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 transmits high-frequency radio signals containing time and distance data that can be picked up by a receiver, allowing the user to pinpoint their precise location anywhere around the globe.

There are two Global Navigation Satellite Systems currently 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 currently being developed in Europe to specifically 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.

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.

Precision
On average, a satellite navigation receiver is accurate to within 15 meters. Thales Navigation employs several technologies to increase the accuracy of their professional and Magellan^®-branded receivers. An accuracy of 3 meters or better is achieved using correction signals from satellite navigation augmentation systems. In the U.S., an accuracy of 3 meters is achieved using signal corrections from a network of ground stations and fixed position satellites known as WAAS (Wide Area Augmentation System). Throughout Europe a similar system provides the same accuracy; EGNOS (European Geostationary Navigation Overlay System). In Asia, satellite navigation signal correction is provided by MSAS (Multifunctional Transport Satellite-based Augmentation System). Other ways to increase the accuracy of satellite navigation include the use of DGPS (Differential Global Positioning System); ground relay stations, set at known positions, that transmit corrected satellite navigation signals. Various methods and applications of DGPS can increase satellite navigation accuracy from a few meters to within a few millimeters. Using DGPS requires a differential beacon receiver and antennae in addition to a satellite navigation device. Accuracy can also be increased using an RTK (Real-Time Kinematic) satellite navigation system. This is a receiver capable of transmitting a phase-corrected signal from a known position to one or more rover receivers.

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:

·                            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.

·                            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.

·                            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.

Thales Navigation receivers make a number of complex mathematic calculations to effectively compensate for other potential errors in positioning:

·                            Atmospheric delay - Satellite navigation signals slow as they pass through the Earth's atmosphere. Thales Navigation receivers calculate the average delay in nanoseconds to compensate.

·                            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. Each Thales Navigation receiver compensates for time differentials by comparing the time signals of several satellites and adjusting its calculations and its clock to match.

GPS (Global Positioning System)

GPS is the U.S. Global Navigation Satellite System (GNSS). A network of 24 satellites continuously transmits high-frequency radio signals, containing time and distance data that can be picked up by any GPS receiver, allowing the user to pinpoint their position anywhere on Earth.

Originally designated NAVSTAR (NAVigation System with Timing And Ranging), development of GPS began in 1973. In 1978, the U.S. Department of Defense launched the first GPS satellite, imposing SA (Selective Availability); the intentional degradation of GPS signals to prevent military adversaries from using the highly accurate positioning data. SA limited GPS to 100-meter accuracy for non-U.S. military users. Magellan^® introduced the first handheld receiver in 1989, making GPS available and practical for many new industrial and recreational applications. The network required to efficiently cover the Earth was completed with the launch of the 24^th satellite in 1994. Replacement satellites continue to be launched, each having a life span of about 10 years.

In 2000, Selective Availability was turned off by presidential order, giving all GPS receivers the potential accuracy of 15 meters without the use of signal correction. The signals are available 24 hours a day in any weather condition, everywhere around the world. When used with WAAS or EGNOS receivers, GPS accuracy can be improved to 3 meters.

GLONASS (GLObal NAvigation Satellite System)

GLONASS is the Russian Global Navigation Satellite System (GNSS). A network of 24 satellites continuously transmits high-frequency radio signals, containing time and distance data that can be picked up by any GLONASS receiver, allowing the user to pinpoint their position anywhere on Earth.

Developed and operated by the Russian Federation Ministry of Defense, the first GLONASS satellite launched in 1982. In 1996 Russia agreed to work with the International space-science community to establish a universal standard for the development of GNSS. The network required to efficiently cover the Earth was completed with the launch of the 24^th GLONASS satellite in 1998.

The signals are available 24 hours a day in any weather condition, everywhere around the world.

Satellite Navigation Augmentation Systems

Satellite-Based Augmentation Systems (SBAS) are networks of ground relay stations and geostatic satellites designed to receive satellite navigation signals and transmit corrected time and distance measurements that greatly improve accuracy. Observation and relay stations have been set at known positions all over the world, while their geostatic satellites continuously maintain a fixed position above the Earth. Using these known values for distance, SBAS corrects satellite navigation signals for atmospheric delays, incorrect satellite positioning and poor geometry, sometimes caused by inline or close alignment of satellites, increasing accuracy in specific regions. SBAS is vital to providing the reliability and precision required by aviation and other precision-critical applications. Using the same signal frequencies as satellite navigation, SBAS-enabled receivers are inter-compatible. Three augmentation systems are currently in varying stages of operation and development covering North America, Europe and Asia. Already the incredibly accurate positioning capabilities of SBAS are being used in agriculture, development, mining and many other industries as well as hiking, boating, hunting, travel and an expanse of other leisure and business activities.

WAAS (Wide Area Augmentation System)
In North America, WAAS provides satellite navigation correction and validation, making WAAS-enabled receivers at least five times more accurate than standard devices. WAAS relay stations have been set at known positions throughout North America.

SBAS-enabled receivers do not require any additional equipment to use WAAS correction signals and, as with satellite navigation signals, there are no setup or subscription fees. WAAS is accurate to within three meters or less. System upgrades are being developed which will soon provide accuracy to well within one meter.

In 2003, the FAA (Federal Aviation Administration) plans to certify WAAS for use in low-altitude maneuvering, instrument approach and other sensitive aviation applications.

EGNOS (European Geostationary Navigation Overlay System)
EGNOS provides satellite navigation correction and validation throughout Europe, making EGNOS-enabled receivers at least three times more accurate than standard devices. EGNOS relay stations have been set at known positions throughout Europe.

SBAS-enabled receivers do not require any additional equipment to use EGNOS correction signals and, as with satellite navigation signals, there are no setup or subscription fees. Providing accuracy to within five meters or less, EGNOS is scheduled for full operation in 2004 and represents the first step toward Europe's GALILEO global satellite navigation system.

More about EGNOS.

MSAS (Multifunctional Transport Satellite-based Augmentation System)
Throughout Asia, MSAS provides satellite navigation correction and validation, making SBAS-enabled receivers at least three times more accurate than standard devices. MSAS relay stations have been set at known positions throughout Asia.

SBAS-enabled receivers do not require any additional equipment to use MSAS correction signals and, as with satellite navigation signals, there are no setup or subscription fees. Providing accuracy to within 5 meters or less, MSAS is scheduled for full operation in 2005 and will expand safety and air-traffic capacity in the Asia pacific regions.