Soil dry layer distinguishing and dry layer thickness measuring method based on distributed temperature sensing

Abstract

The invention discloses a soil body dry layer distinguishing and dry layer thickness measuring method based on distributed temperature sensing, and the method comprises the steps: respectively implanting an AH-DTS measuring pipe and a PI-OFDR measuring pipe into a to-be-measured soil body, and forming a distributed monitoring network covering a target area. Acquiring temperature data of the AH-DTS measuring tube in real time by using a demodulator, and performing a heating test once at a preset time interval; meanwhile, data of the PI-OFDR measuring pipe are collected in real time, and soil temperature and humidity information is obtained. According to a calibration formula, the measured temperature data is converted into the moisture content of the soil body, and in combination with profile data of the temperature, the humidity and the moisture content, an area with an obvious temperature minimum value is comprehensively analyzed, so that the judgment of the dry layer of the soil body and the measurement of the corresponding thickness are realized. According to the invention, continuous and real-time monitoring of soil parameters can be realized, and reliable technical support is provided for determination of the existence state and thickness of a dry layer.

Description

Technical Field

[0001] The present invention relates to the fields of geological engineering, environmental science, and ecological agriculture, and particularly relates to a method for discriminating soil dry layers and measuring the thickness of dry layers based on distributed temperature sensing. Background Art

[0002] The evaporation of soil moisture is one of the main forms of mass and energy exchange at the soil-atmosphere interface, and has an important impact on soil moisture migration and surface energy balance. Existing research shows that the process of soil moisture evaporation can be divided into three stages: the constant rate stage, the decelerating rate stage, and the residual stage. Among them, in the decelerating rate stage and the residual stage, the surface layer moisture of the soil is depleted, forming a dry layer, resulting in the actual evaporation surface moving down to the bottom of the dry layer. During this process, liquid water vaporizes under the action of evaporation and enters the atmosphere in the form of water vapor through diffusion through the dry layer, thus affecting the migration law and evaporation rate of soil moisture. Due to the existence of the dry layer, the resistance to the diffusion of water vapor in the soil to the surface gradually increases, causing the evaporation rate to decrease accordingly. In addition, the dynamic evolution of the dry layer thickness directly affects the water-thermal-mechanical coupling process of the soil and is one of the key parameters in the study of soil-atmosphere interaction.

[0003] At present, the measurement methods for the thickness of the dry layer in soil mainly include the visual inspection method and the analysis method based on the water content profile. The visual inspection method judges the thickness of the dry layer by observing the color change of the soil profile, but this method has strong subjectivity, large errors, and limited applicability; the analysis method based on the water content profile defines the thickness of the dry layer by measuring the depth corresponding to the residual water content, but its application is restricted to a certain extent in the complex environment of alternating rainfall and evaporation. In addition, the existing monitoring of soil water content and the state of the dry layer mostly rely on local sampling or limited sensor point measurements, making it difficult to comprehensively characterize the spatial distribution and dynamic changes of soil internal water parameters. In recent years, the actively heated distributed temperature sensing (AH-DTS) technology and the polyimide-coated optical frequency domain reflectometry (PI-OFDR) technology have the advantages of distributed, high-precision, and long-distance measurement, and show good application potential in the monitoring of soil water and heat flux. The AH-DTS technology can realize the synchronous measurement of multiple parameters such as soil temperature, thermal conductivity, water content, and humidity, and the PI-OFDR technology can realize the synchronous measurement of parameters such as soil temperature, humidity, and suction. These two distributed fiber optic sensing technologies provide technical support for the in-situ monitoring of the internal heat flux distribution in the dry layer. In addition, by winding the optical fiber around the pipe wall, a high-resolution AH-DTS sensor can be prepared, and its spatial resolution can reach the centimeter level, which is conducive to accurately identifying the dry layer in the soil and dynamically monitoring the change process of the dry layer thickness, providing a new monitoring means for the study of soil-atmosphere interaction and promoting the in-depth development of related fields. Summary of the Invention

[0004] The object of the present invention is to provide a method for discriminating the dry layer in soil and measuring the thickness of the dry layer based on distributed temperature sensing, which aims to solve the problems of limited monitoring points, low data spatio-temporal resolution, and insufficient long-term monitoring stability existing in traditional soil water monitoring methods. By comprehensively using the temperature, humidity, and water content data collected by the AH-DTS measuring tube and the PI-OFDR measuring tube, it can be determined in real time whether there is a dry layer in the soil and the thickness of the dry layer can be accurately measured, providing an efficient and reliable technical means for the dynamic monitoring of soil water, the analysis of the evaporation process, and the monitoring of related projects.

