The GPS system was solemnly built for strict military purposes (tracing the enemy, locating its movements etc.), but now it has become a regular part of our life in such a short time.
Like who wouldn’t want to know their exact location on this planet? It’s just like a science fiction story out of our books brought to this real world. The exact precise locations of airplanes, ships, cars and even a person is so easy to track down as even a person can carry a GPS device with him/her.
History of GPS
The Global positioning system (GPS) a space- based navigation system owned by the US government. It is a global navigation system that can provide a user’s location (if the person/machine has a GPS receiver) even in bad weather conditions since it has no telephonic connections. The GPS was first used by the US in 1973 during military warfare and it became fully operational in the year 1995.
The current GPS consists of 3 major parts namely:
- Space Segment: Composed of Space vehicles/satellites traveling around the earth on 6 orbits at an altitude of approximately 20,000km and move around at intervals of 12 hours. They give the proper alignment of a place.
- 2. Control Segment: They are usually stationed on the earth’s surface and are controlled by the National Geo-spatial Intelligence Agency (NGA). They play an important role in monitoring, controlling and maintaining the satellite orbit to make sure that the deviation and GPS time are always within the tolerance level. They also help in tracking a flight’s paths i.e. helping the air traffic control and in weather forecasting.
- User Segment: This is usually called the GPS receivers and is composed of antennas tuned to frequencies transmitted by the satellites. They usually provide the user details of his/her location or speed details.
- At first, the signal is sent to the GPS satellite at a given point.
- Subsequently, the time interval between GPS Satellite and the receiver is calculated to generate the distance of the path.
- Usually, 4 satellites are used for this purpose to minimize the error.
- The error usually arises from a time error on the clock placed in the satellites.
- All the distances calculated between the 4 satellites and the receiver is calculated and averaged to reduce the error
GPS satellites usually use two frequency beams; L1(1575.42MHz) and L2(1227.60MHz). The general public usually uses C/A code which consists of identification codes of each satellite. The data of each satellite is called ephemeris and the data from the all the satellites is called almanac. Using this data the GPS calculates the distance between satellite and receiver in order to get the exact location.
Factors triggering GPS position errors
Ionosphere: It is a layer of the atmosphere. When GPS signals pass through this layer the speed is drastically decreased causing propagation errors.
Troposphere: It is the lowest layer of the atmosphere. Water vapour and radio reflection affect GPS signals.
GPS signals strengths are affected when it hits the ground and structures. It causes position errors.
Applications of GPS
GPS plays a major role in road transport. It is usually used for fleet management, taxi services, public transport services, emergency services,etc. Private car users have also adopted the GPS on a large scale and now most of the automobiles have a GPS fitted in.
Airplanes use GPS for en-route navigation. Automatic Dependent Surveillance-Broadcast (ADS-B) is being developed for future technology for hassle free and unmanned traffic controlling. They are also used for aerial mapping and survey.
Shipping And Rail Transport
Water applications include inshore and sea navigation, port approaches,docking,AIS and cargo handling. Railway applications include stock management, passenger information, cargo-tracking station approaching.
Scientific application of GPS include atmospheric monitoring, animal tracking, meteorology, climate research, etc. it is also used in agriculture for land mapping, yield monitoring, spraying, harvesting and also monitoring fish limits.
Heavy Vehicle Guidance
GPS is used to guide and track heavy vehicles in engineering projects like in mining and construction.
It is used in mainly in telephone networks. GPS allows synchronized UTC time through resolving the signals from atomic clocks around the globe. So it helps in auto updates of the phones time and date according to its location.
Surveying and Mapping
GPS is widely used in aerial mapping and other GIS applications. It is also used to time stamp seismic activities and to monitor position changes in sensitive areas like volcanoes earthquakes etc.
They are widely used in activities like as in sky diving, geotagging photos, cross country cycling, trekking, skiing, geocaching, etc.
GPS helps in scheduling international money transfers, settlements, and trades.
With millions of these transactions occurring every second an accurate time tracking has to be done.
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