Method and device for monitoring transpiration capacity of trees with different heights

Abstract

The invention relates to the technical field of tree transpiration capacity monitoring, and discloses a method and device for monitoring transpiration capacity of trees at different heights, and the method comprises the steps: arranging a heating needle and at least two temperature measuring needles at a set distance in the longitudinal direction of a trunk; periodically executing different-power heating sequences including an excitation stage and a baseline stage on the heating needle, and applying thermal waves with at least two frequencies in the excitation stage; temperature parameters of all the temperature measuring needles are collected in the heating sequence period, and amplitude attenuation and phase lag of thermal waves in the longitudinal direction are calculated according to the temperature parameters; solving a thermal diffusion coefficient of the trunk based on amplitude attenuation, and solving an axial liquid convection velocity of the trunk based on phase lag and the thermal diffusion coefficient; determining the volumetric moisture content of the trunk according to the volumetric heat capacity model, and calculating the liquid flow density of the trunk based on the volumetric moisture content of the trunk; and performing coupling calculation on the liquid flow density, the trunk leaf area and the living xylem area to obtain the transpiration rate of the tree.

Description

Technical Field

[0001] The present invention relates to the technical field of tree transpiration capacity monitoring, and more particularly to a method and device for monitoring the transpiration capacity of trees at different heights. Background Art

[0002] Existing tree transpiration monitoring technologies include heat pulse, thermal diffusion, and Granier needle sensors. These primarily employ single-point heating and temperature measurement devices to invert sap flow parameters based on single-frequency thermal signals or temperature gradients under constant heating.

[0003] However, traditional single-point measurements have difficulty capturing the longitudinal transpiration heterogeneity of trees. The xylem activity and sap flow characteristics of tree trunks vary significantly along the longitudinal direction, especially for tall trees or stratified tree species. For example, monitoring of poplar plantations in the North China Plain in the Journal of Plant Ecology showed that the sap flow rate of trunks of different heights differed by 66% before and after the rainy season. The 4.00-7.00m stem segment is the main water storage site, while the 1.30-4.00m stem segment assumes the main water transport function. However, existing technologies can only obtain sap flow data at a single height and cannot reflect the longitudinal dynamic laws of the overall transpiration of trees.

[0004] At the same time, monitoring accuracy in complex environments is affected by multiple factors. The traditional single-frequency thermal signal method relies on the steady-state assumption and is easily affected by ambient temperature fluctuations and trunk structural heterogeneity, resulting in coupling errors between thermal diffusion and sap flow signals. The thermal diffusion method proposed by Granier calculates sap flow density through upper and lower temperature gradients, but when the temperature difference between day and night is large or the moisture content changes dynamically, its temperature signal cannot separate the effects of heat conduction and convection, resulting in a decrease in the reliability of long-term monitoring data. Although recent studies have attempted dual-mode switching technology, the core issues of multi-frequency signal separation and longitudinal monitoring have not yet been resolved, and the anti-interference ability in complex environments is insufficient. Summary of the Invention

[0005] The present invention provides a method and device for monitoring the transpiration capacity of trees at different heights, which solve the technical problems raised in the background technology.

[0006] In a first aspect, the present invention provides a method for monitoring the transpiration capacity of trees at different heights, comprising: Step 1: Arrange a heating needle and at least two temperature measuring needles at a set distance along the longitudinal direction of the tree trunk; Periodically performing a heating sequence of different powers including an excitation phase and a baseline phase on the heating needle, wherein heat waves of at least two frequencies are applied during the excitation phase; Step 2: During the heating sequence, the temperature parameters of each temperature measuring needle are collected, and the amplitude attenuation and phase lag of the thermal wave in the longitudinal direction are calculated based on the temperature parameters; Step 3, calculating the thermal diffusivity of the trunk based on the amplitude attenuation, and calculating the axial liquid convection velocity of the trunk based on the phase lag and the thermal diffusivity; Step 4: determining the volumetric moisture content of the trunk according to the volumetric heat capacity model, and calculating the sap flow density of the trunk based on the volumetric moisture content of the trunk; Step 5: Obtain the trunk leaf area and living xylem area of the tree trunk, and couple the sap flow density, trunk leaf area, and living xylem area to calculate the transpiration rate of the tree.

