- Know precisely how far you have run and at what pace while trunking your path so you can find your way home
- Pinpoint the perfect fishing spot on the water and easily relocate it
- Get the closest location of your favorite restaurant when you are out-of-town
- Find the nearest airport or identify the type airspace in which you are flying
I. What is GPS?
The Global Positioning System (GPS) is a satellite-based navigation system that sends and receives radio signals. A GPS receiver acquires these signals and provides you with information. Using GPS technology, you can determine location, velocity, and time, 24 hours a day, in any weather conditions anywhere in the world—for free.
GPS, formally known as the NAVSTAR (Navigation Satellite Timing and Ranging) Global Positioning System, originally was developed for the military. Because of its popular navigation capabilities and because you can access GPS technology using small, inexpensive equipment, the government made the system available for civilian use. The USA owns GPS technology and the Department of Defense maintains it.
GPS technology requires the following three segments:
- Space segment
- Control segment
- User segment
Space Segment
At least 24 (FPS satellites orbit the earth twice a clay in a specific pattern. They travel at approximately 7,000 miles per hour about 12,000 miles above the earth’s surface. These satellites are spaced so that a GPS receiver anywhere in the world can receive signals from at least four of them.
Each GPS satellite constantly sends codedradio signals (known as pseudorandom code) to the earth. These GPS satellite signals contain the following information:
- The particular satellite that is sending the information
- Where that satellite should be at any given time (the precise location of the satellite is called ephemeris data)
- Whether or not the satellite is working properly
- The date and time that the satellite sent the signal
The signals can pass through clouds, glass, and plastic. Most solid objects such as buildings attenuate (decrease the power of) the signals. The signals cannot pass through objects that contain a lot of metal or objects that contain water (such as underwater locations).
The GPS satellites are powered by solar energy. If solar energy is unavailable, for example, when the satellite is in the earth’s shadow, the satellites use backup batteries to continue running. Each GPS satellite is built to last about 10 years. The Department of Defense monitors and replaces the satellites to ensure that GPS technology continues to run smoothly for years to come.
Control Segment
The control segment is responsible for constantly monitoring satellite health, signal integrity, and orbital cofiguration from the ground. The control segment includes the following sections:
- Master control station
- Monitor stations
- Ground antennas
Monitor Stations
At least six unmanned monitor stations are located around the world. Each station constantly monitors and receives information from the GPS satellites and then sends the orbital and clock information to the master control station (MCS).
Master Control Station (MCS)
The MC S) is located near Colorado Springs in Colorado. The MCS constantly receives GPS satellite orbital and clock information from the monitor stations. The controllers in the MCS make precise corrections to the data as necessary, and send the information (known as ephemeris data) to the GPS satellites using the ground antennas.
Ground Antennas
Ground antennas receive the corrected orbital and clock information from the MCS, and then send the corrected information to the appropriate satellites.
User Segment
The GPS user segment consists of your GPS receiver. Your receiver collects and processes signals from the GPS satellites that are in view and then uses that information to determine and display your location, speed, time, and so forth. Your GPS receiver does not transmit any information back to the satellites.
II. How Does GPS Technology Work?
The following points provide a summary of the technology at work:
- The control segment constantly monitors the GPS constellation and uploads information to satellites to provide maximum user accuracy.
- Your GPS receiver collects information from the GPS satellites that are in view.
- Your GPS receiver accounts for errors. For more information, refer to the Sources of Errors (Page 7) section.
- Your GPS receiver determines your current location, velocity, and time.
- Your GPS receiver can calculate other information, such as bearing, track, trip distance, distance to destination, sunrise and sunset time, and so forth.
- Your GPS receiver displays the applicable information on the screen.
III. Who Uses GPS?
GPS technology has many amazing applications on land, at sea, and in the air. You might be surprised to learn about the following examples of how people or professions are already using GPS technology:
Agriculture
In precision farming, GPS technology helps monitor the application of fertilizer and pesticides. GPS technology also provides location information that helps farmers plow. harvest. map feilds. and mark areas of disease or weed infestation.
Aviation
Aircraft pilots use GPS technology for en route navigation and airport approaches. Satellite navigation provides accurate aircrat location anywhere on or near the earth.
Environment
GPS technology helps surrey disaster areas and map the movement phenomena (such as fittest fires. oil spills. or hurricanes). lt is even possible in find locatinns that hate been submerged or altered by natural disasters.
Ground Transportation
GPS technology helps with automatic vehicle location and in-vehicle navigation systems. Many navigation systems show the vehicle’s location on an electronic street map, allowing drivers to keep track of where they are and to look up other destinations. Some systems automatically create a route and give tum-by-turn directions. GPS technology also helps monitor and plan routes for delivery vans and emergency vehicles.
Marine
GPS technology helps with marine navigation. traffic routing. underwater surveying. navigational hazard location. and mapping. Commercial fishing fleets use it to navigate to optimum fishing locations and to track fish migrations.
Military
Military aircraft, ships, submarines, tanks, eeps, and equipment use GPS technology for many purposes including basic navigation, target designation, close air support, weapon technology, and rendezvous.
Public Safety
Emergency and other specially fleets use satellite navigation For location and status information
Rail
Precise knowledge of train location is essential tn prevent collisions. maintain smooth trafiic flow, and minimize costly delays. Digital maps and onboard inertial units allow fully-automated train control.
Recreation
Outdoor and exercise enthusiasts use GPS technology to stay apprised of location, heading, bearing, speed, distance, and time. In addition, they can accurately mark and record any location and return to that precise spot.
Space
GPS technology helps track and control satellites in orbit. Future booster rockets and reusable launch vehicles will launch, orbit the earth, return, and land, all under automatic control. Space shuttles also use GPS navigation.
Surveying
Surveyors use GPS technology for simple tasks (such as defining property lines) or for complex tasks (such as building infrastructures in urban centers). Locating a precise point of reference used to be very time consuming. With GPS technology, two people can survey dozens of control points in an hour. Surveying and mapping roads and rail systems can also be accomplished from mobile platforms to save time and money.
Timing
Delivering precise time to any user is one of the most important functions of GPS technology. This technology helps synchronize clocks and events around the world. Pager companies depend on GPS satellites to synchronize the transmission of information throughout their systems. Investment banking firms rely on this service every day to record international transactions simultaneously.
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