Röhrs and Kaleschke (2012) found that thin ice has a unique signature in the emissivity radio in the vertical polarized brightness temperature channels at frequencies between 89.0 GHz and 18.7 GHz in winter. The different sea ice classes especially for water and thin ice are characterized by the emissivity ratios above one. Following the proposed algorithm, we derive sea ice lead fraction from the AMSR2 brightness temperature data for the freezing season (November-April) north of 65°S. The spatial resolution of the data is 6.25 km. The steps are as follows. Firstly, the AMSR2 L1B brightness temperatures at frequencies of 18.7 GHz (TB,18.7V) and 89.0 GHz (TB,89V) are interpolated onto the NSIDC EASE grid with a spatial resolution of 6.25 km. Secondly, the brightness temperature radio r=TB,89V/TB,18.7V is calculated. Thirdly, a mean filter is used to enhance the signal of the leads. Finally, lead fraction which is defined as the area fraction of thin ice compared to other ice classes is computed. The proposed algorithm exhibits advanced ability in detecting sea ice leads in pack ice zone. It can detects leads wider than 3 km and resolves about 50% of the lead area compared to MODIS satellite images.File descriptionsPeriod and temporal resolution: November 1, 2012, to April 30, 2020;Daily for freezing season: November 1 to April 30Coverage and spatial resolution: Arctic north of 65°NSpatial resolution: 6.25 km x 6.25 km, NSIDC EASE grid.Geographic longitude: -180°E to 180°EGeographic latitude: from 65°N to 90°NDimension: 1792 rows x 1216 columnFormat: NetCDF

Please note: We recommend that some post-process procedures should be applied to the lead fraction field to reduce the unrealistic signal. Isolated lead pixels should be removed to reduce the number of fragments, and near-coastal grid cell which is one or two grid cells away from the coast is also recommended to be removed due to potential land spill/contamination.