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Chapter 2: GPS Information
2.1 About Satellite Navigation
Global satellite navigation is an exciting technology, providing enhanced productivity and accuracy in a vast number of
industries. It adds a new level of enjoyment and safety to a wide range of navigation, sports, and recreational activities.
A Global Navigation Satellite System (GNSS) is a network of satellites that transmit high-frequency radio signals containing
time and distance data that can be picked up by a receiver, allowing users to pinpoint their precise locations anywhere
around the globe.
There are two Global Navigation Satellite Systems in operation: the U.S. Global Positioning System (GPS) and the Russian
GLObal NAvigation Satellite System (GLONASS). These systems are constantly being upgraded to meet higher standards of
reliability. A third GNSS named GALILEO, after the Italian astronomer of the early 1600s, is being developed in Europe
specifically to provide a higher standard of integrity and reliability, required to ensure the safety of lives during transport by
air, land and sea, without the use of additional augmentation systems.
While the GPS and GLONASS satellite networks are being developed to achieve maximum performance, Satellite-Based
Augmentation Systems (SBAS) have been established to provide improved accuracy. SBAS provides differential signal
corrections for GPS and GLONASS transmissions with the use of ground stations and geostationary satellites in specific
regions. This is GNSS-1, the first phase in establishing the required integrity for high-precision satellite navigation.
GNSS-2 requires the launching of new satellites into orbit and a complete upgrade of the existing satellite systems. This
second phase is already well underway. GALILEO, scheduled to begin service in 2008, is being developed to meet the
standards of GNSS-2 for rapid and reliable, certified precision positioning.
2.2 How Satellite Navigation Works
Global navigation satellites continuously transmit time and distance information as they orbit Earth in a precise formation.
Navigation satellite receivers use this information to calculate an exact location through triangulation. Every point on Earth is
identified by two sets of numbers called coordinates. These coordinates represent the exact point where a horizontal line,
known as latitude, crosses a vertical line, known as longitude. The receiver locks on to at least three satellites and uses the
information received to determine the coordinates of the receiving device.
By comparing the time the signals were transmitted from the satellites and the time they were recorded, the receiver
calculates how far away each satellite is. The distance of the receiver from three or more satellites reveals its position on the
surface of the planet. With these distance measurements, the receiver might also calculate speed, bearing, trip time,
distance to destination, altitude, and more.
The satellite-navigation device may display its position as longitude/latitude, Universal Transverse Mercator (UTM), Military
Grid (MG), or simply as a point on an electronic map. Many Thales Navigation receivers provide comprehensive mapping
data, making satellite navigation an easy tool to enhance your recreational and industrial activities.
2.2.1 Line of Sight
Satellite-navigation receivers operate by line of sight with global-positioning satellites. This means that at least three
satellites must be in “view” of a receiver in order to calculate longitude and latitude. A fourth satellite must also be within
line of sight to calculate altitude. On average, eight satellites are continuously within line of sight of every position on Earth;
the more satellites in view, the more accurate the positioning.
Though the radio signals of navigation satellites will pass through clouds, glass, plastic, and other lightweight materials,
satellite-navigation receivers will not work underground or in other enclosed spaces.