Method and system for measuring low vegetation canopy conductance

Abstract

This invention relates to the field of smart agroforestry technology, providing a method and system for measuring the canopy conductance of low-growing vegetation. The method includes: determining soil evaporation based on the evaporation of exposed soil and the evaporation of soil shaded by vegetation; determining the canopy transpiration rate based on evapotranspiration per unit time, the projected area of ​​the vegetation canopy, and the soil evaporation; determining the total canopy conductance based on the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure and the canopy transpiration rate; and determining the canopy boundary layer conductance based on the molar mass of water, the latent heat of vaporization of water, air density, air specific heat capacity, the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure, and the canopy transpiration rate; and determining the canopy conductance based on the total canopy conductance and the canopy boundary layer conductance. This allows for rapid and accurate measurement of canopy conductance.

Description

Technical Field

[0001] This invention relates to the field of smart agriculture and forestry technology, and in particular to a method and system for measuring the canopy conductance of low-growing vegetation. Background Technology

[0002] Stomata play a crucial role in plant gas metabolism, including respiration, photosynthesis, and transpiration, acting as the primary gateways for material exchange with the external environment. Stomatal conductance reflects the degree of stomatal opening and closing, influencing the rate of material exchange and impacting transpiration rate, photosynthetic efficiency, and photosynthetic yield. Plants absorb carbon dioxide through stomata during photosynthesis under light, requiring stomata to be open; however, stomatal opening inevitably leads to transpiration. The ratio between photosynthesis and transpiration is defined as plant water use efficiency (WUE). High stomatal conductance increases plant water use efficiency; however, high plant water use efficiency also implies lower stomatal conductance, resulting in reduced photosynthetic yield and ultimately lower crop yield. Therefore, to balance the relationship between stomatal conductance and plant water use efficiency, achieving relatively high plant water use efficiency and increasing crop yield, it is necessary to measure and calculate stomatal conductance. Canopy conductance is a manifestation of vegetation at the population scale. Accurately understanding and simulating the response of canopy conductance to environmental changes is a key parameter for accurately predicting the future climate and carbon cycle feedback relationship. Currently, in terms of canopy conductance monitoring methods and technological inventions, there are no direct observation methods, systems, or equipment for vegetation canopy conductance. Most methods focus on observing stomatal conductance at the leaf scale, as well as indirect estimation methods for canopy conductance established by constructing dynamic models by fusing remote sensing data and coupling vegetation-hydrological models. The canopy conductance measurement devices in these technologies are not only difficult to operate, but also have large errors in the calculation results. Summary of the Invention

[0003] This invention provides a method and system for measuring the canopy conductance of low-growing vegetation, which solves the problems of inaccurate canopy conductance measurement results and low efficiency in the prior art.

[0004] This invention provides a method for measuring the canopy conductance of low-growing vegetation, comprising: Soil evaporation is determined based on the evaporation of bare soil and the evaporation of soil covered by vegetation. The transpiration rate of the vegetation canopy is determined based on the evaporation rate per unit time, the projected area of ​​the vegetation canopy, and the soil evaporation rate. The total conductance of the canopy is determined based on the difference between the saturated vapor pressure of the canopy and the actual vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy. The conductance of the canopy boundary layer is determined based on the molar mass of water, the latent heat of vaporization of water, air density, specific heat capacity of air, the difference between the saturated vapor pressure of the canopy and the actual vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy. The canopy conductance is determined based on the total canopy conductance and the canopy boundary layer conductance.

[0005] According to a method for measuring the canopy conductance of low-lying vegetation provided by the present invention, the evaporation of the exposed soil is obtained as follows: The evaporation rate of the exposed soil was determined based on the surface area of ​​the exposed soil in the sample chamber and the evaporation rate of the exposed soil.

[0006] According to a method for measuring the conductance of low-growing vegetation canopy provided by the present invention, the method for obtaining the evaporation rate of exposed soil is as follows: The evaporation rate of the exposed soil is determined based on the evaporation rate per unit time of the exposed soil chamber and the surface area of ​​the exposed soil chamber; wherein, the evaporation rate per unit time of the exposed soil chamber is determined based on the water vapor concentration at the starting point of the exposed soil chamber, the water vapor concentration at the ending point of the exposed soil chamber, the volume of the exposed soil chamber, and the measurement time interval.

[0007] According to the present invention, a method for measuring the conductance of low-growing vegetation canopy is provided, wherein the evaporation of the soil blocked by vegetation is obtained as follows: The evaporation rate of the soil covered by vegetation is determined based on the evaporation rate of the soil covered by vegetation and the surface area of ​​the soil covered by vegetation; wherein the surface area of ​​the soil covered by vegetation is equal to the projected area of ​​the vegetation canopy.

[0008] According to a method for measuring the conductance of low-growing vegetation canopy provided by the present invention, the method for obtaining the evaporation rate of the soil blocked by vegetation is as follows: The evaporation rate of the vegetation-shaded soil is determined based on the evaporation rate of the exposed soil, the natural constant, the extinction coefficient, and the leaf area index.

[0009] According to a method for measuring the conductance of low-growing vegetation canopy provided by the present invention, the method for obtaining the evaporation rate of the soil blocked by vegetation is as follows: The evaporation rate of the vegetation-shaded soil is determined based on the evaporation rate of the exposed soil, the incident photosynthetically active radiation above the canopy, and the photosynthetically active radiation on the ground surface below the canopy.

[0010] According to the present invention, a method for measuring the canopy conductance of low-growing vegetation is provided, wherein the evapotranspiration per unit time is obtained as follows: The evaporation rate per unit time is determined based on the water vapor concentration at the starting point of the sample chamber, the water vapor concentration at the ending point of the sample chamber, the volume of the sample chamber, and the measurement time interval.

[0011] According to the present invention, a method for measuring the canopy conductance of low-growing vegetation is provided, wherein the canopy saturated vapor pressure is obtained in the following manner: ; in, The saturated vapor pressure of the canopy. Canopy temperature; The method for obtaining the actual atmospheric water vapor pressure is as follows: ; in, This represents the actual water vapor pressure in the air. For air temperature, RH air This refers to the relative humidity of the air.

[0012] According to the present invention, a method for measuring the canopy conductance of low-growing vegetation is provided, wherein the canopy temperature is obtained in the following manner: The raw values ​​obtained from the thermal infrared camera are converted by a conversion factor to obtain the raw canopy temperature. The original canopy temperature was corrected by emissivity, atmospheric transmittance, air temperature, and the distance between the plant canopy and the thermal infrared camera to obtain the initial canopy temperature. The average of the initial canopy temperatures corresponding to all vegetation zones is calculated to determine the canopy temperature.

[0013] The method for measuring the canopy conductance of low-growing vegetation according to the present invention further includes: The single measurement is considered complete when the rate of change of the difference between the canopy saturated water vapor pressure and the actual atmospheric water vapor pressure reaches a set threshold.

[0014] The present invention also provides a low-growing vegetation canopy conductance measurement system, comprising the following modules: The first calculation module is used to determine soil evaporation based on the evaporation of bare soil and the evaporation of soil covered by vegetation. The second calculation module is used to determine the transpiration rate of the vegetation canopy based on the evaporation per unit time, the projected area of ​​the vegetation canopy, and the soil evaporation. The third calculation module is used to determine the total conductance of the canopy based on the difference between the saturated water vapor pressure of the canopy and the actual water vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy, and to determine the canopy boundary layer conductance based on the molar mass of water, the latent heat of vaporization of water, air density, specific heat capacity of air, the difference between the saturated water vapor pressure of the canopy and the actual water vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy. The determination module is used to determine the canopy conductance based on the total canopy conductance and the canopy boundary layer conductance.

[0015] The method and system for measuring the conductance of low-growing vegetation canopy provided by this invention, by setting up an independent bare soil chamber and measuring the conductance simultaneously with the vegetation canopy, and by combining the physical principle that can separate canopy transpiration from soil evaporation, can effectively eliminate the interference of soil moisture evaporation on canopy conductance observation, thereby achieving rapid and accurate measurement of vegetation canopy conductance. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is one of the structural schematic diagrams of the measuring box provided by the present invention.

[0018] Figure 2 This is the second structural schematic diagram of the measuring box provided by the present invention.

[0019] Figure 3 This is a flowchart illustrating the method for measuring the canopy conductance of low vegetation provided by the present invention.

[0020] Figure 4 This is a block diagram of the low vegetation canopy conductance measurement system provided by the present invention.

[0021] Figure 5 This is one of the schematic diagrams of the operation interface of the human-computer interaction module provided by the present invention.

