Recognition And Application Of Polar Leads Based On ICESat Data

In recent years,the melting of sea ice and the rise of sea level in the polar regions caused by global temperature rises have attracted widespread attention.The Arctic Ocean has a severe cold climate and a harsh natural environment.It is covered by snow and ice all the year round.Therefore,the monitoring of polar oceans has always been a challenging task.With the development of satellite remote sensing technology,it is possible to conduct large-scale,all-weather and repeated monitoring of the polar ocean.However,limited by the detection capability of the traditional microwave altimeter,the application of remote sensing of the polar ocean focuses on the extent and type of sea ice,with few achievements in the aspects of sea surface height and sea ice thickness in the polar region.Satellite laser altimeter has the advantages of small spot size,full waveform recording and high elevation measurement accuracy.Laser remote sensing has brought breakthrough progress to the study of polar oceans.Based on the observation data of GLAS,the first laser altimeter for earth observation in the world,this paper studies and discusses the key and difficult problems in the recognition of the polar leads.A method for identifying polar leads based on GLAS waveform characteristic parameters and elevation discrimination is established,and further used to calculate the sea surface height and the freeboard height of sea ice in the region,so as to analyze the seasonal and inter-annual characteristics of the sea surface height and sea ice freeboard height in the polar region.The main research contents are as follows:(1)Analyzing the data products and waveform parameter data provided by GLAS to determine the type of data used in this study.And discussing the key parameters affecting the quality of the original data to determine the criteria and methods for data quality screening of ICESat data.(2)A method of leads recognition based on sea surface waveform characteristics and elevation discrimination is designed.The method is mainly divided into two steps:first,the minimum threshold method is used to determine the sample data of sea surface observation;the cut-off threshold for identifying the sea surface features is determined based on the sample data reflectance,waveform length,echo broadening and echo kurtosis;Thus,establish a waveform criterion for sea surface recognition;then,the data that meets the waveform conditions are further used by the minimum level filtering method to remove the elevation data mixed with sea ice to extract effective sea surface data.(3)Using the ICESat data based on the waveform characteristics and elevation discrimination method,the average sea surface height and sea ice freeboard height of the Arctic Ocean Beaufort Sea from 2003 to 2008 autumn and winter for 10 mission periods were calculated.Characteristics of seasonal and interannual changes of ice freeboard height.The results show that the sea surface height in the region as a whole increased from 2003 to 2008,and the sea ice freeboard height decreased at a rate of about 2 cm / yr.The sea surface height in autumn is higher than that in the adjacent winter.The sea ice freeboard is higher than that of sea ice in autumn.