September 2008 Meeting Summary

On September 11, 2008, the Southern California Chapter of the ION held a meeting, hosted by NavCom in Torrance, CA. The meeting included a presentation from Dr. Todd Walter of Stanford University entitled The Ionosphere and its Effect on Satellite Navigation. About 50 people were in attendance for the meeting. A short biography and abstract of the meeting follows, and the slides used during the meeting are attached.

Biography of Dr. Todd Walter 
Dr. Todd Walter received his B.S. in physics from Rensselaer Polytechnic Institute and his Ph.D. in 1993 from Stanford University. He is currently a senior research engineer in the Department of Aeronautics and Astronautics at Stanford University. He is active in the development of the Minimum Operational Performance Standards for WAAS (Wide Area Augmentation System) and co-chair of the WAAS Integrity Performance Panel focused on the implementation of WAAS. He has served as program chair and general chair for the ION’s NTM and GNSS meetings and is currently the western regional vice president. He was a co-recipient of the 2001 ION early achievement award and is a fellow of the ION.

Abstract of Todd Walter’s Talk
Slides: The Ionosphere and its Effect on Satellite Navigation
The ionosphere creates some of the most significant challenges to the use of precise GPS. Its spatial and temporal variations limit the accuracy of position solutions. The uncertainty of its influence limits the availability of high accuracy and high integrity systems. In equatorial areas the ionosphere can cause a form of self-interference, called scintillation, that can prevent the tracking of the signal altogether. Yet, despite these serious obstacles, the ionosphere itself is not well understood. As the use of GPS becomes more demanding and more wide-spread, it is important to examine the ionosphere and understand the range of possible effects.

The FAA has a network of redundant measuring stations throughout North America that has been used to continuously observe ionospheric behavior for the last 8 years. These data have been used to identify the largest gradients observed at middle latitudes.

Our emphasis, in this research, has been on identifying the extreme behavior that, fortunately, occurs rarely over the United States. We have also examined data from other parts of the globe where large variations can be much more common.

A partial solution to the challenges from the ionosphere is under development in the form of modernization of the GPS signals. However, this solution comes at a cost: the combination of signals to create an ionospheric-free measurement greatly inflates the magnitude of other error sources. Users who are particularly affected by the ionosphere will welcome these new signals that will do much to reduce extreme behavior.

This talk will focus on observations of ionospheric effects ranging from typical observed variations to the extreme behavior of ionospheric superstorms. The effects on satellite navigation will be discussed as well as how to place confidence limits on the possible magnitude of its effect.