WEBVTT
00:00:00.099 --> 00:00:15.749
34C3 preroll music
00:00:15.749 --> 00:00:22.160
Herald: Hello everybody to the next talk,
here at stage Clarke. The next talk will
00:00:22.160 --> 00:00:26.910
be held in English. And here is a quick
announcement in German for the
00:00:26.910 --> 00:00:32.833
translation. Der nächste Vortrag wird in
Englisch sein. Und wir haben eine deutsche
00:00:32.833 --> 00:00:42.239
Übersetzung unter streaming.c3lingo.org.
Und wir haben das auch auf einer Folie.
00:00:42.239 --> 00:00:48.760
Und es wird auch eine französische
Übersetzung geben für diesen Vortrag.
00:00:48.760 --> 00:00:55.569
There will also be a french translation,
as well as an German translation for the
00:00:55.569 --> 00:01:04.239
next talk. And you can find everything
under streaming.c3lingo.org. And, I hope,
00:01:04.239 --> 00:01:18.140
displayed behind me. The next talk is
called "Watching the changing Earth".
00:01:18.140 --> 00:01:23.890
Satellite data and change in the
gravitational field of the earth can tell
00:01:23.890 --> 00:01:29.939
us a lot, especially when there's so much
public domain satelite data coming in from
00:01:29.939 --> 00:01:36.109
different projects or maybe CC-BY
satellite data. And how this is done, this
00:01:36.109 --> 00:01:43.539
new knowledge finding out of this big
heap of data, this will be explained by
00:01:43.539 --> 00:01:50.399
Manuel in the talk. He dropped stuff to
see if gravity still works, or, in fancy
00:01:50.399 --> 00:02:00.045
words, he does gravimetric methods and
sensory in geodesy. Is that pronounced
00:02:00.045 --> 00:02:06.210
right? I'm not sure, but give a big hand
and a round of applause for our speaker
00:02:06.210 --> 00:02:09.860
Manuel.
Applause
00:02:09.860 --> 00:02:26.330
No Audio
Manuel: Geiler Scheiß. Oh, das war Sound.
00:02:26.330 --> 00:02:29.860
So again, so hello and welcome to my
presentation on watching the changing
00:02:29.860 --> 00:02:35.540
earth. This year's call for papers for the
Congress offered me the opportunity to
00:02:35.540 --> 00:02:42.190
talk about my work in the related fields,
which is gravity. As far as Congress is
00:02:42.190 --> 00:02:46.870
concerned, a misunderstood force of
nature. So in the following couple of
00:02:46.870 --> 00:02:53.200
minutes, I want to talk about gravity,
gravitation, about the GRACE satellite
00:02:53.200 --> 00:02:59.180
mission, which maps the earth gravity
field every month, about the gravity
00:02:59.180 --> 00:03:03.790
fields, and I will show good results and
then we will go forward into the future.
00:03:03.790 --> 00:03:11.080
That's nice. So it's actually called,
actually called geodesy. Let me give you a
00:03:11.080 --> 00:03:16.480
short introduction on geodesy. Friedrich
Robert Helmert defined it in 1880 at as
00:03:16.480 --> 00:03:21.320
the science of mapping and measuring the
earth on its surface, and this still holds
00:03:21.320 --> 00:03:29.752
up today. It depends on your methods and
applications, but he was correct. The most
00:03:29.752 --> 00:03:34.611
known profession is probably land
surveying, people with colorful
00:03:34.611 --> 00:03:39.530
instruments and traffic cones. You find
them on construction sites, on the side of
00:03:39.530 --> 00:03:44.610
the road, but we actually have a lot of
applications not only in geodesy but in
00:03:44.610 --> 00:03:49.590
related fields like geophysics,
fundamental physics, if you want to build
00:03:49.590 --> 00:03:57.010
an autonomous car you need geodesists,
metrology. This talk is specifically about
00:03:57.010 --> 00:04:02.040
physical geodesy, which is the mapping of
the gravitational field of the earth, and
00:04:02.040 --> 00:04:07.650
in this case specifically with satellites.
