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Frequently Asked Questions

What is GPS?

The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The system provides critical capabilities to military, civil and commercial users around the world. It is maintained by theUnited States government and is freely accessible to anyone with a GPS receiver.

Common Factors affecting the accuracy of GPS?

GPS Technique employed (i.e.: Autonomous, WADGPS, DGPS, RTK, etc.) Surrounding conditions (satellite visibility and multipath) Number of satellites in view Satellite Geometry (HDOP, GDOP, PDOP etc.) Distance from Reference Receiver(s) (non-autonomous GPS ie: WADGPS, DGPS, RTK) Ionospheric conditions Quality of GPS receiver

Where can GPS work?

GPS reception is available around the globe. You will need to have a clear view of the skies so the receiver can triangulate at least three satellites. An office window works well, but you may have problems receiving signals in the inner area of buildings. In general, metal and masonry block GPS signals, while glass, wood, or plastic does not.

Under specific conditions, GPS will not provide the time. For instance, the 1,542 MHz GPS signal does not penetrate buildings, which makes it difficult to receive signals indoors away from windows. Also the signal can be critically weakened by heavy foliage and interfered with by other sources such as poorly maintained television broadcasting equipment.

Who Pays for GPS?

The American taxpayer pays for the GPS service enjoyed throughout the world. All GPS program funding comes from general U.S. tax revenues. The bulk of the program is budgeted through the Department of Defense, which has primary responsibility for developing, acquiring, operating, sustaining, and modernizing GPS.

How many satellites are in the Global Positioning System constellation?

The US Air Force manages the constellation to ensure the availability of at least 24 GPS satellites, 95% of the time. For the past several years, the US Air Force has been flying 31 operational GPS satellites, plus 3-4 decommissioned satellites (“residuals”) that can be reactivated if needed.