What is GPS System? - Comprehensive 2024 Guide: From Satellites to Real-World Applications

How to Benefit from the Global Positioning System (GPS) for Free

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.

How GPS Works

GPS satellites orbit the Earth twice daily in a very precise orbit and transmit signal information to Earth. GPS receivers take this information and use triangulation to calculate the user's exact location.

A GPS receiver must be locked onto signals from at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude, and altitude).

How Accurate is the Global Positioning System (GPS)?

Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. Garmin's 12 parallel channel receivers quickly lock onto satellites when first turned on and maintain strong locks.

Newer Garmin GPS receivers with WAAS (Wide Area Augmentation System) capability can improve accuracy to less than three meters on average. No additional equipment or fees are required to benefit from WAAS.

GPS Satellite System

The 24 satellites that make up the GPS space segment orbit the Earth at an altitude of approximately 12,000 miles. They are constantly moving, completing two full orbits in less than 24 hours. These satellites travel at speeds of roughly 7,000 miles per hour. GPS satellites are powered by solar energy. They have backup batteries on board to keep them operating during solar eclipses when there is no solar power.

Important Facts About GPS Satellites:

The first GPS satellite was launched in 1978
A full constellation of 24 satellites was achieved in 1994
Each satellite is built to last about 10 years
A GPS satellite weighs approximately 2,000 pounds
Transmitter power is only 50 watts or less

What are GPS Signals?

GPS satellites transmit two low-power radio signals, designated L1 and L2. Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band.

A GPS signal contains three different pieces of information:

Pseudorandom Code: Simply an ID code that identifies the satellite
Ephemeris Data: Information about the satellite's status, date, and time
Almanac Data: The location of each satellite at any time throughout the day

Sources of GPS Signal Errors

Factors that can degrade GPS signals and thus affect accuracy include:

Ionospheric and Tropospheric Delays: Satellite signals slow down when passing through the atmosphere
Signal Multipath: When GPS signals reflect off objects before reaching the receiver
Receiver Clock Errors: The receiver's built-in clock is not as accurate as atomic clocks
Orbital Errors: Inaccurate information about the satellite's position
Number of Visible Satellites: More satellites result in greater accuracy
Satellite Geometry: The relative position of satellites affects accuracy
Intentional Signal Degradation: This system was discontinued in May 2000

What is GPS? | GPS Applications | GPS Glossary

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