Satellite Mapping of Terra Incognita Provides Welcome Relief

The topography of the Earth is less well known than that of Mars or Venus, largely because about three‐fourths of it is hidden beneath the oceans, out of reach of direct observation by satellites. Now, however, the ocean‐floor topography of much of Earth’s Southern Hemisphere has been revealed in an innovative map (see the figure on page 22), created by Walter Smith of the National Oceanographic and Atmospheric Administration and David Sandwell of Scripps Institution of Oceanography. Using the abundant gravimetric data collected by the ERS‐1 and GEOSAT satellites in combination with the few available ships’ depth soundings, they have mapped the region between latitudes 30° S and 70° S with a finer resolution (better than 10 kilometers) than previously available. On the map, variations in hue represent altitude variations, or depth below sea level, as identified in the map scale, while changes in color saturation highlight the topography in light and shadow as it would appear when illuminated from longitude 0°.