Method and equipment for measuring forest evapotranspiration

Abstract

The invention relates to the technical field of forest evapotranspiration measurement, and discloses a forest evapotranspiration measurement method and device. The measuring device comprises a sensor combination of which the installation position is adaptive to the height of a forest canopy, a soil short-wave radiation sensing element adaptive to the height of forest surface soil, and a soil temperature and humidity sensing element adaptive to the height of forest lower soil. The method comprises the following steps: calculating canopy transpiration based on energy balance according to canopy short-wave radiation information, air temperature information and leaf surface average temperature information; acquiring soil short-wave radiation information based on the soil short-wave radiation sensing element, acquiring soil temperature and humidity information based on the soil temperature and humidity sensing element, and calculating under-forest soil evaporation according to the soil short-wave radiation information and the soil temperature and humidity information based on a soil hydrothermal dynamic state; the forest evapotranspiration is calculated based on the double-source evapotranspiration theory according to the canopy evapotranspiration and the under-forest soil evapotranspiration, and the method is accurately applicable to different forest ecological vegetation types and different soil texture conditions.

Description

Technical Field

[0001] The present application relates to the technical field of forest evapotranspiration measurement, and in particular to a method and device for measuring forest evapotranspiration. Background Art

[0002] Evapotranspiration in forest ecosystems plays a vital role in water cycle and energy balance. It not only regulates the water and heat exchange inside and around the forest, but also affects the regional climate and the health of the ecosystem. Evapotranspiration is closely related to the energy balance of forest ecosystems, especially to changes in radiation, temperature and humidity. During evapotranspiration, the evaporation and transpiration of water absorb a large amount of latent heat, thus affecting the temperature of the forest surface. This process is one of the important ways of heat exchange in energy balance.

[0003] However, it is difficult to measure evapotranspiration in forest systems, and the evapotranspiration estimation methods in related technologies, including the Penman-Monteith equation and weighing lysimeter, all have limitations. Summary of the invention

[0004] The present application provides a method and device for measuring forest evapotranspiration, which measures forest evapotranspiration through a measuring device, takes into account the energy balance of the forest canopy to calculate the canopy transpiration, and takes into account the soil water and heat dynamics to calculate the evaporation of the understory soil. It can be accurately applied under different forest ecological vegetation types and different soil texture conditions, and has the advantages of few aerodynamic parameters and high feasibility of calculation and observation.

[0005] In order to achieve the above objectives, the main technical solutions adopted in this application include:

[0006] In a first aspect, an embodiment of the present application provides a forest evapotranspiration measurement method, which is applied to a forest evapotranspiration measurement device, wherein the measurement device comprises a sensor combination whose installation position is adapted to the forest canopy height, a soil shortwave radiation sensor whose installation position is adapted to the forest surface soil height, and a soil temperature and humidity sensor whose installation position is adapted to the forest lower soil height; the sensor combination comprises a canopy shortwave radiation sensor, a canopy temperature and humidity sensor, and an infrared temperature sensor; the method comprises:

[0007] Acquire canopy shortwave radiation information based on the canopy shortwave radiation sensor, acquire air temperature information based on the canopy temperature and humidity sensor, and acquire leaf surface average temperature information based on the infrared temperature sensor;

[0008] Calculate canopy transpiration based on energy balance according to the canopy shortwave radiation information, the air temperature information and the leaf surface average temperature information;

[0009] Acquiring soil shortwave radiation information based on the soil shortwave radiation sensor, acquiring soil temperature and humidity information based on the soil temperature and humidity sensor, and calculating the evaporation of understory soil based on the soil shortwave radiation information and the soil temperature and humidity information based on soil water and heat dynamics;

[0010] The forest evapotranspiration is calculated based on the canopy evapotranspiration and the understory soil evaporation based on the dual-source evapotranspiration theory.

[0011] The forest evapotranspiration measurement method proposed in this application is based on the dual-source evapotranspiration theory, uses infrared temperature measurement technology to collect canopy temperature, uses radiation sensors to collect each canopy radiation energy component, and constructs a low-cost understory soil measurement device based on the soil water and heat dynamic correspondence. The total measurement device on which the measurement method proposed in this application is based is low in cost and has strong scalability.

[0012] This application is based on the dual-source evapotranspiration theory to add the canopy evaporation and the understory soil evaporation to obtain the total forest evaporation, which has the effect of requiring fewer aerodynamic parameters to be measured and high feasibility of calculation and observation. At the same time, the energy balance of the forest canopy is taken into account to calculate the canopy evaporation, and the soil water and heat dynamics are taken into account to calculate the understory soil evaporation. It can be accurately applied under different forest ecological vegetation types and different soil texture conditions. The soil water and heat dynamics are the understory soil moisture and temperature dynamics.

[0013] Moreover, the measuring device provided in the present application has a simple structure and low cost. Once installed, the measuring device can realize long-term, remote, intelligent and high-precision monitoring of forest evapotranspiration, saving a lot of manpower and material resources. Moreover, the measuring device can be flexibly placed in the field, and the soil water and heat state at different depths of a specific soil structure in a certain area and the energy component of the forest canopy can be obtained in situ, preparing for the measurement of forest evapotranspiration.

