2. 外语
  3. Before 1965 many scientists pictured the circulation of the ocean’s water mass as consisting of large, slow-moving currents, suc

Before 1965 many scientists pictured the circulation of the ocean’s water mass as consisting of large, slow-moving currents, suc

admin2014-12-26  43
问题     Before 1965 many scientists pictured the circulation of the ocean’s water mass as consisting of large, slow-moving currents, such as the Gulf Stream. That view, based on 100 years of observations made around the globe, produced only a rough approximation of the true circulation. But in the 1950’s and the 1960’s, researchers began to employ newly developed techniques and equipment, including subsurface floats that move with ocean currents and emit identification signals, and ocean current meters that record data for months at fixed locations in the ocean. These instruments disclosed an unexpected level of variability in the deep ocean. Rather than being characterized by smooth, large-scale currents that change seasonally(if at all), the seas are dominated by what oceanographers call mesoscale fields: fluctuating, energetic flows whose velocity can reach ten times the mean velocity of the major currents.
    Mesoscale phenomena—the oceanic analogue of weather systems—often extend to distances of 100 kilometers and persist for 100 days(weather systems generally extend about 1,000 kilometers and last 3 to 5 days in any given area). More than 90 percent of the kinetic energy of the entire ocean may be accounted for by mesoscale variability rather than by large scale currents. Mesoscale phenomena may, in fact, play a significant role in oceanic mixing, air-sea interactions, and occasional—but far-reaching—climatic events such as El Nino, the atmospheric-oceanic disturbance in the equatorial Pacific that affects global weather patterns.
    Unfortunately, it is not feasible to use conventional techniques to measure mesoscale fields. To measure them properly, monitoring equipment would have to be laid out on a grid at intervals of at most 50 kilometers, with sensors at each grid point lowered deep in the ocean and kept there for many months. Because using these techniques would be prohibitively expensive and time consuming, it was proposed in 1979 that tomography be adapted to measuring the physical properties of the ocean. In medical tomography X-rays map the human body’s density variations(and hence internal organs); the information from the X-rays, transmitted through the body along many different paths, is recombined to form three-dimensional images of the body’ s interior. It is primarily that this multiplicative increase in data obtained from the multipath transmission of signals that accounts for oceanographers’ attraction to tomography: it allows the measurement of vast areas with relatively few instruments. Researchers reasoned that low-frequency sound waves, because they are so well described mathematically and because even small perturbations in emitted sound waves can be detected, could be transmitted through the ocean over many different paths and that the properties of the ocean’s interior—its temperature, salinity, density, and speed of currents—could be deduced on the basis of how the ocean altered the signals. Their initial trials were highly successful, and ocean acoustic tomography was born.
Which of the following, if presented as the first sentence of a succeeding paragraph, would most logically continue the discussion presented in the passage?
选项 A、Ships are another possibility, but they would need to stop every 50 kilometers to lower measuring instruments.
B、To understand how ocean acoustic tomography works, it is necessary to know how sound travels in the ocean.
C、Timekeeping in medical tomography must be precise because the changes in travel time caused by density fluctuations are slight.
D、These variations amount to only about 2 to 3 percent of the average speed of sound in water, which is about 1500 meters per second.
答案B
解析 推断题。根据文章最后一段的最后一句“他们的首次试验非常成功．海洋声学X线断层射影技术就这样诞生了。”可知若有后文，应该承接海洋声学X线断层射影技术这个话题，进行深入的解释说明．选项B“为了理解海洋声学X线断层摄影术是如何工作的，有必要了解声音在海洋中是如何传播的”符合逻辑。所以答案选B。
转载请注明原文地址:https://kaotiyun.com/show/nbh7777K
0

大学英语六级

相关试题推荐
随机试题
最新回复(0)