144 60 3 324 288 252 216 180 108 Fig. 1-5. Mean sea-surface topography. Contour interval: 2 m. (Courtesy NASA/Goddard Space Flight Center.) 72 298.257 1.8 x lo6 OBSERVATIONS GRID, 2M CONTOUR M. l/f= a,=6378137 (GSFC PGS S4 ORBITS) 36 lo - 72 a