CN113125497B - Method for dividing soil moisture evaporation stage based on soil temperature - Google Patents
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Abstract
The invention discloses a method for dividing soil moisture evaporation stages based on soil temperature, which comprises the following steps: preparing a heat pulse sensor; calibrating the probe distance of the heat pulse sensor; installing a heat pulse sensor in soil to be measured, measuring the soil temperature within a certain time, starting a heating needle on the heat pulse sensor, measuring and recording the change conditions of the soil temperature in the soil heating process and after heating, and calculating to obtain the soil heat conductivity, the volumetric heat capacity and the thermal diffusion coefficient; calculating the thickness of the dry soil layer according to the distance between the thermal conductivity of the soil and the probes; setting a critical value of the thickness of the dry soil layer to represent that evaporation enters a second stage from a first stage; and calculating a correlation coefficient between the standard deviation of the soil temperature gradient and the thickness of the dry soil layer, selecting the parameter with the largest correlation coefficient as the parameter for distinguishing the evaporation stage of the soil moisture, and obtaining a critical value of the parameter for distinguishing the evaporation stage. According to the technical scheme, the evaporation stage can be rapidly distinguished according to the temperature values of the soil with different depths within a certain time, time and labor are saved, and the hydrologic cycle, the climate mode and the process of the land ecosystem can be accurately described.
Description
Technical Field
The invention relates to monitoring of a near-surface soil hydrothermal process, in particular to a method for dividing soil moisture evaporation stages based on soil temperature.
Background
Soil moisture evaporation is the process by which water in soil is changed from liquid to gas and diffused into the atmosphere, and is an important component of surface energy balance and hydrologic cycle. Soil moisture evaporation is an important component in Soil Plant Air Continuum (SPAC), and is concerned by multiple subjects such as soil science, agriculture, forestry and meteorology. Most of the existing methods for measuring evaporation assume that latent heat of evaporation occurs on the surface of soil, neglect the position and the dynamic state of soil moisture evaporation, and have less research on the internal mechanism of soil moisture evaporation, thereby misinterpreting the humidity condition of near-surface soil and influencing the cognition of large-scale hydrology and climate modes. In fact, the soil moisture evaporation process is divided into three phases: in the first stage, after rainfall or irrigation, water evaporation occurs on the surface of soil, and the evaporation capacity is close to the potential evaporation capacity and is controlled by atmospheric conditions; in the second and third stages, the evaporation on the soil surface is limited by the upward liquid water transport capacity and gas diffusion of the soil, and the evaporation occurs in a certain soil layer on the ground surface and below. Only by really knowing the process and mechanism of soil moisture evaporation and correctly distinguishing the evaporation stage can the hydrologic cycle, climate mode and land ecosystem process be accurately described.
The method for measuring the soil moisture evaporation mainly comprises a micro lysimeter, an air chamber method, a wave-character ratio energy balance and vorticity correlation method and the like, and the micro lysimeter, the air chamber method and the micro wave-character ratio energy balance method can also be used for measuring the soil moisture evaporation under the plant canopy. However, these methods directly measure or indirectly calculate the overall soil moisture evaporation rate, and cannot deeply explore the position of soil moisture evaporation, the evaporation stage and the internal mechanism.
Soil moisture evaporation was confirmed to occur in three distinct phases. Some researchers distinguish evaporation stages by using the reflectivity of the earth surface, some calculate the evaporation stages in the first, second and third stages respectively by a Priestley-Taylor formula and a three-temperature model, and others judge the evaporation stage of soil moisture by a soil moisture characteristic curve, an actual evaporation and potential evaporation ratio or a difference between soil temperature and atmospheric temperature. The method needs more parameters and special instruments and equipment for parameter determination when dividing the stage of soil moisture evaporation, and is not convenient for developing outdoor field and field experiments.
