The author would have loved to have used GPS years ago in college. We had a class where we used maps and compasses. We were given precise coordinates and had to plot a course through woods and streams and swamps to find and sign in at specific latitude and longitude coordinates. Today, this sport, now called "geocaching", is a popular activity, particularly for outdoor hiking enthusiasts.
GPS signals can also be affected by multipath reflections of the radio signals off the ground and/or surrounding structures (buildings, canyon walls, etc). For long delay multipath signals, the receiver itself can filter the signals out. A variety of receiver techniques, most notably Narrow Correlator spacing, have been developed to mitigate multipath errors.
In 1996, President Bill Clinton issued a policy directive declaring GPS to be a dual-use system, meaning that it could be made avilable for a wide range of civilian and military purposes.
The United States Department of Defense developed the system, officially named NAVSTAR GPS (Navigation Signal Timing and Ranging GPS), and the satellites are managed by the 50th Space Wing at Schriever Air Force Base. Although the cost of maintaining the system is significant, GPS is available for free use in civilian and commercial applications.
GPS is coming into common use in cars these days. Most new cars allow you to purchase GPS technology that will help you plot your trip from one location to the next.
GPS receivers come in a variety of consumer formats, and today can be found in cars, watches, phones boats and planes. Major manufacturers include Trimble, Garmin and Leica, low-end, hand-held consumer units are often available at less than $100 per unit.
More accurate GPS receivers are used these days in surveying to accurately locate boundaries, structures and so on.
The first experimental Block-I GPS satellite was launched in February 1978. The GPS satellites were initially manufactured by Rockwell International and now manufactured by Lockheed Martin.
In 1985, ten experimental Block-I satellites were up. A complete "constellation" of 24 satellites was in orbit by January 17, 1994.
Most ships and airplanes are equipped with GPS systems so that they can accurately plot on a map where they are. In planes, this is especially useful during bad weather, and in ships in knowing where shallow water and other sunken obstacles may lie.
GPS allows the military to accurately target its missile arsenal, largely composed of cruise missiles and precision-guided munitions. This was born out by the use of SOFLAM (Special Operations Forces Laser Acquisition Markers) targeting during the attacks on Tora Bora in Afghanistan. It also improves the accuracy of the US submarine launched ballistic missiles by providing precise locational information to the submarine commanders. Finally, command and control over troops is improved because commanders know precisely where their troops and the enemy are located on the battlefield.
Each satellite repeatedly re-broadcasts the exact time according to its internal atomic clock along with a digital data packet that includes the satellite's precise position, satellite status messages, and an almanac of the approximate position of every other active GPS satellite. The almanac lets GPS receivers use data from the strongest satellite signal to locate other satellites.
GPS is short for (the) Global Positioning System, a satellite navigation system developed by the US Department of Defense. A fleet of more than two dozen GPS satellites broadcasts precise timing signals to GPS receivers, allowing them to accurately determine location anywhere on Earth. In practice, this means that using a GPS device, you can find out where you are in terms of longitude, latitude and altitude.
GPS receivers calculate their current position (latitude, longitude, elevation), and the precise time, using the process of trilateration after measuring the distance to at least four satellites by comparing the satellites' coded time signal transmissions.