Global Positioning System (GPS)
What is Global Positioning System (GPS)?
The Global Positioning System (GPS) is a "constellation" of 31 well-spaced satellites that orbit the Earth and make it possible for people with ground receivers to pinpoint their geographic location. The location accuracy is anywhere from 100 to 10 meters for most equipment and within one meter with special military-approved equipment. GPS equipment is widely used in science and has now become low-cost enough that almost anyone can own a GPS receiver.
The GPS is owned and operated by the U.S. Department of Defense but is available worldwide.
How does GPS work?
The following steps describe the basics of how GPS works:
- Twenty-one GPS satellites and three spare satellites are in orbit at 10,600 miles above the Earth. The satellites are spaced so that four satellites will be above the horizon from any point on Earth.
- Each satellite contains a computer, an atomic clock and a radio. With an understanding of its orbit and the clock, it continually broadcasts its changing position and time. Once a day, each satellite checks its sense of time and position with a ground station and makes any minor corrections.
- On the ground, any GPS receiver contains a computer that "triangulates" its position by getting bearings from three satellites. The result is a geographic position -- longitude and latitude -- to, for most receivers, within 100 meters.
- If the receiver is also equipped with a display screen and a map, the position can be shown as well.
- If it can receive the fourth satellite, the computer can figure out the altitude as well as the geographic position.
- If a person is moving, their receiver can also calculate their speed and direction of travel and give them estimated arrival times to specified destinations.
The GPS has been a useful tool in science to provide data that has never been available in this quantity and degree of accuracy before. Scientists are using the GPS to measure the movement of the arctic ice sheets, the Earth's tectonic plates and volcanic activity.
Mobile GPS technology has equipped today's smartphones with convenient and highly efficient means for end users to receive navigating instructions via a global positioning system process called "trilateration." A phone's built-in GPS receiver also communicates with an array of satellites, which provides navigation instructions for those in an automobile or on foot. More technologically advanced phones can identify individual streets and attractions on maps and provide narrated tracking capability.
