首页 >  2022, Vol. 26, Issue (7) : 1450-1458

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DOI:

10.11834/jrs.20219383

收稿日期:

2019-10-31

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Landsat 8全色影像阴影的扁平冰山出水高度提取
关真富1,程晓1,2,3,4,刘岩1,3,4,璩榆桐1,李腾1
1.北京师范大学 全球变化与地球系统科学研究院遥感科学国家重点实验室, 北京 100875;2.中山大学测绘科学与技术学院, 珠海 519082;3.南方海洋科学与工程广东省实验室(珠海), 珠海 519082;4.中国高校极地联合研究中心, 北京 100875
摘要:

冰山出水高度是测量冰山厚度进而估算冰山体积的一个重要几何参数,是定量评估冰山对海洋的淡水输入量的基础。冬季冰山在海冰上成影且阴影较长,本文提出利用阴影测高模型高精度测量冰山出水高度的方法。试验选择2016年8月29日、9月7日和9月16日中心太阳高度角分别为5.43°、7.49°和11.01°的3期Landsat 8全色15 m影像,以独立扁平冰山为例,自动提取冰山在海冰上的阴影长度计算冰山出水高度,并利用不同时相同名成影点进行交叉验证评估测量精度。结果显示:阴影长度测量误差优于1个像元,在太阳高度角低于11.01°时,全色15 m影像提取的冰山出水高度均方根误差(RMSE)低于2.0 m,平均绝对误差(MAE)低于1.5 m。由此表明:在冬季低太阳高度角下,Landsat 8全色15 m影像可用于高精度测量冰山出水高度,具有大范围测量南极冰山出水高度的潜力。

Extracting icebergs freeboard from the shadows in Landsat 8 panchromatic images
Abstract:

Icebergs are formed either by the calving of the seaward margins of floating glacier tongues or ice shelves or by the fragmentation of existing icebergs. Mass loss caused by iceberg calving represents up to half of the total loss of mass from the Antarctic ice shelves. As they melt and drift with the ocean currents, icebergs provide a significant source of freshwater input to the surface layer of the ocean, enough to affect the stability of stratification in the upper ocean. Any increased freshwater in iceberg discharge, or ice shelf melt, likely has a major impact on the ocean circulation by delivering sufficient freshwater, which will play a critical role in many geophysical and biological processes. The iceberg freeboard is an important geometric parameter for measuring the thickness of an iceberg and estimating its volume. Because of the paucity of high-precision measurements on iceberg thickness, large uncertainties exist on the iceberg’s ice volume estimation of the Southern Ocean. The freeboard of large icebergs has been successfully extracted using the altimetry method. These large uncertainties exist, however, because of the insufficient altimeter coverage of various icebergs. On the basis of the fact that an iceberg can cast an elongated shadow on the surface of sea ice in winter, this study proposes a method to measure the iceberg freeboard by using shadow length and the predefined or estimated solar elevation angle. Three Landsat 8 panchromatic images with center solar elevation angles of 5.43°, 7.49°, and 11.01° on August 29, September 7, and September 16 in 2016, respectively, are selected to test our method. The shadow lengths of five isolated tabular icebergs are automatically extracted to calculate the freeboard height. For an accuracy assessment, we perform cross-validation on the matching points at different times. Results show that the measurement error of shadow length is less than one pixel. When the sun elevation angle is lower than 11.01°, the root-mean-square error (RMSE) of the iceberg freeboard from the 15 m panchromatic image is less than 2.0 m, and the mean absolute error (MAE) is less than 1.5 m. The experiment shows that under the angle of low solar elevation in winter, the Landsat 8 15 m panchromatic images can be used for high-precision measurement of the iceberg freeboard and has the potential to measure the Antarctic iceberg freeboard at a large scale.

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