Radar In Peacetime
After the war, radar research moved easily into nonmilitary pursuits. In 1946 a variation of the Army’s old SCR-271 set bounced pulses off the Moon, opening an extremely productive era of radar astronomy. Radar made it possible for the first time to scrutinize the terrain of cloud-covered Venus, and it was radar mapping that told flight planners where they could safely land spacecraft on the Moon and Mars. Of late, radar astronomy has merged with laser ranging for even greater precision.
Radar has also mapped our own planet. An invention called synthetic aperture radar puts a side-looking radar in an airplane and, using computers, takes advantage of the plane’s steady movement to imitate an antenna many miles long. The result is a radar map of such fine detail that it looks almost like a photograph.
Standard microwave radars have proved expert weather trackers, picking up hail, raindrops, and even the tiny droplets that make up clouds. And Doppler radar is now available to see into a storm and plot wind speeds. One current subject of intense Doppler study is the downward-plunging column of air responsible for wind shear at airports. Doppler radar is also the type used in automobile speed traps.
Doppler principles are also crucial to military “over-the-horizon” radars that can, by bouncing signals off the ionosphere, reach out thousands of miles to pick up targets. The multitude of signals received requires computer processing of the echoes to separate out the useful information. Because the background is stationary, Doppler analysis can help filter it.
Computers are equally inseparable from the “phased-array” defense radars on our seacoasts. These are huge buildings with sloping walls. On each sea-facing wall are thousands of small antennas; the wave timing and signal strength of every antenna is controlled and instantaneously adjusted by computer so that a phased-array can point itself across a broad arc of sky without actually revolving. It’s capable of simultaneously tracking hundreds of ballistic missiles, airplanes, and satellites, and one phased-array radar station in the Aleutians reportedly can find a basketball at more than three thousand miles.
