- UID
- 497255
- 在线时间
- 小时
- 注册时间
- 2009-12-19
- 最后登录
- 1970-1-1
- 主题
- 帖子
- 性别
- 保密
|
5、測量誤差
chinese team 重新測量mountain Everest 的高度，因為British 的測量存在一些錯誤，chinese用了一些新的方法來減小誤差 （by小舞鞋lucia）
原文如下：
GWD26-Q32 to 35
In 1975 Chinese survey teams remeasured Mount Everest, the highest of the Himalayan mountains. Like the British in 1852, they used the age-old technique of “carrying in” sea level: surveyors marched inland from the coast for thousands of miles, stopping at increments of as little as a few feet to measure their elevation, and marking each increment with two poles. To measure the difference in elevation between poles, surveyors used an optical level—a telescope on a level base—placed halfway between the poles. They sighted each pole, reading off measurements that were then used to calculate the change in elevation over each increment. In sight of the peaks the used theodolites telescopes for measuring vertical and horizontal angles—to determine the elevation of the summit.
The Chinese, however, made efforts to correct for the errors that had plagued the British. One source of error is refraction, the bending of light beams as they pass through air layers of different temperature and pressure. Because light traveling down from a summit passes through many such layers, a surveyor could sight a mirage rather than the peak itself. To reduce refraction errors, the Chinese team carried in sea level to within five to twelve miles of Everest’s summit, decreasing the amount of air that light passed through on its way to their theodolites. The Chinese also launched weather balloons near their theodolites to measure atmospheric temperature and pressure changes to better estimate refraction errors. Another hurdle is the peak’s shape. When surveyors sight the summit, there is a risk they might not all measure the same point. In 1975 the Chinese installed the first survey beacon on Everest, a red reflector visible through a theodolite for ten miles, as a reference point. One more source of error is the unevenness of sea level. The British assumed that carrying in sea level would extend an imaginary line from the shore along Earth’s curve to a point beneath the Himalaya. In reality, sea level varies according to the irregular interior of the planet. The Chinese used a gravity meter to correct for local deviations in sea level.
----------------------------------------------------------------
Q32:
It can be inferred from the passage that refraction would be most likely to cause errors in measurements of a mountain’s elevation under which of the following conditions?
A. When there are local variations in sea level
B. When light passes through humid air
C. When theodolites are used relatively far from the mountain peak.
D. When weather balloons indicate low air temperature and pressure.
E. When sea level has been carried in to within five to twelve miles of the summit.
------------------------------------------------------------------
Q33: Which of the following best describes the purpose of the sentence in lines 23-25 (“The Chinese…the British”)?
A. Introduce a definition
B. Signal a transition in focus
C. Summarize the preceding paragraph
D. Draw a contrast between two different theories.
E.  resent information that contradicts the preceding paragraph.
-----------------------------------------------------------------
Q34: Which of the following is NOT mentioned as a possible source of error in surveying mountain elevation?
A. Mirages
B. Refraction
C. Inaccurate instruments
D. Variations in sea level
E. Uncertainty about the exact point to be measured
---------------------------------------------------------------
Q35:
The primary purpose of the passage is to
A. provide details about improvements to a process
B. challenge the assumptions underlying a new method
C. criticize the way in which a failed project was carried out
D. call for new methods to solve an existing problem
E. explain the theory behind a new technique
--------------------------------------------------------------- |
|
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2012-7-11 08:53:51
收藏
收藏
楼主
