Remote Sensing Detection Of The Influence Of Shallow Groundwater On The Surface Energy Balance System

Shallow groundwater level directly affects the size and distribution characteristics of the land surface temperature,the vegetation normalized index(NDVI),the surface energy balance system component,and indirectly determines the strength of surface evapotranspiration.Remote sensing has the characteristics of large amount of data,wide coverage,and strong time series.It has irreplaceable advantages in the study of large-scale relations between water resources and ecological environment.The influence of shallow groundwater on the surface energy balance system can be comprehensively analyzed by using remote sensing to obtain the relevant parameters of land surface in time.The Yili valley of Xinjiang as an important oasis in the northwest of China has been selected as the research area.Guided by the basic theories of hydrology,hydrogeology and remote sensing,the relationship between the buried depth of different groundwater levels and the NDVI and surface temperature is analyzed by using the data of the buried depth of the groundwater level in the region in 2016.Based on the meteorological and remote sensing data,the surface energy balance system(SEBS)was used to invert the regional evapotranspiration and the components of the surface energy balance system,and the variation of the surface energy balance system components under different water levels was further studied.The research results show that:(1)The depth of impact of groundwater depth on NDVI and surface temperature differs between the two periods of the dry season and the wet period.The NDVI is affected by the depth of the groundwater table,the dry season is about 4m,and the wet season is about 6m.The surface temperature is affected by the depth of the groundwater level,the dry season is about 3m,and the wet season is about 3.6m.The linear correlation between the temperature vegetation drought index(TVDI)and water content was further analyzed using the measured data,and the goodness of fit R~2=0.6204.(2)The total amount of annual evapotranspiration in the YIli Valley of Xinjiang showed a downward trend in the past 20 years.The absolute values of the slope equations of the evapotranspiration and TVDI fitting for different water depths increased with the increase of water depth,indicating that in areas where the water depth is less than 5m,the larger the water depth,the more significant the reduction in evapotranspiration with increasing TVDI.(3)The correlation between surface energy balance system component and groundwater depth is obvious.In the area where the water depth is less than 5m,the net radiant flux,soil heat flux and latent heat flux in the two phases of the study area increase with the increase of water depth,and the sensible heat flux decreases;The heat flux and latent heat flux are significantly affected by the water depth,which is more significant than the net radiant flux and soil heat flux.During the dry season,the impact of groundwater depth in the area on the composition of the surface energy balance system is about 3m;the wet period is about 3.5m,which is basically the same as the depth of groundwater depth impact on surface temperature.