Global Navigation Satellite Systems Engineering, Policy, and Design
At one time, GPS was expected to supplant a wide range of navigation technologies in the world’s positioning, navigation, and timing (PNT) portfolio. But an unexpected thing happened along the way.
By Inside GNSS
Francisco Rovira-Más, Agricultural Robotics Laboratory, Universidad Politécnica de ValenciaNow that we have had GNSS-driven precision in the fields for nearly 20 years, with widespread and growing acceptance by farm vehicle manufacturers and farmers, what lies ahead for precision agriculture?
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Dr. John Fulton, Ohio State UniversityNowhere has the fact that GNSS can guide things besides military weapons and transport manifested itself more profoundly than in agriculture.
While Google and automotive manufacturers struggle to figure out how to put autonomous vehicles on the highway, farmers have been using GNSS for well over a decade to guide equipment through their fields — along with a host of other ag-related, site-specific applications.
Indeed, GNSS — along with an array of other high-tech resources — is transforming agriculture at an accelerating rate.
By Inside GNSS
Dennis Odijk, Curtin UniversityThe availability of carrier phase tracking — counting the cycles of GNSS signals between satellites and a receiver — has long enabled high-precision users to achieve greater accuracy than using the navigation messages or pseudoranges. Improvements in high-end receivers and techniques such as real-time kinematic (RTK) and precise point positioning (PPP) have made once inconceivably accurate results almost routinely accessible.
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Gerald Mader, National Geodetic SurveyIn August, a group of scientists at the Scripps Institution of Oceanography reported that the severe drought gripping the western United States in recent years is causing a “uplift” in the western United States.
About the same time, governmental agencies were reporting widespread cases of land subsidence in California’s central San Joaquin Valley caused by overpumping of water from wells there.
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Ken Hudnut, U.S. Geological SurveyFor at least two decades, GPS experts, geodesists, and public agencies have been working together to develop high-accuracy, large-scale continuously operating GPS reference stations that provide them the capability to monitor and model crustal deformation, tectonic plate movement, and the effects of geohazards such as earthquakes and volcanic eruptions.
Now, GNSS-augmented advance warning systems are going into place that can give us a crucial margin of safety in the event of an earthquake.
And none too soon.
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Doug Taggart, Overlook Systems Technologies In the “gee-whiz” awesomeness of proliferating GNSS apps, it’s sometimes hard to remember that Global Positioning System originated as a military system designed to meet strategic and tactical needs on the battlefield.
And, with the U.S. Air Force continuing its 40-year mission as the executive agent for sustaining GPS, that undiminished military role plays no small part in ensuring the availability and reliability of the U.S. contribution to the GNSS system of systems.
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A. J. Van DierendonckThe world’s GNSS systems are entering a phase of transformation — modernization of existing systems (the U.S. Global Positioning System and Russia’s GLONASS) and development of new systems (China’s BeiDou and Europe’s Galileo) that benefit from the lessons learned from the original GNSSs.
Notable among the modernization initiatives is an interest in implementing new satellite signal designs. These include the GPS L5, L2C, and L1C signals as well as those signals designed for Galileo and BeiDou. GLONASS designers are also working on modernized signals.
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Tim Springer, PosiTim UGA common refrain in the world of GNSS is the desire for “interoperability,” the use of signals from multiple systems without a decline — and potentially even an improvement — in the quality of results.
Achieving this depends on large part in establishing comparable parameters — particularly the geodetic references and timing systems — among the GNSSs along with a dense network of ground reference stations that can provide continuous, precise monitoring of satellites’ orbital positions.
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Jules McNeff, Overlook SystemsTechnologies, Inc.EDITOR’S NOTE: Jules McNeff answers additional questions on the subject of spectrum protection and sharing in a special “GNSS Forum” extension of this installment of the "Thought Leadership Series" in this issue of Inside GNSS.
As Mark Twain once famously told a petitioner for investment advice: “Buy land. They are not making it any more.”
So it is with radio frequency spectrum, a limited and finite resource.
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Dr. Inder Gupta, The Ohio State UniversityChris Bartone, Ohio UniversityWith new signals and frequencies coming on line with modernized GNSSs, antennas play a more crucial role than ever in receiver system design.
Antennas are often an overlooked or undervalued aspect of GNSS user equipment.
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Logan Scott, LS ConsultingSometimes GNSS spoofing seems a bit like UFOs: much speculation, occasional alarms at suspected instances, but little real-world evidence of its existence.
As far back as 2001, a U.S. Department of Transportation Volpe Center report suggested that as GPS further penetrates into the civil infrastructure, “it becomes a tempting target that could be exploited by individuals, groups or countries”.
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Prof. Jingnan Liu, Chinese Academy of EngineeringSince announcing plans in late 2006 to build its own GNSS system — BeiDou-2 (BDS), China proceeded quickly to establish a fully operational regional system late last year with a clear plan to complete a global system by 2020.
Beginning with its first launch in April 2007, BDS has put 16 satellites in orbit, some in dual launches, with 14 BeiDou space vehicles currently transmitting healthy signals: 5 in geostationary orbits (GEO), 5 in inclined geosynchronous orbits (IGSO), and 4 middle Earth orbit (MEO) spacecraft.
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