In recent years, a heat pulse technology based on the soil internal heat sensing balance principle can monitor the rate and the occurrence position of soil internal water evaporation, deepens the mechanism cognition of the soil water evaporation process, and is applied to in-situ real-time determination of soil water evaporation in farmlands and woodlands and decomposition research of evaporation. However, the division of the soil moisture evaporation stage is still one of the difficulties restricting the method. Therefore, it is desirable to establish a method for relatively conveniently dividing the soil moisture evaporation stage.
Disclosure of Invention
The invention aims to provide a method for dividing soil moisture evaporation stages based on soil temperature.
The invention discloses a method for dividing soil moisture evaporation stages based on soil temperature, which comprises the following steps: preparing a heat pulse sensor; calibrating the probe distance of the heat pulse sensor; installing a heat pulse sensor in soil to be measured, measuring the soil temperature within a certain time, starting a heating needle on the heat pulse sensor, measuring and recording the change condition of the soil temperature in the soil heating process and after heating, and calculating to obtain the soil heat conductivity, the volumetric heat capacity and the thermal diffusion coefficient; calculating the thickness of the dry soil layer according to the distance between the thermal conductivity of the soil and the probes; setting a critical value of the thickness of the dry soil layer to represent that evaporation enters a second stage from a first stage; and calculating a correlation coefficient between the standard deviation of the soil temperature gradient and the thickness of the dry soil layer, selecting the parameter with the largest correlation coefficient as the parameter for distinguishing the evaporation stage of the soil moisture, and obtaining a critical value of the parameter for distinguishing the evaporation stage.
The invention relates to a method for dividing soil moisture evaporation stages based on soil temperature, wherein the preparation of a heat pulse sensor comprises the following steps: manufacturing a multi-needle heat pulse sensor, wherein the multi-needle heat pulse sensor comprises a vertical rod and nine-needle thermocouples sequentially arranged on the vertical rod, needles 1, 2, 3, 4, 5, 6, 7, 8 and 9 are sequentially arranged from top to bottom, thermocouples for measuring the soil temperature are arranged in the needles 1, 3, 5, 7 and 9, thermocouples and heating wires are arranged in the needles 2, 4, 6 and 8, and the resistivity is 888 omega m-1。
The invention discloses a method for dividing soil moisture evaporation stages based on soil temperature, wherein the step of calibrating the probe distance of a heat pulse sensor comprises the following steps: placing a multi-pin heat pulse sensor in 5g L-1Agar solution (constant volumetric heat capacity, 4.18MJ m)-3℃-1) In the method, the soil thermal property is measured at the constant temperature of 25 ℃, 4 heating needles are sequentially heated at the interval of 1h, the soil temperature is measured in the first 4s, the measuring interval is 1s, the heating needles release heat to agar in the 5 th to 20 th s, meanwhile, the soil temperature of all depths is continuously measured until 180s is finished, the data storage interval is 1s,the temperature probes above and below the heating needle determine and record the temperature change of agar after heating, the temperature change data and the pulse infinite linear heat source model formula of heat conduction are fitted, the volumetric heat capacity and the heating heat quantity of the agar are known, the distance between the heating needle and the upper and lower temperature needles is obtained through final fitting, the distances between all probes are obtained after 4 heating needles are heated in sequence, the whole process is repeated for 10 times, the average value is determined as the distance between the probes, and the pulse infinite linear heat source model formula of heat conduction is as follows:
wherein Δ T (. degree. C.) is a temperature change value, r (m) is a vertical distance of the thermocouple from the linear heat source, and q (J m)-1) Is the heat released by the heating wire per unit length, alpha (m)2 s-1) Is the thermal diffusion coefficient, λ is the thermal conductivity of the soil, equal to the product of α and the volumetric heat capacity (C), Ei (x) is the exponential integral, t0(s) is the length of time the heat pulse is heated.
