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Active Remote Sensing and Lidar - Contenido educativo

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Connect Segment explains how scientist use LIDAR to help them measure aerosols in the atmosphere. It also describes active remote sensing.

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Explain how scientists use LIDAR to help them measure the aerosols in the atmosphere. 00:00:00
Here in our lab at NASA Langley, we use a technique called active remote sensing. 00:00:10
Now that means that we carry our own light source. 00:00:15
We don't wait around for the sun to shine on the object. 00:00:17
And we use, what we do is we use short pulses of laser light to probe the atmosphere. 00:00:20
This technique is called LIDAR. 00:00:26
LIDAR stands for Light Detection and Ranging. 00:00:28
A LIDAR uses short pulses of laser light to detect aerosols in the atmosphere. 00:00:31
NASA Langley is involved in active remote sensing from the ground and in the air. 00:00:37
At NASA Ames in California, LIDAR is flown in a high altitude ER-2 aircraft to record 00:00:43
atmospheric data. 00:00:50
And at NASA Dryden, also in California, a high altitude solar powered unpiloted airplane 00:00:52
is being developed that can stay aloft for weeks, even months, at a time to make atmospheric 00:00:57
measurements. 00:01:03
So, how does LIDAR work? 00:01:04
Well, first of all, we open this trap door and then align our LIDAR under the open sky. 00:01:07
Then we shoot a pulsed laser beam into the atmosphere. 00:01:15
Some of that laser beam scatters off the tiny aerosol particles and scatters light into 00:01:20
this telescope. 00:01:25
The light is then captured by this detector. 00:01:27
By precisely timing the laser pulse going out into the atmosphere and the reflected 00:01:30
light coming back to the telescope, scientists can accurately measure the location and number 00:01:35
of aerosols. 00:01:41
Now, remember, this is active remote sensing, much like that flash on the camera. 00:01:42
Okay, I understand passive and active remote sensing and how LIDAR works, but how do you 00:01:47
measure the distance from the ground to the aerosols in the atmosphere? 00:01:53
You can't use a meter stick. 00:01:57
Okay, let's say you wanted to measure something far away, say like aerosols in the sky. 00:01:59
You're right, you wouldn't use a meter stick. 00:02:06
Scientists at NASA Langley use mathematics. 00:02:11
A pulse of laser light is shot from point A. The beam travels from point A to the aerosols 00:02:14
at point B. 00:02:21
Then, the light reflects off the aerosols and bounces back to point A. If you know how 00:02:22
fast it takes for a pulse of laser light to travel, and you know a little math, then you 00:02:28
can calculate how far away the aerosols are in the atmosphere. 00:02:33
Check it out. 00:02:37
It takes a pulse of light one nanosecond to travel one third of a meter. 00:02:38
What is a nanosecond? 00:02:45
A nanosecond is one billionth of a second. 00:02:47
Basically, it's a really small amount of time. 00:02:50
Anyway, if a scientist shoots a pulse of laser light at the sky, and that beam reflects back, 00:03:00
say in 6,000 nanoseconds, the aerosols in the sky are really 3,000 nanoseconds away. 00:03:12
Why? 00:03:24
Because you have to divide the total time by two in order to find the time one way. 00:03:25
Got it? 00:03:32
So, if you multiply the time one way, 3,000 nanoseconds, by the number of meters in a 00:03:33
nanosecond, one third, you get 1,000 meters. 00:03:39
If you know how to convert meters to kilometers, you can calculate that the aerosols in the 00:03:44
sky are one kilometer away. 00:03:48
Well, that should answer your question, Van. 00:03:51
But you know, in order to get the whole picture, we need to measure aerosols from space. 00:03:55
Let me call a few colleagues of mine over at Hampton University who are working with 00:03:59
NASA Langley Ball Aerospace and the French Space Agency to get them to explain to you 00:04:03
how we can measure aerosols from space. 00:04:07
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Idioma/s:
en
Materias:
Matemáticas
Niveles educativos:
▼ Mostrar / ocultar niveles
      • Nivel Intermedio
Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
397
Fecha:
28 de mayo de 2007 - 16:53
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
04′ 12″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
Resolución:
480x360 píxeles
Tamaño:
25.27 MBytes

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