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34C3 preroll music
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Herald: Hello everybody to the next talk,[br]here at stage Clarke. The next talk will
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be held in English. And here is a quick[br]announcement in German for the
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translation. Der nächste Vortrag wird in[br]Englisch sein. Und wir haben eine deutsche
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Übersetzung unter streaming.c3lingo.org.[br]Und wir haben das auch auf einer Folie.
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Und es wird auch eine französische[br]Übersetzung geben für diesen Vortrag.
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There will also be a french translation,[br]as well as an German translation for the
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next talk. And you can find everything[br]under streaming.c3lingo.org. And, I hope,
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displayed behind me. The next talk is[br]called "Watching the changing Earth".
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Satellite data and change in the[br]gravitational field of the earth can tell
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us a lot, especially when there's so much[br]public domain satelite data coming in from
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different projects or maybe CC-BY[br]satellite data. And how this is done, this
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new knowledge finding out of this big[br]heap of data, this will be explained by
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Manuel in the talk. He dropped stuff to[br]see if gravity still works, or, in fancy
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words, he does gravimetric methods and[br]sensory in geodesy. Is that pronounced
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right? I'm not sure, but give a big hand[br]and a round of applause for our speaker
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Manuel.[br]Applause
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No Audio[br]Manuel: Geiler Scheiß. Oh, das war Sound.
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So again, so hello and welcome to my[br]presentation on watching the changing
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earth. This year's call for papers for the[br]Congress offered me the opportunity to
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talk about my work in the related fields,[br]which is gravity. As far as Congress is
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concerned, a misunderstood force of[br]nature. So in the following couple of
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minutes, I want to talk about gravity,[br]gravitation, about the GRACE satellite
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mission, which maps the earth gravity[br]field every month, about the gravity
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fields, and I will show good results and[br]then we will go forward into the future.
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That's nice. So it's actually called,[br]actually called geodesy. Let me give you a
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short introduction on geodesy. Friedrich[br]Robert Helmert defined it in 1880 at as
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the science of mapping and measuring the[br]earth on its surface, and this still holds
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up today. It depends on your methods and[br]applications, but he was correct. The most
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known profession is probably land[br]surveying, people with colorful
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instruments and traffic cones. You find[br]them on construction sites, on the side of
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the road, but we actually have a lot of[br]applications not only in geodesy but in
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related fields like geophysics,[br]fundamental physics, if you want to build
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an autonomous car you need geodesists,[br]metrology. This talk is specifically about
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physical geodesy, which is the mapping of[br]the gravitational field of the earth, and
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in this case specifically with satellites.[br]So I drop stuff on the earth, which is
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terrestrial gravimetry, this talk is about[br]satellite gravimetry. Now gravity and
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gravitation, we usually talk about[br]gravitational potential. This is a scalar
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field. Gravitational acceleration is the[br]gradient of the gravitational potential
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and when we talk about gravity in geodesy,[br]it's usually the combination of attraction
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of the masses, gravitation, and the[br]centrifugal acceleration, but here we talk
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mostly about gravitation. And the[br]potential can easily be calculated, at
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least according to this very short[br]equation. We have G, which is the
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gravitational constant of the earth, or[br]other planets if you want to do. We have
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an ugly triple integral about the whole[br]earth, and this is basically what breaks
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the neck. We have to integrate about the[br]whole mass of the earth, we divide up into
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small parts and we need to know the[br]density of these parts. So, density times
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small volume, you have the mass of the[br]earth if you integrate over it. So what,
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the density of the whole earth is not[br]known. So if you want to calculate the
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potential sufficiently, you would need the[br]density of a penguin on the other side of
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the world. We don't know that. So, what[br]do you do if you cannot calculate the
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quantity? You write a proposal and get all[br]the funding. This is what happened about,
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let's say, twenty years ago, and the[br]result was the gravity recovery and
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climate experiment, or GRACE for short. In[br]this talk, we will only cover gravity
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recovery, so gravity field of the Earth.[br]As we can see, these are two satellites.
