Comparisons between GEOSAT and SEASAT latimeter tracking over non-ocean surfaces are presented. The GEOSAT tracker shows more agility over the rougher surfaces and therefore is able to maintain lock better than SEASAT. For repeat groundtracks over the Greenland ice sheet, GEOSAT provided twice as many usable height measurements as SEASAT. Large off-nadir attitude excursions caused differences in GEOSAT tracking between repeat cycles. The increased GEOSAT pulse width caused an acquisition problem mostly over the quickly-varying land surfaces. The GEOSAT altimeter was sometimes able to track over surface SEASAT could not but at times the acquisition problem was worse. The effect of all the modifications is that the GEOSAT measurements give more detailed along track information of the small-scale topography. Over the ice sheets GEOSAT yields denser coverage, but over land SEASAT measurements give a better overall picture of the general topography. These results suggest that the GEOSAT elevation data set over land can best be used to augment the information obtained from the SEASAT data and is most valuable when investigating topography at scales less than 100 km. ¿ American Geophysical Union 1990