首页|Extracting iceberg freeboard using shadow length in high-resolution optical images

Extracting iceberg freeboard using shadow length in high-resolution optical images

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Icebergs are big chunks of ice floating on the ocean surface,and melting of icebergs con-tributes for the major part of freshwater flux into ocean.Dynamic monitoring of the icebergs in Antarctica and accurate estimation of their volume are important for predicting the trend of freshwater budget of the Southern Ocean.The iceberg freeboard is a key parameter for measuring the thickness and volume of an iceberg and is defined as the difference between the elevation of iceberg surface and sea level.So far,freeboards of icebergs have been successfully extracted using InSAR DEM,and the laser and radar altimeter.However,uncertain-ties exist in these results mainly caused by missed detection of small icebergs due to the spatially sparse and temporally incomplete data coverage.In addition to the above techniques,optical images can also be used to extract the iceberg freeboard based on its geometric relationship with shadow length,which can effectively compensate for the above shortcom-ings.Although the feasibility has been preliminarily presented,the precision and extensive application of shadow-height method deserves further research,such as estimating the basal melting of icebergs.In this work,we tested an optical image-based freeboard extraction method over icebergs in Prydz Bay,Antarctica.A normalized shadow pixel index(NSPI)is designed to identify iceberg shadows with different shapes in HY-1C/D CZI and Sentinel-2 MSI optical images.The iceberg freeboard can be determined with an acceptable precision(2 m)in optical images compared with laser altimeter(i.e.ICESat-2)measurements.Moreover,basal melting of icebergs has been assessed according to the variation of freeboard using repeated optical observations.The results indicate that icebergs in the study area were with a mean freeboard of about 56 m in early December 2022,and experienced a decrease in freeboard of 1.9 m within two months,in correspondence with the Antarctic seasonal trend.The methodo-logical framework,therefore,turns out to be a reliable complementary approach to studying the iceberg freeboard in polar regions.

Optical remote sensingicebergfreeboardshadow lengthHY-1C/D CZISentinel-2 MSI

Ziyi Suo、Yingcheng Lu、Jianqiang Liu、Jing Ding、Qing Wang、Ling Li、Weimin Ju、Manchun Li

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International Institute for Earth System Science,Nanjing University,Nanjing,China

Collaborative Innovation Center of South China Sea Studies,Nanjing University,Nanjing,China

Key laboratory of Space Ocean Remote Sensing and Application,National Satellite Ocean Application Service,Ministry of Natural Resources,Beijing,China

School of Geography and Ocean Science,Nanjing University,Nanjing,China

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2024

10.1080/10095020.2024.2360525

地球空间信息科学学报(英文版)
武汉大学（原武汉测绘科技大学）

地球空间信息科学学报(英文版)

影响因子：0.207
ISSN：1009-5020
年,卷(期)：2024.27(3)