Backscatter-sensitive retrieval of iceberg areas from Sentinel-1 Extra Wide Swath SAR data

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We present the first systematic study on Arctic iceberg area retrieval from Sentinel-1 Extra Wide Swath SAR data. Our dataset contains 4014 Arctic icebergs in open water. To detect icebergs in Sentinel-1 images, we applied a constant false alarm rate (CFAR) algorithm. Icebergs were matched in co-located Sentinel-1 and optical Sentinel-2 acquisitions for a period from May to September in the years 2016 to 2023. The Sentinel-1 iceberg areas are moderately correlated with the Sentinel-2 reference areas, with Pearson’s r-values of 0.65 at HH- and 0.69 at HV-polarization. The CFAR algorithm mostly overestimates iceberg areas in both channels, but in some cases underestimates iceberg areas in the HV channel when the iceberg backscatter is low. The 10th and 90th percentiles of the relative error are -36% and +569% at HH-, and -37% and +349% at HV-polarization. In addition to a resolution-imposed size-dependency of the error, we find that the HH ocean clutter is moderately negatively correlated with the relative error (Pearson’s r-value: -0.64). Additionally, we observe weak correlations between the HH (HV) iceberg backscatter and the Sentinel-2 iceberg area, with a Pearson’s r-value of 0.34 (0.26). We utilize the analyzed relationships to predict iceberg areas from Sentinel-1 data, using a gradient boosting regression. Backscatter-sensitive retrieval models yield more accurate iceberg areas than backscatter-insensitive models. In the HH (HV) channel, the former models reduce the mean absolute error by 58% (49%). Backscatter-sensitive retrieval of iceberg areas will foster consistent SAR-based observations of Arctic iceberg areas during summer months. Future studies need to quantify the combined impact of iceberg area retrieval and iceberg detection performance on area distributions and total iceberg areas. • 4000 Arctic icebergs in co-located optical and SAR data in summer from 2016 to 2023. • New method uses backscatter statistics to predict iceberg areas from Sentinel-1 data. • Variable ocean and iceberg backscatter drive variations in retrieved iceberg areas.

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