Soil body heat flux profile determination method based on AH-DTS technology

Abstract

The invention discloses a soil body heat flux profile determination method based on an AH-DTS technology, and the method comprises the steps: determining a reference depth at which the soil body temperature is stable along with time through measuring the soil body temperature at different depths and different moments and the corresponding volume water content; calculating the volume heat capacity of the soil body, layering the soil body above the reference depth, and obtaining the average temperature and heat capacity of each layer; and calculating the single-layer heat storage amount and accumulating to obtain the total heat storage amount, and finally obtaining the heat flux profile of the soil body at any target depth. The method comprises the steps of reference depth determination, soil volume heat capacity calculation, soil layer equal division and layered heat storage capacity calculation, heat storage capacity accumulation and heat flux profile solving. The method is easy and convenient to operate and high in spatial resolution, the influence of soil moisture content change on the heat flux can be effectively represented, in-situ continuous measurement of the soil heat flux profile can be achieved, and a reliable technical means is provided for research on the soil moisture and heat transfer law.

Description

Technical Field

[0001] This invention relates to the field of soil heat flux measurement technology, specifically to a method for measuring soil heat flux profiles based on AH-DTS technology. Background Technology

[0002] Soil heat flux is a core component of the Earth's surface energy balance and a crucial bridge for energy exchange between soil and atmosphere, significantly impacting climate change, the hydrological cycle, and agro-ecosystems. Soil heat flux not only controls the intensity of turbulent exchange and boundary layer structure between the surface and atmosphere but also directly influences the regional energy balance in arid and semi-arid regions, playing an irreplaceable role in soil-atmosphere energy exchange. Furthermore, the spatial heterogeneity and temporal dynamics of soil heat flux directly affect surface temperature, evapotranspiration, and the hydrothermal cycle, playing a vital regulatory role in soil hydrothermal coupling and crop growth environment, while also providing scientific basis for preventing agricultural meteorological disasters such as frost.

[0003] Existing methods for measuring soil heat flux mainly include the heat flux plate method, the temperature gradient-thermal property combined measurement method, the thermal pulse method, and remote sensing methods.

[0004] 1. The Heat Flux Plate (HFP) method measures temperature differences by embedding thin-plate sensors with known thermal conductivity in the soil and calculates heat flux based on Fourier's law of heat conduction. This method is simple to operate and allows for continuous monitoring. However, the sensors disturb the soil's thermal field and water vapor transport, interfering with the measurement results. Furthermore, it only obtains single-point heat flux information and cannot reflect the spatial heterogeneity of the soil.

[0005] 2. The temperature gradient-thermal property combined measurement method calculates heat flux by measuring temperature gradients at different depths and soil thermal property parameters. Thermal property parameters are typically obtained using the force-recovery method, conduction-convection method, harmonic method, or half-order time derivative method. While this method is theoretically sound, uncertainties in the thermal property parameters introduce errors, and the measurement is limited to the probe position, making it impossible to obtain continuous longitudinal profiles.

[0006] 3. The thermal pulse method involves applying short-duration thermal pulses to the soil, monitoring the dynamic temperature response, inverting thermophysical parameters, and calculating heat flux. This method causes minimal disturbance to the soil, but the probe length is limited, making it mainly suitable for shallow measurements and difficult to obtain continuous profiles at deeper levels.

[0007] 4. Remote sensing methods use thermal infrared to observe surface temperature and combine the principle of thermal inertia to invert soil heat flux. This method is suitable for regional-scale measurements, but it cannot obtain deep soil heat flux, and its spatial resolution and accuracy are easily affected by meteorological conditions and surface cover.

[0008] In summary, existing methods have obvious limitations. Measurements are mostly at single points or shallow layers, making it difficult to obtain continuous thermal flux profiles of the soil in depth. Measurement accuracy is limited when there is significant soil disturbance or high uncertainty in thermal properties. Furthermore, they lack the ability to perform high spatial resolution, in-situ, and long-term continuous monitoring.

