1 00:00:00,099 --> 00:00:15,749 *34C3 preroll music* 2 00:00:15,749 --> 00:00:22,160 Herald: Hello everybody to the next talk, here at stage Clarke. The next talk will 3 00:00:22,160 --> 00:00:26,910 be held in English. And here is a quick announcement in German for the 4 00:00:26,910 --> 00:00:32,833 translation. Der nächste Vortrag wird in Englisch sein. Und wir haben eine deutsche 5 00:00:32,833 --> 00:00:42,239 Übersetzung unter streaming.c3lingo.org. Und wir haben das auch auf einer Folie. 6 00:00:42,239 --> 00:00:48,760 Und es wird auch eine französische Übersetzung geben für diesen Vortrag. 7 00:00:48,760 --> 00:00:55,569 There will also be a french translation, as well as an German translation for the 8 00:00:55,569 --> 00:01:04,239 next talk. And you can find everything under streaming.c3lingo.org. And, I hope, 9 00:01:04,239 --> 00:01:18,140 displayed behind me. The next talk is called "Watching the changing Earth". 10 00:01:18,140 --> 00:01:23,890 Satellite data and change in the gravitational field of the earth can tell 11 00:01:23,890 --> 00:01:29,939 us a lot, especially when there's so much public domain satelite data coming in from 12 00:01:29,939 --> 00:01:36,109 different projects or maybe CC-BY satellite data. And how this is done, this 13 00:01:36,109 --> 00:01:43,539 new knowledge finding out of this big heap of data, this will be explained by 14 00:01:43,539 --> 00:01:50,399 Manuel in the talk. He dropped stuff to see if gravity still works, or, in fancy 15 00:01:50,399 --> 00:02:00,045 words, he does gravimetric methods and sensory in geodesy. Is that pronounced 16 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 17 00:02:06,210 --> 00:02:09,860 Manuel. *Applause* 18 00:02:09,860 --> 00:02:26,330 *No Audio* Manuel: Geiler Scheiß. Oh, das war Sound. 19 00:02:26,330 --> 00:02:29,860 So again, so hello and welcome to my presentation on watching the changing 20 00:02:29,860 --> 00:02:35,540 earth. This year's call for papers for the Congress offered me the opportunity to 21 00:02:35,540 --> 00:02:42,190 talk about my work in the related fields, which is gravity. As far as Congress is 22 00:02:42,190 --> 00:02:46,870 concerned, a misunderstood force of nature. So in the following couple of 23 00:02:46,870 --> 00:02:53,200 minutes, I want to talk about gravity, gravitation, about the GRACE satellite 24 00:02:53,200 --> 00:02:59,180 mission, which maps the earth gravity field every month, about the gravity 25 00:02:59,180 --> 00:03:03,790 fields, and I will show good results and then we will go forward into the future. 26 00:03:03,790 --> 00:03:11,080 That's nice. So it's actually called, actually called geodesy. Let me give you a 27 00:03:11,080 --> 00:03:16,480 short introduction on geodesy. Friedrich Robert Helmert defined it in 1880 at as 28 00:03:16,480 --> 00:03:21,320 the science of mapping and measuring the earth on its surface, and this still holds 29 00:03:21,320 --> 00:03:29,752 up today. It depends on your methods and applications, but he was correct. The most 30 00:03:29,752 --> 00:03:34,611 known profession is probably land surveying, people with colorful 31 00:03:34,611 --> 00:03:39,530 instruments and traffic cones. You find them on construction sites, on the side of 32 00:03:39,530 --> 00:03:44,610 the road, but we actually have a lot of applications not only in geodesy but in 33 00:03:44,610 --> 00:03:49,590 related fields like geophysics, fundamental physics, if you want to build 34 00:03:49,590 --> 00:03:57,010 an autonomous car you need geodesists, metrology. This talk is specifically about 35 00:03:57,010 --> 00:04:02,040 physical geodesy, which is the mapping of the gravitational field of the earth, and 36 00:04:02,040 --> 00:04:07,650 in this case specifically with satellites. So I drop stuff on the earth, which is 37 00:04:07,650 --> 00:04:15,300 terrestrial gravimetry, this talk is about satellite gravimetry. Now gravity and 38 00:04:15,300 --> 00:04:19,940 gravitation, we usually talk about gravitational potential. This is a scalar 39 00:04:19,940 --> 00:04:25,850 field. Gravitational acceleration is the gradient of the gravitational potential 40 00:04:25,850 --> 00:04:31,840 and when