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They are flying in the same orbit, and the[br]main instrument is distance measurement
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between these two satellites, Here we see[br]the two satellites prior to its launch in
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2002, and this K-Band Microwave ranging,[br]which is the instrument, gives us a high
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resolution gravity field of the Earth.[br]This is spatial resolution of around 200
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kilometers (km). You might think 200 km is[br]not really high resolution, but we have it
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for the whole planet and not, let's say,[br]for Germany. And also we got the temporal
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variations. So for 15 years now, we have[br]each month, with only a few exceptions, a
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picture of the gravitational field of the[br]earth. The satellites fly in height of
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about 450 km, 220 km apart, and we see[br]here the orbits of a single day. So 15
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orbits per day, and we take one month of[br]data to generate one gravity field. The
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working principle is quite simple: The[br]distance between the two satellites is
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affected by gravity, so we measure the[br]distance and then we calculate gravity. In
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a homogenous gravity field, this is quite[br]simple: Let's say we take a spherical
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earth, it has only a single density, the[br]satellites fly along, and the distance
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between the two satellites does not[br]change. There is nothing to pull one or
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another, they just move along, not[br]changing the distance. Now we introduce a
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mass, let's say a mountain, this can be[br]any mass change or density change
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somewhere inside the earth, and the[br]leading satellite experiences a
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gravitational pull by this mass. And as[br]gravitation falls off with distance, it is
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a stronger than the pull experienced by[br]the trailing satellite. So the distance
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between the two satellites increases. Now,[br]the satellite, the trailing the leading
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satellite has passed the mass, and it is[br]still feeling its gravitational pull, but
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now it is being decelerated because the[br]mass is behind. And the trailing satellite
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is still being accelerated towards the[br]mass. This means the distance between the
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satellites decreases. And finally, the[br]second satellite passes the mass and it
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now also feels the gravitational pull[br]decelerating the satellite. The leading
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satellite is feeling less and less[br]gravitational pull and once both
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satellites left the gravitational[br]influence of this mass, we will have the
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same distance as prior to encountering the[br]mass. So the gravitational acceleration is
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a zero sum at this point. So of course,[br]the Earth is a little more complex than a
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single mountain or a single density[br]anomaly in the ground, but this is the
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basic concept. Now, how do we come from[br]these measurements to the actual
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potential? The formula is basically the[br]same as a couple of slides earlier. We are
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still calculating the potential. It looks[br]more complicated, but we don't have triple
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integrals anymore, and all these[br]quantities in here are basically easily
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calculated. We start with the[br]gravitational constant and the mass of the
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earth, which we can get from a physics[br]book, if we like. And then we have a
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couple of geometric quantities, a and r[br]are basically the size of my earth
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ellipsoid, the major axes and r is the[br]distance from a calculating point, let's
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say this podium, for which I want to know[br]the potential value to the center of the
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ellipsoid. And then we have lambda and[br]theta at the end, these are the
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geographical coordinates of this podium. P[br]is short for the associated Legendre
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functions, also depending solely on[br]geometry, not on the mass of the earth,
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depending on the software where you want[br]to implement this formula, it probably has
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already a function to calculate this, and[br]if not, it is easily done by yourself as
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the formulas look very long, but they are[br]quite simple. The interesting part are the
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two parameters C and S, these are[br]spherical harmonic coefficients. They
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include all the information about the[br]mass of the earth, as measured by the
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satellites. So we have the satellites in[br]space, and the user gets just the C and S
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coefficients, which are a couple of[br]thousand for the gravity field. Implements
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this formula and has a potential value.[br]So, these spherical harmonic coefficients
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are calculated from the GRACE Level 1B[br]products. These are the actual
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measurements done by the satellites. This[br]is the ranging information, the distance
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between satellites, satellite orbits, star[br]camera data, and so on. You add a couple
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of additional models for earth's gravity,[br]which you do not want to include in your
0:11:14.309,0:11:19.550
satellite gravity field, and then you do[br]your processing. This is done by a couple
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of different groups JPL and GFZ, which is[br]a German research center for the
