Remote Sensing Estimation Of Soil Salinization In Qingtu Lake And Surrounding Areas

Soil salinization is one of the major problems in the social development of arid inland river basins,so it is of great significance to accurately extract soil salinization information and analyze the main influencing factors of soil salinization to monitor soil salinization,prevent soil secondary salinization,and improve and control salinized land.Qingtu Lake is the tail lake of shiyang river,which belongs to the typical area of the lower reaches of dry inland rivers.Since the implementation of ecological water diversion from hongyashan reservoir to Qingtu Lake in 2010,the change characteristics of soil salinization in Qingtu Lake and surrounding areas and whether the ecological water diversion mode brings soil secondary salinization need to be further explored.Therefore,it is very important to invert the information of soil salinization in Qingtu Lake and its surrounding areas and explore the main factors affecting soil salinization.In this paper,the Qingtu Lake and its surrounding areas were taken as the research area,and multiple salinity indexes and environmental indexes were extracted accurately from soil salinization information using sentry 2 and landsat image data.On this basis,soil salinization distance index model(SDI)and soil salinization comprehensive index model(CSI)were established.By drawing ROC curves of the two soil salinization index models,calculating the AUC and the determination coefficient,and comparing the two index models,it is proved that the CSI model is more accurate than the SDI model in soil salinization information extraction in Qingtu Lake and surrounding areas.The CSI model was used to extract the soil salinization index information of Qingtu Lake and surrounding areas from 2000 to 2018,and the soil salinization change characteristics of different degrees were obtained by grading the index.On this basis,the stability analysis and trend analysis methods are used to quantitatively explore the main areas where soil salinization degree changes and the changing trend of soil salinization degree in Qingtu Lake and surrounding areas,and then discuss the main influencing factors of soil salinization degree changes.Through research,the following conclusions are drawn:(1)In Qingtu Lake and surrounding areas,the accuracy of extracting soil salinization information by CSI model is higher than that of SDI model.The validation of soil salinization index model based on field measurement data shows that the correlation coefficient between CSI and measured data is relatively large,and the root mean square error of determination coefficient of CSI is smaller than that of SDI.According to ROC curve test,the offline area(AUC)of SDI is smaller than that of CSI.Standard error,significance and other information show that CSI has a strong ability to rank the correctness of pixels.(2)The salinized land area ratio in Qingtu Lake and surrounding areas is large,and the change characteristics of soil salinization degree are significantly different in 2010.From 2000 to 2018,soil salinized land area in Qingtu Lake and surrounding areas accounted for more than 80% of the total area,and the change of salinized land area ratio in the past 18 years was relatively small.Before 2010,the degree of soil salinization in Qingtu lake and surrounding areas was relatively low,and the salinized land was mainly mild salinized land,while after 2010,the degree of salinization was relatively high,and most of the mild salinized land was transformed into severe and moderate salinized land.(3)The overall performance of soil salinization in Qingtu Lake and surrounding areas is poor in stability and presents an increasing trend.The stability analysis shows that the area occupied by the Qingtu Lake and its surrounding areas with poor stability is 40.5% and the area occupied by the areas with good stability is 25% from 2000 to 2018,indicating that the soil salinization degree of a large part of the study area has changed significantly in the past 18 years.The trend analysis shows that the proportion of the regions with significantly increasing and increasing soil salinization degree is 42.3%,the proportion of the regions with significantly decreasing and significantly decreasing soil salinization degree is only 0.5%,and the proportion of the regions with significantly increasing soil salinization degree is mainly the shallow water area and peripheral areas of Qingtu Lake.Some areas of Qingtu Lake changed from mild and moderate salinization to non-salinization.(4)The degree of soil salinization in Qingtu Lake and surrounding areas showed obvious seasonal differences.The soil salinization degree was the highest in spring.Winter and summer were followed by moderate and severe salinization in winter and summer.The degree of soil salinization was the lowest in autumn.(5)In 2015,the degree of soil salinization was the lowest,the proportion of mild and moderate salinization was the largest,and the proportion of severe salinization was small.Compared with 2010,in 2015,some areas of Qingtu Lake changed from mildly salinized land to non-salinized land,but in 2018,the soil salinized degree increased,and some moderately salinized land and mildly salinized land changed to severely salinized land.(6)Soil salinization in Qingtu Lake and surrounding areas is related to various factors such as temperature,precipitation,evaporation,soil relative humidity and human factors.A series of climatic characteristics such as higher temperature,less precipitation and large evaporation in Qingtu Lake and its surrounding areas provide natural environment conditions for soil salinization,which is also the main reason for the large proportion of salinized land in this area.After 2010 green lake and the surrounding area soil salinization degree obvious changes in the main influence factors for ecological water conveyance,show that in without obvious changes in climate conditions,the ecological water conveyance is a green earth lake and the surrounding area of the main causes of soil salinization degree changed significantly,the ecological water conveyance in reducing the area of the soil salinization degree of problem,also caused the soil salinization and soil secondary salinization in time there is a certain hysteresis.