[0014] Optionally, the canopy shortwave radiation information includes shortwave radiation information above the canopy, shortwave radiation information below the canopy and canopy reflected shortwave radiation information; the canopy shortwave radiation sensor includes a first canopy shortwave radiation sensor, a second canopy shortwave radiation sensor and a third canopy shortwave radiation sensor; the receiving direction of the first canopy shortwave radiation sensor is opposite to the receiving direction of the second canopy shortwave radiation sensor; the soil shortwave radiation information is obtained based on the soil shortwave radiation sensor, including:

[0015] The shortwave radiation information above the canopy is obtained based on the first canopy shortwave radiation sensor, the shortwave radiation information below the canopy is obtained based on the second canopy shortwave radiation sensor, and the canopy reflected shortwave radiation information is obtained based on the third canopy shortwave radiation sensor.

[0016] Optionally, the soil shortwave radiation information includes net radiation flux information of the forest soil surface; the soil shortwave radiation sensing element includes a net radiation sensor of the forest soil surface; the obtaining of soil shortwave radiation information based on the soil shortwave radiation sensing element includes: obtaining net radiation flux information of the soil surface based on the net radiation sensor;

[0017] The soil temperature and humidity information includes surface soil temperature information, lower soil temperature information and surface soil moisture content information; the soil temperature and humidity sensing element includes a first soil temperature and humidity sensor and a second soil temperature and humidity sensor; a receiving direction of the first soil temperature and humidity sensor is opposite to a receiving direction of the second soil temperature and humidity sensor; obtaining soil temperature and humidity information based on the soil temperature and humidity sensing element includes: obtaining the surface soil temperature information and the surface soil moisture content information based on the first soil temperature and humidity sensor, and obtaining the lower soil temperature information based on the second soil temperature and humidity sensor.

[0018] Optionally, the canopy transpiration is calculated by the following formula:

[0019]

[0020] Where T is the canopy transpiration; λ is the latent heat of evapotranspiration; R CT is the shortwave radiation information above the canopy; R CB is the shortwave radiation information below the canopy; R CR is the canopy reflected shortwave radiation information; T C is the average leaf surface temperature information; T A is the air temperature information; σ is the Stefan Boltzmann constant; K A K is the thermal conductivity of air convection conduction; f is the empirical parameter of the blade shape; L is the blade width; ω is the wind speed.

[0021] Optionally, the evaporation of the understory soil is calculated by the following formula:

[0022]

[0023] Among them, E is the evaporation of soil under the forest; λ is the latent heat of evaporation; R SN is the net radiation flux information of the soil surface; ρ is the air density; C P is the specific heat capacity of air; T ST is the surface soil temperature information; T A is the air temperature information; r S is the aerodynamic resistance value of the forest soil surface; G S is the soil heat flux.

[0024] Optionally, the method further includes: determining the soil heat flux by:

[0025] Determining the soil type of forest soil based on the soil water and heat dynamics; wherein the soil water and heat dynamics include soil water dynamics and soil heat dynamics; the soil water and heat dynamics are obtained based on the analysis of the soil temperature and humidity information;

[0026] determining a target soil thermal conductivity corresponding to the soil type of the forest soil;

[0027] The soil heat flux is determined according to the soil temperature and humidity information, the target soil thermal conductivity and the installation position of the soil temperature and humidity sensor.

[0028] Optionally, the soil temperature and humidity information includes surface soil temperature information and lower soil temperature information; the soil temperature and humidity sensing element includes a first soil temperature and humidity sensor for collecting surface soil temperature information and a second soil temperature and humidity sensor for collecting lower soil temperature information;

[0029] The determining of the soil heat flux according to the soil temperature and humidity information, the target soil thermal conductivity, and the installation position of the soil temperature and humidity sensor comprises:

[0030] Determining a height difference between the first soil temperature and humidity sensor and the second soil temperature and humidity sensor based on an installation position of the soil temperature and humidity sensor;

[0031] Calculating according to the surface soil temperature information, the lower soil temperature information, the target soil thermal conductivity and the height difference to obtain the soil heat flux;

[0032] The soil heat flux is calculated by the following formula:

[0033]

[0034] Among them, G S is the soil heat flux; k S is the thermal conductivity of soil; T ST is the surface soil temperature information; T SB is the lower soil temperature information; ΔZ is the height difference.

[0035] Optionally, the soil type is loam or sandy soil; when the soil type is loam, the target soil thermal conductivity is calculated by the following formula:

[0036]

[0037] When the soil type is sandy soil, the target soil thermal conductivity is calculated by the following formula:

[0038]

[0039] Among them, k S is the thermal conductivity of soil; θ is the weight moisture content of soil profile; ρ b It is the soil bulk density.

[0040] Optionally, the soil temperature and humidity information includes surface soil moisture content; the aerodynamic resistance value of the forest soil surface is calculated in the following manner:

[0041]

[0042] Among them, r S is the aerodynamic resistance value of the forest soil surface; θ ST is the surface soil moisture content; θ fc is the field water holding capacity of the lower soil layer; θ res is the residual moisture content of the soil; r Smin is the minimum soil resistance of the soil.

