More accurate GPS receivers are used these days in surveying to accurately locate boundaries, structures and so on.
In late 2005, the US government introduced the first in a series of new generation GPS staellites offering new capabilities. Chief among these is a second civilian GPS signal called L2C for greater accuracy and reliability.
GPS has become a vital global utility, indispensable for modern navigation on land, sea, and air around the world, as well as an important tool for map-making, and land surveying. GPS also provides an extremely precise time reference, required for telecommunications and some scientific research, including the study of earthquakes.
GPS derives in part from its predecssor, the LORAN navigation system. LORAN was designed for ship and airplane navigation in the 1940s for use during World War II.
Because GPS is as much an accurate time keeper as a locator, one of the most common applications for GPS units is as a reference clock for time code generators or NTP clocks. For instance, when monitoring earthquakes, each seismic sensor can be synched with the GPS system to provide a synchronized, precise time source for measurements.
In 1998, Vice President Al Gore announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety.
The US military has developed the ability to locally deny GPS (and other navigation services) to hostile forces in a specific area of crisis without affecting the rest of the world or its own military systems. Such Navigation Warfare uses techniques such as local jamming to replace the blunt, world-wide degradation of civilian GPS service that SA represented.
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.
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.
Hand-held GPS units are often used by hikers and mountain climbers to plot their courses and to accurately reflect exactly where they are. The author once used GPS to organize a helicopter evacuation of an injured motorcycle rider in a remote region of the La Sal mountains in Utah. A reading was taken, coordinates given, and the pilot was able to find us with ease.
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.
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.
Commercial civilian GPS receivers are purposefully less accurate than they might be. In specific, they are required to have limits on the velocities and altitudes at which they will report coordinates in order to prevent them from being used to create improvised missiles.
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.