Infra-Red Is Watching

What does a blacked-out city look like to a modern reconnaissance airplane, or to the computing ego of a guided missile boring down from space? Answer: if viewed with up-to-date infra-red equipment, it stands out like a neon sign. Its smokestacks shine like lighthouses; its highways gleam like long bright lines. Nothing can be securely concealed if it is a few degrees warmer or colder than other things around it.

This week Servo Corp. of America, which specializes in infrared, released pictures of the Long Island plant of Republic Aviation Corp. taken with heat waves emitted by its warm surfaces. The roofs of the plant show clearly. So do some of the runways on the flying field near by (see cut). This means that they have been warmed up by the exhausts of jet planes; runways that are not so busy show dimly or not at all. Two highways running past the plant are conspicuous because their pavement has been warmed by the tires and exhausts of heavy Long Island traffic. Warm driveways near the plant tell how Republic's employees get in and out of the parking lot.

Tanks & Girdles. A big, busy factory is an easy subject for infra-red observation. Much subtler tricks are possible, such as tracing narrow roads through heavy forests. Military vehicles are hard to hide: a tank that has turned off a road to take cover under thick foliage sends heat waves that strike through the leaves, telling just where it is. Rivers show clearly : at night their surface water is generally warmer than the leaves of vegetation on their banks. Boats leave conspicuous wakes by mixing warm surface water with colder water from below.

Servo's infra-red engineers are not permitted to tell how their apparatus works. There seem to be several types. The picture of the Republic plant looks as if it were made by some sort of scanning technique. Servo says that its instruments take their pictures on ordinary photographic film, first translating the heat image into a light image. If necessary, the instruments can be made sensitive to very small differences of temperature. An object that is one degree warmer or colder than its environment is detectable under field conditions. In the laboratory much smaller contrasts are sufficient. A woman's legs photograph bright because her stockings are transparent to heat from her skin. Her girdle shows faintly under her skirt because it is in close contact with body heat.

Telltale Warmth. A trained intelligence expert can extract all sorts of information from an infra-red photograph. He can follow traffic along the roads and into underground hiding places. He can tell by the temperature of its winches whether a ship is handling cargo. He can decide at a glance whether an airfield is in use. Infra-red camouflage is theoretically possible, but even if a plant or missile station is put deep underground, it will have trouble dumping its heat in a way that will not show.

Infra-red technique is developing rapidly, and most of the interesting details are still secret. It has been announced that certain air-to-air guided missiles seek their prey by feeling for heat rays and steering toward their source, which may be the exhaust or warm wing edges of a fast airplane. Long-range missiles can probably feel for enemy cities, and reconnaissance missiles may some day return from high-arching flights with heat pictures of an enemy's secret factories and bases. An obvious steering system for antimissile missiles would be a heat-sensitive device to feel for the warm nose of an intercontinental missile while it is still far out in space.

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