we talk about gravity in geodesy, it's usually the combination of attraction 41 00:04:31,840 --> 00:04:37,490 of the masses, gravitation, and the centrifugal acceleration, but here we talk 42 00:04:37,490 --> 00:04:42,361 mostly about gravitation. And the potential can easily be calculated, at 43 00:04:42,361 --> 00:04:47,850 least according to this very short equation. We have G, which is the 44 00:04:47,850 --> 00:04:52,870 gravitational constant of the earth, or other planets if you want to do. We have 45 00:04:52,870 --> 00:04:58,270 an ugly triple integral about the whole earth, and this is basically what breaks 46 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 47 00:05:04,330 --> 00:05:11,020 small parts and we need to know the density of these parts. So, density times 48 00:05:11,020 --> 00:05:16,170 small volume, you have the mass of the earth if you integrate over it. So what, 49 00:05:16,170 --> 00:05:19,680 the density of the whole earth is not known. So if you want to calculate the 50 00:05:19,680 --> 00:05:25,120 potential sufficiently, you would need the density of a penguin on the other side of 51 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 52 00:05:29,210 --> 00:05:35,780 quantity? You write a proposal and get all the funding. This is what happened about, 53 00:05:35,780 --> 00:05:40,470 let's say, twenty years ago, and the result was the gravity recovery and 54 00:05:40,470 --> 00:05:46,780 climate experiment, or GRACE for short. In this talk, we will only cover gravity 55 00:05:46,780 --> 00:05:54,530 recovery, so gravity field of the Earth. As we can see, these are two satellites. 56 00:05:54,530 --> 00:05:59,280 They are flying in the same orbit, and the main instrument is distance measurement 57 00:05:59,280 --> 00:06:06,400 between these two satellites, Here we see the two satellites prior to its launch in 58 00:06:06,400 --> 00:06:12,000 2002, and this K-Band Microwave ranging, which is the instrument, gives us a high 59 00:06:12,000 --> 00:06:17,330 resolution gravity field of the Earth. This is spatial resolution of around 200 60 00:06:17,330 --> 00:06:23,150 kilometers (km). You might think 200 km is not really high resolution, but we have it 61 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 62 00:06:29,300 --> 00:06:35,040 variations. So for 15 years now, we have each month, with only a few exceptions, a 63 00:06:35,040 --> 00:06:41,320 picture of the gravitational field of the earth. The satellites fly in height of 64 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 65 00:06:49,290 --> 00:06:55,771 orbits per day, and we take one month of data to generate one gravity field. The 66 00:06:55,771 --> 00:06:59,990 working principle is quite simple: The distance between the two satellites is 67 00:06:59,990 --> 00:07:05,697 affected by gravity, so we measure the distance and then we calculate gravity. In 68 00:07:05,697 --> 00:07:10,270 a homogenous gravity field, this is quite simple: Let's say we take a spherical 69 00:07:10,270 --> 00:07:16,990 earth, it has only a single density, the satellites fly along, and the distance 70 00:07:16,990 --> 00:07:21,419 between the two satellites does not change. There is nothing to pull one or 71 00:07:21,419 --> 00:07:27,680 another, they just move along, not changing the distance. Now we introduce a 72 00:07:27,680 --> 00:07:33,810 mass, let's say a mountain, this can be any mass change or density change 73 00:07:33,810 --> 00:07:38,940 somewhere inside the earth, and the leading satellite experiences a 74 00:07:38,940 --> 00:07:44,740 gravitational pull by this mass. And as gravitation falls off with distance, it is 75 00:07:44,740 --> 00:07:49,330 a stronger than the pull experienced by the trailing satellite. So the distance 76 00:07:49,330 --> 00:07:58,810 between the two satellites increases. Now, the satellite, the trailing the leading 77 00:07:58,810 --> 00:08:05,010 satellite has passed the mass, and it is still feeling its gravitational pull, but 78 00:08:05,010 --> 00:08:10,560 now it is being decelerated because the mass is behind. And the trailing satellite 79 00:08:10,560 --> 00:08:16,450 is still being accelerated towards the