Learn How a GPS System Operates
GPS, or Global Positioning System, is a satellite-based system of navigation that was placed into orbit, in the 1980s. Although the U.S. Department of Defense originally intended to reserve the technology for military applications, it has been available to the civilian market for several decades now. GPS is a free system that is available to anyone with a compatible device, anywhere on the planet. The most common uses for the technology today are for use with passenger vehicles, for driving directions and maps, and by recreational outdoorsmen. The GPS calculates exact location by using multiple satellites and a portable receiving device and then taking the difference between the time when a signal from the receiver was received and when it was generated by the satellites. This triangular calculation uses a more complicated and accurate technology that the predecessor, RADAR. By sending additional satellites into space, the result is more accurate locations and streams of information, like speed and distance traveled. At least three satellites are needed to yield useful information in a basic, two dimensional scenarios.
US Department of Defense Satellite Navigation System
The department of defense has heavily relied upon GPS for many years to measure vehicle speed, distances and for other tactical applications. GPS is comprised of different parts that all play an important role in making the system function properly. These parts are the space segment, user segment, and control segment
- Department of Defense News – DOT and DOD determine need for civilian access to GPS technology
- Global Positioning System Overview – Space segment which deals with the satellites in space
- GPS Future – User segment discusses air, land, and sea operators and the hardware that they use
GPS Positioning Services Specified in the Federal Radionavigation Plan
The U.S. government has gained collaboration from several departments in developing this plan, including the Department of Defense, the Department of Homeland Security, and the Department of Transportation. The plan has been created to regulate and monitor the Nation’s security as well as increasing the safety and effectiveness of our transportation system.
- Example of 2008 Federal Radionavigation Plan – An overview of a complete plan
- GPS Capabilities – A comparison between precise positioning and standard positioning services
- FAQs about GPS – Talks about some differences between military and civilian GP
GPS Satellite Signals
GPS satellite signals are transmitted from the satellite to handheld or receiving devices on the ground. Since the technology is dependant on a signal to work properly, a clear view of the sky from where the receiving equipment is located provides the best results. The signals move at the speed of light and there are at least 24 operational satellites in orbit at all times.
- A GPS Overview – A wealth of info with a detailed piece on signals
- How GPS Works – Explains the basics of how everything ties in together
- Space Storms Disrupt Satellite Signals – Explains the importance of uninterrupted signal transmission
- Signal Specification – A tremendous amount of information about the signals in GPS technology
GPS Data
GPS Data is commonly transferred at a rate of 1(PPS), or pulse per second. This equates to about a microsecond, which is extremely fast. A tremendous amount of data is exchanged between the satellite and the receiver. This allows distances and speed to be monitored and calculated to a very precise point.
- GPS Data Archive – Archives of data detailed to the year, month, and day
- The GPS 1PPS explained – A scientific overview of 3 GPS receivers tested for speed and consistency
- Useful GPS Info – A range of examples that illustrate the practicality of the GPS data
- The Evolution of GPS – Visits the history of the GPS in 1973 and talks about improvements in the equipment and data
Position and Time from GPS
GPS can accurately track position and time by utilizing a serious of complicated mathematical formulas. Triangulation uses multiple satellites in relation to the receiver to determine the precise position. Time expressed as speed in a vehicle uses the same formula with the addition facet of repeated calculations. One is compared with the next, many times over and useful data can be collected like changes in position and time lapsed from one location to the next.
- GPS Info – Discusses differential code phase tracking and general GPS info, as well
- How GPS Gathers Data – Very good, easy to understand information
- The Navigator GPS Receiver – A GPS system for high orbits
- The Importance of Traceability – Discusses the requirements for receiver tracking
GPS Error Sources
GPS errors can result from a number of sources that are both man made and natural. Some examples include weather, trees, buildings, atmospheric conditions, and even satellite positions. All these factors must be considered when incomplete or illogical data appears.
- GPS Explained: Error Sources – Many sources of errors and why they occur
- Estimating Your Receiver’s Accuracy – Explores the difference between repeatability and accuracy
Additional Resources
For more information on popular GPS receiver units, please visit the following links:
