GPS Satellites Gain Prominence4 Dec, 2007 By: Andrew G. Roe,P.E.
Recent developments in satellite and GPS technology will improve the quality of GPS data that land professionals can use in their projects.
While the work of civil engineers, planners, and other land professionals typically focuses on the Earth’s surface, vital activities affecting our professions also occur miles above us. Most of us have relied on global positioning system (GPS) data at one time or another, but many are probably not aware of some recent developments in satellite-based positioning.
In the past few months, a new satellite was launched to upgrade the U.S. GPS system, and the U.S. government announced plans to totally eliminate intentional degradation of GPS signals. And in other parts of the world, new satellite-based positioning systems are being launched to mimic the North American-geared GPS network and provide more options for satellite-based positioning around the globe.
The October launch of the GPS 2R-17 satellite reportedly will provide better accuracy and more resistance to interference for GPS users in the United States and elsewhere, according to the Spaceflight Now Web site. The fourth in a series of eight launches by the U.S. Air Force, the GPS 2R-17 replaces the GPS 2A-14 satellite, which was launched in 1992 with a seven-year design life. The four remaining satellites of the Block 2R generation are slated for launch over the next year. The newer satellites transmit additional signals and remove navigation errors caused by the Earth's ionosphere. The U.S. GPS network currently has 30 operational satellites, which emit signals that allow users to determine latitude, longitude, and altitude.
|A U.S. GPS satellite (image courtesy of U.S. Air Force).|
Another generation of satellites with even more advancements, called the GPS 2F series, is scheduled to debut in 2009. These satellites will provide a 12-year design life, faster processors with more memory, and a new civilian signal.
And still more improvements are planned. The U.S. Air Force issued a request for proposals earlier this year to build yet another generation of satellites called GPS III, which will transmit a new civilian signal and be interoperable with navigation systems in Europe. The GPS III constellation will also reportedly allow the entire GPS constellation to be updated from a single ground station instead of waiting for each satellite to orbit in view of a ground antenna. GPS III is projected to begin launch in 2013.
No More Degradation
Another significant development occurred when the U.S. Department of Defense (DoD) announced plans earlier this year to permanently remove selective availability (SA) from future satellites. Originally intended for security purposes, SA intentionally degraded the accuracy of civil signals. The United States stopped the practice in 2000, so the recent action will not materially improve present GPS data accuracy, but it “eliminates a source of uncertainty in GPS performance that has been of concern to civil GPS users worldwide for some time,” according to the DoD announcement.
The White House swiftly accepted the DoD recommendation and stated that the decision “reflects the United States' strong commitment to users of GPS that this free global utility can be counted on to support peaceful civil activities around the world." The next generation GPS III satellites will reportedly not carry SA capability.
Other Global Systems
Meanwhile, other nations continue to pursue satellite-based position systems. The European Union's Galileo satellite navigation system, which would provide an alternative to the U.S. GPS network, has experienced some setbacks, but recently gained momentum for future funding, according to GPS World. The system reportedly will require users to pay a fee, but it will include more accurate locations than the free GPS system. It could be operational by 2013.
Russia's GLONASS constellation, which fell into disrepair in the 1990s, has been revamped with additional satellites and an agreement to share information more openly with the United States. Three GLONASS satellites were launched this year, bringing the current number of usable satellites in the constellation to 10, according to the Russian Space Agency.
China is also advancing plans for a satellite-based navigation, launching a fourth experimental satellite to join three launched between 2000 and 2003.
Why It Matters
While developments in satellite and GPS technology may seem somewhat detached from the day-to-day grind of developing municipal maps, designing subdivisions, and preparing construction plans, the opportunities for GPS applications are numerous and growing. Hand-held GPS devices are becoming more commonplace, resulting in more opportunities to collect preliminary location data. Field survey crews are increasingly relying on GPS technology for both data collection and construction staking, and it can produce impressive accuracy when used properly. Astute professionals should maintain at least a rudimentary knowledge of basic GPS principles and monitor trends to help ensure GPS information is used properly when the opportunity arises.
About the Author: Andrew G. Roe
Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!