[0005] To achieve the above functions, the present invention designs a method for discriminating the dry layer in soil and measuring the thickness of the dry layer based on distributed temperature sensing. For the soil to be measured, the following steps S1 - S7 are executed to complete the discrimination of whether there is a dry layer in the soil to be measured and the measurement of the dry layer thickness:

[0006] Step S1: Insert the AH-DTS measuring tube and the PI-OFDR measuring tube into the soil to be measured respectively;

[0007] Step S2: Conduct heating tests on the AH-DTS measuring tube at preset time intervals, and collect the temperature data of the soil to be measured before heating, during heating, and after heating in real time;

[0008] Step S3: Use the PI-OFDR measuring tube to collect the temperature and humidity data at each depth position in the soil to be measured in real time;

[0009] Step S4: According to the temperature data in the heating test of the AH-DTS measuring tube collected in Step S2, use the calibration formula to calculate the water content at each depth position of the soil to be measured; according to the temperature and humidity data at each depth position in the soil to be measured collected in Step S3, obtain the temperature profile, humidity profile, and water content profile of the soil to be measured at different times;

[0010] Step S5: According to the temperature profile of the soil to be measured, preliminarily determine whether there is a dry layer inside the soil to be measured. If it is preliminarily determined that there is a dry layer inside the soil to be measured, go to Step S6 for further judgment; otherwise, end the judgment and output the judgment result that there is no dry layer inside the soil to be measured;

[0011] Step S6: According to the humidity profile and water content profile of the soil to be measured, further determine whether there is a dry layer in the soil to be measured, and output the judgment result;

[0012] Step S7: Based on the judgment result of Step S6, if it is judged that there is a dry layer inside the soil to be measured, calculate its thickness and conduct dynamic monitoring.

[0013] Beneficial effects: Compared with the prior art, the advantages of the present invention include:

[0014] 1. Based on the distributed temperature sensing technology, the present invention combines the comprehensive analysis of soil temperature, humidity, and water content data, can accurately identify the presence of soil dry layers, and can dynamically measure the thickness of the dry layer and track its changes according to the position of the evaporation surface.

[0015] 2. The present invention requires fewer soil parameters, and the process of discriminating soil dry layers is simple.

[0016] 3. The present invention is economical, safe, easy to operate, has strong anti-interference ability, and reliable and effective accuracy.

[0017] 4. The present invention uses AH-DTS and PI-OFDR measuring tubes for monitoring, with stable data collection, high durability, low equipment maintenance cost, and is suitable for long-term monitoring requirements.

[0018] 5. The present invention helps to improve the accuracy and reliability of the distributed temperature sensing technology for monitoring and discriminating the dry layer of in-situ soil, enhance its adaptability to different types of soil, and further promote the popularization and application of this technology in the fields of hydrogeology, environmental science, ecological agriculture, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flowchart of a method for discriminating the dry layer of soil and measuring the dry layer thickness based on distributed temperature sensing according to an embodiment of the present invention;

[0020] Figure 2 is a schematic diagram of an experimental device for a method for discriminating the dry layer of soil and measuring the dry layer thickness based on distributed temperature sensing according to an embodiment of the present invention;

[0021] Figure 2 In the figure: 1, generator; 2, voltage stabilizer; 3, computer; 4, demodulator; 5, automatic controller; 6, PI-OFDR sensor measuring tube; 7, AH-DTS sensor measuring tube; 8, soil;

[0022] Figure 3 is a schematic diagram of a high-resolution AH-DTS sensor according to an embodiment of the present invention;

[0023] Figure 4 is a diagram of the state parameters of the soil measured by the AH-DTS sensor according to an embodiment of the present invention;

[0024] Figure 5 is a comparison diagram of the soil temperature and moisture content within the range of 0 - 1 m according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following further describes the present invention with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and should not be used to limit the protection scope of the present invention.

