User tools
Student Activity - Using GPS
Activity idea
By the end of this activity, students should understand:
- how GPS works
- how GPS can be used to record slow slip events
- how to read and plot data on slow slips
What you will need:
Access to the Internet.
How does GPS work?
Slow slip events can only be detected by global positioning systems (GPS) as they don’t show up on seismometers. Very sensitive GPS is used, which is able to detect small movements in the ground – the equivalent to you moving about 20 centimetres very slowly over two weeks!
GPS has three parts to it – the space segment, the user segment and the control segment. http://www.ictp.trieste.it/~radionet/ghana1998/GPS/PAGE4.HTM
- The space segment consists of 24 satellites, each in its own orbit 20,000 kilometres above the Earth. Follow this link to find out more about the satellites.
- The user segment consists of receivers, which you can hold in your hand or mount in your car. Follow this link to find out more about the receivers.
- The control segment consists of five ground stations, located around the world, that make sure the satellites are working properly. Follow this link to find out more about the stations.
This link shows how GPS works:
http://www.ictp.trieste.it/~radionet/ghana1998/GPS/PAGE5.HTM
This link gives another overview:
http://www.aero.org/education/primers/gps/howgpsworks.html
How scientists use GPS
The user segment is the part that is important to the scientists. The receivers are stuck into the ground at places that the scientists choose. The scientists know exactly where these receivers are – they have map coordinates, such as 37 25.818’N, 122 05.36’W, which accurately gives the position on Earth.
These receivers move if there is a slow slip event and the satellites pick up this movement. The data is recorded in the form of several coordinates and these can be plotted onto a large scale map to show whether there has been movement or not.
More about coordinates
Every position has two coordinates – one for latitude and one for longitude. For the coordinate 123° 24' 30.8" W Longitude
- 123 is the number of degrees
- 24 is the number of minutes (a minute is 1/60th of a degree)
- 30.8 is the number of seconds (a second is 1/60th of a minute, or 1/3600th of a degree).
This site gives more information about coordinates if you are interested.
Find out more about map references
Visit Google Earth, and find your home town or street. Locate the coordinates at the bottom of the screen. Move the cursor around even just a little bit and see how the coordinates change.
Instructions
- Write down the different parts of the global positioning system and their role.
- Using the animation, find out how the satellites can tell the position of a receiver.
- Using Google Earth, and an area of your choosing, find a street with a row of houses on at least one side. Work out the series of coordinates that will plot a short journey for someone travelling three houses down the street. This is the same as plotting the coordinates of a slow slip event. Can you work out how far you have traveled?
