As professionals, they state the observations and facts and don't cross into the realm of speculation.

So the signal is jammed by something sending a noise signal around the L1 frequency, whether intentionally or not.

https://www.nrk.no/finnmark/stoy-fra-russland-slo-ut-gps-sig...

This time it was only blocking GPS signals. Previously this year Russia spoofed GPS signals over the black sea, sending false position data to ships in the area.

https://maritime-executive.com/editorials/mass-gps-spoofing-...

Could be the Russians are up to something? Jamming GPS signals would be a significant strategic advantage in war time.

> Develop measures to prevent the hostile use of GPS and its augmentations to ensure that the United States retains a military advantage without unduly disrupting or degrading civilian uses.

GPS only being jammed at higher altitudes, but not on the ground fits the above pretty well imo. We don't know how this jamming would affect US military GPS usage, but it's not impossible to think that it doesn't.

[0] https://www.faa.gov/about/office_org/headquarters_offices/at...

Glonass is a couple hundred megaherz away from GPS L1.

The best bet is to use as many positing systems as possible in order to prevent attacks narrowly targeting one positioning system.

Yes, that's what I am saying. Don't rely on one system. Using more also increases accuracy.