Study On Surface Energy Fluxes Of Xuzhou Area Based On Satellite-ground Observation

Surface energy balance is one of the key problems in the study of the earth atmosphere system.The direct observation of the fluxes between the earth and the atmosphere can accurately obtain the energy exchange between the earth and the atmosphere.The tower based eddy covariance technology can directly obtain the fluxes exchange between the earth and the atmosphere for a long time and with high accuracy,but so it can't realize the measurement on the regional scale.With the development of remote sensing technology,remote sensing technology plays an increasingly important role in the study of flux exchange on the regional scale.The research object of this paper is the characteristics of surface energy flux exchange in Xuzhou from 2017 to 2018.Firstly,this paper based on the observation data of tower based eddy correlation(EC)system in China University of mining and technology of Xuzhou,the flux is calculated by the principle of eddy correlation technology.Then,this paper used the remote sensing technology as the main means,extract the surface characteristic parameters,and use SEBS(surface energy balance system)model to estimate the surface energy flux of Xuzhou City.The accuracy of SEBS model was verified by combining the results of EC system observation and SEBS model estimation.On this basis,the temporal variation characteristics,spatial distribution characteristics of surface energy flux in Xuzhou City and the distribution characteristics of surface energy flux in typical areas(urban area,lake,farmland)are analyzed.The main conclusions of this paper are as follows:(1)Net radiation(R_n),latent heat flux(Q_E)and soil heat flux(Q_G)were the highest in summer and the lowest in winter,while sensible heat flux(Q_H)was the highest in spring.As a whole,R_n was transformed into Q_E at most(42.74%),followed by Q_H(34.53%)and QG at least near the observation tower.The diurnal variation of R_N,Q_H and Q_E were almost synchronous,reaching the peak at noon and keeping low at night.The soil heat flux(Q_G)decreased before 7:00,and increased from 7:00 to 16:00.The turning point of the trend was generally after sunrise and before sunset.The correlation coefficient between Q_G and soil temperature difference in different depths is 0.97.(2)Taking EC system observation data as the real value,the SEBS model is verified.It is found that the estimation results of R_n and Q_H of SEBS model are of high accuracy and best fitting degree,while the accuracy of Q_E and Q_G is low.The results of parameter sensitivity analysis show that RN and Q_G are more sensitive to surface emissivity,surface albedo,surface temperature and atmospheric temperature,while Q_H and Q_E are more sensitive to atmospheric pressure,surface temperature,atmospheric temperature,wind speed and relative humidity.(3)In terms of spatial distribution,the net radiation and latent heat flux of water body are the largest,the latent heat flux of urban area is the lowest,the sensible heat flux of water body is the lowest,and the Q_H and Q_G of urban area are the highest.The distribution characteristics of surface energy flux are different in different regions.The Q_E proportion of urban area is smaller than that of lake and farmland,and the Q_E proportion of lake is the highest(over 70%).Q_H in Lake area is negative in spring,less than other seasons,and positive in autumn,which is a unique phenomenon in Lake area.There are 43 figures,8 tables and 89 references in this paper.