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geosciences. CSR is the center for space[br]research at university Austin. These three
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institutes also provides these GRACE Level[br]1B data. So they take the raw satellite
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data, process it to theGRACE Level 1B[br]products, which are accessible for all
0:11:47.529,0:11:54.420
users, and then calculate further these[br]coefficients, C and S. But there are also
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additional groups who provide gravity[br]fields who calculate these coefficients,
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for example, Institute for Geodesy of the[br]University of Graz, or the Astronomical
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Institute of the University of Bern. They[br]all have slightly different approaches to
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topic and come to more or less the same[br]conclusions. There are countless papers,
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comparing these different gravity fields[br]with each other, but the user usually
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starts with the coefficients C and S, and[br]then it takes a formula like the one on
0:12:25.829,0:12:31.639
top of this slide and calculates your[br]gravity value or whatever you want. Now,
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I'm talking about potential, I'm talking[br]about accelaration. These are not really
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useful quantities in day to day life. If[br]someone told to you in Greenland gravity
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decrease by 50 microGal, you have two[br]choices, you can say "wow, awesome" or you
0:12:48.440,0:12:53.910
can say "oh no, we're all gonna die" It's[br]a 50:50 chance you'd say the correct
0:12:53.910,0:13:01.350
thing. So we are looking for a more useful[br]representation of the changes in
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gravity field. Now gravity field reflects[br]mass redistributions and the most dynamic
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redistribution we have is water storage,[br]summer/winter, more snow, more rain, less
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water in summer, so we express our gravity[br]change in a unit called equivalent water
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height. This is the layer of water on the[br]surface with a thickness, equivalent to
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the mass change measured with the[br]satellites. This is also easily
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calculated. This is my last equation, I[br]promise, but this looks familiar. The
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second half of this equation, is basically[br]the same we saw one slide prior and the
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parameters in front of the sum is the[br]average density of earth, which is around
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5500 kg/m^3. We need the density or water,[br]let's say it 1000 kg/m^3. And in this
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fraction in the middle, we need to[br]parameter K, which are the so-called Love
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numbers. Now, this is not a numerical[br]representation of mutual attraction, but
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was put forward by, I think, Albert Love[br]in 1911, and they are parameters
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concerning the elastic response of the[br]earth to forces. So, if you put a lot of
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weight on a part of the earth, the earth[br]deforms and these parameters, describe the
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elastic response of the earth to such[br]loading. Now we have calculated our
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equivalent water height, let's say for two[br]months, let's say, in May 2002 and 15
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years later in May 2017 and we just[br]subtract these two gravity fields, these
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two equivalent waterheights, from these[br]two epoches. What we have left is the
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change in gravity between these 2 epochs, [br]15 years apart, expressed in water layer
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equivalent to the change in gravity[br]measured. And we can see a couple of
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features here. There should not be any[br]seasonal variations because it's the same
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month, just 15 years apart. So we see long[br]term gravity change between these two
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epochs. And what we see is, for example,[br]mass loss in the northern and southern ice
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shields, and we see two red blobs, one in[br]northern canada and one in northern
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europe, which are geophysical processes.[br]So this is glacial isostastic adjustment
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and during the last ice age the ice[br]shields deformed the earth downward.
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The material in the "Mantel" had to flow[br]aside, and now that the ice is gone, the
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lead is uplifting and the material in the[br]"Mantel" is flowing back. So it's flowing
0:16:10.059,0:16:14.459
back and the earth is uplifting. This[br]process has been going on for 10000 years
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and will probably a couple of years[br]longer. Now how do you get your data?
0:16:23.279,0:16:27.009
Everyone can get the GRACE Level 1B data,[br]which are the observations by the
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satellite, like again, ranging information[br]between the satelite, orbits,
0:16:32.399,0:16:39.949
accelerometer data, star camera data and[br]so on. You can get them without hurdles at
0:16:39.949,0:16:44.919
the ISDC, which is the information system,[br]a data center at the Geoforschungszentrum
0:16:44.919,0:16:53.740
Potsdam, or at the Physical Oceanography [br]Distributed Active Archive Center run by
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JPL. And if you'd like, you can calculate[br]your own spherical harmonic coefficients
0:16:59.879,0:17:06.269
for gravity fields. Or you can compare for[br]example, satelite orbits they give you
0:17:06.269,0:17:11.199
with one you integrated yourself using[br]your own gravity field, to see if they fit
0:17:11.199,0:17:19.910
together or not. You can get gravity field[br]models, if you'd like. A large collection
0:17:19.910,0:17:25.609
is at the International Centre for Global[br]Earth Models. They have recent and
0:17:25.609,0:17:30.789
historic gravity models all in the same[br]data format. So you only need to implement
0:17:30.789,0:17:36.639
your software once from the 1970s to[br]today. They also have the proper
0:17:36.639,0:17:43.070
references, the papers you want to read to[br]work with them. These are so-called Level
0:17:43.070,0:17:47.510
2 Products. So, you can take a gravity[br]field from there, use the equation, I
0:17:47.510,0:17:51.528
showed you earlier and calculate your[br]equivalent water height, if you'd like.