[0043] In a second aspect, an embodiment of the present application provides a computer device, including:

[0044] A memory and a processor, wherein the memory and the processor are connected to communicate with each other, the memory stores computer instructions, and the processor executes the above-mentioned forest evapotranspiration measurement method by executing the computer instructions. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 A flow chart of a method for measuring forest evapotranspiration provided by an embodiment of the present invention;

[0047] Figure 2 A schematic diagram of a device for measuring forest evapotranspiration provided by an embodiment of the present invention;

[0048] Figure 3 A schematic diagram of a forest evapotranspiration measurement process provided by an embodiment of the present invention;

[0049] In the figure, 1. the first canopy shortwave radiation sensor, 2. the third canopy shortwave radiation sensor, 3. the infrared temperature sensor, 4. the second canopy shortwave radiation sensor, 5. the net radiation sensor, 6. the first soil temperature and humidity sensor, 7. the second soil temperature and humidity sensor, 8. the solar panel, 9. the anemometer, 10. the canopy temperature and humidity sensor, 11. the atmospheric pressure sensor, 12. the 4G network antenna, 13. the data acquisition power box, 14. the vertical main body bracket, 15. the lower right horizontal bar, 16. the upper right horizontal bar, 17. the second left horizontal bar, 18. the first left horizontal bar. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0051] Evapotranspiration in forest ecosystems plays a vital role in water cycle and energy balance. It not only regulates the water and heat exchange inside and around the forest, but also affects the regional climate and the health of the ecosystem. Evapotranspiration is closely related to the energy balance of forest ecosystems, especially to changes in radiation, temperature and humidity. During evapotranspiration, the evaporation and transpiration of water absorb a large amount of latent heat, thus affecting the temperature of the forest surface. This process is one of the important ways of heat exchange in energy balance.

[0052] However, it is difficult to measure evapotranspiration in forest systems, and the evapotranspiration estimation methods in related technologies, including the Penman-Monteith equation and weighing lysimeter, all have limitations.

[0053] The Penman-Monteith equation requires high-quality meteorological data and cannot take into account the effects of plant water limitation. The weighing lysimeter is subject to space limitations, equipment cost, and operational complexity, and has a narrow scope of application. Satellite images (such as SEBAL and METRIC models) provide remote sensing monitoring methods, but their low temporal resolution makes it difficult to capture intraday evapotranspiration changes, especially when soil moisture is low. Micrometeorological methods (such as eddy covariance method) are suitable for large-scale uniform areas, but are not suitable for areas with strong vegetation heterogeneity. They are complex to apply and costly.

[0054] Reference Figure 1 and Figure 2The embodiment of the present application provides a forest evapotranspiration measurement method, which is applied to a forest evapotranspiration measurement device, the measurement device including a sensor combination whose installation position is adapted to the forest canopy height, a soil shortwave radiation sensor whose installation position is adapted to the forest surface soil height, and a soil temperature and humidity sensor whose installation position is adapted to the forest lower soil height; the sensor combination includes a canopy shortwave radiation sensor, a canopy temperature and humidity sensor, and an infrared temperature sensor.

[0055] Specifically, the bottom of the vertical main support 14 of the measuring device is fixed by concrete grouting, and its top height is preferably higher than the canopy height of the tree to be observed, and the 4G network antenna 12 is located directly above it. The data acquisition power box 13 is connected to the 4G network antenna 12 to achieve real-time transmission of observation data to the server monitoring personnel. The lower right crossbar 15, the upper right crossbar 16, the second left crossbar 17 and the first left crossbar 18 are fixedly connected to the vertical main support 14 by welding.

[0056] The data acquisition power supply box 13 can be opened and has good sealing performance. The data acquisition power supply box 13 includes a data collector connected to each sensor and a power supply connected to the solar panel 8. Its height is about 120 cm to facilitate the collection and setting of the collector. The solar panel 8 supplies power to the data acquisition power supply box 13, so that all sensors and data collectors can work normally at night and on rainy days.

[0057] The measuring device includes a sensor combination, a soil shortwave radiation sensor and a soil temperature and humidity sensor. The sensor combination includes an upward first canopy shortwave radiation sensor 1, a downward third canopy shortwave radiation sensor 2, an upward second canopy shortwave radiation sensor 4, a canopy temperature and humidity sensor 10, and an infrared temperature sensor 3. The soil shortwave radiation sensor includes an upward net radiation sensor 5; the soil temperature and humidity sensor includes a first soil temperature and humidity sensor 6 for collecting soil surface temperature and humidity and a second soil temperature and humidity sensor 7 for collecting soil lower layer temperature and humidity.

[0058] The height of the welded upper right crossbar 16 should preferably be higher than and close to the canopy, and the infrared temperature sensor 3 is preferably close to the canopy leaves at a distance of 20 cm, and the arrangement angle is 20° to 30° downward. The first canopy shortwave radiation sensor 1 facing upward and the third canopy shortwave radiation sensor 2 facing downward are respectively fixed on the upper right crossbar 16 as close to the end as possible, that is, close to the top of the canopy.

[0059] The second left cross bar 17 (lower left cross bar) welded and fixed to the vertical main body support 14 is set at a height close to the canopy height of the tree (the height difference is less than 20 cm), and the canopy temperature and humidity sensor 10 and the atmospheric pressure sensor 11 are fixed above the second left cross bar 17.

[0060] The first left crossbar 18 (upper left crossbar) welded and fixed to the vertical main body support 14 is set about 40 cm higher than the second left crossbar 17. The solar panel 8 and the anemometer 9 are fixed above the first left crossbar 18. The solar panel 8 faces south and avoids being covered.

[0061] The lower right cross bar 15 welded and fixed on the vertical main body support 14 is preferably close to the soil surface under the forest, with a height of 2 cm to 10 cm. The upward second canopy shortwave radiation sensor 4 and the upward net radiation sensor 5 are fixed on the lower right cross bar 15. The vertical position of the second canopy shortwave radiation sensor 4 should be below the forest canopy coverage area.

[0062] The first soil temperature and humidity sensor 6 in the upper layer of forest soil is buried at a depth of 1 cm to 5 cm, 2 cm is recommended; the vertical depth difference between the second soil temperature and humidity sensor 7 in the lower layer and the first soil temperature and humidity sensor 6 should be ΔZ, 5 cm to 20 cm is recommended, and 10 cm is preferred.