[0022] Figure 6 This is the second schematic diagram of the operation interface of the human-computer interaction module provided by the present invention.

[0023] Figure 7 This is the third schematic diagram of the operation interface of the human-computer interaction module provided by the present invention.

[0024] Figure label: 1. Measuring box; 11. First box body; 111. First opening; 112. First side plate; 113. Second side plate; 12. Second box body; 121. Second opening; 13. Third box body; 131. First cover plate; 132. Second cover plate; 133. Third side plate; 134. Fourth side plate; 14. Analysis box body; 15. Bare soil box body; 151. Box body; 152. Cover body; 16. First linear drive component; 17. Second linear drive component; 18. First linear guide rail; 19. Second linear guide rail; 20. Base; 21. Third linear drive component; 22. Fourth linear drive component; 23. Fifth linear drive component; 24. Sixth linear drive component. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0026] like Figure 1 and Figure 2 As shown, the low vegetation canopy conductance measurement system of this invention includes: a measurement box 1, a sensor module, and a control motherboard.

[0027] The measuring chamber 1 includes a sample chamber, a gas analysis chamber, and a bare soil chamber. The volume of the sample chamber is adjustable and it is in fluid communication with the gas analysis chamber. For example, the sample chamber is adjustable in height, thereby achieving volume adjustment to accommodate vegetation at different heights.

[0028] The sensor module is used to measure the water vapor concentration in the bare soil chamber, the water vapor concentration in the sample chamber, the canopy temperature, the air temperature, the relative humidity, the sample chamber volume, the projected area of ​​the vegetation canopy, the surface area of ​​the bare soil in the sample chamber, the canopy transmittance, and the atmospheric pressure. The sensor module includes a first infrared moisture sensor, a second infrared moisture sensor, a thermal infrared camera, a temperature sensor, a humidity sensor, a rangefinder, a depth camera, a quantum optical sensor, and an atmospheric pressure sensor. It should be noted that the temperature and humidity sensors can also be integrated. Specifically, the first infrared moisture sensor measures the water vapor concentration in the sample chamber, the second infrared moisture sensor measures the water vapor concentration in the bare soil chamber, the thermal infrared camera measures the canopy temperature, the temperature sensor measures the air temperature, the humidity sensor measures the relative humidity, the rangefinder measures the height of the sample chamber to indirectly obtain the sample chamber volume, the depth camera measures the projected area of ​​the vegetation canopy and the surface area of ​​the bare soil in the sample chamber, the quantum optical sensor measures the canopy transmittance, and the atmospheric pressure sensor measures the atmospheric pressure.

[0029] The sensor module is electrically connected to the control motherboard, which receives and processes various data sent by the sensor module. Specifically, the control motherboard is configured to: determine soil evaporation based on the evaporation of exposed soil and evaporation of soil shaded by vegetation; determine the canopy transpiration rate based on evapotranspiration per unit time, the projected area of ​​the vegetation canopy, and soil evaporation; determine the total canopy conductance based on the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure and the canopy transpiration rate; determine the canopy boundary layer conductance based on the molar mass of water, the latent heat of vaporization of water, air density, specific heat capacity of air, the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure, and the canopy boundary layer conductance; and determine the canopy conductance based on the total canopy conductance and the canopy boundary layer conductance. It should be noted that the latent heat of vaporization of water, air density, and specific heat capacity of air can be obtained from tables based on atmospheric pressure.

[0030] Specifically, the movement of water vapor is affected by a series of frictional resistances. Different impedances together determine the water vapor exchange efficiency. Therefore, the "series structure" method is usually used when calculating the water vapor conductance of the canopy.

[0031] The total impedance during water vapor movement in low-lying vegetation is a combination of the stomatal impedance of the canopy and the boundary layer impedance of the canopy:

[0032] in, Canopy resistance (s·m) -1 ); Canopy stomatal resistance (s·m) -1 ); Canopy boundary layer resistance (S·m) -1 ).

[0033] Total conductance of the canopy G t Canopy conductance G c Canopy boundary layer conductance G b These are the reciprocals of their respective resistances:

[0034] Among them, G t Canopy conductance for water vapor (mol·m) -2 ·s -1 ); G c Canopy stomatal conductance for water vapor, mol·m-2 ·s -1 ); G b Canopy boundary layer conductance for water vapor (mol·m) -2 ·s -1 ).

[0035] Substituting formula 1-2 into formula 1-1, we get:

[0036] Therefore, the formula for calculating the conductance of low-growing vegetation canopy is:

[0037] Among them, for the total conductance of the canopy (G t In terms of: G t This can be simplified to the plant transpiration rate E. c The proportional relationship between the evaporation driving force ΔW, i.e., the water vapor concentration gradient from the intercellular spaces of the leaf to the atmosphere, is shown in the following formula:

[0038] in, Canopy transpiration rate (mol·m -2 ·s -1 ); ΔW is the water vapor concentration gradient.

[0039] The water vapor concentration gradient ΔW is calculated based on the difference between the saturated water vapor pressure between leaf cells and the actual atmospheric water vapor pressure. In this invention, the evaporation driving force is converted from the difference in water vapor pressure between the leaf and the air to the difference in water vapor pressure between the canopy and the air. The saturated water vapor pressure at the canopy level replaces the saturated water vapor pressure of the leaf cells in the original formula. Therefore, Formula 2-1 is transformed into:

[0040] VPD is the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure (Vapor Pressure Deficit, kPa).

[0041] For the canopy boundary layer conductance (G) b In terms of: When an object absorbs or releases heat, its phase changes but its temperature remains constant; this heat is called latent heat. Latent heat flux represents the energy required for water vapor to evaporate from the canopy. It is directly proportional to the product of air density and specific heat capacity, and also directly proportional to the ratio of the vapor transport gradient (VPD) to the physical impedance. The formula is as follows:

[0042] Where λE is the latent heat flux (W·m). -2 p is the air density (kg·m³). -3 ); Specific heat capacity of air (J·kg) -1 ·K -1 ); Canopy boundary layer resistance (S·m) -1 ); The water vapor saturation pressure of the canopy (kPa); This is the actual vapor pressure of air (kPa).

[0043] Substituting formulas 1-2a and 3-1 into formula 5-1, the result is as follows:

[0044] Where VPD is the difference between the canopy saturated water vapor pressure and the actual atmospheric water vapor pressure (kPa); G b Canopy boundary layer conductance for water vapor (mol·m) -2 ·s -1 ) To facilitate the final formula integration and calculation, the energy flux λE needs to be converted into the mass flux E here. c Because latent heat is often used to estimate surface evapotranspiration, which is composed of soil evaporation, water surface evaporation, and vegetation canopy transpiration, the two can be converted into each other after specific calculations.

[0045] Latent heat flux ( W·m -2 ) and transpiration rate (E c mol·s -1 ·m -2The unit conversion formula between regions is:

[0046] in, The latent heat of vaporization of water (J·kg) -1 ); Canopy transpiration rate (mol·s⁻¹) -1 ·m -2 ); The molar mass of water (0.018 kg·mol⁻¹) -1 ).

[0047] Substituting the constant value into formula 5-3, we can calculate:

[0048] Substituting Equation 5-4 into Equation 5-2, the canopy boundary layer conductance ( )for:

[0049] The main principle of the box method is to cover the entire plant with a box. The rate at which water accumulates inside the box within a short period is the plant's transpiration rate. Here, "entire plant" refers to a single plant or multiple plants (two or more). The box types are mainly divided into open and closed types. This invention uses a closed box.

[0050] Since the transpiration rate measured in a closed chamber includes both canopy transpiration and soil evapotranspiration, soil evapotranspiration needs to be separated from total transpiration. The TEBS (Two-Source Energy Balance) model is a two-source energy balance model used to estimate surface evapotranspiration. It estimates the contributions of canopy transpiration and soil evapotranspiration by distinguishing the energy exchange processes between the vegetation canopy and the soil surface.

[0051] The TEBS model has two impedance structures: parallel structure and series structure. When calculating different energy sources, the summation of energy is more consistent with the physical meaning of the series structure. Therefore, it is believed that the transpiration per unit time of the air cell containing vegetation and soil is the sum of the canopy transpiration and the soil evaporation.

[0052] in, Evaporation rate of the sample chamber per unit time (mol·s) -1 ); The transpiration rate of the vegetation canopy (rate per unit area, mol·s)-1 ·m -2 ); The projected area of ​​the vegetation canopy (m²) 2 ); Soil evaporation rate (per unit area rate, mol·s) -1 ·m -2 ); The soil surface area of ​​the sample chamber (m²) 2 ).

