Method and system for monitoring preferential flow in frozen soil based on soil temperatures of different depths

Abstract

The invention provides a method and system for monitoring preferential flow in frozen soil based on soil temperatures of different depths, and the method comprises the steps: selecting a date when the temperature of at least one layer of soil is lower than 0 DEG C, and the date is a freezing period; deleting soil layers with daily soil temperature difference lower than a threshold value to obtain statistical soil layers; the date is calculated, and the moment when the soil temperature of each layer of depth reaches the maximum value is determined; deleting the date when the highest temperature value of the surface layer of the soil layer is less than 0 DEG C to obtain the processed date; and comparing the moments when the temperatures of the two adjacent layers of soil are maximum, and judging the priority flow. According to the method, the preferential flow is identified by analyzing the long-term soil temperatures at different depths and comparing the time when the peak values of the soil temperatures at different depths appear, so that the influence of the preferential flow on the hydrothermal characteristics of the soil and the influence factors thereof can be further analyzed.

Description

Technical Field

[0001] The present invention belongs to the technical field of frozen soil detection, and in particular, relates to a method and system for monitoring preferential flow in frozen soil based on soil temperatures at different depths. Background Art

[0002] Preferential flow has an important influence on the energy and water dynamics in frozen soil. However, due to the limitations of observation methods, existing soil moisture sensors can only monitor liquid soil moisture. Therefore, it is impossible to directly use long-term observations of soil moisture to identify preferential flow in frozen soil. It is difficult to accurately quantify the impact of preferential flow on water migration and energy transfer and understand its occurrence mechanism.

[0003] There are four main types of energy exchange in the soil, namely: thermal convection along the temperature gradient in the soil; energy exchange between the soil and the external environment; energy release and absorption caused by water phase change; and energy transfer caused by water migration. Due to the diurnal variation of solar radiation, the temperature of the shallow soil will show periodic changes. During the day, the surface energy is greater than that of the deep soil, and energy is transferred from the surface to the deep layer. However, it takes a certain amount of time for energy to be transferred from the surface to the deep layer, resulting in the time when the soil temperature peak gradually lags behind with increasing depth.

[0004] However, if there are large pores in frozen soil, the water from the melting snow and frozen soil on the surface will directly reach the deep soil through the large pores and release heat in the deep layer. The movement of soil water in frozen soil is accompanied by the phase change of water, and the specific heat capacity of water is much greater than that of soil, so even a small amount of water movement will cause a significant change in soil temperature. When preferential flow occurs in frozen soil, the deep soil will receive additional energy inflow, causing the soil temperature peak to appear earlier. Therefore, water movement can be analyzed by monitoring soil temperature.

[0005] Due to the harsh natural environment and low temperature, traditional monitoring methods require field experiments to observe preferential flow in frozen soil, and can only obtain preferential flow characteristics during the experiment. The present invention proposes a method for identifying preferential flow in frozen soil by monitoring soil temperature at different depths. By deploying soil temperature sensors in the field in advance and monitoring them for a long time, the long-term characteristics of preferential flow can be obtained without the need for maintenance. Summary of the invention

[0006] In view of the defects in the prior art, the object of the present invention is to provide a method and system for monitoring preferential flow in frozen soil based on soil temperatures at different depths.

[0007] A method for monitoring preferential flow in frozen soil based on soil temperatures at different depths provided by the present invention comprises:

[0008] Step S1: selecting a date when at least one layer of soil temperature is below 0 degrees Celsius as a freezing period;

[0009] Step S2: Delete the soil layers whose daily soil temperature difference is lower than the threshold value to obtain statistical soil layers;

[0010] Step S3: Calculate the date of the statistical soil layer as the statistical date, and determine the time when the maximum soil temperature appears at each depth of the layer;

[0011] Step S4: Delete the date when the maximum value of the soil surface temperature is less than 0 degrees Celsius to obtain the processed date;

[0012] Step S5: Compare the time when the maximum temperature of two adjacent layers of soil appears on the processed date to determine the priority flow.

[0013] Preferably, the temperature of the soil at time t at depth z is

[0014] Wherein, T represents temperature;

[0015] t represents time;

[0016] z represents depth;

[0017] d represents the feature depth;

[0018] A represents the average soil temperature in each cycle;

[0019] ω represents the angular frequency;

[0020] τ represents the period;

[0021] φ represents a phase constant.

[0022] The feature depth

[0023] Among them, α T represents the thermal diffusivity of soil.

[0024] Preferably, the heat transfer time lag between two adjacent layers of soil in step S5 is

[0025] Among them, τ represents the period;

[0026] α T Indicates soil thermal diffusion coefficient, less than 36cm -2 h -1 ;

[0027] Δz represents the distance between two adjacent soil temperature measurement depths;

[0028] Δz is 10cm, 15cm or 20cm.

