## 7 Outlook  
Evaluation in winter and in the Central Arctic could be done using SAR data. Retrieving SIC from SAR data is challenging and would require more analysis than we can provide in the framework of this paper. We recommend it as a direction for future research, especially as we expect a good performance of our merged dataset due to the large thermal contrast between water and sea ice in winter. The meaningful use of MODIS thermal infrared data is limited to winter and spring conditions. In summer, visible data can provide similar fine-resolution data which can be used for the merging. Especially as most of the ship traffic is in summer, this would be a valuable extension of our dataset. A study comparing our dataset to the coarser-resolution passive microwave SIC algorithms based on the 19 GHz and 37 GHz frequency channels could be done to demonstrate the advantage of the fine resolution of the merged SIC over these algorithms. The MODIS instruments aboard Aqua and Terra have exceeded their design lifespans and successor missions like NASA's VIIRS (since 2011) aboard the Suomi NPP satellite or the SLSTR and OLCI on ESA's Sentinel-3A (since 2016) and Sentinel-3B (since 2018) satellites are already operational. Visible and thermal infrared data from these satellites can assure continuity of our merged dataset once MODIS ceases operation. A possible follow-up for the AMSR2 passive microwave data is the Copernicus Imaging Microwave Radiometer (CIMR) whose launch is scheduled for 2028. Conceptualization, V.L., G.S. and L.T.P. ; Funding acquisition, G.S. ; Investigation, V.L. ; Methodology, V.L. ; Resources, G.S. ; Supervision, G.S. and L.T.P. ; Validation, V.L. ; Visualization, V.L. ; Writing--original draft, V.L. ; Writing--review & editing, G.S. and L.T.P. All authors have read and agreed to the published version of the manuscript. This research was funded by the Institutional Strategy of the University of Bremen, funded by the German Excellence Initiative, and by the Deutsche Forschungsgemeinschaft (DFG) through the International Research Training Group IRTG 1904 ArcTrain and the Transregional Collaborative Research Center--TRR 172 'Arctic Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms', (AC)3 (project no. 268020496). The APC was funded by the University of Bremen. **Acknowledgments:** We thank the editors and three anonymous reviewers for their constructive comments which greatly improved our manuscript. This research was funded by the Institutional Strategy of the University of Bremen, funded by the German Excellence Initiative, and by the Deutsche Forschungsgemeinschaft (DFG) through the International Research Training Group IRTG 1904 ArcTrain and the Transregional Collaborative Research Center--TRR 172 'Arctic Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms', (AC)3 (project no. 268020496). MODIS Ice Surface Temperature data were provided by the National Snow and Ice Data Center (NISDC) at [[https://nsicdc.org/data/MYD29/versions/6](https://nsicdc.org/data/MYD29/versions/6)]([https://nsicdc.org/data/MYD29/versions/6](https://nsicdc.org/data/MYD29/versions/6)) (last access 12 September 2020). MODIS geolocation and cloud mask data were provided by the Level-1 and Atmosphere Archive & Distribution System (LAADS) Distributed Active Archive Center (DAAC) at [[https://ladsweb.modaps.eosdis.nasa.gov/archive/allData/61/MYD03/](https://ladsweb.modaps.eosdis.nasa.gov/archive/allData/61/MYD03/)]([https://ladsweb.modaps.eosdis.nasa.gov/archive/allData/61/MYD03/](https://ladsweb.modaps.eosdis.nasa.gov/archive/allData/61/MYD03/)) (last access 12 September 2020). We thank JAXA ([[http://www.jaxa.jp/index_e.html](http://www.jaxa.jp/index_e.html)]([http://www.jaxa.jp/index_e.html](http://www.jaxa.jp/index_e.html))) for the provision of AMSR2 data. We gratefully acknowledge the provision of Copernicus Sentinel data provided by the European Union via the Copernicus Open Access Hub (sciubub.copernicus.eu).