National Geographic : 1969 Jan
Seeing with sound Sonar echoes from a target reveal distance and bearing, but not the object's features-a short coming that may be solved by experiments at Douglas Advanced Research Laboratories in Huntington Beach, California. Using a six-foot submarine model as their target (top), scientists bombard it with sound waves. As the waves break around the sub, a scanning microphone sends the sound pattern to an oscilloscope to be recorded on Polaroid film (center). A laser's intense light, projected through the film nega tive called a sonoptogram, yields a remarkable three-dimensional view (bottom). Side-looking radar Veiled by clouds, southeastern Panama and north western Colombia defied aerial map makers for 20 years. Then U. S. Army Engineers and Westing house tried radar mapping by plane. In eight ocean-to-ocean passes at 20,000 feet, the side-look ing radar created a mosaic (above) that changed earlier ground surveys. It revealed that the broad Rio Tuira, upper center, meanders in unsuspected turns, and that Isla Mangle, near its fork, lies farther upriver than formerly charted. Unmapped mountains rise northeast of the Tuira-vital data for future extension of the Pan American Highway. To depict landscape in such detail, side-looking radar scans in overlapping strips (right). A con verter changes returning echoes into electron beams, which flash a line at a time across a cath ode-ray tube. A camera records each line on mov ing film to build up the final image. With its capacity for all-weather mapping, side looking radar looms as a likely technique for charting the seven million square miles of earth normally hidden under dense cloud cover.