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If you don't want to do this, there is[br]someone to help you, a service called
0:17:56.529,0:18:01.809
"TELLUS", which is a play on words I[br]don't want to go into detail about. They
0:18:01.809,0:18:08.330
offer equivalent water heights calculated[br]for each monthly solution from the GRACE
0:18:08.330,0:18:13.870
satellites. This tells us a lot about the[br]earth, if you look closer into it. In the
0:18:13.870,0:18:20.500
following, I will use the monthly[br]solutions from the ITSG-GRACE 2016,
0:18:20.500,0:18:25.860
provided by Institute for Geodesy at[br]University of Graz. The previous graph I
0:18:25.860,0:18:32.289
showed you was also created with that[br]gravity model. I will not go into detail
0:18:32.289,0:18:40.140
about further processing like filtering[br]and gravity reductions done to this, not
0:18:40.140,0:18:47.120
enough time. So here are some results,[br]let's start with the most obvious one, the
0:18:47.120,0:18:54.919
greenland ice shield, which has, as we saw[br]earlier, the greatest loss of mass
0:18:54.919,0:19:04.460
according to the gravity field and we see[br]here, a water layer on the whole landmass,
0:19:04.460,0:19:10.142
describing the loss of mass expressed as a[br]water layer of a certain thickness.
0:19:10.142,0:19:15.337
So let's say in the southern tip, you have[br]one meter water layer. This would be
0:19:15.337,0:19:23.700
equvalent in gravity to the actual mass[br]lost in Greenland. But we also see, that
0:19:23.700,0:19:28.950
the signal is not very localized. So it's[br]not bound to the land mass. It's also in
0:19:28.950,0:19:34.910
the ocean. This effect is called leakage.[br]If you do signal processing you will know
0:19:34.910,0:19:45.471
this. There are methods to reduce leakage.[br]My next slide will show such a result, but
0:19:45.471,0:19:49.110
I have done no reduction to this. So if[br]you use my formula I showed you, you will
0:19:49.110,0:19:55.710
pretty much get a result like this. This[br]gives you a trend of around 280 gigatons
0:19:55.710,0:20:01.679
per year in mass loss over the whole land[br]mass of greenland. And now gigatons is
0:20:01.679,0:20:08.470
also not very useful an expression. One[br]cubic meter of water has a weight of a
0:20:08.470,0:20:15.850
1000 kilos; one tonne, 1 gigatonne is[br]10^9 tonne, if you are familiar with ball
0:20:15.850,0:20:23.792
sports, 1 soccer field with the 140 km[br]high water column has the weight of
0:20:23.792,0:20:33.490
1 gigatonne, or if you are not fan of sports[br]ball, if you're more of a plane guy or girl
0:20:33.490,0:20:42.690
the A380-800 has a maximum takeoff weight[br]of 575 tonne, so we need 1.7 mio of these
0:20:42.690,0:20:52.950
airplanes for one gigatonne. So this is a more[br]beautiful representation of the process in
0:20:52.950,0:20:58.929
greenland, done by NASA JPL. If you go to[br]the website of the GRACE project, they
0:20:58.929,0:21:06.441
have a couple of these illustrations, they[br]obviously worked hard on the leakage.
0:21:06.441,0:21:12.460
You can see localized where most of the[br]gravity, most of the mass is lost on the
0:21:12.460,0:21:20.490
left and on the right you see accumulated[br]over time, the mass which is lost, and
0:21:20.490,0:21:26.539
which trend it gives you. Also, if look[br]closely in the center of greenland, you
0:21:26.539,0:21:36.577
see black lines, these are the ice flow,[br]as determined by radar interferometry.
