中文摘要：

ENVISAT卫星可覆盖至南北纬81．4°，其携带的RA-2雷达高度计为极地海冰研究提供了周期性的主动微波海冰探测途径。本文用ENVISAT雷达高度计探测的Ku波段后向散射系数对2011年南极和北极各月份的海冰覆盖特征（范围和海冰表面属性）进行详细研究。利用海水和海冰的不同散射特征，设置后向散射系数阈值为13dB可成功分离海冰和海水。除夏季外，雷达高度计和美国冰雪数据中心基于辐射计获取的极区海冰覆盖边界高度符合。因北极中央区域（81．4°N以北）没有轨迹覆盖，本文只估计了南极海冰的覆盖面积，夏季海冰的覆盖范围面积比辐射计探测结果偏大，这和雷达高度计对离散薄冰较强的观测能力有关，在海冰密集分布的其他季节结果则有很好的符合，其中冬季面积平均差异为0．17Mkm2。分析南极和北极海冰的分布特征差异，和南极相比北极冬季海冰表面较粗糙干燥，而夏季海冰表面湿度较大。结果表明ENVISAT雷达高度计可准确地探测包括海冰覆盖和海冰表面属性变化在内的海冰季节性演变过程，可在海冰监测、极地科考等领域中发挥重要作用。

英文摘要：

The tracks of ENVISAT RA-2 altimeter can reach up to the high latitude of 81.4~of north and south, which provides a way of active microwave sensing to monitor sea ice. A method is developed using backscatter coefficients （00） based on the ENVISAT satellite radar altimeter RA-2 to detect the monthly changes of polar sea ice extent and surface properties. Considering the variations of scattering characteristics of the sea water and ice sur- face, it is proved that a threshold of ]3 dB fore0 can distinguish the sea ice cover from sea. Except for summer times, a highly correspondence between sea ice boundaries from altimeter and from radiometer released by NSIDC is presented. For lacking of satellite tracks on the central areas of Arctic, it is only can estimated the sea ice ex- tent of Antarctic zones, And theENVASAT altimeter givesa greater value in summer months compared to the radi- ometer result from NSIDC, which relates to the excellent capacity of altimeter to sensing the dispersed thin ice. tn other seasons with high sea ice concentration, the difference of sea ice extent is pretty small as the mean difference of winter is just O. 17 Mkmz, The discrepancy of sea ice properties over two polar zones is also researched, and the result shows that in Arctic the sea ice surface is more rough and dry in in the winter and more wet in the summer than Antarctica. Based on this research, the ENVlSAT radar altimeter can precisely detect seasonal evolution of sea ice cover and surface properties and is proved to be a useful tool in sea ice monitoring and polar exploration.