A method for determining ground component sensible heat flux based on a ground-canopy three-branch coupling conductance network

Abstract

The application provides a surface component sensible heat flux determination method based on a surface-crown three-branch coupled conductance network, and relates to the technical fields of surface energy exchange and remote sensing quantitative inversion. Firstly, remote sensing data, meteorological data, surface component temperature data and surface-crown structure data of a target region are acquired to form a remote sensing-meteorological-surface component multi-mode data set; a three-branch coupled conductance network is constructed to determine air thermal conductance, crown effective thermal conductance and soil effective thermal conductance; the crown air temperature is taken as the shared air node temperature to determine the crown sensible heat flux, the soil sensible heat flux and the total sensible heat flux, and the physical consistency of the surface component sensible heat flux determination result is improved.

Description

Technical Field

[0001] This invention relates to the field of surface energy exchange and remote sensing quantitative inversion technology, and in particular to a method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy. Background Technology

[0002] Sensible heat flux is an important component of the Earth's surface energy balance, used to characterize the heat transferred between the Earth's surface and the near-surface atmosphere through turbulent exchange. Accurate determination of sensible heat flux is of great significance for regional surface energy budget analysis, land-atmosphere interaction studies, agricultural drought monitoring, ecological environment assessment, and evapotranspiration estimation.

[0003] Existing methods for calculating surface sensible heat flux typically determine the heat exchange between the Earth's surface and the atmosphere based on surface temperature, air temperature, and aerodynamic drag or air thermal conductivity. One type of method treats the vegetation canopy and soil surface as a single surface heat source, usually calculating the total sensible heat flux using the temperature difference between the equivalent surface temperature and the air temperature at a reference altitude, which can be expressed as, for example, as... ,in Equivalent surface temperature, For reference altitude air temperature, This refers to air thermal conductivity. While this type of method has a relatively simple calculation process, it struggles to reflect the temperature difference between the canopy and soil. Another type of dual-source or multi-source method treats the vegetation canopy and soil surface as different heat exchange components, typically calculating the canopy sensible heat flux and soil sensible heat flux separately based on the temperature difference between the vegetation canopy and air, and the temperature difference between the soil surface and air. For example, it can be expressed as... , Then by The total sensible heat flux is obtained. This type of treatment essentially connects the vegetation canopy heat exchange pathway and the soil surface heat exchange pathway directly to the reference height air temperature, or sets empirical air node temperatures and resistance parameters separately. However, in cases of uneven vegetation cover, significant canopy shading of the soil surface, soil surface temperatures significantly higher than canopy temperatures, or canopy transpiration causing canopy temperatures to be lower than soil surface temperatures, directly using the reference height air temperature as the common boundary for the two component pathways easily overlooks the convergence effect of the internal canopy air layer on soil and canopy heat, resulting in deviations in the distribution of canopy sensible heat flux, soil sensible heat flux, and total sensible heat flux. Simultaneously, some methods fail to adequately express the coupling of effective leaf area index, soil exposure level, and the combined heat transfer capacity of the canopy and soil pathways. Therefore, under conditions of uneven vegetation cover and significant differences between canopy and soil temperatures, the physical consistency and interpretability of the component sensible heat fluxes still have room for improvement.

[0004] Therefore, it is necessary to propose a new method for determining the sensible heat flux of surface components. This method fully utilizes remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data to construct a three-branch coupled conductance network of the surface-canopy, consisting of heat exchange branches for air above the canopy, vegetation canopy, and soil surface. Air thermal conductivity, effective canopy thermal conductivity, and effective soil thermal conductivity are used to characterize the heat exchange capacity of the air above the canopy, the vegetation canopy, and the soil surface, respectively. Canopy air temperature is used as the shared air node temperature connecting the three heat exchange branches, achieving nodal thermal coupling between air temperature, vegetation canopy temperature, and soil surface temperature. Based on this, the sensible heat flux of the canopy and soil are calculated separately and synthesized into a total sensible heat flux, thereby improving the structural clarity, physical consistency, and engineering applicability of the calculation of sensible heat flux of vegetation cover surface components. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy. This method can solve the problems of insufficient differentiation between the heat exchange mechanisms of vegetation canopy and soil surface, unclear expression of component heat exchange capacity, and lack of canopy air node constraints in the existing methods for determining sensible heat flux. It can achieve physical consistency determination of canopy sensible heat flux, soil sensible heat flux, and total sensible heat flux.

[0006] To achieve the above objectives, the present invention provides the following solution: A method for determining the sensible heat flux of surface components based on a surface-canopy three-branch coupled conductivity network includes: Remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data of the target area are acquired. Spatial resampling and temporal matching are performed on the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data to form a remote sensing-meteorological-surface component multi-model dataset that includes air temperature, vegetation canopy temperature, and soil surface temperature, with the matched spatial units as the calculation units. Based on the remote sensing-meteorological-surface component multi-model dataset, a surface-canopy three-branch coupled conductance network was constructed, including the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch. The air thermal conductivity, the effective thermal conductivity of the canopy, and the effective thermal conductivity of the soil were determined respectively. The canopy air temperature is used as the temperature of the shared air node that connects the heat exchange branches of the air above the canopy, the vegetation canopy, and the soil surface. The canopy air temperature is determined according to the heat conservation relationship at the shared air node based on the thermal conductivity of the air, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the air temperature, the vegetation canopy temperature, and the soil surface temperature. Based on the canopy air temperature, canopy effective thermal conductivity, soil effective thermal conductivity, vegetation canopy temperature, and soil surface temperature, the canopy sensible heat flux and soil sensible heat flux are determined, and the canopy sensible heat flux and soil sensible heat flux are combined into the total sensible heat flux.

[0007] Preferably, remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data of the target area are acquired, and spatial resampling and temporal matching are performed on the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data to form a remote sensing-meteorological-surface component multi-model dataset including air temperature, vegetation canopy temperature, and soil surface temperature, with matched spatial units as the calculation units, including: Using remote sensing pixels, flux station observation range, target study area grid or preset computing unit as spatial reference, remote sensing data, meteorological data, surface component temperature data and surface-canopy structure data are matched to the same spatial unit; Based on the remote sensing transit time, component temperature acquisition time, flux observation time step or preset target time, time matching is performed on remote sensing data, meteorological data, surface component temperature data and surface-canopy structure data that are matched to the same spatial unit. Based on remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data after spatial resampling and temporal matching, a remote sensing-meteorological-surface component multi-model dataset is formed. The remote sensing-meteorological-surface component multi-model dataset includes air temperature, vegetation canopy temperature, soil surface temperature, frictional wind speed, air temperature reference height, zero plane displacement height, thermal roughness length, effective leaf area index, soil exposure exchange coefficient, air thermal conductivity, air density, air specific heat at constant pressure, leaf characteristic scale, and soil surface exchange characteristic scale.

[0008] Preferably, a land surface-canopy three-branch coupled conductance network is constructed based on a remote sensing-meteorological-land surface component multi-model dataset, including an air heat exchange branch above the canopy, a vegetation canopy heat exchange branch, and a soil surface heat exchange branch. The air thermal conductivity, canopy effective thermal conductivity, and soil effective thermal conductivity are determined respectively, including: Based on frictional wind speed, air temperature reference height, zero plane displacement height, thermal roughness length, and thermal stability correction term, determine the air thermal conductivity corresponding to the air heat exchange branch above the canopy. Based on the effective leaf area index, air thermal conductivity, comprehensive heat transfer intensity of canopy paths, air density, specific heat of air at constant pressure, and leaf characteristic scale, the effective thermal conductivity of the canopy corresponding to the heat exchange branches of the vegetation canopy is determined. Based on the soil exposure exchange coefficient, air thermal conductivity, soil path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and soil surface exchange characteristic scale, the effective thermal conductivity of the soil corresponding to the soil surface heat exchange branch is determined.

[0009] Preferably, the air thermal conductivity corresponding to the air heat exchange branch above the canopy is determined based on frictional wind speed, air temperature reference height, zero-plane displacement height, thermal roughness length, and thermal stability correction term, including: Frictional wind speed is used as a parameter for the intensity of momentum exchange in the air above the canopy. The air temperature reference height, zero plane displacement height, and thermal roughness length are used as height correction parameters for the air heat exchange branch above the canopy. The height correction parameter is stabilized based on the thermal stability correction term, and the air thermal conductivity is determined to characterize the heat exchange capacity between the air above the canopy and the shared air nodes.