So I drop stuff on the earth, which is
00:04:07.650 --> 00:04:15.300
terrestrial gravimetry, this talk is about
satellite gravimetry. Now gravity and
00:04:15.300 --> 00:04:19.940
gravitation, we usually talk about
gravitational potential. This is a scalar
00:04:19.940 --> 00:04:25.850
field. Gravitational acceleration is the
gradient of the gravitational potential
00:04:25.850 --> 00:04:31.840
and when we talk about gravity in geodesy,
it's usually the combination of attraction
00:04:31.840 --> 00:04:37.490
of the masses, gravitation, and the
centrifugal acceleration, but here we talk
00:04:37.490 --> 00:04:42.361
mostly about gravitation. And the
potential can easily be calculated, at
00:04:42.361 --> 00:04:47.850
least according to this very short
equation. We have G, which is the
00:04:47.850 --> 00:04:52.870
gravitational constant of the earth, or
other planets if you want to do. We have
00:04:52.870 --> 00:04:58.270
an ugly triple integral about the whole
earth, and this is basically what breaks
00:04:58.270 --> 00:05:04.330
the neck. We have to integrate about the
whole mass of the earth, we divide up into
00:05:04.330 --> 00:05:11.020
small parts and we need to know the
density of these parts. So, density times
00:05:11.020 --> 00:05:16.170
small volume, you have the mass of the
earth if you integrate over it. So what,
00:05:16.170 --> 00:05:19.680
the density of the whole earth is not
known. So if you want to calculate the
00:05:19.680 --> 00:05:25.120
potential sufficiently, you would need the
density of a penguin on the other side of
00:05:25.120 --> 00:05:29.210
the world. We don't know that. So, what
do you do if you cannot calculate the
00:05:29.210 --> 00:05:35.780
quantity? You write a proposal and get all
the funding. This is what happened about,
00:05:35.780 --> 00:05:40.470
let's say, twenty years ago, and the
result was the gravity recovery and
00:05:40.470 --> 00:05:46.780
climate experiment, or GRACE for short. In
this talk, we will only cover gravity
00:05:46.780 --> 00:05:54.530
recovery, so gravity field of the Earth.
As we can see, these are two satellites.
00:05:54.530 --> 00:05:59.280
They are flying in the same orbit, and the
main instrument is distance measurement
00:05:59.280 --> 00:06:06.400
between these two satellites, Here we see
the two satellites prior to its launch in
00:06:06.400 --> 00:06:12.000
2002, and this K-Band Microwave ranging,
which is the instrument, gives us a high
00:06:12.000 --> 00:06:17.330
resolution gravity field of the Earth.
This is spatial resolution of around 200
00:06:17.330 --> 00:06:23.150
kilometers (km). You might think 200 km is
not really high resolution, but we have it
00:06:23.150 --> 00:06:29.300
for the whole planet and not, let's say,
for Germany. And also we got the temporal
00:06:29.300 --> 00:06:35.040
variations. So for 15 years now, we have
each month, with only a few exceptions, a
00:06:35.040 --> 00:06:41.320
picture of the gravitational field of the
earth. The satellites fly in height of
00:06:41.320 --> 00:06:49.290
about 450 km, 220 km apart, and we see
here the orbits of a single day. So 15
00:06:49.290 --> 00:06:55.771
orbits per day, and we take one month of
data to generate one gravity field. The
00:06:55.771 --> 00:06:59.990
working principle is quite simple: The
distance between the two satellites is
00:06:59.990 --> 00:07:05.697
affected by gravity, so we measure the
distance and then we calculate gravity. In
00:07:05.697 --> 00:07:10.270
a homogenous gravity field, this is quite
simple: Let's say we take a spherical
00:07:10.270 --> 00:07:16.990
earth, it has only a single density, the
satellites fly along, and the distance
00:07:16.990 --> 00:07:21.419
between the two satellites does not
change. There is nothing to pull one or
00:07:21.419 --> 00:07:27.680
another, they just move along, not
changing the distance. Now we introduce a
00:07:27.680 --> 00:07:33.810
mass, let's say a mountain, this can be
any mass change or density change
00:07:33.810 --> 00:07:38.940
somewhere inside the earth, and the
leading satellite experiences a
00:07:38.940 --> 00:07:44.740
gravitational pull by this mass. And as
gravitation falls off with distance, it is
00:07:44.740 --> 00:07:49.330
a stronger than the pull experienced by
the trailing satellite. So the distance
00:07:49.330 --> 00:07:58.810
between the two satellites increases. Now,
the satellite, the trailing the leading
00:07:58.810 --> 00:08:05.010