The invention relates to a method for dividing soil moisture evaporation stages based on soil temperature, wherein a thermal pulse sensor device is used for measuring soil, an uppermost probe is flush with the surface of the soil, the soil temperature is measured in the first 60s of each hour, the measurement interval is 1s, and the average value is recorded; and (3) starting the measurement of the thermal conductivity of the soil 1min after the temperature measurement is finished, starting 1 heating needle each time, measuring for 300s, wherein the 125 th 133s heating needle releases heat to the soil, the storage interval of the soil temperature is also 1s, measuring and recording the change conditions of the soil temperature in the soil heating process and after the soil is heated by using the temperature probes above and below the heating needles, fitting the soil temperature change data with a pulse infinite linear heat source model formula of heat conduction, knowing the probe distance and the heating heat quantity, and finally fitting to obtain the thermal characteristics of the soil, namely the thermal conductivity, the volumetric heat capacity and the thermal diffusion coefficient.
The invention discloses a method for dividing soil moisture evaporation stages based on soil temperature, wherein the step of calculating the thickness of a dry soil layer according to the distance between soil thermal conductivity and a probe comprises the following steps: the formula for calculating the thickness of the dry soil layer is as follows:
ztrans＝zdry+zwet
Ztrans,Zdryand ZwetThickness of the whole soil layer, dry soil layer and wet soil layer, lambdatransThermal conductivity of the entire soil layer, 1-2 pin thermal conductivity value, lambda, measured for a thermal pulse sensordryIs the thermal conductivity of the dry soil layer, is the thermal conductivity of the air-dried soil, lambdawetThe thermal conductivity of the wet soil layer is measured by a thermal pulse sensor, and the thermal conductivity value is 2-3 needles.
The invention relates to a method for dividing the soil moisture evaporation phase based on the soil temperature, wherein T1、T2、T3、T4、T5、T6、T7、T8And T9Respectively representing the soil temperature data measured by 9 probes at a certain time, r1、r2、r3、r4、r5、r6、r7、r8The distances between the 9 probes are indicated, and T is selected1，(T2-T1)/r1，(T2-T1)/r1And (T)3-T2)/r2Standard deviation of or (T)2-T1)/r1Standard deviation from other arbitrary depth temperature gradients, (T)2-T1)/r1、(T3-T2)/r2And (T)4-T3)/r3Standard deviation of or (T)2-T1)/r1、(T3-T2)/r2And taking the standard deviation of the temperature gradient with any depth as a parameter related to the soil temperature, calculating a correlation coefficient between the soil temperature related parameter and the thickness of the dry soil layer, selecting the parameter with the maximum correlation coefficient as the parameter for distinguishing the soil moisture evaporation stage, and obtaining a critical value of the parameter for distinguishing the evaporation stage.
According to the technical scheme, the evaporation stage can be rapidly distinguished according to the temperature values of the soil with different depths within a certain time, time and labor are saved, and the hydrologic cycle, the climate mode and the process of the land ecosystem can be accurately described.
Drawings
FIG. 1 is a schematic diagram of a heat pulse sensor;
FIG. 2 is a graph of daily precipitation during monitoring;
FIG. 3 is a schematic illustration of the change in the thickness of the dry soil layer and the daily precipitation during monitoring;
FIG. 4 is a schematic diagram of the thermal pulse sensor measured multiple depth soil temperature dynamics and daily precipitation;
FIG. 5 is a schematic representation of soil temperature gradient changes at multiple depths during monitoring;
FIG. 6 is a dynamic diagram of the variation of the surface soil temperature and the surface soil temperature gradient of 0-6mm during monitoring and a standard differential diagram between the soil temperature gradients at different depths;
FIG. 7 is a schematic diagram showing the dynamic state of the standard deviation of the temperature gradient of the soil around noon and the thickness of the dry soil layer and the relationship between the standard deviation of the temperature gradient and the thickness of the dry soil layer during the monitoring period;
FIG. 8 is a graph showing the comparison of water evaporation rate and soil moisture evaporation rate during monitoring and the dynamic of the standard deviation between the 3 and 9.6mm soil temperature gradients used to distinguish evaporation stages.
Detailed Description
As shown in fig. 1, 2 and 3, the method for dividing the soil moisture evaporation stage based on the soil temperature of the present invention comprises: preparing a heat pulse sensor; calibrating the probe distance of the heat pulse sensor; installing a heat pulse sensor in soil to be measured, measuring the soil temperature within a certain time, starting a heating needle on the heat pulse sensor, measuring and recording the change conditions of the soil temperature in the soil heating process and after heating, and calculating to obtain the soil heat conductivity, the volumetric heat capacity and the thermal diffusion coefficient; calculating the thickness of the dry soil layer according to the distance between the thermal conductivity of the soil and the probes; setting a critical value of the thickness of the dry soil layer to represent that evaporation enters a second stage from a first stage; and calculating a correlation coefficient between the standard deviation of the soil temperature gradient and the thickness of the dry soil layer, selecting the parameter with the largest correlation coefficient as the parameter for distinguishing the evaporation stage of the soil moisture, and obtaining a critical value of the parameter for distinguishing the evaporation stage.
The invention relates to a method for dividing soil moisture evaporation stages based on soil temperature, wherein the preparation of a heat pulse sensor comprises the following steps: manufacturing a multi-needle heat pulse sensor, wherein the multi-needle heat pulse sensor comprises a vertical rod and nine-needle thermocouples sequentially arranged on the vertical rod, needles 1, 2, 3, 4, 5, 6, 7, 8 and 9 are sequentially arranged from top to bottom, thermocouples for measuring the soil temperature are arranged in the needles 1, 3, 5, 7 and 9, thermocouples and heating wires are arranged in the needles 2, 4, 6 and 8, and the resistivity is 888 omega m-1。
The invention discloses a method for dividing soil moisture evaporation stages based on soil temperature, wherein the step of calibrating the probe distance of a heat pulse sensor comprises the following steps: placing a multi-pin heat pulse sensor in 5g L-1Agar solution (constant volumetric heat capacity, 4.18MJ m)-3℃-1) In the method, the thermal property of the soil is measured at a constant temperature of 25 ℃, 4 heating needles are sequentially heated at an interval of 1h, the soil temperature is measured only in the first 4s, the measurement interval is 1s, the heating needles release heat to the agar in the 5 th to 20 th s, meanwhile, the soil temperature of all depths is continuously measured until 180s is finished, the data storage interval is 1s, the temperature probes above and below the heating pins measure and record the temperature change of agar during heating and after heating, the temperature change data and a heat conduction pulse infinite linear heat source model formula are fitted, the volume heat capacity and the heating heat quantity of the agar are known, the distance between the heating pins and the upper and lower temperature pins is finally obtained through fitting, the distance between all the probes is obtained after 4 heating pins are sequentially heated, the whole process is repeated for 10 times, the average value is determined as the distance between the probes, and the heat conduction pulse infinite linear heat source model formula is as follows:
wherein Δ T (. degree. C.) is a temperature change value, r (m) is a vertical distance of the thermocouple from the linear heat source, and q (J m)-1) Is the heat released by the heating wire per unit length, alpha (m)2 s-1) Is the thermal diffusion coefficient, λ is the thermal conductivity of the soil, equal to the product of α and the volumetric heat capacity (C), Ei (x) is the exponential integral, t0(s) is the length of time the heat pulse is heated.
The invention relates to a method for dividing soil moisture evaporation stages based on soil temperature, wherein a thermal pulse sensor device is used for measuring soil, a probe at the uppermost part is flush with the surface of the soil, the soil temperature is measured in the first 60s of each hour, the measurement interval is 1s, and the average value is recorded; and (3) starting the measurement of the thermal conductivity of the soil 1min after the temperature measurement is finished, starting 1 heating needle each time, measuring for 300s, wherein the 125 th 133s heating needle releases heat to the soil, the storage interval of the soil temperature is also 1s, measuring and recording the change conditions of the soil temperature in the soil heating process and after the soil is heated by using the temperature probes above and below the heating needles, fitting the soil temperature change data with a pulse infinite linear heat source model formula of heat conduction, knowing the probe distance and the heating heat quantity, and finally fitting to obtain the thermal characteristics of the soil, namely the thermal conductivity, the volumetric heat capacity and the thermal diffusion coefficient.
