Recent Antarctic Sea Ice Surface Melt from Satellite Remote Sensing(REASSESS)

2017年1月，日本在南极洲的Syowa站附近发生了大规模的海冰表面融化事件。破冰船RV Shirase的现场小组报告说，在陆地和自由浮冰的顶部有多个融化池。一年前，也就是2016年1月，在麦克默多湾观察到大量的池塘。融化池，即海冰上的融水水坑，在北极夏季很常见，但在南极洲却极为罕见。在目前正在进行的REASSESS项目中，我们利用卫星数据表明，在Syowa站附近不仅在2017年1月观测到融化池，而且在2018年1月、2019年1月、2020年1月也观测到融化池，从而证明了一些融化池之前由于缺乏现场观测而被忽视。我们首次展示了全球南极融化池比例图，这些图是根据某一天所有卫星飞越的每日平均值绘制的，并在冰雪覆盖的南大洋的其他地区定位了更多潜在的融化池事件。这些新数据正在被汇编成第一个一致的全球南极融池/蓝冰数据集。我们不再对“南极融化池很少”进行定性估计，而是能够根据多年的卫星数据，提供由卫星得出的南大洋融化池和蓝冰的面积比例。然而，适合验证我们检索所需的特定条件（阳光，无云条件）的现场活动很少，因此开发检索的验证和校准很短。在拟议的更新计划中，我们计划进行由AWI资助的专用飞机计划。它的目标之一将是观察南极陆地和自由漂浮的浮冰顶部的融冰池/蓝冰。这次活动的结果将是一个独特的原位数据集，它将作为我们遥感融化池检索的验证和校准。此外，我们计划使用非常高空间分辨率的卫星图像作为验证数据的另一个来源。这些数据也将作为飞机行动的后续行动而获得，并可能提供验证时间序列。校正后的融池分数检索将用于新计划的融池数据集与南极海冰下水母原位数据的跨学科比较。因此，我们验证了一个假设，即冰下生态系统通过增加的海冰透射率受到地表海冰条件的影响。基于上述研究将产生的改进的融池比例趋势将阐明南极海冰在最近20年的卫星观测中变化了多少。

In January 2017, a massive sea ice surface melt event occurred in the vicinity of the Japanese Syowa station in Antarctica. The field party of the icebreaker RV Shirase reported multiple melt ponds on top of landfast and free floating ice. Massive ponding has been observed in McMurdo Sound a year earlier, in January 2016.Melt ponds, puddles of melt water on top of the sea ice, are common in the Arctic during summer but are thought of as extremely rare in Antarctica. In the currently running project REASSESS we have shown with the aid of satellite data that the melt ponding observed in the vicinity of Syowa station not only in January 2017 but also in January 2018, 2019, 2020, and thus proved that some melt ponds have been simply overlooked before due to lack of in situ observations. We have for the first time presented global Antarctic melt pond fraction maps produced as daily average from all the satellite overflights of a given day, and located more potential melt ponding events also in other regions of the ice-covered Southern Ocean. These new data are being compiled into the first consistent, global Antarctic melt pond/blue ice dataset. Instead of qualitative estimates “Antarctic melt ponds are rare”, we are able to provide satellite-derived area fractions of the melt ponds and blue ice in the Southern Ocean for many years of satellite data.However, the in situ campaigns fitting to the specific conditions needed to validate our retrievals (sunlight, cloud free conditions) are rare, so that the validation and calibration of the developed retrievals comes short.In the proposed renewal project, we plan to carry out a dedicated aircraft campaign funded by AWI. One of its objectives will be to observe the melt ponds/blue ice on top of Antarctic landfast and freely floating pack ice. The outcome of this campaign will be a unique in situ dataset which will serve as validation and calibration for our remote sensing melt pond retrieval. In addition, we plan to employ satellite imagery of very high spatial resolution as one more source of validation data. These data will be acquired also as follow-up to the aircraft campaign and will potentially provide validation time series. The calibrated melt pond fraction retrieval will be used for a newly planned interdisciplinary comparison of melt pond dataset with the jellyfish in situ data under the Antarctic sea ice. Thus, we test a hypothesis that the under-ice ecosystem is affected by the sea ice conditions on the surface via the increased sea ice transmittance.The improved melt pond fraction trends which will be produced based on the above research will clarify how much did the Antarctic sea ice change in the recent 20 years of satellite observations.