Study On Multi-scale Simulation Methods Of Forest Canopy Thermal Radiation

Land surface temperature(LST),as one of the important physical parameters of the earth,is closely related to the generation of natural resources,the growth of vegetation,climate change and human daily production and life.As an important part of the surface,forest temperature directly affects the surrounding climate and it is important in forestry resource investigation and planning,dynamic monitoring,fire or early warning of pests and diseases.Based on ENVI-met and RAPID 3-D coupling model,the thermal radiation simulation of forest canopy can help to obtain the prior knowledge of canopy thermal radiation,improve the accuracy of satellite temperature inversion and enhance the monitoring ability of forest resources.The simulation resolution is an important parameter in the simulation process of different scale study areas,which directly affects the precision and simulation time of thermal radiation simulation.To understand the thermal radiation simulation method and the optimal simulation resolution of ENVI-met and RAPID 3-D coupling models in different scale study areas are the core scientific problems in this paper.According to the size of study areas,the scale of the thermal radiation simulation is divided to small scale(study side length<50m);middle scale(50<study side length<1000m);large scale(study side length? 1000m).The simulation resolution is not only closely related to the size of the study area,but also affects the simulation accuracy and simulation efficiency.In this study,we selected three research areas of Jilin Jiaohe Pinus koraiensis coniferous and broad-leaved mixed natural forest(small scale),Hebei Huai Lai Platycladus orientalis plantation(middle scale),North Carolina natural coniferous forest(large scale).According to the scale of different study area,we set different simulated spatial resolution,including 0.1m,lm,5m,10m,20m,50m and 100m.Combined with basic data including meteorological data and 3-D structure survey data of forest,we drived ENVI-met and RAPID coupling model and compared the coupling simulation method with different spatial resolution at different scales and evaluated the simulation precision and simulation efficiency.1)In the small scale-Jiaohe study area,when the simulated resolution is 0.1m,the simulated error of the thermal radiation of the undergrowth vegetation is 0.5?.In the middle scale-Huailai study area,When the simulated resolution are lm,5m and 10m,the simulated error of the thermal radiation of the canopy are 1.3 ?,1.8? and 2.4? respectively.In the large scale-North America study area,when the simulated resolution are 10m,20m,50m and 100m,the simulation error of forest canopy thermal radiation are 2.3?,3.5?,12? and 15? respectively.When ENVI-met and RAPID coupling model simulation resolution is set higher,the three-dimensional scene is more fine and the thermal radiation simulation accuracy is higher.2)In the small scale study area,we can carry out the investigation of every single tree in the forest to obtain the forest detailed 3-D structure,meteorological data and component temperature as the simulation input,the simulation results are more accurate.In the large and middle scale study area,we propose a multi source remote sensing data to realization of canopy thermal radiation simulation.Such as LiDAR can be used to quickly obtain 3D structure(LAI and CHM)of forest and build the coupling model simulation scene.We can get simulation of continuous component temperature in ENVI-met,and then put that in RAPID for canopy thermal radiation simulation.This method can reduce the thermal radiation simulation workload and improve the thermal radiation simulation efficiency.3)Comprehensive analysis on simulated accuracy and time-consuming of forest thermal radiation in medium and large scale study area,we find that the simulation accuracy of canopy thermal radiation increases with the increase of resolution,but the simulation time is also increasing obviously.When we set ENVI-met and RAPID coupling models simulation resolutionas 8?10m in medium and large scale study area,that is,the length of the study area is>50m,the high precision thermal radiation simulation data can be obtained quickly.4)Other valuable conclusions:a)In the simulation of thermal radiation in the small scale study area,we find that under the small zenith angle,the effect of shrubon on the thermal radiation of the forest canopy is greater when it is more dense.In the observation of the main plane,effect of thick shrubon the forest canopy thermal radiation simulation is up to about 1 ?.Shrubon can not be neglected in the simulation process of canopy thermal radiation.b)The simulation of forest thermal radiation in small and medium scale study area is relatively fine.In the process of thermal radiation simulation and field observation,the vegetation canopy has obvious "hot spot" effect,and the azimuth angle and zenith consistent of the sun.