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Question What is a GPS? How does it work?

Answer

The Global Positioning System (GPS) tells you where you are on Earth.

GPS III Satellite. U.S. Government photo, GPS.gov Multimedia Library.

It’s eleven o’clock … do you know where your kids are? Would you like to? One way to track them would be to have a GPS receiver installed in the car! The GPS, or Global Positioning System, is one of the hottest technologies around, and no wonder. Consider these diverse uses:

  • Minnesota scientists use GPS to study movements and feeding habits of deer.
  • Surveyors used GPS to measure how the buildings shifted after the bombing in Oklahoma City.
  • GPS helps settle property disputes between land owners.
  • Marine archaeologists use GPS to guide research vessels hunting for shipwrecks.
  • GPS data has revealed that Mt. Everest is getting taller!
USGS and National Park Service personnel placed a GPS-transmitter on a California Condor at Pinnacles National Monument. Photo was taken when the bird was released after attaching the transmitter. Jack Glendening, photographer. USGS Multimedia Library

GPS answers five questions simultaneously:

  1. “Where am I?”
  2. “Where am I going?”
  3. “Where are you?”
  4. “What’s the best way to get there?
  5. “When will I get there?”

GPS is the only system today that can show your exact position on the Earth anytime, in any weather, no matter where you are!

CDC staff member Yoshinori, using the global positioning system (GPS) receiver in his computer tablet, to navigate and record additional geographic information in the West African country of Sierra Leone. Later, he would send these GPS files to colleagues in Atlanta, where the data would be shared with others involved in the country’s Ebola response efforts. Public Health Image Library, Centers for Disease Control and Prevention

Development

Like so many other high-tech developments, GPS was designed by the U. S. military. The concept started in the late ’60s but the first satellite wasn’t launched until February 1978. In 1989 the Magellan Corp. introduced the first hand-held GPS receiver. In 1992 GPS was used in Operation Desert Storm. On March 1996 the President decided to make GPS free for civilian users.

Earth – The Blue Marble. Photo from NASA’s Visible Earth

System Description

GPS has three ‘segments’:

  1. The space segment now consists of 28 satellites, each in its own orbit about 11,000 nautical miles above the Earth.
  2. The user segment consists of receivers, which you can hold in your hand or mount in your car.
  3. The control segment consists of ground stations (five of them, located around the world) that make sure the satellites are working properly.
Outstanding in the Field: USGS Research Geologist Dr. Erika Lentz is conducting real-time kinematic GPS surveys on barrier island dunes, part of her research looking at how coastal landscapes respond to sea-level rise. September, 2018,  Woods Hole Coastal and Marine Science Center. USGS Multimedia Library

Civilian Use

At first, the military did not want to let civilians use GPS, fearing that smugglers, terrorists, or hostile forces would use it. Finally, bowing to pressure from the companies that built the equipment, the Defense Department made GPS available for non-military purposes, with some restrictions. On May 1, 2000, President Clinton lifted the restrictions, and announced that the option to degrade civil GPS signals during emergencies would be phased out by 2010. The federal government is committed to providing GPS technology for peaceful uses on a worldwide basis, free of charge.

Using the Grasshopper Hazard Forecast computer program that combines satellite GPS technology with GIS software, entomologist Bill Kemp (standing) and computer specialist Tom Kalaris check projections for the state of Nebraska. Jack Dykinga, photographer. Agricultural Research Service, USDA Image Gallery.

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