NOAA@NSIDC is pleased to announce the upcoming release of Sea Ice Index, Version 4, available at the National Snow and Ice Data Center on August 1. This new version transitions from SSMIS to AMSR2 data due to the end of access to SSMIS data. The AMSR2 instrument provides high-quality sea ice concentration data that will ensure the continued reliability of the Sea Ice Index product.
Please note that AMSR2 typically locates the ice edge slightly inboard compared to SSMIS, resulting in somewhat smaller ice extent measurements:
- Northern hemisphere: differences less than about 0.1 million sq km
- Southern hemisphere: differences less than about 0.15 million sq km
These differences will make the calculated trend in ice extent slightly more negative. The input AMSR2 data for the Sea Ice Index has been processed to minimize differences with SSMIS data, though the intercalibration is preliminary with further improvements planned. We will provide documentation illustrating the differences resulting from this transition to AMSR2.
Sea Ice Index, Version 3 will be retired and will no longer be available once Version 4 is released. However, data prior to 1 January 2025 in Version 4 will not be reprocessed, so it will remain identical to Version 3 data. Starting 1 January 2025, all Sea Ice Index images and values will be derived from AMSR2 data.
We are sending this notice in advance to give users time to prepare for this transition. If you have any questions, please contact the User Services Office at nsidc@nsidc.org.