Typical Applications Of ICESat To Polar Studies

The global climate ecosystem is closely related to our production and living, and global climate change has become a hot topic for human beings for a long time. However, there are still a lot of uncertainties in predicting the global climate change and studying the major cause of the global climate change. Since polar environment is hard to be interfered by the human activities directly, it can truly reflect the global climate change and also react on the global climate change. The melting of ice sheet, ice shelf and sea ice is accelerated by global warming, which will not only result in increased global mean sea level but also affect the global water circulation. The further cryosphere research is significant. However, human's exploration and research on the polar have been seriously hindered by the harsh polar environment. The developments of the altimetry satellite make it possible to monitor the polar even without going to the polar area in person, and thus help to overcome the difficulty from the harsh natural conditions of polar area.ICESat was the first laser radar altimetry satellite on earth. Compared with other radar altimetry satellites, it has smaller errors in the radar retrievals due to inaccurate modeling of surface penetration and large ladar footprion, which will lead to a higher accuracy for ICESat's laser retrieved elevations. ICESat has provided powerfull data for polar research. So the importance of how to use the ICESat data for polar study more effectively is increasing prominent and deserves to be further studied.The Antarctic digital elevation model (DEM) is an assurance for Antarctic exploration and important data set for the Antarctic related science research. The mass change of Antarctica Ice Sheet is significantly influenced by the global climate change, and plays more and more important roles in global sea level change. Changes of Arctic sea ice reflects global climate change, ice loss of Arctic was not only affecting Arctic residents'living derectly, but also breaking the original ecological balance which will threaten many biological species inside the Arctic. Both the DEM and the mass change of the Antarctic ice sheet, as well as the freeboard of the Arctic sea ice occupy an important position in polar geoscience. The three focus areas are studied in this paper based on ICESat altimetry data.The main contents and results of this paper include:(1) We created DEMs with two small scale regions of Antarctic Ice Sheet by usingdifferent interpolation algorithms. The DEMs were validated against the sample data which was reserved from the survey data for comparison. The results indicate Kriging algorithm has the best reliability and the highest stability. A new DEM of the Antarctic Ice Sheet has been derived from ICESat Data using Kriging algorithm. The uncertainty of the DEM was assessed using GPS data collected by the inland team of Chinese National Antarctic Research Expedition. The results show the precision of the DEM is strongly correlated with the slop and coverage, the DEM is in good agreement with the GPS data over the low sloped area and complete coverage.(2) The repeat orbit methods were improved based on the status of the low resolution of the Antarctic DEMs. A slope correction between the different tracks and reference track were applied to estimate the elevation changes of the Antarctic ice sheet. A surface slope and aspect at about 200 m scale were retrieved by the slopes we have got. There was a strong agreement between our slopes and GPS results in Dome A area. Combining the snow density model, the mass change of the Antarctic Ice Sheet has been estimated after removing the corrections from GIA and system error of ICESat. The mass balance of Antarctic Ice Sheet is calculated to be-44±21 Gt/yr including-26±6Gt/yr for West Antarctica and-18 ±20Gt/yr for East Antarctica using 5 years ICESat altimetry data from October 2003 to December 2008, and the contribution of the Antarctic Ice Sheet loss to global sea level is about 0.12mm/yr.The difference between our result and other results have been analyzed and showed a strong agreement. The results showed the mass losing of the Antarctic Ice Sheet is mainly concentrated near the Amundsen Sea in West Antarctica and Poinsett Cape in East Antarctica.(3) The features of Arctic sea ice and the factors that caused changes of Arctic sea ice were presented. Based on the hypothesis that the lowest levels measured represent the open water in sea ice, freeboard height of the Arctic sea ice is derived using accuracy ICESat data from 2003 to 2008. The seasonal and interannual variation characteristics of Arctic sea ice during the five years are analyzed. The results show a decline in sea ice freeboard over the 5 years, with a record minimum in the summer of 2007. The reasons for the rapid decline of the Arctic sea ice in the summer of 2007 have been presented in this research. System deviation of the retrieved results has been discussed and analyzed using the ULS field data.