satellite has passed the mass, and it is
still feeling its gravitational pull, but
00:08:05.010 --> 00:08:10.560
now it is being decelerated because the
mass is behind. And the trailing satellite
00:08:10.560 --> 00:08:16.450
is still being accelerated towards the
mass. This means the distance between the
00:08:16.450 --> 00:08:24.710
satellites decreases. And finally, the
second satellite passes the mass and it
00:08:24.710 --> 00:08:30.669
now also feels the gravitational pull
decelerating the satellite. The leading
00:08:30.669 --> 00:08:34.659
satellite is feeling less and less
gravitational pull and once both
00:08:34.659 --> 00:08:39.389
satellites left the gravitational
influence of this mass, we will have the
00:08:39.389 --> 00:08:44.240
same distance as prior to encountering the
mass. So the gravitational acceleration is
00:08:44.240 --> 00:08:51.009
a zero sum at this point. So of course,
the Earth is a little more complex than a
00:08:51.009 --> 00:08:56.800
single mountain or a single density
anomaly in the ground, but this is the
00:08:56.800 --> 00:09:04.480
basic concept. Now, how do we come from
these measurements to the actual
00:09:04.480 --> 00:09:14.292
potential? The formula is basically the
same as a couple of slides earlier. We are
00:09:14.292 --> 00:09:21.180
still calculating the potential. It looks
more complicated, but we don't have triple
00:09:21.180 --> 00:09:24.930
integrals anymore, and all these
quantities in here are basically easily
00:09:24.930 --> 00:09:30.950
calculated. We start with the
gravitational constant and the mass of the
00:09:30.950 --> 00:09:35.470
earth, which we can get from a physics
book, if we like. And then we have a
00:09:35.470 --> 00:09:42.519
couple of geometric quantities, a and r
are basically the size of my earth
00:09:42.519 --> 00:09:48.709
ellipsoid, the major axes and r is the
distance from a calculating point, let's
00:09:48.709 --> 00:09:53.220
say this podium, for which I want to know
the potential value to the center of the
00:09:53.220 --> 00:09:57.399
ellipsoid. And then we have lambda and
theta at the end, these are the
00:09:57.399 --> 00:10:06.029
geographical coordinates of this podium. P
is short for the associated Legendre
00:10:06.029 --> 00:10:11.730
functions, also depending solely on
geometry, not on the mass of the earth,
00:10:11.730 --> 00:10:16.769
depending on the software where you want
to implement this formula, it probably has
00:10:16.769 --> 00:10:22.110
already a function to calculate this, and
if not, it is easily done by yourself as
00:10:22.110 --> 00:10:28.429
the formulas look very long, but they are
quite simple. The interesting part are the
00:10:28.429 --> 00:10:34.980
two parameters C and S, these are
spherical harmonic coefficients. They
00:10:34.980 --> 00:10:38.790
include all the information about the
mass of the earth, as measured by the
00:10:38.790 --> 00:10:44.731
satellites. So we have the satellites in
space, and the user gets just the C and S
00:10:44.731 --> 00:10:51.277
coefficients, which are a couple of
thousand for the gravity field. Implements
00:10:51.277 --> 00:10:56.760
this formula and has a potential value.
So, these spherical harmonic coefficients
00:10:56.760 --> 00:11:01.190
are calculated from the GRACE Level 1B
products. These are the actual
00:11:01.190 --> 00:11:04.499
measurements done by the satellites. This
is the ranging information, the distance
00:11:04.499 --> 00:11:11.120
between satellites, satellite orbits, star
camera data, and so on. You add a couple
00:11:11.120 --> 00:11:14.309
of additional models for earth's gravity,
which you do not want to include in your
00:11:14.309 --> 00:11:19.550
satellite gravity field, and then you do
your processing. This is done by a couple
00:11:19.550 --> 00:11:27.170
of different groups JPL and GFZ, which is
a German research center for the
00:11:27.170 --> 00:11:33.329
geosciences. CSR is the center for space
research at university Austin. These three
00:11:33.329 --> 00:11:39.810
institutes also provides these GRACE Level
1B data. So they take the raw satellite
00:11:39.810 --> 00:11:47.529
data, process it to theGRACE Level 1B
products, which are accessible for all
00:11:47.529 --> 00:11:54.420
users, and then calculate further these
coefficients, C and S. But there are also
00:11:54.420 --> 00:11:59.750
additional groups who provide gravity
fields who calculate these coefficients,
00:11:59.750 --> 00:12:04.350