mass. This means the distance between the 80 00:08:16,450 --> 00:08:24,710 satellites decreases. And finally, the second satellite passes the mass and it 81 00:08:24,710 --> 00:08:30,669 now also feels the gravitational pull decelerating the satellite. The leading 82 00:08:30,669 --> 00:08:34,659 satellite is feeling less and less gravitational pull and once both 83 00:08:34,659 --> 00:08:39,389 satellites left the gravitational influence of this mass, we will have the 84 00:08:39,389 --> 00:08:44,240 same distance as prior to encountering the mass. So the gravitational acceleration is 85 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 86 00:08:51,009 --> 00:08:56,800 single mountain or a single density anomaly in the ground, but this is the 87 00:08:56,800 --> 00:09:04,480 basic concept. Now, how do we come from these measurements to the actual 88 00:09:04,480 --> 00:09:14,292 potential? The formula is basically the same as a couple of slides earlier. We are 89 00:09:14,292 --> 00:09:21,180 still calculating the potential. It looks more complicated, but we don't have triple 90 00:09:21,180 --> 00:09:24,930 integrals anymore, and all these quantities in here are basically easily 91 00:09:24,930 --> 00:09:30,950 calculated. We start with the gravitational constant and the mass of the 92 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 93 00:09:35,470 --> 00:09:42,519 couple of geometric quantities, a and r are basically the size of my earth 94 00:09:42,519 --> 00:09:48,709 ellipsoid, the major axes and r is the distance from a calculating point, let's 95 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 96 00:09:53,220 --> 00:09:57,399 ellipsoid. And then we have lambda and theta at the end, these are the 97 00:09:57,399 --> 00:10:06,029 geographical coordinates of this podium. P is short for the associated Legendre 98 00:10:06,029 --> 00:10:11,730 functions, also depending solely on geometry, not on the mass of the earth, 99 00:10:11,730 --> 00:10:16,769 depending on the software where you want to implement this formula, it probably has 100 00:10:16,769 --> 00:10:22,110 already a function to calculate this, and if not, it is easily done by yourself as 101 00:10:22,110 --> 00:10:28,429 the formulas look very long, but they are quite simple. The interesting part are the 102 00:10:28,429 --> 00:10:34,980 two parameters C and S, these are spherical harmonic coefficients. They 103 00:10:34,980 --> 00:10:38,790 include all the information about the mass of the earth, as measured by the 104 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 105 00:10:44,731 --> 00:10:51,277 coefficients, which are a couple of thousand for the gravity field. Implements 106 00:10:51,277 --> 00:10:56,760 this formula and has a potential value. So, these spherical harmonic coefficients 107 00:10:56,760 --> 00:11:01,190 are calculated from the GRACE Level 1B products. These are the actual 108 00:11:01,190 --> 00:11:04,499 measurements done by the satellites. This is the ranging information, the distance 109 00:11:04,499 --> 00:11:11,120 between satellites, satellite orbits, star camera data, and so on. You add a couple 110 00:11:11,120 --> 00:11:14,309 of additional models for earth's gravity, which you do not want to include in your 111 00:11:14,309 --> 00:11:19,550 satellite gravity field, and then you do your processing. This is done by a couple 112 00:11:19,550 --> 00:11:27,170 of different groups JPL and GFZ, which is a German research center for the 113 00:11:27,170 --> 00:11:33,329 geosciences. CSR is the center for space research at university Austin. These three 114 00:11:33,329 --> 00:11:39,810 institutes also provides these GRACE Level 1B data. So they take the raw satellite 115 00:11:39,810 --> 00:11:47,529 data, process it to theGRACE Level 1B products, which are accessible for all 116 00:11:47,529 --> 00:11:54,420 users, and then calculate further these coefficients, C and S. But there are also 117 00:11:54,420 --> 00:11:59,750 additional groups who provide gravity fields who calculate these coefficients, 118 00:11:59,750 --> 00:12:04,350 for example, Institute for Geodesy of the University of Graz, or the Astronomical 119 00:12:04,350 --> 00:12:11,660 Institute of the University of Bern. They all have slightly different approaches to 120 00:12:11,660 --> 00:12:16,160 topic and come to more or less the same conclusions. There are countless papers, 121 00:12:16,160 --> 00:12:20,689 comparing these different gravity fields with each other, but the user usually 122 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 123 00:12:25,829 --> 00:12:31,639 top of this slide and calculates your gravity value or whatever you want. Now, 124 00:12:31,639 --> 00:12:36,749 I'm talking about potential, I'm talking about accelaration. These are not really 125 00:12:36,749 --> 00:12:42,769 useful quantities in day to day life. If someone told to you in Greenland gravity 126 00:12:42,769 --> 00:12:48,440 decrease by 50 microGal, you have two choices, you can say "wow, awesome" or you 127 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 128 00:12:53,910 --> 00:13:01,350 thing. So we are looking for a more useful representation of the changes in 129 00:13:01,350 --> 00:13:07,329 gravity field. Now gravity field reflects mass redistributions and the most dynamic 130 00:13:07,329 --> 00:13:15,870 redistribution we have is water storage, summer/winter, more snow, more rain, less 131 00:13:15,870 --> 00:13:25,600 water in summer, so we express our gravity change in a unit called equivalent water 132 00:13:25,600 --> 00:13:31,950 height. This is the layer of water on the surface with a thickness, equivalent to 133 00:13:31,950 --> 00:13:39,939 the mass change measured with the satellites. This is also easily 134 00:13:39,939 --> 00:13:47,179 calculated. This is my last equation, I promise, but this looks familiar. The 135 00:13:47,179 --> 00:13:55,480 second half of this equation, is basically the same we saw one slide prior and the 136 00:13:55,480 --> 00:14:02,529 parameters in front of the sum is the average density of earth, which is around 137 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 138 00:14:13,709 --> 00:14:19,429 fraction in the middle, we need to parameter K, which are the so-called Love 139 00:14:19,429 --> 00:14:26,149 numbers. Now, this is not a numerical representation of mutual attraction, but 140 00:14:26,149 --> 00:14:33,790 was put forward by, I think, Albert Love in 1911, and they are parameters 141 00:14:33,790 --> 00:14:37,670 concerning the elastic response of the earth to forces. So, if you put a lot of 142 00:14:37,670 --> 00:14:44,330 weight on a part of the earth, the earth deforms and these parameters, describe the 143 00:14:44,330 --> 00:14:51,769 elastic response of the earth to such loading. Now we have calculated our 144 00:14:51,769 --> 00:14:59,120 equivalent water height, let's say for two months, let's say, in May 2002 and 15 145 00:14:59,120 --> 00:15:04,790 years later in May 2017 and we just subtract these two gravity fields, these 146 00:15:04,790 --> 00:15:11,110 two equivalent waterheights, from these two epoches. What we have left is the 147 00:15:11,110 --> 00:15:17,899 change in gravity between these 2 epochs, 15 years apart, expressed in water layer 148 00:15:17,899 --> 00:15:23,069 equivalent to the change in gravity measured. And we can see a couple of 149 00:15:23,069 --> 00:15:28,190 features here. There should not be any seasonal variations because it's the same 150 00:15:28,190 --> 00:15:35,480 month, just 15 years apart. So we see long term gravity change between these two 151 00:15:35,480 --> 00:15:40,129 epochs. And what we see is, for example, mass loss in the northern and southern ice 152 00:15:40,129 --> 00:15:46,379 shields, and we see two red blobs, one in northern canada and one in northern 153 00:15:46,379 --> 00:15:53,009 europe, which are geophysical processes. So this is glacial isostastic adjustment 154 00:15:53,009 --> 00:15:58,800 and during the last ice age the ice shields deformed the earth downward. 