[0053] Therefore, the formula for calculating the transpiration rate of the vegetation canopy in the sample chamber is:

[0054] in, This refers to the amount of soil evaporation within the sample chamber.

[0055] In this embodiment, by setting up an independent bare soil chamber and simultaneously measuring conductance with the vegetation canopy, and by combining this with the physical principle of separating canopy transpiration from soil evaporation, the interference of soil moisture evaporation on canopy conductance observation can be effectively eliminated. Furthermore, the control motherboard can quickly and accurately measure vegetation canopy conductance based on various data measured by the sensor modules and the built-in calculation model.

[0056] In an optional embodiment, the control board is configured to determine the evaporation of bare soil based on the surface area of ​​bare soil in the sample chamber and the evaporation rate of bare soil. The control board is also configured to determine the evaporation of vegetated soil based on the evaporation rate of vegetated soil and the surface area of ​​vegetated soil; wherein the surface area of ​​vegetated soil is equal to the projected area of ​​the vegetation canopy.

[0057] Specifically, soil evaporation within the sample chamber It needs to be broken down into evaporation from vegetated soil and evaporation from bare soil, and evaporation from the sample chamber soil. The calculation formula is:

[0058] in, The soil surface area (m²) of the sample chamber is covered by vegetation. 2 ); The surface area of ​​the bare soil in the sample chamber (m²) 2 ); Evaporation rate of exposed soil (mol·s) -1 ·m -2 ); To prevent soil evaporation rate (mol·s) in the sample chamber from being blocked by vegetation -1 ·m -2 ).

[0059] In an optional embodiment, the control board is configured to determine the evaporation rate of the exposed soil based on the evaporation rate per unit time of the exposed soil chamber and the surface area of ​​the exposed soil chamber; wherein, the control board is further configured to determine the evaporation rate per unit time of the exposed soil chamber based on the water vapor concentration at the starting point of the exposed soil chamber, the water vapor concentration at the ending point of the exposed soil chamber, the volume of the exposed soil chamber, and the measurement time interval.

[0060] To separate soil evaporation rate from the results, this study added a bare soil chamber without vegetation to calculate the soil evaporation rate. The soil evaporation rate in the bare soil chamber is:

[0061] in, Evaporation rate per unit time in bare soil chamber (mol·s) -1 ); Water vapor concentration at the starting point in the bare soil chamber (mol·m -3 ); Water vapor concentration at the end point of the bare soil chamber (mol·m -3 ); The volume of the bare soil chamber box (m³) 3 ); The measurement time interval (s) is used.

[0062] Ess represents the evaporation rate per unit time for the bare soil chamber. Subsequent calculations require converting this to the evaporation rate per unit area. The evaporation rate per unit time for the bare soil chamber is Ess (mol·s). -1 ) and the evaporation rate of bare soil (Ese, mol·s) -1 ·m -2 The unit conversion formula between regions is:

[0063] in, The surface area of ​​the bare soil chamber (m²) 2 ); Evaporation rate of exposed soil (mol·s) -1 ·m -2 ).

[0064] In an optional embodiment, the control board is configured to determine the evaporation rate of the vegetation-shaded soil based on the evaporation rate of the bare soil, the natural constant, the extinction coefficient, and the leaf area index.

[0065] In simplified bare soil stripping calculations, the soil evaporation rate in vegetated environments is typically assumed to be the same as that in bare soil environments. However, this calculation method neglects the impact of vegetation on soil evaporation. To ensure the accuracy of the calculation results, the attenuation of soil evaporation due to vegetation presence needs to be considered. Since soil evaporation is closely related to the amount of solar radiation absorbed by the soil, the attenuation of incident radiation reduces the energy available for soil evaporation, thus lowering the evaporation rate. This phenomenon is similar to the Beer-Lambert Law (radiation attenuates exponentially as it passes through media such as plant canopies). Therefore, we assume that when vegetation intercepts solar radiation, the soil evaporation rate should follow the same exponential attenuation as the radiation, calculated using the following formula:

[0066] in, To prevent soil evaporation rate (mol·s) in the sample chamber from being blocked by vegetation -1 ·m -2 ); k is the extinction coefficient (0.92-0.98); LAI is the leaf area index.

[0067] In an optional embodiment, the control board is configured to determine the evaporation rate of vegetation-shaded soil based on the evaporation rate of bare soil, the incident photosynthetically active radiation above the canopy, and the photosynthetically active radiation of the ground surface below the canopy.

[0068] We can also directly observe the ratio of incident radiation to radiation absorbed by the soil to calculate the reduced evapotranspiration rate of the shaded soil. The calculation formula is as follows:

[0069] in, Photosynthetically active radiation (mol·s) of the surface below the canopy -1 ·m -2 ); Photosynthetically active radiation incident above the canopy (mol·s) -1 ·m -2 ).

[0070] The soil surface area covered by vegetation in the sample chamber can be approximately equal to the projected area of ​​the vegetation canopy. Therefore, formulas 6-6 and 6-7 can be modified as follows:

[0071] In an optional embodiment, the control board is configured to determine the evaporation rate per unit time based on the water vapor concentration at the beginning of the sample chamber, the water vapor concentration at the end of the sample chamber, the volume of the sample chamber, and the measurement time interval.

[0072] Within a closed enclosure, the moisture content in the air increases with transpiration from the plants. To calculate the transpiration rate, a time interval needs to be determined, during which sensors measure various parameters, including water vapor concentration, at a high time frequency. The actual water vapor volume is the product of the water vapor concentration difference and the system volume.

[0073] The evaporation rate of the sample chamber per unit time is:

[0074] in, Evaporation rate of the sample chamber per unit time (mol·s) -1 ); The initial water vapor concentration in the sample chamber (mol·m -3 ); The water vapor concentration at the end of the sample chamber (mol·m -3 ); The volume of the sample chamber (m³) 3 ); The measurement time interval (s) is used.

[0075] In an optional embodiment, the control board is configured to determine the canopy saturated vapor pressure based on the canopy temperature and the actual air vapor pressure based on the air temperature and relative humidity. Here, VPD typically refers to the difference between the actual air vapor pressure and the saturated vapor pressure at the same temperature; in this study, it specifically refers to the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure.

[0076] The formula for calculating VPD is as follows:

[0077] in, The water vapor saturation pressure of the canopy (kPa); This is the actual vapor pressure of air (kPa).

[0078] The Tetens formula can be used to calculate the saturated vapor pressure of the canopy and the actual vapor pressure of the air.

[0079] The formula for calculating the saturated vapor pressure of the canopy is:

[0080] in, Canopy temperature (°C).

[0081] The formula for calculating the actual water vapor pressure of air is:

[0082] in, Air temperature (°C); RH air Relative humidity of air (%).

[0083] Substituting formulas 3-2 and 3-3 into formula 3-1, the water vapor pressure difference at the interface between the vegetation canopy and the atmosphere is:

[0084] For vegetation canopy temperature (Tc), considering multiple factors, this study uses infrared thermal imaging technology to obtain vegetation canopy temperature.

[0085] First, the DN values ​​obtained from the thermal infrared camera are converted:

[0086] in, DN is the original temperature (°C); f is the original value acquired by the camera; f is the conversion factor, with a default value of 10.

[0087] The original temperature was then corrected using emissivity, atmospheric transmittance, air temperature, and the distance between the plant canopy and the thermal infrared camera to obtain the initial temperature.

[0088] in, Emittance, default value is 0.98; Atmospheric transmittance, with a default value of 1; D is the distance (m) between the plant canopy and the thermal infrared camera. Air temperature (°C).

[0089] Then, the initial temperatures within all vegetated areas are averaged to obtain the average canopy temperature:

[0090] in, is the average canopy temperature (°C); N is the number of pixels in the thermal imaging image of the vegetation canopy. The temperature value (°C) of the i-th pixel in the vegetation canopy.

[0091] The final calculated average canopy temperature is the canopy temperature required for this study.

[0092] Based on the above analysis, substituting formulas 6-3, 6-4, 6-5, 6-8, 6-9, and 6-10 into formula 6-2, we can obtain the canopy transpiration rate within the vegetation box as follows:

[0093] Substituting formulas 2-2 and 5-5 into formula 1-4, the formula for calculating canopy conductance is:

[0094] Considering that the water vapor pressure generated by vegetation canopy transpiration can interfere with the stomatal conductance measurement results, this study determined the maximum canopy conductance value observed during the measurement period as the canopy conductance of the vegetation.

