Observing Icebergs in the Amundsen Sea from Space

Abstract:

Icebergs are an important part of the Antarctic climate-ice-ocean system as about half the ice loss from Antarctica is through iceberg calving, leading to a vast amount of ice drifting around as icebergs. Tracking these icebergs’ trajectories and monitoring their extent is essential to reduce risk for maritime operators and to improve our understanding of many interrelations of the Antarctic environment including oceanographic, biological and physical processes. The objective of this study therefore is to track iceberg locations and shape in satellite data. Icebergs can be manually recognized in images acquired at different times of the year and under different environmental conditions using different satellite sensors. Changes in the orientation and shape of icebergs can be quantified in sequences of satellite imagery. Images in the visible spectrum offer the advantage of daily coverage, but are only useful during daylight and in the absence of clouds. In contrast, Synthetic Aperture Radar (SAR) data are independent of clouds and daylight. They also offer high spatial resolution and frequent coverage. However, the SAR backscatter is ambiguous when the sea surface is rough, presenting an obstacle to the automatic detection of icebergs. Satellite altimetry observations are of lower spatial and temporal resolution, but allow us to distinguish ocean from icebergs with confidence. In this study, we use different satellite techniques in synergy to detect the outline and area of eight different icebergs (60-1500 sq. km in size) in the Amundsen Sea and to track their movement and rotation over seven years. We also calculate changes in area over time, as the icebergs disintegrate and pieces break off at the sides. The outcome of this study will not only reveal a better understanding of the life cycle of icebergs, but also provide important information for operational users and shipping.