Tracking Large Tabular Icebergs in Antarctica Using AMSR2 Observations and Random Forest: A Case Study of A23A

초록

Icebergs can significantly influence sea ice-ocean environments and pose serious hazards to maritime navigation in polar regions. Therefore, detecting and tracking icebergs is essential for scientific and operational purposes. This study investigates the feasibility of using passive microwave observations to detect and track large tabular icebergs in Antarctica, focusing on the iceberg A23A in the Weddell Sea. A Random Forest (RF) iceberg detection model was developed using the Advanced Microwave Scanning Radiometer 2 (AMSR2) observations. Reference datasets were constructed by combining Sentinel-1 SAR images with co-located AMSR2 pixels to label iceberg and non-iceberg. Brightness temperatures from all AMSR2 channels, along with auxiliary parameters commonly used in sea ice concentration retrieval algorithms, were employed as input variables for model development. The RF model showed an F1-score of 0.84 on an independent test dataset, indicating reasonably robust performance. While the grid size of AMSR2 data (10 x 10 km) limited the accurate delineation of iceberg area, the model effectively identified the location of A23A and tracked its drift over time. Among the input variables, the difference between horizontally and vertically polarized brightness temperatures at 89 GHz was significant for distinguishing iceberg from surrounding sea ice and open water. The central positions of A23A estimated by the RF model from July 2012 to September 2023 showed a root mean square deviation of 11.3 km compared with data from the Antarctic Iceberg Database. Considering the size of A23A (similar to 65 x 70 km) and the grid size of the AMSR2 data, this deviation is relatively small. However, the RF model failed to detect A23A after September 2023, likely due to changes in its microwave radiation properties as it drifted into lower latitudes and underwent surface melting.

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