Mapping the Air by Sound

At Queen Victoria's funeral in 1901, cannons in London boomed a ceremonial farewell--and villagers 90 miles away were startled by the rumbling volley. Yet not a shot was heard in towns halfway between. What caused the funereal boom to leapfrog?

Turn-of-the-century scientists theorized that the cannons' ascending roar had been bent by a freak atmospheric condition that sent it tumbling back to earth. But not until men began probing the upper atmosphere with instrumented rockets could the conditions that caused this sound bounce be fully understood. Early this month, scientists at the White Sands Missile Range used a phenomenon like that at Victoria's funeral to help them chart a region of the upper atmosphere.

Since 1958, Army Meteorologist Marvin Diamond had fired more than 1,000 rockets deep into the atmosphere above White Sands. Probing high above the maximum altitude of sounding balloons, his investigative missiles dropped metalized parachutes carrying temperature-measuring devices and providing tracking radars with easily detectable targets. By charting their drift, Diamond hoped to map the weather through which the U.S. must fire its growing family of space vehicles.

On the way up, Diamond's rockets passed through the 125-knot "jet stream," which boots airliners along from west to east some 35,000 ft. above the earth. Far above that, they found a speedier "upper jet stream," which reversed its direction with the changing seasons. During the fall and winter, it zooms out of the west at some 150 knots. In spring and summer, it slows to 100 knots and drives from east to west.

In either direction, its altitude seems to be about 150,000 ft. Significantly, the upper jet stream is a warm wind, ideal for refracting sound waves.

Diamond knew that the speed of sound is greater in warm air than in cold air. If a sound wave, rising through the sub-zero temperatures below the upper jet stream, suddenly hit a layer nearly as warm as the earth's surface, the top of the wave front, he figured, would accelerate. The whole front would then bend back earthward and rumble down. Diamond figured that he might be able to bounce a boom off the upper stream, predict its course, and record the boom as it came back to earth, thus helping to confirm his rocket data.

Finally he got the weather he was waiting for. The still, windless desert air was shattered by the roar of a 5,000-lb.

explosive charge. Ten miles away, in his White Sands headquarters, Diamond saw only the flash. The sound waves traveling along the surface had been muffled by the dense lower air. Yet 200 miles to the north, four microphones caught the roar of the explosion after it caromed back to earth--in much the same way that the cannons' roar was bent at Victoria's funeral.

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