Roger writes:

The only thing I found was slightly different. "These corrections
messages are then broadcast to receivers onboard the aircraft using
the frequency as the GPS". It said nothing about being broadcast
through communications satellites, or I missed it.

As I recall, the WAAS correction data are broadcast over large areas by
relaying them through communication satellites. However, these communication
satellites are not part of the GPS system, and they are not GPS satellites.

IF correction messages can be sent from local areas back to satellites
that would make they very vulnerable to tampering with the data.

Yes. But the satellites in question are not part of GPS, fortunately.

It _is_ a bit unfortunate that WAAS is using the same frequencies to create
pseudosatellites, which is essentially spoofing GPS, and it's not a good idea
to have spoofing technology in such widespread use, no matter what the
justification.

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