[0026] The method for discriminating the dry layer of soil and measuring the dry layer thickness based on distributed temperature sensing provided by the embodiment of the present invention, for the soil to be measured, with reference to Figure 1 , perform the following steps S1 - step S7 to complete the discrimination of whether there is a dry layer in the soil to be measured and the measurement of the dry layer thickness:

[0027] Step S1: Respectively implant the AH-DTS measuring tube and the PI-OFDR measuring tube into the soil to be measured;

[0028] The lengths of the AH-DTS measuring tubes and the PI-OFDR measuring tubes are greater than 2 m, and they are both evenly arranged along the depth direction of the soil to be measured. Moreover, the horizontal distance between the AH-DTS measuring tubes and the PI-OFDR measuring tubes is greater than 20 cm, so as to effectively prevent mutual interference caused by heat conduction during the heating test, and at the same time ensure the construction of a distributed monitoring network covering the target area with high spatial resolution in the soil to be measured.

[0029] Step S2: Conduct a heating test on the AH-DTS measuring tubes every 6 hours. The duration of the heating test is 20 minutes, and the temperature data of the soil to be measured before heating, during heating, and after heating are collected in real time.

[0030] Connect the automatic control module to the AH-DTS measuring tubes. The automatic control module is used to automatically trigger the heating test of the AH-DTS measuring tubes at a preset time interval.

[0031] Step S3: Use the PI-OFDR measuring tubes to collect the temperature and humidity data at each depth position in the soil to be measured in real time.

[0032] The temperature and humidity data collected by the PI-OFDR measuring tubes can be used to calibrate and compensate the temperature data collected by the AH-DTS measuring tubes, thereby improving the accuracy of temperature measurement and the reliability of moisture content calculation.

[0033] Step S4: According to the temperature data in the heating test of the AH-DTS measuring tubes collected in Step S2, use the calibration formula to calculate the moisture content at each depth position of the soil to be measured; according to the temperature and humidity data at each depth position in the soil to be measured collected in Step S3, obtain the temperature profile, humidity profile, and moisture content profile of the soil to be measured at different times.

[0034] It is necessary to continuously collect the profile data of the soil temperature, humidity, and moisture content for a long time, comprehensively analyze the three data, and determine whether there is a dry layer on the soil surface.

[0035] The specific method of Step S4 is as follows:

[0036] In the heating test of the AH-DTS measuring tubes, a constant power heating method is adopted. There is a quantitative relationship between the soil temperature T and the soil moisture content θ during the heating process. The calibration formula is obtained by fitting a large amount of test data. The calibration formula between the soil temperature T and the soil moisture content θ during the heating process is as follows:

[0037]

[0038] In the formula, T t is the temperature of the soil to be measured at time t during the heating process, and θ is the volumetric moisture content of the soil (m 3 ·m 3),A, B, and D are constants related to the soil type, obtained from the fitting results of the T t -θ calibration test.

[0039] Step S5: According to the temperature profile of the soil to be measured, preliminarily determine whether there is a dry layer inside the soil to be measured. If it is preliminarily determined that there is a dry layer inside the soil to be measured, then proceed to Step S6 for further judgment; otherwise, end the judgment and output the discrimination result that there is no dry layer inside the soil to be measured.

[0040] The specific method of Step S5 is as follows:

[0041] For the long-term collected temperature profile of the soil to be measured, find the minimum temperature value in the temperature profiles at multiple moments.

[0042] If there is no stable minimum temperature value within the depth range of 1 m from the ground surface in the temperature profiles at multiple moments, that is then it is determined that there is no dry layer in the soil to be measured, and Step S5 ends.

[0043] If there is a stable minimum temperature value within the depth range of 1 m from the ground surface in the temperature profiles at multiple moments, that is then it is preliminarily determined that there is a dry layer in the soil to be measured, and proceed to Step S6.

[0044] where T is the temperature of the soil to be measured and z is the depth of the soil to be measured.

[0045] Step S6: According to the humidity profile and water content profile of the soil to be measured, further determine whether there is a dry layer in the soil to be measured and output the discrimination result.

[0046] The specific steps of Step S6 are as follows:

[0047] Step S6.1: Calculate the water content θ of the soil at the depth where the minimum temperature value is located j , and compare it with the residual water content θ r :

[0048] If |θ j -θ r | > 0.03, then it is determined that there is no dry layer in the soil to be measured, and Step S6 ends.