[0010] Preferably, the effective thermal conductivity of the canopy corresponding to the heat exchange branch of the vegetation canopy is determined based on the effective leaf area index, air thermal conductivity, comprehensive heat transfer intensity of the canopy path, air density, specific heat at constant pressure, and leaf characteristic scale, including: The canopy path Reynolds number is determined based on the wind speed inside the canopy, the characteristic scale of the blades, and the kinetic viscosity of the air. The Rayleigh number of the canopy path is determined based on gravitational acceleration, the absolute value of the temperature difference between the vegetation canopy temperature and the canopy air temperature, air temperature, leaf characteristic scale, air kinematic viscosity, and air thermal diffusivity. The canopy path mixing convection discriminant is determined based on the canopy path Reynolds number, canopy path Rayleigh number, Prandtl number, and discriminant stability parameters. The forced convection heat transfer component of the canopy path is determined based on the Reynolds number and Prandtl number of the canopy path, and the natural convection heat transfer component of the canopy path is determined based on the Rayleigh number of the canopy path. Based on the canopy path mixing convection discrimination factor, determine the canopy path forced convection fusion weight and the canopy path natural convection fusion weight; The overall heat transfer intensity of the canopy path is determined based on the forced convection heat transfer component of the canopy path, the natural convection heat transfer component of the canopy path, the forced convection fusion weight of the canopy path, and the natural convection fusion weight of the canopy path. Based on the effective leaf area index, air thermal conductivity, canopy path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and leaf characteristic scale, the effective thermal conductivity of the canopy is determined to characterize the comprehensive heat exchange capacity between the vegetation canopy and shared air nodes after expansion at the leaf area scale.

[0011] Preferably, the effective thermal conductivity of the soil corresponding to the heat exchange branch on the soil surface is determined based on the soil exposure exchange coefficient, air thermal conductivity, soil path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and soil surface exchange characteristic scale, including: The soil exposure exchange coefficient was determined based on the effective leaf area index and the soil exposure attenuation coefficient. The soil path Reynolds number is determined based on near-surface wind speed, soil surface exchange characteristics, and air kinetic viscosity. The Rayleigh number of soil pathways is determined based on gravitational acceleration, the absolute value of the temperature difference between soil surface temperature and canopy air temperature, air temperature, soil surface exchange characteristic scale, air kinematic viscosity, and air thermal diffusivity. The soil path mixing convection discriminant is determined based on the soil path Reynolds number, soil path Rayleigh number, Prandtl number, and discriminant stability parameters. The forced convection heat transfer component of the soil path is determined based on the Reynolds number and Prandtl number of the soil path, and the natural convection heat transfer component of the soil path is determined based on the Rayleigh number of the soil path. Based on the soil path mixing convection discrimination value, determine the soil path forced convection fusion weight and the soil path natural convection fusion weight; The comprehensive heat transfer intensity of the soil path is determined based on the forced convection heat transfer component of the soil path, the natural convection heat transfer component of the soil path, the forced convection fusion weight of the soil path, and the natural convection fusion weight of the soil path. Based on the soil exposure exchange coefficient, air thermal conductivity, soil path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and soil surface exchange characteristic scale, the effective thermal conductivity of soil is determined to characterize the comprehensive heat exchange capacity between the soil surface and shared air nodes after canopy shading correction.

[0012] Preferably, the canopy air temperature is used as the temperature of the shared air node connecting the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch. Based on air thermal conductivity, effective canopy thermal conductivity, effective soil thermal conductivity, air temperature, vegetation canopy temperature, and soil surface temperature, the canopy air temperature is determined according to the heat conservation relationship at the shared air node, including: Establish a surface-canopy three-branch coupled conductance network with canopy air temperature as the shared air node temperature; Connect the air heat exchange branch above the canopy to the air temperature and the canopy air temperature, connect the vegetation canopy heat exchange branch to the vegetation canopy temperature and the canopy air temperature, and connect the soil surface heat exchange branch to the soil surface temperature and the canopy air temperature. The canopy air temperature is determined based on the constraint that the heat exchange branches of the air above the canopy, the vegetation canopy, and the soil surface at the shared air node, which satisfy the heat conservation. The canopy air temperature is determined based on the air thermal conductivity, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the air temperature, the vegetation canopy temperature, and the soil surface temperature.

[0013] Preferably, the canopy air temperature is used as the temperature of the shared air node connecting the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch. The canopy air temperature is determined based on air thermal conductivity, effective canopy thermal conductivity, effective soil thermal conductivity, air temperature, vegetation canopy temperature, and soil surface temperature, according to the heat conservation relationship at the shared air node. The method further includes: Use air temperature as the initial value for canopy air temperature; Based on the canopy air temperature determined in this study, the comprehensive heat transfer intensity of the canopy path used to calculate the effective thermal conductivity of the canopy and the comprehensive heat transfer intensity of the soil path used to calculate the effective thermal conductivity of the soil are determined. The effective thermal conductivity of the canopy is updated based on the comprehensive heat transfer intensity along the canopy path, and the effective thermal conductivity of the soil is updated based on the comprehensive heat transfer intensity along the soil path. The canopy air temperature is re-determined based on the updated effective thermal conductivity of the canopy and the updated effective thermal conductivity of the soil until the canopy air temperature determined in two consecutive intervals meets the preset convergence condition.

[0014] Preferably, the sensible heat flux of the canopy and the sensible heat flux of the soil are determined based on the canopy air temperature, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the vegetation canopy temperature, and the soil surface temperature, and the sensible heat flux of the canopy and the sensible heat flux of the soil are combined into the total sensible heat flux, including: The canopy sensible heat flux is determined based on air density, specific heat of air at constant pressure, effective thermal conductivity of the canopy, and the temperature difference between the vegetation canopy temperature and the canopy air temperature. The soil sensible heat flux is determined based on air density, specific heat of air at constant pressure, effective thermal conductivity of soil, and the temperature difference between soil surface temperature and canopy air temperature. The sensible heat flux of the canopy and the sensible heat flux of the soil are combined to form the total sensible heat flux.

[0015] Preferably, the positive and negative directions of the canopy sensible heat flux and the soil sensible heat flux are determined as follows: The sensible heat flux transmitted from the vegetation canopy to the shared air node is defined as the positive direction of the canopy sensible heat flux, and the sensible heat flux transmitted from the shared air node to the vegetation canopy is defined as the negative direction of the canopy sensible heat flux. The sensible heat flux transmitted from the soil surface to the shared air node is defined as the positive direction of the soil sensible heat flux, and the sensible heat flux transmitted from the shared air node to the soil surface is defined as the negative direction of the soil sensible heat flux.

[0016] The present invention discloses the following beneficial effects: This invention constructs a three-branch coupled conductance network for the land surface and canopy based on a multi-model dataset of remote sensing, meteorology, and land surface components. The heat exchange branches of the air above the canopy, the vegetation canopy, and the soil surface are represented as air thermal conductivity, canopy effective thermal conductivity, and soil effective thermal conductivity, respectively. This allows the heat exchange relationships between the air above the canopy, the vegetation canopy, and the soil surface within a vegetated land surface to be expressed within the same network structure, avoiding the simplistic representation of the vegetation canopy and soil surface as a single heat source. Furthermore, this invention uses the canopy air temperature as the shared air node temperature connecting the three heat exchange branches and determines the canopy air temperature according to the heat conservation relationship at the shared air node. This enables air temperature, vegetation canopy temperature, and soil surface temperature to be thermally coupled through the same shared air node, thereby enhancing the physical correlation between canopy heat exchange and soil surface heat exchange. Finally, this invention determines the canopy sensible heat flux and soil sensible heat flux separately based on the canopy air temperature, and combines the two into the total sensible heat flux. This can simultaneously characterize the contribution of vegetation canopy and soil surface to the surface sensible heat flux, and improve the structural clarity, physical consistency and engineering applicability of the determination results of surface component sensible heat flux. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart of the method provided in an embodiment of the present invention; Figure 2 A detailed calculation flowchart is provided for embodiments of the present invention; Figure 3 This is a schematic diagram of the system structure provided in an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1The method flowchart provided in the embodiments of the present invention is as follows: Figure 1 As shown, this embodiment provides a method for determining the sensible heat flux of surface components based on a surface-canopy three-branch coupled conductivity network, including: Step 100: Acquire remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data of the target area, and perform spatial resampling and temporal matching on the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data to form a remote sensing-meteorological-surface component multi-model dataset that includes air temperature, vegetation canopy temperature, and soil surface temperature, with the matched spatial units as the calculation units; Step 200: Construct a surface-canopy three-branch coupled conductance network based on the remote sensing-meteorology-surface component multi-model dataset, including the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch, and determine the air thermal conductivity, the effective thermal conductivity of the canopy, and the effective thermal conductivity of the soil, respectively. Step 300: Using the canopy air temperature as the temperature of the shared air node that connects the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch, the canopy air temperature is determined according to the heat conservation relationship at the shared air node based on the air thermal conductivity, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the air temperature, the vegetation canopy temperature, and the soil surface temperature. Step 400: Determine the sensible heat flux of the canopy and the sensible heat flux of the soil based on the canopy air temperature, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the vegetation canopy temperature, and the soil surface temperature, and combine the sensible heat flux of the canopy and the sensible heat flux of the soil into the total sensible heat flux.