[0063] The measuring device provided in the present application has a simple structure and low cost. Once installed, the measuring device can realize long-term, remote, intelligent and high-precision monitoring of forest evapotranspiration, saving a lot of manpower and material resources. The measuring device can be flexibly placed in the field, and the soil water and heat state at different depths of a specific soil structure in a certain area and the energy component of the forest canopy can be obtained in situ, preparing for the measurement of forest evapotranspiration.

[0064] The measurement method includes: S100, obtaining canopy shortwave radiation information based on a canopy shortwave radiation sensor, obtaining air temperature information based on a canopy temperature and humidity sensor, and obtaining leaf surface average temperature information based on an infrared temperature sensor.

[0065] Please refer to Figure 3 Based on the sensor combination, multi-dimensional data about the growth environment of forest trees are obtained. The canopy shortwave radiation sensor can measure the shortwave radiation reaching the plant canopy, usually referring to the visible light and near-infrared radiation of the sun; the canopy temperature and humidity sensor 10 can be a digital temperature and humidity sensor, such as DHT22, AM2302, etc.; the infrared temperature sensor 3 can be an infrared thermal imager or an infrared thermometer, which can estimate the temperature non-contactly by detecting the infrared radiation on the leaves of forest trees or other plant surfaces, and monitor the average leaf temperature.

[0066] S200, calculating canopy transpiration based on energy balance according to canopy shortwave radiation information, air temperature information and leaf surface average temperature information.

[0067] Among them, canopy shortwave radiation information is expressed as R C Indicates that the air temperature information is T A The average leaf surface temperature information is represented by T C express.

[0068] Specifically, canopy transpiration is represented by T, and canopy transpiration is calculated according to the following formula:

[0069]

[0070] Where T is the canopy transpiration in mm / s, applying the energy balance to a single leaf and extending it to the entire forest canopy; λ is the latent heat of evapotranspiration in J / kg; LE C is the canopy latent heat transpiration flux, in W / m 2 , subscript C stands for canopy.

[0071] The latent heat of evaporation is calculated according to the following formula:

[0072] λ=(2.501-0.00237*(T A -273.15))*10 6

[0073] Among them, T A is the air temperature information, which is obtained based on the canopy temperature and humidity sensor 10. The canopy latent heat transpiration flux is calculated according to the following formula:

[0074] LE C =Q C -L C -A C

[0075] To assess the actual canopy transpiration of a forest ecosystem, the energy balance is applied to a single leaf and upscaled to the entire forest canopy. The above formula is the energy balance formula; where Q C is the total energy absorbed by the canopy, in W / m 2 ; L C is the longwave radiation emitted by the canopy, in W / m 2 ; A C Energy exchange with air through convection and conduction, unit: W / m 2 ;

[0076] The total energy absorbed by the canopy is composed of absorbed shortwave radiation and longwave radiation, which is calculated according to the following formula:

[0077] Q C =Q CL +R C

[0078] Among them, Q CL is the longwave radiation absorbed by the canopy, in W / m 2 ; R C is the shortwave radiation absorbed by the canopy, i.e. the canopy shortwave radiation information, in W / m2 .

[0079] The longwave radiation absorbed by the canopy is calculated according to the following formula:

[0080]

[0081] Where ε is the emissivity, which is 0.96; assuming that both sides of the leaves in the forest canopy absorb long-wave ground radiation equally, α CL is the long-wave absorption coefficient, which is approximately the emissivity; σ is the Stefan Boltzmann constant, which is 5.6704*10 -8 , unit is m 2 *K 4 .

[0082] The long-wave radiation emitted by the canopy can be calculated based on the average leaf temperature information, assuming that both sides of the leaves in the forest canopy emit long-wave radiation equally, according to the following formula:

[0083]

[0084] Among them, T C is the average leaf surface temperature information, which is obtained based on the infrared temperature sensor 3.

[0085] The energy exchange with the air through convection and conduction is proportional to the difference between the air temperature and the leaf surface temperature. Based on the Fourier equation, the energy exchange is calculated as follows:

[0086]

[0087] Among them, K A is the thermal conductivity of air convection-conduction, with a value of 0.0259 and a unit of W / (m*K); T C is the average leaf surface temperature information; T A is the air temperature information; d is the boundary layer thickness, in m.

[0088] The measuring device also includes an anemometer 9 whose installation position is adapted to the forest canopy height. The boundary layer thickness is calculated according to the following formula:

[0089]

[0090] Among them, K f is the empirical parameter of the leaf shape, with a value of 0.0057 and a unit of m / s; L is the leaf width, with a unit of m, which is directly measured by a field measurement tape; w is the wind speed, with a unit of m / s, which is obtained based on anemometer 9.

[0091] In summary, canopy transpiration T is calculated according to the following formula:

[0092]

[0093] Among them, R CT is the shortwave radiation information above the canopy; R CB is the shortwave radiation information below the canopy; R CR It is the shortwave radiation information reflected by the canopy.

[0094] S300, obtaining soil shortwave radiation information based on soil shortwave radiation sensors, obtaining soil temperature and humidity information based on soil temperature and humidity sensors, and calculating understory soil evaporation based on soil shortwave radiation information and soil temperature and humidity information based on soil water and heat dynamics.

