In case anyone is curious, the terrestrial system is not gps, is fairly inaccurate, and obsolete. https://en.m.wikipedia.org/wiki/LORAN The tower system is WAAS, which simply improves accuracy, especially for vertical navigation. Which was a boon to GPS IFR approaches. https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/waas/howitworks