[0009] To address the aforementioned issues, Actively Heated Distributed Temperature Sensing (AH-DTS) technology has attracted attention due to its small fiber optic cable size, resistance to electromagnetic interference, high temperature measurement accuracy, and ability to perform distributed measurements. AH-DTS fiber optic cables can simultaneously serve as a heating source and a temperature sensor, enabling high spatial resolution measurement of temperature distribution. This technology has already been applied to in-situ measurements of soil thermal conductivity and volumetric water content, providing a new technical approach for obtaining in-depth profiles of soil heat flux. Based on AH-DTS technology combined with Fourier's law of heat conduction, continuous profile determination of soil heat flux can be achieved through calorimetry, and its reliability can be verified in situ, providing key technical support for high-resolution profile acquisition of soil heat flux and research on soil moisture and heat transport. Summary of the Invention

[0010] The purpose of this invention is to address the limitations of existing methods for measuring soil heat flux, such as low spatial resolution, significant soil disturbance, strong parameter dependence, and difficulty in achieving in-situ continuous profile measurements. This invention provides a method for measuring soil heat flux profiles based on AH-DTS technology. This method can obtain continuous, deep-seated heat flux profiles of soil in situ, achieving high spatial resolution, long-term continuous measurement, and high precision.

[0011] To achieve the above functions, this invention designs a method for measuring soil heat flux profiles based on AH-DTS technology. For the target soil, the following steps S1-S7 are performed to complete the measurement of the soil heat flux profile at any target depth:

[0012] Step S1: Sampling is performed on the target soil. AH-DTS logging tubes are used to obtain basic physical data of the soil at different depths and times, including soil temperature. The corresponding volumetric water content θ is then obtained, and the dry density of the soil is determined through geotechnical testing. Soil particle density;

[0013] Step S2: Based on the soil temperature at different depths and times, select a depth where the soil temperature changes negligibly with time. At this depth, the heat flux is zero, and this depth is determined as the reference depth. ;

[0014] Step S3: Based on soil dry density Soil particle density And the volumetric water content θ, calculate the volumetric heat capacity C of the soil at each depth;

[0015] Step S4: Set the reference depth The soil mass above is divided into N layers along the depth direction. Calculate the average temperature of each layer. Average volumetric heat capacity ;

[0016] Step S5: Based on the average temperature of each soil layer during the time interval between the two tests. Average volumetric heat capacity Calculate the heat storage Δ of each soil layer during the time interval. ;

[0017] Step S6: The heat storage of each layer of soil is accumulated to obtain the total heat storage ΔS of the soil at the target depth;

[0018] Step S7: Calculate the soil heat flux profile at any target depth based on the total heat storage ΔS of the soil at the target depth. .

[0019] As a preferred technical solution of the present invention, the specific steps of step S1 are as follows:

[0020] Step S1.1: For the target soil, use a ring sampler to take samples at different depths in the soil test pit to obtain soil samples, and conduct various preset geotechnical tests to determine the dry density of the soil. Soil particle density ;

[0021] Step S1.2: Heat the soil sample and calculate the temperature rise as follows:

[0022] ;

[0023] In the formula, T t T represents the temperature rise, in °C; T(t) represents the sensor temperature at heating time t, in °C; T0 represents the initial temperature of the target soil, in °C; and Q represents the heating power per unit length, in W·m. -1 λ is the thermal conductivity of the target soil, with units of W·m. -1 ·K -1 d is T t – The intercept of the lnt linear regression curve, in °C;

[0024] Step S1.3: Based on the temperature rise value T t Calculate the soil temperature and volumetric water content θ of the target soil:

[0025] ;

[0026] In the formula, θ is the volumetric water content of the soil (m³). -3 m -3 A, B, and D are constants related to the soil type. Parameters A, B, and D can be derived from T. t The fitting results of the –θ calibration experiment were obtained.

[0027] As a preferred technical solution of the present invention, the specific method of step S2 is as follows:

[0028] For the target soil mass, a threshold is set for the change in soil temperature over time. The depth corresponding to the change in soil temperature over time that is less than the threshold is considered the depth where the change in soil temperature over time is negligible. ;

[0029] At this depth The heat flux profile satisfies ,by As a reference depth.

[0030] As a preferred embodiment of the present invention: the volumetric heat capacity of the soil in step S3 is calculated according to the following formula:

[0031] ;

[0032] In the formula, C represents the volumetric heat capacity of the soil, ρ d This refers to the dry density of the soil, expressed in g / cm³. 3 , ρ s This refers to the density of soil particles, expressed in g / cm³. 3 C s This refers to the volumetric heat capacity of soil particles, expressed in J / (m³). 3 K), its value is 1.26 × 10 6 J / (m 3 K), θ is the volumetric water content, in cm³. 3 / cm 3 C w This refers to the volumetric heat capacity of water, expressed in J / (m³). 3 K), its value is 4.2 × 10 6 J(m) 3 K), where n is the soil porosity.