[0095] Among them, the evaporation of soil under the forest is represented by E. Specifically, soil water and heat dynamics can be the interaction and change process of water and heat (temperature) in the soil at different time and space scales. Soil water dynamics, that is, soil water dynamics, can be the state and distribution of water in the soil, including hygroscopic water, capillary water and gravity water. The dynamic changes of soil moisture are affected by factors such as precipitation, evaporation, plant water absorption, and groundwater recharge. Soil thermal dynamics, that is, soil temperature dynamics, is an important factor affecting soil biological activity and chemical reaction rates. The heat of the soil mainly comes from solar radiation, and the soil's heat capacity, thermal conductivity, water content and other characteristics determine the temperature changes of the soil.

[0096] The evaporation of soil under the forest was calculated according to the following formula:

[0097]

[0098] Where E is the evaporation of soil under the forest, in mm / s, which is calculated by considering the soil water and heat dynamics; λ is the latent heat of evaporation, in J / kg; LE S is the soil latent heat evaporation flux, in W / m 2 , subscript S stands for soil.

[0099] The soil latent heat evaporation flux is calculated according to the following formula:

[0100] LE S =R SN -H S -G S

[0101] In order to evaluate the actual evaporation of understory soil in forest ecosystems, the energy balance is applied to forest soil, considering the soil water and heat dynamics. The above formula is the energy balance formula; where R SN is the net radiation flux information of the soil surface, in W / m 2 , is obtained based on the net radiation sensor 5; H Sis the soil sensible heat flux, in W / m 2 ; G S is the soil heat flux, in W / m 2 .

[0102] The soil sensible heat flux is obtained by dividing the temperature gradient between soil and air by the vertical flux resistance, which is calculated according to the following formula:

[0103]

[0104] Where ρ is the air density in kg / m 3 ; C P is the specific heat capacity of air, with a value of 1005 and a unit of J / (kg*K); T ST is the surface soil temperature information, which is obtained based on the first soil temperature and humidity sensor 6; T A is the air temperature information; r S It is the aerodynamic resistance value of the forest soil surface, in s / m.

[0105] The sensor assembly also includes an atmospheric pressure sensor 11; the air density is calculated by the ideal gas equation, specifically according to the following formula:

[0106]

[0107] Where, d is dry air; M d is the gas constant of dry air, with a value of 287.05 and a unit of J / (kg*K); p d is the dry air partial pressure, in Pa; v is water vapor; M v is the gas constant of water vapor, with a value of 461.5 and a unit of J / (kg*K); p v is the water vapor partial pressure, in Pa.

[0108] The dry air partial pressure is calculated according to the following formula: d =p A -p v

[0109] Among them, p A is the total air pressure, which is obtained based on the atmospheric pressure sensor 11.

[0110] The water vapor partial pressure is calculated according to the following formula:

[0111]

[0112] RH is relative humidity, in %, and is obtained based on the canopy temperature and humidity sensor 10 .

[0113] In summary, the evaporation of soil under the forest is calculated according to the following formula:

[0114]

[0115] Where E is the evaporation of soil under the forest, in mm / s.

[0116] S400, based on the dual-source evapotranspiration theory, calculates forest evapotranspiration based on canopy evaporation and understory soil evaporation.

[0117] Specifically, the canopy evaporation T and the understory soil evaporation E are added together to obtain the total forest evaporation, expressed as ET, ET=E+T.

[0118] The dual-source evapotranspiration theory decomposes energy exchange and surface temperature into two parts: soil and vegetation. It divides evapotranspiration into two different evapotranspiration sources: forest soil and canopy vegetation, to distinguish the different processes of soil evaporation and vegetation transpiration. The single energy source model in the related art is not effective on the surface covered with some vegetation. In contrast, the dual-source evapotranspiration theory of this application effectively calculates the evapotranspiration of forest ecosystems and widely uses data based on remote sensing monitoring methods for calculation.

[0119] Forest evapotranspiration is calculated according to the following formula:

[0120]

[0121] Among them, ET is forest evapotranspiration.

[0122] The forest evapotranspiration measurement method proposed in this application is based on the dual-source evapotranspiration theory, uses infrared temperature measurement technology to collect canopy temperature, uses radiation sensors to collect each canopy radiation energy component, and constructs a low-cost understory soil measurement device based on the soil water and heat dynamic correspondence. The total measurement device on which the measurement method proposed in this application is based is low in cost and has strong scalability.

[0123] This application is based on the dual-source evapotranspiration theory to add the canopy evaporation and the understory soil evaporation to obtain the total forest evaporation, which has the effect of requiring fewer aerodynamic parameters to be measured and high feasibility of calculation and observation. At the same time, the energy balance of the forest canopy is taken into account to calculate the canopy evaporation, and the soil water and heat dynamics are taken into account to calculate the understory soil evaporation. It can be accurately applied under different forest ecological vegetation types and different soil texture conditions. The soil water and heat dynamics are the understory soil moisture and temperature dynamics.

[0124] As an implementation method, the canopy shortwave radiation information includes shortwave radiation information above the canopy, shortwave radiation information below the canopy and canopy reflected shortwave radiation information; the canopy shortwave radiation sensor includes a first canopy shortwave radiation sensor 1, a second canopy shortwave radiation sensor 4 and a third canopy shortwave radiation sensor 2; the receiving direction of the first canopy shortwave radiation sensor 1 is opposite to the receiving direction of the second canopy shortwave radiation sensor 4; the soil shortwave radiation information is obtained based on the soil shortwave radiation sensor, including:

[0125] The shortwave radiation information above the canopy is obtained based on the first canopy shortwave radiation sensor 1, the shortwave radiation information below the canopy is obtained based on the second canopy shortwave radiation sensor 4, and the canopy reflected shortwave radiation information is obtained based on the third canopy shortwave radiation sensor 2.

