National Geographic : 1969 Jan
Remote Sensing: New Eyes to See the World have given us revealing new views of our abode and stirred the imagination of scien tists and laymen (pages 54-5, 59, and 65).* As I have traveled about the country, I have found university laboratories, aerospace corporations, and Government agencies deep ly involved in finding ways to study our en vironment from space. The Geological Sur vey, Department of Agriculture, Naval Ocean ographic Office, Environmental Science Serv ices Administration, and Bureau of Commer cial Fisheries-all these pursue the subject for their special interests. So, too, does the National Aeronautics and Space Administration. From the Manned Spacecraft Center in Houston, Texas, NASA planes regularly fly sensing instruments in experiments that may lead within a few years to an "earth resources satellite." Radar Gets Down to Bedrock Perhaps even more significant a spur to this growing technology is the extraordinary devel opment of hot- and cold-war reconnaissance. Secrecy, of course, shrouds the most advanced techniques for ferreting out hidden knowl edge, yet the veil is being gradually lifted. One of the most valuable military instru ments to become available in this way to civilian scientists is side-looking radar. Orig inally developed to look sideways from a reconnaissance plane as it flies behind battle lines, it produces remarkably clear images even through clouds or darkness, when pho tography is impossible. Its antenna, in the side of the plane, is larger and its electronic techniques far more sophisticated than those of ordinary navigation radar. The images reveal details not evident in photographs and have all sorts of uses for map makers, geologists, oceanographers, farmers, and hydrologists (pages 70-71). Side-looking radar of long wavelength can penetrate to bedrock through dense vegetation or as much as three feet of dry soil. Other highlights in the current art of sur veillance give an idea of some of the eventual possibilities of remote sensing. No secrets are revealed here; these facts are all now public. * Aerial cameras today achieve focal lengths (distance from lens to film) of 20 to 60 feet by means of folded optics-that is, by bouncing the light between mirrors inside the camera before it reaches the film. Since a longer focal length increases scale and thus magnifies de tail, such cameras, with improved films, can pinpoint objects smaller than a Volkswagen from altitudes of 100 to 300 miles. * Today's highly sophisticated surveillance satellites fly at these 100- to 300-mile alti tudes. The U. S. versions are launched into orbits roughly from Pole to Pole, so that they survey every square mile of land and sea as the earth turns majestically beneath them. They watch for the telltale heat trails of rock et launchings and nuclear submarine wakes; photograph suspicious areas such as missile sites, using radiations from different parts of the electromagnetic spectrum. They can send their pictures and information back by radio, or actually return the film to earth in para chuted capsules that are snagged from mid air over the Pacific.t * At Cloudcroft, New Mexico, an Air Force electro-optical device known as AN/FSR-2 could spot an orbiting basketball 20,000 miles up. It is but one of a variety of powerful space surveillance sensors. * In war the enemy may be detected by elec tronic devices that sniff his body odor, sense the vibration of his passing on a trail, pick up the heat radiation from his body even in dense jungle (pages 72-3), or turn radar echoes from moving troops into clearly identifiable whooshing sounds. * Starlight scopes in Viet Nam have denied the night to the Communists. These light intensifiers magnify starlight 45,000 times, producing images as bright as day and letting GI's see the enemy without being seen. Everything Emits Infrared When Gaspard Felix Tournachon, who called himself Nadar, snapped the world's first aerial photograph while ballooning over Paris in the late 1850's, he could hardly have imagined such refinements as these. Nor could he have foreseen the widespread use of sens ing that does not depend on visible light. I think he would have been particularly in trigued by infrared radiation, which most of us think of as heat. What makes infrared so useful is the fact that every physical object on earth-your body, a rock, a tree, a piece of iron-contin uously gives off electromagnetic radiation in proportion to its temperature, because of oscillations of its atoms and molecules. If the *See "The Earth From Orbit," by Paul D. Lowman, Jr., NATIONAL GEOGRAPHIC, November 1966. tSee "Countdown for Space," by Kenneth F. Weaver, GEOGRAPHIC, May 1961.