Sentinel-1 wave mode SAR monitoring of icebergs around Antarctica

The high-quality global wave mode (WV) synthetic aperture radar (SAR) vignettes routinely collected by Sentinel-1 are today extensively exploited for various oceanic and atmospheric phenomena. Yet, these observations remain largely untapped for iceberg monitoring in the Southern Ocean. As a follow-up to our previous work, a dedicated SAR image classifier is built to detect icebergs of sizes from meters to kilometers in length that are commonly underrepresented in current recording systems. It has been fine-tuned from the Inception-v3 deep convolutional neural network using a curated dataset of 2,062 iceberg and 15,338 non-iceberg cases. Independent evaluations, based on three additional datasets, achieve high precision and recall rates of over 90%. Applied to all WV images acquired between 2016 and 2018 unveils iceberg occurrences around Antarctica. About ∼ 7 . 5 % of the detected icebergs drift into 40°S to 50°S latitudes, while the majority are concentrated poleward of 55°S. The seasonal patterns of SAR icebergs are generally consistent with altimeter-detection estimates and exhibit advances over the sea ice regions. Linking these WV SAR icebergs to the reported large icebergs reveals that the former are more likely to be located to the east of larger iceberg trajectories, suggesting that the primary driver of their drift is the underlying ocean currents. Although precise identification of the shape and position of these km-sized icebergs remains challenging, WV SAR vignettes provide added value to iceberg investigations at scales beyond current operational reports. Not only relevant for the precise monitoring of icebergs across a wider range of sizes, but it can also become instrumental for our understanding of iceberg tracking, associated dissolution, along with freshwater transport, and their broader impact on global and local climate processes. • Global Sentinel-1 SAR data aid monitoring of km-sized icebergs around Antarctica. • A deep learning model is developed to identify SAR vignettes containing icebergs. • Icebergs are common in the Southern Ocean with 8% drifting northward beyond 50°S. • Tracking iceberg dissolution helps manifest Southern Ocean currents and dynamics.