Definition
A GPS receiver placed at a precisely surveyed ground location whose role is to compare its known position with the position calculated from incoming GPS satellite signals. The difference between the two becomes a correction signal that is broadcast to nearby aircraft, improving the accuracy of their own GPS receivers. It is the ground-based half of a Differential GPS (DGPS) system.
Plain English
A GPS receiver on the ground that already knows exactly where it is. By comparing its true location to what the satellites say, it works out how wrong the GPS signal is right now and sends that correction to aircraft nearby so their GPS can be more accurate.
Context Anchor
Seen in discussions of Differential GPS, where a ground station improves GPS position accuracy by sending correction information.
Derivation
Reference' comes from the Latin referre, meaning 'to carry back' or 'to relate to.' In this context the receiver is the trusted point of comparison — the fixed truth that everything else is measured against. That is why it is called a reference receiver rather than just a ground receiver.
Why Pilots Care
Provides the position corrections that allow DGPS to achieve the accuracy required for Category I approaches and other low-visibility operations.
Intuition Check
Do not picture the reference receiver as the GPS unit in the airplane. In this context, it is the fixed ground receiver used as the known comparison point.
Example Sentence 1
The DGPS reference receiver at the airport detected a small timing error in the satellite signal and broadcast a correction to inbound aircraft.
Example Sentence 2
Pilots using DGPS rely on data from the reference receiver to maintain the tight lateral and vertical guidance needed during an ILS-like approach.