[0022] Specifically, Figure 2 A specific calculation flowchart is provided for embodiments of the present invention. For example... Figure 2 As shown, Figure 2 exist Figure 1Based on the overall methodology shown, the determination of sensible heat flux of surface components is further expanded into six calculation steps: First, acquire basic data of the target area under the same spatial unit and time step, and form a remote sensing-meteorological-surface component multi-model dataset; Second, determine the air thermal conductivity corresponding to the air heat exchange branch above the canopy based on frictional wind speed, air temperature reference height, zero plane displacement height, and thermal roughness length; Third, determine the effective thermal conductivity of the canopy corresponding to the heat exchange branch of the vegetation canopy based on the effective leaf area index, air thermal conductivity, comprehensive heat transfer intensity of the canopy path, air density, specific heat at constant pressure of air, and leaf characteristic scale; Fourth, determine the effective thermal conductivity of the canopy based on the soil exposure exchange coefficient, air thermal conductivity, soil path... The effective thermal conductivity of the soil is determined by considering the comprehensive heat transfer intensity, air density, specific heat at constant pressure of air, and soil surface exchange characteristics. Fifth, the canopy air temperature is used as the temperature of the shared air node connecting the canopy air heat exchange branch, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch. The canopy air temperature is determined based on the heat conservation relationship at the shared air node. Sixth, the sensible heat flux of the canopy is determined based on the effective thermal conductivity of the canopy and the temperature difference between the vegetation canopy temperature and the canopy air temperature. The sensible heat flux of the soil is determined based on the effective thermal conductivity of the soil and the temperature difference between the soil surface temperature and the canopy air temperature. The sensible heat flux of the canopy and the sensible heat flux of the soil are then combined into the total sensible heat flux.

[0023] Step 1: Obtain basic data of the target region within the same spatial cell and at the same time step.

[0024] Remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data of the target area are acquired. Spatial resampling and temporal matching are then performed on these data to form a multi-model dataset of remote sensing, meteorological, and surface component data, with the matched spatial units as the computational units. Specifically, during spatial resampling and temporal matching, the target computational units are first determined. Remote sensing pixels are preferentially used as the spatial reference; when used for flux station validation, the observation range or flux footprint range of the flux station is used as the spatial reference; when used for regional statistics or mapping, a pre-defined study area grid is used as the spatial reference. After determining the spatial reference, the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data are unified to the same coordinate reference system, spatial extent, and spatial resolution.

[0025] Temporal matching employs a diurnal scale approach, using the target date as a unified time reference to match remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data acquired within the same date to the same computational unit. For intraday multi-time meteorological data or flux station data, the daily average value within the target date or the observation value closest to the remote sensing transit time is used as the input value for that day; for diurnal scale remote sensing products, the data value corresponding to the target date is directly used. When remote sensing data is affected by clouds, cloud shadows, snow, water bodies, or invalid fill values, affected pixels are removed according to the quality control identifier of the corresponding product; when target pixels lack vegetation canopy temperature, soil surface temperature, air temperature, frictional wind speed, leaf area index, or other necessary input data, temporal interpolation of valid times before and after the same data source is prioritized for supplementation. After the above processing, a multi-model dataset of remote sensing-meteorology-surface components is formed, with matched pixels, flux station observation ranges, or preset study area grids as computational units.

[0026] The remote sensing-meteorological-land surface component multi-model dataset includes essential input parameters, intermediate computational parameters, and auxiliary output parameters. The dataset may also include reference height wind speed, wind speed reference height, surface air pressure, air humidity, leaf area index, canopy aggregation, canopy height, momentum roughness length, land cover type, canopy path integrated heat transfer intensity, and soil path integrated heat transfer intensity. Frictional wind speed, air density, air thermal conductivity, air specific heat at constant pressure, zero-plane displacement height, momentum roughness length, thermal roughness length, effective leaf area index, soil exposure exchange coefficient, canopy path integrated heat transfer intensity, and soil path integrated heat transfer intensity are obtained from at least one of the following: observational data, remote sensing products, reanalysis data, flux station products, land cover type lookup results, or model output results.

[0027] Required input parameters include: air temperature The unit is The data originates from meteorological stations, flux stations, or reanalysis meteorological data; vegetation canopy temperature. The unit is The data originates from surface component temperature inversion products, multi-angle thermal infrared remote sensing products, or ground infrared thermometry data; soil surface temperature. The unit is Sources include surface component temperature inversion products, multi-angle thermal infrared remote sensing products, or ground infrared temperature measurement data; frictional wind speed. The unit is Sources include flux site products, reanalysis data, or boundary layer meteorological products; air temperature reference altitude. The unit is Metadata from meteorological observations or reanalysis data; zero-plane displacement height The unit is The data is derived from table lookup results for canopy height and land cover type; thermal roughness length. The unit is This information is derived from a lookup table of land cover types or roughness parameter products; effective leaf area index. Dimensionless, derived from remote sensing leaf area index products and canopy aggregation products; soil exposure exchange coefficient. Dimensionless, derived from the results of effective leaf area index and land cover type determination; leaf characteristic scale. The unit is Derived from vegetation type; soil surface exchange characteristics scale The unit is The value is derived from land cover type, soil surface roughness, or empirical table lookup results; air thermal conductivity. The unit is In one implementation, take air density The unit is In one implementation, take Specific heat of air at constant pressure The unit is In one implementation, take .

[0028] Intermediate calculation parameters include: air thermal conductivity The unit is Due to frictional wind speed Air temperature reference altitude Zero plane displacement height and thermal roughness length The effective thermal conductivity of the canopy was calculated. The unit is Based on the effective leaf area index thermal conductivity of air Comprehensive heat transfer intensity along the canopy path air density Specific heat of air at constant pressure and leaf characteristic scale Calculated effective thermal conductivity of soil The unit is Based on soil exposure exchange coefficient thermal conductivity of air Comprehensive heat transfer intensity along soil pathways air density Specific heat of air at constant pressure Exchange characteristic scale with soil surface Calculated.

[0029] Canopy path comprehensive heat transfer intensity The parameter is dimensionless, and the heat transfer component is caused by canopy path forced convection. Canopy path natural convection heat transfer component Canopy path forced convection fusion weights Weighting of natural convection along canopy paths The result is obtained through fusion. Among them, and All are dimensionless parameters; Reynolds number of canopy path Prandtl numbers Canopy path forced convection coefficient and heat transfer index , Calculated; Rayleigh number of canopy pathway Canopy path natural convection coefficient and heat transfer index Calculated. , , and All of these are intermediate calculation parameters, and all are dimensionless quantities.

[0030] Comprehensive heat transfer intensity along soil pathways The parameter is dimensionless, and the heat transfer component is caused by soil path forced convection. Soil path natural convection heat transfer component Soil path forced convection fusion weight Integrating weights with natural convection along soil pathways The result is obtained through fusion. Among them, and All are dimensionless parameters; Reynolds number of soil path Prandtl numbers Soil path forced convection coefficient and heat transfer index , Calculated; Rayleigh number based on soil pathways Soil path natural convection coefficient and heat transfer index Calculated. , , and All of these are intermediate calculation parameters, and all are dimensionless quantities.

[0031] air thermal diffusivity And Prandtl This is an auxiliary intermediate quantity in heat transfer calculations, where The unit is , Dimensionless quantity; Canopy air temperature To share air node temperature, the unit is... Due to air thermal conductivity Effective thermal conductivity of the canopy Soil effective thermal conductivity air temperature vegetation canopy temperature and soil surface temperature Determined jointly. Canopy path forced convection coefficient Canopy path natural convection coefficient Soil path forced convection coefficient Soil path natural convection coefficient Heat transfer index , , , , , Integration Index , and the transition sensitivity parameters of the convection mechanism , These are preset model coefficients, all of which are dimensionless parameters and can be determined based on the results of table lookup or sample calibration according to the land cover type.

