Science: Eagle-Eyed Shoran

Army radar men told proudly last week of another of radar’s triumphs. One of its varieties, “shoran,” could measure long distances on the earth’s surface “within a few feet of perfect accuracy.” This meant that the world’s maps could be checked, and unmapped areas mapped, with greatly increased ease.

Shoran, like most radar devices, is simple in principle. A transmitter in a highflying airplane shoots bursts of radio waves at a station on the ground. The station picks up the signals, rebroadcasts them to the plane. An electronic gadget measures in micro-seconds (millionths of a second) the time they take for the round trip. Since radio waves travel with the speed of light, the time interval can be translated promptly into the distance in miles and feet between the plane and the ground station.

In mapping, the plane carries two transmitters and flies between two ground stations, “interrogating” them simultaneously. Their two distances from the plane form the sides of a triangle. The plane’s height above the ground is the triangle’s altitude. From these figures the ground distance between the stations can be computed.

The Gist of It. The ground stations are portable. One of them is set up at a point whose location is known accurately. The other is carried, in ship or truck or airplane, to the spot that is to be definitely located. The shoran-equipped plane makes a cruise between them, and the job is done.

The radio waves which shoran uses at present cannot be received much beyond the horizon. But a mapping airplane flying as high as practicable, some 40,000 feet, can measure the distance between two stations about 500 miles apart. Later, the Army hopes the range will increase materially. So will the accuracy.

Shoran’s first full-dress mapping job: the Rocky Mountain region near Denver. This summer the U.S. Coast and Geodetic Survey will use it along the coast of Maine, and in the Caribbean. U.S. experts suspect that some Caribbean islands are not quite where the maps say they are.