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  3. Scientists have begun using satellite-based systems to predict volcanic eruptions. This allows blanket coverage of the entire wo

Scientists have begun using satellite-based systems to predict volcanic eruptions. This allows blanket coverage of the entire wo

admin2022-01-18  53
问题     Scientists have begun using satellite-based systems to predict volcanic eruptions. This allows blanket coverage of the entire world. Envisat is the most advanced craft of this type. It has sensors that, by recognizing the characteristic optical signature of various substances in the atmosphere, can detect the presence of specific gases, such as sulphur dioxide (二氧化硫). These may indicate an imminent (即将来临的) volcanic eruption.
    Mike Abrams, a scientist at America’s space agency, NASA, says that the limiting factor on all such satellites is, surprisingly, not technological, but temporal. The orbits in which they are placed allow them to observe the entire earth, but they cannot pass over a particular spot more frequently than once every 15 days or so. Dr. Abrams argues that more satellites are needed to gather sufficient data on the earth’s volcanoes. Existing satellites, though, do at least serve as an early warning system. If one of them detects something amiss, local volcanologists can then intensify their local monitoring efforts. If necessary, they can even initiate an evacuation.
    In addition, it is important to predict lahars (火山泥流) , flowing mixtures of rock, debris, ash and water, which are often set off when hot lava meets cold snow. Lahars can travel down a mountain as fast as 60 kilometres per hour. In 1985 a lahar set off by the eruption of the Nevada del Ruiz volcano in Colombia killed 25,000 people. With acoustic flow monitors, such as those developed by the USGS in the last five years, such a tragic loss of life might have been averted. The flow monitors are seismometers (地震检波器), which measure vibration, and are sensitive to higher frequencies than those often used to record earthquakes and volcanic activity. This lets them hear lahars from a long way off, creating a valuable extra hour of time that can be used to evacuate. Such systems are now in place all round the world.
    Volcanic eruptions are dangerous not only to people on the ground, but also to those in the air.
    According to the USGS, more than 80 commercial aircraft have run into unexpected volcanic ash in the past 15 years, with the resulting damage costing hundreds of millions of dollars. If the optimists are right, the threat from volcanoes could one day become a known one. There is a problem, though. The work that needs to be done relies on the continual use of satellites and ground monitoring. Volcanologists are now issuing a new warning: it is particularly hard to get funding for this kind of work. This is something that everybody should be bothered about.
How can existing satellites predict volcanic eruptions?
选项 A、They use monitoring systems to detect the presence of specific gases.
B、They use sensors to detect the presence of specific gases.
C、They detect the presence of specific gases by gathering data on the earth’s volcanoes.
D、Their orbits allow them to observe the entire earth and predict volcanic eruptions.
答案B
解析 由题干中的existing satellites predict volcanic eruptions定位至第一段。细节辨认题。定位段指出，恩维萨特的传感器通过识别大气中各种物质的光学识别标记能测出像二氧化硫这类特殊气体的存在，由此可以预测即将到来的火山爆发。故答案为B)“它们利用传感器来测出特殊气体的存在”。
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