How Satellite Navigation Works?
Global navigation
satellites continuously transmit time and distance information as they orbit the
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 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.
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.
Errors
A number of positioning errors can occur, limiting accuracy to within 15 to 25 meters. These errors are monitored and compensated for in a number of ways:
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Orbiting errors - Occasionally a satellite's reported position does not match its actual trajectory. In the U.S., the Department of Defense continuously monitors each satellite, making orbital corrections with onboard booster rockets.
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Poor geometry - If all the satellites within line of site of a receiver are clustered closely together, or lined up relative to the position of the receiver, the geometric calculations necessary for triangulating a position become difficult and less reliable. The use of differential correction signals from satellite-based augmentation systems or DGPS can compensate for both orbital errors and poor geometry.
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Multi-path signals - Signals may be reflected off tall buildings or other obstructions before reaching the receiver, increasing the distance a signal travels, reducing accuracy.
Promark3 receivers make a number of complex mathematic calculations to effectively compensate for other potential errors in positioning:
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Atmospheric delay - Satellite navigation signals slow as they pass through the Earth's atmosphere. Promark3 receivers calculate the average delay in nanoseconds to compensate.
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Clock errors - The clock built into a receiver is not as accurate as the atomic clock on a navigation satellite, which is accurate to one second every million years. Promark3 receiver compensates for time differentials by comparing the time signals of several satellites and adjusting its calculations and its clock to match.
