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How does GPS work?

Did you know..
Satellite systems can warn us about tsunamis?

We all remember the terrible tragedy that struck Asia on Boxing Day 2004, costing hundreds of thousands of human lives. People were not forewarned and had no time to find shelter. In most Western countries this wouldn’t have happened, due to a warning system using seismometers and ocean buoy data.

The seismometers give out the first alert for large earthquakes and the ocean buoys can sense a change in the altitude of the sea level. Two disadvantages of the current buoy system are that it’s very high maintenance and that it can only be used locally.
Scientists are now investigating the possibility of a global, buoy-based tsunami warning system which, with the help of GPS, will improve future tsunami danger assessments. Because with GPS, warning systems can also tell exactly how much the ocean floor has moved. 

When it’s introduced, GALILEO will in addition provide the buoy system with more signals over a larger bandwidth. Making it more reliable, more accurate (recognising altitude changes of mere centimetres - essential for the prediction of tsunamis) and enabling the buoys to send us warning signals.
Here, the GALILEO and GPS satellites will work a bit like radar, their signals bouncing off the earth’s surface, including water surfaces, back into orbit. Where some of the bounced signals will be caught by another satellite, from which we can measure the altitude of the water’s surface.

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