Definition
Ground-based GPS receivers, installed at precisely surveyed locations on or near an airport, that form part of a Ground Based Augmentation System (GBAS). Each receiver tracks the GPS satellites in view and compares the satellite-derived position with its own known surveyed position. The differences are used to calculate correction and integrity data, which a GBAS ground station then transmits via VHF data broadcast to aircraft for use during precision approach and landing.
Plain English
These are GPS receivers fixed at known points on the ground at an airport. Because the equipment knows exactly where it is, it can measure how far off the GPS signals are, and that error information is sent to aircraft so their GPS positions become accurate enough for precision landings.
Context Anchor
Seen in GBAS and NextGen diagrams that show how airport-based equipment supports satellite-based instrument approaches.
Derivation
GBAS stands for Ground Based Augmentation System. 'Reference' here comes from the Latin 'referre,' meaning to carry back or relate to — these receivers serve as the trusted reference point that GPS signals are compared against. They're the 'known truth' the system uses to measure GPS error.
Why Pilots Care
Enables lower decision altitudes and curved approaches using GPS without needing traditional ground-based navigation aids.
Analogy
Think of a surveyor's benchmark: a known point used to measure everything else against. These receivers are GPS benchmarks for the airport.
Grounding Statement
Picture several fixed antennas on airport property, each in a known spot, checking the satellite picture before an aircraft uses it for guidance.
Intuition Check
“Reference” does not mean a book or manual here. It means a receiver at a known location used as a standard for comparison.
Example Sentence 1
The GBAS reference receivers at the airport detected the GPS signal errors and passed the corrections to the ground station for broadcast to arriving aircraft.
Example Sentence 2
Before flying the GBAS approach, the crew confirmed the status of the reference receivers on the approach chart.