[0032] Auxiliary output parameters include: canopy sensible heat flux The unit is Soil sensible heat flux The unit is Total sensible heat flux ,unit Depending on the application requirements, the air thermal conductivity can also be obtained. Effective thermal conductivity of the canopy Soil effective thermal conductivity Canopy air temperature Comprehensive heat transfer intensity along the canopy path Combined heat transfer intensity with soil path As a result of process diagnosis.

[0033] The data sources and calculation methods for each parameter are as follows.

[0034] air temperature Surface air pressure, air humidity, and reference altitude wind speed are derived from ERA5-Land reanalysis data. Among them, air temperature is the 2m air temperature of ERA5-Land, surface air pressure is the surface air pressure variable, air humidity is converted from 2m dew point temperature, and reference altitude wind speed is synthesized from 10m zonal wind component and 10m meridional wind component.

[0035] Vegetation canopy temperature and soil surface temperature The data is derived from land surface component temperature data. In one embodiment, the land surface component temperature data is obtained by joint inversion of MODIS land surface temperature / emissivity products and vegetation structure products; wherein, land surface temperature and land surface emissivity are obtained from the MODIS Terra satellite MOD11A1 day-scale land surface temperature / emissivity product, leaf area index is obtained from the MODIS Terra / Aqua synthesized MCD15A3H leaf area index / absorbed photosynthetically active radiation ratio product, and land cover type is obtained from the MODIS Terra / Aqua synthesized MCD12Q1 land cover type product. For areas where vegetation canopy temperature and soil surface temperature cannot be directly obtained, MODIS land surface temperature, land surface emissivity, leaf area index, and land cover type can be used as inputs for component temperature decomposition to obtain vegetation canopy temperature. and soil surface temperature .

[0036] Frictional wind speed It is derived from flux station eddy covariance products or FLUXNET station products; when the target area does not have flux station frictional wind speed data, it can be calculated based on the 10m wind speed, air temperature reference height, zero plane displacement height and roughness parameters of ERA5-Land according to the near-surface wind speed profile relationship.

[0037] Leaf area index MCD15A3H leaf area index / photosynthetically active radiation ratio product derived from MODIS Terra / Aqua synthesis; canopy aggregation. Determined based on the preset canopy aggregation parameter table corresponding to the MCD12Q1 land cover type; effective leaf area index. according to and canopy aggregation Calculated.

[0038] Land cover type is derived from the MODIS Terra / Aqua synthesized MCD12Q1 land cover type product. Canopy height Derived from GEDI level 3 gridded land surface index products; when there are no valid GEDI observations in the target area, the height is determined by referring to a table based on the typical canopy height corresponding to the land cover type in MCD12Q1. Zero plane displacement height and thermal roughness length According to canopy height The parameters for land cover type are determined by looking up the table.

[0039] Leaf characteristic scale Determined by referring to the table based on the vegetation type corresponding to the MCD12Q1 land cover type; soil surface exchange characteristic scale. The soil exposure attenuation coefficient is determined by referring to a table based on the MCD12Q1 land cover type, soil surface roughness grade, or bare soil / sparse vegetation type. The soil exposure exchange coefficient is determined by referring to a table based on the land cover type. according to Calculated.

[0040] thermal conductivity of air air density Specific heat at constant pressure of air In one embodiment, using preset air properties, , , Air thermal diffusivity according to The Prandtl number was calculated. according to The calculated viscosity of air motion is... The parameters can be determined by using preset air properties or by referring to a table based on air temperature.

[0041] Wind speed inside the canopy Based on the 10m wind speed and canopy height of ERA5-Land Zero plane displacement height The near-surface wind speed is obtained by converting the momentum roughness length and the preset canopy wind speed attenuation coefficient. Based on the 10m wind speed and canopy height of ERA5-Land The soil surface exchange height and the preset wind speed attenuation coefficient below the canopy are used to calculate the result.

[0042] Canopy path forced convection coefficient Canopy path natural convection coefficient Soil path forced convection coefficient Soil path natural convection coefficient Heat transfer index , , , , , Integration Index , and the transition sensitivity parameters of the convection mechanism , All parameters were determined based on the parameter table corresponding to the MCD12Q1 land cover type.

[0043] Step 2: Determine the thermal conductivity of the air corresponding to the heat exchange branch above the canopy.

[0044] The air heat exchange branch above the canopy is used to characterize the heat exchange between the air above the canopy and the shared air nodes. This embodiment uses a logarithmic wind profile under a near-neutral stratification to determine the air thermal conductivity. To ensure the air thermal conductivity formula has physical meaning, the air temperature reference height is [not specified]. It should be greater than the zero plane displacement height. With thermal roughness length The sum of them satisfies and make The thermal conductivity of the air corresponding to the heat exchange branch above the canopy is determined based on the frictional wind speed, air temperature reference height, zero-plane displacement height, and thermal roughness length.

[0045] The thermal conductivity of air satisfies the following relationship:

[0046] In the formula, Thermal conductivity of air; It is the von Kármán constant; Frictional wind speed; This is the reference altitude for air temperature. Zero plane displacement height; This is the thermal roughness length; This is a correction term for thermal stability.

[0047] In this embodiment, air thermal conductivity is calculated on a daily scale and an equivalent near-neutral stratification is used. The thermal stability correction expressions for stable, near-neutral, and unstable stratifications are no longer differentiated; that is, the thermal stability correction term is taken as... Frictional wind speed The data is preferentially sourced from flux station eddy covariance products or FLUXNET station products; when the target area does not have flux station frictional wind speed data, the frictional wind speed is calculated by back-calculating the near-surface wind speed profile relationship based on the 10m wind speed, air temperature reference height, zero plane displacement height, and roughness parameters of ERA5-Land.

[0048] Air thermal conductivity is used to characterize the heat exchange capacity between the air above the canopy and shared air nodes. The higher the air thermal conductivity, the stronger the heat exchange capacity between the air above the canopy and the shared air nodes.

[0049] Step 3: Determine the effective thermal conductivity of the canopy corresponding to the heat exchange branch of the vegetation canopy.

[0050] The vegetation canopy heat exchange pathway is used to characterize the heat exchange between the vegetation canopy and shared air nodes. The effective thermal conductivity of the canopy is determined based on the effective leaf area index, air thermal conductivity, canopy path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and leaf characteristic scales.

[0051] The effective thermal conductivity of the canopy satisfies the following relationship:

[0052] In the formula, The effective thermal conductivity of the canopy; Effective leaf area index; The thermal conductivity of air is used to characterize the ability of air as a medium to conduct heat. In one embodiment, it is taken as... ; The overall heat transfer intensity of the canopy path; Let be the air density, and in one embodiment, take . ; As the specific heat of air at constant pressure, in one embodiment, it is taken as... ; This is a characteristic scale for the leaf.

[0053] in, The overall heat transfer intensity of the canopy pathway is specifically the dimensionless overall Nusselt number, used to characterize the relative enhancement of heat transfer after the fusion of forced convection and natural convection heat transfer components in the vegetation canopy heat exchange pathway. It is not a dimensionless heat transfer coefficient.

[0054] From a dimensional perspective, the thermal conductivity of air The unit is Leaf characteristic scale The unit is ,therefore The unit is , which can represent the convective heat transfer coefficient at the single-blade scale or the characteristic scale of the blade. Since the sensible heat flux can be expressed as... ,in The unit is , The unit is The unit of temperature difference is ,therefore The unit should be The heat transfer coefficient at the single-leaf scale Divide by Afterwards, the unit was obtained as Heat exchange conductance; further multiplied by effective leaf area index. Then, the effective thermal conductivity of the canopy at the canopy scale was obtained. From this, it can be seen that... The dimensions are It is used to characterize the heat exchange capacity between the vegetation canopy and shared air nodes after expansion on the effective leaf area index scale. The larger the value, the stronger the ability of the vegetation canopy to transfer sensible heat to the shared air nodes under a unit temperature difference.

[0055] The effective thermal conductivity of the canopy is used to characterize the overall heat exchange capacity between the vegetation canopy and shared air nodes after expansion at the leaf area scale.

[0056] When the effective leaf area index needs to be calculated from canopy structure parameters, the effective leaf area index is determined based on the leaf area index and canopy aggregation:

[0057] In the formula, Effective leaf area index; Canopy aggregation degree; Leaf area index.

