GPSGlobal Positioning System

INTRODUCTION The Global Positioning System (GPS) is a

satellite-based navigation system GPS was originally intended for military

applications in the 1980s, the government made the

system available for civilian use

HOW IT WORKS? GPS satellites circle the earth twice a day in

a very precise orbit and transmit signal information to earth. GPS receivers take this information and use trilateration to calculate the user's exact location.

TRILATERATION Trilateration is a method for determining

the intersections of three sphere surfaces given the centers and radio of the three spheres.

ESSENTIALLY the GPS receiver compares the time a signal

was transmitted by a satellite with the time it was received.

The time difference tells the GPS receiver how far away the satellite is.

The receiver can determine the user's position and display it on the unit's electronic map.

THE GPS SATELLITE SYSTEM

24 satellites are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hours

WHO USES GPS?

APPLICATIONS Timing Roads & Highways Space Aviation Agriculture Marine Rail Environment . Topography and Geodesy Public Safety & Disaster Relief . Salvage and

Rescue. Surveying & Mapping Geocaching Recreation and sports.

SOURCES OF GPS SIGNAL ERRORS

Ionosphere and troposphere delays Signal multipath – This increase the travel time of signal Receiver clock errors – slight timing errors Orbital errors – inaccuracies of the satellite´s reported location Number of satellites visible Satellite geometry/shading – the relative position of

the satellites Intentional degradation of the satellite

signal - prevent military adversaries

HISTORY - TIMELINE The first satellite navigation system, Transit, used

by the United States Navy, was first successfully tested in 1960.

In 1978 the first experimental Block-I GPS satellite was launched.

In 1994 a complete constellation of 24 satellites was in orbit.

Full Operational Capability was declared by NAVSTAR in April 1995.

In 2004, the United States Government signed a historic agreement with the European Community establishing cooperation related to GPS and Europe's planned Galileo system.

November 2004, QUALCOMM announced successful tests of Assisted-GPS for mobile phones.

OTHER SYSTEMS Other satellite navigation systems in use or

various states of development include: Galileo –European Union planned to be

operational by 2013. Beidou – People's Republic of China's

experimental regional system. COMPASS – A proposed global satellite positioning

system by the People's Republic of China GLONASS – Russia's global system IRNSS – India's regional navigation system

covering Asia and the Indian Ocean only QZSS – Japanese proposed regional system

covering Japan only.