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What is GPS?
A brief history…
The first ever satellite based positioning system was developed by the US for use by their Navy during the early 1960’s and began service in 1964. It was called ‘Transit’ and used five satellites to enable a receiver to establish its location within around an hour to an accuracy of around 200 meters. It contained very rudimentary technology and no timing devices. A few years later they developed the ‘Timation’ satellite which proved the concept of placing accurate clocks in space, technology that GPS now relies on.
At the time of writing, The Global Positioning System (GPS) is the only fully functioning Global Navigation Satellite System (GNSS) in the World. It is officially called ‘NAVSTAR-GPS’ but is commonly abbreviated to GPS. GPS currently uses 31 operational satellites which are managed by the US Air Force 50th Space Wing, although there are similar systems undergoing development and testing by the Russians (GLONASS), Chinese (COMPASS), Indians (IRNSS) and Europeans (Galileo).
The first of the GPS satellites, designed to eventually replace the aging ‘Transit’ system, was launched in 1978. It facilitated the start of far greater positioning accuracy and speed, and incorporated reliable and stable atomic clocks for additional functionality. The oldest GPS satellite still in operation was launched in July 1991 and the newest was launched in March 2008. There are now 32 in orbit, of which one has failed.
The first applications for GPS were for military navigation and weapons aiming. However, after a tragedy in 1983 in which a Korean commercial airliner was shot down killing 269 people after inadvertently flying into restricted USSR airspace, President Reagan issued a directive to make GPS technology available to civilians. Little did he know that GPS technology would quickly become part of everyday life, with many adults in the Western World today owning or using several GPS enabled devices.
How it works…
The GPS receiver calculates its precise location by timing microwave messages that are continually being sent by the GPS satellites at the speed of light. These messages include the precise time the message was sent, the location of the satellite that sent it, and proximity of the other GPS satellites. By recording the arrival time of each message, it can calculate the distance it is from each and therefore its location. This data can then be converted to useful information, such as latitude and longitude, or position on a map. Having established more than one instance of location and time, the receiver can calculate direction, speed and acceleration.
Most applications require sight of a minimum of four satellites, although if one variable is already known precisely, altitude for example, a receiver can determine its location using just three. With 31 operational satellites, the orbits are arranged so that a minimum of six are in line of sight from any position on earth at any time, providing excellent coverage, accuracy and reliability, even if several satellites fail. The arrangement can be altered, for example to provide optimum coverage in a war-zone.
GPS receivers are referred to as the ‘User Segment’ (US) of the system. They typically consist of a combined receiver-processor chip (on average approximately 15mm square), battery and antenna integrated onto a circuit board, and sometimes a display. Receivers are sometimes described by their number of channels, meaning the number of satellites it can receive signals from simultaneously. Early receivers were only four or five channel, but now 20 channel receivers are commonplace. Many GPS receivers can relay data to a PC or other device using one of several protocols which can be read by open source tools without violating intellectual property rights. This allows software to be written that greatly increases the number and functionality of applications that can benefit from GPS technology. Unfortunately, GPS receivers can sometimes interfere with devices including a serial connection such as USB or Bluetooth.
Current Applications…
There are a large number of applications for GPS technology using one or more of the three basic components, ‘Absolute Location’ (where is it?), ‘Relative Movement’ (where is it going?) and ‘Time Transfer’ (how fast is it going?). Here are just a few.
Military
Civilian
A brief history…
The first ever satellite based positioning system was developed by the US for use by their Navy during the early 1960’s and began service in 1964. It was called ‘Transit’ and used five satellites to enable a receiver to establish its location within around an hour to an accuracy of around 200 meters. It contained very rudimentary technology and no timing devices. A few years later they developed the ‘Timation’ satellite which proved the concept of placing accurate clocks in space, technology that GPS now relies on.
At the time of writing, The Global Positioning System (GPS) is the only fully functioning Global Navigation Satellite System (GNSS) in the World. It is officially called ‘NAVSTAR-GPS’ but is commonly abbreviated to GPS. GPS currently uses 31 operational satellites which are managed by the US Air Force 50th Space Wing, although there are similar systems undergoing development and testing by the Russians (GLONASS), Chinese (COMPASS), Indians (IRNSS) and Europeans (Galileo).
The first of the GPS satellites, designed to eventually replace the aging ‘Transit’ system, was launched in 1978. It facilitated the start of far greater positioning accuracy and speed, and incorporated reliable and stable atomic clocks for additional functionality. The oldest GPS satellite still in operation was launched in July 1991 and the newest was launched in March 2008. There are now 32 in orbit, of which one has failed.