[0033] As a preferred technical solution of the present invention: in step S4, the reference depth The soil above is divided into N layers, and the thickness of each layer is... ,in, According to target depth With reference depth The distance between layers and the number of layers N are determined and adjusted according to spatial resolution or measurement accuracy requirements; the average temperature of each soil layer is calculated. Average volumetric heat capacity .

[0034] As a preferred embodiment of the present invention: In step S5, the heat storage Δ of the i-th layer of soil during the time interval is... As shown in the following formula:

[0035] ;

[0036] In the formula, and Let z be the average volumetric heat capacity of the i-th soil layer at times t+∆t and t, respectively, and let z be the average volumetric heat capacity of the soil layer above and below the i-th layer. i Let be the depth of the i-th soil layer. and Δt and Δt are the average temperatures of the i-th soil layer at times t+∆t and t, respectively. The values ​​are the average temperatures of the upper and lower layers of the soil layer. ∆t is the time interval between the two tests, in seconds.

[0037] As a preferred technical solution of the present invention: the total heat storage ΔS of the soil in step S6 is obtained by summing the heat storage of each layer of soil above the reference depth, as shown in the following formula:

[0038] ;

[0039] in, The heat stored in the i-th soil layer during the time interval is denoted as N, where N is the number of soil layers above the reference depth.

[0040] As a preferred technical solution of the present invention: the soil heat flux profile at any target depth mentioned in step S7 The calculation is as follows:

[0041] ;

[0042] in, Indicates reference depth Heat flux profile. This indicates the total heat storage capacity of the soil.

[0043] And because Then any target depth Soil heat flux profile .

[0044] As a preferred technical solution of the present invention: AH-DTS measuring tube is used to obtain continuous spatial distribution information of soil temperature, thereby realizing in-situ continuous measurement of soil heat flux profile.

[0045] As a preferred technical solution of the present invention: the time interval The settings are based on the soil's thermal conductivity characteristics and monitoring accuracy requirements.

[0046] Beneficial effects: Compared with the prior art, the advantages of the present invention include:

[0047] 1. Based on the calorimetric method to invert the heat flux of soil, it does not depend on the thermal conductivity of soil, and can effectively reduce the uncertainty caused by soil heterogeneity and moisture content changes.

[0048] 2. By combining AH-DTS technology, continuous thermal flux profile measurement of soil can be achieved, overcoming the limitations of traditional single-point measurement and significantly improving the spatial resolution of thermal flux profile.

[0049] 3. No need to bury traditional heat flow plate sensors, reducing disturbance to the original soil structure, suitable for long-term in-situ monitoring;

[0050] 4. It can simultaneously reflect the impact of soil moisture changes on heat flux, providing a reliable technical means for the study of soil hydrothermal coupling processes; the method has a clear process, is simple to implement, and is suitable for various application scenarios in the field and indoors. Attached Figure Description

[0051] Figure 1 This is a flowchart of a method for measuring soil heat flux profile based on AH-DTS technology according to an embodiment of the present invention;

[0052] Figure 2 This is a schematic diagram of the AH-DTS test tube provided according to an embodiment of the present invention;

[0053] Figure 3 This is a schematic diagram of an in-situ soil testing device provided according to an embodiment of the present invention;

[0054] Figure 4 This is a soil temperature profile provided according to an embodiment of the present invention;

[0055] Figure 5 This is a soil volumetric water content profile provided according to an embodiment of the present invention;

[0056] Figure 6 This is a profile of soil dry density and porosity provided according to an embodiment of the present invention;

[0057] Figure 7 This is a cross-sectional view of the volumetric heat capacity of soil provided according to an embodiment of the present invention;

[0058] Figure 8 This is a heat storage distribution diagram of a 1.45 cm thick soil layer according to an embodiment of the present invention;

[0059] Figure 9 This is a soil heat flux profile provided according to an embodiment of the present invention. Detailed Implementation

[0060] The present invention will be further described below 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 scope of protection of the present invention.

