(Table 1) Summary statistics of in situ sea-ice characteristics of Ice Station Belgica sites Fabra, Patria/Liège and Brussels in October 2007

Three ice type regimes at Ice Station Belgica (ISB), during the 2007 International Polar Year SIMBA (Sea Ice Mass Balance in Antarctica) expedition, were characterized and assessed for elevation, snow depth, ice freeboard and thickness. Analyses of the probability distribution functions showed great potential for satellite-based altimetry for estimating ice thickness. In question is the required altimeter sampling density for reasonably accurate estimation of snow surface elevation given inherent spatial averaging. This study assesses an effort to determine the number of laser altimeter 'hits' of the ISB floe, as a representative Antarctic floe of mixed first- and multi-year ice types, for the purpose of statistically recreating the in situ-determined ice-thickness and snow depth distribution based on the fractional coverage of each ice type. Estimates of the fractional coverage and spatial distribution of the ice types, referred to as ice 'towns', for the 5 km**2 floe were assessed by in situ mapping and photo-visual documentation. Simulated ICESat altimeter tracks, with spot size ~70 m and spacing ~170 m, sampled the floe's towns, generating a buoyancy-derived ice thickness distribution. 115 altimeter hits were required to statistically recreate the regional thickness mean and distribution for a three-town assemblage of mixed first- and multi-year ice, and 85 hits for a two-town assemblage of first-year ice only: equivalent to 19.5 and 14.5 km respectively of continuous altimeter track over a floe region of similar structure. Results have significant implications toward model development of sea-ice sampling performance of the ICESat laser altimeter record as well as maximizing sampling characteristics of satellite/airborne laser and radar altimetry missions for sea-ice thickness.

2007年国际极地年期间开展的SIMBA（南极海冰质量平衡，Sea Ice Mass Balance in Antarctica）考察中，研究人员对贝尔吉卡冰站（Ice Station Belgica, ISB）的三种冰型区域，完成了高程、积雪深度、冰面干舷(ice freeboard)与冰厚的特征表征与评估。对概率分布函数(probability distribution functions)的分析表明，星载测高术(satellite-based altimetry)在海冰厚度估算领域具备巨大应用潜力。本次研究聚焦的核心问题为：考虑到固有空间平均效应(spatial averaging)，若要实现积雪表面高程的合理精准估算，测高仪所需的采样密度究竟为何值。本研究旨在确定ISB浮冰(floe)（作为兼具一年冰(first-year ice)与多年冰(multi-year ice)混合类型的典型南极浮冰）所需的激光测高仪(laser altimeter)有效命中次数，以基于各冰型的覆盖占比，统计重构野外原位(in situ)实测获取的冰厚与积雪深度分布。针对这块面积5 km²的浮冰，研究人员通过野外测绘与影像记录，对被称为冰"镇区"(ice "towns")的各冰型覆盖占比与空间分布进行了估算。研究人员模拟了光斑尺寸(spot size)约70米、采样间距(spacing)约170米的ICESat测高仪飞行航迹，对浮冰的各冰镇区进行采样，由此生成了基于浮力反演(buoyancy-derived)的冰厚分布。对于由一年冰与多年冰混合组成的三镇区冰型组合，要统计重构该区域的冰厚均值与分布，需要115次测高仪有效命中；而仅针对一年冰组成的两镇区冰型组合，则仅需85次命中——这分别对应在结构相似的浮冰区域上，连续采集19.5千米与14.5千米长度的测高仪航迹数据。本研究结果对于ICESat激光测高仪观测数据的海冰采样性能模型开发，以及优化星载/机载激光与雷达测高(radar altimetry)任务在海冰厚度反演中的采样特性，均具有重要指导意义。