[0007] Furthermore, the temperature measuring needle includes an upper temperature measuring needle and a lower temperature measuring needle, and the upper temperature measuring needle and the lower temperature measuring needle are symmetrically arranged up and down with the heating needle as the center.

[0008] Furthermore, during the heating sequence, the temperature parameters of each temperature measuring needle are collected, and the amplitude attenuation and phase lag of the thermal wave in the longitudinal direction are calculated based on the temperature parameters, including: Sure and ,in, Indicates the temperature parameters of the upper temperature measuring needle timing, Indicates the temperature parameters of the lower temperature measuring needle timing; Set the temperature parameter of the timing and Perform fast Fourier transform to obtain frequency domain parameters and Among them, for or The i-th frequency domain parameter in is expressed as: , represents the amplitude, Indicates the phase, represents the angular frequency, , represents the frequency of the heat wave, represents the natural base, express or 's index; Based on frequency domain parameters and Extract the upper temperature probe amplitude , lower temperature probe amplitude , Upper temperature measuring needle phase and the phase of the lower temperature needle ; The formula for calculating amplitude attenuation is as follows: ; in, represents the amplitude attenuation at frequency f, represents the amplitude ratio at frequency f; The calculation formula for phase lag is as follows: ; in, represents the phase lag at frequency f, represents the phase difference at frequency f.

[0009] Furthermore, the thermal diffusion coefficient of the tree trunk is obtained based on the amplitude attenuation, including: Based on the fact that the thermal wave amplitude decays exponentially with distance in one-dimensional steady-state convection, the thermal diffusivity of the tree trunk is obtained by inversion as follows: ; in, represents the thermal diffusivity of the trunk at frequency f, Indicates the set distance between the heating needle and the temperature measuring needle; Determine the thermal diffusivity of the trunk at each frequency, and take the average of the thermal diffusivity of the trunk at all frequencies as the thermal diffusivity of the trunk .

[0010] Furthermore, the axial liquid convection velocity of the trunk is calculated based on the phase lag and the thermal diffusion coefficient, including According to the one-dimensional convection diffusion heat wave, the axial liquid convection velocity of the tree trunk is obtained by inverting the relationship between the phase lag and the axial liquid convection velocity, as follows: ; in, represents the axial liquid convection velocity of the trunk at frequency f; Determine the axial liquid convection velocity of the trunk at each frequency, and take the average of the axial liquid convection velocity of the trunk at all frequencies as the axial liquid convection velocity of the trunk .

[0011] Furthermore, the volumetric water content of the tree trunk is determined based on the volumetric heat capacity model, including: Based on prior knowledge, determine the volumetric heat capacity of the tree trunk in a dry state; the volumetric heat capacity is the product of the density and specific heat capacity of the tree trunk in a dry state; The volumetric water content of the trunk is determined based on a linear mixture of the volume fraction of the trunk with dry living xylem and free water as follows: ; in, represents the volumetric moisture content of the tree trunk, represents the volume heat capacity of the trunk in a dry state, represents the volumetric heat capacity of water, represents the volume heat capacity of the trunk in the growing state; Among them, the volume heat capacity of the trunk in the growth state is The results are obtained based on the temperature response method: Apply step heating to the heating needle to obtain the temperature parameters of the upper and lower temperature measuring needles in time sequence; The temperature parameters of the time series are fitted to a one-dimensional transient heat conduction model to obtain the volumetric heat capacity of the trunk in the growth state.

[0012] Furthermore, the sap flow density of the trunk is calculated based on the volumetric water content of the trunk, including: Sap flow density of tree trunk It is the product of the volumetric water content of the trunk and the axial liquid convection velocity.

