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 GPS, formally known as the Navstar Global Positioning System, was initiated in 1973 to reduce the proliferation of navigation aids. By creating a system that overcame the limitations of many existing navigation systems, GPS became attractive to a broad spectrum of users worldwide. GPS has been successful in virtually all navigation applications, and because its capabilities are accessible using small, inexpensive equipment, GPS is being utilized in a wide variety of applications across the globe.
The Global Positioning System (GPS) is a space-based radio-navigation system consisting of a constellation of satellites and a network of ground stations used for monitoring and control. A minimum of 24 GPS satellites orbit the Earth at an altitude of approximately 11,000 miles providing users with accurate information on position, velocity, and time anywhere in the world and in all weather conditions.
GPS is operated and maintained by the Department of Defense (DoD). The Federal Aviation Administration is investigating and applying the use of GPS as it pertains to aviation.
How Accurate is GPS?
100 meters: Accuracy of the original GPS system, which was subject to accuracy degradation under the government-imposed Selective Availability (SA) program.
15 meters: Typical GPS position accuracy without SA
3-5 meters: Typical differential GPS (DGPS) position accuracy.
< 3 meters: Typical WAAS position accuracy.
What is GPS?
 GPS provides the following:
- 24-hour, worldwide service
- Extremely accurate, three-dimensional location information
(providing latitude, longitude, and altitude readings)
- Extremely accurate velocity information
- Precise timing services
- A worldwide common grid that is easily converted to any local grid
- Continuous real-time information
- Accessibility to an unlimited number of worldwide users
- Civilian user support at a slightly less accurate level
GPS satellites orbit the earth every 12 hours emitting continuous navigation signals on two different L-band frequencies. The signals are so accurate, time can be figured to within 100 nanoseconds, velocity can be figured to within a fraction of a mile per hour and location can be figured to within meters.
GPS Tutorials
Nice tutorial sponsored by the National Air and Space Museum
FAQ by the Aerospace Corporation
Flash GPS Tutorial by Trimble
How GPS Works by How Stuff Works
A Practical Guide to GPS by Don Bartlett
Global Positioning System Overview at University of Colorado
GPS FAQs
Federal Avaiation Adminstration GPS FAQ
What is Wide Area Augmentation System (WAAS)?
The Wide Area Augmentation System (WAAS) uses a system of ground stations to provide necessary augmentations to the GPS navigation signal. A network of precisely surveyed ground reference stations are strategically positioned across the country including Alaska, Hawaii, and Puerto Rico to collect GPS satellite data. Using this information, a message is developed to correct any signal errors. These correction messages are then broadcast to GPS receivers that are equipped to receive and process the signals. WAAS can increase the accuracy of GPS signals from about 20 feet to about 1 foot.
WAAS FAQs
WAAS FAQ as it applies to Aircraft Navigation
GPS WAAS Operation: Your questions Answered by Joe Mehaffey
WAAS at Stanford University
Guide to using WAAS
Nice graphic showing accuracy of WAAS verses plain GPS
US Government Web sites
US Coast Guard GPS Navigation Center - Core information site for GPS
GPS use by the US Forest Service
Global Positioning System satellite ephemerides ("orbits") information from NOAA
GPS Application Exchange hosted by NASA
Satellite navigation at the FAA
Other Government Web sites
UK: National GPS Network
Australia: Geoscience Australia
GPS Technical Information
GPS Technical Library at NAVSTAR GPS Joint Program Office
List of GPS satellites currently in orbit
Increased accuracy throught the uses of Differential GPS (DGPS)
Innovative uses for GPS Around the World
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SICGN
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The Southern California Integrated GPS Network is a collaborative project to install 250 permanent, continuously recording Global Positioning System (GPS) receivers in and around the Los Angeles basin to provide accurate deformation information that will improve our estimates of earthquake hazards.
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Pest Control
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In the news recently there has been much activity on the topic of pest control. Africanized honey bees attacking and causing serious injury to humans, crop damage from wheat midges and weevils, diseases affecting both humans and animals from mosquitoes and ticks; these are merely a few examples that illustrate why pest tracking and control is such an important topic. This paper will provide an overview of the combination of GIS and GPS can be used to monitor the activity and spread of pests.
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