[0058] In this embodiment, the overall heat transfer intensity along the canopy path is... It is calculated from the Reynolds number, Rayleigh number, forced convection heat transfer component, natural convection heat transfer component, and corresponding fusion weights of the canopy path. Specifically, the canopy path Reynolds number, canopy path Rayleigh number, and canopy path mixed convection discrimination factor are first determined.

[0059] The Reynolds number for the canopy path is:

[0060] The Rayleigh number for the canopy path is:

[0061] The discriminant for canopy path mixing convection is:

[0062] In the formula, The Reynolds number for the canopy path; Rayleigh number for canopy paths; This is a discriminant for mixed convection along the canopy path. Wind speed inside the canopy; For leaf characteristics; The viscosity of air in motion; It is the acceleration due to gravity; The absolute temperature of the air; Temperature of the vegetation canopy; The temperature of the canopy air; Air thermal diffusivity; It is a Prandtl number; This is used to identify stable parameters and to avoid the denominator being zero.

[0063] Among them, the temperature difference in the Rayleigh number of canopy path is represented by the vegetation canopy temperature. With canopy air temperature The absolute value of the difference between them, i.e. This is used to characterize the intensity of natural convection caused by temperature differences. Therefore, regardless of... Higher than Still lower , All values ​​are non-negative, representing the natural convection heat transfer component along the canopy path. All fractional exponents yield valid real results. The sign of the temperature difference is not used to determine the intensity of natural convection, but rather in the subsequent canopy sensible heat flux. The direction of heat transfer is reflected in the middle: when When, the canopy sensible heat flux is positive; when At that time, the canopy sensible heat flux was negative.

[0064] This embodiment does not separately introduce the air volume thermal expansion coefficient. Instead, it is taken as an ideal gas according to the approximation relationship. This has been substituted into the Rayleigh number formula for the canopy path. Therefore, in the Rayleigh number formula for the canopy path... It represents the absolute temperature of air, used to equivalently characterize the thermal expansion of air volume.

[0065] Among them, the air thermal diffusivity and Prandtl number can be expressed as:

[0066]

[0067] In the formula, Air thermal diffusivity; It is a Prandtl number.

[0068] The heat transfer components of canopy path forced convection are expressed as:

[0069] The natural convection heat transfer components of the canopy path are expressed as:

[0070] In the formula, For the forced convection heat transfer component of the canopy path; This represents the heat transfer component of natural convection along the canopy path. The canopy path forced convection coefficient; The natural convection coefficient of the canopy path; , and The canopy path heat transfer index is used. In this embodiment, the canopy path heat transfer index adopts a preset fixed value, namely... , , . , These are dimensionless empirical parameters preset according to land cover type. Specifically, the parameter values ​​are determined based on the IGBP classification in the MODIS MCD12Q1 land cover type product. The canopy path forced convection coefficient and the canopy path natural convection coefficient can be determined as follows: ENF corresponds to , ; EBF correspondence , DNF Correspondence , DBF correspondence , ;MF corresponds , CSH corresponds to , ;OSH correspondence , WSA Correspondence , SAV correspondence , GRA correspondence , WET corresponds to , CRO corresponds , CNV correspondence , .

[0071] The canopy path natural convection fusion weights and canopy path forced convection fusion weights are determined based on the canopy path mixing convection discriminant:

[0072]

[0073] In the formula, Weights for natural convection fusion along canopy paths; Weights for canopy path-forced convection fusion; This is the transition sensitivity parameter for the canopy path convection mechanism.

[0074] in, Used to control the weighting of natural convection fusion Discriminant of mixed convection along canopy path The rate at which something increases and changes. As a dimensionless preset parameter, in one implementation method, take When calibration is required based on actual measured samples, Available to The range is selected, and the objective is to minimize the error between the measured sensible heat flux at the flux station and the total sensible heat flux calculated by this method. As can be seen from the above weighting formula, when... Approaching hour, Approaching , Approaching This indicates that the canopy path is dominated by forced convection; when and hour, and All This indicates the combined effect of forced convection and natural convection; when As it gradually increases, As it increases, It decreases accordingly; when When it approaches infinity, Approaching , Approaching This indicates that the canopy path is dominated by natural convection. Therefore, the fusion weights can achieve a continuous transition between forced convection dominance, mixed convection, and natural convection dominance.

[0075] The overall heat transfer intensity along the canopy path is expressed as:

[0076] In the formula, The overall heat transfer intensity of the canopy path; The fusion index represents the heat transfer component along the canopy path.

[0077] Therefore, the heat exchange branches of the vegetation canopy, through the canopy path, comprehensively increase the heat transfer intensity. and effective leaf area index Together they characterize the overall heat exchange capacity at the canopy scale.

[0078] Step 4: Determine the effective thermal conductivity of the soil corresponding to the heat exchange branch on the soil surface.

[0079] The soil surface heat exchange branch is used to characterize the heat exchange between the soil surface and the shared air node. The effective thermal conductivity of the soil is determined based on the soil exposure exchange coefficient, air thermal conductivity, soil path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and soil surface exchange characteristic scale.

[0080] The effective thermal conductivity of soil satisfies the following relationship:

[0081] In the formula, The effective thermal conductivity of the soil; Soil exposure exchange coefficient; The thermal conductivity of air is used to characterize the ability of air as a medium to conduct heat. In one embodiment, it is taken as... ; The overall heat transfer intensity along the soil path; Let be the air density, and in one embodiment, take . ; As the specific heat of air at constant pressure, in one embodiment, it is taken as... ; It is a scale for soil surface exchange characteristics.

[0082] Soil effective thermal conductivity is used to characterize the overall heat exchange capacity between the soil surface and shared air nodes after correction for canopy shading.

[0083] When the soil exposure exchange coefficient needs to be calculated from canopy structure parameters, it is determined based on the effective leaf area index:

[0084] In the formula, Soil exposure exchange coefficient; Soil exposure attenuation coefficient; Effective leaf area index. Soil exposure exchange coefficient. The range of values ​​is It is used to characterize the proportion of soil surface that can still participate in effective heat exchange under the shading effect of the canopy. The closer This indicates that the higher the degree of soil surface exposure, the stronger the effective heat exchange capacity between the soil surface and the shared air node; The closer This indicates that the stronger the soil surface is shaded by the canopy, the weaker the effective heat exchange capacity of the soil surface.

[0085] Soil exposure attenuation coefficient The parameter is a dimensionless preset parameter used to characterize the intensity of the decrease in soil surface heat exchange capacity due to the increase of effective leaf area index. The classification is determined by referring to the IGBP classification in the MODIS MCD12Q1 land cover type product. In one embodiment, forest land cover... Pick shrubland surface Pick savanna-like surface Pick grassland surface Pick farmland surface Pick Farmland / natural vegetation mosaic Pick For bare ground or sparsely vegetated surfaces, the effective leaf area index is close to... , near For sparsely vegetated surfaces, Usually in to For high-coverage canopy surfaces, Usually less than For water bodies, snow and ice, and urban construction land, soil surface heat exchange branches are not calculated, or they are excluded as invalid surface types.

[0086] When calculating the overall heat transfer intensity of soil paths, the soil path Reynolds number, soil path Rayleigh number, and soil path mixed convection discrimination quantity are first determined.

[0087] The soil path Reynolds number is:

[0088] The Rayleigh number for soil pathways is:

[0089] The soil path mixing convection discriminant is:

[0090] In the formula, For soil path Reynolds number; Rayleigh number for soil pathways; This is a measure for discriminant analysis of soil path mixing and convection. This refers to near-surface wind speed; It is a scale for soil surface exchange characteristics; The viscosity of air in motion; It is the acceleration due to gravity; The absolute temperature of the air; The soil surface temperature; The temperature of the canopy air; Air thermal diffusivity; It is a Prandtl number; To determine stable parameters.

[0091] In this embodiment, the soil surface heat exchange path and the vegetation canopy heat exchange path use the same hybrid convection discrimination framework, but their characteristic wind speeds and characteristic scales are determined separately. The vegetation canopy heat exchange path uses the wind speed inside the canopy. and leaf characteristic scale The soil surface heat exchange path adopts near-surface wind speed. Exchange characteristic scale with soil surface .

