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| 一切与雷达有关的故事 |
| http://english.enwell.net 2007-12-20 来源:新浪教育 |
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Radar is a new development in radio science.It plays an increasingly important part in meteorology for cloud，precipitation，hail and thunderstorm detection as well as the navigation of aircraft and ships.
雷达是无线电科学的一项新发展。它在对云层、降水、冰雹和雷暴的气象探测以及在船舰和飞机的导航中，起着日益重要的作用。
Let'sbegin with the reflection of sound waves and light waves as well as their uses in finding objects.
我们先从声波、光波的反射及其在探测目标方面的应用谈起。
Suppose that you are standing on a flat piece of open land，on which there is a house some distance away.You face it shout aloud “Hello”and a little later an answering “Hello”is heard.It is an echo and the house act the relector of the sound.This phenomenon offers a way to measuring the distance and range of a target which plays its part here as a reflector.Nevertheless the speed at which sound travels is too slow for such a purpose.Thus this soundwave echo method has its limitation in practical use.
假设你站在一块开阔的平地上，不远处有一幢房屋。你对着它高喊“喂”，一会儿就可以听见另一声“喂”。这就是回音。这幢房屋就起着声波反射体的作用。这种现象提供了一种测定反射体距离和范围的方法。不过，对测定目标物距离来说，声波运行的速度太慢，因此，声波回声测距法在实用中有其局限性。
Now，turn our attention to the reflection oflight waves.When you switch your flashlamp，the light waves sent out by the flashlamp return from the object on which the light falls and reach your eyes.Since the speed of light is about a million times as great as that of sound waves，the reflection of light waves may very well be applied in detecting a target and its distance.However，we must not forget that this very method is affected to a great extent by weather conditions such as fog，cloud，rain，snowand the like.
现在我们再来看一看光波的反射现象。当你打亮闪光灯时，它射出的光波，就从照射到的物体上反射到你的眼睛。光速大约为声速的100万倍，因此光波的反射现象可以有效地用来探测目标物及其距离。但是，不要忘记，这种方法在很大程度上要受到诸如雾、云层、雨、雪等天气条件的影响。
Astothe wireless waves with travelling speed as great as that of light waves，for all practical purposes，not only be reflected but also completely unaffected by temperature，barometric pressure，darkness，daylight or other weather conditions.So wireless waves are just the most suitable to be used in detecting a distant target and measuring its distance.And this is exactly what a radar set，the equipment that sends out wireless signals and receives their echoes，bases on.
至于无线电波，它的传播速度和光速一样快。在实际应用中，它不但能反射，而且完全不受温度、气压、黑暗、日光或其他天气条件的影响。因此，无线电波是最宜于用以探测远距离目标并测定其距离的波，而这正是雷达装置——发射无线电信号和接收其回波的设备的基础原理。
Tofind a target and determine its position，any radar station has to basically consist of a transmitter，a receiver，an antenna，an antenna duplexer，a display and a timer.
为了要发现目标和确定其位置，任何雷达站基本上都必须包括发射机、接收机、天线、天线转换开关、显示器和定时装置。
Theradar signal，usually in the form of a repetitive train of short pulses，is generated by a transmitter and radiated into space by an antenna.Reflecting objects or targets intercept and reradiate a portion of the radar signal；asmall amount returns in the direction of the radar and is collected by the antenna.Detection of echo energy could reveal the presence of a target and its location，size，shape，density and intensity.
雷达信号(其形式通常为重复的短脉冲序列)由发射机产生，通过天线发射，反射物(目标)拦截并反射部分雷达信号，其中一小部分向雷达方向反射回来，被天线接收。检测回波能量就可获知目标物的存在、位置、大小、形状、浓度及强度
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| 更多关于“雷达”的新闻 |
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世界上的一队小小的漂泊者呀，请留下你们的足印在我的文字里。
A troupe of little vagrants of the world, leave your footprints in my words.
世界对着它的爱人，把它浩翰的面具揭下了。它变小了，小如一首歌，小如一回永恒的接吻。
The world puts off its mask of vastness to its lover. It
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