[0061] This invention provides a method for measuring soil heat flux profiles based on AH-DTS technology, targeting the target soil and referring to... Figure 1 Perform the following steps S1-S7 to complete the determination of the soil heat flux profile at any target depth:

[0062] Step S1: Sampling is performed on the target soil. AH-DTS logging tubes are used to obtain basic physical data of the soil at different depths and times, including soil temperature. The corresponding volumetric water content θ is then obtained, and the dry density of the soil is determined through geotechnical testing. Soil particle density C s ;

[0063] The specific steps of step S1 are as follows:

[0064] Step S1.1: For the target soil, use a ring sampler to take samples at different depths in the soil test pit to obtain soil samples, and conduct various preset geotechnical tests to determine the dry density of the soil. Soil particle density ;

[0065] Step S1.2: Heat the soil sample and calculate the temperature rise as follows:

[0066] ;

[0067] In the formula, T t T represents the temperature rise, in °C; T(t) represents the sensor temperature at heating time t, in °C; T0 represents the initial temperature of the target soil, in °C; and Q represents the heating power per unit length, in W·m. -1 λ is the thermal conductivity of the target soil, with units of W·m. -1 ·K -1 d is T t – The intercept of the lnt linear regression curve, in °C;

[0068] Step S1.3: Based on the temperature rise value T t Calculate the soil temperature and volumetric water content θ of the target soil:

[0069] ;

[0070] In the formula, θ is the volumetric water content of the soil (m³). -3 m -3 A, B, and D are constants related to the soil type. Parameters A, B, and D can be derived from T. t The fitting results of the –θ calibration experiment were obtained.

[0071] Step S2: Based on the soil temperature at different depths and times, select a depth where the soil temperature changes negligibly with time. At this depth, the heat flux is zero, and this depth is determined as the reference depth. ;

[0072] For the target soil mass, a threshold is set for the change in soil temperature over time. The depth corresponding to the change in soil temperature over time that is less than the threshold is considered the depth where the change in soil temperature over time is negligible. ;

[0073] At this depth The heat flux profile satisfies ,by As a reference depth.

[0074] Step S3: Based on soil dry density Soil particle density C s , and the volumetric water content θ, calculate the volumetric heat capacity C of the soil at each depth;

[0075] The volumetric heat capacity of the soil is calculated according to the following formula:

[0076] ;

[0077] In the formula, C represents the volumetric heat capacity of the soil, ρ d This refers to the dry density of the soil, expressed in g / cm³. 3 , ρ s This refers to the density of soil particles, expressed in g / cm³. 3 C s This refers to the volumetric heat capacity of soil particles, expressed in J / (m³). 3 K), its value is 1.26 × 10 6 J / (m 3 K), θ is the volumetric water content, in cm³. 3 / cm 3 C w This refers to the volumetric heat capacity of water, expressed in J / (m³). 3 K), its value is 4.2 × 10 6 J(m) 3K), where n is the soil porosity.

[0078] Step S4: Set the reference depth The soil mass above is divided into N layers along the depth direction. Calculate the average temperature of each layer. Average volumetric heat capacity ;

[0079] The reference depth The soil above is divided into N layers, and the thickness of each layer is... ,in, According to target depth With reference depth The distance between the layers and the number of layers N are determined and adjusted according to the sampling point interval or measurement accuracy requirements; the average temperature of each soil layer is calculated. Average volumetric heat capacity .

[0080] Step S5: Based on the average temperature of each soil layer during the time interval between the two tests. Average volumetric heat capacity Calculate the heat storage Δ of each soil layer during the time interval. ;

[0081] Based on the principle of substituting the difference quotient for the derivative, the heat storage Δ of the i-th soil layer during the time interval is... As shown in the following formula:

[0082] ;

[0083] In the formula, and Let z be the average volumetric heat capacity of the i-th soil layer at times t+∆t and t, respectively, and let z be the average volumetric heat capacity of the soil layer above and below the i-th layer. i Let be the depth of the i-th soil layer. and Δt and Δt represent the average temperatures of the i-th soil layer at times t+Δt and t, respectively. Δt is the average temperature between the upper and lower layers of the soil layer, and Δt is the time interval between the two tests, in seconds. The time interval... The settings are based on the soil's thermal conductivity characteristics and monitoring accuracy requirements.

