Sea ice is frozen seawater floating on the surface of the ocean. Some sea ice is semi-permanent, persisting from year to year, and some is seasonal, melting and refreezing from season to season. The sea ice cover reaches its minimum extent at the end of each summer and the remaining ice is called the perennial ice cover.
Duing the summer of 2009, the arctic sea ice reached its minimum extent on September 12th. The 2009 minimum extent was the third lowest extent measured since the beginning of the satellite record in 1979. This animation shows the summer retreat of sea ice over the Arctic from 7/1/2009 through 9/12/2009. The sea ice was defined by a 3-day moving average of the AMSR-E 12.5 km sea ice concentration, showing the region where the sea ice concentration was greater than 15%. The false color of the sea ice was derived from the AMSR-E 6.25 km brightness temperature.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 18.104.22.168.0