Changes in a Giant Iceberg Created from the Collapse of the Larsen C Ice Shelf, Antarctic Peninsula, Derived from Sentinel-1 and CryoSat-2 Data  
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Satellite radar remote sensing is useful for monitoring icebergs, because it can observe the Earth's surface regardless of weather conditions and sun altitude. The Brigham Young University and National Ice Center (NIC) have constructed a comprehensive database for Antarctic iceberg tracking, by analyzing microwave scatterometer data, and provide information about the locations and rotations of icebergs [12]. Satellite microwave scatterometers can observe the whole of Antarctica daily, but the spatial resolution of data generated is several tens of kilometers [12; 13], which is not enough to observe changes in icebergs in detail. Using synthetic aperture radar (SAR), which provides higher spatial resolution data, a detailed analysis of even small changes in icebergs is possible. Many studies have used SAR to monitor changes in Antarctic icebergs [14; 15; 16; 17; 18]. For example, [PERSON] and [PERSON] [16] analyzed the drift characteristics of iceberg C33 calved from the Nansen Ice Shelf, East Antarctica, using Sentinel-1 SAR images shortly after the ice shelf collapsed. [PERSON] et al. [17] observed the evolution of the tabular icebergs C28A and C28B between 2010 and 2012 using ENVISAT Advanced Synthetic Aperture Radar (ASAR) images, which originated from the Mertz Ice Tongue in East Antarctica.  
Satellite altimeters are necessary to analyze iceberg thinning. The radar altimeter (RA) is more useful than the laser altimeter in polar regions due to frequent cloudy weather. CryoSat-2 SAR/Interferometric Radar Altimeter (SIRAL) is more useful for observing iceberg freeboard change than previous generation RAs such as the RA on board ERS-1/2 and the RA-2 on board ENVISAT. This is because it can estimate ice topography with higher accuracy and higher spatial resolution [19]. In recent research on icebergs C28A and C28B [17], CryoSat-2 data were very helpful for analyzing freeboard change.  
In July 2017, a supersized iceberg broken away from the Larsen C Ice Shelf in the Antarctic Peninsula, named A68 by the NIC. The initial area of the A68 was about 5800 km\({}^{2}\) when it calved [20], which accounts for approximately 10% of the Larsen C Ice Shelf [21; 22]. Based on the iceberg tracking database operated by the Brigham Young University and NIC, iceberg A68 is currently the largest iceberg in Antarctica and the sixth largest on satellite observation records. Iceberg A68 is surrounded by dense sea ice throughout the year and the nearby seabed is shallow [23]. This means that it is expected to show complex evolution, different from freely moving icebergs. Although the evolution of iceberg A68 could have a significant impact on the marine environment around the Antarctic Peninsula, few studies on iceberg A68 have been conducted so far. There is one study on the changes in area and drift of the iceberg based on SAR image analysis [18], observing the changes for only six months after the iceberg formation. Moreover, the environmental factors affecting the changes of iceberg have not been analyzed.  
The objectives of this study are to (1) analyze the initial evolution of iceberg A68 in terms of changes in its area, drift speed, rotation, and freeboard over the 1.5-year period since it calved from the Larsen C Ice Shelf using Sentinel-1 SAR and CryoSat-2 SIRAL observations and (2) investigate the effects of environmental factors on these changes. Descriptions of the iceberg and the dataset used in this research are presented in Section 2. Section 3 explains the methods adopted for deriving information about the iceberg's evolution from satellite data. Section 4 provides a discussion of the results and the observed iceberg changes, and Section 5 provides a conclusion.