(Table 1) Ice thickness at lake Nam Co, Tibet, during 2008-2009

Lake ice change is one of the sensitive indicators of regional and global climate change. Different sources of data are used in monitoring lake ice phenology nowadays. Visible and Near Infrared bands of imagery (VNIR) are well suited for the observation of freshwater ice change, for example data from AVHRR and MODIS. Active and passive microwave data are also used for the observation of lake ice, e.g., from satellite altimetry and radiometry, backscattering coefficient from QuickSCAT, brightness temperature (Tb) from SSM/I, SMMR, and AMSR-E. Most of the studies are about lake ice cover phenology, while few studies focus on lake ice thickness. For example, Hall et al. using 5 GHz (6 cm) radiometer data showed a good relationship between Tb and ice thickness. Kang et al. found the seasonal evolution of Tb at 10.65 GHz and 18.7 GHz from AMSR-E to be strongly influenced by ice thickness. Many studies on lake ice phenology have been carried out since the 1970s in cold regions, especially in Canada, the USA, Europe, the Arctic, and Antarctica. However, on the Tibetan Plateau, very little research has focused on lake ice-cover change; only a small number of published papers on Qinghai Lake ice observations. The main goal of this study is to investigate the change in lake ice phenology at Nam Co on the Tibetan Plateau using MODIS and AMSR-E data (monitoring the date of freeze onset, the formation of stable ice cover, first appearance of water, and the complete disappearance of ice) during the period 2000-2009.

湖冰变化是区域与全球气候变化的敏感指示因子之一。当前学界监测湖冰物候常采用多源数据：可见光近红外（Visible and Near Infrared, VNIR）影像波段非常适用于淡水冰变化监测，例如先进甚高分辨率辐射计（AVHRR）与中分辨率成像光谱仪（MODIS）所获取的观测数据；主动与被动微波数据同样可用于湖冰观测，涵盖卫星测高、微波辐射计数据，快速散射计（QuickSCAT）的后向散射系数，以及专用扫描微波辐射计（SSM/I）、多通道扫描微波辐射计（SMMR）与先进微波扫描辐射计地球观测系统（AMSR-E）等传感器获取的亮温（brightness temperature, Tb）。现有研究多聚焦于湖冰覆盖物候，针对湖冰厚度的探讨则相对较少：例如Hall等人借助5 GHz（6 cm）辐射计数据，证实了亮温与冰厚度之间存在显著相关性；Kang等人则发现，AMSR-E传感器在10.65 GHz与18.7 GHz波段获取的亮温季节演化特征，受湖冰厚度的影响极为显著。自20世纪70年代以来，学界已在寒冷地区开展了大量湖冰物候相关研究，尤以加拿大、美国、欧洲、北极与南极区域为甚。但针对青藏高原的湖冰覆盖变化研究却相对匮乏，仅公开报道过少量关于青海湖湖冰的观测研究。本研究的核心目标为：以2000-2009年为研究时段，借助MODIS与AMSR-E数据，对青藏高原纳木错的湖冰物候变化展开分析，具体监测指标包括封冻起始日、稳定冰盖形成日、首次无冰出现日以及冰盖完全消融日。