Sea ice concentration and sea ice drift based on satellite data are used to investigate sea ice drift trajectories. First, the sea ice extent is calculated for every week. Only grid cells with at least 15% sea ice concentration contribute to the extent. Each of these grid cells is treated as a Lagrange particle which moves according to the mean weekly sea ice drift (derived from the NSIDC ice drift data set). The position of that cell is tracked for every week and the number of weeks the particle remains inside the area given by the sea ice extent, which is calculated anew for every week, is summed up which gives the age. If the particle is located outside this area after its translation due to the sea ice drift then it is assumed that the sea ice in that grid cell has melted. Every year in September, between week 37 and 38, upon commence of freezing conditions the age of all still existing grid cells is rounded up to the successive full year, e.g. a grid cell of age 45 weeks with > 15% first-year ice (rest is open water) becomes 2nd-year ice (images at top: "1" --> "2") while a grid cell of the age 2 years and 50 weeks i.e. 3rd-year ice of > 15% (rest is open water) becomes 4th-year ice (in images at top: "3" --> "4").
Co-existence of ice of different age in one grid cells results in the survive of the older one in order to take into account that younger and hence thinner sea ice deforms and melts more easily. Also here a threshold value of 15% is used: A grid cell with 15% ice 6 years old and 85% first-year ice is assigned 6-year old ice.
See the references for more details about the method and possible applications.
This is the netCDF version of the NSIDC / CCAR Arctic Sea Ice Age data set version 3 offered here: http://nsidc.org/data/nsidc-0611, downloaded in April 2016 / March 2017.
Last data set update at ICDC: April 5 2017.