Data depicts monthly averages of sea-ice concentration in modern polar oceans. Averages were derived from the Scanning Multichannel Microwave Radiometer and Special Sensor Microwave/Imager instruments aboard satellites of U.S. Air Force Defense Meteorological Satellite Program from 1978 through 1992. Data are provided as 8-bit images using the Hierarchical Data Format developed by the National Center for Supercomputing Applications.