[0126] The shortwave radiation absorbed by the canopy is calculated according to the following formula:

[0127] R C =R CT +R CB +R CR

[0128] Among them, R CT It is the shortwave radiation information above the canopy, in W / m 2 , subscript T is above, which is obtained based on the first canopy shortwave radiation sensor 1; R CB It is the shortwave radiation information below the canopy, in W / m 2 , subscript B is below, which is obtained based on the second canopy shortwave radiation sensor 4; R CR It is the canopy reflected shortwave radiation information, in W / m 2 , the subscript R is reflectance, which is obtained based on the third canopy shortwave radiation sensor 2.

[0129] As an implementation mode, the soil shortwave radiation information includes the net radiation flux information of the forest soil surface; the soil shortwave radiation sensor includes the net radiation sensor 5 of the forest soil surface; obtaining the soil shortwave radiation information based on the soil shortwave radiation sensor includes: obtaining the net radiation flux information of the soil surface based on the net radiation sensor 5;

[0130] The soil temperature and humidity information includes surface soil temperature information, lower soil temperature information and surface soil moisture content information; the soil temperature and humidity sensing element includes a first soil temperature and humidity sensor 6 and a second soil temperature and humidity sensor 7; the receiving direction of the first soil temperature and humidity sensor 6 is opposite to the receiving direction of the second soil temperature and humidity sensor 7; obtaining soil temperature and humidity information based on the soil temperature and humidity sensing element includes: obtaining surface soil temperature information and surface soil moisture content information based on the first soil temperature and humidity sensor 6, and obtaining lower soil temperature information based on the second soil temperature and humidity sensor 7.

[0131] As an implementation method, canopy transpiration is calculated by the following formula:

[0132]

[0133] Where T is the canopy transpiration; λ is the latent heat of evapotranspiration; R CT is the shortwave radiation information above the canopy; R CB is the shortwave radiation information below the canopy; R CR is the canopy reflected shortwave radiation information; T C is the average leaf surface temperature information; T A is the air temperature information; σ is the Stefan Boltzmann constant; K A K is the thermal conductivity of air convection conduction; f is the empirical parameter of the blade shape; L is the blade width; ω is the wind speed.

[0134] As an implementation method, the evaporation of soil under the forest is calculated by the following formula:

[0135]

[0136] Among them, E is the evaporation of soil under the forest; λ is the latent heat of evaporation; R SN is the net radiation flux information of the soil surface; ρ is the air density; C P is the specific heat capacity of air; T ST is the surface soil temperature information; T A is the air temperature information; r S is the aerodynamic resistance value of the forest soil surface; G S is the soil heat flux.

[0137] As an implementation mode, the method further includes: determining the soil heat flux by:

[0138] S310, determining the soil type of forest soil based on soil water and heat dynamics; wherein the soil water and heat dynamics include soil water dynamics and soil heat dynamics; the soil water and heat dynamics are obtained based on soil temperature and humidity information analysis;

[0139] S330. Determine a target soil thermal conductivity corresponding to the soil type of forest soil.

[0140] S350: Determine soil heat flux according to soil temperature and humidity information, target soil thermal conductivity, and installation location of soil temperature and humidity sensors.

[0141] As an implementation method, the soil temperature and humidity information includes surface soil temperature information and lower soil temperature information; the soil temperature and humidity sensor includes a first soil temperature and humidity sensor 6 for collecting surface soil temperature information and a second soil temperature and humidity sensor 7 for collecting lower soil temperature information.

[0142] The soil heat flux is determined based on the soil temperature and humidity information, the target soil thermal conductivity, and the installation location of the soil temperature and humidity sensor, including:

[0143] S346. Determine the height difference between the first soil temperature and humidity sensor 6 and the second soil temperature and humidity sensor 7 based on the installation position of the soil temperature and humidity sensor.

[0144] S348. Calculate the soil heat flux based on the surface soil temperature information, the lower soil temperature information, the target soil thermal conductivity and the height difference.

[0145] Considering the soil thermal dynamics based on soil temperature and humidity information, the soil heat flux is calculated by the following formula:

[0146]

[0147] Among them, G S is the soil heat flux; k S is the soil thermal conductivity, in W / (m*K), which is calculated based on the forest soil texture and the Kersten model; T ST is the surface soil temperature information, which is obtained based on the first soil temperature and humidity sensor 6; T SB is the lower soil temperature information, which is obtained based on the second soil temperature and humidity sensor 7; ΔZ is the height difference, in meters.

[0148] As an implementation method, the soil type is loam or sandy soil; the soil temperature and humidity information includes surface soil humidity information and lower soil humidity information. The method may also include:

[0149] S342. Calculate the weight moisture content of the soil profile based on the surface soil moisture information and the lower soil moisture information.

[0150] S344. The soil thermal conductivity of different soil types is calculated based on the weight moisture content of the soil profile.

[0151] In the case where the soil type is loam, and generally in the case where the soil type is clay, the target soil thermal conductivity is calculated by the following formula:

[0152]

[0153] When the soil type is sandy soil, the target soil thermal conductivity is calculated by the following formula:

[0154]

[0155] Among them, k S is the thermal conductivity of soil; θ is the weight moisture content of soil profile, in g / g; ρ b is the soil bulk density, in kg / m 3 , which is obtained by collecting field soil samples and measuring them in the laboratory.

[0156] The second soil temperature and humidity sensor 7 can also be used to obtain the moisture content information of the lower soil layer; the weight moisture content of the soil profile is calculated according to the following formula:

[0157]

[0158] Among them, θ ST is the surface soil moisture content information, unit is m 3 / m 3 , is obtained based on the first soil temperature and humidity sensor 6, θ BT is the moisture content of the lower soil, in m 3 / m 3 , which is obtained based on the second soil temperature and moisture sensor 7.

