冰架崩解是南极冰盖物质损失的主要原因之一。冰山是冰架崩解的产物，其源源不断向南大洋输入淡水，影响南大洋深层海洋水形成进而影响全球气候变化。冰山出水高度是测量冰山厚度进而估算其体积的一个重要几何参数。受观测数据和方法的限制，大规模精确获取南大洋冰山出水高度难以实现，因此，南极冰山对南大洋的淡水输入量的估算还存在很大的不确定性。本研究提出了一种利用低太阳高度角下光学影像上冰山的阴影信息精确提取冰山出水高度的方法，并利用此方法提取了环南极近岸冰山的出水高度，结合南大洋冰山面积数据，估算了冰山对南大洋淡水输入量。具体的研究内容如下：

（1）提出了一种新的、高效的阴影测高方法，利用低太阳高度角下中分辨率光学影像阴影高精度测量冰山出水高度，同时提出了利用双时相测量自动剔除粗差的方法。研究基于4期Landsat-8 全色影像进行了冰山出水高度的提取试验，测量了各种类型冰山的出水高度，并根据双时相方法测量与无人机DSM数据提取的冰山出水高度进行比较，评估并验证了阴影测高方法的精度。结果表明，在太阳高度角5.2°时，使用15 m分辨率的Landsat-8 全色影像，64.1%冰山出水高度有效测量点的测高精度优于1 m，86.9%优于2 m，相当于使用高分辨率光学影像立体摄影测量方法所能获取的精度。研究实现了整个处理流程的自动化，可用于南大洋大范围冰山出水高度快速测量。

（2）提出了一种南大洋冰山淡水输入量的估算方案，并估算了环南极冰山对南大洋的淡水输入量。基于本研究提出的阴影测高方法，提取了2019年8月到10月环南极71景Landsat-8全色影像上的冰山出水高度。研究将南极冰山分成扁平冰山(Tabular)、块状冰山(Blocky)、楔型冰山(Wedge)和尖顶型冰山(Pinnacle)，按冰山的类型和尺度分类统计南极冰山的出水高度和厚度，结合南大洋冰山面积数据，估算全南极近岸冰山的质量和其对南大洋的淡水输入量。研究结果表明：当假设冰山密度为850 kg/m3时，利用阴影测高数据集计算的1997、2000和2008年全南极冰山的总质量分别为：3047.85 Gt、4497.79 Gt和3480.23 Gt。与假设冰山厚度为单一值(250 m)时估算的全南极冰山质量相差超过1000 Gt，这表明在精细评估南极冰山对于南大洋的淡水输入中精确计算冰山的出水高度和厚度等参数是十分必要的。

Ice shelves collapse is one of the main reasons for the mass loss of the Antarctic ice sheet. Icebergs are the product of ice shelf disintegration, which is a continuous input of freshwater to the Southern Ocean and affects the formation of deep ocean water in the Southern Ocean and thus global climate change. Iceberg freeboard is an important geometric parameter for measuring iceberg thickness and estimating its volume. Due to the limitation of observation data and methods, it is difficult to accurately obtain the freeboard of icebergs in the Southern Ocean on a large scale. Therefore, there are still great uncertainties in the estimation of the freshwater input from Antarctic icebergs to the Southern Ocean. In this study, we propose a method to accurately extract the freeboard of icebergs using the shadow information of icebergs on optical images at low solar elevation angles and use this method to extract the Near-Coastal Antarctic iceberg freeboard and estimate the flux of freshwater from icebergs to the Southern Ocean in combination with the area data of icebergs in the Southern Ocean. The specific research content includes:
：1) This study developed a new, highly efficient shadow-height method to precisely measure the freeboard of various icebergs surrounded by sea ice using the medium resolution optical image shadows at low-solar-elevation angles, and a method to eliminate gross errors automatically by using the bi-temporal measurement is proposed. In this study, the iceberg freeboard extraction test based on 4-phases Landsat-8 panchromatic imagery was conducted to measure the freeboards of various types of icebergs, and evaluated and validated shadow length precision according to bi-temporal measurements and comparison with the measurements from the unmanned aerial vehicle. The results show that at the solar elevation angles of 5.2°, the freeboard precision of 64.1% data could reach 1 m and 86.9% could reach 2 m, which is equivalent to the accuracy that can be obtained by using high-resolution optical image stereophotogrammetry. This study automates the entire processing process and can be used for rapid measurements of iceberg freeboard over a large scale of the Southern Ocean.

2) In this paper, an estimation scheme of freshwater flux from icebergs in the Southern Ocean is proposed, and the freshwater flux from the Near-Coastal Antarctic icebergs to the Southern Ocean is estimated. Based on the shadow height method, the iceberg freeboards of 71 Landsat-8 panchromatic images around Antarctica from August to October in 2019 were extracted. In this study, Antarctic icebergs were classified into Tabular, Blocky, Wedge and Pinnacle icebergs, and the freeboard and thickness of Antarctic icebergs were classified by type and scale of icebergs, combined with the area data of Southern Ocean icebergs to estimate the mass of Near-Coastal Antarctic icebergs and their freshwater input to the Southern Ocean. The results show that when the density of icebergs is 850 kg/m3, the total masses of icebergs in 1997, 2000, and 2008 calculated by using shadow height dataset are 3047.85 Gt, 4497.79 Gt, and 3480.23 Gt, respectively. The difference between the mass of the Antarctic iceberg estimated when the iceberg thickness is a single value (250 m) is more than 1000 Gt, which indicates that it is very necessary to accurately calculate the freeboard and thickness of the icebergs in the fine evaluation of the freshwater input from the Antarctic icebergs to the Southern Ocean.