155 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 156 00:16:04,579 --> 00:16:10,059 lead is uplifting and the material in the "Mantel" is flowing back. So it's flowing 157 00:16:10,059 --> 00:16:14,459 back and the earth is uplifting. This process has been going on for 10000 years 158 00:16:14,459 --> 00:16:23,279 and will probably a couple of years longer. Now how do you get your data? 159 00:16:23,279 --> 00:16:27,009 Everyone can get the GRACE Level 1B data, which are the observations by the 160 00:16:27,009 --> 00:16:32,399 satellite, like again, ranging information between the satelite, orbits, 161 00:16:32,399 --> 00:16:39,949 accelerometer data, star camera data and so on. You can get them without hurdles at 162 00:16:39,949 --> 00:16:44,919 the ISDC, which is the information system, a data center at the Geoforschungszentrum 163 00:16:44,919 --> 00:16:53,740 Potsdam, or at the Physical Oceanography Distributed Active Archive Center run by 164 00:16:53,740 --> 00:16:59,879 JPL. And if you'd like, you can calculate your own spherical harmonic coefficients 165 00:16:59,879 --> 00:17:06,269 for gravity fields. Or you can compare for example, satelite orbits they give you 166 00:17:06,269 --> 00:17:11,199 with one you integrated yourself using your own gravity field, to see if they fit 167 00:17:11,199 --> 00:17:19,910 together or not. You can get gravity field models, if you'd like. A large collection 168 00:17:19,910 --> 00:17:25,609 is at the International Centre for Global Earth Models. They have recent and 169 00:17:25,609 --> 00:17:30,789 historic gravity models all in the same data format. So you only need to implement 170 00:17:30,789 --> 00:17:36,639 your software once from the 1970s to today. They also have the proper 171 00:17:36,639 --> 00:17:43,070 references, the papers you want to read to work with them. These are so-called Level 172 00:17:43,070 --> 00:17:47,510 2 Products. So, you can take a gravity field from there, use the equation, I 173 00:17:47,510 --> 00:17:51,528 showed you earlier and calculate your equivalent water height, if you'd like. 174 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 175 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 176 00:18:01,809 --> 00:18:08,330 offer equivalent water heights calculated for each monthly solution from the GRACE 177 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 178 00:18:13,870 --> 00:18:20,500 following, I will use the monthly solutions from the ITSG-GRACE 2016, 179 00:18:20,500 --> 00:18:25,860 provided by Institute for Geodesy at University of Graz. The previous graph I 180 00:18:25,860 --> 00:18:32,289 showed you was also created with that gravity model. I will not go into detail 181 00:18:32,289 --> 00:18:40,140 about further processing like filtering and gravity reductions done to this, not 182 00:18:40,140 --> 00:18:47,120 enough time. So here are some results, let's start with the most obvious one, the 183 00:18:47,120 --> 00:18:54,919 greenland ice shield, which has, as we saw earlier, the greatest loss of mass 184 00:18:54,919 --> 00:19:04,460 according to the gravity field and we see here, a water layer on the whole landmass, 185 00:19:04,460 --> 00:19:10,142 describing the loss of mass expressed as a water layer of a certain thickness. 186 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 187 00:19:15,337 --> 00:19:23,700 equvalent in gravity to the actual mass lost in Greenland. But we also see, that 188 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 189 00:19:28,950 --> 00:19:34,910 the ocean. This effect is called leakage. If you do signal processing you will know 190 00:19:34,910 --> 00:19:45,471 this. There are methods to reduce leakage. My next slide will show such a result, but 191 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 192 00:19:49,110 --> 00:19:55,710 pretty much get a result like this. This gives you a trend of around 280 gigatons 193 00:19:55,710 --> 00:20:01,679 per year in mass loss over the whole land mass of greenland. And now gigatons is 194 00:20:01,679 --> 00:20:08,470 also not very useful an expression. One cubic meter of water has a weight of a 195 00:20:08,470 --> 00:20:15,850 1000 kilos; one tonne, 1 gigatonne is 10^9 tonne, if you are familiar with ball 196 00:20:15,850 --> 00:20:23,792 sports, 1 soccer field with the 140 km high water column has the weight of 197 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 198 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 199 00:20:42,690 --> 00:20:52,950 airplanes for one gigatonne. So this is a more beautiful representation of the process in 200 00:20:52,950 --> 00:20:58,929 greenland, done by NASA JPL. If you go to the website of the GRACE project, they 201 00:20:58,929 --> 00:21:06,441 have a couple of these illustrations, they obviously worked hard on the leakage. 