What is GPS?

February 11, 2013

Hi, I’m Emerald Robinson, and in this “What Is” video, we’re going to answer the question, “What is GPS?”

GPS is an acronym for Global Positioning System. Many people use the term “GPS” when referring to the receiver that’s found in their car, but that’s not entirely true. GPS is more accurately defined as a navigational system that relies on satellite signals to show an object’s location.

Although scientists have been working on satellite-based navigation systems since the 1950s, the current GPS system’s predecessor was created in 1973. It was originally commissioned by the United States Department of Defense for use by the military. But during the 1980s, the government started permitting civilians to use the system.

Devices that use GPS work by receiving signals from special satellites that orbit the earth twice a day at an altitude of about 13,000 miles. There’s a minimum number of satellites required for the GPS to function – 24 – but there are usually about 30 satellites circling the globe in case one fails.

GPS satellites continually emit signals that state two pieces of information:

- one, the current time, and

- two, where exactly above the earth the satellite is at that time.

GPS receivers use this information to do a special calculation called triangulation. The receivers compare the time that the signal was sent from the satellite with the time that the signal was received. The difference in time indicates the distance between the receiver and the satellite. A GPS receiver needs to get signals from three satellites to calculate latitude and longitude; if it gets a signal from four satellites it can also calculate altitude.

GPS is used in many ways. Scientists use GPS to gather data about earthquakes; surveyors use it to determine property lines; and businesses use it to track delivery vehicles.

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