General Information About GPS and its Uses Engineering

General Information About GPS and its Uses Engineering Measurments Ali Bosrour 201602189 Youssef Moussa 201600217 Abdulmohsen almomen 201400875

Outline: • Background • High Precision Permanent GPS Station • How Can Studying GPS Motion be Useful to Society? • Components of GPS System • Geographical Information System • Satellite Errors • Observation Errors • Receiver Errors • Multiple Errors

Background • The Global Positioning System (GPS) is a space-based Global navigation satellite system that provides location and time information. • The project was started in 1973 to overcome the limitations of previous navigation system. • GPS was created by the US department of defenses and was originally run with 24 satellites. • It became fully operational in 1994 at the cost of twelve billion US taxpayer dollars. • Freely accessible by anyone with a GPS receiver.

HIGH PRECISION PERMANENT GPS STATION GPS antenna inside of dome Monument solidly attached into the ground with braces. If the ground moves, the station moves. • Solar panel for power Equipment enclosure: • GPS receiver. • Power/batteries • Communications/ radio/ modem. • Data storage/ memory.

HIGH PRECISION PERMANENT GPS STATION What is the function of what the arrow is pointing to? • Power source • Receives satellite signal • Records data • Communication • Anchors station to ground

HOW CAN STUDYING GPS MOTION BE USEFUL TO SOCIETY? What GPS can measure: • Movement of ground near earthquake faults • Movement of ground during earthquakes • Movement of ground movement of magma underground • Movement of ground due to changing size of glaciers • Movement of ground due to changing snow depth • Movement of ground due to changing amount of groundwater within the • • ground Amount of water in the atmosphere Amount of soil moisture Vegetation growth Sea level

Components of GPS Systems *Consists of 3 Main Components: 1) GPS Ground Control Station: • The control segment uses measurements collected by the monitor stations to predict the behavior of each satellite's orbit and atomic clocks. • The prediction data is linked up to the satellites for transmission to users. 2) GPS Satellites: • GPS satellites orbit in circular orbits at 17, 440 km altitude, each orbit lasting 12 hours. • The satellites are powered by solar cells to continually orientate themselves to point the solar panels towards the Sun and the antennas towards the Earth.

Components of GPS System 3) GPS Receivers: • When you buy a GPS, you are actually buying only the GPS receiver and get free use of the other two main components, worth billions of dollars.

Geographical Information System (GIS) • GIS is a computer program that is designed to capture, analyze, interpret and store data that has been transmitted from GPS and make the information available for use. • GIS is used to provide visual representations of data. • GIS is used to show the relationship between two different locations and the proximity of two locations on a map.

Satellite Error • Though they use atomic clocks, they are still subject to small inaccuracies in their time keeping. These inaccuracies will translate into positional errors. ▪ Orbit Uncertainty: • The satellites position in space is also important as it’s the beginning for all calculations they drift slightly from their predicted orbit.

Observation Errors * GPS signals transmit the information via radio waves * It is assumed that a radio wave travels at the speed of light. * GPS signals must travel through a number of layers making up the atmosphere. * As they travel through these layers the signal gets delayed * This delay translates into an error in the calculation of the distance between the satellite air timing between the satellite

Receiver Error Unfortunately not all the receivers are perfect. They can introduce errors of their own • Receiver clock drift • Internal receiver noise

Multipath Error • When the GPS signal arrives at earth it may reflect off various obstructions • First the antenna receives the signal by the direct route and then the reflected signal arrives a little later

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