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 GPS works in any weather conditions, anywhere in the world, 24
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 triangulation to calculate the user's exact location.
GPS receiver compares the time a signal was transmitted by a satellite with the time it was receive user's position and display it on the unit's electronic map.
A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and 3D position.
HOW ACCURATE IS GPS?
GPS receivers are extremely accurate, that are using parallel multi-channel design.
GARMIN's 12 parallel channel receivers are quick to lock onto satellites when first turned onand they maintain strong locks,
Newer GARMIN GPS receivers with WAAS (Wide Area Augmentation System) capability can improve accuracy to less than three meters on average
Users can also get better accuracy with Differential GPS (DGPS), which corrects GPS signals to within an average of three to five meters.
The U.S. Coast Guard operates the most common DGPS correction service.
THE GPS SATELLITE SYSTEM
The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles.
These satellites are traveling at speeds of roughly 7,000 miles an hour. GPS satellites are powered by solar energy. They have backup batteries
Small rocket boosters on each satellite keep them flying in the correct path.
The first GPS satellite was launched in 1978. A full constellation of 24 satellites was achieved in 1994.
A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended. Transmitter power is only 50 watts or less.
WHAT'S THE SIGNAL?
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. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic
A GPS signal contains three different bits of information — a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information.
Ephemeris data, which is constantly transmitted by each satellite, contains important information This part of the signal is essential for determining a position.
Each satellite transmits almanac data showing the orbital information for that satellite and for every other satellite in the system.
SOURCES OF GPS SIGNAL ERRORS Factors that can degrade the GPS signal and thus affect accuracy include the following: Ionosphere and troposphere delays — The satellite signal slows as it passes through the atmosphere. Signal multipath — This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver GPS units typically will not work indoors, underwater or underground. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.
GPS USES IN EVERYDAY LIFE : The GPS system was developed to meet military needs of the Department of Defense. As you have read, the system has been used in aircraft and ships, but there are many other ways to benefit from GPS. GPS is also helping to save lives. Many police, fire, and emergency medical service units are using GPS receivers to determine the police car, fire truck, or ambulance nearest to an emergency, enabling the quickest possible response in life-or-death situations.
Automobile manufacturers are offering moving-map displays guided by GPS receivers as an option on new vehicles.
Ground Control Stations and Receivers The GPS control, or ground, segment consists of unmanned monitor stations located around the world Ex: Pacific Ocean, Indian Ocean ,Atlantic Ocean, Colorado. GPS receivers can be hand carried or installed on aircraft, ships, tanks, submarines, cars, and trucks. These receivers detect, decode, and process GPS satellite signals.
MILITARY USES FOR GPS Although the GPS satellite constellation was completed only recently, it has already proved to be a most valuable aid to U.S. military forces. The terrain looks much the same for miles. Without a reliable navigation system, U.S. forces could not have performed the maneuvers of Operation Desert Storm. The demand was so great that, before the end of the conflict, more than 9,000 commercial receivers were in use in the Gulf region They were carried by foot soldiers and attached to vehicles, helicopters, and aircraft instrument panels.
GPS has become important for nearly all military operations and weapons systems.
SATELLITES IN SPACE the complete GPS space system includes 24 satellites, 11,000 nautical miles above the Earth, which take 12 hours each to go around the Earth once They are positioned so that we can receive signals from six of them nearly 100 percent of the time at any point on Earth. The first GPS satellite was launched in 1978. The first 10 satellites were developmental satellites, called Block I. From 1989 to 1993, 23 production satellites, called Block II, were launched. The launch of the 24th satellite in 1994 completed the system.
WHAT IS NAVIGATION? people have been trying to figure out a reliable way to tell where they are, to help guide them to where they are going, and to get them back home again. Unfortunately for Odysseus and all the other mariners, the stars are only visible at night - and only on clear nights.
Previously this service of GPS was confined only the military and law enforcements agencies , but now this is a extended for civilian.
GPS provided good substitute for route mapping in navigation