[0095] In an optional embodiment, the control board is configured to determine the end of a single measurement when the rate of change of the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure reaches a set threshold.

[0096] The closed chamber calculates the transpiration rate by detecting the cumulative rate of water vapor concentration inside the chamber, which has significant advantages over the open chamber in terms of simple structure and low energy consumption. However, unlike the application of photosynthetic rate measurement, the application of transpiration rate measurement faces two major challenges: (1) the response of transpiration rate to VPDcanopy: the accumulation of water vapor generated by canopy transpiration leads to a rapid decrease in VPDcanopy, which in turn inhibits canopy conductance, causing the water vapor growth curve to show a non-linear saturation ("rapid increase-rapid stop") parabolic trend, resulting in an underestimation of the measured value; (2) soil evaporation interference: although the soil evaporation is relatively small, the dynamic increase of water vapor is composed of the water vapor contribution from soil evaporation and the superposition of canopy transpiration, and direct calculation will lead to an overestimation of Ec.

[0097] Analysis of over 50 sets of repeated experimental data revealed the following two main patterns in water vapor changes within the sealed chamber: (1) Positive feedback relationship between VPDcanopy and water vapor growth: Cross-time series analysis showed that VPDcanopy was significantly positively correlated with water vapor growth per unit time (ΔW) (r = 0.45 ± 0.14, p<0.001), which conforms to the feedback mechanism of "VPDcanopy increase - transpiration enhancement - water vapor accumulation - VPDcanopy decrease - stomatal conductance decrease - water vapor growth slows down or stops growing".

[0098] (2) Skewed distribution of water vapor growth per unit time: During the 300s observation period, the non-negative water vapor growth per unit time showed a consistent left-skewed distribution, that is, the frequency of low-increase events was high and the frequency of high-increase events was low. This study assumes that the high-frequency low-growth events are dominated by relatively stable soil evaporation and diffusion processes, while the low-frequency high-growth events are dominated by canopy transpiration.

[0099] Based on the above-mentioned patterns, this invention designs an algorithm to extract canopy transpiration (wvege) and effective transpiration time (Δtc) from the water vapor dynamic curve.

[0100] Utilize the characteristic that the VPD canopy drops rapidly, and determine the end of the transpiration-dominated stage at the time point when the water vapor growth tends to level off. Accumulate the water vapor before this time as the water vapor produced by transpiration (Water vapor produced by transpiration, wvege). Based on the skewed distribution, mark the non-negative water vapor growth per unit time into three intervals: transpiration-dominated (mean < Δw), water vapor diffusion-dominated (0.25mean < Δw < mean), and soil evaporation-dominated (0 < Δw < 0.25mean). Calculate the mean of Δw marked as soil evaporation-dominated and regard it as the soil evaporation rate (Soil evaporation rate, Esoil).

[0101] First, record the measurement time as t (unit: s).

[0102] Fit all the data within the measurement time to obtain Equation 8-1 as follows:

[0103] where a, b, and c are fitting coefficients; is the difference between the canopy saturated water vapor pressure and the actual water vapor pressure in the atmosphere at t seconds of measurement.

[0104] Differentiate Equation 8-1 to obtain Equation 8-2, ′ represents the change rate of the difference between the canopy saturated water vapor pressure and the actual water vapor pressure in the atmosphere:

[0105] When the change rate of the difference between the canopy saturated water vapor pressure and the actual water vapor pressure in the atmosphere reaches the set threshold x, the water vapor pressure difference reaches the minimum value, and it can be considered that the observation experiment can end at this time:

[0106] Record this time as the end time t of the effective transpiration of the canopy e , which is (unit: s).

[0107] where x is the threshold for determining the end of a single observation.

[0108] In an optional embodiment, the low vegetation canopy conductance measurement system further includes a power supply module, and the sensor module and the control main board are electrically connected to the power supply module.

[0109] It should be noted that the power supply module is used to power all functional components, providing a 12V regulated power output. The power supply module includes a solar panel, a solar controller, and a battery. The solar panel converts solar energy into electrical energy, the solar controller manages charging and discharging, safely stores solar energy in the battery, performs overcharge and undervoltage protection, and distributes power to ensure long-term stable operation of the system in the field.

[0110] In an optional embodiment, the low vegetation canopy conductance measurement system further includes: a human-machine interaction module electrically connected to the control motherboard, the human-machine interaction module being configured to receive parameter setting instructions, manual measurement control instructions, automatic measurement control instructions, and to display data information.

[0111] The human-computer interaction module will be described in detail below.

[0112] like Figure 5 As shown, after the low vegetation canopy conductance measurement system is powered on, the main interface is displayed. The main interface has two entry points: measurement and instrument presets. Figure 6 As shown, the instrument's preset interface allows modification of default parameter values, mainly including: chamber lifting height, reference chamber (bare soil chamber) volume and bottom area, and sample chamber (sample room) layer volume and bottom area. After setting, return to the main interface. Figure 7 As shown, the measurement interface includes two functions: data display and instrument operation. The measurement interface displays temperature and humidity parameters, photosynthetically active radiation parameters, water vapor concentration parameters, other parameters, and the final calculation results. The instrument operation section allows for both automatic and manual measurement settings. In manual measurement mode, the ventilation and lifting / lowering status of the measurement chamber can be controlled.

[0113] Secondly, such as Figure 1 and Figure 2 As shown, the measuring box 1 for measuring the canopy conductance of low-lying vegetation according to an embodiment of the present invention includes: First box 11; The second housing 12 is slidably disposed on the outside of the first housing 11; The third box 13 is slidably disposed outside the second box 12; wherein the first box 11, the second box 12 and the third box 13 enclose a sample chamber. The analysis chamber 14 has a gas analysis chamber that is in fluid communication with the sample chamber; The bare soil box 15 has a bare soil chamber; both the sample chamber and the bare soil chamber can be connected to or disconnected from the outside. Specifically, the sample chamber and the bare soil chamber are simultaneously connected to or disconnected from the outside.

[0114] It should be noted that the depth camera inside the sample chamber can accurately measure the height of the vegetation canopy, thereby adjusting the distance between the top of the sample chamber and the top of the vegetation canopy. Combined with the "Russian doll" box design, the height of the box can be automatically adjusted according to the height of the vegetation while maintaining the integrity and stability of the box structure. Furthermore, the multi-dimensional box openings ensure efficient air circulation between the inside and outside of the box when not being measured. This overcomes the problem that a fixed height of the box restricts the natural growth of vegetation, making long-term automatic measurement in the field impossible.

[0115] It should be noted that four sets of temperature and humidity sensors can be installed. Sensor 1 is installed inside the first chamber 11, sensor 2 inside the third chamber 13, sensor 3 on the inner wall of the bare soil chamber, and sensor 4 on the outside of the third chamber 13. Two sets of infrared moisture sensors can be installed, with an observation frequency ≥10 Hz. Sensor 1 is installed outside the sample chamber (i.e., inside the gas analysis chamber), connected to the top, middle, and bottom layers of the sample chamber via a flexible hose interface. Sensor 2 is installed outside the bare soil chamber 15, connected to the bare soil chamber via a flexible hose interface. The depth camera and infrared camera are located at the top center of the third chamber 13. Two sets of quantum optical sensors are used to acquire data on soil radiation absorption by vegetation. Sensor 1 is a linear rod-type quantum optical sensor installed inside the sample chamber, below the vegetation canopy; sensor 2 is a point-type quantum optical sensor installed outside the sample chamber, above the third chamber 13. A pressure sensor is used to acquire data on pressure changes within the sample chamber. One pressure sensor can be installed. The pressure sensor can be located inside the third chamber 13.

[0116] To achieve automatic control of the height of the measuring box 1, in an optional embodiment, such as... Figure 1 As shown, the measuring box 1 used for measuring the canopy conductance of low-growing vegetation also includes: The first linear drive 16 is disposed in the sample chamber and located between the first box 11 and the second box 12, and is configured to drive the second box 12 to move relative to the first box 11 along the height of the measuring box 1. The second linear drive 17 is disposed outside the sample chamber and between the second chamber 12 and the third chamber 13, and is configured to drive the third chamber 13 to move relative to the second chamber 12 along the height of the measuring chamber 1.

[0117] It should be noted that both the first linear drive component 16 and the second linear drive component 17 can be electric actuators.

[0118] Understandably, when the height between the top of the box and the vegetation surface reaches the target distance control threshold, such as 50cm, the electric push rod will automatically rise so that the height of the box can adapt to the needs of plant growth.