[0013] Furthermore, the sap flow density, trunk leaf area and living xylem area are coupled and calculated to obtain the tree's transpiration rate; Trunk leaf area Acquired based on the optical LAI method; Living wood area The steps to obtain are as follows: Determination of living xylem thickness by electrical resistance tomography , and get the diameter of the trunk, then the radius of the trunk is: , the radius of the non-living xylem is: ; Living wood area The calculation formula is as follows: ; The transpiration rate of trees is calculated as follows: ; in, represents the transpiration rate of trees, represents the density of water, Represents the molar mass of water.

[0014] In a second aspect, a device for monitoring the transpiration capacity of trees at different heights comprises: A heating needle and at least two temperature measuring needles; When the one heating needle and the at least two temperature measuring needles perform a tree transpiration capacity monitoring operation, a method for monitoring the transpiration capacity of trees at different heights as described in any one of the items is executed.

[0015] The beneficial effects of the present invention are: 1. By introducing sinusoidal thermal waves of at least two frequencies and combining them with fast Fourier transforms, we analyze the amplitude decay and phase lag of the temperature signal. Amplitude decay reflects the characteristics of thermal diffusion, while phase lag is directly related to the convection velocity of the liquid flow. The joint inversion of the two avoids the ambiguity of a single parameter. Compared with existing technologies, this application significantly reduces the impact of environmental noise and improves monitoring stability under complex working conditions, making it particularly suitable for long-term continuous monitoring scenarios.

[0016] 2. By placing heating needles at intervals along the trunk's longitudinal axis and symmetrical temperature measuring needles, combined with multi-frequency thermal wave excitation and frequency domain analysis, key parameters such as thermal diffusivity and axial liquid convection velocity at different heights can be directly measured. This allows for quantitative monitoring of the tree's transpiration capacity at different longitudinal heights, solving the vertical monitoring problem for complex tree shapes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of a method for monitoring the transpiration capacity of trees at different heights according to the present invention; Figure 2 The present invention is a front view of a device for monitoring the transpiration capacity of trees at different heights. DETAILED DESCRIPTION

[0018] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed solely to enable those skilled in the art to better understand and implement the subject matter described herein, and that the functions and arrangements of the elements discussed may be varied without departing from the scope of this specification. Various examples may omit, substitute, or add various processes or components as needed. In addition, features described with respect to some examples may also be combined in other examples.

[0019] like Figures 1 and 2 As shown, a method for monitoring the transpiration capacity of trees at different heights comprises: Step 1: Arrange a heating needle and at least two temperature measuring needles at a set distance along the longitudinal direction of the tree trunk; Periodically performing a heating sequence of different powers including an excitation phase and a baseline phase on the heating needle, wherein heat waves of at least two frequencies are applied during the excitation phase; Step 2: During the heating sequence, the temperature parameters of each temperature measuring needle are collected, and the amplitude attenuation and phase lag of the thermal wave in the longitudinal direction are calculated based on the temperature parameters; Step 3, calculating the thermal diffusivity of the trunk based on the amplitude attenuation, and calculating the axial liquid convection velocity of the trunk based on the phase lag and the thermal diffusivity; Step 4: determining the volumetric moisture content of the trunk according to the volumetric heat capacity model, and calculating the sap flow density of the trunk based on the volumetric moisture content of the trunk; Step 5: Obtain the trunk leaf area and living xylem area of the tree trunk, and couple the sap flow density, trunk leaf area, and living xylem area to calculate the transpiration rate of the tree.

[0020] Preferably, the height of the tree is determined, and the tree is divided by experts to obtain multiple segments; for each segment, the transpiration rate of each segment is obtained by testing, and the average value of the transpiration rate is taken as the comprehensive transpiration rate of the trunk, so as to realize the transpiration capacity monitoring of trees of different heights.