0:21:36.577,0:21:43.000
So now pretty much know where ice is lost,[br]where mass is lost. This goes into the
0:21:43.000,0:21:52.029
ocean, and this would be a good idea to[br]see, to check our GRACE results, the mass
0:21:52.029,0:21:56.799
we find missing on earth, so the melted[br]ice, and the additional mass in the ocean,
0:21:56.799,0:22:03.700
does this agree with other methods who[br]determine the sea level rise. One of these
0:22:03.700,0:22:09.289
methods is satellite radar altimetry, that[br]started in the 70's, but since 1991, we
0:22:09.289,0:22:15.269
have lots of dedicated satellite missions,[br]which only job is basically mapping the
0:22:15.269,0:22:21.540
global sea surface. So, they send down a[br]radar pulse, which is reflected at the sea
0:22:21.540,0:22:27.049
surface. They measure the run time and[br]then they have a geometric representation
0:22:27.049,0:22:35.480
of the global sea surface. Now, if we[br]compare this with the mass we calculated
0:22:35.480,0:22:41.330
or we got from the GRACE result, calculate[br]a sea level rise rise from this additional
0:22:41.330,0:22:46.580
mass in the ocean than these two systems[br]would not add up. The geometric sea level
0:22:46.580,0:22:51.820
rise is higher than just the additional[br]mass. So there is the second process which
0:22:51.820,0:22:58.759
is thermal expansion of the water. If[br]water gets warm it needs more space.
0:22:58.759,0:23:07.159
In 2000 the deployment of so-called ARGO[br]floats started. These are free-floating
0:23:07.159,0:23:13.389
devices in the ocean. Currently, there are[br]over 3000 and they measure temperature and
0:23:13.389,0:23:20.679
salinity between sea surface and a depth[br]of 2000 meters. These are globally
0:23:20.679,0:23:28.870
distributed. So, we have at least for the[br]upper layer of the ocean, how much thermal
0:23:28.870,0:23:36.710
expansion there is. And what we want to[br]see is, do these components of additional
0:23:36.710,0:23:41.450
mass in the ocean as determined by GRACE[br]and thermal expansion of the upper ocean
0:23:41.450,0:23:47.460
layer come to the same result as[br]geometrical measurements done by satellite
0:23:47.460,0:23:52.900
altimetry? On the left we see an image[br]taken from the last IPCC report on climate
0:23:52.900,0:23:59.769
change from 2013. In green we see the[br]sealevel rise as measured with satellite
0:23:59.769,0:24:06.279
altimetry in the time span 2005 to 2012[br]and in orange we see the combination of
0:24:06.279,0:24:13.200
additional mass, as measured by GRACE, and[br]thermal extension as determined with ARGO
0:24:13.200,0:24:21.720
inside the ocean. And these 2 graphs follow[br]each other quite well. On the right. We
0:24:21.720,0:24:27.799
see a recent publication by Chen, Wilson[br]and Tapley, the latter one being one of
0:24:27.799,0:24:34.460
the PIs of the GRACE mission, who[br]accumulated the data from 2005 to 2011. We
0:24:34.460,0:24:41.350
basically come to the same conclusion. So[br]now if you really don't want to do the
0:24:41.350,0:24:48.870
math, there are online services who make[br]the graphs for you. One of those is
0:24:48.870,0:24:55.219
EGSIEM European Gravity Service for[br]Improved Emergency Control. If we can
0:24:55.219,0:25:00.659
measure how much water is stored in a certain[br]area, we know that this amount of water
0:25:00.659,0:25:04.929
has sooner or later to be removed from[br]this area. This can be a flood, for
0:25:04.929,0:25:08.840
example, and with a mission like GRACE, we[br]can determine how much mass, how much
0:25:08.840,0:25:15.289
water is there and are the rivers large[br]enough to allow for this water to be
0:25:15.289,0:25:22.970
flowing away. That was the intention[br]behind this service. Oops, no, this is not
0:25:22.970,0:25:39.299
the future. So, I wanted to do the life[br]demo but. So, yeah, the live demo did not
0:25:39.299,0:25:46.909
work as expected. So, you will be greeted[br]with this graphic. You can plot for all
0:25:46.909,0:25:50.649
areas in the world. The first thing you[br]have to do is you change your gravity
0:25:50.649,0:25:56.989
functional, we want water heights. This is[br]what I talked about in this talk. Then you
0:25:56.989,0:26:03.200
want to look at the data set and at the[br]bottom you see a large list of GRACE
0:26:03.200,0:26:07.190
gravity fields. These are different[br]groups, I mentioned, providing these
0:26:07.190,0:26:15.440
monthly solutions. And so we choose one of[br]these groups. Then we choose an area which
