The Seasat spacecraft was launched in late June 1978, and during its brief 110-day lifetime, collected 90 days of nearly continuous radar altimeter data between the latitudes of 72 deg South and 72 deg North. The spacecraft maintained its 108 degree inclination, performing in a 17-day repeat groundtrack until September 9 and then a 3-day repeat pattern until it stopped operations on October 10. Although designed only for measurements over water, the Seasat radar altimeter acquired more than 600,000 useful altimeter range measurements over the continental ice sheets of Greenland and Antarctica. Processing of the ice altimetry returns are explained in more detail in Martin et al., 1983. For more information on Seasat go to the Jet Propulsion Laboratory (JPL) web site.