[0049] If |θ j -θ r | ≤ 0.03, then further determine that there is a dry layer in the soil to be measured.

[0050] Step S6.2: Calculate the humidity RH at the depth where the minimum temperature value is located j , and determine whether it satisfies the saturation-unsaturation boundary condition:

[0051] If the soil humidity RH above this depth j <100%, and the soil humidity RH below this depth j = 100%, then it is further determined that there is a dry layer inside the soil to be measured, and the interface corresponding to this depth is the evaporation surface, and step S7 is entered;

[0052] If the above conditions are not met, it is determined that there is no dry layer in the soil to be measured, and step S6 ends.

[0053] Step S7: Based on the discrimination result of step S6, if it is discriminated that there is a dry layer inside the soil to be measured, then calculate its thickness and perform dynamic monitoring.

[0054] When it is determined that there is a soil dry layer, the thickness of the dry layer is defined as the depth value corresponding to the minimum temperature (i.e., the evaporation surface), and since the soil parameters are affected by environmental conditions and can change with time, the change information of the dry layer thickness at different times can be obtained through continuous monitoring.

[0055] Dry layer thickness H dry Is determined by the evaporation surface (i.e., the depth where the minimum temperature is located), and the dry layer thickness is calculated as follows:

[0056] H dry = Z

[0057] Wherein, H dry Represents the dry layer thickness, and Z represents the depth where the minimum temperature is located.

[0058] The following is an application embodiment of the present invention:

[0059] The method of the present invention is applied to the on-site test for discriminating the dry layer of in-situ soil and measuring the dry layer thickness. The specific steps are as follows:

[0060] Step 1: Install the AH-DTS and PI-OFDR sensors, and the steps are as follows:

[0061] (1) Vertically place the AH-DTS sensor measuring tube with a length of 2m into the test pit, make it close to the inner wall of the test pit, and the top is flush with the soil surface;

[0062] (2) Install a PI-OFDR sensor measuring tube with the same length 20 cm away from the AH-DTS measuring tube in the test pit, and the top is flush with the soil surface to measure the soil temperature and humidity, providing reference data for Tt-θ calibration;

[0063] (3) Backfill the test pit in layers (20 cm per layer), and use in-situ loess for filling to reduce the error caused by the difference in soil properties;

[0064] (4) After backfilling, compact the test pit to make the soil density match that of the in-situ loess, and minimize the impact of porosity on subsequent measurements. During compaction, pay attention to avoid displacement or damage of the sensors;

[0065] (5) After backfilling is completed, leave the test pit static for two months to reach a stable state, so as to ensure that the moisture distribution and temperature field inside the soil reach a natural equilibrium state during subsequent measurements.

[0066] Step 2: After the test pit is stable, assemble the experimental device system for discriminating the dry layer of the soil body, as Figure 2 shown. The heating module is supplied with 220V AC power by the generator 1 and has a stable output through the voltage regulator 2, while supporting voltage adjustment to ensure accurate control of the heating power. Bury the PI-OFDR sensor 6 and the AH-DTS sensor tube 7 in the soil body 8 to be measured and connect them to the demodulator 4 respectively to realize real-time acquisition of temperature and humidity data. At the same time, the AH-DTS sensor tube 7 is connected to the voltage regulator 2 through the automatic control device 5 to control the heating time (heat for 20 minutes every 6 hours). The demodulator 4 is connected to the computer 3 through the data transmission interface, and the data is processed and controlled by the demodulation software. The soil temperature, humidity and related test data collected by the demodulator are transmitted to the computer 3 in real time for system recording and analysis, providing data support for subsequent discrimination of the dry layer of the soil body and determination of the thickness.

[0067] Step 3: The schematic diagram of the high-resolution AH-DTS sensor refers to Figure 3 , where Figure 3 (a) is the sensor structure diagram; Figure 3 (b) is the circuit distribution diagram inside the steel wire hose; Use the AH-DTS and PI-OFDR sensor tubes to conduct the test for discriminating the dry layer of the soil body. The specific steps are as follows:

[0068] (1) Apply a heating power of 66.35 W / m per unit length on the AH-DTS sensor tube every 6 hours, with a duration of 20 minutes, and collect the temperature change data in real time.

