| Taking Chaoyang city,Liaoning province as the research area,this paper selects MODIS remote sensing images from may to September in 2016 and 2017 as the data source,and combines the measured soil water content of each sampling point in 2016 and 2017.Through envi and ArcGIS platform,MODIS remote sensing image data are preprocessed in a series of ways,such as radiometric calibration,butterfly effect processing,geometric correction,image mosaic,image cropping,etc.At the same time,the model parameters such as normalized vegetation index,vegetation coverage,total band albedo,surface temperature and day-night temperature difference are calculated and analyzed.According to the actual situation in the study area and the applicability and characteristics of various remote sensing drought inversion methods.Four remote sensing drought inversion methods and measured soil water content were selected to construct a remote sensing drought monitoring model,and the fitting relationship between each evaluation index and soil water content of different depths was analyzed,and the signifiance analysis and accuracy verification were carried out.So as to choose the index model with the greatest correlation as the remote sensing drought monitoring model in Chaoyang city,Liaoning province.The main conclusions of this study are as follows:(1)Thermal inertia method(ATI)and vertical drought index method(PDI)are suitable for areas with low vegetation coverage or bare land areas.When the soil depth is 0-10 ?,the thermal inertia ATI inversion effect of soil moisture content is good.With the increase of soil depth,the fitting effect of thermal inertia ATI and soil water content gradually deteriorates,and it becomes irregular with the increase of soil depth.When the soil depth is 10-20 ?,the vertical drought index PDI has the best effect in retrieving soil water content.There is a negative correlation between vertical drought index PDI and soil water content,that is,the smaller the value of vertical drought index PDI is,the weter the soil is,the higher the soil water content is.(2)Modified vertical drought index(mpdi)and temperature vegetation drought index(tvdi)are suitable for areas with high vegetation coverage.When the soil depth is 0-10 ?,the correction of vertical drought index mpdi has a good effect on retrieving soil water content.There is a negative correlation between modified vertical drought index mpdi and soil water content.the larger the value of modified vertical drought index mpdi is,the drier the soil is,and the lower the soil water content is.Tvdi inversion of soil moisture content in 0-10 ? is the best.the fitting correlation coefficient of soil moisture content presents a unimodal pattern,and the peak value appears on August 12 th with its complex correlation coefficient of 0.631.(3)When the vegetation coverage is low,the linear regression correlation between PDI and 10-20 ? soil water content is extremely significant,and the model inversion accuracy is higher,with the average accuracy of 90.4 %.In this paper,the model of vertical drought index PDI and soil moisture content is selected as the basic model to conduct drought monitoring research.(4)When the vegetation coverage is high,the linear regression correlation between tvdi and 0-10 ? soil moisture content is extremely significant.In this paper,the model constructed by tvdi and soil moisture content is selected as the basic model to conduct drought monitoring research,and the model inversion accuracy is higher,with the average accuracy being 88.14 %.(5)From May to June of 2016,it was mainly light drought.In July,the drought mainly accounted for 51.06%,and the drought was the most severe,with light drought as the main factor in August and September.From May to September of 2017,the drought is mainly due to drought,and the drought conditions in chaoyang city in May and July gradually increased.The drought in July increased to 70.21%,and the drought situation in 2017 was further intensified compared with 2016. |
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