for example, Institute for Geodesy of the
University of Graz, or the Astronomical
00:12:04.350 --> 00:12:11.660
Institute of the University of Bern. They
all have slightly different approaches to
00:12:11.660 --> 00:12:16.160
topic and come to more or less the same
conclusions. There are countless papers,
00:12:16.160 --> 00:12:20.689
comparing these different gravity fields
with each other, but the user usually
00:12:20.689 --> 00:12:25.829
starts with the coefficients C and S, and
then it takes a formula like the one on
00:12:25.829 --> 00:12:31.639
top of this slide and calculates your
gravity value or whatever you want. Now,
00:12:31.639 --> 00:12:36.749
I'm talking about potential, I'm talking
about accelaration. These are not really
00:12:36.749 --> 00:12:42.769
useful quantities in day to day life. If
someone told to you in Greenland gravity
00:12:42.769 --> 00:12:48.440
decrease by 50 microGal, you have two
choices, you can say "wow, awesome" or you
00:12:48.440 --> 00:12:53.910
can say "oh no, we're all gonna die" It's
a 50:50 chance you'd say the correct
00:12:53.910 --> 00:13:01.350
thing. So we are looking for a more useful
representation of the changes in
00:13:01.350 --> 00:13:07.329
gravity field. Now gravity field reflects
mass redistributions and the most dynamic
00:13:07.329 --> 00:13:15.870
redistribution we have is water storage,
summer/winter, more snow, more rain, less
00:13:15.870 --> 00:13:25.600
water in summer, so we express our gravity
change in a unit called equivalent water
00:13:25.600 --> 00:13:31.950
height. This is the layer of water on the
surface with a thickness, equivalent to
00:13:31.950 --> 00:13:39.939
the mass change measured with the
satellites. This is also easily
00:13:39.939 --> 00:13:47.179
calculated. This is my last equation, I
promise, but this looks familiar. The
00:13:47.179 --> 00:13:55.480
second half of this equation, is basically
the same we saw one slide prior and the
00:13:55.480 --> 00:14:02.529
parameters in front of the sum is the
average density of earth, which is around
00:14:02.529 --> 00:14:13.709
5500 kg/m^3. We need the density or water,
let's say it 1000 kg/m^3. And in this
00:14:13.709 --> 00:14:19.429
fraction in the middle, we need to
parameter K, which are the so-called Love
00:14:19.429 --> 00:14:26.149
numbers. Now, this is not a numerical
representation of mutual attraction, but
00:14:26.149 --> 00:14:33.790
was put forward by, I think, Albert Love
in 1911, and they are parameters
00:14:33.790 --> 00:14:37.670
concerning the elastic response of the
earth to forces. So, if you put a lot of
00:14:37.670 --> 00:14:44.330
weight on a part of the earth, the earth
deforms and these parameters, describe the
00:14:44.330 --> 00:14:51.769
elastic response of the earth to such
loading. Now we have calculated our
00:14:51.769 --> 00:14:59.120
equivalent water height, let's say for two
months, let's say, in May 2002 and 15
00:14:59.120 --> 00:15:04.790
years later in May 2017 and we just
subtract these two gravity fields, these
00:15:04.790 --> 00:15:11.110
two equivalent waterheights, from these
two epoches. What we have left is the
00:15:11.110 --> 00:15:17.899
change in gravity between these 2 epochs,
15 years apart, expressed in water layer
00:15:17.899 --> 00:15:23.069
equivalent to the change in gravity
measured. And we can see a couple of
00:15:23.069 --> 00:15:28.190
features here. There should not be any
seasonal variations because it's the same
00:15:28.190 --> 00:15:35.480
month, just 15 years apart. So we see long
term gravity change between these two
00:15:35.480 --> 00:15:40.129
epochs. And what we see is, for example,
mass loss in the northern and southern ice
00:15:40.129 --> 00:15:46.379
shields, and we see two red blobs, one in
northern canada and one in northern
00:15:46.379 --> 00:15:53.009
europe, which are geophysical processes.
So this is glacial isostastic adjustment
00:15:53.009 --> 00:15:58.800
and during the last ice age the ice
shields deformed the earth downward.
00:15:58.800 --> 00:16:04.579
The material in the "Mantel" had to flow
aside, and now that the ice is gone, the
00:16:04.579 --> 00:16:10.059
lead is uplifting and the material in the
"Mantel" is flowing back. So it's flowing
00:16:10.059 --> 00:16:14.459
back and the earth is uplifting. This
process has been going on for 10000 years
00:16:14.459 --> 00:16:23.279
and will probably a couple of years
longer. Now how do you get your data?