[0119] To achieve stability in the movement between the enclosures and to improve the structural strength of the enclosures, in optional embodiments, such as Figure 1 As shown, the measuring box 1 used for measuring the canopy conductance of low-growing vegetation also includes: The first linear guide 18 and the first slider are disposed in the first housing 11 and the first slider is disposed in the second housing 12. The first slider is slidably disposed in the first linear guide 18. A second linear guide rail 19 and a first slider are provided. The second linear guide rail 19 is disposed in the second housing 12, and the second slider is disposed in the third housing 13. The second slider is slidably disposed on the second linear guide rail 19. For example, both the first slider and the second slider can be sliders.

[0120] In optional embodiments, such as Figure 1 As shown, the top of the side of the first housing 11 is provided with a first opening 111, and the top of the side of the second housing 12 is provided with a second opening 121; wherein, when the second housing 12 moves relative to the first housing 11 along the height of the measuring box 1, the sample chamber is connected to or cut off from the outside through the first opening 111; when the third housing 13 moves relative to the second housing 12 along the height of the measuring box 1, the sample chamber is connected to or cut off from the outside through the second opening 121.

[0121] It should be noted that the first opening 111 can be located on any one of the four sides of the first housing 11, for example, two first openings 111 can be symmetrically arranged. The second opening 121 can be located on any one of the four sides of the second housing 12, for example, two second openings 121 can be symmetrically arranged.

[0122] Understandably, to prevent rainwater erosion, measuring box 1 adopts a nested structure, with each layer increasing in size from bottom to top. Furthermore, the frame material can be industrial aluminum profiles and high-transparency acrylic sheets. Sealing silicone strips are installed at the joints between the acrylic sheet and the aluminum profiles, and airtight weatherstripping is installed at each point of relative movement within the box to ensure airtightness.

[0123] This invention utilizes a multi-layered box structure design reminiscent of Russian nesting dolls, where multiple layers are nested together and connected by electro-hydraulic rods, allowing for a minimum height of a single layer. During testing, each layer remains sealed to prevent gas exchange between the inside and outside of the box. However, even with the box sealed, changes in temperature and humidity can lead to differences in the internal and external environments, impacting vegetation growth.

[0124] To this end, the present invention further leverages the structural advantages of the "Russian doll" design, enabling ventilation between the layers of the box in non-measuring states, and can be equipped with an active gas flow module, such as a fan, to achieve rapid balance between the internal and external environments.

[0125] In optional embodiments, such as Figure 1 As shown, the measuring box 1 for measuring the canopy conductance of low vegetation also includes a base 20 and a third linear drive 21. The first box 11 is mounted on the base 20 via the third linear drive 21. Under the drive of the third linear drive 21, the first box 11 can be separated from or connected to the base 20.

[0126] In practical applications, the bare soil box 15 includes a housing 151 and a cover 152. The housing 151 is disposed within the base 20, and the cover 152 is disposed within the first housing 11. When the third linear drive 21 drives the first housing 11 to move relative to the base 20, the cover 152 can be separated from or connected to the housing 151. In this way, the bare soil box 15 can be automatically opened and closed.

[0127] It is particularly important to note that precise movement of the second housing 12 relative to the first housing 11 can be achieved by setting proximity switches, for example, by controlling the movement of the first linear drive 16. Similarly, precise movements of the second linear drive 17 and the third linear drive 21 can be controlled by corresponding proximity switches.

[0128] To further improve ventilation, in optional embodiments, such as Figure 2 As shown, the side of the first box 11 includes a first side plate 112 and a second side plate 113, with the first side plate 112 located below the second side plate 113; the measuring box 1 for measuring the canopy conductance of low vegetation also includes a fourth linear drive 22, which is connected to the first side plate 112. Under the drive of the fourth linear drive 22, the first side plate 112 can move relative to the second side plate 113 so that the sample chamber can be connected to or cut off from the outside.

[0129] It should be noted that the ventilation opening is formed by moving the first side plate 112 relative to the second side plate 113. The ventilation opening can be set on any one of the four sides of the first housing 11, for example, two ventilation openings are set symmetrically.

[0130] To further improve ventilation, in optional embodiments, such as Figure 2As shown, the side of the third box 13 includes a third side plate 133 and a fourth side plate 134, with the third side plate 133 located above the fourth side plate 134; the measuring box 1 for measuring the canopy conductance of low vegetation also includes a fifth linear drive 23, which is connected to the third side plate 133. Under the drive of the fifth linear drive 23, the third side plate 133 can move relative to the fourth side plate 134 so that the sample chamber can be connected to or cut off from the outside.

[0131] It should be noted that the ventilation opening is formed by moving the third side plate 133 relative to the fourth side plate 134. The ventilation opening can be set on any one of the four sides of the third housing 13, for example, two ventilation openings are set symmetrically.

[0132] To further improve ventilation, in optional embodiments, such as Figure 1 and 2 As shown, the top of the third box 13 includes a first cover plate 131 and a second cover plate 132; the measuring box 1 for measuring the canopy conductance of low vegetation also includes a sixth linear drive 24, which is connected to the first cover plate 131. Under the drive of the sixth linear drive 24, the first cover plate 131 can move relative to the second cover plate 132 so that the sample chamber can be connected to or cut off from the outside.

[0133] Understandably, the top of the third chamber 13 uses a flat-pull roller shutter design, which can not only allow the air inside and outside the sample chamber to circulate fully in the horizontal and vertical directions and improve ventilation efficiency, but also ensure that the natural lighting of the sample chamber is not obstructed and that it can receive rainfall when not being measured, thus reducing the impact on the natural growth of vegetation.

[0134] In practical applications, the analysis chamber 14 includes a chamber body, a gas guide pipe, and a gas pump. The chamber body is located outside the second chamber 12 and forms a gas analysis chamber. Under the action of the gas pump, water vapor in the sample chamber enters the gas analysis chamber through the gas guide pipe and flows back to the sample chamber.

[0135] Specifically, the air duct can be made of a porous, deformable tubular material and is laid out in both vertical and horizontal directions. This material is connected to the atmospheric water vapor infrared analyzer and can move as the measuring chamber 1 is raised and lowered. The atmospheric water vapor infrared analyzer has its own air pump sampling component, which can collect gas samples from all directions inside the chamber. The collected gas samples are uniformly mixed in the infrared gas analysis chamber and then measured to obtain the average atmospheric water vapor concentration inside the chamber, providing data for the observation and calculation of vegetation canopy conductance.

[0136] Understandably, using high-frequency infrared analysis to measure atmospheric water vapor, with a maximum frequency of 20Hz, can quickly, synchronously, and accurately analyze the rising velocity of water vapor within chamber 14, and determine the observation end time based on the established model algorithm. Furthermore, it has developed a multi-dimensional atmospheric sampling and water vapor analysis method, covering vertical, horizontal, and distance dimensions from the blades, effectively avoiding the low accuracy of canopy conductance observations caused by fixed monitoring times and single-point sampling.

[0137] The following is an overall description of the operation process of the low vegetation canopy conductance measurement system according to an embodiment of the present invention.

[0138] Step 1: System startup, power supply self-test and parameter initialization After the equipment is powered on, the power supply system begins to supply power to the control motherboard and various functional modules. The system starts up and performs a diagnostic check on the power status (battery voltage, solar panel charging current), then loads the user-preset measurement parameters (including measurement interval, acquisition frequency, initial height of the enclosure, water vapor concentration threshold, etc.). Subsequently, the system self-test program is executed to diagnose the status of each sensor and each electric actuator, confirming that each module is functioning normally.

[0139] Step 2: Automatically adjust the height of the cabinet In non-measuring states, the equipment is periodically activated, with the control motherboard driving a depth camera to monitor the distance between the top of the vegetation canopy and the top of the enclosure. The control system compares this measurement with a set threshold; if it is less than the threshold, it drives an electric actuator to automatically adjust the enclosure height, ensuring that the top of the enclosure and the top of the canopy maintain a preset optimal relative position to minimize microenvironmental disturbances.

[0140] Step 3: Start high-frequency data acquisition After ventilation is complete, the equipment closes all openings and vents to form a closed system. It monitors environmental conditions such as temperature, humidity, and light intensity inside the chamber, as well as changes in H2O gas concentration, and transmits the data back to the control mainboard.

[0141] Step 4: Balance the internal and external environments of the chamber Before each measurement, the top covers of the sample chamber and the bare soil chamber are opened, and the forced ventilation system is activated to allow for sufficient air exchange between the chamber and the external environment. The system monitors the internal temperature and H2O gas concentration in real time. Once the difference between the internal and external environments reaches a set threshold range, the forced ventilation process ends, and the chamber is ready to enter the closed measurement state.