[0021] Preferably, a stainless steel probe with a diameter of 0.8 mm and a length of 3 cm is used, with a built-in high-precision heating resistor (resistance 1Ω±5%), supporting 0.01-1W power adjustment and 0.002-0.02Hz sine wave output to ensure that heat waves are evenly injected into the living wood.

[0022] Preferably, a thermocouple probe (accuracy ±0.02°C, response time <0.5s) with a diameter of 0.5 mm and a length consistent with the heating needle is selected.

[0023] Optimally, the heating probe and temperature measuring probe are inserted into a constant-temperature water bath (25°C ± 0.1°C) and the no-load resistance value is measured. The resistance difference between the three is required to be less than 10% to avoid local overheating or temperature measurement deviation. When the heating probe was tested in an in vitro wood sample with a diameter at breast height of 20 cm and a moisture content of 30%, the peak temperature difference between the temperature measuring probes was less than 0.8°C when an average power of 0.5W was applied, ensuring that the activity of the xylem was not damaged. The temperature measuring probe was calibrated at multiple points using a standard thermocouple (grade ±0.01°C) to correct for temperature offset (temperature offset ≤ ±0.05°C), and the calibration coefficient was recorded for later data processing.

[0024] Preferably, the heating sequence is designed as an 8-minute cycle: Excitation phase (1 minute): Superimpose 0.002Hz and 0.01Hz dual-frequency sine wave heating, with an average power of 0.5W, to stimulate thermal wave signals; Decay stage (7 minutes): Stop heating, collect the temperature decay curve of the temperature measuring needle at a frequency of 1 Hz, and record the amplitude decay and phase lag data; Baseline stage: Low power (0.2W) DC heating to offset ambient temperature fluctuations and stabilize the baseline.

[0025] In one embodiment of the present invention, the temperature measuring needle includes an upper temperature measuring needle and a lower temperature measuring needle, and the upper temperature measuring needle and the lower temperature measuring needle are symmetrically arranged up and down with the heating needle as the center.

[0026] Preferably, the heating needles are arranged symmetrically up and down with the heating needle as the center, with a longitudinal spacing of 8 cm to meet the axial propagation distance requirement of the one-dimensional heat conduction model.

[0027] In one embodiment of the present invention, the frequencies corresponding to the heat waves include at least any two sinusoidal frequencies of 0.002, 0.005, 0.01 and 0.02 Hz.

[0028] In one embodiment of the present invention, the temperature parameters of each temperature measuring needle are collected during the heating sequence, and the amplitude attenuation and phase lag of the thermal wave in the longitudinal direction are calculated based on the temperature parameters, including: Sure and ,in, Indicates the temperature parameters of the upper temperature measuring needle timing, Indicates the temperature parameters of the lower temperature measuring needle timing; Set the temperature parameter of the timing and Perform fast Fourier transform to obtain frequency domain parameters and Among them, for or The i-th frequency domain parameter in is expressed as: , represents the amplitude, Indicates the phase, represents the angular frequency, , represents the frequency of the heat wave, represents the natural base, express or 's index; Based on frequency domain parameters and Extract the upper temperature probe amplitude , lower temperature probe amplitude , Upper temperature measuring needle phase and the phase of the lower temperature needle ; The formula for calculating amplitude attenuation is as follows: ; in, represents the amplitude attenuation at frequency f, represents the amplitude ratio at frequency f; The calculation formula for phase lag is as follows: ; in, represents the phase lag at frequency f, represents the phase difference at frequency f.

[0029] In one embodiment of the present invention, based on frequency domain parameters and Extract the upper temperature probe amplitude , lower temperature probe amplitude , Upper temperature measuring needle phase and the phase of the lower temperature needle ,include: Step 41, and It is a frequency domain complex parameter obtained by fast Fourier transform. Each parameter corresponds to a specific frequency f, as shown in the following example. , which contains the amplitude and phase information.

[0030] Step 42, For each frequency domain complex parameter in , calculate its modulus (absolute value): , the mode length is the amplitude of the upper temperature measuring needle at frequency f .

