Undergraduate roommate, he is quite funny from Northeast China. Recently, he often emphasizes that he is Bingbing's fellow villager. One time I went to Huangshan with a trip. I climbed to the top and looked down at the mountains, and I saw the small mountains. Isn’t it magnificent? However, it is not possible to climb up the highest point of the mountain because there is a weather station here, and only the staff and invited people can enter.
Huangshan Guangmingding Meteorological Station (photo taken by the author in autumn 2018)
There is such a weather station on the top of Huangshan, which is old-fashioned!
, the weather station was found in 1956. It was expanded more than ten years ago and became what it is now
, so big a football player, what a thing?
That's not football, it's radar
. I've seen the radar, it's like a pot, look at the Red Alert:
Select the Soviet camp in the game, build this radar, you will get the small map view in the upper right corner and the reconnaissance aircraft options (from the game " Command and Conquer : Red Alert 2") There are many types of
radars, and the red Alert is the most conventional radar, and a model has been drawn. The radar here is called Doppler radar. It is actually like a pot inside, and the outside is a special shell to protect the antenna. A slightly larger weather station now has this high-tech product
, just like this football? Is it so powerful?
That's it, Doppler radar is powerful...
, then I understand, it should be more like this thing, it's always overbearing!
Weather Controller, the Allied camp's " Super Weapon " in the game can summon " Lightning Storm " to bring a fatal blow to the enemy base (from the game "Command and Conquest: Red Alert 2")
This is the radar used by our civilians for weather forecasting, not a weather controller, and cannot summon lightning...
So what's the use of this "football"?
is of great use, so listen to me slowly telling
radar , and everyone may have heard of it. In the popular science books in primary schools, there will be: humans invented radar by studying the principles of bat hunting.
radar can emit electromagnetic waves or sound waves, and calculate the time difference between the transmitted signal and the reflected signal to estimate the position and size of the object. Radar can be widely used in war, agriculture, meteorology, aerospace, etc., and is a very common equipment.
radar is most well-known for its shape as a big pot, with an antenna in the center, looking upwards at the sky diagonally, while turning, detecting what flying objects are in the air, just like the game depicted.
However, if you add a " Doppler " to the radar, maybe many people have never heard of it. At the same time, people can notice that there is a mysterious spherical or semi-spherical building on many weather stations and tower on the edge of the airport. Looking closely, it looks like a football.
Sichuan Provincial Meteorological Bureau , Shenzhen Meteorological Bureau , Pudong Airport Tower
(pictured from image.baidu.com)
Taishantop Meteorological Station (Photo taken by the author in summer 2019)
So, what is "Doppler radar"?
This involves a physical concept in middle school - Doppler effect .
Doppler effect refers to the phenomenon that when a moving object emits a wave not perpendicular to the direction of movement relative to a reference object, the wavelength of the wave will change accordingly.
The most common Doppler effect in life is the Doppler effect of sound. When a car whizzes past you, the sound it makes will go from high to low, and the pitch of the sound is related to the wavelength of the sound wave. The higher the pitch, the smaller the wavelength, the higher the frequency of the sound wave.
Therefore, for objects with the same direction as the sound wave propagation, the tone will become higher and the wavelength will become shorter; for objects with the opposite direction of the sound wave, the tone will become lower and the wavelength will become longer.
Doppler effect (from Wikipedia)
After understanding the Doppler effect, it is easy to understand the detection principle of Doppler radar.It will continuously emit electromagnetic wave signals or sound wave signals. By detecting the rebounding electromagnetic wave/sonic wave frequency of the object, a frequency difference is obtained, and then the object's motion speed is deduced. According to the results of reflections at different emission frequencies, the direction and distance of the object can be deduced.
The biggest difference between it and ordinary radar is that it needs to be kept on, and then use integrated circuits and computers to distinguish effective information from the frequency differences of waves reflected by objects. Ordinary radar calculates object motion information by calculating the time difference from the transmitted signal to the received reflected signal, and the information obtained is simpler.
radar detection diagram (from Wikipedia)
Doppler radar used in meteorological observation usually emits microwaves (an electromagnetic wave, the wave emitted in the microwave oven belongs to microwaves). Through the Doppler effect, the movement speed of airflows of different heights can be calculated, and the vertical distribution of wind speed, water vapor and other information in nearby areas can be obtained.
For different observation objects, the emission frequency of meteorological Doppler radar will vary because the reflectivity of different objects to electromagnetic waves will change with the frequency.
Generally speaking, the operating frequency range of of a single radar is relatively limited, and the specific operating frequency is only more accurate when detecting particles of a specific size. For example, cloud measurement radar is suitable for detecting cloud particles with smaller particles, which is used to detect clouds in middle and high layers, measure the cloud bottom and cloud top height, etc.; while rain measurement radar has a longer wavelength and a lower frequency, which is suitable for detecting raindrops with larger particles and rain clouds in lower layers, and is suitable for tracking clouds that may produce precipitation, so as to achieve the purpose of real-time observation of weather, so it is also called weather radar .
also has a "Very high frequency/ultra-high frequency radar", which has a short wavelength, which can be used to detect atmospheric turbulence and charged particles in the atmosphere, which is suitable for monitoring lightning and other phenomena.
Weather radar echo map (also nicknamed "Tomato Scrambled Egg Map")
2017 Typhoon "Tian Ge" landed, the heavier the clouds, the redder the color
So why is the radar of the meteorological observatory spherical?
This ball shell is called " Radar Cover ".
In fact, the true core part of Doppler radar is still the shape of a big pot plus an antenna, which is not significantly different from ordinary radars. The reason why a football-like shell is mainly used to protect the internal antenna and extend the service life, because the Doppler radar needs to be turned on all day, so adding a radome is more useful.
radar cover can also play a role in allowing the signal to be evenly distributed. But at the same time, the radar cover will cause signal attenuation and the resolution will become worse, so some radars with higher resolution requirements will not install this cover.
Radar cover from a Japanese base (from Wikipedia)
Doppler radar is currently widely used in meteorological and military aspects, and is an extremely important facility. According to industry statistics, my country currently has 270 new generation weather radars (estimated in 2020, basically Doppler radar), X-band radar (used during emergency support or during major events), wind profile radar (as of 2016, there are 69 units, concentrated in large urban agglomerations) and other networks to form a meteorological observation network covering the whole country.
Reference :
1. Weather radar detection and application (edited by Hu Mingbao, Meteorological Press, 2007.11)
2. Radar Meteorology (Zhang Peichang et al. Edited by Meteorological Press, 2005.1)
3.https://en.wikipedia.org/wiki/Weather_radar
4.https://en.wikipedia.org/wiki/Doppler_effect
5.https://zhidao.baidu.com/question/118723014.html
6. China Net National Conditions Questions and Answers: What is the content of the Special Plan for Meteorological Radar Development (2017-2020)?
7. Some pictures are from Google, Baidu, Wikipedia, Red Alert Game, China Weather Network, etc.
Written by: Zhang Yuheng
Editor: Li Ying
Original title: How can there be a "football" on the top of the meteorological observatory? What a thing?
Source: Stone Popular Science Studio
Editor: Guanshan Buyi
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