conductive layer of the coaxial cable is divided into two equal strands and soldered to the upper ends of the steel tubes 3 of the two outer probes respectively. After each probe is fabricated, polyvinyl chloride material is poured into a mold to make handles 5 to fix each probe.

[0035] The method of using a device for monitoring salinity in permafrost includes the following steps: S1. Insert the detection end of the probe connected to the time domain reflectometer into the soil of the area to be monitored; S201. If the soil temperature in the area to be monitored is >0℃, data should be collected directly using a probe. S202. If the soil temperature in the area to be monitored is ≤0℃, first turn on the heating component to heat and melt the frozen water in the soil around the probe and form unfrozen water. Then turn off the heating component and use the probe to collect data. S3. The collected data is transferred to the terminal device using a time domain reflectometer for calculation to obtain the soil electrical conductivity. S4. Calculate soil salinity based on soil electrical conductivity.

[0036] The specific method for inserting the probe's detection end into the soil of the area to be monitored in step S1 is as follows: When the soil temperature is above 0℃, a soil profile is formed by excavating the topsoil layer, and a probe is inserted horizontally into the topsoil layer. Then the soil is backfilled, with the probe 8-15cm away from the surface.

[0037] When the soil is in the thawing phase (i.e., the temperature is above 0℃), a soil profile is dug in the topsoil of saline-alkali wasteland, grassland, woodland, and cultivated land (representing different salinity levels). The probe is inserted horizontally into the soil at the target depth, 10 cm from the surface, and then the soil is backfilled. The matching time domain reflectometer, battery, and other measuring instruments are placed in a rainproof box and connected to an external solar panel for continuous power supply.

[0038] If it is necessary to determine the salinity of unfrozen soil, the conductivity can be directly measured using a probe during the soil thawing period. When the temperature gradually drops below 0℃, the probe is automatically heated by a DC time-controlled switch using a battery for 20 seconds. Data is then collected using a time-domain reflectometer, and each measurement is repeated three times.

[0039] The collected data is transferred to a computer on a terminal device, and the soil electrical conductivity is obtained using calculation methods such as Heimovaara.

[0040] The relationship between soil electrical conductivity and soil salinity in step S4 is f(x) = 3.92x + 1.38, where x is soil electrical conductivity and f(x) is soil salinity.

[0041] f(x) = 3.92x + 1.38 represents the relationship between electrical conductivity and salinity in coastal saline-alkali soil.

[0042] II. Performance Testing At the Haixing Saline-Alkali Land High-Efficiency Utilization Experimental Base, the soil salinity of the topsoil layer of saline-alkali soil was monitored using both the standard reference method titration and the frozen soil salinity monitoring equipment of this invention. The experimental data are shown in Table 1.

[0043] Table 1 shows a comparison between soil salinity measured using the frozen soil salinity monitoring device and soil salinity measured by titration. The results show that the salinity measured by the frozen soil salinity monitoring device in this invention is in good agreement with the soil salinity measured by titration, with a root mean square difference of 1.04 g / kg.

[0044] This indicates that the measurement results of the permafrost salinity monitoring device in this invention are accurate and reliable, and can meet the needs of accurate monitoring of soil salinity in permafrost environments.

Claims

1. A device for monitoring salinity in permafrost, comprising a time-domain reflectometer and a probe, wherein the signal output end of the probe is connected to the time-domain reflectometer via a connecting line (1), characterized in that, The probe is equipped with a heating element at its detection end, which melts the frozen water in the soil around the probe and forms unfrozen water.

2. The monitoring device for salinity in permafrost according to claim 1, characterized in that, The heating assembly includes an insulating resistance wire (2), the detection end of the probe is a hollow steel tube (3), the insulating resistance wire (2) is located inside the cavity of the steel tube (3), and the two ends of the insulating resistance wire (2) are respectively connected to the power supply device. The steel tube (3) is also filled with a fixing layer (4) for fixing the insulating resistance wire (2).

3. The monitoring device for salinity in permafrost according to claim 2, characterized in that, The fixing layer (4) is an epoxy resin with a thermal conductivity ≥0.5 W / (m·K).

4. The monitoring device for salinity in permafrost according to claim 2, characterized in that, The heating component is also connected to a control device, which connects the heating component to the power supply device and allows it to be switched on and off.

5. The monitoring device for salinity in permafrost according to claim 4, characterized in that, The power supply device includes a solar panel and a battery, and the control device includes a solar power controller and a DC time switch. The output end of the solar panel is connected to the input end of the battery via the solar power controller, and the output end of the battery is connected to the power supply end of the heating component via the DC time switch.

6. The monitoring device for salinity in permafrost and its method of use according to claim 2, characterized in that, The probe is provided in at least three groups, and multiple groups of the probe are fixed together on the handle (5). The signal output end of each group of probes is connected to the time domain reflectometer via a connecting line (1).

7. A method of using a monitoring device for salinity in permafrost, for use with the monitoring device as described in claim 1, characterized in that, The method of use includes the following steps: S1. Insert the detection end of the probe connected to the time domain reflectometer into the soil of the area to be monitored; S201. If the soil temperature in the area to be monitored is >0℃, data should be collected directly using a probe. S202. If the soil temperature in the area to be monitored is ≤0℃, first turn on the heating component to heat and melt the frozen water in the soil around the probe and form unfrozen water. Then turn off the heating component and use the probe to collect data. S3. The collected data is transferred to the terminal device using a time domain reflectometer for calculation to obtain the soil electrical conductivity. S4. Calculate soil salinity based on soil electrical conductivity.

8. The method of using the monitoring device for salinity in permafrost according to claim 7, characterized in that, The specific method for inserting the probe's detection end into the soil of the area to be monitored in step S1 is as follows: When the soil temperature is above 0℃, a soil profile is formed by excavating the topsoil layer, and a probe is inserted horizontally into the topsoil layer. Then the soil is backfilled, with the probe 8-15cm away from the surface.

9. The method of using the monitoring device for salinity in permafrost according to claim 7, characterized in that, The relationship between soil electrical conductivity and soil salinity in step S4 is f(x) = 3.92x + 1.38, where x is soil electrical conductivity and f(x) is soil salinity.

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