[0142] Step 5: Create a closed measurement environment and start the measurement and analysis. Once the internal and external environments reach equilibrium, the ventilation channels close and the box rises to a set threshold distance from the top of the vegetation canopy, cutting off airflow between the inside and outside of the box and creating a closed environment through the lifting box.

[0143] Step Six: Collect high-frequency data and analyze and determine the measurement end time in real time. When the enclosed environment of the chamber is established, the sensor module, data acquisition module, and control motherboard work in coordination. The sensor module uses high-frequency detection to measure atmospheric water vapor and temperature, canopy temperature, and air pressure inside the chamber, as well as atmospheric temperature and humidity outside the chamber. This information is transmitted to the data acquisition module, which converts the electrical signals into digital signals and sends them to the control motherboard. Based on the acquired high-frequency water vapor content data inside the chamber, the control motherboard uses a built-in algorithm model to determine the end time of the measurement in real time. When a specified threshold is reached, the measurement is considered complete. Simultaneously, atmospheric water vapor data is acquired in the bare soil chamber and the sample chamber.

[0144] Step 7: Calculate the canopy conductance Based on the above data and the built-in calculation model, the control motherboard automatically calculates and outputs the total conductance value of the canopy.

[0145] Step 8: Data Storage and Result Display The control motherboard stores all raw monitoring data and calculation results in its local storage unit. This data can be displayed on the local interface or transmitted to external devices via a data interface, depending on the settings.

[0146] Step 9: Restore test waiting state After completing this measurement, the device enters a low-power standby state, waiting for the next measurement interval to be triggered, and automatically starts a new measurement cycle from step two.

[0147] Thirdly, such as Figure 3 As shown, the method for measuring the canopy conductance of low-lying vegetation according to an embodiment of the present invention includes: S101, Soil evaporation is determined based on the evaporation of bare soil and the evaporation of soil covered by vegetation; S102, the vegetation canopy transpiration rate is determined based on the evapotranspiration per unit time, the vegetation canopy projection area and the soil evaporation. S103, the total conductance of the canopy is determined based on the difference between the saturated water vapor pressure of the canopy and the actual water vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy, and the conductance of the canopy boundary layer is determined based on the molar mass of water, the latent heat of vaporization of water, air density, air specific heat capacity, the difference between the saturated water vapor pressure of the canopy and the actual water vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy. S104, canopy conductance is determined based on total canopy conductance and canopy boundary layer conductance.

[0148] Specifically, the movement of water vapor is affected by a series of frictional resistances. Different impedances together determine the water vapor exchange efficiency. Therefore, the "series structure" method is usually used when calculating the water vapor conductance of the canopy.

[0149] The total impedance during water vapor movement in low-lying vegetation is a combination of the stomatal impedance of the canopy and the boundary layer impedance of the canopy:

[0150] in, Canopy resistance (s·m) -1 ); Canopy stomatal resistance (s·m) -1 ); Canopy boundary layer resistance (S·m) -1 ).

[0151] Total conductance of the canopy G t Canopy conductance G c Canopy boundary layer conductance G b These are the reciprocals of their respective resistances:

[0152] Among them, G t Canopy conductance for water vapor (mol·m) -2 ·s -1 ); G c Canopy stomatal conductance for water vapor, mol·m -2 ·s -1 ); G b Canopy boundary layer conductance for water vapor (mol·m) -2 ·s -1 ).

[0153] Substituting formula 1-2 into formula 1-1, we get:

[0154] Therefore, the formula for calculating the conductance of low-growing vegetation canopy is:

[0155] Among them, for the total conductance of the canopy (G t In terms of: G t This can be simplified to the plant transpiration rate E. cThe proportional relationship between the evaporation driving force ΔW, i.e., the water vapor concentration gradient from the intercellular spaces of the leaf to the atmosphere, is shown in the following formula:

[0156] in, Canopy transpiration rate (mol·m -2 ·s -1 ); ΔW is the water vapor concentration gradient.

[0157] The water vapor concentration gradient ΔW is calculated based on the difference between the saturated water vapor pressure between leaf cells and the actual atmospheric water vapor pressure. In this invention, the evaporation driving force is converted from the difference in water vapor pressure between the leaf and the air to the difference in water vapor pressure between the canopy and the air. The saturated water vapor pressure at the canopy level replaces the saturated water vapor pressure of the leaf cells in the original formula. Therefore, Formula 2-1 is transformed into:

[0158] VPD is the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure (Vapor Pressure Deficit, kPa).

[0159] For the canopy boundary layer conductance (G) b In terms of: When an object absorbs or releases heat, its phase changes but its temperature remains constant; this heat is called latent heat. Latent heat flux represents the energy required for water vapor to evaporate from the canopy. It is directly proportional to the product of air density and specific heat capacity, and also directly proportional to the ratio of the vapor transport gradient (VPD) to the physical impedance. The formula is as follows:

[0160] Where λE is the latent heat flux (W·m). -2 p is the air density (kg·m³). -3 ); Specific heat capacity of air (J·kg) -1 ·K -1 ); Canopy boundary layer resistance (S·m) -1 ); The water vapor saturation pressure of the canopy (kPa); This is the actual vapor pressure of air (kPa).

[0161] Substituting formulas 1-2a and 3-1 into formula 5-1, the result is as follows:

[0162] Where VPD is the difference between the canopy saturated water vapor pressure and the actual atmospheric water vapor pressure (kPa); G b Canopy boundary layer conductance for water vapor (mol·m) -2 ·s -1 ) To facilitate the final formula integration and calculation, the energy flux λE needs to be converted into the mass flux Ec. Since latent heat is often used to estimate the surface evapotranspiration, which is composed of soil evaporation, water surface evaporation, and vegetation canopy transpiration, the two can be converted into each other after specific calculations.

[0163] Latent heat flux ( W·m -2 ) and transpiration rate (E c mol·s -1 ·m -2 The unit conversion formula between regions is:

[0164] in, The latent heat of vaporization of water (J·kg) -1 ); Canopy transpiration rate (mol·s⁻¹) -1 ·m -2 ); Molar mass of water (0.018 kg·mol⁻¹) -1 ).

[0165] Substituting the constant value into formula 5-3, we can calculate:

[0166] Substituting Equation 5-4 into Equation 5-2, the canopy boundary layer conductance ( )for:

[0167] The main principle of the box method is to cover the entire plant with a box. The rate at which water accumulates inside the box within a short period is the plant's transpiration rate. The boxes are mainly divided into open and closed types. This invention uses a closed box.

[0168] Since the transpiration rate measured in a closed chamber includes both canopy transpiration and soil evapotranspiration, soil evapotranspiration needs to be separated from total transpiration. The TEBS (Two-Source Energy Balance) model is a two-source energy balance model used to estimate surface evapotranspiration. It estimates the contributions of canopy transpiration and soil evapotranspiration by distinguishing the energy exchange processes between the vegetation canopy and the soil surface.

[0169] The TEBS model has two impedance structures: parallel structure and series structure. When calculating different energy sources, the summation of energy is more consistent with the physical meaning of the series structure. Therefore, it is believed that the transpiration per unit time of the air cell containing vegetation and soil is the sum of the canopy transpiration and the soil evaporation.

[0170] in, Evaporation rate of the sample chamber per unit time (mol·s) -1 ); The transpiration rate of the vegetation canopy (rate per unit area, mol·s) -1 ·m -2 ); The projected area of ​​the vegetation canopy (m²) 2 ); Soil evaporation rate (per unit area rate, mol·s) -1 ·m -2 ); The soil surface area of ​​the sample chamber (m²) 2 ).

[0171] Therefore, the formula for calculating the transpiration rate of the vegetation canopy in the sample chamber is:

[0172] in, This refers to the amount of soil evaporation within the sample chamber.

[0173] In this embodiment, by setting up an independent bare soil chamber and measuring conductance simultaneously with the vegetation canopy, and by combining the physical principle that can separate canopy transpiration from soil evaporation, the interference of soil moisture evaporation on canopy conductance observation can be effectively eliminated, thereby achieving rapid and accurate measurement of vegetation canopy conductance.

[0174] In an optional embodiment, the evaporation rate of exposed soil is obtained as follows: The evaporation rate of the exposed soil was determined based on the surface area of ​​the exposed soil in the sample chamber and the evaporation rate of the exposed soil.