[0069] (2) The PI-OFDR tube continuously and real-time collects the temperature and humidity data at each depth position in the soil body;

[0070] (3) Combine the calibration formula to calculate the volumetric water content θ of the soil body, T t - The calibration formula for θ is as follows:

[0071]

[0072] In the formula, θ is the volumetric water content of the soil body (m 3 ·m 3),A, B, and D are constants related to the soil type. Among them, the parameters A, B, and D can be obtained from the fitting results of the T t -θ calibration test.

[0073] Step 4: According to the test data, obtain the soil temperature profile, humidity profile, and water content profile at different times, and use the temperature minimum method to determine the dry layer of the soil. The state parameter diagram of the soil measured by the AH-DTS sensor is referred to Figure 4 , where Figure 4 (a) is the soil temperature, Figure 4 (b) is the soil thermal conductivity, Figure 4 (c) is the soil volumetric water content. It can be seen from Figure 4 that in the temperature profiles at multiple times, there are stable temperature minima within the depth range of less than 1 m from the ground surface, that is, there is a temperature minimum value at a depth of 0.246 m, and the temperature gradient at this depth satisfies It can be preliminarily determined that this depth may correspond to the actual evaporation surface, but further verification is still needed in combination with the humidity and water content data.

[0074] Step 5: For the soil area where there is a minimum value in the temperature profile, further determine whether a dry layer is formed in combination with the water content and humidity at this depth. The specific steps are as follows:

[0075] (1) Calculate the humidity RH at this depth j , and judge whether it meets the saturated-unsaturated boundary condition. If the humidity RH of the soil above this depth j <100%, and the humidity RH of the soil below this depth j =100%, then it is determined that there is a dry layer inside the soil, and the interface corresponding to this depth is the evaporation surface; The comparison of the soil temperature and water content within the range of 0-1 m is referred to Figure 5 , where Figure 5 (a) is the soil temperature, Figure 5 (b) is the soil volumetric water content; It can be seen from Figure 5 (a) that the temperature profiles of the soil at multiple times all show temperature lows at 0.246 m, which indicates that this position is affected by evaporation for a long time, and the evaporation surface gradually moves deep with the loss of surface soil moisture, and there will be a temperature minimum at the actual evaporation surface. Therefore, it can be preliminarily judged that the position of the evaporation surface is at 0.246 m;

[0076] (2) Calculate the water content θ of the soil at this depth j , and compare it with the residual water content θ r : If |θ j -θ r |≤0.03, it indicates that the soil in this area has reached the residual water content state, that is, a dry layer is formed. It can be seen from Figure 5As can be seen from (b), the volumetric water contents at 0.246 m are 0.0381, 0.0505, and 0.0537 cm 3 / cm 3 in spring, summer, and autumn respectively. These values are all very close to the residual water content of the loess (0.05 cm 3 / cm 3 ), indicating that the moisture in this area is mainly controlled by the residual suction, and then the position of the actual evaporation surface corresponding to this depth is determined;

[0077] Step Six: Based on the discrimination results of Step Four and Step Five, if it is determined that there is a dry layer inside the soil mass, then calculate its thickness and conduct dynamic monitoring: The thickness H of the dry layer dry is determined by the evaporation surface (i.e., the depth where the minimum temperature is located), that is:

[0078] H dry = Z

[0079] where Z represents the depth where the minimum temperature is located. Therefore, there is a dry layer with a thickness of 0.246 m at the test site. In subsequent dynamic monitoring, the evolution law of the dry layer and its influence on soil moisture migration can be further analyzed by long-term observation of the change in the position of the evaporation surface (i.e., the depth where the minimum temperature is located) and combining temperature, humidity, and water content data.

[0080] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge scope of those of ordinary skill in the art.