[0031] Step 43, For each frequency domain complex parameter, calculate its amplitude and angle, and use the inverse tangent function to obtain the phase of the upper temperature measuring needle at that frequency. .

[0032] Step 44, repeat the operation of step 42, Calculate the modulus of each frequency domain complex parameter in and get the amplitude of the temperature measuring needle at the corresponding frequency .

[0033] Step 45, repeat the operation of step 43, Calculate the phase angle of each frequency domain complex parameter in and get the phase of the temperature measuring needle at the corresponding frequency .

[0034] In detail, when the heat wave propagates longitudinally in the trunk, the absorption and scattering of heat by the wood will lead to energy loss, which is manifested as amplitude attenuation. The amplitude of the lower temperature needle Ratio , which reflects the change in intensity of the heat wave after it propagates from bottom to top. Taking the natural logarithm of this ratio, the logarithmic operation can convert the multiple relationship of the amplitude into a linear measure, which is convenient for analyzing the attenuation law. , which can eliminate the influence of the difference in absolute amplitude values at different frequencies and focus on the characterization of relative attenuation characteristics. It conforms to the objective law of amplitude attenuation in thermal wave propagation and can effectively reflect the energy loss of thermal waves during longitudinal propagation.

[0035] Detailed, It represents the phase difference between the upper and lower temperature probes of the same frequency. When the heat wave propagates longitudinally in the trunk, it is affected by factors such as sap flow velocity and wood structure, which will cause the phase of the heat wave received by the upper temperature probe to lag behind that of the lower temperature probe. This difference quantifies the phase change characteristics during the heat wave propagation process. Convert radians to degrees.

[0036] In one embodiment of the present invention, obtaining the thermal diffusivity of a tree trunk based on amplitude attenuation includes: Based on the fact that the thermal wave amplitude decays exponentially with distance in one-dimensional steady-state convection, the thermal diffusivity of the tree trunk is obtained by inversion as follows: ; in, represents the thermal diffusivity of the trunk at frequency f, Indicates the set distance between the heating needle and the temperature measuring needle; Determine the thermal diffusivity of the trunk at each frequency, and take the average of the thermal diffusivity of the trunk at all frequencies as the thermal diffusivity of the trunk .

[0037] In detail, in the one-dimensional steady-state convection model, the thermal wave amplitude decays exponentially along the propagation distance x, which can be expressed mathematically as This formula describes the amplitude attenuation law caused by thermal diffusion when the heat wave propagates in the tree trunk. By inverting the one-dimensional steady-state convection model, the thermal diffusion coefficient can be obtained. The calculation formula .in, This is the amplitude attenuation calculated based on the amplitude ratio of the upper and lower probes, representing the degree of energy loss during the heat wave's propagation distance x. By combining the heat wave's angular frequency, propagation distance, and amplitude attenuation, the thermal diffusivity of the tree trunk can be inverted.

[0038] In one embodiment of the present invention, the axial liquid convection velocity of the trunk is obtained based on the phase lag and the thermal diffusion coefficient, including: According to the one-dimensional convection diffusion heat wave, the axial liquid convection velocity of the tree trunk is obtained by inverting the relationship between the phase lag and the axial liquid convection velocity, as follows: ; in, represents the axial liquid convection velocity of the trunk at frequency f; Determine the axial liquid convection velocity of the trunk at each frequency, and take the average of the axial liquid convection velocity of the trunk at all frequencies as the axial liquid convection velocity of the trunk .

[0039] In detail, in the one-dimensional steady-state conduction-convection model, the phase lag Axial liquid convection velocity , thermal diffusivity , angular frequency There is an intrinsic correlation. Based on the thermal diffusion of heat waves (determined by the thermal diffusion coefficient By inverting this equation, we get The physical model of heat wave convection-diffusion is coupled to reflect the quantitative relationship between liquid flow velocity and phase lag, heat diffusion characteristics and heat wave frequency.

