I think they're talking about environmental factors that affect the propagation speed of the GPS radio signals from the satellites to the surface. This would gi

I think they're talking about environmental factors that affect the propagation speed of the GPS radio signals from the satellites to the surface. This would give them higher resolution timings on the arrival of the GPS signals and thus better accuracy. I don't think this has anything to do with the actual speed of light as that is constant (in empty space). On a related note, one of the recent SpaceX launches caused some perturbations in the ionosphere and that had a measurable effect on GPS accuracy: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017SW001738 https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017...