The invention discloses a method for dividing soil moisture evaporation stages based on soil temperature, wherein the step of calculating the thickness of a dry soil layer according to the distance between soil thermal conductivity and a probe comprises the following steps: the formula for calculating the thickness of the dry soil layer is as follows:
ztrans＝zdry+zwet
Ztrans,Zdryand ZwetThickness of the whole soil layer, dry soil layer and wet soil layer, lambdatransThermal conductivity of the entire soil layer, 1-2 pin thermal conductivity value, lambda, measured for a thermal pulse sensordryIs the thermal conductivity of the dry soil layer, is the thermal conductivity of the air-dried soil, lambdawetThermal conductivity of wet soil layer, measured for heat pulse sensor 2-3 pin thermal conductivity value.
The invention relates to a method for dividing the soil moisture evaporation phase based on the soil temperature, wherein T1、T2、T3、T4、T5、T6、T7、T8And T9Respectively representing the soil temperature data measured by 9 probes at a certain time, r1、r2、r3、r4、r5、r6、r7、r8T represents the distance between 9 probes, respectively1，(T2-T1)/r1，(T2-T1)/r1And (T)3-T2)/r2Standard deviation of or (T)2-T1)/r1Standard deviation from other arbitrary depth temperature gradients, (T)2-T1)/r1、(T3-T2)/r2And (T)4-T3)/r3Standard deviation of or (T)2-T1)/r1、(T3-T2)/r2And taking the standard deviation of the temperature gradient with any other depth as a parameter related to the soil temperature, calculating a correlation coefficient between the soil temperature related parameter and the thickness of the dry soil layer, selecting the parameter with the maximum correlation coefficient as a parameter for distinguishing the soil moisture evaporation stage, and obtaining a critical value of the parameter for distinguishing the evaporation stage.
According to the technical scheme, the evaporation stage can be quickly distinguished according to the temperature values of the soil at different depths within a certain time, time and labor are saved, and the hydrologic cycle, the climate mode and the land ecosystem process can be accurately described.
Install 9 needle heat pulse sensors at the artifical camphor pine forest downstream central point in sand and put, the installation is: a small pit is dug by a small shovel, a flat small section is arranged, the 9-pin thermal pulse sensor is installed perpendicular to the section, the 1 pin at the top is just positioned on the surface of soil, only a thin layer of soil is covered, the soil is dug out after the installation is finished and backfilled, and the disturbance to the probe and the soil is reduced as much as possible in the backfilling process.
The soil under the sand land camphor pine forest is sandy soil, the sand grain content of the soil with the surface layer of 0-10cm is 86.8%, and the powder particle content is 13.2%. The measurement time is 20 days in total from 8 months 22 days to 9 months 10 days in 2019, namely from 234 days to 253 days in 2019. The number of days of precipitation during the monitoring period was 9 days, with day 238, 240 and 241 days of precipitation exceeding 5mm, 11.6, 46.4 and 17mm respectively.
The soil temperature dynamics of 9 depths are measured by using a 9-pin heat pulse sensor, and the soil thermal characteristics of 8 soil layers including volumetric heat capacity, heat conductivity and thermal diffusivity are measured according to a method for measuring the soil thermal characteristics by using a heat pulse method, wherein one heating is performed every 1h for releasing heat for soil, and 4 heating pins are required for 4h for releasing heat once. According to formula 2 and formula 3, r in FIG. 1 is used1And r2Thermal conductivity of soil layer Dry soil layer thickness was calculated, where λdryIs 0.376W m-1℃-1，ZtransIs 6mm, lambdatransIs measured as r1Layer soil thermal conductivity, λwetUsing measured r2Thermal conductivity of layer soil, r measured by heat pulse sensor1And r2The thermal conductivity of the layer soil is dynamic, and the thickness dynamic of the dry soil layer is obtained through calculation, namely the figure 3.