[0040] For each frequency The axial liquid convection velocity determined under Due to factors such as differences in local trunk structure and measurement noise, the There is a deviation. By taking all frequencies The final axial liquid convection velocity is the mean of , reducing the impact of deviation.

[0041] In one embodiment of the present invention, determining the volumetric moisture content of a tree trunk according to a volumetric heat capacity model includes: Based on prior knowledge, determine the volumetric heat capacity of the tree trunk in a dry state; the volumetric heat capacity is the product of the density and specific heat capacity of the tree trunk in a dry state; The volumetric water content of the trunk is determined based on a linear mixture of the volume fraction of the trunk with dry living xylem and free water as follows: ; in, represents the volumetric moisture content of the tree trunk, represents the volume heat capacity of the trunk in a dry state, represents the volumetric heat capacity of water, represents the volume heat capacity of the trunk in the growing state; Among them, the volume heat capacity of the trunk in the growth state is The results are obtained based on the temperature response method: Apply step heating to the heating needle to obtain the temperature parameters of the upper and lower temperature measuring needles in time sequence; The temperature parameters of the time series are fitted to a one-dimensional transient heat conduction model to obtain the volumetric heat capacity of the trunk in the growth state.

[0042] Detailed, is the volumetric heat capacity of the trunk in the growing state, including the combined contribution of the dry trunk and water; is the volumetric heat capacity of the dry trunk, is the volumetric heat capacity of water.

[0043] The denominator represents the increase in the heat capacity of the trunk due to the presence of water. It represents the heat capacity increase per unit volume of water compared to the dry trunk. , which reflects the volume ratio of water in the living xylem (volume water content).

[0044] Specifically, a step heating process is applied to the heating needles, i.e., a sudden, steady heat input (for example, the heating power reaches and maintains a constant value within a very short period of time). This creates a transient thermal excitation within the tree trunk, causing heat to propagate axially along the trunk. The time-series temperature parameters recorded by the upper and lower temperature probes are used to determine the dynamic temperature changes within the trunk after the thermal excitation.

[0045] The one-dimensional transient heat conduction model describes the law of heat conduction along the trunk axis over time. Its mathematical expression is the unsteady-state partial differential equation for heat conduction, which includes key parameters such as the thermal diffusivity and volume heat capacity of the trunk. The time series temperature data of the upper and lower temperature probes are substituted into the unsteady-state partial differential equation for heat conduction, and the volume heat capacity in the model is adjusted by fitting using the least squares method. The value of is chosen so that the temperature value calculated by the unsteady-state heat conduction partial differential equation fits the actual measured temperature value.

[0046] In one embodiment of the present invention, the unsteady-state heat conduction partial differential equation includes: , ; in, represents the density of the tree trunk, represents the specific heat capacity of the trunk, Indicates the temperature value, Indicates time, represents the thermal conductivity, 、 and They represent the rate of change of temperature in the x, y and z directions respectively.

[0047] In one embodiment of the present invention, the sap flow density of the tree trunk is calculated based on the volumetric moisture content of the tree trunk, including: Sap flow density of tree trunk It is the product of the volumetric water content of the trunk and the axial liquid convection velocity.

[0048] Detailed, liquid flow density The volume of liquid passing through a unit cross-sectional area per unit time. The volumetric water content indicates the proportion of water per unit volume of the trunk, while the axial liquid convection velocity indicates the speed at which water flows along the trunk's axis.

[0049] In one embodiment of the present invention, the sap flow density, trunk leaf area, and living xylem area are coupled and calculated to obtain the transpiration rate of the tree; Trunk leaf area Acquired based on the optical LAI method; Living wood area The steps to obtain are as follows: Determination of living xylem thickness by electrical resistance tomography , and get the diameter of the trunk, then the radius of the trunk is: , the radius of the non-living xylem is: ; Living wood area The calculation formula is as follows: ; The transpiration rate of trees is calculated as follows: ; in, represents the transpiration rate of trees, represents the density of water, Represents the molar mass of water.