[0084] Step S6: The heat storage of each layer of soil is accumulated to obtain the total heat storage ΔS of the soil at the target depth;

[0085] The total heat storage capacity ΔS of the soil is obtained by summing the heat storage capacity of each soil layer above the reference depth, as shown in the following formula:

[0086] ;

[0087] in, The heat stored in the i-th soil layer during the time interval is denoted as N, where N is the number of soil layers above the reference depth.

[0088] Step S7: Calculate the soil heat flux profile at any target depth based on the total heat storage ΔS of the soil at the target depth. .

[0089] Soil heat flux profile at any target depth The calculation is as follows:

[0090] ;

[0091] in, Indicates reference depth Heat flux profile. This indicates the total heat storage capacity of the soil.

[0092] And because Then any target depth Soil heat flux profile .

[0093] The following is an application embodiment of the present invention, which uses a soil heat flux profile measurement method based on AH-DTS technology designed in this invention to perform in-situ heat flux measurement on soil at a certain site:

[0094] Step 1: Select observation points at the test site, manually excavate a test pit with a diameter of 1 m and a depth of 30 m, collect undisturbed soil samples at different depths in the test pit during the excavation process, and send them to the laboratory for various geotechnical tests such as dry density and particle size analysis to obtain the basic physical parameters of the soil required for subsequent calculations.

[0095] Step 2: Vertically place the fabricated 30m long AH-DTS probe along the test pit into the soil to be tested, and simultaneously place a neutron tube. The neutron tube is used to acquire volumetric water content data of the soil at different depths for in-situ calibration of the AH-DTS sensor. After placement, backfill with in-situ soil in layers and compact.

[0096] The schematic diagram of the AH-DTS probe is shown in the reference diagram. Figure 2 The system includes an internal resistance heating optical cable 8-1, an electrical conductor 8-2, a conduit 8-3, and a heat-shrinkable protective sleeve 8-4. The internal resistance heating optical cable 8-1 is tightly wound in a spiral around the outside of the conduit 8-3. The conduit, around which the internal resistance heating optical cable 8-2 is wound, is completely wrapped with the heat-shrinkable protective sleeve 8-4. The electrical conductor 8-2 connects the internal resistance heating optical cable 8-2 to the intelligent power supply module. The internal resistance heating optical cable is connected to the optical signal acquisition and processing module via an optical fiber patch cord, and the optical signal acquisition and processing module is connected to the intelligent power supply module.

[0097] Step 3: Install the in-situ soil testing system, referring to... Figure 3 The system consists of ten parts: generator 1, transformer 2, computer 3, DTS demodulator 4, temperature calibration box 5, wires 6, optical fiber cable 7, AH-DTS sensor 8, neutron tube 9, and the soil to be measured 10. Each device is connected sequentially according to its functional requirements to form a complete power supply, data acquisition, and processing system.

[0098] Step 4: Before starting the heating, first use the neutron probe to measure the soil volumetric water content profile along the depth; at the same time, connect the AH-DTS probe to the DTS demodulator to collect and record the initial soil temperature profile under natural conditions.

[0099] Step 5: Connect the electrical leads of the AH-DTS probe to the intelligent power supply module, set a constant heating power per unit length (66.35 W / m in this embodiment), and continuously supply power to the probe for 20 minutes for heating. Throughout the heating and cooling period, the optical signal acquisition and processing module needs to continuously and synchronously acquire temperature data. The obtained soil temperature distribution profile along the depth direction is shown below. Figure 4 As shown, Figure 4 (a) in the diagram is a cross-sectional view from 0 to 29.56 m. Figure 4 Figure (b) shows the profile from 0 to 9.7 m. Within the measured depth range, the soil temperature can be divided into a variable temperature zone and a constant temperature zone along the depth direction. Specifically, the 0–9.7 m zone is the variable temperature zone, where the soil temperature changes significantly with depth and time; the 9.7–29.56 m zone is the constant temperature zone, where the soil temperature does not change significantly with depth and time, remaining generally stable. As shown in the figure, the constant temperature zone begins at a depth of approximately 9.7 m. When the depth exceeds this depth, the soil temperature gradient approaches zero, and the corresponding soil heat flux also approaches zero.

