英文演讲-报告-活动-对话稿件(关于雷达科技)

1W:Well,today we have Professor chen and professor wei in our studio to talk about the Radar technical,good afternoon ,professors.2IntroductionRadar is a variant of radio technology and has been widely utilized in various areas.we will helps you have a rough idea of what the radar technology is,how it came into being and where it has been applied. We mainly talk about the radar technical overvie:its general principles and the Cavity Magnetron,one of its critical devices,which can create high power high frequency electromagnetic pulses. 3W1: Can you tell us the Radar technicals devolop? In 1888 Heinrich Hertz showed that the invisible electromagnetic waves radiated by suitable electrical circuits travel with the speed of light, and that they are reflected in a similar way. From time to time in the succeeding decades it was suggested that these properties might be used to detect obstacles to navigation, but the first successful experiments that made use of them were in an entirely different context, namely, to determine the height of the reflecting layers in the upper atmosphere. One of these experiments, that of Tuve and Breit, made use of short repeated pulses of radiation, and this technique was employed in most of the developments of radar.4-(5)-62: How can we know about the target than its distance use the Radar technical? Electromagnetic radiation travels in empty space at a speed of 2.998 x 108 metres per second, and in air only slightly less rapidly; we can think of its speed as very nearly 300,000 kilometers per second. This speed is denoted by the letter c. Let us suppose that a very short pulse of radiation is directed towards an object at a distance r, and that a small fraction of this is reflected back to the starting point, so that it has traversed the distance 2r. For useful terrestrial distances t is very small; an object 15 km away, for example, will return a signal in one ten-thousandth of a second.7W3: How can we get more target ? This is done by arranging an antenna system to project a suitable radiation pattern that can be rotated in azimuth or elevation. As may be deduced from what follows, a very great deal of ingenuity and engineering skill has been devoted to the design of radar antennas. This is the place to mention a fundamental fact, namely, that the size of antenna needed to produce a beam of radiation of a given angular width is directly proportional to the wavelength of the radiation, or inversely proportional to its frequency. The first successful radar installations in Great Britain in the years 1935 to 1939 used wavelengths in the 6 to 15 m band, and required very large antennas.5: whats the PPI in a radar apparatus?The radar illustrated in this diagram would display the range and direction on a plan position indicator or PPI, in which the cathode-ray tube displays a circular section of a map with the radar station at the centre. From this centre an outward range sweep is rotated in synchronism with the rotation of the antenna. A target will be shown as a bright spot as the sweep passes it. If the cathode ray tube is provided with a phosphor that continues to emit light for more than the period of rotation of the sweep, a more or less continuous display will result, so that all targets within range will appear as on a map (Figure 1).W6:The apparatus has been developed?Perhaps the most significant British contribution to radar was the development of the cavity magnetron. This device, pictured (Figure 2), created high power (10 to 50 kW peak power) high frequency electromagnetic pulses that facilitated the production of more accurate and compact radar designs. Systems capable of being mounted in aircraft became possible. The higher frequencies, and so shorter wavelengths, enabled smaller antenna beamwidths. This increased detection accuracy.The device was developed by J.T. Randall and H.A.H. Boot working at the University of Birmingham under Professor Mark Oliphant. It was one of the pieces of secret technology brought to Canada as part of the Tizard mission. Lets have a rest and watch a short movie about radar.8-9101.Beside above,what can Radar do in our daily life ?One of the first things many of us do before leaving the house each morning is check the weather forecast.Many people maybe dont know weather forecasts is due, in large part, to the use of weather radar.W2.Unbelivable, how did they find that radar could be used to detect precipitation?It was first suggested in 1941. A year later, testing of early radar systems showed that rain did show up on radar screens. In fact, when the weather showed up on these early radar screens it created big problems. Engineers found that storms appeared as large areas of moving “clutter” on their screens and obscured the targets (such as ships or airplanes) that they were seeking. The military were quick to exploit the discovery that radar could be used to detect weather.W3. Weather radar research is actively supported Following World War II, isnt it?Yes, Radar probing of the interior of storms provided an invaluable tool for cloud physicists, meteorologists and hydrologists. Initially, the weather service in the United States, then called the Weather Bureau, used military surplus radars left over from World War II. In 1960, research on the application of Doppler radar for probing the atmosphere began to have meteorological applications.4.What is Doppler ,and how is it used?The Doppler effect is a frequency shift caused by radar waves bouncing off a moving object. In radar, this change of “pitch” in the reflected radar signals can be interpreted by circuits in the radar receiver and used to determine the speed of a storm. The latest Doppler radar sets locate feature of tornadoes that provide meteorologists with the information needed to issue reliable hazard warnings tens of minutes before a tornado even touches the ground.11W6.Is there anything more about Doppler radar?Doppler radar is also used to detect the microburst, a type of wind shear occurring near the ground resulting from the outflow from a thunderstorm. A series of microburst-induced aircraft crashes prompted the United States Federal Aviation Administration to develop a technology called the Terminal Doppler Weather Radar to detect and automatically report timely warning of the airspeed loss associated with low altitude wind shear. The TDWR was the first operational weather radar to provide hazard warnings and wind shift predictions without requiring interpretation by a trained meteorologist. 7.Is the weather radar widely used now in airline safety?Yes, by about 1948, early experiments suggested that airborne weather radar could identify severe storms, thus helping the pilot avoid them. This led to their installation in most aircraft in later years, and by1964 they were mandatory in all passenger aircraft. Airborne weather radar is especially important for aircraft operating over the ocean where there is no other source of hazardous weather information.12Well, thank you for give us a detailed introduction about radar. Is there any questions you want to ask him about radar and its application?.W4: What is the components of a radar apparatus?These comprise a powerful high-frequency oscillator, a modulator to cause it to emit pulses, and a transmitting antenna, as well as a receiving antenna and a sensitive receiver, the output of which is applied to a cathode-ray tube in the manner familiar to those acquainted with television technique.5.What is the weather radar organization ,and how does it operate?In the United States, the federal government operates a network of weather radar stations called NEXRAD, which completely covers the entire country. The data generated by