[0050] In detail, the optical LAI method is based on the attenuation characteristics of light in the plant canopy and the Beer-Lambert law. By measuring the incident light intensity above the canopy and the transmitted light intensity below the canopy, the degree of light attenuation is analyzed and the leaf area index is inferred. .

[0051] Specifically, electrical resistance tomography (ERT) measures the thickness of living xylem by measuring the difference in electrical resistance at different locations on the trunk, based on the difference in electrical resistance between living xylem and non-living xylem.

[0052] Detailed, liquid flow density It expresses the sap flow volume per unit time and per unit area of living wood. It represents the total volume of sap flowing through the living xylem per unit time. It expresses the mass flow rate of sap per unit time to quantify the quality of water transport within the trunk.

[0053] It represents the mass transpiration rate per unit leaf area, and normalizes the data from the entire trunk to the unit leaf area, making the transpiration rates of different trees comparable.

[0054] Used to convert mass transpiration rate to molar transpiration rate, a common expression of transpiration rate in ecological studies.

[0055] A device for monitoring the transpiration capacity of trees at different heights, comprising: A heating needle and at least two temperature measuring needles; When the one heating needle and the at least two temperature measuring needles perform a tree transpiration capacity monitoring operation, a method for monitoring the transpiration capacity of trees at different heights as described in any one of the items is executed.

[0056] The above describes the embodiments of this embodiment, but this embodiment is not limited to the above specific implementation methods. The above specific implementation methods are merely illustrative and not restrictive. Ordinary technicians in this field can also make many forms based on the inspiration of this embodiment, all of which are protected by this embodiment.

Claims

1. A method for monitoring the transpiration capacity of trees at different heights, characterized in that: include: Step 1: Arrange a heating needle and at least two temperature measuring needles at a set distance along the longitudinal direction of the tree trunk; Periodically performing a heating sequence of different powers including an excitation phase and a baseline phase on the heating needle, wherein heat waves of at least two frequencies are applied during the excitation phase; Step 2: During the heating sequence, the temperature parameters of each temperature measuring needle are collected, and the amplitude attenuation and phase lag of the thermal wave in the longitudinal direction are calculated based on the temperature parameters; Step 3, calculating the thermal diffusivity of the trunk based on the amplitude attenuation, and calculating the axial liquid convection velocity of the trunk based on the phase lag and the thermal diffusivity; Step 4: determining the volumetric moisture content of the trunk according to the volumetric heat capacity model, and calculating the sap flow density of the trunk based on the volumetric moisture content of the trunk; Step 5: Obtain the trunk leaf area and living xylem area of the tree trunk, and couple the sap flow density, trunk leaf area, and living xylem area to calculate the transpiration rate of the tree.

2. The method for monitoring the transpiration capacity of trees at different heights according to claim 1, characterized in that: The temperature measuring needle comprises an upper temperature measuring needle and a lower temperature measuring needle, and the upper temperature measuring needle and the lower temperature measuring needle are symmetrically arranged up and down with the heating needle as the center.

3. The method for monitoring the transpiration capacity of trees at different heights according to claim 2, characterized in that: During the heating sequence, the temperature parameters of each temperature probe are collected, and the amplitude attenuation and phase lag of the thermal wave in the longitudinal direction are calculated based on the temperature parameters, including: Sure and ,in, Indicates the temperature parameters of the upper temperature measuring needle timing, Indicates the temperature parameters of the lower temperature measuring needle timing; Set the temperature parameter of the timing and Perform fast Fourier transform to obtain frequency domain parameters and Among them, for or The i-th frequency domain parameter in is expressed as: , represents the amplitude, Indicates the phase, represents the angular frequency, , represents the frequency of the heat wave, represents the natural base, express or 's index; Based on frequency domain parameters and Extract the upper temperature probe amplitude , lower temperature probe amplitude , Upper temperature measuring needle phase and the phase of the lower temperature needle ; The formula for calculating amplitude attenuation is as follows: ； in, represents the amplitude attenuation at frequency f, represents the amplitude ratio at frequency f; The calculation formula for phase lag is as follows: ； in, represents the phase lag at frequency f, represents the phase difference at frequency f.