202 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 203 00:21:12,460 --> 00:21:20,490 left and on the right you see accumulated over time, the mass which is lost, and 204 00:21:20,490 --> 00:21:26,539 which trend it gives you. Also, if look closely in the center of greenland, you 205 00:21:26,539 --> 00:21:36,577 see black lines, these are the ice flow, as determined by radar interferometry. 206 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 207 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 208 00:21:52,029 --> 00:21:56,799 we find missing on earth, so the melted ice, and the additional mass in the ocean, 209 00:21:56,799 --> 00:22:03,700 does this agree with other methods who determine the sea level rise. One of these 210 00:22:03,700 --> 00:22:09,289 methods is satellite radar altimetry, that started in the 70's, but since 1991, we 211 00:22:09,289 --> 00:22:15,269 have lots of dedicated satellite missions, which only job is basically mapping the 212 00:22:15,269 --> 00:22:21,540 global sea surface. So, they send down a radar pulse, which is reflected at the sea 213 00:22:21,540 --> 00:22:27,049 surface. They measure the run time and then they have a geometric representation 214 00:22:27,049 --> 00:22:35,480 of the global sea surface. Now, if we compare this with the mass we calculated 215 00:22:35,480 --> 00:22:41,330 or we got from the GRACE result, calculate a sea level rise rise from this additional 216 00:22:41,330 --> 00:22:46,580 mass in the ocean than these two systems would not add up. The geometric sea level 217 00:22:46,580 --> 00:22:51,820 rise is higher than just the additional mass. So there is the second process which 218 00:22:51,820 --> 00:22:58,759 is thermal expansion of the water. If water gets warm it needs more space. 219 00:22:58,759 --> 00:23:07,159 In 2000 the deployment of so-called ARGO floats started. These are free-floating 220 00:23:07,159 --> 00:23:13,389 devices in the ocean. Currently, there are over 3000 and they measure temperature and 221 00:23:13,389 --> 00:23:20,679 salinity between sea surface and a depth of 2000 meters. These are globally 222 00:23:20,679 --> 00:23:28,870 distributed. So, we have at least for the upper layer of the ocean, how much thermal 223 00:23:28,870 --> 00:23:36,710 expansion there is. And what we want to see is, do these components of additional 224 00:23:36,710 --> 00:23:41,450 mass in the ocean as determined by GRACE and thermal expansion of the upper ocean 225 00:23:41,450 --> 00:23:47,460 layer come to the same result as geometrical measurements done by satellite 226 00:23:47,460 --> 00:23:52,900 altimetry? On the left we see an image taken from the last IPCC report on climate 227 00:23:52,900 --> 00:23:59,769 change from 2013. In green we see the sealevel rise as measured with satellite 228 00:23:59,769 --> 00:24:06,279 altimetry in the time span 2005 to 2012 and in orange we see the combination of 229 00:24:06,279 --> 00:24:13,200 additional mass, as measured by GRACE, and thermal extension as determined with ARGO 230 00:24:13,200 --> 00:24:21,720 inside the ocean. And these 2 graphs follow each other quite well. On the right. We 231 00:24:21,720 --> 00:24:27,799 see a recent publication by Chen, Wilson and Tapley, the latter one being one of 232 00:24:27,799 --> 00:24:34,460 the PIs of the GRACE mission, who accumulated the data from 2005 to 2011. We 233 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 234 00:24:41,350 --> 00:24:48,870 math, there are online services who make the graphs for you. One of those is 235 00:24:48,870 --> 00:24:55,219 EGSIEM European Gravity Service for Improved Emergency Control. If we can 236 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 237 00:25:00,659 --> 00:25:04,929 has sooner or later to be removed from this area. This can be a flood, for 238 