Global Navigation Systems Technology

Satellite-based time and location services are now available at low cost to anyone who needs to put such services to use. Amateur radio operators have developed the Automatic Packet Reporting System or APRS, combining amateur packet radio networks with satellite navigation systems for automatic real-time tracking applications including public service networks supporting running or bicyling races, or emergency communications scenarios including determining forest fire boundaries. A future story on APRS will appear in Ham Radio Online.

Most of us have learned at least a little bit about using a map and compass to navigate our way through a forest trail, or perhaps across a large lake in a small boat or maybe even in a light plane. The compass, using only the Earth's own magnetic field for guidance, is a great navigational tool. To be used properly, you need to know about local magnetic disturbances and the local delta between magnetic North pole and the True North pole. Fortunately, learning to use a compass is easy and it never requires new batteries :-)

With little more than a compass and maps, navigators have relied upon time honored techniques such as dead reckoning (plot a course, sail that way for a time period, and hope you get there), pilotage (watching for landmarks) or the mariner's skill and understanding of celestial navigation (literally using nighttime stars and the angle of the sun in the daytime sky) to determine one's position.

The 20th century brought new technologies like LORAN (Long Range Navigation using medium wave radio signals) or the VOR (VHF Omni Range station for aircraft).

In the late 1980s, two satellite based global navigation systems were placed in orbit: The Global Positioning System or GPS, launched by the United States; and the Global Navigation System or GLONASS, launched by Russia. Through the use of these satellite based navigation systems, users on the ground can obtain precise latitude, longitude, altitude and time information. By combining this information with digital map databases, satellite navigation systems are replacing many traditional forms of navigation.

Spaceborne navigation systems operate by transmitting precisely coded time signals from multiple spacecraft. Navigation units on earth interpret the time signals using complex mathematics to determine a precise location. An excellent, easy reading tutorial is available online from Trimble navigation products: What is GPS - A Tutorial

If you want to peel away the fluff and get down to the technical details, visit Global Positioning System Overview by Peter H. Dana, Department of Geography, University of Texas at Austin.

You can learn much more About GLONASS - the Russian spaceborne navigation system.

Complete GPS system status is available from the United States Coast Guard.

GPS Satellite. Photo from U.S. Coast Guard GPS System web site.