Watching the changing Earth (34c3)

For a few decades by now, satellites offer us the tools to observe the whole Earth with a wide variety of sensors. The vast amount of data these Earth observations systems collect enters the public discourse reduced to a few numbers, numbers like 3 or even 300. So, how do we know the amount of ice melting in the arctic or how much rain is falling in the Amazon? Are groundwater aquifers stable or are they are being depleted? Are these regular seasonal changes or is there a trend? How can we even measure these phenomena on a global scale? This talk will provide one possible answer: gravity. about this event: https://fahrplan.events.ccc.de/congress/2017/Fahrplan/events/8964.html