[0159] Furthermore, forest evapotranspiration is calculated according to the following formula:

[0160]

[0161] In the case of loam soil, and generally in the case of clay soil, forest evapotranspiration is calculated according to the following formula:

[0162]

[0163] When the soil type is sandy, forest evapotranspiration is calculated according to the following formula:

[0164]

[0165] As an implementation method, the soil temperature and humidity information includes the surface soil moisture content; based on the soil temperature and humidity information and considering the soil water dynamics, the aerodynamic resistance value of the forest soil surface is calculated in the following way:

[0166]

[0167] Among them, r S is the aerodynamic resistance value of the forest soil surface, in s / m; θ ST is the surface soil moisture content, in m 3 / m 3, is obtained based on the first soil temperature and humidity sensor 6; θ fc is the field water holding capacity of the lower soil layer, in m 3 / m 3 , obtained by collecting field soil samples and measuring them in the laboratory; θ res is the residual moisture content of the soil, in m 3 / m 3 , obtained by collecting field soil samples and measuring them in the laboratory; r Smin is the minimum soil resistance of the soil, which is 50 and is expressed in s / m.

[0168] The present application provides a forest evapotranspiration measurement system, which is applied to a forest evapotranspiration measurement device. The measurement device includes a sensor combination whose installation position is adapted to the forest canopy height, a soil shortwave radiation sensor whose installation position is adapted to the forest surface soil height, and a soil temperature and humidity sensor whose installation position is adapted to the forest lower soil height; the sensor combination includes a canopy shortwave radiation sensor, a canopy temperature and humidity sensor, and an infrared temperature sensor; the system includes an acquisition module, a canopy evapotranspiration module, an understory soil module, and a forest evapotranspiration module:

[0169] The acquisition module is configured to acquire canopy shortwave radiation information based on the canopy shortwave radiation sensor, acquire air temperature information based on the canopy temperature and humidity sensor, and acquire leaf surface average temperature information based on the infrared temperature sensor.

[0170] The canopy transpiration module is configured to calculate the canopy transpiration amount based on energy balance according to the canopy shortwave radiation information, air temperature information and leaf surface average temperature information.

[0171] The understory soil module is configured to obtain soil shortwave radiation information based on the soil shortwave radiation sensor, obtain soil temperature and humidity information based on the soil temperature and humidity sensor, and calculate the understory soil evaporation based on the soil shortwave radiation information and the soil temperature and humidity information based on the soil water and heat dynamics.

[0172] The forest evapotranspiration module is configured to calculate forest evapotranspiration based on canopy evapotranspiration and understory soil evaporation based on the dual-source evapotranspiration theory.

[0173] The present application provides a computer device, including: a memory and a processor, the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes a forest evapotranspiration measurement method provided in the above embodiment by executing the computer instructions.

[0174] The computer device includes: one or more processors, memory, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components are connected to each other using different buses for communication, and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple computer devices can be connected, and each device provides some necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system).

[0175] The processor may be a central processing unit, a network processor or a combination thereof. The processor may further include a hardware chip. The hardware chip may be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic or any combination thereof.

[0176] The memory stores instructions executable by at least one processor, so that the at least one processor executes the method shown in the above embodiment.

[0177] The memory may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created according to the use of the computer device, etc. In addition, the memory may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the storage may optionally include a memory remotely arranged relative to the processor, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0178] The memory may include volatile memory, such as random access memory; the memory may also include non-volatile memory, such as flash memory, hard disk or solid state drive; the memory may also include a combination of the above types of memory.

[0179] The computer device also includes a communication interface, which is used for the computer device to communicate with other devices or a communication network.

[0180] The present application provides a computer-readable storage medium, on which computer instructions are stored, and the computer instructions are used to enable a computer to execute a forest evapotranspiration measurement method provided in the above embodiment.

[0181] The embodiment of the present application also provides a computer-readable storage medium. The above method according to the embodiment of the present application can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium through a network download, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state hard disk, etc.; further, the storage medium can also include a combination of the above types of memories. It can be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor, or hardware, the method shown in the above embodiment is implemented.

[0182] The embodiment of the present application provides a computer program product, which includes computer instructions, which are stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, so that the computer device executes the method of any embodiment of the present application.

[0183] Although the embodiments of the present application are described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present application, and such modifications and variations are all within the scope defined by the appended claims.

[0184] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0185] For the convenience of description, the above device is described in various units according to their functions. Of course, when implementing the present application, the functions of each unit can be implemented in the same or multiple software and / or hardware.

[0186] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0187] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0188] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0189] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0190] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0191] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0192] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

[0193] Although the embodiments of the present application have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present application, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for measuring forest evapotranspiration, characterized in that: A measuring device for forest evapotranspiration, the measuring device comprising a sensor combination whose installation position is adapted to the forest canopy height, a soil shortwave radiation sensor whose installation position is adapted to the forest surface soil height, and a soil temperature and humidity sensor whose installation position is adapted to the forest lower soil height; the sensor combination comprises a canopy shortwave radiation sensor, a canopy temperature and humidity sensor, and an infrared temperature sensor; the method comprises: Acquire canopy shortwave radiation information based on the canopy shortwave radiation sensor, acquire air temperature information based on the canopy temperature and humidity sensor, and acquire leaf surface average temperature information based on the infrared temperature sensor; Calculate canopy transpiration based on energy balance according to canopy shortwave radiation information, the air temperature information and the leaf surface average temperature information; Acquiring soil shortwave radiation information based on the soil shortwave radiation sensor, acquiring soil temperature and humidity information based on the soil temperature and humidity sensor, and calculating the evaporation of understory soil based on the soil shortwave radiation information and the soil temperature and humidity information based on soil water and heat dynamics; The forest evapotranspiration is calculated based on the canopy evapotranspiration and the understory soil evaporation based on the dual-source evapotranspiration theory.

