North Korean ICBM launch detected using GPS

These distortions are not constant. They change from time to time. There are many different ways to account for them. One of the most accurate solution is to keep a GPS receiver on a well known location. Since you know that this receiver haven’t moved you can use the signal measured to estimate the parameters of the ionosphere between that station and the satelite.

Normally these signals are used to correct GPS navigational solutions. You take the closest station to your moving receiver and assume that whatever way the ionosphere was distorting for that station will do the same for your receiver too. This is valuable so there are network of such GPS stations in a lot of places.

Here they use the data collected by these stations differently. Instead of correcting a navigational solution they visualise the measured state of the ionosphere as seen by a bunch of these stations.

GPS receivers work by figuring out how far away they are from a number (>3) of GPS satellites. The receiver knows where the GPS satellites are (since the satellites broadcast their orbit parameters) so if a receiver knows how far it is from several satellites it can work out where it is itself.

Now, as the GPS satellite signals travel through Earth's atmosphere, they can be slowed down by different atmospheric effects. A slower signal will cause the receiver to think it's farther away from a satellite than it really is, so the receiver might estimate that it's position has changed a little bit. However, if you know the receiver's position hasn't change (maybe it's fixed in place to a big rock), then you can attribute the receiver's measured "change in position" to a change in atmosphere characteristics.

In this paper, they seem to have lots of fixed GPS receivers all over the place. By looking at all of them together, they can make a sort of map of the atmosphere characters in a part of the sky that's affected by rocket launches. The authors see these big ripples emanating from a Falcon Heavy launch in the US and this tweet shows those same ripples emanating from a launch site in North Korea.

https://gcn.gsfc.nasa.gov/gcn3/32744.gcn3 ("GRB221009A: Detection as sudden ionospheric disturbances (SID)")

https://www.qsl.net/df3lp/grb221009/KLM_grb221009a_magnitude... (from the above link)

http://abelian.org/vlf/grb221009a-DHO.png

http://abelian.org/vlf/grb221009a-NAA.png

http://abelian.org/vlf/grb221009a-NSY.png

[0] https://news.ycombinator.com/item?id=33215572 ("Record-breaking gamma-ray burst possibly most powerful explosion ever recorded")

This was detected with VLF radio, but I wonder if this kind of event also has an effect on GPS signals? The time-of-arrival of astrophysical gamma rays isn't uniform across the earth.

https://geodesy.noaa.gov/CORS_Map/

https://www.e-education.psu.edu/geog862/node/1830

https://learn.sparkfun.com/tutorials/how-to-build-a-diy-gnss...