[0175] The method for obtaining the evaporation of soil blocked by vegetation is as follows: The evaporation of the vegetated soil is determined based on the evaporation rate of the vegetated soil and the surface area of ​​the vegetated soil; wherein the surface area of ​​the vegetated soil is equal to the projected area of ​​the vegetation canopy.

[0176] Specifically, soil evaporation within the sample chamber It needs to be broken down into evaporation from vegetated soil and evaporation from bare soil, and evaporation from the sample chamber soil. The calculation formula is:

[0177] in, The soil surface area (m²) of the sample chamber is covered by vegetation. 2 ); The surface area of ​​the bare soil in the sample chamber (m²) 2 ); Evaporation rate of exposed soil (mol·s) -1 ·m -2 ); To prevent soil evaporation rate (mol·s) in the sample chamber from being blocked by vegetation -1 ·m -2 ).

[0178] In an optional embodiment, the evaporation rate of exposed soil is obtained as follows: The evaporation rate of exposed soil is determined based on the evaporation rate per unit time in the exposed soil chamber and the surface area of ​​the exposed soil chamber. Specifically, the evaporation rate per unit time in the exposed soil chamber is determined based on the water vapor concentration at the starting point and the water vapor concentration at the ending point of the exposed soil chamber, the volume of the exposed soil chamber, and the measurement time interval.

[0179] To separate soil evaporation rate from the results, this study added a bare soil chamber without vegetation to calculate the soil evaporation rate. The soil evaporation rate in the bare soil chamber is:

[0180] in, Evaporation rate per unit time in bare soil chamber (mol·s) -1 ); Water vapor concentration at the starting point in the bare soil chamber (mol·m -3 ); Water vapor concentration at the end point of the bare soil chamber (mol·m -3 ); The volume of the bare soil chamber box (m³)3 ); The measurement time interval (s) is used.

[0181] Ess represents the evaporation rate per unit time for the bare soil chamber. Subsequent calculations require converting this to the evaporation rate per unit area. The evaporation rate per unit time for the bare soil chamber is Ess (mol·s). -1 ) and the evaporation rate of bare soil (Ese, mol·s) -1 ·m -2 The unit conversion formula between regions is:

[0182] in, The surface area of ​​the bare soil chamber (m²) 2 ); Evaporation rate of exposed soil (mol·s) -1 ·m -2 ).

[0183] In an optional embodiment, the soil evaporation rate blocked by vegetation is obtained as follows: The evaporation rate of soil shaded by vegetation was determined based on the evaporation rate of bare soil, natural constant, extinction coefficient, and leaf area index.

[0184] In simplified bare soil stripping calculations, the soil evaporation rate in vegetated environments is typically assumed to be the same as that in bare soil environments. However, this calculation method neglects the impact of vegetation on soil evaporation. To ensure the accuracy of the calculation results, the attenuation of soil evaporation due to vegetation presence needs to be considered. Since soil evaporation is closely related to the amount of solar radiation absorbed by the soil, the attenuation of incident radiation reduces the energy available for soil evaporation, thus lowering the evaporation rate. This phenomenon is similar to the Beer-Lambert Law (radiation attenuates exponentially as it passes through media such as plant canopies). Therefore, we assume that when vegetation intercepts solar radiation, the soil evaporation rate should follow the same exponential attenuation as the radiation, calculated using the following formula:

[0185] in, To prevent soil evaporation rate (mol·s) in the sample chamber from being blocked by vegetation -1 ·m -2 ); k is the extinction coefficient (0.92~0.98); LAI is the leaf area index.

[0186] In an optional embodiment, the soil evaporation rate blocked by vegetation is obtained as follows: The evaporation rate of soil shaded by vegetation was determined based on the evaporation rate of bare soil, the incident photosynthetically active radiation above the canopy, and the photosynthetically active radiation on the ground surface below the canopy.

[0187] We can also directly observe the ratio of incident radiation to radiation absorbed by the soil to calculate the reduced evapotranspiration rate of the shaded soil. The calculation formula is as follows:

[0188] in, Photosynthetically active radiation (mol·s) of the surface below the canopy -1 ·m -2 ); Photosynthetically active radiation incident above the canopy (mol·s) -1 ·m -2 ).

[0189] The soil surface area covered by vegetation in the sample chamber can be approximately equal to the projected area of ​​the vegetation canopy. Therefore, formulas 6-6 and 6-7 can be modified as follows:

[0190] In an optional embodiment, the evaporation rate per unit time is obtained as follows: The evaporation rate per unit time is determined based on the water vapor concentration at the starting point of the sample chamber, the water vapor concentration at the ending point of the sample chamber, the volume of the sample chamber, and the measurement time interval.

[0191] In a closed enclosure, the moisture content in the air increases with transpiration from the plants. To calculate the transpiration rate, time intervals need to be set, measuring the indoor water vapor concentration at the beginning and again at the end. The actual water vapor volume is the product of the water vapor concentration difference and the system volume.

[0192] The evaporation rate of the sample chamber per unit time is:

[0193] in, Evaporation rate of the sample chamber per unit time (mol·s) -1 ); The initial water vapor concentration in the sample chamber (mol·m -3 ); The water vapor concentration at the end of the sample chamber (mol·m -3 ); The volume of the sample chamber (m³) 3 ); The measurement time interval (s) is used.

[0194] In an optional embodiment, the canopy saturated vapor pressure is obtained as follows: ; 3-2 in, The saturated vapor pressure of the canopy. Canopy temperature; The actual atmospheric water vapor pressure is obtained as follows: ; 3-3 in, This represents the actual water vapor pressure in the air. For air temperature, RH air This refers to the relative humidity of the air.

[0195] Substituting formulas 3-2 and 3-3 into formula 3-1, the water vapor pressure difference at the interface between the vegetation canopy and the atmosphere is:

[0196] In an optional embodiment, the canopy temperature is obtained as follows: The raw values ​​obtained from the thermal infrared camera are converted by a conversion factor to obtain the raw canopy temperature. The original canopy temperature was corrected by emissivity, atmospheric transmittance, air temperature, and the distance between the plant canopy and the thermal infrared camera to obtain the initial canopy temperature. The average of the initial canopy temperatures corresponding to all vegetation zones is calculated to determine the canopy temperature.

[0197] For vegetation canopy temperature (Tc), considering multiple factors, this study uses infrared thermal imaging technology to obtain vegetation canopy temperature.

[0198] First, the DN values ​​obtained from the thermal infrared camera are converted:

[0199] in, DN is the original temperature (°C); f is the original value acquired by the camera; f is the conversion factor, with a default value of 10.

[0200] The original temperature was then corrected using emissivity, atmospheric transmittance, air temperature, and the distance between the plant canopy and the thermal infrared camera to obtain the initial temperature.

[0201] in, Emittance, default value is 0.98; Atmospheric transmittance, with a default value of 1; D is the distance (m) between the plant canopy and the thermal infrared camera. Air temperature (°C).

[0202] Then, the initial temperatures within all vegetated areas are averaged to obtain the average canopy temperature:

[0203] in, is the average canopy temperature (°C); N is the number of pixels in the thermal imaging image of the vegetation canopy. The temperature value (°C) of the i-th pixel in the vegetation canopy.

[0204] The final calculated average canopy temperature is the canopy temperature required for this study.

[0205] Based on the above analysis, substituting formulas 6-3, 6-4, 6-5, 6-8, 6-9, and 6-10 into formula 6-2, we can obtain the canopy transpiration rate within the vegetation box as follows:

[0206] Substituting formulas 2-2 and 5-5 into formula 1-4, the formula for calculating canopy conductance is:

[0207] Considering that the water vapor pressure generated by vegetation canopy transpiration can interfere with the stomatal conductance measurement results, this study determined the maximum canopy conductance value observed during the measurement period as the canopy conductance of the vegetation.

[0208] In an optional embodiment, it further includes: The single measurement is considered complete when the rate of change of the difference between the canopy saturated water vapor pressure and the actual atmospheric water vapor pressure reaches a set threshold.

[0209] First, record the measurement time as t (unit: s).

[0210] By fitting all the data within the measurement time period, we obtain Formula 8-1 as follows:

[0211] Where a, b, and c are the fitting coefficients; To measure the difference between the canopy saturated water vapor pressure and the actual atmospheric water vapor pressure at time t seconds.

[0212] Differentiating Equation 8-1, we obtain Equation 8-2. ′ represents the rate of change of the difference between the canopy saturated water vapor pressure and the actual atmospheric water vapor pressure:

[0213] When the rate of change of the difference between the canopy saturated water vapor pressure and the actual atmospheric water vapor pressure reaches a set threshold x, the water vapor pressure difference reaches its minimum value, and the observation experiment can be considered to have ended at this point.