0:26:15.440,0:26:21.809
we are interested in. You can freely[br]choose one area like here Finno-Scandia,
0:26:21.809,0:26:29.070
or you can use pre-determined areas, for[br]example, the Amazon river basin or Elbe
0:26:29.070,0:26:35.570
river or something like that. These areas[br]all over the world and you can see the
0:26:35.570,0:26:41.059
gravity change in this area. So let's look[br]here at Finno-Scandia, and then you are
0:26:41.059,0:26:47.250
greeted with a plot like this. This is[br]equivalent water height, even though this
0:26:47.250,0:26:51.740
is a geophysical process. So we see here[br]the layer of water, which would have been
0:26:51.740,0:27:01.580
added to the region as selected, and we[br]see a clear trend upward. Again, this is a
0:27:01.580,0:27:08.750
geophysical process. This is not[br]additional ice or water or anything. Can I
0:27:08.750,0:27:20.240
return to my...? No, I cannot. So, yeah,[br]live demo did not work. If you want to do
0:27:20.240,0:27:26.710
this yourself. I have uploaded to the[br]Fahrplan all my resources, all my links.
0:27:26.710,0:27:31.510
And the EGSIEM page also includes the[br]description of what is done in the backend
0:27:31.510,0:27:37.649
and were the data comes from and what you[br]can see in the various fields. Now I want
0:27:37.649,0:27:42.289
to give a last impression on the future,[br]because unfortunately while I was
0:27:42.289,0:27:46.730
preparing my abstract for this conference,[br]one of the GRACE satellites was turned off
0:27:46.730,0:27:51.750
due to age. It was launched in 2002,[br]planned for a five mission year; it
0:27:51.750,0:27:56.970
survived 15 years, which is quite good,[br]but now we have no more ranging
0:27:56.970,0:28:01.250
information between these satellites. We[br]had ranging information in micrometer
0:28:01.250,0:28:09.049
accuracy, a couple of micrometer, and now[br]we cannot rely on these information
0:28:09.049,0:28:14.320
anymore. And this means mo more gravity[br]fields with high spatial resolution, and
0:28:14.320,0:28:17.799
I'm not sure about the temporal[br]resolution. So, the current work which is
0:28:17.799,0:28:23.270
done is taking all satellites which are in[br]the low-enough orbits and calculate the
0:28:23.270,0:28:26.799
gravity field from their positions,[br]because everything which is in low-earth
0:28:26.799,0:28:32.870
orbit is affected by the Earth's gravity[br]field. So, if I take the satellite orbits,
0:28:32.870,0:28:38.690
look "how does this orbit change" and the[br]reason is gravity, then I can calculate
0:28:38.690,0:28:46.110
the gravity field. Unfortunately, not in[br]this higher resolution we are used to.
0:28:46.110,0:28:50.019
And... But fortunately, there already is a[br]next-generation gravity field mission on
0:28:50.019,0:28:58.410
its way. It arrived last week in the US,[br]where it will be launched in late March,
0:28:58.410,0:29:05.330
early April by SpaceX. You might look at[br]this image and think, "I just saw this
0:29:05.330,0:29:10.990
earlier" and you are quite correct: The[br]mission called "Grace Follow On" is a copy
0:29:10.990,0:29:16.419
of Grace, which improved components, of[br]course, and now with lasers. We see not
0:29:16.419,0:29:21.500
only the microwave ranging between the two[br]satellites, but additionally a laser
0:29:21.500,0:29:26.289
interferometer. So, from micrometer[br]accuracy in the distance measurements we
0:29:26.289,0:29:33.324
go to nanometer accuracy, hopefully. But[br]the main instrument will be the
0:29:33.324,0:29:36.669
microwave ranging. So, in conclusion,
0:29:36.669,0:29:42.130
I hope I showed you that the gravity field[br]can show mass transport on the surface and
0:29:42.130,0:29:47.889
inside the Earth; that this offers, in[br]combination with other methods, new
0:29:47.889,0:29:54.179
insights and also some kind of mutual[br]verification. If several different types
0:29:54.179,0:29:57.960
of observations coming to the same[br]conclusion, none of them can be awfully
0:29:57.960,0:30:03.700
wrong; and that the access to these[br]methods are relatively easy: the data is
0:30:03.700,0:30:09.480
available, all the methods are described[br]in geodesy textbooks and the technical
0:30:09.480,0:30:14.600
documentation; and there are other[br]applications, other than, let's say,
0:30:14.600,0:30:22.029
climate change; you can look into drought[br]and flood prediction; the El Niño–Southern
0:30:22.029,0:30:29.989
Oscillation you can predict from Grace's[br]gravity field data. So, lot's of work to do.
