Definitely interesting stuff. I think it's pretty easy to forget GPS availability isn't guaranteed.  And it's pretty frightening to think of how much less useful our navigational electronics become with the system down.  

On another note, I thought I head the jamming was supposed to be above 3,500 feet but I don't see that in this article nor can I find definitive confirmation at first glance.

Ben

Last week I got interviewed as part of a study being done for the "Cybersecurity and Infrastructure Security Agency (CISA) at the
Department of Homeland Security (DHS)" regarding GPS, specifically:

"1) How has the introduction of GPS impacted the industry? – For example, how is GPS used
in each portion of the maritime sector above? Who benefits from the use of GPS and by how
much? If GPS had not been introduced, what alternatives would have been used?

2) What would the economic consequences be of an unexpected 30-day failure of the
current GPS system? – Suppose that there was an unexpected failure of the GPS system that
lasted for 30 days. How would this impact each portion of the maritime sector above? What
can be done to mitigate these consequences?"

The research company is well along and the report will become public sometime this year.

I'm hoping it's part of the path to a secondary electronic positioning system, but that's purely speculative.

Good to see that the Resilient Navigation and Timing Foundation is still on the case:

https://rntfnd.org/blog/enewsletter-archive/

This was disturbing to read "The wide range of reports makes clear that interference affects aircraft differently, and recovery may not occur immediately after the aircraft exits the jammed area." and "an aircraft lost navigation capability and did not regain it until after landing." 

This potentially indicates that (i) GPS products have use cases where they won't reactivate after moving out of range of jamming (ii) pilots don't know (or have the ability) to reset their GPS after the interference stops, or worse (iii) there are software bugs, integration issues, and/or installation mistakes that are not considered in use case testing or accounted for in the human to vehicle interface.

How might these issues appear in recreational and commercial boats?

GPS sensors are generally wide open antenna pattern and could receive jamming interference from anywhere. A $20 circuit board antenna in a much more expensive plastic case/mount/cable.

If an airplane had a shielded antenna blocking interference from ground sources and allowed the GPS to receive only from a certain range of sky elevations, it could potentially be substantially more jam proof. Nothing says GPS jamming wouldn't come from above, but if it's malicious, it would be much easier to track and identify in the sky compared to a bad actor on the ground.

Furthermore if one had 4 GPS receivers mounted in isolated metal dividers (such as seen in the four quadrants of a radar reflector) it could be 4x as jam proof compared to shielding from ground sources alone as each receiver would only receive 1/4 of the sky and if one quadrant were jammed the other quadrants might be enough SNR to maintain service. This could be used on a boat if needed but nobody wants to add complexity.