Tuesday, March 09, 2010

GPS: Your Own Atomic Clock

Hiking Tip: Consult your GPS when you need the time.

Need to update your watch? Cellphone ran out of juice? Don’t worry. If you carry a GPS then you’ve got an atomic clock in the palm of your hand. Check it out:

Global Positioning Systems (GPS) offer a great way to record distances, elevation, and memorable waypoints along the trail. Our guides use them, and we find that more and more of our guests use them every year.

GPS works by collecting signals from orbiting satellites and then triangulating a position based on those signals. The signals contain various pieces of information including satellite ID, satellite health, and satellite orbital information. The most notable piece of transmitted information, however, is the time.

Each satellite has its own atomic clock and it broadcasts the time from this clock to the GPS receiver out on the trail. The receiver compares the time that the signal was transmitted, with the time that it was received, and uses the difference to calculate its distance from the satellite. In short, it’s the time it takes the signal from the satellite to reach our reciever that allows us to determine our position here on earth. Add the distances from a few more satellites, and voila, we’ve established a triangulation.

All of this leads to a point: (Pun intended). If you need a source for accurate time, then fire up your GPS. You’ve got access to an atomic clock in the palm of your hand.

Note: The clock reading software in a modern GPS is not as accurate as the atomic clock in a satellite. (Though it’s extremely accurate for every day use-to within seconds and parts of a second). Clock accuracy varies by model.

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