00:16:23.279 --> 00:16:27.009
Everyone can get the GRACE Level 1B data,
which are the observations by the
00:16:27.009 --> 00:16:32.399
satellite, like again, ranging information
between the satelite, orbits,
00:16:32.399 --> 00:16:39.949
accelerometer data, star camera data and
so on. You can get them without hurdles at
00:16:39.949 --> 00:16:44.919
the ISDC, which is the information system,
a data center at the Geoforschungszentrum
00:16:44.919 --> 00:16:53.740
Potsdam, or at the Physical Oceanography
Distributed Active Archive Center run by
00:16:53.740 --> 00:16:59.879
JPL. And if you'd like, you can calculate
your own spherical harmonic coefficients
00:16:59.879 --> 00:17:06.269
for gravity fields. Or you can compare for
example, satelite orbits they give you
00:17:06.269 --> 00:17:11.199
with one you integrated yourself using
your own gravity field, to see if they fit
00:17:11.199 --> 00:17:19.910
together or not. You can get gravity field
models, if you'd like. A large collection
00:17:19.910 --> 00:17:25.609
is at the International Centre for Global
Earth Models. They have recent and
00:17:25.609 --> 00:17:30.789
historic gravity models all in the same
data format. So you only need to implement
00:17:30.789 --> 00:17:36.639
your software once from the 1970s to
today. They also have the proper
00:17:36.639 --> 00:17:43.070
references, the papers you want to read to
work with them. These are so-called Level
00:17:43.070 --> 00:17:47.510
2 Products. So, you can take a gravity
field from there, use the equation, I
00:17:47.510 --> 00:17:51.528
showed you earlier and calculate your
equivalent water height, if you'd like.
00:17:51.528 --> 00:17:56.529
If you don't want to do this, there is
someone to help you, a service called
00:17:56.529 --> 00:18:01.809
"TELLUS", which is a play on words I
don't want to go into detail about. They
00:18:01.809 --> 00:18:08.330
offer equivalent water heights calculated
for each monthly solution from the GRACE
00:18:08.330 --> 00:18:13.870
satellites. This tells us a lot about the
earth, if you look closer into it. In the
00:18:13.870 --> 00:18:20.500
following, I will use the monthly
solutions from the ITSG-GRACE 2016,
00:18:20.500 --> 00:18:25.860
provided by Institute for Geodesy at
University of Graz. The previous graph I
00:18:25.860 --> 00:18:32.289
showed you was also created with that
gravity model. I will not go into detail
00:18:32.289 --> 00:18:40.140
about further processing like filtering
and gravity reductions done to this, not
00:18:40.140 --> 00:18:47.120
enough time. So here are some results,
let's start with the most obvious one, the
00:18:47.120 --> 00:18:54.919
greenland ice shield, which has, as we saw
earlier, the greatest loss of mass
00:18:54.919 --> 00:19:04.460
according to the gravity field and we see
here, a water layer on the whole landmass,
00:19:04.460 --> 00:19:10.142
describing the loss of mass expressed as a
water layer of a certain thickness.
00:19:10.142 --> 00:19:15.337
So let's say in the southern tip, you have
one meter water layer. This would be
00:19:15.337 --> 00:19:23.700
equvalent in gravity to the actual mass
lost in Greenland. But we also see, that
00:19:23.700 --> 00:19:28.950
the signal is not very localized. So it's
not bound to the land mass. It's also in
00:19:28.950 --> 00:19:34.910
the ocean. This effect is called leakage.
If you do signal processing you will know
00:19:34.910 --> 00:19:45.471
this. There are methods to reduce leakage.
My next slide will show such a result, but
00:19:45.471 --> 00:19:49.110
I have done no reduction to this. So if
you use my formula I showed you, you will
00:19:49.110 --> 00:19:55.710
pretty much get a result like this. This
gives you a trend of around 280 gigatons
00:19:55.710 --> 00:20:01.679
per year in mass loss over the whole land
mass of greenland. And now gigatons is
00:20:01.679 --> 00:20:08.470
also not very useful an expression. One
cubic meter of water has a weight of a
00:20:08.470 --> 00:20:15.850
1000 kilos; one tonne, 1 gigatonne is
10^9 tonne, if you are familiar with ball
00:20:15.850 --> 00:20:23.792
sports, 1 soccer field with the 140 km
high water column has the weight of
00:20:23.792 --> 00:20:33.490
1 gigatonne, or if you are not fan of sports
ball, if you're more of a plane guy or girl
00:20:33.490 --> 00:20:42.690
the A380-800 has a maximum takeoff weight
of 575 tonne, so we need 1.7 mio of these
00:20:42.690 --> 00:20:52.950
airplanes for one gigatonne. So this is a more
beautiful representation of the process in
00:20:52.950 --> 00:20:58.929
greenland, done by NASA JPL. If you go to
the website of the GRACE project, they
00:20:58.929 --> 00:21:06.441
have a couple of these illustrations, they
obviously worked hard on the leakage.
