GNSS News

Inside GNSS News

News and commentary about the Global Navigation Satellite System
  • Lockheed Martin announced that its second-generation satellite-based augmentation system (2nd Gen SBAS) testbed started broadcasting in dual frequency, multi-constellation (DFMC) during testing this week that was moved up from originally scheduled dates.

  • Spirent Communications plc, a leader in Galileo, GPS and other global navigation satellite systems (GNSS) testing solutions, this week announced a partnership with Cranfield University, a global leader for education and transformational research in technology and management. The two organizations will be collaborating to develop connected autonomous vehicle (CAV) technologies.

  • Nominations for the Institute of Navigation (ION) Fellows and Annual Awards are now being accepted. The ION Annual Awards Program is sponsored by The Institute of Navigation and recognizes individuals making significant contributions or demonstrating outstanding performance relating to the art and science of navigation.

You can submit your nominations today for ION’s Fellows and Annual Awards at ion.org/awards. Nominations are due October 15.



The use of single and dual frequency satellite radio navigation systems, like the Global Positioning System (GPS), has grown dramatically in the last decade. GPS receivers are now in nearly every cell phone and in many automobiles, trucks, and any equipment that moves and needs precision location measurements. High precision dual frequency GPS systems are used for farming, construction, exploration, surveying, snow removal and many other applications critical to a functional society. Other satellite navigation systems in orbit include the European Galileo system and the Russian GLONASS system.

There are several ways in which space weather impacts GPS function. GPS radio signals travel from the satellite to the receiver on the ground, passing through the Earth’s ionosphere. The charged plasma of the ionosphere bends the path of the GPS radio signal similar to the way a lens bends the path of light. In the absence of space weather, GPS systems compensate for the “average” or “quiet”  ionosphere, using a model to calculate its effect on the accuracy of the positioning information. But when the ionosphere is disturbed by a space weather event, the models are no longer accurate and the receivers are unable to calculate an accurate position based on the satellites overhead.

In calm conditions, single frequency GPS systems can provide position information with an accuracy of a meter or less. During a severe space weather storm, these errors can increase to tens of meters or more. Dual frequency GPS systems can provide position information accurate to a few centimeters. In this case the two different GPS signals are used to better characterize the ionosphere and remove its impact on the position calculation. But when the ionosphere becomes highly disturbed, the GPS receiver cannot lock on the satellite signal and position information becomes inaccurate.

Geomagnetic storms create large disturbances in the ionosphere. The currents and energy introduced by a geomagnetic storm enhance the ionosphere and increase the total height-integrated number of ionospheric electrons, or the Total Electron Count (TEC). GPS systems cannot correctly model this dynamic enhancement and errors are introduced into the position calculations. This usually occurs at high latitudes, though major storms can produce large TEC enhancements at mid-latitudes as well.

Near the Earth’s magnetic equator there are current systems and electric fields that create instabilities in the ionosphere. The instabilities are most severe just after sunset. These smaller scale (tens of kilometers) instabilities, or bubbles, cause GPS signals to “scintillate”, much like waves on the surface of a body of water will disrupt and scatter the path of light as it passes through them. Near the equator, dual frequency GPS systems often lose their lock due to “ionospheric scintallation”. Ionospheric scintallations are not associated with any sort of space weather storm, but are simply part of the natural day-night cycle of the equatorial ionosphere.

Phenomena: 
*All of the information and plots on this page are from the Space Weather Prediction Center, which is a division of the National Weather Service & National Oceanic and Atmospheric Administration.

C4Gnet remained online during Hurricane Isaac but eleven CORS sites went offline for the most part due to power outages in the wake of the storm. C4G will be working to get all of these sites back online as soon as possible. While network solutions are still possible in Southeast Louisiana, extra care should be taken do checks on important points until the network density is restored in this area.

 

 

GULFNet LSU Center for GeoInformatics invites qualified professionals* to join the C4G Real-Time Network! C4G RTN is a network of Continually Operating GPS Reference Stations (CORS) that delivers Real Time Network error corrections for GPS data providing the next step of sophistication serving the aims of research in surveying, geology, subsidence, hurricane safety engineering and much more. C4G RTN provides real-time data for use by surveyors, construction crews, precision farming and others with appropriate equipment and training to further enable uniform ties to the National Spatial Reference System (NSRS) in Louisiana.

LSU C4G Real-Time Network (RTN) presently consists of over sixty CORS distributed throughout the state that allow 
RTN members to login and start working anywhere in the state of Louisiana. C4G RTN members can also subscribe to a post processing service that has access to 1 second RINEX data from any or the CORS in the network and the ability to create Virtual Reference Stations anywhere in the state and generate RINEX files on the fly for these locations. C4G RTN has deployed the infrastructure to support the GLONASS satellite system and members can currently access GLONASS subnets anywhere in the state of Louisiana.

 
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