[0092] Among them, near-surface wind speed This indicates the effective wind speed participating in heat exchange near the soil surface. Reference height wind speed. The 10m wind speed from ERA5-Land can be converted to near-surface wind speed using the following formula:

[0093] In the formula, In one implementation method, the minimum effective wind speed near the ground surface is taken as... ; This is the wind speed attenuation coefficient below the canopy; It represents the effective leaf area index. The IGBP classification is determined by referring to the table in the MODIS MCD12Q1 land cover type product.

[0094] Soil surface exchange characteristic scale Instead of using the remote sensing pixel scale, the effective exchange scale of soil surface rough units or exposed patches is used to characterize the characteristic length of the thermal boundary layer near the soil surface. The values ​​are determined by referring to the IGBP classification in the MODIS MCD12Q1 land cover type product. The wind speed attenuation coefficient beneath the canopy and the soil surface exchange characteristic scale can be assigned the following values: ENF, EBF, DNF, DBF, MF corresponding to... , CSH and OSH correspondences , WSA and SAV correspondences , GRA correspondence , CRO corresponds , WET corresponds to , CNV correspondence , BSV correspondence , .

[0095] The soil path forced convection heat transfer component is expressed as:

[0096] The natural convective heat transfer component of the soil path is expressed as:

[0097] In the formula, For soil path forced convection heat transfer component; The heat transfer component via natural convection through the soil path; The soil path forced convection coefficient; The soil path natural convection coefficient; , and The soil path heat transfer index.

[0098] Soil path forced convection coefficient Soil path natural convection coefficient Soil path heat transfer index , , Soil path heat transfer component fusion index Transition sensitivity parameters of soil path convection mechanism All of these are preset model coefficients, and all are dimensionless parameters. They can be determined based on the table results or sample calibration results of the land cover type.

[0099] Determine the soil path natural convection fusion weight and soil path forced convection fusion weight based on the soil path mixing convection discriminant:

[0100]

[0101] In the formula, Weighting of natural convection along soil pathways; For soil path forced convection fusion weights; This is the transition sensitivity parameter for soil path convection mechanism.

[0102] The overall heat transfer intensity along the soil path is expressed as:

[0103] In the formula, The overall heat transfer intensity along the soil path; The fusion index represents the soil path heat transfer component.

[0104] Therefore, the overall heat transfer intensity of the soil surface heat exchange branches through the soil path is thus determined. and soil exposure exchange coefficient Together, they characterize the overall heat exchange capacity of the soil surface after correction by canopy shading.

[0105] Step 5: Determine the canopy air temperature

[0106] Using canopy air temperature as the shared air node temperature that connects the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch, a three-branch coupling conductance network between the ground surface and the canopy is established.

[0107] Based on the heat conservation relationship at the shared air node, the canopy air temperature can be obtained:

[0108] In the formula, The temperature of the canopy air; Air temperature; Temperature of the vegetation canopy; The soil surface temperature; Thermal conductivity of air; The effective thermal conductivity of the canopy; The effective thermal conductivity of the soil.

[0109] Due to the overall heat transfer intensity of the canopy path Combined heat transfer intensity with soil path All of these are related to the canopy air temperature. In this embodiment, the canopy air temperature is determined using a successive update method. The specific calculation process is as follows.

[0110] First, the air temperature As the initial value of the canopy air temperature, it is denoted as The thermal conductivity of the air is calculated based on the frictional wind speed, air temperature reference height, zero plane displacement height, and thermal roughness length. Then, with the first Subcanopy air temperature Using the input as input, calculate the Rayleigh number of the canopy path. Soil path Rayleigh number Canopy path mixing convection discriminant Soil path mixed convection discriminant Further calculation of the forced convection heat transfer components along the canopy path. Canopy path natural convection heat transfer component Soil path forced convection heat transfer component Soil path natural convection heat transfer component And the corresponding fusion weights, to obtain the comprehensive heat transfer intensity of the canopy path. Combined heat transfer intensity with soil path .

[0111] Subsequently, according to Calculate the effective thermal conductivity of the canopy and according to Calculate the effective thermal conductivity of soil Then , , , , and Substituting into the canopy air temperature formula, we obtain the updated canopy air temperature. :

[0112] when At that time, it was assumed that the canopy air temperature met the convergence condition, and The final canopy air temperature; when the number of iterations reaches the preset maximum update number. If the convergence condition is still not met by then, the ... The canopy air temperature obtained in the next update is used as the calculation result, and a non-convergence flag is recorded for that calculation unit. If any issues arise during the calculation process... If necessary input data is missing, the calculation unit will be marked as an invalid calculation unit, and the canopy sensible heat flux, soil sensible heat flux, and total sensible heat flux will not be calculated.

[0113] Through the above relationships, air temperature, vegetation canopy temperature, and soil surface temperature are all thermally coupled through the same shared air node, avoiding the separate connection of the vegetation canopy heat exchange path and the soil surface heat exchange path to the reference altitude air.

[0114] Step 6: Determine the canopy sensible heat flux, soil sensible heat flux, and total sensible heat flux.

[0115] The canopy sensible heat flux is determined based on the effective thermal conductivity of the canopy and the temperature difference between the vegetation canopy temperature and the canopy air temperature.

[0116] The soil sensible heat flux is determined based on the effective thermal conductivity of the soil and the temperature difference between the soil surface temperature and the canopy air temperature.

[0117] The sensible heat flux from the canopy and the soil is combined to form the total sensible heat flux:

[0118] In the formula, Canopy sensible heat flux, in units of ; Soil sensible heat flux, unit: ; Total inductive heat flux, in units of ; Let be the air density, and in one embodiment, take . ; As the specific heat of air at constant pressure, in one embodiment, it is taken as... ; The effective thermal conductivity of the canopy is expressed in units of... ; The effective thermal conductivity of soil is expressed in units of... ; The temperature of the vegetation canopy is expressed in units of 100°C. ; Soil surface temperature, in units of ; Canopy air temperature, in units of .

[0119] This embodiment defines the sensible heat flux transferred from surface components to shared air nodes as positive. Specifically, when the vegetation canopy temperature... Temperature above the canopy air hour, A positive value indicates that the vegetation canopy is transferring sensible heat to the shared air nodes; when... Below hour, A negative value indicates that the shared air node transfers sensible heat to the vegetation canopy. When the soil surface temperature... Temperature above the canopy air hour, A positive value indicates that sensible heat is transferred from the soil surface to the shared air node; when... Below hour, A negative value indicates that the shared air node transfers sensible heat to the soil surface. Therefore, this embodiment allows... , and The value is negative, which indicates that the corresponding heat transfer direction is opposite to the preset positive direction.

[0120] The canopy sensible heat flux obtained in this embodiment Soil sensible heat flux and total sensible heat flux All values ​​represent flux per unit horizontal area, calculated at the same scale as the target computational unit. When the target computational unit is a remote sensing pixel, the result is the pixel-scale sensible heat flux; when the target computational unit is a study area grid, the result is the grid-scale sensible heat flux. When compared with the total sensible heat flux observed by the flux tower, the pixel results within the flux tower observation range or flux footprint range are weighted and aggregated to obtain the total sensible heat flux at the station scale.

[0121] In the formula, Total sensed heat flux at the site scale, in units of ; For the first Total induced heat flux per pixel, in units of ; For the first The area weight or flux footprint weight corresponding to each pixel. When the flux footprint weight is missing, the area-weighted average of the effective pixels within the observation range of the flux station is used as the total sensible heat flux at the station scale.

[0122] Finally, the canopy sensible heat flux, soil sensible heat flux, and total sensible heat flux of the target area are obtained according to pixels, sites, target study areas, or preset statistical units.

[0123] In one embodiment, the specific calculation process of the present invention is illustrated using farmland pixels corresponding to the US-Ro2 flux station as the target calculation unit. According to the US-Ro2 station information, the land cover type of this station is CRO. Remote sensing data uses the MODIS Aqua satellite MYD11A1 daily-scale land surface temperature / emissivity product with a spatial resolution of 1 km; leaf area index uses the MODIS Terra / Aqua synthesized MCD15A3H leaf area index / absorbed photosynthetically active radiation ratio product with a spatial resolution of 500 m; land cover type uses the MODIS Terra / Aqua synthesized MCD12Q1 land cover type product with a spatial resolution of 500 m. Meteorological and flux observation data uses half-hourly-scale data from the Ameri Flux US-Ro2 station.