00:21:06.441 --> 00:21:12.460
You can see localized where most of the
gravity, most of the mass is lost on the
00:21:12.460 --> 00:21:20.490
left and on the right you see accumulated
over time, the mass which is lost, and
00:21:20.490 --> 00:21:26.539
which trend it gives you. Also, if look
closely in the center of greenland, you
00:21:26.539 --> 00:21:36.577
see black lines, these are the ice flow,
as determined by radar interferometry.
00:21:36.577 --> 00:21:43.000
So now pretty much know where ice is lost,
where mass is lost. This goes into the
00:21:43.000 --> 00:21:52.029
ocean, and this would be a good idea to
see, to check our GRACE results, the mass
00:21:52.029 --> 00:21:56.799
we find missing on earth, so the melted
ice, and the additional mass in the ocean,
00:21:56.799 --> 00:22:03.700
does this agree with other methods who
determine the sea level rise. One of these
00:22:03.700 --> 00:22:09.289
methods is satellite radar altimetry, that
started in the 70's, but since 1991, we
00:22:09.289 --> 00:22:15.269
have lots of dedicated satellite missions,
which only job is basically mapping the
00:22:15.269 --> 00:22:21.540
global sea surface. So, they send down a
radar pulse, which is reflected at the sea
00:22:21.540 --> 00:22:27.049
surface. They measure the run time and
then they have a geometric representation
00:22:27.049 --> 00:22:35.480
of the global sea surface. Now, if we
compare this with the mass we calculated
00:22:35.480 --> 00:22:41.330
or we got from the GRACE result, calculate
a sea level rise rise from this additional
00:22:41.330 --> 00:22:46.580
mass in the ocean than these two systems
would not add up. The geometric sea level
00:22:46.580 --> 00:22:51.820
rise is higher than just the additional
mass. So there is the second process which
00:22:51.820 --> 00:22:58.759
is thermal expansion of the water. If
water gets warm it needs more space.
00:22:58.759 --> 00:23:07.159
In 2000 the deployment of so-called ARGO
floats started. These are free-floating
00:23:07.159 --> 00:23:13.389
devices in the ocean. Currently, there are
over 3000 and they measure temperature and
00:23:13.389 --> 00:23:20.679
salinity between sea surface and a depth
of 2000 meters. These are globally
00:23:20.679 --> 00:23:28.870
distributed. So, we have at least for the
upper layer of the ocean, how much thermal
00:23:28.870 --> 00:23:36.710
expansion there is. And what we want to
see is, do these components of additional
00:23:36.710 --> 00:23:41.450
mass in the ocean as determined by GRACE
and thermal expansion of the upper ocean
00:23:41.450 --> 00:23:47.460
layer come to the same result as
geometrical measurements done by satellite
00:23:47.460 --> 00:23:52.900
altimetry? On the left we see an image
taken from the last IPCC report on climate
00:23:52.900 --> 00:23:59.769
change from 2013. In green we see the
sealevel rise as measured with satellite
00:23:59.769 --> 00:24:06.279
altimetry in the time span 2005 to 2012
and in orange we see the combination of
00:24:06.279 --> 00:24:13.200
additional mass, as measured by GRACE, and
thermal extension as determined with ARGO
00:24:13.200 --> 00:24:21.720
inside the ocean. And these 2 graphs follow
each other quite well. On the right. We
00:24:21.720 --> 00:24:27.799
see a recent publication by Chen, Wilson
and Tapley, the latter one being one of
00:24:27.799 --> 00:24:34.460
the PIs of the GRACE mission, who
accumulated the data from 2005 to 2011. We
00:24:34.460 --> 00:24:41.350
basically come to the same conclusion. So
now if you really don't want to do the
00:24:41.350 --> 00:24:48.870
math, there are online services who make
the graphs for you. One of those is
00:24:48.870 --> 00:24:55.219
EGSIEM European Gravity Service for
Improved Emergency Control. If we can
00:24:55.219 --> 00:25:00.659
measure how much water is stored in a certain
area, we know that this amount of water
00:25:00.659 --> 00:25:04.929
