Receiver Techniques for Detecting and Characterizing RFI
Jun 1, 2008
By:
Phillip W. Ward
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How do users know that their receivers are being jammed and not suffering some other type of malfunction? The author look at simple techniques that can be incorporated into the design of a GNSS receiver to detect, characterize, and actually mitigate radio-frequency interference to benefit civilian and military users alike.
Time Differences for Kinematic Positioning with Low-Cost Receivers
May 1, 2008
By:
Johannes Traugott, Dennis Odijk, Oliver Montenbruck, Gottfried Sachs, Christian Tiberius
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One of the difficulties with RTK-style positioning is resolving carrier-phase ambiguities. If you time-difference sequential carrier-phase measurements, the ambiguity actually disappears, and you can determine accurate relative positions using time-differenced carrier-phase measurements. But there are some caveats.
How Far Have We Come?
Apr 1, 2008
By:
Andreas Wieser
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To reduce road-maintenance costs, some administrations are charging per kilometer of travel with data coming from an odometer recording. To fairly implement such schemes, accurate odometers are critical. Could an odometer based on GNSS be a solution?
Getting a Better Handle on the Biases
Mar 1, 2008
By:
Don Kim, Richard B. Langley
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How accurate modeling of atmospheric effects coupled with an ionosphere-free ambiguity resolution process results in successful long-range RTK.
How Ionospheric Observations Might Improve the Global Warning System
Feb 1, 2008
By:
Giovanni Occhipinti, Attila Komjathy, Philippe Lognonné
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Recent investigations have demonstrated that GPS might be an effective tool for improving the tsumani early-warning system through rapid determination of earthquake magnitude using data from GPS networks. A less obvious approach is to use the GPS data to look for the tsunami signature in the ionosphere.
Expanding the Wide Area Augmentation System
Jan 1, 2008
By:
Timothy R. Schempp
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While WAAS was already a much-valued addition to standalone GPS, significant improvements were made to WAAS over the past three years, including expansion of the reference station network and the commissioning of two new GEOs. 2008 will see even more enhancements. In this month's column, we take a look at WAAS's recent upgrades and take a peek into its future.
Chip-Scale Atomic Frequency References
Nov 1, 2007
By:
John Kitching
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New marvels of miniaturization — the fabrication and performance of chip-scale atomic frequency references — will be moving from the lab to the factory any day now.
Sensing Land and Ice from Low Earth Orbit
Oct 1, 2007
By:
Scott T. Gleason
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An out-of-the-ordinary application of GPS uses signals reflected off the Earth's surface to sense land and ice, as well as the ocean surface, from low Earth orbit. Analysis of these signals holds great promise for measuring ocean roughness, ice conditions, vegetation cover, and even soil moisture.
Processing GPS Data with Neural Networks
Sep 1, 2007
By:
Rodrigo F. Leandro, Carlos A.U. da Silva, Paulo C.L. Segantine, Marcelo C. Santos
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Primarily developed for computing applications, such as pattern recognition, neural networks have been adapted for use in several fields of science, including geodesy. Those adaptations are needed because usually the situations and problems encountered in computer science are different from those in other fields. Geodesy is no exception.
