In addition to longitude, latitude, and altitude, the Global Positioning System provides a critical fourth dimension - time. Each GPS satellite contains multiple atomic clocks that contribute very precise time data to the GPS signals. GPS receivers decode these signals, effectively synchronizing each receiver to the atomic clocks. This enables users to determine the time to within 100 billionths of a second, without the cost of owning and operating atomic clocks.
Precise time is crucial to a variety of economic activities around the world. Communication systems, electrical power grids, and financial networks all rely on precision timing for synchronization and operational efficiency. The free availability of GPS time has enabled cost savings for companies that depend on precise time and has led to significant advances in capability.
For example, wireless telephone and data networks use GPS time to keep all of their base stations in perfect synchronization. This allows mobile handsets to share limited radio spectrum more efficiently. Similarly, digital broadcast radio services use GPS time to ensure that the bits from all radio stations arrive at receivers in lockstep. This allows listeners to tune between stations with a minimum of delay.
Companies worldwide use GPS to time-stamp business transactions, providing a consistent and accurate way to maintain records and ensure their traceability. Major financial institutions use GPS to obtain precise time for setting internal clocks used to create financial transaction timestamps. Large and small businesses are turning to automated systems that can track, update, and manage multiple transactions made by a global network of customers, and these require accurate timing information available through GPS.
The U.S. Federal Aviation Administration uses GPS to synchronize reporting of hazardous weather from its 45 Terminal Doppler Weather Radars located throughout the United States.
Instrumentation is another application that requires precise timing. Distributed networks of instruments that must work together to precisely measure common events require timing sources that can guarantee accuracy at several points. GPS-based timing works exceptionally well for any application in which precise timing is required by devices that are dispersed over wide geographic areas. For example, integration of GPS time into seismic monitoring networks enables researchers to quickly locate the epicenters of earthquakes and other seismic events.
Power companies and utilities have fundamental requirements for time and frequency to enable efficient power transmission and distribution. Repeated power blackouts have demonstrated to power companies the need for improved time synchronization throughout the power grid. Analyses of these blackouts have led many companies to place GPS-based time synchronization devices in power plants and substations. By analyzing the precise timing of an electrical anomaly as it propagates through a grid, engineers can trace back the exact location of a power line break.
"Timing is rapidly becoming a critical element for many industries. As the need for precise timing grows, more and more users are turning to GPS technology," said Dennis L. Workman, VP and General Manager, Trimble Component Technologies Division.
Some users, such as national laboratories, require the time at a higher level of precision than GPS provides. These users routinely use GPS satellites not for direct time acquisition, but for communication of high-precision time over long distances. By simultaneously receiving the same GPS signal in two places and comparing the results, the atomic clock time at one location can be communicated to the other. National laboratories around the world use this "common view" technique to compare their time scales and establish Coordinated Universal Time (UTC). They use the same technique to disseminate their time scales to their own nations.
New applications of GPS timing technology appear every day. Hollywood studios are incorporating GPS in their movie slates, allowing for unparalleled control of audio and video data, as well as multi-camera sequencing. The ultimate applications for GPS, like the time it measures, are limitless.
As GPS becomes modernized, further benefits await users. The addition of the second and third civilian GPS signals have increased the accuracy and reliability of GPS time, which will remain free and available to the entire world.
- Widespread availability of atomic clock time, without the atomic clocks.
- Precise synchronization of communications systems, power grids, financial networks, and other critical infrastructure.
- More efficient use of limited radio spectrum by wireless networks.
- Improved network management and optimization, making traceable time tags possible for financial transactions and billing.
- Communication of high-precision time among national laboratories using "common view" techniques.
Operated by Air Force Space Command's 50th Space Wing at Schriever Air Force Base, located east of Colorado Springs, Colo., the GPS constellation provides precise positioning, navigation and timing services worldwide as a free service provided by the U.S. Air Force, seven days a week, 24 hours a day. The GPS constellation is healthy, stable and robust with 12 GPS IIRs, seven GPS IIR-Ms, and 12 GPS IIF satellites on orbit providing precise global positioning, navigation, and timing services to users around the globe.
The latest generation of GPS IIF satellites provides improved signals to support both the warfighter and the growing civilian needs of a global economy. Featuring a new third civil signal -- L5 -- that benefits commercial aviation and safety-of-life applications, the GPS IIF series provides improved accuracy through advanced atomic clocks, and a longer design life than previous GPS satellites on orbit.
The Space and Missile Systems Center, located at Los Angeles Air Force Base in El Segundo, Calif., is the Air Force's center of acquisition excellence for acquiring and developing military space systems. Its portfolio includes the Global Positioning System, military satellite communications, defense meteorological satellites, space launch and range systems, satellite control networks, space based infrared systems and space situational awareness capabilities.