Study On Spatial-temporal Change Of Arctic Sea Ice Thickness Based On Satellite Altimetry

Under the background of global climate and environment change becoming more and more serious, sea ice change which seems as indictor and amplifier of chlimate change is getting more and more attention by the word. Arctic is the most important and extensive study area of sea ice research, which is also the key and sensitive area of climate change. However, the knowledge and information of Arctic sea ice espically Arctic sea ice thickness is insufficient till now since the reason of its harsh natural environment and observation limitation. As the Arctic sea ice continues to shrink, a series of problems are emerging, such as climate warming, extreme weather events, ecological security and so on. So it’s urgent and necessary to carry research on Arctic sea ice and sea ice thickness.Sea ice thickness is one of the most important parameter of sea ice, is the third dimension of sea ice change research. Sea ice thickness is sensitive to the coupling role between atmosphere and ocean, which directly determines exchange rate of energy and matter between them. Sea ice thickness dominates thermodynamics and dynamics process of sea ice, influence the motion, deformation, frozen and melt of sea ice, which feedback to climate, environment and ecological global system. Accruately obtain the information of sea ice thickness change is not only help to understand the climate and environment change, but also has pracitical significance to resources utilization and maritime shipping.Sea ice thickness is also the most difficult parameter of sea ice measurement. At present, different approaches inclulding instu drilling, upward looking sonar measurements, electromagnetic induction, remote sensing have been applied to retrieve sea ice thickness, while only satellite altimeter (laser or radar) has been proven to provide hemispheric estimates of sea ice thickness distribution. Satellite altimetry is an effective and promising method to estimate sea ice thickness at a hemisphere scale, however, how to develop and apply this technology to obtain the reliable and continuous information of sea ice thickness change, become a hot and difficult issue of sea ice research.This dissertation aims at improving the capability and accuracy of retrieving Arctic sea ice thickness, as well as assessing the quality of spatial-temporal change results, which includes three steps:uncertainty analysis-algorithms comparison and improving-change analysis. Factors affecting accuracy of retrieving sea ice thickness from altimetry data are assessed to get optimal parameters and algorithm with high accuracy, so as to reveal the distribution and temporal variation of Arctic sea ice thickness of the past ten years. The main contents of the dissertation are followed.(1) Sea ice thickness research is statistically analysed and systematic summarized using bibliometric and content analysis method, so as to get the basic information and research status of sea ice and sea ice thickness in the past and present. Meanwhile, it analyses and concludes the research emphasis of this dissertation.(2) Factors affecting the precision of sea ice thickness from satellite altimetry are assessed to explor the influence to sea ice thickness retrieval results using sensitive analysis method. Meanwhile, four widely used algorithms are comparied and validated to determine the best algorithm with high precision at present.(3) Freeboard is estimatied by selecting lead discrimnation algorithms of waveform classification and minimum elevation threshold for laser and radar altimetry. For radar freeboard, inversions are applied to obtain more reliable freeboard considing the penetration of radar wave to the snow above the sea ice and the difference of wave speed between the snow and the ice.(4) A set of optimal input parameters for sea ice thickness retrieval are determined by comparing the sea ice thikness retrieval results to veditation data. Besides, the parameters of sea ice density and snow depth are improved by considing the fraction of sea ice type so as to achieve the best input parameters.(5) The new algorithm with freeboard inversion and optimal input parameters has been built and comparied with current algorithm. The retrieved sea ice thickness of two algorithms are vaditated to determine the better algorithms and model parameter for sea ice thickness retrieval from satellite altimetry.(6) Spatial and temporal variation of Arctic sea ice thickness retrieved by the new algorithm is analysed using time series analysis, including the change of Arctic and its important sea regions, seasonal and annual changes, first year and muti year sea ice thickness changes and so on.