Advanced Microwave Scanning Radiometer aboard EOS (AMSR-E) data are used to produce a data set of the lead area fraction for Arctic sea ice for the freezing season (November - April) on the NSIDC polar-stereographic grid with 6.25 km grid resolution.
For this purpose AMSR-E brightness temperatures observed at 19 GHz and 89 GHz (TB19 and TB89) are interpolated onto the 6.25 km NSIDC polar-stereographic grid. From these the ratio r = TB89/TB19 is computed. This ratio takes considerably larger values over leads and thin ice than over the adjacent thicker sea ice. By moving a 7x7 grid cell search window over maps of r, grid cells are identified which exhibit a substantially larger r than the background value; the latter is computed as Median(r) and subsequently the difference between actual (the center grid cell of the 7x7 window) and the background is computed: r' = r - Median(r). By using coincident MODIS visible imagery tie points are selected which permit to translate r' into the lead ice concentration or lead area fraction which is computed for every grid cell. More details about the approach can be found in Roehrs and Kaleschke (2012) and Roehrs et al. (2012) (see References).
This data set has been put into our data base on Dec. 19, 2013.