Research

Evaluation of the ESA Sea Ice CCI (SICCI) project sea ice concentration data set

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Abstract

During phase 1 of the European Space Agency’s (ESA) climate change initiative (CCI) sea ice project (SICCI project) a sea ice concentration (SIC) data product was produced by employing a hybrid SIC retrieval algorithm comprising the Bristol and the Comiso-Bootstrap algorithm in frequency mode. SIC was computed from brightness temperatures (TB) measured at 19.4 GHz [18.7 GHz] and 37.0 GHz [36.5 GHz] by the space-borne microwave radiometer Special Sensor Microwave / Imager (SSM/I) [Advanced Microwave Scanning Radiometer aboard EOS (AMSR-E)] in both polar hemispheres. The product has daily temporal and 25 km x 25 km grid resolution and is available for the period 1992-2008 (SSM/I) and 2002-2011 (AMSR-E) from, e.g., http://icdc.zmaw.de. Each data file contains a limited (to the range 0% … 100%) and an unlimited (see below) SIC, SIC retrieval uncertainty, SIC smearing uncertainty from the gridding process, and SIC total uncertainty. A flag layer allows to identify where SIC may be less reliable. The unlimited SIC contains the full range of SIC values retrieved. The natural variability of the measured TBs around the typical TBs at 0% and 100% SIC (the so-called tie points) causes SIC to spread around these two SIC values; consequently SIC can be negative or above 100%. In order to fully evaluate SICCI SIC this natural variability needs to be taken into account. In contrast to most other SIC retrieval algorithms the SICCI algorithm does not filter spurious sea ice over open water with a weather filter because by doing so often substantial portions of the sea ice cover along the ice edge are discarded.