4. The method for monitoring the transpiration capacity of trees at different heights according to claim 3, characterized in that: The thermal diffusivity of the tree trunk is calculated based on the amplitude attenuation, including: Based on the fact that the thermal wave amplitude decays exponentially with distance in one-dimensional steady-state convection, the thermal diffusivity of the tree trunk is obtained by inversion as follows: ； in, represents the thermal diffusivity of the trunk at frequency f, Indicates the set distance between the heating needle and the temperature measuring needle; Determine the thermal diffusivity of the trunk at each frequency, and take the average of the thermal diffusivity of the trunk at all frequencies as the thermal diffusivity of the trunk .

5. The method for monitoring the transpiration capacity of trees at different heights according to claim 4, characterized in that: The axial liquid convection velocity of the trunk is calculated based on the phase lag and the thermal diffusivity, including According to the one-dimensional convection diffusion heat wave, the axial liquid convection velocity of the tree trunk is obtained by inverting the relationship between the phase lag and the axial liquid convection velocity, as follows: ； in, represents the axial liquid convection velocity of the trunk at frequency f; Determine the axial liquid convection velocity of the trunk at each frequency, and take the average of the axial liquid convection velocity of the trunk at all frequencies as the axial liquid convection velocity of the trunk .

6. The method for monitoring the transpiration capacity of trees at different heights according to claim 1, characterized in that: The volumetric water content of the tree trunk is determined based on the volumetric heat capacity model, including: Based on prior knowledge, determine the volumetric heat capacity of the tree trunk in a dry state; the volumetric heat capacity is the product of the density and specific heat capacity of the tree trunk in a dry state; The volumetric water content of the trunk is determined based on a linear mixture of the volume fraction of the trunk with dry living xylem and free water as follows: ； in, represents the volumetric moisture content of the tree trunk, represents the volume heat capacity of the trunk in a dry state, represents the volumetric heat capacity of water, represents the volume heat capacity of the trunk in the growing state; Among them, the volume heat capacity of the trunk in the growth state is The results are obtained based on the temperature response method: Apply step heating to the heating needle to obtain the temperature parameters of the upper and lower temperature measuring needles in time sequence; The temperature parameters of the time series are fitted to a one-dimensional transient heat conduction model to obtain the volumetric heat capacity of the trunk in the growth state.

7. The method for monitoring the transpiration capacity of trees at different heights according to claim 5 or 6, characterized in that: The sap flow density of the tree trunk is calculated based on the volumetric water content of the tree trunk, including: Sap flow density of tree trunk It is the product of the volumetric water content of the trunk and the axial liquid convection velocity.

8. The method for monitoring the transpiration capacity of trees at different heights according to claim 7, characterized in that: The transpiration rate of trees is obtained by coupling the sap flow density, trunk leaf area and living xylem area. Trunk leaf area Acquired based on the optical LAI method; Living wood area The steps to obtain are as follows: Determination of living xylem thickness by electrical resistance tomography , and get the diameter of the trunk, then the radius of the trunk is: , the radius of the non-living xylem is: ; Living wood area The calculation formula is as follows: ； The transpiration rate of trees is calculated as follows: ； in, represents the transpiration rate of trees, represents the density of water, Represents the molar mass of water.

9. A device for monitoring the transpiration capacity of trees at different heights, characterized in that: include: A heating needle and at least two temperature measuring needles; When the one heating needle and the at least two temperature measuring needles perform a tree transpiration capacity monitoring operation, a method for monitoring the transpiration capacity of trees at different heights as claimed in any one of claims 1 to 8 is performed.

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