National Geographic : 1969 Jan
Bahamas from space With psychedelic splendor, a color-coded photograph highlights depths on the Great Bahama Bank. Tongue of the Ocean, a mile-deep trough at lower left, licks a corrugated lip; red and yellow shallows separate it from Exuma Sound to the northeast. Prototype of a new map-making art, the garish composite grew from a soft-toned Gemini 5 photograph taken from an altitude of 140 miles (above). To enhance readability of Gemini photographs, whose delicate shadings often conceal details, scientists at Philco-Ford in Palo Alto, California, isolated each subtle tone in the Bahamas picture. Projecting 12 tones one at a time, they assigned a color to each, producing 12 separate overlays. At left, red shows depths to six feet and yellow, six to nine, while clouds appear in shades of purple, according to brightness. Great depths in the Tongue and cloud shadows appear white, because no color was given to darkest tones. An 18-diameter enlargement of the lip of the Tongue (below) shows water depths from a few feet in purplish red to more than 30 feet in blue.