【Title】SEA ICE ALBEDO OBSERVATIONS DURING NAVIGATIONS THROUGH PRYDZ BAY, ANTARCTICA, IN THE AUSTRAL SUMMER OF 2013-2014
Li Mingguang, Lei Ruibo, Li Zhijun, Han Hongwei,Tian Zhongxiang
【摘要】 在 2013—2014年南半球夏季时对南极普里兹湾海区的反照率进行了走航观测。利用安装于破冰船船头的高光谱辐照度计测量入射和反射的350—920 nm的太阳短波辐射, 基于此观测数据, 经计算得到了反照率。分析比较不同下垫面的反照率, 通过比较不同航段的观测结果, 得到了反照率的空间变化以及从海冰融化期至冻结初期的变化。不同下垫面的反照率差异较大, 有积雪覆盖的固定冰反照率最大, 有积雪覆盖的浮冰其次, 而积雪融化的浮冰则反照率有所降低。新冰的反照率较低, 有积雪覆盖的新冰反照率迅速增加。比较不同波段的反照率, 发现融化期由于积雪含水量较大, 增加了对近红外辐射的吸收, 降低了该波段的反照率。结合卫星遥感(AMSR-2)和人工观测的海冰密集度, 发现区域平均的反照率主要取决于海冰密集度, 然而也受下垫面物理特征影响, 例如2月底至3月初形成的新冰, 反照率只有老冰的1/3— 1/2。新冰形成, 会直接增加海冰密集度, 但由于其反照率较低, 对空间平均反照率的贡献较小。因此, 若要建立合理的冰水混合区的反照率参数化方案, 必须充分考虑海冰类型和冰面积雪的物理状态, 并考虑反照率的波长依赖性。
【Abstract】 Underway incident and reflected solar irradiance were measured onboard the R/V Xuelong during its navigations in Prydz Bay, Eastern Antarctica, during the Australian summer of 2013–2014. The albedo of seawater and sea ice was calculated from the observed data. Albedo obtained from different navigational segments from late November to early March was compared. This period spanned the seasons of sea ice melt to growth. Landfast ice covered by snow had the largest albedo (~0.70). The second highest was pack ice with snow (~0.55—0.65), while, the albedo of pack ice without snow cover could decrease to about 0.40. The albedo of new ice was very low (~0.15—0.30). However, snow cover would increase it to about 0.40, which was comparable with second-year ice without snow cover. The observed albedo was linked to sea ice concentration derived from AMSR2 data and visual observations from the bridge of the R/V Xuelong. Regional average albedo depended mainly on sea ice concentration, although it was also affected by the physics of the underlying surface. For example, the albedo of new ice formed from late February to early March was only 30%—50% that of second-year pack ice. Therefore, the contribution of new ice to the regional average albedo is not as great as to regional ice concentration. During the melt season, the relatively large water content within the snow cover can reduce near-infrared spectral reflection. Thus, ice concentration alone is insufficient to establish a reasonable albedo parameterization for the mixing zone of sea ice and water. Instead, the influences of ice and snow types should also be considered.