Remote Sensing Retrieval Of Electrical Conductivity Of Saline Soil In West Jilin Province And Research On Temporal Variation In Thirty Years

Soil salinization is a severe phenomenon of land degradation,which significantly affects regional economic and agricultural development.The western part of Jilin Province is a part of Songnen Plain,and the problem of soil salinization is prominent.On the one hand,human activities and climate change have aggravated soil salinization.On the other hand,the intervention of improvement measures has effectively alleviated the degree of salinization.Time series change monitoring of salt-affected soil,which can not only analyze the influencing factors of salinization but also provide data support for rational land use,which is of great practical significance.Because of its high timeliness and strong data comprehensiveness,remote sensing can obtain time-series data to monitor the temporal and spatial changes of salt-affected soil,which has become the most effective technology to carry out large-scale soil salinization monitoring.This study was funded by the National Natural Science Foundation of China“Research on real-time measurement of moisture and salinity of saline-alkali soil under different surface forms using near-surface multi-source remote sensing method(No.41671350)”.This paper established the inversion model of electrical conductivity(EC)of salt-affected soil in western Jilin Province,which based on the machine learning algorithm,and obtained the Landsat images in west Jilin Province from 1989 to 2019 employing Google Earth Engine(GEE)platform.According to the inversion model,we got the EC results of salt-affected soil.Finally,the temporal variation of soil salinization in western Jilin Province was analyzed.The main contents and conclusions of the thesis were as follows:(1)Field experiments were carried out in June 2019.After the Box-Cox transformation of the sampled soil,measured EC has satisfied the normal distribution.According to the correlation between the EC and the spectral reflectance of Sentinel-2MSI bands,the optimal spectral parameters was constructed.Then,the Linear regression model,Support Vector Machine(SVM),Regression Trees(RT),Gaussian Process Regression(GPR),Ensemble Tree(ET)were used to build EC inversion models.The test results of the model to the validation dataset showed that the GPR performance was optimal(R~2=0.66,RMSE=0.48 m S/cm,MAE=0.52 m S/cm),which was 29.04%higher than the traditional Linear regression model.(2)On the basis of Landsat and Sentianl-2 image reflectance matching,the EC of salt-affected soil was obtained in western Jilin Province by GPR model inversion,which based on the GEE platform.To get Landsat TM/OLI time-series data from 1989to 2019.After that,according to the EC data obtained by inversion,the classification of salt-affected soil was carried out according to the Kissell and Sonon(2008)classification criteria,and the spatial and temporal dynamics of salt-affected soil of different grades was analyzed by area statistics,dynamic degree,and transfer matrix.The results showed that in the last 30 years,the salinized land in the western part of Jilin Province presents the trend of increasing and then decreasing in spatial dimension.Those areas mainly distributed in Da'an City and Tongyu County.The salinized soil gradually increases from east to west.On the time dimension,the area of salt-affected soil increased rapidly from 2001 to 2007,and the total area increased by 2181.24 km~2,with an average annual growth rate of 3.3%.A significant decrease with an overall area reduction of 3219.96 km~2 from 2013 to 2019,an annual reduction rate of 7.4%.This data showed that soil salinization was effectively controlled and improved during this period.Combined with land use data,the results showed that salt-affected soil was mainly converted into agricultural land and grassland from 1989 to 2019.(3)The meteorological data of evaporation and precipitation and the temporal variation of salt-affected soil were analyzed in seven counties(cities)in Taobei,Da'an,Qian'an,Qianguo,Tongyu,Changling and Fuyu from 1996 to 2016.The results showed that the accumulated evaporation in the western region of Jilin Province was much higher than the accumulated precipitation for many years.The difference between the accrued evaporation and the accumulated precipitation in each county and city was closely related to the change of the area of salt-affected soil,especially in Da'an City,Gian'an County,and Tongyu County,where the soil salinization is more serious.