Near-real-time images are derived from gridded brightness temperatures (TBs) from the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager/Sounder (SSMIS) passive microwave radiometer. The TBs are calculated for each 25 kilometer grid cell. An algorithm is applied to produce an estimate of melt or no melt present for each grid cell. The data, images, and graphs are produced daily.
The colored areas on the daily image map records those grid cells that indicate surface melt from the algorithm, as a binary determination (melt / no melt). The melt extent graph indicates what percent of the ice sheet area is mapped as having surface melt, again from the binary determination per grid cell, using the summed area of the melt grid cells divided by the total ice sheet area.
Isolated areas of missing data occasionally occur in near-real-time data. The daily melt map shows any areas of missing data as dark gray regions, speckles, or spider web patterns. However, in the time series chart we account for the missing data by averaging the extent for that region from the day before and the day after the gap, a mathematical technique called interpolation.
Daily melt data are provided by Thomas Mote at University of Georgia. These data are based on the NASA NSIDC DAAC data set Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures.