| As a bridge connecting the interaction between various spheres,lakes have a huge impact on the global climate and ecological environment through the interaction of lakes and atmosphere.The changes of lake air interaction,such as Lake expansion,recession,lake freezing and thawing,will cause changes in regional and global climate and ecological environment.The lake ice formed in autumn and winter in the middle latitude and high altitude area is a sensitive indicator of climate and environment change,which can not only reflect the characteristics of regional climate change,but also reflect the interaction between regional climate and lake;at the same time,lake ice plays an important role in human production and life,such as Arctic transportation,strategic military,cryosphere service,etc.The Qinghai Tibetan Plateau is greatly affected by climate change,and the feedback makes the region have an amplification effect on climate and environment change,at the same time,the region's ecological environment is fragile and sensitive.In addition,there are many lakes with large area,and seasonal lake ice is widely developed.The characteristics of lake ice in the plateau area affect the climate and ecological environment of the third polar region and even the whole world.However,at present,the research on lake ice is mainly concentrated in northern Europe,Canada and other regions,and the research on the characteristics of lake ice change in the Qinghai Tibet plateau area is lack of systematic research.In this paper,taking Qinghai Lake as an example,18 GHz,19 GHz and 18.7 19GHz are remotely sensed by long time series passive microwave brightness temperature data,optical remote sensing data?MODIS,Landsat series data and sentinel 2A data?,measured lake ice thickness data?1983-2018?and air temperature,wind speed,precipitation?snow?data?1961-2018?of four stations around the lake,ground penetrating radar field observation data are used to analyze the characteristics of ice phenology change,lake ice thickness change,freeze-thaw spatial distribution of Qinghai Lake.In this paper,the method and experience of extracting lake ice thickness are introduced,and the response mechanism of lake ice change characteristics to climate change is described.At the same time,the reason of lake ice change is analyzed by combining Lake form factors and using MODIS surface temperature data with GEE platform.It provides a method guidance for the study of lake evolution,lake ice characteristics and climate change in the Qinghai Tibet Plateau.Through the analysis of remote sensing data and measured data,the main results of this paper are as follows:1.Under the background of climate changing in Qinghai Lake Basin,the ice phenology of Qinghai Lake obtained by using passive microwave brightness temperature data shows that:the freezing on date of Qinghai Lake is delayed?0.23 d·a-1?,the melting onset date is obviously advanced?0.33 d·a-1?,the freezing on date of lake ice are significantly reduced,and reduction rate is 0.57 d·a-1;The results of MRR data showed that:the freezing on date of Qinghai Lake was delayed?0.32 d·a-1?,and the melting onset date was advanced?0.34 d·a-1?,which was more intense than that of bright temperature extraction,and the ice recession trend of Qinghai Lake in the past two decades was more obvious.2.Remote sensing data shows that Qinghai Lake began to freeze in early December,completely frozen at the end of December and early January,and began to melt at the end of March of the following year,and completely melted in early April;borehole observation data shows that maximum lake ice thickness of 0.59 m appeared in February,and the average lake ice thickness for many years is 0.29 m.Geophysical,remote sensing,model simulation and other methods can be used to obtain the characteristics of lake ice thickness changes.The higher frequency of ground penetrating radar?frequency of 250 MHz and above?has more advantages in spatial distribution of lake ice thickness;inversion of lake ice thickness using Landsat albedo has a higher accuracy?RMSE=2.25 cm?;the results of lake ice thickness simulation using Stefan equation combined with air temperature data show that the ice thickness of Qinghai Lake thins at a rate of 0.46 cm·a-1.The advantages and disadvantages of different methods for obtaining lake ice thickness are summarized and compared.3.The formation and melting of Qinghai Lake has obvious spatial distribution characteristics.In winter,Qinghai Lake mainly begins to freeze from Haiyan Bay area in the east and begins to melt from Heima River and other areas in the west.There are spatial differences in the process of freezing and ablation.Remote sensing data shows that during the freezing process of Qinghai Lake,water is mainly converted into primary ice and secondary ice,and then superimposed ice and aggregated ice are generated.The distribution characteristics of lake ice types at different times and different locations are different.4.Finally,by analyzing the influencing factors of lake freezing and thawing characteristics,it is found that winter temperature in Qinghai Lake Basin is a key factor affecting the ice production and dissipation of Qinghai Lake,and wind speed,snowfall and atmospheric circulation are also important factors affecting the development and melting of lake ice.The morphological factors of lakeshore in Qinghai Lake affect the lake ice phenology and thickness of the lake ice through the heat transfer of water and land.The changes of surface temperature and water level of the lake ice are also important factors influencing the freezing and thawing of lake.This article explores the characteristics of Qinghai Lake ice change and its response to climate change in terms of climate change,lake ice phenology,lake ice thickness,freeze-thaw spatial changes,and major factors affecting lake ice.At the same time,different remote sensing methods were used to monitor the characteristics of lake ice phenology and ice thickness.This study reveals the characteristics of lake ice phenology changes and the temporal and spatial characteristics of lake ice thickness over the past 40 years in Qinghai Lake,and confirms the feasibility of inversion of lake ice thickness by remote sensing.These studies are conducive to the study of the plateau lake-atmosphere interaction process and the physical mechanism between lake ice and climate change.With the development of the cryosphere service industry,this article also provides important method guidance for the winter tourism service of Qinghai Lake,and also provides a theoretical basis and method for the extraction of lake ice thickness in the third pole region,and provides a response to the lake ice-regional climate change Research ideas. |
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