The first applications for GPS were for military navigation and weapons aiming. However, after a tragedy in 1983 in which a Korean commercial airliner was shot down killing 269 people after inadvertently flying into restricted USSR airspace, President Reagan issued a directive to make GPS technology available to civilians. Little did he know that GPS technology would quickly become part of everyday life, with many adults in the Western World today owning or using several GPS enabled devices.
How it works…
The GPS receiver calculates its precise location by timing microwave messages that are continually being sent by the GPS satellites at the speed of light. These messages include the precise time the message was sent, the location of the satellite that sent it, and proximity of the other GPS satellites. By recording the arrival time of each message, it can calculate the distance it is from each and therefore its location. This data can then be converted to useful information, such as latitude and longitude, or position on a map. Having established more than one instance of location and time, the receiver can calculate direction, speed and acceleration.
Most applications require sight of a minimum of four satellites, although if one variable is already known precisely, altitude for example, a receiver can determine its location using just three. With 31 operational satellites, the orbits are arranged so that a minimum of six are in line of sight from any position on earth at any time, providing excellent coverage, accuracy and reliability, even if several satellites fail. The arrangement can be altered, for example to provide optimum coverage in a war-zone.
GPS receivers are referred to as the ‘User Segment’ (US) of the system. They typically consist of a combined receiver-processor chip (on average approximately 15mm square), battery and antenna integrated onto a circuit board, and sometimes a display. Receivers are sometimes described by their number of channels, meaning the number of satellites it can receive signals from simultaneously. Early receivers were only four or five channel, but now 20 channel receivers are commonplace. Many GPS receivers can relay data to a PC or other device using one of several protocols which can be read by open source tools without violating intellectual property rights. This allows software to be written that greatly increases the number and functionality of applications that can benefit from GPS technology. Unfortunately, GPS receivers can sometimes interfere with devices including a serial connection such as USB or Bluetooth.
Current Applications…
There are a large number of applications for GPS technology using one or more of the three basic components, ‘Absolute Location’ (where is it?), ‘Relative Movement’ (where is it going?) and ‘Time Transfer’ (how fast is it going?). Here are just a few.
Military
- Navigation – Helps Soldiers carry out their duties in unfamiliar territory and low-light conditions and Commanders co-ordinate the movement of personnel and supplies. The GPS receivers used by Commanders and Soldiers are called the ‘Commanders Digital Assistant’ and ‘Soldiers Digital Assistant’.
- Tracking – Potential targets are tracked using GPS before they are confirmed hostile. Co-ordinates can then be passed to aircraft and precision-guided munitions systems so that the target can be engaged accurately.
- Projectile Guidance – GPS receivers incorporated within weapons including cruise missiles ensure that they reach their target. Receivers capable of withstanding acceleration of up to 12,000G have been developed.
- Search and Rescue – Downed pilots and missing Soldiers can be located more quickly when they have a GPS receiver.
- Mapping – GPS is used extensively to aid mapping and reconnaissance in unfamiliar territory.
- Nuclear Detection – Although not a primary function, the GPS satellites are equipped with a set of nuclear detonation detectors which form part of the US Nuclear Detonation Detection System.
Civilian
- Navigation – An increasing number of new cars now incorporate navigation systems as standard and the after-market continues to grow. Dedicated systems are now available for motorbikes, marine and aviation use, and there are hand-held devices for hikers and climbers.
- Location – The growing use of road safety/speed cameras has led to a wide range of products being developed to provide road users with advance warning of their presence. The kenbuster is an innovative new product that warns road users when they are within the London congestion charge zone. It can arrange payment of the charge too! Vehicles fitted with GPS tracking devices have an excellent recovery record in the event of a theft, as Police are precisely and covertly alerted to their whereabouts.
- Tracking – GPS receivers have reduced in size and cost to the point that attaching one to a dog collar or child’s coat has become a reality. Being able to pinpoint the exact location of a child, elderly relative or pet provides peace of mind unheard of a few years ago. Zoomback are one of the market leaders with their Dog Locator for pets and Universal Locator designed to track people, but also suitable for a variety of other applications.
- Emergency – Aimed at hikers, climbers, skiers and others engaged in extreme sports, the SPOT personal tracker is a GPS personal safety device that contacts the appropriate emergency services if the need arises and advises a precise location. It can also send a regular signal to a loved-one to confirm all is well.
- Sport – GPS cycling and running devices monitor and track performance, as well as provide the users location, distance and speed. Some even incorporate heart-rate monitors. Golfers can improve their handicap by using the latest hand-held devices to provide essential information and advice on negotiating thousands of courses Worldwide.
- Leisure - Geocaching is an outdoor treasure-hunting game where participants use hand-held devices to hide and seek ‘caches of treasure’ all over the World. Geotagging is the process of tagging media such as photographs, video and websites to locations for other’s future interest. Fishfinders take the pain away from fishing by providing an insight into what’s happening below the surface.