These sea ice concentration data are retrieved with the ARTIST Sea Ice (ASI) algorithm (Spreen et al., 2008) which is applied to microwave radiometer data of the sensors AMSR-E (Advanced Microwave Scanning Radiometer for EOS) on the NASA satellite Aqua, and AMSR2 (Advanced Microwave Scanning Radiometer 2) on the JAXA satellite GCOM-W1. The ASI algorithm using AMSR-E data was first implemented at IUP in 2002 and has been continuously producing sea ice concentration data since then. As several details of the processing chain have changed over the years, in 2018, all ASI ice concentration data for the Arctic and Antarctic based on AMSR-E and AMSR2 were reprocessed with exactly the same parameters, settings and software. The result are ASI data, version 5.4. The details are explained in the following sections.