[0214] This moment is recorded as the end of effective canopy transpiration, t. e That is (Unit: s).

[0215] Where x is the threshold for determining the end of a single observation.

[0216] The low vegetation canopy conductance measurement system provided by the present invention is described below. The low vegetation canopy conductance measurement system described below can be referred to in correspondence with the low vegetation canopy conductance measurement method described above.

[0217] like Figure 7 As shown, the low vegetation canopy conductance measurement system includes: a first calculation module 401, a second calculation module 402, a third calculation module 403, and a determination module 404.

[0218] The first calculation module 401 is used to determine the soil evaporation based on the evaporation of bare soil and the evaporation of soil covered by vegetation. The second calculation module 402 is used to determine the transpiration rate of the vegetation canopy based on the evaporation rate per unit time, the projected area of ​​the vegetation canopy, and the soil evaporation rate. The third calculation module 403 is used to determine the total conductance of the canopy based on the difference between the saturated water vapor pressure of the canopy and the actual water vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy, and to determine the canopy boundary layer conductance based on the molar mass of water, the latent heat of vaporization of water, air density, air specific heat capacity, the difference between the saturated water vapor pressure of the canopy and the actual water vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy. The determination module 404 is used to determine the canopy conductance based on the total canopy conductance and the canopy boundary layer conductance.

[0219] On the other hand, the present invention also provides a computer program product, which includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the low-growing vegetation canopy conductance measurement method provided by the above methods. The method includes: step 101, determining soil evaporation based on the evaporation of bare soil and the evaporation of soil covered by vegetation; step 102, determining the vegetation canopy transpiration rate based on evapotranspiration per unit time, the projected area of ​​the vegetation canopy, and the soil evaporation; step 103, determining the total canopy conductance based on the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure and the vegetation canopy transpiration rate, and determining the canopy boundary layer conductance based on the molar mass of water, the latent heat of vaporization of water, air density, air specific heat capacity, the difference between the canopy saturated vapor pressure and the actual atmospheric vapor pressure, and the vegetation canopy transpiration rate; and step 104, determining the canopy conductance based on the total canopy conductance and the canopy boundary layer conductance.

[0220] In another aspect, the present invention also provides a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements a method for measuring the conductance of low-lying vegetation canopy provided by the methods described above. This method includes: step 101, determining soil evaporation based on the evaporation of bare soil and the evaporation of soil shaded by vegetation; step 102, determining the transpiration rate of the vegetation canopy based on evapotranspiration per unit time, the projected area of ​​the vegetation canopy, and the soil evaporation; step 103, determining the total conductance of the canopy based on the difference between the saturated vapor pressure of the canopy and the actual vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy, and determining the canopy boundary layer conductance based on the molar mass of water, the latent heat of vaporization of water, air density, air specific heat capacity, the difference between the saturated vapor pressure of the canopy and the actual vapor pressure of the atmosphere, and the transpiration rate of the vegetation canopy; and step 104, determining the canopy conductance based on the total canopy conductance and the canopy boundary layer conductance.

[0221] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0222] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0223] Finally, it should be noted that the terms "parallel" and "perpendicular" in the embodiments of this invention should not be strictly limited to a geometric sense. At least manufacturing and installation errors should be considered. For example, an error of ±10° should be within the protection range of the embodiments of this invention. The above embodiments are only used to illustrate the technical solutions of this invention, and not to limit it. Although the invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this invention.

Claims

1. A method for measuring the canopy conductance of low-growing vegetation, characterized in that, include: Soil evaporation is determined based on the evaporation of bare soil and the evaporation of soil covered by vegetation. The transpiration rate of the vegetation canopy is determined based on the evaporation rate per unit time, the projected area of ​​the vegetation canopy, and the soil evaporation rate. The total conductance of the canopy is determined based on the difference between the saturated vapor pressure of the canopy and the actual vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy. The conductance of the canopy boundary layer is determined based on the molar mass of water, the latent heat of vaporization of water, air density, specific heat capacity of air, the difference between the saturated vapor pressure of the canopy and the actual vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy. The canopy conductance is determined based on the total canopy conductance and the canopy boundary layer conductance.

2. The method for measuring the conductance of low-lying vegetation canopy according to claim 1, characterized in that, The method for obtaining the evaporation rate of the exposed soil is as follows: The evaporation rate of the exposed soil was determined based on the surface area of ​​the exposed soil in the sample chamber and the evaporation rate of the exposed soil.

3. The method for measuring the canopy conductance of low-lying vegetation according to claim 2, characterized in that, The method for obtaining the evaporation rate of the exposed soil is as follows: The evaporation rate of the exposed soil is determined based on the evaporation rate per unit time of the exposed soil chamber and the surface area of ​​the exposed soil chamber; wherein, the evaporation rate per unit time of the exposed soil chamber is determined based on the water vapor concentration at the starting point of the exposed soil chamber, the water vapor concentration at the ending point of the exposed soil chamber, the volume of the exposed soil chamber, and the measurement time interval.

4. The method for measuring the conductance of low-lying vegetation canopy according to claim 2, characterized in that, The method for obtaining the evaporation rate of the soil blocked by vegetation is as follows: The evaporation rate of the soil covered by vegetation is determined based on the evaporation rate of the soil covered by vegetation and the surface area of ​​the soil covered by vegetation; wherein the surface area of ​​the soil covered by vegetation is equal to the projected area of ​​the vegetation canopy.

5. The method for measuring the conductance of low-lying vegetation canopy according to claim 4, characterized in that, The method for obtaining the soil evaporation rate blocked by vegetation is as follows: The evaporation rate of the vegetation-shaded soil is determined based on the evaporation rate of the exposed soil, the natural constant, the extinction coefficient, and the leaf area index.

6. The method for measuring the canopy conductance of low-lying vegetation according to claim 4, characterized in that, The method for obtaining the soil evaporation rate blocked by vegetation is as follows: The evaporation rate of the vegetation-shaded soil is determined based on the evaporation rate of the exposed soil, the incident photosynthetically active radiation above the canopy, and the photosynthetically active radiation on the ground surface below the canopy.

7. The method for measuring the canopy conductance of low-lying vegetation according to claim 1, characterized in that, The method for obtaining the evaporation rate per unit time is as follows: The evaporation rate per unit time is determined based on the water vapor concentration at the starting point of the sample chamber, the water vapor concentration at the ending point of the sample chamber, the volume of the sample chamber, and the measurement time interval.

8. The method for measuring the canopy conductance of low-lying vegetation according to claim 1, characterized in that, The method for obtaining the canopy saturated vapor pressure is as follows: ； in, The saturated vapor pressure of the canopy. Canopy temperature; The method for obtaining the actual atmospheric water vapor pressure is as follows: ； in, This represents the actual water vapor pressure in the air. For air temperature, RH air This refers to the relative humidity of the air.

9. The method for measuring the canopy conductance of low-lying vegetation according to claim 8, characterized in that, The canopy temperature is obtained as follows: The raw values ​​obtained from the thermal infrared camera are converted by a conversion factor to obtain the raw canopy temperature. The original canopy temperature was corrected by emissivity, atmospheric transmittance, air temperature, and the distance between the plant canopy and the thermal infrared camera to obtain the initial canopy temperature. The average of the initial canopy temperatures corresponding to all vegetation zones is calculated to determine the canopy temperature.

10. The method for measuring the canopy conductance of low-lying vegetation according to claim 1, characterized in that, Also includes: The single measurement is considered complete when the rate of change of the difference between the canopy saturated water vapor pressure and the actual atmospheric water vapor pressure reaches a set threshold.

11. A system for measuring the conductance of low-lying vegetation canopy, characterized in that, include: The first calculation module is used to determine soil evaporation based on the evaporation of bare soil and the evaporation of soil covered by vegetation. The second calculation module is used to determine the transpiration rate of the vegetation canopy based on the evaporation per unit time, the projected area of ​​the vegetation canopy, and the soil evaporation. The third calculation module is used to determine the total conductance of the canopy based on the difference between the saturated water vapor pressure of the canopy and the actual water vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy, and to determine the canopy boundary layer conductance based on the molar mass of water, the latent heat of vaporization of water, air density, specific heat capacity of air, the difference between the saturated water vapor pressure of the canopy and the actual water vapor pressure of the atmosphere and the transpiration rate of the vegetation canopy. The determination module is used to determine the canopy conductance based on the total canopy conductance and the canopy boundary layer conductance.

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