Definition
A precisely surveyed ground station within the Wide Area Augmentation System (WAAS) network that continuously receives signals from GPS satellites, measures any errors in those signals, and forwards that data to a WAAS master station for processing into correction messages broadcast to aircraft.
Plain English
A ground station at a known, fixed location that listens to GPS satellites, works out how far off the satellite signals are, and passes those errors along so they can be corrected for pilots using GPS.
Context Anchor
Seen in WAAS discussions, especially when learning how GPS corrections are created before they reach the cockpit navigator.
Derivation
Wide Area' refers to the large geographic region the WAAS network covers (the continental United States and beyond). 'Reference Station' comes from surveying, where a reference point is a location whose position is already known with high precision, used as the basis for measuring others. The station's known position is what allows it to detect satellite errors.
Why Pilots Care
These stations enable the precise corrections that make WAAS approaches possible with vertical guidance down to decision altitudes as low as 200 feet.
Analogy
It is like checking several watches against one clock that you know is correct. The known clock does not make the watches run better by itself, but it reveals how far off they are so a correction can be made.
Intuition Check
Do not read “reference station” as just any radio site or navigation aid. Here it means a fixed WAAS ground site with a known exact position, used as a standard for checking GPS signal errors.
Example Sentence 1
Wide Area Reference Stations across the country measure GPS signal errors and feed that information to the WAAS master stations.
Example Sentence 2
Pilots on a WAAS approach benefit from data that originated at multiple Wide Area Reference Stations across the region.