| The polar regions have a great impact on the global climate and environment change as the cold source of the world. Research of the polar regions is very important for understanding and monitoring the global climate change since the change of atmosphere, ocean and glaciers in North and South Pole would lead to a global change of atmosphere and ocean circulation directly or indirectly. Arctic climate system is extremely sensitive to the global warming. The speed of warming in Arctic is much faster than the global mean, which shows the great importance and urgency of the study of Arctic. Dissapearing of the ice and snow is the prominent impact of warming climate on Arctic envionment, with an obvious acceleration of shrinking of Arctic sea ice and melting of the Greeland Ice Sheet since the 21st centry. Sea ice plays a key role of Arctic climate system, the layer of sea ice and snow prevents the heat absorption from solar radiation and seperates the heat exchange betweem atmosphere and ocean, which keeps the low temperature of Arctic. The change of sea ice would strongly affect the atmosphere and ocean in polor region, leading to a global climate change. The affect of ice sheet melting is more directly and has a great impact for human habitation, complete melting of the Greenland Ice Sheet would lead to a rise of global sea level of about 7m. Although the present melting of Greenland Ice Sheet only contributes 0.5mm/yr for the global sea level rise, some big cities in coast region and a few islands in South Pacific Ocean are in dangerous with the continual acceleration of its melting.A great progress of polar research has been made since the development of satellite, especially the technique of satellite remote sensing, which provides large scale and long term monitoring of sea ice extent, ice sheet melt area and atmosphere. ICESat satellite laser altimetry provids new aspects and methods for the study of polar region. It can collect elevation imformation of North and South Pole with an unpresented accuracy with the advantage of small footprint, no penetration on ice and less sensitive to surface slope compared to traditional radar altimetry, providing reliable data source for determination of sea ice thickness and ice sheet elevation change.The theme of this thesis is analyzing the change of snow and ice in Arctic with ICESat data, determination of the Arctic sea surface hight, sea ice freeboard and trend of Greenland Ice Sheet melting, discussion of the change of Arctic sea ice thickness and mass loss of Greenland Ice Sheet, based on the analysis of the accuracy and error sources of ICESat data in Arctic, study of the methods of determing the sea ice freeboard and ice sheet elevation change. Main contents of this thesis include:1) The importance and urgency of Arctic research has been reviewed by introducing the trend of Arctic sea ice and Greenlan Ice Sheet change; the formation and growth of sea ice, the interaction between sea ice and Arctic climate, and the mechanism of surface melting and mass loss of Greenland Ice Sheet, and the state and techniques of sea ice and ice sheet research have been expounded.2) The basic methodology of ICESat laser altimetry has been reviewed, the main error source of ICESat altimetry and the Inter-Campaign bias has been analyzed, the data filtering of ICESat altimetry on ice sheet have been discussed, and the accuracy of ICESat altimetry has been estimated.3) Lowest-level filtering and Empirical relation method for determining ice-covered sea surface hight with ICESat data has been introduced. Based on variation characters of sea surface height and parameters of ICESat return pulse waveform, waveform and height method has been proposed for sea surface height determination. According to the analysis of systematic error originated from data processing, the optimal value of some parameters has been discussed.4) With 2003-2008 ICESat Arctic sea ice altimetry data, mean sea surface hight of Arctic Ocean has been determined. The difference of this sea surface model and DTU13 model is 9.9+7.1 cm, which means our result has a better precision than similar foreign studies. The prominent character of ocean current captured by the mean dynamic topography based on this sea surface height and the compatible results of ICESat and tide gauge data derived seasonal variability of Arctic sea surface height show the capacity of ICESat data on ice-coverd sea surface hight determination.5) Arctic sea ice freeboard and its trend has been determined with 2003-2008 ICESat data. Relating to the Arctic climate, the change of component of first year and second year sea ice has been discussed according to the sea ice freeboard fraction. The method of conversion from sea ice freeboard to thickness has been studied, and the trend of Arctic sea ice thickness has been reviewed. The result shows a 15 cm/yr decrease of multi-year sea ice, while the decrease of first-year ice is less than 4 cm/yr.6) The determination of ice sheet elevation change with ICESat crossovers and repeat tracks has been studied. By comparison of different methods, the effect of surface slope and track arangement for elevation change determination has been introduced in detail.7) The elevation/volumn change of Greenland Glacier from 2003 to 2009 has been determined, showing a 16.44 cm/yr decrease of the elevation which equals to a decrease of 295.33km3/yr in volumn. Based on the drainage system, the change of Greenland Glacier has been discussed in detail and the present situation of the mass loss of the glacier has been reviewed. |
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