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Renato Marando

on 24 March 2015

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Transcript of GPS


A GPS (Global Positioning System) is a satellite navigation system which is used to locate precise positions on the earth. It is made up of 24 satellites (6 extra in case others fail) which orbit the earth at specific locations at approximately 17 700km from the earths surface. The system was created by the USA, particularly for military. The Department of Defence developed the system further and it became fully operational to the public in 1995.
Well what is a satellite....

A satellite is a man-made object which
orbits around the earth at specific locations. They come in many shapes and sizes and have many roles, in this case
. The GPS satellite is what transmits the signal to the GPS receiver. This is used in the process of triangulation.

Triangulation is a process used to accurately find the location of a GPS receiver on the earths surface, it can be also known as trilateration, however this is the 2D representation of it. Examples of a GPS receiver are a phone, navigator and car. The receiver must be visible by at least three GPS satellites in orbit and the distance from the satellite must be known in order for its location to be found. Furthermore, a minimum of four visible satellites is more accurate as it determines the altitude of the GPS receiver as well. The point in which each satellites spherical radii intersect is where the GPS receiver is located on the earth
(This process is represented in the follwing image)
. A limitation of triangulation is that if the GPS receiver is hidden, in a blocked position or is not visible to three or more satellites then the signal cannot give an accurate reading of its position.
Both GPS satellite and receiver emit a signal at the same instant. The signals are transmitted as radio waves which is a part of the electromagnetic spectrum.

In order to calculate how long it takes for the GPS satellite to send a signal to the GPS receiver, an atomic clock is required. There is an atomic clock located in each GPS satellite, it is the most accurate clock as it is synchronised to the nanosecond (billionth of a second). With this, the time it takes for the radio signals or microwaves to travel from the GPS satellite to receiver, or vise versa can be calculated most accurately. The atomic clock allows satellites to transmit signals which are synchronised with other satellites.

- Navigation
- Target Tracking
- Missile and Projectile Guidance
- Search and Rescue
- Sport
- Navigation
- Astronomy
- Automated Vehicles
- Robotics
Well what are waves....

A wave is a transfer of energy from one place to another. In this case, the waves associated with the transfer of GPS signals are electromagnetic waves. An electromagnetic wave is an oscillation of electromagnetic fields. This means the wave has an electric and magnetic field which are perpendicular to each other.
Due to the waves being electromagnetic they travel at the speed of light which is 299792458m/s, therefore you can calculate the time it will take for the signal to travel from the satellite to receiver, known as the
signal transit time
by using Speed=Distance/Time formula. Moreover, each satellite transmits two navigational signals called L1 and L2. L1 has a frequency of 1575.42 MHz and L2 has a frequency of 1227.6 MHz. Both these signals are microwaves and are transferred to the earth (the GPS receiver).
Each satellite has its own unique pseudo random code (PRC). This is a long digital pattern which is in the form of a square wave and it is known as a random electrical noise. There are two types of PRC's, the first one is C/A-code (coarse-acquisition code), this uses the L1 wave and is used for civilian GPS. The second one is P-code (precise code), this uses L1 and L2 waves and is used for military and encrypting.
- GPS works in all weather
- Costs very low compared to other navigational systems
- 100% coverage of the planet
- Useful to civilians as they can find places to go easily e.g restaurant, hotel
- The system is updated regularly, therefore it is very advanced.

GPS has an immense impact on society, this is because it has changed the way people travel and it has many uses which can assist individulas as well as organisations. As a result of the the evolvement of technology people can know where they are going very easily without using hand held maps or any other sources. Furthermore, the GPS is used for more significant aspects in society particular to assist with governement initiatives like defence and world issues e.g natural disasters.

The environment is also particularly affected by the GPS because it can help monitor environmental issues like sea levels and ground elevations. This can help orgnisations take early action and therefore prevent issues that can affect the environment.
- If a receiver is hidden or is not visible to three or more satellites, it will not have an accurate reading.
- The system relies on satellite signals so if some fail it could cause malfunctions.
- GPS can cause accidents as peope focus on them rather than the road.

The satellites have an atomic clock, whereas the receivers have a quartz clock. The quartz clock is manufactured to be delayed on earth so that it is on time in space. The quartz clock regularly resets in order to maintain its synchronisation with the atomic clock. The PRC's are what shift the signals so that the time delay from the quartz and atomic clock can be adjusted.
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