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    Susceptibility of GPS to CME, Rationale for CN?
    From: Brad Morris
    Date: 2018 Sep 28, 15:20 -0400
    I asked Dr. Langley to help me understand the effect of a coronal mass ejection (solar activity) on the GNSS system.  Would the solar effect be large enough to indicate a rationale for CN?  


    In the recommended scholarly article, Dr. Langley discusses the propagation delay of the GNSS signals and how the number of free electrons in the radio path affect that delay.  As increased solar activity increases the number of free electrons, the propagation delay also increases.  This affects the precision of the GNSS system.   

    The magnitude of error in precision would likely be unnoticed by marine users, with the largest stated error being greater than 50 meters in the vertical axis for a given solar event.   Unless I missed it, the error in the horizontal axis during this same event was unstated for the L1 channel.  I further assume that this event was some sort of local maxima.  Even if the error in the horizontal axis was an order of magnitude greater (500 meters) than the stated error in the vertical axis( 50 meters) this is still not going to affect any marine navigator's ability to make landfall; although this magnitude of error might be noticed in tight maneuvering spaces.  It would certainly have an affect on aviation (landings), although I'm unsure of how CN is going to remedy that situation.

    Further, Dr. Langley stated that "In the few very worst cases, GNSS-based positioning, navigation, and timing might not be possible at all for a short interval of time during very high ionospheric activity."   Ah ha! This is approaching the answer I seek.  CN gets only a few fixes per day.  Substituting CN for GPS during this "short interval of time" may or may not provide a justification for CN. The substitution depends upon what the definition of "short interval of time" is, and the initial level of "very high ionospheric activity".  The length of the outage will be proportional to the time is takes for the anomalous number of free electrons to return to reasonable levels.  

    Dr Langley, would you mind lending some clarity here?  I realize that the terms are all relative.  The paucity of precise data from prior solar cycles may limit your ability to predict future levels of activity.  However, you are best situated to provide guidance.


    PS:I hope I understood the articles correctly and properly formulated my conclusions.  Any errors are strictly my own. 

    On Sep 28, 2018 12:54 PM, "Richard B. Langley" <NoReply_Langley@fer3.com> wrote:

    "There is an additional event which recently came to mind.  A coronal mass ejection, commonly known as a solar storm, can take out satellites.  I wonder about the vulnerability of the GNSS system to this type of event.  If you have the time, Dr. Langley, I would appreciate it if you could educate us! Thanks!"

    This article discusses the effects of solar activity on GPS (and, by inference, other GNSS) signals: http://gpsworld.com/innovation-gnss-and-ionosphere-11036/

    Reduced signal availabilty and accuracy are potential outcomes. If by "can take out satellites" you mean damaging the satellites themselves by corpuscular radiation as has happened to some geostationary communication satellites, you should know that GPS satellites are hardened against radiation so the likelihood of them being damaged by a solar outburst is low. The GPS III-F satellites will have even more hardening, not just to protect them from solar outbursts, but also to protect them during a possible space war: https://nationalinterest.org/blog/the-buzz/air-force-hardens-satellites-prepare-space-war-think-russia-25027

    -- Richard Langley


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