has sooner or later to be removed from
this area. This can be a flood, for
00:25:04.929 --> 00:25:08.840
example, and with a mission like GRACE, we
can determine how much mass, how much
00:25:08.840 --> 00:25:15.289
water is there and are the rivers large
enough to allow for this water to be
00:25:15.289 --> 00:25:22.970
flowing away. That was the intention
behind this service. Oops, no, this is not
00:25:22.970 --> 00:25:39.299
the future. So, I wanted to do the life
demo but. So, yeah, the live demo did not
00:25:39.299 --> 00:25:46.909
work as expected. So, you will be greeted
with this graphic. You can plot for all
00:25:46.909 --> 00:25:50.649
areas in the world. The first thing you
have to do is you change your gravity
00:25:50.649 --> 00:25:56.989
functional, we want water heights. This is
what I talked about in this talk. Then you
00:25:56.989 --> 00:26:03.200
want to look at the data set and at the
bottom you see a large list of GRACE
00:26:03.200 --> 00:26:07.190
gravity fields. These are different
groups, I mentioned, providing these
00:26:07.190 --> 00:26:15.440
monthly solutions. And so we choose one of
these groups. Then we choose an area which
00:26:15.440 --> 00:26:21.809
we are interested in. You can freely
choose one area like here Finno-Scandia,
00:26:21.809 --> 00:26:29.070
or you can use pre-determined areas, for
example, the Amazon river basin or Elbe
00:26:29.070 --> 00:26:35.570
river or something like that. These areas
all over the world and you can see the
00:26:35.570 --> 00:26:41.059
gravity change in this area. So let's look
here at Finno-Scandia, and then you are
00:26:41.059 --> 00:26:47.250
greeted with a plot like this. This is
equivalent water height, even though this
00:26:47.250 --> 00:26:51.740
is a geophysical process. So we see here
the layer of water, which would have been
00:26:51.740 --> 00:27:01.580
added to the region as selected, and we
see a clear trend upward. Again, this is a
00:27:01.580 --> 00:27:08.750
geophysical process. This is not
additional ice or water or anything. Can I
00:27:08.750 --> 00:27:20.240
return to my...? No, I cannot. So, yeah,
live demo did not work. If you want to do
00:27:20.240 --> 00:27:26.710
this yourself. I have uploaded to the
Fahrplan all my resources, all my links.
00:27:26.710 --> 00:27:31.510
And the EGSIEM page also includes the
description of what is done in the backend
00:27:31.510 --> 00:27:37.649
and were the data comes from and what you
can see in the various fields. Now I want
00:27:37.649 --> 00:27:42.289
to give a last impression on the future,
because unfortunately while I was
00:27:42.289 --> 00:27:46.730
preparing my abstract for this conference,
one of the GRACE satellites was turned off
00:27:46.730 --> 00:27:51.750
due to age. It was launched in 2002,
planned for a five mission year; it
00:27:51.750 --> 00:27:56.970
survived 15 years, which is quite good,
but now we have no more ranging
00:27:56.970 --> 00:28:01.250
information between these satellites. We
had ranging information in micrometer
00:28:01.250 --> 00:28:09.049
accuracy, a couple of micrometer, and now
we cannot rely on these information
00:28:09.049 --> 00:28:14.320
anymore. And this means mo more gravity
fields with high spatial resolution, and
00:28:14.320 --> 00:28:17.799
I'm not sure about the temporal
resolution. So, the current work which is
00:28:17.799 --> 00:28:23.270
done is taking all satellites which are in
the low-enough orbits and calculate the
00:28:23.270 --> 00:28:26.799
gravity field from their positions,
because everything which is in low-earth
00:28:26.799 --> 00:28:32.870
orbit is affected by the Earth's gravity
field. So, if I take the satellite orbits,
00:28:32.870 --> 00:28:38.690
look "how does this orbit change" and the
reason is gravity, then I can calculate
00:28:38.690 --> 00:28:46.110
the gravity field. Unfortunately, not in
this higher resolution we are used to.
