Altimetric data are particularly useful for observing oceanographic phenomena in the tropical oceans where the zonal scales are large and the meridional scales are relatively small, making the orbit errors less important because their effects are primarily on large meridional scales. However, careful treatment of the orbit errors still makes a difference when the errors are as large as in the early versions of the Geosat data [ Cheney and Miller, 1990]. There has been significant progress in all three tropical oceans.