00:25:04,929 --> 00:25:08,840 example, and with a mission like GRACE, we can determine how much mass, how much 239 00:25:08,840 --> 00:25:15,289 water is there and are the rivers large enough to allow for this water to be 240 00:25:15,289 --> 00:25:22,970 flowing away. That was the intention behind this service. Oops, no, this is not 241 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 242 00:25:39,299 --> 00:25:46,909 work as expected. So, you will be greeted with this graphic. You can plot for all 243 00:25:46,909 --> 00:25:50,649 areas in the world. The first thing you have to do is you change your gravity 244 00:25:50,649 --> 00:25:56,989 functional, we want water heights. This is what I talked about in this talk. Then you 245 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 246 00:26:03,200 --> 00:26:07,190 gravity fields. These are different groups, I mentioned, providing these 247 00:26:07,190 --> 00:26:15,440 monthly solutions. And so we choose one of these groups. Then we choose an area which 248 00:26:15,440 --> 00:26:21,809 we are interested in. You can freely choose one area like here Finno-Scandia, 249 00:26:21,809 --> 00:26:29,070 or you can use pre-determined areas, for example, the Amazon river basin or Elbe 250 00:26:29,070 --> 00:26:35,570 river or something like that. These areas all over the world and you can see the 251 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 252 00:26:41,059 --> 00:26:47,250 greeted with a plot like this. This is equivalent water height, even though this 253 00:26:47,250 --> 00:26:51,740 is a geophysical process. So we see here the layer of water, which would have been 254 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 255 00:27:01,580 --> 00:27:08,750 geophysical process. This is not additional ice or water or anything. Can I 256 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 257 00:27:20,240 --> 00:27:26,710 this yourself. I have uploaded to the Fahrplan all my resources, all my links. 258 00:27:26,710 --> 00:27:31,510 And the EGSIEM page also includes the description of what is done in the backend 259 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 260 00:27:37,649 --> 00:27:42,289 to give a last impression on the future, because unfortunately while I was 261 00:27:42,289 --> 00:27:46,730 preparing my abstract for this conference, one of the GRACE satellites was turned off 262 00:27:46,730 --> 00:27:51,750 due to age. It was launched in 2002, planned for a five mission year; it 263 00:27:51,750 --> 00:27:56,970 survived 15 years, which is quite good, but now we have no more ranging 264 00:27:56,970 --> 00:28:01,250 information between these satellites. We had ranging information in micrometer 265 00:28:01,250 --> 00:28:09,049 accuracy, a couple of micrometer, and now we cannot rely on these information 266 00:28:09,049 --> 00:28:14,320 anymore. And this means mo more gravity fields with high spatial resolution, and 267 00:28:14,320 --> 00:28:17,799 I'm not sure about the temporal resolution. So, the current work which is 268 00:28:17,799 --> 00:28:23,270 done is taking all satellites which are in the low-enough orbits and calculate the 269 00:28:23,270 --> 00:28:26,799 gravity field from their positions, because everything which is in low-earth 270 00:28:26,799 --> 00:28:32,870 orbit is affected by the Earth's gravity field. So, if I take the satellite orbits, 271 00:28:32,870 --> 00:28:38,690 look "how does this orbit change" and the reason is gravity, then I can calculate 272 00:28:38,690 --> 00:28:46,110 the gravity field. Unfortunately, not in this higher resolution we are used to. 273 00:28:46,110 --> 00:28:50,019 And... But fortunately, there already is a next-generation gravity field mission on 274 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, 275 00:28:58,410 --> 00:29:05,330 early April by SpaceX. You might look at this image and think, "I just saw this 276 00:29:05,330 --> 00:29:10,990 earlier" and you are quite correct: The mission called "Grace Follow On" is a copy 277 00:29:10,990 --> 00:29:16,419 of Grace, which improved components, of course, and now with lasers. We see not 278 00:29:16,419 --> 00:29:21,500 only the microwave