2. The method according to claim 1, characterized in that The canopy shortwave radiation information includes shortwave radiation information above the canopy, shortwave radiation information below the canopy and canopy reflected shortwave radiation information; the canopy shortwave radiation sensor includes a first canopy shortwave radiation sensor, a second canopy shortwave radiation sensor and a third canopy shortwave radiation sensor; The receiving direction of the first canopy shortwave radiation sensor is opposite to the receiving direction of the second canopy shortwave radiation sensor; The obtaining of soil shortwave radiation information based on the soil shortwave radiation sensor comprises: The shortwave radiation information above the canopy is obtained based on the first canopy shortwave radiation sensor, the shortwave radiation information below the canopy is obtained based on the second canopy shortwave radiation sensor, and the canopy reflected shortwave radiation information is obtained based on the third canopy shortwave radiation sensor.

3. The method according to claim 1, characterized in that The soil shortwave radiation information includes net radiation flux information of the forest soil surface; the soil shortwave radiation sensing element includes a net radiation sensor of the forest soil surface; the obtaining of soil shortwave radiation information based on the soil shortwave radiation sensing element includes: obtaining net radiation flux information of the soil surface based on the net radiation sensor; The soil temperature and humidity information includes surface soil temperature information, lower soil temperature information and surface soil moisture content information; the soil temperature and humidity sensing element includes a first soil temperature and humidity sensor and a second soil temperature and humidity sensor; a receiving direction of the first soil temperature and humidity sensor is opposite to a receiving direction of the second soil temperature and humidity sensor; obtaining soil temperature and humidity information based on the soil temperature and humidity sensing element includes: obtaining the surface soil temperature information and the surface soil moisture content information based on the first soil temperature and humidity sensor, and obtaining the lower soil temperature information based on the second soil temperature and humidity sensor.

4. The method according to claim 1, characterized in that: The canopy transpiration is calculated by the following formula: Where T is the canopy transpiration; λ is the latent heat of evapotranspiration; R CT is the shortwave radiation information above the canopy; R CB is the shortwave radiation information below the canopy; R CR is the canopy reflected shortwave radiation information; T C is the average leaf surface temperature information; T A is the air temperature information; σ is the Stefan Boltzmann constant; K A K is the thermal conductivity of air convection conduction; f is the empirical parameter of the blade shape; L is the blade width; ω is the wind speed.

5. The method according to claim 1, characterized in that The soil evaporation under the forest is calculated by the following formula: Among them, E is the evaporation of soil under the forest; λ is the latent heat of evaporation; R SN is the net radiation flux information of the soil surface; ρ is the air density; C P is the specific heat capacity of air; T ST is the surface soil temperature information; T A is the air temperature information; r S is the aerodynamic resistance value of the forest soil surface; G S is the soil heat flux.

6. The method according to claim 5, characterized in that Also includes: The soil heat flux is determined by: Determining the soil type of forest soil based on the soil water and heat dynamics; wherein the soil water and heat dynamics include soil water dynamics and soil heat dynamics; the soil water and heat dynamics are obtained based on the analysis of the soil temperature and humidity information; determining a target soil thermal conductivity corresponding to the soil type of the forest soil; The soil heat flux is determined according to the soil temperature and humidity information, the target soil thermal conductivity and the installation position of the soil temperature and humidity sensor.

7. The method according to claim 6, characterized in that The soil temperature and humidity information includes surface soil temperature information and lower soil temperature information; the soil temperature and humidity sensor includes a first soil temperature and humidity sensor for collecting surface soil temperature information and a second soil temperature and humidity sensor for collecting lower soil temperature information; The determining of the soil heat flux according to the soil temperature and humidity information, the target soil thermal conductivity, and the installation position of the soil temperature and humidity sensor comprises: Determining a height difference between the first soil temperature and humidity sensor and the second soil temperature and humidity sensor based on an installation position of the soil temperature and humidity sensor; Calculating according to the surface soil temperature information, the lower soil temperature information, the target soil thermal conductivity and the height difference to obtain the soil heat flux; The soil heat flux is calculated by the following formula: Among them, G S is the soil heat flux; k S is the thermal conductivity of soil; T ST is the surface soil temperature information; T SB is the lower soil temperature information; ΔZ is the height difference.

8. The method according to claim 6, characterized in that The soil type is loam or sandy soil. When the soil type is loam, the target soil thermal conductivity is calculated by the following formula: When the soil type is sandy soil, the target soil thermal conductivity is calculated by the following formula: Among them, k S is the thermal conductivity of soil; is the weight moisture content of the soil profile; ρ b It is the soil bulk density.

9. The method according to claim 5, characterized in that The soil temperature and humidity information includes the surface soil moisture content; the aerodynamic resistance value of the forest soil surface is calculated by the following method: Among them, r S is the aerodynamic resistance value of the forest soil surface; θ ST is the surface soil moisture content; θ fc is the field water holding capacity of the lower soil layer; θ res is the residual moisture content of the soil; r Smin is the minimum soil resistance of the soil.

10. A computer device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the forest evapotranspiration measurement method according to any one of claims 1 to 9 by executing the computer instructions.

Images