[0029] Preferably, the soil temperature difference in step S2 is the difference between the maximum and minimum soil temperatures of each day.

[0030] The threshold value is 0.1 degrees Celsius.

[0031] The angular frequency ω=2π / τ.

[0032] The period τ is 24 hours.

[0033] Preferably, in step S5, the order of the occurrence of the maximum values ​​of the lower soil layer and the upper soil layer is determined. If they are earlier or simultaneous, the priority flow occurs and the date is recorded; if they are later, the priority flow does not occur and the determination continues for the next date.

[0034] According to the present invention, a preferential flow monitoring system in frozen soil based on soil temperatures at different depths is provided, comprising:

[0035] Module M1: Select the date when at least one layer of soil temperature is below 0 degrees Celsius as the freezing period;

[0036] Module M2: Delete the soil layers with daily soil temperature difference below the threshold to obtain statistical soil layers;

[0037] Module M3: Calculate the date of the statistical soil layer as the statistical date, and determine the time when the maximum soil temperature appears at each depth of the layer;

[0038] Module M4: Delete the date when the maximum value of the soil surface temperature is less than 0 degrees Celsius to obtain the processed date;

[0039] Module M5: Compare the moments when the maximum soil temperature appears in two adjacent layers on the processed date to determine the priority flow.

[0040] Preferably, the temperature of the soil at time t at depth z is

[0041] Wherein, T represents temperature;

[0042] t represents time;

[0043] z represents depth;

[0044] d represents the feature depth;

[0045] A represents the average soil temperature in each cycle;

[0046] ω represents the angular frequency;

[0047] τ represents the period;

[0048] Represents the phase constant.

[0049] The feature depth

[0050] Among them, α T represents the thermal diffusivity of soil.

[0051] Preferably, the heat transfer time lag between two adjacent layers of soil in the module M5 is

[0052] Among them, τ represents the period;

[0053] α T Indicates soil thermal diffusion coefficient, less than 36cm -2 h -1 ;

[0054] Δz represents the distance between two adjacent soil temperature measurement depths;

[0055] Δz is 10cm, 15cm or 20cm.

[0056] Preferably, the soil temperature difference in the module M2 is the difference between the maximum and minimum soil temperatures of each day.

[0057] The threshold value is 0.1 degrees Celsius.

[0058] The angular frequency ω=2π / τ.

[0059] The period τ is 24 hours.

[0060] Preferably, the module M5 determines the order of the occurrence of the maximum values ​​of the lower soil layer and the upper soil layer. If they are earlier or simultaneous, the priority flow occurs and the date is recorded; if they are later, the priority flow does not occur and the next date is determined.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] 1. The present invention adopts a soil temperature sensor to replace the traditional soil moisture sensor to solve the problem that the soil moisture sensor cannot be applied to frozen soil where the temperature and water phase change dramatically, and thus cannot monitor the preferential flow, thereby realizing the long-term observation of the preferential flow in frozen soil and analyzing its influence on the hydrothermal characteristics of the frozen soil.

[0063] 2. The present invention solves the problem that dyeing experiments and geophysical methods cannot monitor preferential flow in frozen soil for a long time by analyzing long-term soil temperature data and the time when soil temperature peaks occur at different depths, and simplifies the judgment process.

[0064] 3. The present invention compares the moments when soil temperature peaks occur at different depths to identify preferential flow, thereby being able to further analyze the impact of preferential flow on soil hydrothermal characteristics and its influencing factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0066] Figure 1 Schematic diagram of the process of preferential flow monitoring method in frozen soil based on soil temperature at different depths.

[0067] Figure 2 Schematic diagram of the concept of preferential flow monitoring in frozen soil based on soil temperature at different depths. DETAILED DESCRIPTION

[0068] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0069] According to a method for monitoring preferential flow in frozen soil based on soil temperatures at different depths provided by the present invention, Figure 1 As shown, the specific steps are as follows:

[0070] Step S1: Select a date when at least one layer of soil temperature is below 0 degrees Celsius to determine the freezing period, and this date is the freezing period.

[0071] Traditional methods mostly use soil moisture changes to identify preferential flow, but they are not applicable to frozen soils where temperature and water phase change dramatically. Using soil temperature is more suitable for long-term observation of preferential flow in the field, so as to analyze its impact on the hydrothermal characteristics of frozen soils.

[0072] According to the soil heat transfer equation, the change of soil temperature at any time and depth can be calculated by the following formula:

[0073]

[0074] Where: T represents temperature;

[0075] t is time;

[0076] z is the depth;

[0077] d is the feature depth,

[0078] Where: α T is the thermal diffusivity of soil.

