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  3. Please Fasten Your Seatbelts Severe turbulence(湍流)can kill aircraft passengers. Now, in test flights over the Rocky Mountain

Please Fasten Your Seatbelts Severe turbulence(湍流)can kill aircraft passengers. Now, in test flights over the Rocky Mountain

admin2014-09-13  88
问题                      Please Fasten Your Seatbelts
    Severe turbulence(湍流)can kill aircraft passengers. Now, in test flights over the Rocky Mountains, NASA(美国航空航天局)engineers have successfully detected clear-air turbulence up to 10 seconds before an aircraft hits it.
    Clear-air turbulence often catches pilots by surprise. Invisible to radar, it is difficult to forecast and can hurl(用力抛出去)passengers about the cabin. In December 1997, one passenger died and a hundred others were injured when unexpected rough air caused a United Airlines flight over the Pacific to drop 300 meters in a few seconds.
    However, passengers can avoid serious injury by fastening their seatbelts. "It is the only antidote(对策)for this sort of thing, " says Rod Bogue, project manager at NASA’ s Dryden Flight Research Center in Edwards, California.
    The Center’ s new turbulence detector is based on lidar, or laser-radar. Laser pulses are sent ahead of the plane and these are then reflected back by particles in the air. The technique depends on the Doppler Effect(多普勒效应). The wavelength of the light shifts according to the speed at which the particles are approaching. In calm air, the speed equals the plane’ s airspeed. But as the particles swirl(打漩)in rough air, their speed of approach increases or decreases rapidly. The rate of change in speed corresponds to the severity(激烈程度)of the turbulence.
    In a series of tests that began last month, a research jet flew repeatedly into disturbed air over the mountain ridges(山脉)near Pueblo, Colorado. The lidar detector spotted turbulence between 3 and 8 kilometers ahead, and its forecasts of strength and duration corresponded closely with the turbulence that the plane encountered.
    Bogue says that he had "a comfortable amount of time" to fasten his seatbelt. The researchers are planning to improve the lidar’ s range with a more powerful beam. The system could be installed on commercial aircraft in the next few years.
The turbulence detector can tell the severity of the turbulence by measuring
选项 A、the speed of the plane
B、the speed of the light
C、the number of particles in the air
D、the changes of the particles’ speed
答案D
解析 根据第四段最后一句可知，晴空湍流的强度与微粒速度的变化有关。
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