Claims

1. A method for determining soil dry layer and dry layer thickness based on distributed temperature sensing, characterized in that: For the soil body to be tested, the following steps S1 to S7 are executed to determine whether there is a dry layer in the soil body to be tested and to determine the thickness of the dry layer: Step S1: implanting the AH-DTS measuring tube and the PI-OFDR measuring tube into the soil to be tested respectively; Step S2: Perform heating test on the AH-DTS measuring tube at preset time intervals, and collect temperature data of the soil to be tested before, during and after heating in real time; Step S3: Using the PI-OFDR measuring tube to collect the temperature and humidity data of each depth position in the soil to be measured in real time; Step S4: Calculate the moisture content at each depth of the soil to be tested using a calibration formula according to the temperature data collected in the AH-DTS tube heating test in step S2; and obtain the temperature profile, humidity profile, and moisture content profile of the soil to be tested at different times according to the temperature and humidity data at each depth of the soil to be tested collected in step S3; Step S5: Preliminarily determine whether there is a dry layer inside the soil to be tested according to the temperature profile of the soil to be tested. If it is preliminarily determined that there is a dry layer inside the soil to be tested, proceed to step S6 for further determination. Otherwise, the determination is terminated and a determination result that there is no dry layer inside the soil to be tested is outputted. Step S6: further determining whether there is a dry layer in the soil to be tested according to the humidity profile and the water content profile of the soil to be tested, and outputting the determination result; Step S7: Based on the determination result of step S6, if it is determined that there is a dry layer inside the soil to be tested, its thickness is calculated and dynamic monitoring is performed.

2. The method for determining soil dry layer and measuring dry layer thickness based on distributed temperature sensing according to claim 1, characterized in that: In step S1, the length of the AH-DTS measuring tube and the PI-OFDR measuring tube is greater than 2 m, and both are evenly arranged along the depth direction of the soil to be measured, and the horizontal distance between the AH-DTS measuring tube and the PI-OFDR measuring tube is greater than 20 cm.

3. The method for determining soil dry layer and measuring dry layer thickness based on distributed temperature sensing according to claim 1, characterized in that: In step S2, a heating test is performed on the AH-DTS test tube every 6 hours, and the heating test lasts for 20 minutes.

4. The method for determining soil dry layer and measuring dry layer thickness based on distributed temperature sensing according to claim 1, characterized in that: The specific method of step S4 is as follows: The AH-DTS test tube adopts a constant power heating method in the heating test. The calibration formula between the soil temperature T and the soil moisture content θ during the heating process is as follows: Where, T t is the soil temperature at time t during the heating process, θ is the soil volume moisture content, A, B and D are constants related to the soil type, and T t The fitting results of the -θ calibration test are obtained.

5. The method for determining soil dry layer and measuring dry layer thickness based on distributed temperature sensing according to claim 1, characterized in that: The specific method of step S5 is as follows: For the long-term collected temperature profile of the soil to be tested, find the temperature minimum value in the temperature profile at multiple times; If there is no stable temperature minimum within the depth range of 1m from the surface in the temperature profile at multiple times, that is, It is determined that there is no dry soil layer in the soil to be tested, and step S5 ends; If there is a stable temperature minimum within a depth range of 1m from the surface in the temperature profile at multiple times, that is, It is preliminarily determined that there is a dry layer in the soil to be tested, and the process goes to step S6; Where T is the temperature of the soil to be tested, and z is the depth of the soil to be tested.

6. The method for determining soil dry layer and measuring dry layer thickness based on distributed temperature sensing according to claim 5, characterized in that: The specific steps of step S6 are as follows: Step S6.1: Calculate the soil moisture content θ at the depth where the temperature minimum is located j and the residual moisture content θ r For comparison: If |θ j -θ r |>0.03, it is determined that the soil to be tested has no dry layer, and step S6 ends; If |θ j -θ r |≤0.03, it is further determined that there is a dry layer in the soil to be tested; Step S6.2: Calculate the humidity RH at the depth where the temperature minimum is located j , determine whether the saturation-unsaturation boundary condition is met: If the soil humidity RH above this depth j <100%, and the soil humidity below this depth is RH j =100%, it is further determined that there is a dry layer inside the soil to be tested, and the interface corresponding to this depth is the evaporation surface, and the process goes to step S7; If the above conditions are not met, it is determined that there is no dry layer in the soil to be tested, and step S6 ends.

7. The method for determining soil dry layer and measuring dry layer thickness based on distributed temperature sensing according to claim 1, characterized in that: If it is determined that there is a dry layer inside the soil to be tested, the thickness of the dry layer is calculated in step S7 as follows: H dry =Z Among them, H dry represents the thickness of the dry layer, and Z represents the depth of the temperature minimum.

8. The method for determining soil dry layer and measuring dry layer thickness based on distributed temperature sensing according to claim 1, characterized in that: An automatic control module is connected to the AH-DTS measuring tube, and the automatic control module is used to automatically trigger a heating test of the AH-DTS measuring tube according to a preset time interval.

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