It can be seen that the thickness of the dry soil layer varies in relation to the precipitation, and that the thickness of the dry soil layer is approximately 0 at the time of precipitation and for some time thereafter, i.e. no dry soil layer is formed, and as the soil moisture continues to evaporate, the dry soil layer begins to form, i.e. the thickness of the dry soil layer increases, e.g. on day 248, the thickness of the dry soil layer increases to 4.6 mm. Therefore, the soil moisture evaporation stage can be distinguished according to the thickness of the dry soil layer and the precipitation data. Considering that there is some error in the thermal conductivity of the heat pulse measurement, if the thickness of the dry soil layer exceeds 0.5mm, the soil moisture is evaporated into the second stage.
The different degree of depth soil temperature developments of 9 needle heat pulse sensor survey can be influenced by the precipitation, when the precipitation takes place or a period of time afterwards, soil water content is great, the soil temperature day of each layer is relatively poor all less, and difference also less between the different degree of depth soil temperature, along with soil moisture continuous evaporation, when soil moisture evaporation gets into the second stage, the relatively poor increase of top soil temperature day, difference between the different degree of depth soil temperature also increases, difference between the soil temperature gradient also increases (fig. 5). This provides the basis for distinguishing the evaporation stages according to the soil temperature.
FIG. 6 is a graph showing the dynamic of the standard deviation among the surface soil temperature, the surface soil temperature gradient of 0-6mm and the soil temperature gradients of different depths, and it is found that the dynamic of the standard deviation among the soil temperature gradients of different depths and the thickness of the dry soil layer have higher consistency, and the thickness of the dry soil layer corresponds to the larger standard deviation. Since the difference between the temperature gradients of the soil at different depths at night is small, the temperature gradient close to the noon time is extracted, the correlation between the temperature gradient and the thickness of the dry soil layer at the same time is calculated, and the index related to the soil temperature with the highest correlation is selected for distinguishing the soil moisture evaporation stage (fig. 7), namely, the correlation between the standard deviation of the temperature gradients at 3mm and 9.6mm and the thickness of the dry soil layer is highest (R is the standard deviation of the temperature gradients at 3mm and 9.6 mm)20.762) the standard deviation of the soil temperature gradients of 3 and 9.6mm at a dry soil layer thickness of 0.5 was used for the evaporation stage differentiation, i.e. the threshold was 36.68.
Soil moisture evaporation (E)s) Evaporate from the water (E)w) Can be used to distinguish evaporation stages, E when evaporation is in the first stagesAnd EwClose, when evaporation enters the second stage, EsIs less than Ew. As can be seen in FIG. 8, EsLess than EwIs consistent with a period of SD greater than the threshold value of 36.68, confirming the accuracy of the soil evaporation stage partitioning method identified in this patent based on soil temperature.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (2)
1. A method for dividing soil moisture evaporation stages based on soil temperature is characterized by comprising the following steps: preparing a heat pulse sensor; calibrating the probe distance of the heat pulse sensor; installing a heat pulse sensor in the soil to be measured, measuring the soil temperature within a certain time, and startingThe heating needle on the heat pulse sensor is used for measuring and recording the change condition of the soil temperature in the soil heating process and after heating, and calculating to obtain the soil thermal conductivity, the volume thermal capacity and the thermal diffusion coefficient; calculating the thickness of the dry soil layer according to the distance between the thermal conductivity of the soil and the probes; setting a critical value of the thickness of the dry soil layer to represent that evaporation enters a second stage from a first stage; calculating a correlation coefficient between the standard deviation of the soil temperature gradient and the thickness of the dry soil layer, selecting the maximum correlation coefficient as a parameter for distinguishing the evaporation stage of the soil moisture, and obtaining a critical value of the parameter for distinguishing the evaporation stage, wherein the preparation of the heat pulse sensor comprises the following steps: manufacturing a multi-needle heat pulse sensor, wherein the multi-needle heat pulse sensor comprises a vertical rod and nine-needle thermocouples