Study On The Characteristics And Relationship Of Energy Flux Between Impervious Surface And Ground Surface In Xi'an

China's urbanization has developed rapidly in recent years,but the impervious surfaces swift growth has changed the energy balance and aggravated the thermal environment.Xi'an is one of the national central cities,and devoted to establish the national forest city.Xi'an is facing double pressure of developing and environment.Research the relationship between impervious surfaces and surface energy flux has great significance for urban management,microclimate improvement and ecocity construction.Established the impervious surface extraction model based on remote sensing data of 1994-2016 years.Extract the impervious surface distribution by NDBI and INDBI respectively,and compared the results for accuracy of the results.On this basis,in order to acquire the impervious coverage,use the linear spectral mixing model to unmix spectral.Established the triangle model based on remote sensing data and meteorological data.According existing research results to verify the surface energy flux.The relationships between impervious surface and surface energy flux are discussed.The conclusions are as follows.(1)The established model has high precision and meet the research needs.INDBI is better than NDBI model,it can remove noise from bare soil,water and sparse vegetation.The results of the linear spectral mixed model are verified,the results show that the RMSE is mostly less than 0.02.It is concluded that the accuracy can meet the research needs.The ground surface temperature is the basis of triangle model.The comparison results show that the single window algorithm of Qin Zhihao is superior to the other three models.According to the existing research results,the triangle model can extract the surface energy flux effectively.(2)The impervious surface area has obvious regional differences in the spatial distribution.The impervious surface area is distributed in the construction area of Xi'an city and the districts.The impervious surface coverage is mainly high coverage grade and extremely high coverage grade,showing a decreasing trend from the city to the outside.Impervious surface area distributed sporadically in each township,the coverage grade was mainly low and middle coverage.The index of landscape pattern indicates that the fragmentation degree of impervious surface is increasing in the process of rapid urbanization in Xi'an,The fragmentation of impervious surface area increased first and then decreased with the increase of the impervious surface coverage.(3)In the past 1994-2016 years,the impervious surface area has changed significantly in Xi'an.A large number of natural surfaces were replaced by impervious surfaces area,the reduction of natural surface area is significant,and a total reduction of 831.91km2.The grade of imperviou surface coverage increased significantly with time.The area of grade increase was significantly larger than that of grade decline.Between 1994 and 2016,The comprehensive dynamic degree of impervious surface area shows that the degree of impervious surface coverage in the study area changes significantly,the change of low coverage level impervious surface coverage contributes the most to it.The contribution index of impervious surface coverage shows that Yanta district,Weiyang district and Baqiao district are main contribution areas of the impervious surface coverage in the past 20 years.Xincheng district,Lianhu district and Beilin district are restricted by the scope of the administrative region,their contribution to the impervious surface coverage has not changed much.The contribution of Changan district,Gaoling district,Lintong district and Yan Liang district to the overall impervious surface coverage is increasing.Huyi District,Lantian County and Zhouzhi County has been at a low level.(4)Surface energy flux has obvious regional differences in the spatial distribution.The area with wide distribution of impervious surface is the low value region of net radiation flux and latent heat flux,and the high value region of soil heat flux and sensible heat flux,It is shown that the value of available energy to sensible heat flux in this area is increased.The profile analysis shows that the surface energy flux varies with the types of surface.The latent heat flux in the downtown area of Xi'an is lower than that in the surrounding area,and the sensible heat flux is higher than that of the surrounding area,thermal environment is more severe than the surrounding area.(5)There is a significant correlation between the surface energy flux and the impervious surface coverage.Heat flux,soil heat flux and impervious surface coverage has significant positive correlation between,while there was a significant negative correlation between net radiation flux,latent heat flux and impervious surface coverage.For every 10%increase in the impervious surface coverage,the H/Rn increased 0.7%,the G/Rn increased 0.4%,and the LE/Rn decreased 1.1%,Boven ratio increased 2.9%.It is shown that with the increase of the impervious surface coverage,the value of the sensible heat flux that can be allocated to the latent heat flux by using energy increases,while the value allocated to the latent heat flux decreases,the near surface air temperature rises,the thermal environment intensifies.(6)The surface energy fluxes of each functional regionalization show different laws of variation in different grades.The rising speed of Bowen ratio is as follows:ecological coordination area>urban construction area>urban ecological construction buffer zone>ecological control area>big Qinling ecological reserve.The increasing speed of Bowen ratio in ecological coordination area and urban construction area is more than other functional areas,which indicates that special attention should be paid to the ecological construction of these two areas.There are significant differences in surface energy flux between different grades of impervious surface.In urban construction areas and ecological coordination areas when the coverage grade of impervious surface is extremely high,the Bowen ratio increases fastest and the value is the largest.It is very important to pay attention to the ecological construction.