Definition
A system that improves the accuracy, integrity, and availability of basic GPS signals by using a network of ground reference stations to measure GPS errors, then broadcasting correction and integrity data to aircraft via geostationary satellites. In the United States, the SBAS implementation is the Wide Area Augmentation System (WAAS), which enables GPS to be used for precision-like instrument approaches with vertical guidance.
Plain English
A helper system that watches GPS for errors and sends out corrections through a satellite, so the GPS in your aircraft becomes accurate and trustworthy enough to fly approaches down to low minimums.
Context Anchor
Seen in GPS instrument approach discussions, especially approaches that use the Wide Area Augmentation System for improved vertical and lateral guidance.
Derivation
Built from three plain words: 'satellite-based' (the corrections are broadcast from a satellite), 'augmentation' (from Latin augmentare, to increase or add to — here, adding accuracy and integrity to GPS), and 'system' (the whole network working together). The key idea is in 'augmentation': SBAS does not replace GPS, it adds to it.
Why Pilots Care
Enables lower decision altitudes and safer landings by supporting vertical guidance on approaches that would otherwise lack it.
Analogy
SBAS is like having a trusted spotter check your measurements and send you a correction before you use them. The original measurement still comes from the satellite navigation system, but SBAS helps make it more reliable.
Intuition Check
Do not think of SBAS as a separate navigation system that replaces GPS. It is an added support system that improves and checks satellite navigation signals.
Example Sentence 1
Because the aircraft was equipped with an SBAS-capable GPS, the crew was able to fly the LPV approach down to 250 feet above the runway.
Example Sentence 2
SBAS corrections allowed the aircraft to meet the required navigation performance for the LPV minimums.