1 What is GPS?

The Global Positioning System Constellation GPS is a global navigation satellite system developed by the U.S. Department of Defense, managed by the U.S. Air Force. Free for anyone to use. Provides geographic locations at any time, anywhere.

WGS 1984 Geographic Coordinate System Notation Degrees, Minutes, Seconds (DMS) and Degrees, Minutes, Seconds (DMS) and Decimal Degrees (DD) 0° 0’ 0” N 45° 0’ 0” 0° 0’ 0” N 90° 0’ 0” S 90° 0’ 0” S 45° 0’ 0” E 90° 0’ 0” E 180° 0’ 0” W 90° 0’ 0” W 180° 0’ 0”

The Global Positioning System Constellation GPS is a global navigation satellite system developed by the U.S. Department of Defense, managed by the U.S. Air Force. Free for anyone to use. Provides geographic locations at any time, anywhere earth orbiting satellites

A GPS satellite 5 Solar panels – power Atomic clock – precisely records time in UTC Radio transmitter – broadcasts a continuous signal containing the time, and ephemeris (identification and positional information)

San Diego Aerospace Museum 6 GPS satellite on display

The Global Positioning System Constellation GPS is a global navigation satellite system developed by the U.S. Department of Defense, managed by the U.S. Air Force. Free for anyone to use. Provides geographic locations at any time, anywhere earth orbiting satellites GPS receivers Contain a clock, computer, radio wave receiver. Dime sized to dinner plate sized Receive signals from GPS satellites Computes distance to satellite by comparing time: signal sent vs. received. Receiving four satellite signals allows a position calculation using trilateration

Trilateration – location determination through the measurement of distances. If the distance to 3 satellites is known, where these 3 spheres intersect can be calculated. Trilateration is the method used by a GPS receiver to determine one’s position on earth. Watch the explanation by a NASA scientist:

GPS uses – Navigation Penn State University Geospatial Revolution Videos, Episode 1 (minutes 2:00 – 2:45) 9

GPS uses – Navigation (land, air, water) 10

GPS uses - Commercial 11 Precision agricultureFleet management

GPS uses: Military Weapon targeting and guidance 12 Troop deployment and navigation

Mission Planning to aid accuracy

GPS devices – Survey, mapping, recreational Survey grade – Very sophisticated receivers, able to receive many signals. Centimeter accuracy possible. Cost: several thousand $$. Mapping grade – ~1 meter accuracy, possible. Cost: $700 and up. Recreational – User friendly, 10 meter accuracy. Cost: $100 and up.

GPS Summary satellites in orbit at 20,200 km Continuous 24-hour, worldwide coverage Position and time data transmitted from satellites through coded radio waves. Accuracy is depends on the sophistication of the receiver, number of signals received, and ranges from 10 meter to centimeter accuracy. Satellites controlled by U.S. Dept. of Defense (clock adjustments, activation, signal scrambling) WGS 1984 coordinate system used Wide range of applications For a more involved presentation on GPS, go herehere