[time-nuts] Re: BOAT ionospheric effects

[Michael Wouters]

Hello Phil

"Whether this
GRB-induced increase of a fraction of picosecond makes any difference to a
single frequency GNSS PLL or other timing loop is something I'm not
qualified to answer, but perhaps others can respond."

The code tracking PLL has noise at the level of a ns whereas the
carrier phase tracking is noisy at the ten  ps level.
I'm guessing the GRB is a mouse's squeak to a lion's roar.

Cheers
Michael

On Sun, Oct 23, 2022 at 3:45 PM Phil Erickson via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> Hi Bob and the list,
>
>   [First of all, apologies to anyone who tried to follow the link to the
> Nature paper and hit a paywall.  There appears to not be an open access
> version out there.  Not sure how to solve that.]
>
>   Now I understand the question.  Sure, single frequency devices far
> outnumber any dual frequency systems, although those new uBlox dual
> frequency chips might make a dent in that some day.  So seeing as this is a
> time-nuts mailing list, I did some calculations as follows:
>
>   We need to start with an estimate of the electron density profile between
> 20 and 80 km in both normal conditions and under gamma ray burst impact.
> The same Umran Inan at Stanford wrote a later paper - open access this
> time! - showing modeled profiles during a massive daytime GRB - Figure 4 of
> this paper gives profiles before ("ambient"), at flare time, 0.1 sec and 5
> sec postflare.  (FYI, by 1000 seconds postflare, we're back to ambient.)
>
> Inan, U. S., Lehtinen, N. G., Moore, R. C., Hurley, K., Boggs, S., Smith,
> D. M., and Fishman, G. J. (2007), Massive disturbance of the daytime lower
> ionosphere by the giant γ-ray flare from magnetar SGR 1806–20, Geophys.
> Res. Lett., 34, L08103, doi:10.1029/2006GL029145.
> https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2006GL029145
>
>   I used those profiles and integrated between 20 and 80 km altitude to
> calculate a total electron content value, expressed in m^-2 (e.g. number of
> electrons in a column with 1 m^2 cross sectional area).  You can convert
> that to an induced ionospheric group propagation delay in seconds using the
> formula at the bottom of the TEC page here:
>
> https://en.wikipedia.org/wiki/Total_electron_content
>
>   Using a frequency of 1575.42 MHz (GNSS L1), the numbers work out as
> follows:
>
> Over 20-80 km altitude:
> Ambient delay = 0.38 ps
> 0.1 s post-GRB delay = 0.71 ps (89% increase over ambient)
> 5 s post-GRB delay = 0.46 ps (23% increase over ambient)
>
>   Looks like a large effect.  But: compare this with a typical mid-latitude
> total group delay from the whole ionosphere out to 20,000 km, using a
> nominal 20 TEC unit value typical of continental US values in the
> mid-afternoon this month (e.g.):
>
> Total ionospheric delay = 10.8 ns
>
>   So the GRB-impacted region generates delays that are negligible compared
> with the overall ionospheric delay which dominates.  Whether this
> GRB-induced increase of a fraction of picosecond makes any difference to a
> single frequency GNSS PLL or other timing loop is something I'm not
> qualified to answer, but perhaps others can respond.
>
> Cheers
> Phil
>
>
>
>
>
>
> On Sat, Oct 22, 2022 at 8:01 AM Bob kb8tq <kb8tq at n1k.org> wrote:
>
> > Hi
> >
> > Thanks !!!!!
> >
> > There are a lot of devices that do “single band” GNSS for timing.
> > The reason is pretty simple: cost. On those devices, you don’t get
> > the internal correction for atmosphere that you do on a multi band
> > device.
> >
> > So, the rephrased / corrected / enhanced question becomes: Are
> > single band issues likely in this case / did anybody see them?
> >
> > Thanks again,
> >
> > Bob
> >
> > > On Oct 22, 2022, at 6:58 AM, Phil Erickson via time-nuts <
> > time-nuts at lists.febo.com> wrote:
> > >
> > > Hi all,
> > >
> > >  John Ackermann mentioned this thread.  I'm an ionospheric observational
> > > physics person.
> > >
> > >  The disturbance from a gamma ray flare is primarily on VLF propagation
> > > (10s of kHz) because it penetrates so low in the atmosphere and enhances
> > > the "sub-D region" between 40 and 80 km or so.  D region is highly
> > > absorptive due to strong ion-neutral collisions in events where it gets
> > > enhanced.
> > >
> > >  VLF ionospheric propagation effects from gamma ray bursts weren't really
> > > confirmed until this 1988 Nature paper by Fishman and Inan on a strong
> > 1983
> > > burst:
> > >
> > > Fishman, G. J., and U. S. Inan. "Observation of an ionospheric
> > disturbance
> > > caused by a gamma-ray burst." Nature 331, no. 6155 (1988): 418-420.
> > > https://www.nature.com/articles/331418a0.pdf?origin=ppub
> > >
> > >  There are a number of publications since that one.  Because VLF paths
> > are
> > > inherently transcontinental and interhemispheric in the earth-Ionosphere
> > > waveguide (ground to bottom of the D region), this was seen only on a
> > very
> > > long path reception.  Check out Figure 2 - I think that's one of the
> > > reasons why it took so long to conclusively identify it - as they say:
> > >
> > > "Figure 2 shows a portion of the record from the three stations between
> > > 21:40 UT and 23:00 UT on 1 August 1983. A clear indication of a
> > disturbance
> > > beginning at 22:14:10±10UT is seen in the radio station GBR signal.
> > Weaker,
> > > barely detectable decreases in amplitude are seen simultaneously in the
> > two
> > > other signals. Without the GBR signal, these other two signals alone
> > would
> > > have been considered uneventful as similar weak fluctu- ations are seen
> > in
> > > their records near the time of the burst. The disturbance in the GBR
> > signal
> > > differs in its rise-and-fall time from any other disturbances seen within
> > > 60 h of the burst."
> > >
> > >  So identifying the spike using multiple simultaneous receptions was
> > > needed to disambiguate it from something like whistlers (lightning),
> > flares
> > > (SIDs), etc.  The SpaceWeather article that Bob KB8TQ mentioned shows a
> > > similar type of detection of the recent super-GRB.
> > >
> > >  Back to the topic though: the ionization deposit would be very wide
> > > spread (not localized) and would however I think contribute not very much
> > > to the total electron content (TEC), which is of course the critical
> > thing
> > > for dual frequency GNSS measurements at L band.  The way I could see
> > > something occurring is if irregularities were created in the region of
> > > enhanced ionization, but they wouldn't last too long.
> > >
> > >  Consider also that the ionosphere's natural electron density variability
> > > is 1 to a few % on any day of the year, and you can see this clearly in
> > > differential TEC from things like traveling ionospheric disturbance (TID)
> > > waves and the like (many many studies).  Those don't significantly impact
> > > timing solutions due to the dual frequency nature of the GNSS system
> > which
> > > subtracts out ionospheric delay, so I can't imagine this event would
> > change
> > > those either.
> > >
> > >  Of course, I could be wrong - please correct!
> > >
> > > 73
> > > Phil W1PJE
> > > MIT Haystack Observatory
> > > Westford, MA
> > > _______________________________________________
> > > time-nuts mailing list -- time-nuts at lists.febo.com
> > > To unsubscribe send an email to time-nuts-leave at lists.febo.com
> >
> >
>
> --
> ----
> Phil Erickson
> phil.erickson at gmail.com
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com