0:30:29.989,0:30:35.929
So, this would be the end for my talk.[br]I thank you for your interest in the topic.
0:30:35.929,0:30:46.775
applause
0:30:46.775,0:30:51.250
Herald: Thank you, Manuel, for the talk.[br]And I think we have time for one or two,
0:30:51.250,0:30:57.350
maybe two very short questions. Please be[br]seated during the Q&A session. Is there
0:30:57.350,0:31:02.250
some questions? Okay, microphone 3,[br]please.
0:31:02.250,0:31:05.741
Mic 3: Yeah, hi. In a quiet voice[br]Hi, hello? Can you hear me? Now loud
0:31:05.741,0:31:07.859
Herald: Yeah.[br]Mic 3: Okay. Hey. So, my question is
0:31:07.859,0:31:12.945
regarding acceleration. What's the[br]influence of Earth atmosphere and all the
0:31:12.945,0:31:18.678
planetary bodies, like the moon, and does[br]it need to be accounted for?
0:31:18.678,0:31:22.236
Manuel: The external gravity needs to be[br]accounted for, so the tidal effects of sun
0:31:22.236,0:31:26.976
and moon would be one of those additional[br]models you put into the processing of the
0:31:26.976,0:31:32.340
satellite data. The Earth's atmosphere has[br]an effect on the satellites themselves,
0:31:32.340,0:31:37.159
which is measured onboard by[br]accelerometers and then reduced. And the
0:31:37.159,0:31:43.289
gravitational effect of the atmosphere:[br]Part of this is averaged out, because we
0:31:43.289,0:31:48.369
take a month of time series, and the rest[br]are also inclu... provide as extra
0:31:48.369,0:31:54.279
products; at least by the Institute for[br]Geodesy in Graz. So atmosphere... the mass
0:31:54.279,0:31:58.900
of the atmosphere is... has to be[br]accounted for, yes.
0:31:58.900,0:32:04.280
Herald: Okay. Microphone 2 has vanished[br]all of a sudden. Then, microphone 1,
0:32:04.280,0:32:08.700
please.[br]Mic 1: Hi. Is it possible to measure
0:32:08.700,0:32:16.206
changes in the temperature of the oceans[br]or of the ocean streams, like... Can you
0:32:16.206,0:32:25.362
see if El Niño is active by just measuring[br]the gravity... change in gravity fields?
0:32:25.362,0:32:29.999
Manuel: As a precursor tool, El Niño, as I[br]understand it... certain regions of the
0:32:29.999,0:32:35.690
ocean get warmer; it's a density change;[br]and, of course, this would be measured as
0:32:35.690,0:32:42.070
part of ARGO and it's also in the GRACE[br]gravity field. There are probably papers
0:32:42.070,0:32:47.799
on it. So, the last... the extend of the[br]last El Niño was predicted by GRACE. I
0:32:47.799,0:32:51.665
don't know to what extend this was[br]correct, but...
0:32:51.665,0:32:55.360
Mic 1: Okay, then.[br]Herald: Good. Then, that's all the time we
0:32:55.360,0:32:57.924
have. A big round of applause for Manuel[br]and his talk, please.
0:32:57.924,0:33:00.690
Applause
0:33:00.690,0:33:07.790
34C3 Music
0:33:07.790,0:33:22.000
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