Spatial And Temporal Distribution Of Soil Moisture And Analysis Of Influencing Factors Based On TVDI Index

For the loess hilly and gully regions,the ecological environment is fragile,and vegetation growth status is an important index reflecting the ecological environment in the region.Soil moisture is an important factor affecting vegetation growth.At present,there are few studies on the spatial distribution pattern of soil moisture in Loess Hilly and gully regions,less weather stations Moreover,because of the complicated terrain and the difficulty of obtaining the measured data when satellite transit,The dynamic changes of soil moisture remote sensing technology,remote sensing data of the area and spatial characteristics,It provides basic data for monitoring soil drought for a long period of time in the Dakou catchment,and at the same time provides a certain guiding significance for the ecological restoration of the area.The Chakou watershed is located at the junction of Yonghe County,Lu County and Shilou County,Linfen City,Shanxi Province,and it is mainly located in Yonghe County.The total area is approximately 126.48km2.The study area belongs to the typical loess hilly gully region,with undulating hills and broken terrain.The rainy season is concentrated on July-August,Precipitation intensity is greater,the erosion of the surface runoff is easy to soil and water loss,It is a typical ecologically fragile area.How to Speeding up Harnessment of Soil and Water Loss and Improving the Eco-environment is particularly important.With the rapid development of remote sensing and GIS technology,remote sensing technology can obtain soil moisture in a large area in real time and quickly.There are many models to retrieve surface temperature,such as Crop water stress index model,Energy equilibrium model,Temperature Vegetation Dryness Index(TVDI),Microwave remote sensing model,one of the most widely used method of temperature vegetation drought index.This paper uses temperature vegetation drought index method to invert the soil moisture in 2015 growing season based on Landsat data;Due to the lack of measured data,this paper uses meteorological data and QuickBird data to verify the inversion results indirectly.In the inversion of the surface temperature,the study selected radiation transmission equation and improved single-window algorithm,The average error of the improved single window algorithm is lower than that of the radiation transmission based on brightness temperature data and meteorological data verification;Finally,using the improved single-window algorithm to invert the surface temperature(LST)and the normalized vegetation index(NDVI)to construct the temperature vegetation drought index(TVDI).Finally,based on DEM data and meteorological data,the influence of factors such as topography,air temperature,rainfall,and vegetation type on TVDI was analyzed,and the reliability of TVDI inversion results was analyzed.The main conclusions are as follows(1)The spatial pattern of soil moisture generally shows wet-arid-semi-aridity from the northwest and the middle to the southeast of the basin,and this trend has the effect of topography(2)The soil moisture was semiarid and arid in general in the vegetation growing season.The spatial pattern of soil moisture is that the central region showed dry situations,The area of semi-arid area is 98.67 km2,accounting for 73.14%,and the area of drought-prone area is 36.03 km2,accounting for 26.71%.The TVDI values ranged from 0.51 to 0.85,and were classified into four levels in the GIS using natural discontinuities,The TVDI values ranged from 0.51 to 0.6 for the wetting area and northward to the drainage area.TVDI ranged from 0.6 to 0.8 for the drought-stricken area and southeast of the drainage area TVDI>0.8 is the arid area located in the central part of the basin,and the result is consistent with the TVDI indicating soil moisture classification(3)When retrieving the surface temperature in the Loess Hilly-gully region,The average error of the improved single window algorithm is lower than that of the radiation transmission based on brightness temperature data and meteorological data verification;The spatial distribution of land surface temperature in the study area has obvious differences.On the one hand,the surface temperature of different underlying surface types presents in general:orchard>grassland>residential area>arable land>woodland>pit surface;on the other hand,Radiation Transfer Equation>Improved Single Window Algorithm>T10 Brightness>Temperature.The results of the study can better estimate the surface temperature of different underlying surfaces in the loess hilly-gully region and more effectively assess the soil moisture in the region(4)Land cover types,topography and rainfall are important factors affecting the spatial variation of soil moisture.The soil moisture of different vegetation cover types is quite different.For this area,the soil moisture of arbor forest is the highest.In a certain elevation range,the soil moisture content increases with the elevation;the soil moisture content during the rainy season is obviously higher than that in other months;and the TVDI index is used in the loess hilly and gully region to achieve better results through the qualitative analysis of TVDI.,And can well reflect the wet and dry conditions of soil moisture in the area.This result is consistent with the results obtained by Yang Ling et al.in the study of the factors affecting the spatial and temporal pattern of soil moisture.