Design & Test

Innovation: Where Is GIOVE-A Exactly?

July 1, 2009By
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Using Microwaves and Laser Ranging for Precise Orbit Determination
Though Galileo’s GIOVE-A is a test satellite not necessarily ready for scientific use, orbit analyses with a reduced accuracy can help to identify weaknesses and suggest improvements. This month, the authors share work being carried out to precisely determine the orbit of GIOVE-A using SLR and microwave observations. This preliminary investigation will benefit the procedures to be implemented for the future Galileo constellation. read more

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Innovation: GNSS Antennas

February 1, 2009By
FIGURE 7. Quantifying multipath caused by vertical object reflections.

An Introduction to Bandwidth, Gain Pattern, Polarization and All That
How do you find best antenna for particular GNSS application, taking into account size, cost, and capability? We look at the basics of GNSS antennas, introducing the various properties and trade-offs that affect functionality and performance. Armed with this information, you should be better able to interpret antenna specifications and to select the right antenna for your next job. read more

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Innovation: Tsunami Detection by GPS

February 1, 2008By
QuickBird satellite image of Kalutara Beach on the southwestern coast of Sri Lanka showing the receding waters and beach damage from the Sumatra tsunami.

How Ionospheric Observations Might Improve the Global Warning System
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. read more

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Integer ambiguity validation: Still an open problem?

July 30, 2007By

By Sandra Verhagen High-precision Global Navigation Satellite System (GNSS) positioning results are obtained with carrier phase measurements, once the integer cycle ambiguities have been successfully resolved. The position solution is obtained in four steps: 1. Float solution:least-squares, discarding integer nature. 2. Integer solution: real-valued float ambiguities mapped to integer-valued ambiguities.Examples of integer estimators (Teunissen, 1998a): Integer Least-Squares: optimal, requires search... read more

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Spirent Intros Customizable Software for GPS Test, Simulation

June 1, 2007By

Navigation and positioning test system supplier Spirent Communications this week introduced a software suite for the STR4500 GPS simulator, enabling users to generate their own test cases based on motion data that fits their specific requirements, the company said. read more

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Antenna-Induced Biases in GNSS Receivers

May 17, 2007By

By Inder Jeet Gupta It is well known that the phase center of a GNSS antenna can vary with the satellite direction. This phase center movement leads to aspect dependent carrier phase and code phase biases in the satellite signal. For precise geo-location, one needs to characterize the antenna-induced carrier and code phase biases over the upper hemisphere. In the... read more

Innovation: The International GNSS Service: Any Questions? (PDF)

January 1, 2007By

Innovation: The International GNSS Service: Any Questions? (PDF) By Angelyn W. Moore Published: January 2007 GPS World In this month’s column, Angelyn Moore, the IGS Central Bureau’s deputy director, overviews the organization’s service, history, and future, demonstrating that the IGS is a model of scientific collaboration of which not just the GNSS community but the whole world should be proud.—Richard... read more

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Update: GNSS Accuracy: Lies, Damn Lies, and Statistics

January 1, 2007By

This update to a seminal article first published here in 1998 explains how statistical methods can create many different position accuracy measures. As the driving forces of positioning and navigation change from survey and precision guidance to location-based services, E911, and so on, some accuracy measures have fallen out of common usage, while others have blossomed. The analysis changes further when the constellation expands to ombinations of GPS, SBAS, Galileo, and GLONASS. Software scripts, provided online, help bridge the gap between theory and reality. read more

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