Using Multi-Source Satellite Altimetry Data To Monitor The Water Level Change Of Qinghai Lake

Lake is an important water resource for human production and life and one of the key factors affecting ecological environment changes.At present,satellite altimetry technology has been widely used to monitor lake water level changes,making up for the deficiencies of traditional water level monitoring.This paper uses Jason-2 and Cryosat-2/SIRAL altimetry satellites to extract the water level information of Qinghai Lake from 2009 to 2016,and analyzes the reasons for the changes in the water level of Qinghai Lake.The main work and research results are as follows:(1)Method of extracting and screening Qinghai Lake water level data using altimetry satellite dataSince the original data of altimetry satellites have large errors,in order to reduce the influence of errors on the extracted water level sequence,it is necessary to filter and edit the original data.The GDR data of Jason-2 and Cryosat-2/SIRAL altimetry satellites were combined,and Qinghai Lake 2009 was extracted after data selection within the lake,water level calculation,water level abnormal value removal,reduction processing,and coordinate system conversion.-2016 water level sequence.Since the elevation datums used by the two satellite altimeters are not the same,it is necessary to perform elevation datum conversion.After calculation,it is found that there is a 0.7m difference between the T/P ellipsoid elevation coordinate system and the WGS84 elevation coordinate.(2)Comparative analysis of three waveform re-tracking methods in Cryosat-2/SIRAL GDR dataThis paper selects Refined CFI,UCL and Refined OCOG in Cryosat-2/SIRAL GDR data to extract the water level data of Qinghai Lake from 2012 to 2016.Experiments have found that the amount of data extracted by the Refined CFI algorithm is significantly more than that of the other two algorithms.This is due to the freezing period of Qinghai Lake,while the two algorithms of UCL and Refined OCOG cannot normally extract the lake water level during the freezing period,and the extracted Qinghai The lake water level values are all 0,so the water level sequence extracted by the Refined CFI algorithm is selected as the water level value of Qinghai Lake from 2012 to 2016,but in the non-icing period,the Refined OCOG algorithm has better extraction effect,indicating that the Refined OCOG algorithm is more suitable Extract the lake water level sequence without freezing period.(3)Water level change of Qinghai Lake and its cause analysisFor the constructed water level sequence from 2009 to 2016,inter-annual variation analysis and seasonal variation analysis are performed.It can be seen from the annual average water level change that the water level of Qinghai Lake has been increasing continuously from 2009 to 2016,and the fastest year of growth was 2016,when the water level increased by 0.33 m.Through seasonal change analysis,it is found that the water level of Qinghai Lake has seasonal changes.It starts to increase in spring and reaches the high tide period in September,and then the water level begins to decline.Since Qinghai Lake is sparsely populated,natural factors have become the main reason for the changes in the water level of Qinghai Lake.This paper analyzes from the three perspectives of temperature,precipitation and evaporation.After calculation,it is found that the average temperature in the Qinghai Lake basin from 2009 to 2016 is positive,indicating that the temperature is increasing,and the increase in temperature indirectly affects the water level change of Qinghai Lake;the analysis found The change trend of precipitation in the Qinghai Lake basin on the interannual scale is consistent with the change trend of water level.Precipitation begins to increase rapidly in May and reaches its peak in July-August.However,the change of water level is lagging,so the highest value of water level generally appears in In September,the annual precipitation mainly depends on large-scale continuous precipitation from June to September.The precipitation in the Qinghai Lake basin has gradually increased from 2009 to 2016,with an average annual increase of 9.2mm/a,which is conducive to providing sufficient water sources for Qinghai Lake.The amount of evaporation showed a decreasing trend from 2009 to2016.The amount of evaporation in 2009 was 982.3mm,and the amount of evaporation in2016 was 763.9mm.Through comparative analysis,it is found that the evaporation in the Qinghai Lake basin is about twice the precipitation,and there is a positive correlation between evaporation,precipitation,and water level in summer and autumn,and a negative correlation in spring and winter.It is precisely because of the interaction of these three influencing factors that the water level of Qinghai Lake rises year by year.