AMSR-E (Advanced Microwave Scanning Radiometer for EOS) on the NASA satellite Aqua was operational from 2002 to 2011.

The satellite "Shizuku" (GCOM-W1) that carries AMSR2 (the successor of AMSR-E) has been launched successfully on May 18, 2012. It has been delivering data since August 2012. On Januray 25, 2013, the calibrated brightness temperature data have been released to the public. Since 26 January 2013, we  have been producing daily sea ice concentration maps from these data.

Note that thorough calibration of the AMSR2/ARTIST Sea Ice (ASI) data has not been finished yet.

As the same frequency (89 GHz) is used as on the AMSR-E instrument and the resolution of AMSR2 is similar, the same ARTIST Sea Ice (ASI) algorithm is applied using the same tie points (calibration constants). The data should be used carefully until full calibration of the AMSR2 / ASI sea ice concentrations has been accomplished

The announced switch to ASI version 5.4 for the daily sea ice concentration datal has taken  place on Nov 23, 2018. The only effect is a slight change in file names, as explained here ('v5.4' instead of 'v5').

For backwards compatibility, symbolic links of the HDF and TIFF files are being created which still have the old file name. This will only be done temporarily.

We have just completed reprocessing all ASI ice concentration data based on AMSR-E or AMSR2 data for the  complete period, i.e.,

• 1 June, 2002 to 4 Oct, 2011 (AMSR-E)
•  July, 2012 to 17 Nov, 2018 (AMSR2).

The reprocessing has been done for the hemispheric maps only. i.e., Arctic/Antarctic (6.25 km grid spacing) and Arctic3125/Antarctic3125 (3.125 km grid spacing).

The tie points of the ASI algorithm were the same (version 5). However, some other details as the version of GMT (generic mapping tools) used for gridding the data and defining land masks and coast lines have changed over the years. The reprocessed data are therefore consistent with respect to  all this, and have the version number 5.4. The full version number is also part of all file names ('v5.4'); the new files are stored alongside the files of previous versions  5.2 and 5.3 which just have 'v5' in their file names.

The new data being processed every day have been switched to version 5.4 on Nov. 23, 2018 which implies the mentioned change in the file names ('v5.4' instead of just 'v5')

All details about the ASI ice concentration data can be found in the the new ASI user guide

Occasionally, there are gaps in the stream of AMSR2 data because of planned satellite maneuvres or unexpected incidents. The largest gap comprises 4 days in May 2013. Gaps of a few hours usually go unnoticed as there is some overlap in of all overpasses of one day. See here for the full list of missing AMSR2 data