ranging between the two satellites, but additionally a laser 279 00:29:21,500 --> 00:29:26,289 interferometer. So, from micrometer accuracy in the distance measurements we 280 00:29:26,289 --> 00:29:33,324 go to nanometer accuracy, hopefully. But the main instrument will be the 281 00:29:33,324 --> 00:29:36,669 microwave ranging. So, in conclusion, 282 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 283 00:29:42,130 --> 00:29:47,889 inside the Earth; that this offers, in combination with other methods, new 284 00:29:47,889 --> 00:29:54,179 insights and also some kind of mutual verification. If several different types 285 00:29:54,179 --> 00:29:57,960 of observations coming to the same conclusion, none of them can be awfully 286 00:29:57,960 --> 00:30:03,700 wrong; and that the access to these methods are relatively easy: the data is 287 00:30:03,700 --> 00:30:09,480 available, all the methods are described in geodesy textbooks and the technical 288 00:30:09,480 --> 00:30:14,600 documentation; and there are other applications, other than, let's say, 289 00:30:14,600 --> 00:30:22,029 climate change; you can look into drought and flood prediction; the El Niño–Southern 290 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. 291 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. 292 00:30:35,929 --> 00:30:46,775 *applause* 293 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, 294 00:30:51,250 --> 00:30:57,350 maybe two very short questions. Please be seated during the Q&A session. Is there 295 00:30:57,350 --> 00:31:02,250 some questions? Okay, microphone 3, please. 296 00:31:02,250 --> 00:31:05,741 Mic 3: Yeah, hi. *In a quiet voice* Hi, hello? Can you hear me? *Now loud* 297 00:31:05,741 --> 00:31:07,859 Herald: Yeah. Mic 3: Okay. Hey. So, my question is 298 00:31:07,859 --> 00:31:12,945 regarding acceleration. What's the influence of Earth atmosphere and all the 299 00:31:12,945 --> 00:31:18,678 planetary bodies, like the moon, and does it need to be accounted for? 300 00:31:18,678 --> 00:31:22,236 Manuel: The external gravity needs to be accounted for, so the tidal effects of sun 301 00:31:22,236 --> 00:31:26,976 and moon would be one of those additional models you put into the processing of the 302 00:31:26,976 --> 00:31:32,340 satellite data. The Earth's atmosphere has an effect on the satellites themselves, 303 00:31:32,340 --> 00:31:37,159 which is measured onboard by accelerometers and then reduced. And the 304 00:31:37,159 --> 00:31:43,289 gravitational effect of the atmosphere: Part of this is averaged out, because we 305 00:31:43,289 --> 00:31:48,369 take a month of time series, and the rest are also inclu... provide as extra 306 00:31:48,369 --> 00:31:54,279 products; at least by the Institute for Geodesy in Graz. So atmosphere... the mass 307 00:31:54,279 --> 00:31:58,900 of the atmosphere is... has to be accounted for, yes. 308 00:31:58,900 --> 00:32:04,280 Herald: Okay. Microphone 2 has vanished all of a sudden. Then, microphone 1, 309 00:32:04,280 --> 00:32:08,700 please. Mic 1: Hi. Is it possible to measure 310 00:32:08,700 --> 00:32:16,206 changes in the temperature of the oceans or of the ocean streams, like... Can you 311 00:32:16,206 --> 00:32:25,362 see if El Niño is active by just measuring the gravity... change in gravity fields? 312 00:32:25,362 --> 00:32:29,999 Manuel: As a precursor tool, El Niño, as I understand it... certain regions of the 313 00:32:29,999 --> 00:32:35,690 ocean get warmer; it's a density change; and, of course, this would be measured as 314 00:32:35,690 --> 00:32:42,070 part of ARGO and it's also in the GRACE gravity field. There are probably papers 315 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 316 00:32:47,799 --> 00:32:51,665 don't know to what extend this was correct, but... 317 00:32:51,665 --> 00:32:55,360 Mic 1: Okay, then. Herald: Good. Then, that's all the time we 318 00:32:55,360 --> 00:32:57,924 have. A big round of applause for Manuel and his talk, please. 319 00:32:57,924 --> 00:33:00,690 *Applause* 320 00:33:00,690 --> 00:33:07,790 *34C3 Music* 321 00:33:07,790 --> 00:33:22,000 subtitles created by c3subtitles.de in the year 2020. Join, and help us!