Sea ice concentration observed by different remote sensing methods

In February, the sea ice north of Greenland is normally densely packed. In 2018, however, there was a large area of open water persisting over 3 weeks. It started to open on February 14th and lasted until March 7th. High-frequency passive microwave sea ice concentration (SIC) data offer a high enough resolution (5 km, Spreen et al., 2008) to monitor the overall extent of such a large opening (upper right panel). The most common SIC algorithms at 12 km (e.g. Comiso, 1995) fail to display the opening (lower left panel). However, there is still room for improvement of the 5 km product: By merging thermal infrared observations with 1 km resolutions with the 5 km product, we can resolve a lot of features which are otherwise smeared out (upper left panel). The lower right panel shows a SAR image for reference, the outlines of which are marked in the other panels.

The merged product uses ASI-AMSR2 SIC (Spreen et al., 2008, Kaleschke et al., 2001) and SIC derived from MODIS thermal infrared observations based on an improved version of Drüe et al, 2003. The merging procedure works as follows: We assume that the ASI-AMSR2 SIC are correct within their 5-by-5 km box. Further, we assume that the MODIS SIC show the relative differences within this box correctly. Thus, we modify the MODIS SIC such that their mean within the 5-by-5 km box corresponds to the ASI-AMSR2 SIC. The distribution of the MODIS SIC is preserved.

The 5 km product is the ASI-AMSR2 SIC mentioned above. The 12 km product uses the Bootstrap algorithm (Comiso, 1995). The MODIS data were downloaded from nsidc.org, the ASI-AMSR2 and Bootstrap-AMSR2 SIC were calculated internally at the University of Bremen. The SAR-Sentinel 1B image was downloaded from https://scihub.copernicus.eu.

Further information:

http://nsidc.org/arcticseaicenews/2018/05/arctic-winter-warms-up-to-a-low-summer-ice-season/. Accessed 20180518

References:

Copernicus Sentinel data 20180218. Retrieved from Copernicus SciHub, processed by ESA. Accessed 20180427.

Drue, C.; Heinemann, G. High-resolution maps of the sea-ice concentration from MODIS satellite data. Geophys. Res. Lett. 2004, 31, L20403.

Hall, D. K. and G. Riggs. 2015. MODIS/Terra Sea Ice Extent 5-Min L2 Swath 1km, Version 6. 20180218. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/MODIS/MOD29.006. Accessed 20180327.