[0124] by Year moon Using the target date as the day, the effective half-hourly observation data from the US-Ro2 flux station on that day were processed into a daily average to obtain the air temperature. vegetation canopy temperature Soil surface temperature Frictional wind speed Reference altitude wind speed Leaf area index Station observation of daily-scale sensible heat flux Air temperature reference altitude Zero plane displacement height thermal roughness length Canopy aggregation The effective leaf area index Leaf characteristic scale Soil surface exchange characteristics scale Soil exposure attenuation coefficient Wind speed attenuation coefficient below the canopy air thermal conductivity air density Specific heat of air at constant pressure .

[0125] The air thermal conductivity is calculated based on the frictional wind speed, air temperature reference height, zero-plane displacement height, and thermal roughness length. .

[0126] air temperature As the initial value of the canopy air temperature, we obtain The canopy path integrated heat transfer intensity, soil path integrated heat transfer intensity, canopy effective thermal conductivity, and soil effective thermal conductivity are calculated according to the successive update rules; when the change in canopy air temperature between two adjacent intervals is less than... When the iteration is considered to have converged, in this embodiment, the convergence result of the canopy air temperature is: Effective thermal conductivity of the canopy Soil effective thermal conductivity .

[0127] Further calculations were made of canopy sensible heat flux, soil sensible heat flux, and total sensible heat flux:

[0128]

[0129]

[0130] Corresponding daily sensible heat flux observed at the US-Ro2 site on the same date The absolute error between the total sensible heat flux calculated by the method of this invention and the station observation value is: The relative error is less than Therefore, this invention can maintain consistency with remote sensing products and meteorological data on a daily scale, and while the total sensible heat flux is close to the station observation value, it further provides the canopy sensible heat flux and soil sensible heat flux, with the canopy contributing [amount missing]. Soil contribution This enhances the interpretability of surface component sensible heat flux results.

[0131] As can be seen from the above embodiments, the present invention can construct a three-branch coupled conductance network of the surface and canopy based on remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data. The heat exchange capacity of the air above the canopy, the vegetation canopy, and the soil surface is characterized by air thermal conductivity, canopy effective thermal conductivity, and soil effective thermal conductivity, respectively. Furthermore, the canopy air temperature is used as a shared air node temperature to uniformly connect the air temperature, vegetation canopy temperature, and soil surface temperature, and the canopy sensible heat flux, soil sensible heat flux, and total sensible heat flux are determined separately, which improves the physical consistency and engineering applicability of the calculation of sensible heat flux of vegetation cover surface components.

[0132] In one implementation, such as Figure 3 As shown, the present invention also provides a system for determining the sensible heat flux of surface components based on a three-branch coupled conductivity network of the surface and canopy. This system includes a data acquisition module, an air thermal conductivity determination module, a canopy effective thermal conductivity determination module, a soil effective thermal conductivity determination module, a canopy air temperature determination module, a sensible heat flux determination module, and a result output module.

[0133] The data acquisition module is used to acquire remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data of the target area. It also performs spatial resampling and temporal matching on the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data to form a remote sensing-meteorological-surface component multi-model dataset with the matched spatial units as the calculation units.

[0134] The air thermal conductivity determination module is used to determine the air thermal conductivity corresponding to the air heat exchange branch above the canopy based on frictional wind speed, air temperature reference height, zero plane displacement height, and thermal roughness length.

[0135] The canopy effective thermal conductivity determination module is used to determine the canopy effective thermal conductivity corresponding to the heat exchange branch of the vegetation canopy based on the effective leaf area index, air thermal conductivity, comprehensive heat transfer intensity of the canopy path, air density, air specific heat at constant pressure, and leaf characteristic scale.

[0136] The effective thermal conductivity determination module is used to determine the effective thermal conductivity of the soil corresponding to the heat exchange branch on the soil surface based on the soil exposure exchange coefficient, air thermal conductivity, soil path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and soil surface exchange characteristic scale.

[0137] The canopy air temperature determination module is used to determine the canopy air temperature as the shared air node temperature that connects the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch. The module determines the canopy air temperature based on the air thermal conductivity, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the air temperature, the vegetation canopy temperature, and the soil surface temperature.

[0138] The sensible heat flux determination module is used to determine the canopy sensible heat flux based on the effective thermal conductivity of the canopy and the temperature difference between the vegetation canopy temperature and the canopy air temperature, and to determine the soil sensible heat flux based on the effective thermal conductivity of the soil and the temperature difference between the soil surface temperature and the canopy air temperature. The canopy sensible heat flux and the soil sensible heat flux are then combined into the total sensible heat flux.

[0139] The results output module is used to obtain the canopy sensible heat flux, soil sensible heat flux, and total sensible heat flux of the target area.

[0140] This invention provides a method and system for determining sensible heat flux of land surface components based on a three-branch coupled conductance network of the land surface and canopy. The method constructs a three-branch coupled conductance network of the land surface and canopy using remote sensing data, meteorological data, land surface component temperature data, and land surface-canopy structure data. Air thermal conductivity, canopy effective thermal conductivity, and soil effective thermal conductivity are used to characterize the heat exchange capacity of the air above the canopy, the vegetation canopy, and the soil surface, respectively. Furthermore, canopy air temperature is used as a shared air node temperature, unifying air temperature, vegetation canopy temperature, and soil surface temperature into the same thermal coupling framework. Based on this, the sensible heat flux of the canopy and the soil are determined separately and synthesized into the total sensible heat flux. This method and system avoid the shortcomings of simply equating the vegetation canopy and soil surface to a single heat source, and can simultaneously reflect the contributions of the canopy and the soil, improving the physical consistency, structural clarity, and engineering applicability of the calculation of sensible heat flux of vegetation cover land surface components.

[0141] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0142] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for determining the sensible heat flux of surface components based on a surface-canopy three-branch coupled conductivity network, characterized in that, include: Remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data of the target area are acquired, and spatial resampling and temporal matching are performed on the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data to form a remote sensing-meteorological-surface component multi-model dataset that includes air temperature, vegetation canopy temperature, and soil surface temperature, with the matched spatial unit as the calculation unit. Based on the aforementioned remote sensing-meteorological-surface component multi-model dataset, a surface-canopy three-branch coupled conductance network was constructed, including the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch. The air thermal conductivity, the effective thermal conductivity of the canopy, and the effective thermal conductivity of the soil were determined respectively. The canopy air temperature is used as the temperature of the shared air node that connects the heat exchange branches of the air above the canopy, the vegetation canopy, and the soil surface. The canopy air temperature is determined according to the heat conservation relationship at the shared air node based on the thermal conductivity of the air, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the air temperature, the vegetation canopy temperature, and the soil surface temperature. Based on the canopy air temperature, the canopy effective thermal conductivity, the soil effective thermal conductivity, the vegetation canopy temperature, and the soil surface temperature, the canopy sensible heat flux and the soil sensible heat flux are determined, and the canopy sensible heat flux and the soil sensible heat flux are combined into the total sensible heat flux.

2. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy as described in claim 1, characterized in that, Remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data of the target area are acquired. Spatial resampling and temporal matching are then performed on the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data to form a remote sensing-meteorological-surface component multi-model dataset, including air temperature, vegetation canopy temperature, and soil surface temperature, with matched spatial units as the computational units. This dataset includes: Using remote sensing pixels, flux station observation range, target study area grid or preset computing unit as spatial reference, the remote sensing data, the meteorological data, the surface component temperature data and the surface-canopy structure data are matched to the same spatial unit; Based on the remote sensing transit time, component temperature acquisition time, flux observation time step, or preset target time, the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data matched to the same spatial unit are time-matched. Based on the remote sensing data, meteorological data, surface component temperature data, and surface-canopy structure data after spatial resampling and temporal matching, a remote sensing-meteorological-surface component multi-model dataset is formed. The remote sensing-meteorological-surface component multi-model dataset includes air temperature, vegetation canopy temperature, soil surface temperature, frictional wind speed, air temperature reference height, zero-plane displacement height, thermal roughness length, effective leaf area index, soil exposure exchange coefficient, air thermal conductivity, air density, air specific heat at constant pressure, leaf characteristic scale, and soil surface exchange characteristic scale.

3. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy as described in claim 1, characterized in that, Based on the aforementioned remote sensing-meteorological-surface component multi-model dataset, a surface-canopy three-branch coupled conductance network was constructed, comprising the air heat exchange branch above the canopy, the vegetation canopy heat exchange branch, and the soil surface heat exchange branch. The air thermal conductivity, canopy effective thermal conductivity, and soil effective thermal conductivity were determined, including: The air thermal conductivity corresponding to the air heat exchange branch above the canopy is determined based on the frictional wind speed, air temperature reference height, zero plane displacement height, thermal roughness length, and thermal stability correction term. The effective thermal conductivity of the canopy corresponding to the heat exchange branch of the vegetation canopy is determined based on the effective leaf area index, air thermal conductivity, comprehensive heat transfer intensity of the canopy path, air density, specific heat of air at constant pressure, and leaf characteristic scale. The effective thermal conductivity of the soil corresponding to the heat exchange branch on the soil surface is determined based on the soil exposure exchange coefficient, air thermal conductivity, soil path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and soil surface exchange characteristic scale.

4. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy as described in claim 3, characterized in that, The air thermal conductivity corresponding to the air heat exchange branch above the canopy is determined based on frictional wind speed, air temperature reference height, zero-plane displacement height, thermal roughness length, and thermal stability correction term, including: The frictional wind speed is used as a parameter for the intensity of air momentum exchange above the canopy; The air temperature reference height, the zero plane displacement height, and the thermal roughness length are used as height correction parameters for the air heat exchange branch above the canopy. The height correction parameter is stabilized based on the thermal stability correction term, and the air thermal conductivity, which characterizes the heat exchange capacity between the air above the canopy and the shared air nodes, is determined.

5. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy as described in claim 3, characterized in that, Based on the effective leaf area index, air thermal conductivity, comprehensive heat transfer intensity of the canopy path, air density, specific heat at constant pressure of air, and leaf characteristic scales, the effective thermal conductivity of the canopy corresponding to the heat exchange branch of the vegetation canopy is determined, including: The canopy path Reynolds number is determined based on the wind speed inside the canopy, the characteristic scale of the blades, and the kinetic viscosity of the air. The Rayleigh number of the canopy path is determined based on gravitational acceleration, the absolute value of the temperature difference between the vegetation canopy temperature and the canopy air temperature, the air temperature, the leaf characteristic scale, the air kinematic viscosity, and the air thermal diffusivity. The canopy path mixing convection discriminant is determined based on the canopy path Reynolds number, the canopy path Rayleigh number, Prandtl number, and the discriminant stability parameter. The forced convection heat transfer component of the canopy path is determined based on the Reynolds number and Prandtl number of the canopy path, and the natural convection heat transfer component of the canopy path is determined based on the Rayleigh number of the canopy path. Based on the canopy path mixing convection discrimination factor, determine the canopy path forced convection fusion weight and the canopy path natural convection fusion weight; The overall heat transfer intensity of the canopy path is determined based on the forced convection heat transfer component of the canopy path, the natural convection heat transfer component of the canopy path, the forced convection fusion weight of the canopy path, and the natural convection fusion weight of the canopy path. The effective thermal conductivity of the canopy is determined based on the effective leaf area index, the air thermal conductivity, the comprehensive heat transfer intensity of the canopy path, the air density, the specific heat of air at constant pressure, and the leaf characteristic scale. This canopy effective thermal conductivity is used to characterize the comprehensive heat exchange capacity between the vegetation canopy and shared air nodes after expansion at the leaf area scale.

6. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy as described in claim 3, characterized in that, Based on the soil exposure exchange coefficient, air thermal conductivity, soil path comprehensive heat transfer intensity, air density, air specific heat at constant pressure, and soil surface exchange characteristic scale, the effective thermal conductivity of the soil corresponding to the soil surface heat exchange branch is determined, including: The soil exposure exchange coefficient is determined based on the effective leaf area index and the soil exposure attenuation coefficient. The soil path Reynolds number is determined based on near-surface wind speed, soil surface exchange characteristics, and air kinetic viscosity. The Rayleigh number of the soil path is determined based on the gravitational acceleration, the absolute value of the temperature difference between the soil surface temperature and the canopy air temperature, the air temperature, the soil surface exchange characteristic scale, the air kinematic viscosity, and the air thermal diffusivity. The soil path mixing convection discriminant is determined based on the soil path Reynolds number, the soil path Rayleigh number, Prandtl number, and the discriminant stability parameter. The forced convection heat transfer component of the soil path is determined based on the Reynolds number and Prandtl number of the soil path, and the natural convection heat transfer component of the soil path is determined based on the Rayleigh number of the soil path. Based on the soil path mixing convection discrimination value, determine the soil path forced convection fusion weight and the soil path natural convection fusion weight; The comprehensive heat transfer intensity of the soil path is determined based on the forced convection heat transfer component of the soil path, the natural convection heat transfer component of the soil path, the forced convection fusion weight of the soil path, and the natural convection fusion weight of the soil path. Based on the soil exposure exchange coefficient, the air thermal conductivity, the soil path comprehensive heat transfer intensity, the air density, the air specific heat at constant pressure, and the soil surface exchange characteristic scale, the effective thermal conductivity of the soil, after canopy shading correction, is determined to characterize the comprehensive heat exchange capacity between the soil surface and the shared air node.

7. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy as described in claim 1, characterized in that, Using the canopy air temperature as the temperature of a shared air node connecting the heat exchange branches above the canopy, the vegetation canopy, and the soil surface, the canopy air temperature is determined based on the air thermal conductivity, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the air temperature, the vegetation canopy temperature, and the soil surface temperature, according to the heat conservation relationship at the shared air node, including: Establish a surface-canopy three-branch coupled conductance network with the canopy air temperature as the shared air node temperature; The air heat exchange branch above the canopy is connected between the air temperature and the canopy air temperature; the vegetation canopy heat exchange branch is connected between the vegetation canopy temperature and the canopy air temperature; and the soil surface heat exchange branch is connected between the soil surface temperature and the canopy air temperature. The canopy air temperature is determined based on the constraint that the heat exchange branches of the air above the canopy, the vegetation canopy, and the soil surface are in a shared air node. The canopy air temperature is determined based on the air thermal conductivity, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the air temperature, the vegetation canopy temperature, and the soil surface temperature.

8. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductivity network of the surface and canopy as described in claim 7, characterized in that, Using the canopy air temperature as the temperature of a shared air node connecting the heat exchange branches above the canopy, the vegetation canopy, and the soil surface, the canopy air temperature is determined based on the air thermal conductivity, the effective thermal conductivity of the canopy, the effective thermal conductivity of the soil, the air temperature, the vegetation canopy temperature, and the soil surface temperature, according to the heat conservation relationship at the shared air node. This also includes: The air temperature is used as the initial value of the canopy air temperature; Based on the canopy air temperature determined in this study, the comprehensive heat transfer intensity of the canopy path used to calculate the effective thermal conductivity of the canopy and the comprehensive heat transfer intensity of the soil path used to calculate the effective thermal conductivity of the soil are determined. The effective thermal conductivity of the canopy is updated based on the comprehensive heat transfer intensity of the canopy path, and the effective thermal conductivity of the soil is updated based on the comprehensive heat transfer intensity of the soil path. The canopy air temperature is re-determined based on the updated effective thermal conductivity of the canopy and the updated effective thermal conductivity of the soil, until the canopy air temperature determined in two consecutive intervals meets the preset convergence condition.

9. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy as described in claim 1, characterized in that, Based on the canopy air temperature, the canopy effective thermal conductivity, the soil effective thermal conductivity, the vegetation canopy temperature, and the soil surface temperature, the canopy sensible heat flux and the soil sensible heat flux are determined, and the canopy sensible heat flux and the soil sensible heat flux are combined into a total sensible heat flux, including: The sensible heat flux of the canopy is determined based on air density, specific heat of air at constant pressure, effective thermal conductivity of the canopy, and the temperature difference between the vegetation canopy temperature and the canopy air temperature. The soil sensible heat flux is determined based on the air density, the specific heat of air at constant pressure, the effective thermal conductivity of the soil, and the temperature difference between the soil surface temperature and the canopy air temperature. The canopy sensible heat flux and the soil sensible heat flux are combined to form the total sensible heat flux.

10. The method for determining the sensible heat flux of surface components based on a three-branch coupled conductance network of the surface and canopy as described in claim 1, characterized in that, The positive and negative directions of the canopy sensible heat flux and the soil sensible heat flux are determined as follows: The sensible heat flux transmitted from the vegetation canopy to the shared air node is defined as the positive direction of the canopy sensible heat flux, and the sensible heat flux transmitted from the shared air node to the vegetation canopy is defined as the negative direction of the canopy sensible heat flux. The sensible heat flux transmitted from the soil surface to the shared air node is defined as the positive direction of the soil sensible heat flux, and the sensible heat flux transmitted from the shared air node to the soil surface is defined as the negative direction of the soil sensible heat flux.

Images