[0079] A represents the average soil temperature in each cycle;

[0080] ω is the angular frequency (=2π / τ, h -1 );

[0081] τ is the period (e.g. 24 hours);

[0082] is the phase constant.

[0083] Step S2: Delete the soil layers whose daily soil temperature difference (i.e., the difference between the maximum and minimum soil temperatures of each day) is lower than the threshold (0.1 degrees Celsius) to obtain statistical soil layers to reduce the impact of instrument measurement errors on the results.

[0084] Step S3: Calculate the date of the statistical soil layer (i.e., the soil temperature difference is greater than 0.1 degrees Celsius) as the statistical date, and determine the time when the maximum soil temperature appears at each depth.

[0085] Step S4: Delete the dates with the maximum surface temperature less than 0 degrees Celsius to obtain processed dates to ensure that there may be snowmelt or surface frozen soil melting.

[0086] Step S5: Compare the time when the maximum temperature of two adjacent layers of soil appears on the processed date, and determine the order of the time when the maximum value of the lower soil layer and the upper soil layer appears. If it is earlier or at the same time, the priority flow occurs and the date is recorded; if it is later, the priority flow does not occur and the next date is determined.

[0087] The heat transfer time lag between two adjacent layers of soil, that is, the time interval between the peak values ​​of the temperature of two adjacent layers of soil, can be calculated by the following formula:

[0088]

[0089] Where: Δz is the distance between two adjacent soil temperature measurement depths (10cm, 15cm and 20cm). The thermal diffusion coefficient of the soil is less than 36cm -2 h -1 , so the soil heat transfer time lag between any adjacent soil layers is greater than 3.6 hours (much greater than the 30-minute resolution of soil temperature monitoring).

[0090] Whether preferential flow occurs can be identified simply by comparing the moment when the maximum soil temperature occurs. Compared with analyzing the entire soil temperature time series to identify preferential flow, this greatly reduces the complexity of the analysis and simplifies the judgment process.

[0091] The present invention also provides a system for monitoring preferential flow in frozen soil based on soil temperatures at different depths. The system for monitoring preferential flow in frozen soil based on soil temperatures at different depths can be realized by executing the process steps of the method for monitoring preferential flow in frozen soil based on soil temperatures at different depths, that is, those skilled in the art can understand the method for monitoring preferential flow in frozen soil based on soil temperatures at different depths as a preferred implementation of the system for monitoring preferential flow in frozen soil based on soil temperatures at different depths.

[0092] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, the system and its various devices, modules, and units provided by the present invention can be completely realized in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps to realize the same functions. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0093] According to the present invention, a preferential flow monitoring system in frozen soil based on soil temperatures at different depths is provided, comprising:

[0094] Module M1: Select the date when at least one layer of soil temperature is below 0 as the freezing period;

[0095] Module M2: Delete the soil layers with daily soil temperature difference below the threshold to obtain statistical soil layers;

[0096] Module M3: Calculate the date of the statistical soil layer as the statistical date, and determine the time when the maximum soil temperature appears at each depth of the layer;

[0097] Module M4: Delete the date when the maximum value of the soil surface temperature is less than 0 degrees Celsius to obtain the processed date;

[0098] Module M5: Compare the moments when the maximum soil temperature appears in two adjacent layers on the processed date to determine the priority flow.

[0099] In more preferred embodiments, the temperature of the soil at time t and depth z is

[0100] Wherein, T represents temperature;

[0101] t represents time;

[0102] z represents depth;

[0103] d represents the feature depth;

[0104] A represents the average soil temperature in each cycle;

[0105] ω represents the angular frequency;

[0106] τ represents the period;

[0107] Represents the phase constant.

[0108] The feature depth

[0109] Among them, α T represents the thermal diffusivity of soil.

[0110] In more preferred embodiments, the heat transfer time lag between two adjacent layers of soil in the module M5 is

[0111] Among them, τ represents the period;

[0112] α T Indicates soil thermal diffusion coefficient, less than 36cm -2 h -1 ;

[0113] Δz represents the distance between two adjacent soil temperature measurement depths;

[0114] Δz is 10cm, 15cm or 20cm.

[0115] In more preferred examples, the soil temperature difference in the module M2 is the difference between the maximum and minimum soil temperatures of each day.

[0116] The threshold value is 0.1 degrees Celsius.

[0117] The angular frequency ω=2π / τ.

[0118] The period τ is 24 hours.

[0119] In more preferred examples, the module M5 determines the order of occurrence of the maximum values ​​of the lower soil layer and the upper soil layer. If they are earlier or simultaneous, the priority flow occurs and the date is recorded; if they are later, the priority flow does not occur and the next date is determined.

