How exactly does a GPS monitor the volcano to see if it is deflating or inflating?

GPS Global Positioning system





please explain in a detailed but simple term|||So, I'm assuming you don't know how a GPS works (which you might, but bear with me, this makes it easier to explain). A GPS can tell you where, at any given time, you are on the earth and what your altitude (how far about the ocean) is.





Imagine a volcano --any volcano. Now, around the caldera, or top, put a bunch of random dots netted around it. Those dots are all GPSs. Each of those dots is saying exactly where that particular GPS is located and how high it is. And all of them are doing that constantly, or can be accessed at any time to find out that information.





Say you look at the data today, and then you look at it again tomorrow and most of the GPS's are reporting that they are a few meters higher in altitude that they had been (this is extreme, normally it would be mm's to cm's). This would mean that the volcano is inflating.





Conversely, if they all suddenly were to say that they were a few meters closer to sea level, then it would be deflating.





I hope this made some sense.|||It sends satellite waves into the ground to detect certain vibrations in tectonic plates. It also digitally transfers data from sound waves in the atmosphere, to view images of earth, and locate where each telephone line is connected