GIS Live 2004
"Crossing Boundaries with GIS"

Sessions Previews

What in the World is GPS?
Curt Johnson, NC Geodetic Survey

Description:

Global Positioning Systems

Our ancestors had to go to pretty extreme measures to keep from getting lost. They erected monumental landmarks, laboriously drafted detailed maps and learned to read the stars in the night sky.
Things are much, much easier today. As long as you have a GPS receiver and a clear view of the sky, you'll never be lost again.

The Global Positioning System is a space based navigation system. A constellation of 24 satellites orbits earth every 12 hours at an altitude of 14,000 miles from the earth's centre. Each satellite is armed with four atomic clocks, which keep the time to a superlative degree of accuracy. They each broadcast their precisely timed radio signals through the atmosphere and onto the earth's surface at the speed of light. The signals from each satellite arrive at any particular point on or above the earth's surface at slightly different times. This timing is proportional to the distance between the satellite and that particular point. Thus each radio beam acts as a 20,200 km (10,900 nm) long ruler.

GPS is used to support land, sea, and airborne navigation, surveying, geophysical exploration, mapping and geodesy, conservation research, habitat modelling, vehicle location systems, farming, transportation systems, archaeology, mountaineering, fishing and a wide variety of other additional applications.

Preparing for the Session:

K

What do you already know about GPS? Have you ever seen or used a GPS receiver before? Where did you see it? How have you used GPS?

W

What have you learned about how GPS works and how it is used?

L

If you had a GPS receiver how would you use it? What are some other applications of GPS?