Global Positioning System
Handheld GPS units are receivers designed to integrate with GPS satellites. The GPS, or Global Positioning System, consists of a series of 27 satellites in geosynchronous orbits which send location signals to receivers like handheld GPS units. At any given time, at least four satellites are above anyplace on earth, allowing for precise locations on the handheld units.
With almost all handheld GPS receivers now being WAAS, or Wide Area Augmentation System, equipped, they are now accurate to within several feet. WAAS had been the exclusive domain of Military GPS units until President Clinton lifted the WAAS military restrictions for consumer use in the mid 1990s.
GPS receivers pick up radio wave transmissions/signals from the orbiting satellites. These signals contain several pieces of information including almanac and ephemeris data, and a pseudorandom code. Almanac data gives the receiver information about the satellite, and date and time. Ephemeris data tells the GPS receiver where the satellite should be at any time during the day, and the pseudorandom code is the satellite's ID code.
While accurate and handy, GPS handheld receivers are not without errors. Common causes of inaccurate GPS readings are ionosphere and troposphere delays, where the satellite signal slows from atmospheric conditions, signal multipath caused from signal reflection, and other degradations of the satellite signal.
Free of Charge
Since the lifting of military-only restrictions on GPS signals, handhelds have become widespread in use. GPS signals are available 24 hours a day, every day of the year at no charge to the GPS handheld user. A good selection of handheld GPS units are available at Trails.com.
Article Written By Eric Cedric
A former Alaskan of 20 years, Eric Cedric now resides in California. He's published in "Outside" and "Backpacker" and has written a book on life in small-town Alaska, "North by Southeast." Cedric was a professional mountain guide and backcountry expedition leader for 18 years. He worked in Russia, Iceland, Greece, Turkey and Belize. Cedric attended Syracuse University and is a private pilot.