00:28:46.110 --> 00:28:50.019
And... But fortunately, there already is a
next-generation gravity field mission on
00:28:50.019 --> 00:28:58.410
its way. It arrived last week in the US,
where it will be launched in late March,
00:28:58.410 --> 00:29:05.330
early April by SpaceX. You might look at
this image and think, "I just saw this
00:29:05.330 --> 00:29:10.990
earlier" and you are quite correct: The
mission called "Grace Follow On" is a copy
00:29:10.990 --> 00:29:16.419
of Grace, which improved components, of
course, and now with lasers. We see not
00:29:16.419 --> 00:29:21.500
only the microwave ranging between the two
satellites, but additionally a laser
00:29:21.500 --> 00:29:26.289
interferometer. So, from micrometer
accuracy in the distance measurements we
00:29:26.289 --> 00:29:33.324
go to nanometer accuracy, hopefully. But
the main instrument will be the
00:29:33.324 --> 00:29:36.669
microwave ranging. So, in conclusion,
00:29:36.669 --> 00:29:42.130
I hope I showed you that the gravity field
can show mass transport on the surface and
00:29:42.130 --> 00:29:47.889
inside the Earth; that this offers, in
combination with other methods, new
00:29:47.889 --> 00:29:54.179
insights and also some kind of mutual
verification. If several different types
00:29:54.179 --> 00:29:57.960
of observations coming to the same
conclusion, none of them can be awfully
00:29:57.960 --> 00:30:03.700
wrong; and that the access to these
methods are relatively easy: the data is
00:30:03.700 --> 00:30:09.480
available, all the methods are described
in geodesy textbooks and the technical
00:30:09.480 --> 00:30:14.600
documentation; and there are other
applications, other than, let's say,
00:30:14.600 --> 00:30:22.029
climate change; you can look into drought
and flood prediction; the El Niño–Southern
00:30:22.029 --> 00:30:29.989
Oscillation you can predict from Grace's
gravity field data. So, lot's of work to do.
00:30:29.989 --> 00:30:35.929
So, this would be the end for my talk.
I thank you for your interest in the topic.
00:30:35.929 --> 00:30:46.775
applause
00:30:46.775 --> 00:30:51.250
Herald: Thank you, Manuel, for the talk.
And I think we have time for one or two,
00:30:51.250 --> 00:30:57.350
maybe two very short questions. Please be
seated during the Q&A session. Is there
00:30:57.350 --> 00:31:02.250
some questions? Okay, microphone 3,
please.
00:31:02.250 --> 00:31:05.741
Mic 3: Yeah, hi. In a quiet voice
Hi, hello? Can you hear me? Now loud
00:31:05.741 --> 00:31:07.859
Herald: Yeah.
Mic 3: Okay. Hey. So, my question is
00:31:07.859 --> 00:31:12.945
regarding acceleration. What's the
influence of Earth atmosphere and all the
00:31:12.945 --> 00:31:18.678
planetary bodies, like the moon, and does
it need to be accounted for?
00:31:18.678 --> 00:31:22.236
Manuel: The external gravity needs to be
accounted for, so the tidal effects of sun
00:31:22.236 --> 00:31:26.976
and moon would be one of those additional
models you put into the processing of the
00:31:26.976 --> 00:31:32.340
satellite data. The Earth's atmosphere has
an effect on the satellites themselves,
00:31:32.340 --> 00:31:37.159
which is measured onboard by
accelerometers and then reduced. And the
00:31:37.159 --> 00:31:43.289
gravitational effect of the atmosphere:
Part of this is averaged out, because we
00:31:43.289 --> 00:31:48.369
take a month of time series, and the rest
are also inclu... provide as extra
00:31:48.369 --> 00:31:54.279
products; at least by the Institute for
Geodesy in Graz. So atmosphere... the mass
00:31:54.279 --> 00:31:58.900
of the atmosphere is... has to be
accounted for, yes.
00:31:58.900 --> 00:32:04.280
Herald: Okay. Microphone 2 has vanished
all of a sudden. Then, microphone 1,
00:32:04.280 --> 00:32:08.700
please.
Mic 1: Hi. Is it possible to measure
00:32:08.700 --> 00:32:16.206
changes in the temperature of the oceans
or of the ocean streams, like... Can you
00:32:16.206 --> 00:32:25.362
see if El Niño is active by just measuring
the gravity... change in gravity fields?
00:32:25.362 --> 00:32:29.999
Manuel: As a precursor tool, El Niño, as I
understand it... certain regions of the
00:32:29.999 --> 00:32:35.690
ocean get warmer; it's a density change;
and, of course, this would be measured as
00:32:35.690 --> 00:32:42.070
part of ARGO and it's also in the GRACE
gravity field. There are probably papers
00:32:42.070 --> 00:32:47.799
on it. So, the last... the extend of the
last El Niño was predicted by GRACE. I
00:32:47.799 --> 00:32:51.665
don't know to what extend this was
correct, but...
00:32:51.665 --> 00:32:55.360
Mic 1: Okay, then.
Herald: Good. Then, that's all the time we
00:32:55.360 --> 00:32:57.924
have. A big round of applause for Manuel
and his talk, please.
00:32:57.924 --> 00:33:00.690
Applause
00:33:00.690 --> 00:33:07.790
34C3 Music
00:33:07.790 --> 00:33:22.000
subtitles created by c3subtitles.de
in the year 2020. Join, and help us!