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为什么这个天文台会向卫星发射激光

Why this observatory fires lasers at satellites

If you want to know where you are, you can check on your phone.
如果你想知道你的定位 你可以在手机上查看
It listens for signals from whole constellations of satellites in orbit,
它能接收到来自整个在轨卫星系统的信号
and by triangulating all those signals and using a lot of maths,
通过对这些信号进行三角测量及大量数学运算
it works out where you are and shows you a little dot on a map.
就能获取你的定位 将其显示为地图上的一个小点
But how do the satellites know where they are?
但这些卫星怎么知道自己在哪呢?
There aren’t any landmarks in orbit for them to refer to.
它们的轨道上没有任何可供参考的坐标
If satellites are in a high enough orbit, well away from the atmosphere,
如果卫星所在的轨道足够高 距大气层足够远
then they can predict their position.
它们就能推测自己的位置
They’ll just keep orbiting in about the same path:
它们运行的轨道基本不变:
there’s no atmosphere to slow them down.
没有大气层削减它们的速度
But that’s not precise enough.
但这样得出的结果不够精确
There will be distortions caused by gravity from the sun and moon,
太阳和月球的重力 甚至是地球上的山脉
or even from mountain ranges down on Earth.
都会导致偏差
So maybe they could use the other satellite signals, like GPS.
或许它们也可以利用其他卫星信号 例如GPS
But if they’re all relying on each other, that could steadily drift apart from reality.
但如果卫星全都相互依赖 结果就会慢慢失真
Maybe they could track the stars or the features down on Earth,
或许它们可以追踪恒星或地球上的标志物
but that’s not precise enough either.
但这样结果也不够精准
At some point, something down here on Earth has to look up in the sky
因此 地球需要从特定点将某种东西射向天空
and work out the position precisely.
并计算出卫星的具体位置
And one of those somethings is hidden away in the countryside of southern England.
其中一个设备就藏在英格兰南部的乡村里
It looks like a regular observatory, but it’s not looking at the stars.
它看起来与普通天文台相似 却并不用来观星
– We track manmade satellites in various orbits doing various jobs.
我们追踪处于不同轨道 具有不同功能的人造卫星
They all have to have special reflectors that enables the light to be returned to us.
它们都需要有特制的反光板将光线反射给我们
And so we can measure the time of flight, and from the time of flight, derive the distance.
这样我们就能测量光的飞行时间并用其测算距离
You send out a very short pulse of laser light.
只需发射一束脉冲非常短的激光
You do that a thousand times a second.
并且每秒钟发射一千次
Each of those shots, because you’re using such a tiny short-pulsed laser,
由于所使用的是脉冲极短的激光
is 10 picoseconds long, which is about 3mm.
每次发射只需10皮秒 约等于3毫米长的光波
That’s the limitation on your precision. So each shot is about 3-4mm precision.
这就限制了精准度 所以每次发射都有3至4毫米的误差
– This station works around the clock, whenever the sky is clear.
只要天气晴朗 该站全天工作
That’s why I’m here today:
所以今天我来到了这里
there will be some genuine observations when the clouds break,
当云散开后 我们将能观察到真实状况
but right now, I’m not actually disrupting anything.
但现在我啥也看不清
But it does look significantly better after dark.
不过天黑后 就好观察多了
– Because it’s a laser, it’s a very specific wavelength.
因为我们用的是激光 有特定的波长
So you can filter, and that’s what lets you work in day and night.
所以你可以对其进行筛选并实现全天工作
The main problem with the atmosphere is: the speed of light in a vacuum is a very well known constant.
大气层带来的主要问题在于 众所周知 光在真空中的速度为常数
The speed of light through the atmosphere is variable
而光在大气层中的速度是不定的
according to the mainly the pressure, but also temperature and humidity.
其主要取决于气压 也取决于温度和湿度
So we measure those things on site, as well.
所以我站也会测量这些数据
There’s probably about 35 active stations scattered around the globe,
地球上分布着大约35个正在工作的站点
located predominantly in the northern hemisphere, which is a slight problem from a science point of view.
主要分布在北半球 而这可能不太符合科学的观念
You’d like them evenly distributed all around the globe.
它们本该均匀分布在世界各地
There’s a couple in Australia which are really important
澳大利亚有一些站点 起到很大作用
because they’re providing a bulk of the data from southern hemisphere.
因为它们提供了大量来自南半球的数据
Ideally, we’d have a more even distribution.
理想状态下 站点分布应更加均匀
– Of course, as the light fades, there’s one assumption that we’ve been working on throughout this video:
当然 随着光的衰减 在整个视频中我们一直在假设
that the earth, the ground we’re standing on, doesn’t move.
地球 也就是我们脚下的这片土地 是静止的
And that’s not strictly true.
但这严格来说并不属实
– In the early days of laser ranging, in the 60s,
在激光测距刚刚出现的六十年代
it was the primary method by which they were deriving those early measurements of the drift between us and North America.
这是测量我们和北美之间的漂移的主要方法
So you can see long-term trends,
你可以发现一种大趋势
like the ice caps melting and the redistribution of mass from the ice caps to the equator.
比如冰盖的融化 质量从极地冰盖到赤道的重新分布
All the data goes off to international databases, from all the sites all around the world.
这些来自全球站点的数据都将进入国际数据库
Anyone, any researcher, anywhere can go and grab the international data set,
各地的研究人员都能获得这些国际数据集
the data from us, from Australia, from North America, from China, from Russia,
包括来自英国 澳大利亚 北美 中国 和俄国的数据
and can use that data to derive the orbits and do the research they need to do.
然后用这些数据来计算轨道以及做研究
– Thanks very much to all the team at the Space Geodesy Facility.
非常感谢空间大地测量站的所有团队
You can find out more about them and their work at the link in the description.
请点击视频介绍中的链接以获取更多有关他们及其工作内容的信息

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视频概述

本视频解释了一个来自英格兰南部乡村的天文台向卫星发射激光射线的原因,科技爱好者请进!

听录译者

收集自网络

翻译译者

茫鹤。

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视频来源

https://www.youtube.com/watch?v=vdvIY0CJaXw

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