WEBVTT FILE

1
00:00:00.000 --> 00:00:00.867
[Upbeat Music]

2
00:00:00.867 --> 00:00:02.268
Narrator: Where are you right now?

3
00:00:02.268 --> 00:00:04.571
Or better yet, how do you know where you are?

4
00:00:05.305 --> 00:00:08.808
Most likely you are using an app that is using a GPS

5
00:00:08.842 --> 00:00:11.444
to pinpoint where exactly you are on Earth.

6
00:00:12.245 --> 00:00:15.181
But what you might not know
is that behind your favorite navigation

7
00:00:15.181 --> 00:00:16.349
app is an invisible

8
00:00:16.349 --> 00:00:20.687
infrastructure of systems working together
to provide you an accurate location,

9
00:00:21.287 --> 00:00:24.491
and that the foundation of these systems
is a TRF

10
00:00:24.491 --> 00:00:26.793
or terrestrial reference frame.

11
00:00:27.861 --> 00:00:31.998
Dr. Stephen Merkowitz: So reference frame is fundamental

12
00:00:32.032 --> 00:00:37.771
to any kind of mapping, location,
positioning, navigation application.

13
00:00:37.804 --> 00:00:42.976
Narrator: That's Dr. Stephen Merkowitz,
NASA's Space Geodesy Project Manager

14
00:00:43.076 --> 00:00:45.345
Simply put, geodesy is the science

15
00:00:45.345 --> 00:00:47.914
of measuring and understanding the shape of the Earth,

16
00:00:48.348 --> 00:00:52.619
its orientation in space and gravity,
and how they change over time.

17
00:00:53.019 --> 00:00:57.891
Dr. Stephen Merkowitz: Earth is constantly changing shape,
and the land masses are constantly moving.

18
00:00:57.924 --> 00:01:02.095
It's at small levels, so it's not something
you would feel, you know, yourself.

19
00:01:02.228 --> 00:01:04.197
So we're constantly measuring

20
00:01:04.197 --> 00:01:07.801
what's happening with the Earth as a whole
and the Earth's surface.

21
00:01:08.034 --> 00:01:11.671
Narrator: To do this, NASA and international partners
monitor measurement

22
00:01:11.671 --> 00:01:15.475
stations dotted across the globe
that help us determine where,

23
00:01:15.742 --> 00:01:18.812
how much and in which direction
our planet is changing.

24
00:01:19.646 --> 00:01:22.582
Dr. Stephen Merkowitz: Since the Earth's surface
is always moving, any measurement

25
00:01:22.682 --> 00:01:24.851
isn't just in a fixed coordinate system.

26
00:01:24.851 --> 00:01:26.319
It needs to take into account

27
00:01:26.319 --> 00:01:27.620
the fact that it's related

28
00:01:27.620 --> 00:01:31.491
to the landmass and where that landmass
is at any given time.

29
00:01:31.524 --> 00:01:34.427
Narrator: And just like a coordinate system
plotted on a piece of paper,

30
00:01:34.627 --> 00:01:38.565
the TRF has an origin or in this case,
the center mass of the

31
00:01:38.565 --> 00:01:40.200
Earth - called the geocenter.

32
00:01:41.801 --> 00:01:44.104
Because of this, many Earth observing satellites

33
00:01:44.104 --> 00:01:48.675
orbit around the center mass of the Earth,
not the Earth's geographic center.

34
00:01:49.042 --> 00:01:52.245
So it's critical for scientists to pinpoint where that is

35
00:01:52.245 --> 00:01:54.647
to make sure our Earth observations are accurate.

36
00:01:54.681 --> 00:01:57.250
Dr. Stephen Merkowitz: One complication is that the center
mass of the Earth

37
00:01:57.851 --> 00:02:00.186
is constantly changing over time

38
00:02:00.353 --> 00:02:02.555
with respect to the Earth's surface.

39
00:02:02.555 --> 00:02:06.759
Narrator: Earthquakes, volcanoes, or even
atmospheric pressure changes all impact

40
00:02:06.759 --> 00:02:09.395
where exactly the center
mass of the Earth is.

41
00:02:10.363 --> 00:02:14.400
But by using a network of ground stations
equipped with telescopes and lasers

42
00:02:14.400 --> 00:02:18.705
that fire pulses at specific satellites,
scientists can calculate

43
00:02:18.738 --> 00:02:23.710
where the geocenter of the Earth
is at any given time to a few millimeters.

44
00:02:23.943 --> 00:02:28.781
Dr. Stephen Merkowitz: This is a very important product
that we generate for orbiting satellites,

45
00:02:28.781 --> 00:02:30.717
particularly for missions

46
00:02:30.717 --> 00:02:34.320
that are either doing mapping
the gravitational field of the Earth or

47
00:02:35.054 --> 00:02:38.825
mapping the height of the Earth's surface,
whether it be land, vegetation,

48
00:02:38.825 --> 00:02:40.293
or sea level.

49
00:02:40.293 --> 00:02:42.362
We make that available to the public,

50
00:02:42.362 --> 00:02:45.498
we use the data there
to generate a higher level

51
00:02:45.665 --> 00:02:49.569
of products, geodetic products,
that can be used by NASA missions

52
00:02:50.170 --> 00:02:53.439
for many scientific applications.

53
00:02:53.673 --> 00:02:57.277
Since this is a global measurement, NASA can't do it alone.

54
00:02:57.610 --> 00:03:00.079
We rely on the global community to

55
00:03:00.680 --> 00:03:04.551
provide all the data that's needed to provide global coverage.

56
00:03:06.686 --> 00:03:07.520
Narrator: Having an agreed

57
00:03:07.520 --> 00:03:11.257
upon international system is
what makes measuring our planet possible,

58
00:03:11.591 --> 00:03:16.029
whether it be from land,
sea, air, or even space.