Research On Water Volume Change Of Qinghai Lake Based On Multi-source Satellite

As an important hub connecting the atmosphere,hydrosphere and biosphere,the changes of lakes have an important impact on the local natural environment and human production and life.Qinghai Lake is the largest inland saltwater lake in my country,located in the northeastern part of the Qinghai-Tibet Plateau.Before the 21st century,Qinghai Lake was in a state of shrinking.Under the influence of global climate change,it has shown a trend of rapid expansion in the past decade.As an indicator of its response to the external environment,the water volume change of Qinghai Lake can indirectly reflect the change of the external environment.Mastering the dynamic changes of lake water level,area and water volume and their causes has guiding significance for maintaining regional ecological balance and formulating reasonable protection policies.This paper is based on multi-source altimetry satellite data:Topex/Poseidon,Envisat RA-2,HY-2B,Jason-1/2,Sentinel-3A/3B and optical remote sensing images:Landsat-5 TM,Landsat-7ETM,Landsat 8 OLI monitored the changes of lake surface area and water level in Qinghai Lake from 2002 to 2019,and inverted the monthly average area changes of Qinghai Lake by fitting the water level-area relationship,so as to calculate the monthly and annual average changes of Qinghai Lake water volume from 2002 to 2019.Change time series;according to the reconstructed data of gravity satellite,the equivalent water height sequence of Qinghai Lake was calculated by the latitude cosine weighting method,and the reasons for the change of the water level of Qinghai Lake were analyzed from the two aspects of mass change and thermal expansion;The contribution ratio of factors to the recharge of Qinghai Lake into the lake;finally,the LSTM model was established to predict the change of water volume from April to September,2022.The specific conclusions are as follows:(1)Using multi-source altimetry satellite data,the lake surface water level of Qinghai Lake was calculated,and the monthly average water level and annual average water level of Qinghai Lake from 2002 to 2019 were obtained.The accuracy of the multi-source altimetry satellite data was analyzed in combination with the measured water level at Xiashe Station.The standard deviation of T/P measurement was 14 cm,and the standard deviation of the remaining altimetry satellite data was all within 10 cm.Among them,Sentinel-3B had the highest measurement accuracy.(2)The change of the water level of Qinghai Lake from 2002 to 2019 was studied,and the influence of the quality change on the water level change was analyzed.From the perspective of changes during the year,the water level of Qinghai Lake showed a trend of first decreasing,then increasing and then decreasing.The water level was the lowest from March to April,the highest from September to October,and the largest fluctuation during the year was about 0.40 m.From the perspective of inter-annual changes,the water level of Qinghai Lake first decreased and then increased.The water level decreased by 10 cm at a rate of 5 cm/a during 2002-2004,and increased by 3.11 m at a rate of 21 cm/a during 2004-2019.The change trend of area and water volume is basically consistent with the change trend of water level,both follow the trend of first decline and then rise,and 2004 is the inflection point.The quality of Qinghai Lake is basically the same as the trend of water level changes.April-September is the rising period,and October-December is the falling period,which is more consistent with the actual situation.From the overall change trend,there are two stages in which the water level and mass change trends are opposite:the change trend of the equivalent water height during 2002/04-2004/05 was 16.26cm/a,the water level change trend was-8.33 cm/a,and the mass change rate was 16.26 cm/a.It is about twice the rate of water level rise;from 2016/06 to 2018/06,the water level increased with a trend of 76 cm/a,and the equivalent water height decreased with a trend of-17.54 cm/a.This opposite trend may be caused by the following three reasons:(1)The Qinghai Lake area is smaller than the minimum monitoring range of the gravity satellite,resulting in unstable data quality;(2)The gravity satellite was just launched in April 2002,and the data reliability during the commissioning period was low;(3)There may be human influence.(3)The contribution ratio of various factors to the recharge of Qinghai Lake from 2002 to2019 was studied.The results show that runoff and lake surface precipitation are the main recharge methods of lake water,accounting for 56.39%and 30.32%of the total recharge,respectively.(4)The changes of Qinghai Lake water volume from 2002 to 2019 were studied.The optimal prediction parameters of the LSTM model are obtained by the control variable method,and the correlation between the prediction results and the actual values is as high as 98%.According to the LSTM model,from April to September 2022,the relative water volumes of Qinghai Lake are:151.26×10~8m~3,155.37×10~8m~3,157.21×10~8m~3,161.38×10~8m~3,166.35×10~8m~3,174.53×10~8m~3.There are 39 figures,8 tables,and 96 references in this thesis.