sequentially arranged on the vertical rod, needles 1, 2, 3, 4, 5, 6, 7, 8 and 9 are sequentially arranged from top to bottom, thermocouples for measuring the soil temperature are arranged in the needles 1, 3, 5, 7 and 9, thermocouples and heating wires are arranged in the needles 2, 4, 6 and 8, and the resistivity is 888 omega m-1Calibrating the probe spacing of the heat pulse sensor comprises: placing a multi-pin heat pulse sensor in 5g L-1In the agar solution, soil thermal characteristics are measured at a constant temperature of 25 ℃, 4 heating needles are sequentially heated, the interval is 1h, the soil temperature is only measured in the first 4s, the measuring interval is 1s, the heating needles release heat into agar in the 5 th to 20 th s, meanwhile, the soil temperature of all depths is continuously measured until 180s is finished, the data storage interval is 1s, the temperature probes above and below the heating needles measure and record the temperature change between the heated agar and the heated agar, the temperature change data and a pulse infinite linear heat source model formula of heat conduction are fitted, the volume heat capacity and the heating heat quantity of the agar are known, the distance between the heating needles and the upper and lower temperature needles is finally fitted, the distances between all the probes are obtained after the 4 heating needles are sequentially heated, the whole process is repeated for 10 times, and the average value is determined as the distance between the probes, the impulse infinite linear heat source model formula of heat conduction is as follows:
wherein Δ T (. degree. C.) is a temperature change value, r (m) is a vertical distance of the thermocouple from the linear heat source, and q (J m)-1) Is the heat released by the heating wire per unit length, alpha (m)2s-1) Is the thermal diffusion coefficient, λ is the thermal conductivity of the soil, equal to the product of α and the volumetric heat capacity (C), Ei (x) is the exponential integral, t0(s) the thermal pulse heating time length, aligning the thermal pulse sensor device to the soil to be measured, the uppermost probe to the surface of the soil, measuring the soil temperature in the first 60s per hour, measuring the interval of 1s and recording the average value; 1min after the temperature measurement is finished, measuring the thermal conductivity of the soil, starting 1 heating needle each time, measuring the time for 300s, wherein the 125 th 133s heating needle releases heat to the soil, the storage interval of the soil temperature is also 1s, measuring and recording the change conditions of the soil temperature in the soil heating process and after the soil is heated by using the temperature probes above and below the heating needles, fitting the soil temperature change data with a pulse infinite linear heat source model formula of heat conduction, knowing the distance between the probes and the heating heat quantity, finally fitting to obtain the thermal characteristics of the soil, namely the thermal conductivity, the volumetric heat capacity and the thermal diffusion coefficient, and calculating the thickness of the dry soil layer according to the distance between the thermal conductivity of the soil and the probes comprises the following steps: the formula for calculating the thickness of the dry soil layer is as follows:
ztrans＝zdry+zwet
Ztrans,Zdryand ZwetThickness of the whole soil layer, dry soil layer and wet soil layer, lambdatransThermal conductivity of the entire soil layer, 1-2 pin thermal conductivity value, lambda, measured for a thermal pulse sensordryIs the thermal conductivity of the dry soil layer, is the thermal conductivity of the air-dried soil, lambdawetThe thermal conductivity of the wet soil layer is measured by a thermal pulse sensor, and the thermal conductivity value is 2-3 needles.
2. The method for staging soil moisture evaporation based on soil temperature as claimed in claim 1 wherein T is1、T2、T3、T4、T5、T6、T7、T8And T9Respectively representing the soil temperature data measured by 9 probes at a certain time, r1、r2、r3、r4、r5、r6、r7、r8T represents the distance between 9 probes, respectively1，(T2-T1)/r1，(T2-T1)/r1And (T)3-T2)/r2Standard deviation of or (T)2-T1)/r1Standard deviation from other arbitrary depth temperature gradients, (T)2-T1)/r1、(T3-T2)/r2And (T)4-T3)/r3Standard deviation of or (T)2-T1)/r1、(T3-T2)/r2And taking the standard deviation of the temperature gradient with any depth as a parameter related to the soil temperature, calculating a correlation coefficient between the soil temperature related parameter and the thickness of the dry soil layer, selecting the parameter with the maximum correlation coefficient as the parameter for distinguishing the soil moisture evaporation stage, and obtaining a critical value of the parameter for distinguishing the evaporation stage.
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