[0100] Step Six: Based on the temperature data obtained in Step Five, determine the depth where the soil temperature changes negligibly within the time interval, and set this depth as the reference depth z. ref At this depth, the soil heat flux should satisfy G(z) ref )=0. Therefore, the reference depth in this embodiment is 0. At this depth, the soil heat flux is 0.

[0101] Step 7: Perform in-situ calibration of the AH-DTS sensor using the neutron method to establish T t The correspondence between -θ and the soil volumetric water content along the depth direction is calculated based on this relationship. Figure 5 As shown, Figure 5 (a) in the diagram is a cross-sectional view from 0 to 29.56 m. Figure 5 (b) in the diagram is a cross-sectional view from 0 to 1.00 m; Figure 5 (a) shows that the volumetric water content of the soil generally increases and then decreases along the depth, with the range of 3.5–6.0 m being the range with relatively high volumetric water content; Figure 5 (b) is a magnified view of the 0–1 m shallow soil profile, showing that the volumetric water content of the shallow soil changes significantly over time, while the change is smaller at depths below 1 m. It should be noted that the volumetric water content of frozen soil cannot be directly measured by AH-DTS, and the corresponding depth data for winter is missing.

[0102] Step 8: Based on the soil dry density and particle density obtained in Step 1, calculate the soil porosity, referring to... Figure 6 , Figure 6 (a) in the figure represents the dry density of the soil. Cross-sectional view, Figure 6 (b) in the diagram is a profile of porosity n; and combined with the soil volumetric water content obtained in step seven, refer to... Figure 5 Calculate the volumetric heat capacity of the soil at depths above the reference depth to obtain... Figure 7 A profile showing the distribution of the volumetric heat capacity C of soil along its depth. Figure 7 It can be seen that the variation trend of soil volumetric heat capacity along the depth direction is in good agreement with the distribution of soil dry density.

[0103] Step 9: Divide the soil above the reference depth into several layers along the depth direction. In this example, the sampling point interval of the AH-DTS measuring tube is 1.45 cm. , combined This allows us to determine the number of layers in the excavated soil. Based on this, the average temperature and average volumetric heat capacity of each soil layer are calculated, and the heat storage ΔS of each soil layer is calculated based on the temperature changes of the soil at adjacent time points. i ,get Figure 8 This is a schematic diagram of the heat storage distribution of a single layer of soil with a thickness of 1.45 cm. Figure 8 (a) in the diagram is a schematic diagram of the soil heat storage distribution on June 28, 2019. Figure 8 (b) shows the distribution of soil heat storage on October 10, 2019. It should be noted that when calculating the heat flux profile, the soil temperature and volumetric heat capacity on March 19, 2019, were used as initial values ​​to calculate the heat flux profiles for June 28, 2019, and October 30, 2019. Therefore, the time intervals ∆t between the two tests on June 28, 2019, and October 30, 2019, are 8722192 s and 10724125 s, respectively. Subsequently, the heat storage of each soil layer above the reference depth is accumulated to obtain the total soil heat storage ΔS at the target depth.

[0104] Step 10: Under the condition that the soil heat flux is 0 at the reference depth, the calculated total heat storage of the soil is the soil heat flux value at the target depth, thus obtaining the distribution profile of soil heat flux along the depth direction, realizing in-situ continuous measurement of the soil heat flux profile. The results are as follows: Figure 9 As shown, Figure 9 (a) in the figure is a soil heat flux profile on June 28, 2019. Figure 9 (b) is a soil heat flux profile on October 10, 2019; it can be seen that the method can effectively obtain the continuous distribution of soil heat flux along the depth direction under different seasonal conditions, and is suitable for in-situ continuous measurement of soil heat flux.

[0105] 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. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for determining soil heat flux profiles based on AH-DTS technology, characterized in that, For the target soil, perform the following steps S1-S7 to complete the determination of the soil heat flux profile at any target depth: Step S1: Sampling is performed on the target soil. AH-DTS logging tubes are used to obtain basic physical data of the soil at different depths and times, including soil temperature. The corresponding volumetric water content θ is then obtained, and the dry density of the soil is determined through geotechnical testing. Soil particle density ; Step S2: Based on the soil temperature at different depths and times, select a depth where the soil temperature changes negligibly with time. At this depth, the heat flux is zero, and this depth is determined as the reference depth. ; Step S3: Based on soil dry density Soil particle density And the volumetric water content θ, calculate the volumetric heat capacity C of the soil at each depth; Step S4: Set the reference depth The soil mass above is divided into N layers along the depth direction. Calculate the average temperature of each layer. Average volumetric heat capacity ; Step S5: Based on the average temperature of each soil layer during the time interval between the two tests. Average volumetric heat capacity Calculate the heat storage Δ of each soil layer during the time interval. ; Step S6: The heat storage of each layer of soil is accumulated to obtain the total heat storage ΔS of the soil at the target depth; Step S7: Calculate the soil heat flux profile at any target depth based on the total heat storage ΔS of the soil at the target depth. .

2. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, The specific steps of step S1 are as follows: Step S1.1: For the target soil, use a ring sampler to take samples at different depths in the soil test pit to obtain soil samples, and conduct various preset geotechnical tests to determine the dry density of the soil. Soil particle density ; Step S1.2: Heat the soil sample and calculate the temperature rise as follows: ； In the formula, T t T represents the temperature rise, in °C; T(t) represents the sensor temperature at heating time t, in °C; T0 represents the initial temperature of the target soil, in °C; and Q represents the heating power per unit length, in W·m. -1 λ is the thermal conductivity of the target soil, with units of W·m. -1 ·K -1 d is T t – The intercept of the lnt linear regression curve, in °C; Step S1.3: Based on the temperature rise value T t Calculate the soil temperature and volumetric water content θ of the target soil: ； In the formula, θ is the volumetric water content of the soil (m³). -3 m -3 A, B, and D are constants related to the soil type, where parameters A, B, and D are determined by T. t The fitting results of the –θ calibration experiment were obtained.

3. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, The specific method for step S2 is as follows: For the target soil mass, a threshold is set for the change in soil temperature over time. The depth corresponding to the change in soil temperature over time that is less than the threshold is considered the depth where the change in soil temperature over time is negligible. ; At this depth The heat flux profile satisfies ,by As a reference depth.

4. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, The volumetric heat capacity of the soil in step S3 is calculated according to the following formula: ； In the formula, C represents the volumetric heat capacity of the soil, ρ d This refers to the dry density of the soil, expressed in g / cm³. 3 , ρ s This refers to the density of soil particles, expressed in g / cm³. 3 C s This refers to the volumetric heat capacity of soil particles, expressed in J / (m³). 3 K), its value is 1.26 × 10 6 J / (m 3 K), θ is the volumetric water content, in cm³. 3 / cm 3 C w This refers to the volumetric heat capacity of water, expressed in J / (m³). 3 K), its value is 4.2 × 10 6 J(m) 3 K), where n is the porosity of the soil.

5. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, In step S4, the reference depth is... The soil above is divided into N layers, and the thickness of each layer is... ,in, According to target depth With reference depth The distance between the layers and the number of layers N are determined and adjusted according to the sampling point interval or measurement accuracy requirements; the average temperature of each soil layer is calculated. Average volumetric heat capacity .

6. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, In step S5, the heat storage Δ of the i-th soil layer during the time interval is... As shown in the following formula: ； In the formula, and Let z be the average volumetric heat capacity of the i-th soil layer at times t+∆t and t, respectively, and let z be the average volumetric heat capacity of the soil layer above and below the i-th layer. i Let be the depth of the i-th soil layer. and Δt and Δt are the average temperatures of the i-th soil layer at times t+∆t and t, respectively. The values ​​are the average temperatures of the upper and lower layers of the soil layer. ∆t is the time interval between the two tests, in seconds.

7. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, The total heat storage ΔS of the soil in step S6 is obtained by summing the heat storage of each soil layer above the reference depth, as shown in the following formula: ； in, The heat stored in the i-th soil layer during the time interval is denoted as N, where N is the number of soil layers above the reference depth.

8. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, The soil heat flux profile at any target depth mentioned in step S7 The calculation is as follows: ； in, Indicates reference depth Heat flux profile. This indicates the total heat storage capacity of the soil. And because Then any target depth Soil heat flux profile .

9. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, The continuous spatial distribution information of soil temperature is obtained by using the AH-DTS measuring tube, thereby realizing the in-situ continuous measurement of soil heat flux profile.

10. The method for determining soil heat flux profiles based on AH-DTS technology according to claim 1, characterized in that, The time interval The settings are based on the soil's thermal conductivity characteristics and monitoring accuracy requirements.

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