[0120] like Figure 2 As shown, the present invention identifies preferential flow by comparing the time when the soil temperature peaks at different depths appear, so as to further analyze the influence of preferential flow on soil hydrothermal characteristics and its influencing factors. Simultaneous monitoring of soil temperature and moisture can comprehensively analyze the influence of preferential flow on soil hydrothermal conditions, and help to clarify the occurrence mechanism of preferential flow at different stages of the entire freeze-thaw cycle.

[0121] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for monitoring preferential flow in frozen soil based on soil temperature at different depths, characterized in that: include: Step S1: selecting a date when at least one layer of soil temperature is below 0 degrees Celsius as a freezing period; Step S2: Delete the soil layers whose daily soil temperature difference is lower than the threshold value to obtain statistical soil layers; Step S3: Calculate the date of the statistical soil layer as the statistical date, and determine the time when the maximum soil temperature appears at each depth of the layer; Step S4: Delete the date when the maximum value of the soil surface temperature is less than 0 degrees Celsius to obtain the processed date; Step S5: Compare the time when the maximum temperature of two adjacent layers of soil appears on the processed date to determine the priority flow.

2. The method for monitoring preferential flow in frozen soil based on soil temperature at different depths according to claim 1, characterized in that: The temperature of the soil at depth z at time t is T(z,t), Wherein, T represents temperature; t represents time; z represents depth; d represents the feature depth; A represents the average soil temperature in each cycle; ω represents the angular frequency; τ represents the period; represents the phase constant; The feature depth Among them, α T represents the thermal diffusivity of soil.

3. The method for monitoring preferential flow in frozen soil based on soil temperature at different depths according to claim 1, characterized in that: The heat transfer time lag between two adjacent layers of soil in step S5 is: Among them, τ represents the period; α T Indicates soil thermal diffusion coefficient, less than 36cm -2 h -1 ; Δz represents the distance between two adjacent soil temperature measurement depths; Δz is 10cm, 15cm or 20cm.

4. The method for monitoring preferential flow in frozen soil based on soil temperature at different depths according to claim 2, characterized in that: The soil temperature difference in step S2 is the difference between the maximum and minimum soil temperatures of each day; The threshold is 0.1 degrees Celsius; The angular frequency ω=2π / τ; The period τ is 24 hours.

5. The method for monitoring preferential flow in frozen soil based on soil temperature at different depths according to claim 1, characterized in that: In step S5, the order of the occurrence of the maximum values ​​of the lower soil layer and the upper soil layer is determined. If they are earlier or simultaneous, the priority flow occurs and the date is recorded; if they are later, the priority flow does not occur and the next date is determined.

6. A system for monitoring preferential flow in frozen soil based on soil temperature at different depths, characterized in that: include: Module M1: Select the date when at least one layer of soil temperature is below 0 degrees Celsius as the freezing period; Module M2: Delete the soil layers with daily soil temperature difference below the threshold to obtain statistical soil layers; Module M3: Calculate the date of the statistical soil layer as the statistical date, and determine the time when the maximum soil temperature appears at each depth of the layer; Module M4: Delete the date when the maximum value of the soil surface temperature is less than 0 degrees Celsius to obtain the processed date; Module M5: Compare the moments when the maximum soil temperature appears in two adjacent layers on the processed date to determine the priority flow.

7. The system for monitoring preferential flow in frozen soil based on soil temperature at different depths according to claim 6, characterized in that: The temperature of the soil at depth z at time t is T(z,t), Wherein, T represents temperature; t represents time; z represents depth; d represents the feature depth; A represents the average soil temperature in each cycle; ω represents the angular frequency; τ represents the period; represents the phase constant; The feature depth Among them, α T represents the thermal diffusivity of soil.

8. The system for monitoring preferential flow in frozen soil based on soil temperature at different depths according to claim 6, characterized in that: The heat transfer time lag between two adjacent soil layers in module M5 is: Among them, τ represents the period; α T Indicates soil thermal diffusion coefficient, less than 36cm -2 h -1 ; Δz represents the distance between two adjacent soil temperature measurement depths; Δz is 10cm, 15cm or 20cm.

9. The system for monitoring preferential flow in frozen soil based on soil temperature at different depths according to claim 7, characterized in that: The soil temperature difference in the module M2 is the difference between the maximum and minimum soil temperatures of each day; The threshold is 0.1 degrees Celsius; The angular frequency ω=2π / τ; The period τ is 24 hours.

10. The system for monitoring preferential flow in frozen soil based on soil temperature at different depths according to claim 6, characterized in that: The module M5 determines the order of the times when the maximum values ​​of the lower and upper soil layers appear. If they are earlier or simultaneous, the priority flow occurs and the date is recorded; if they are later, the priority flow does not occur and the next date is determined.

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