GBAS stands for Ground-Based Augmentation System. It's an aviation navigation system that improves the accuracy, integrity, and availability of the  global navigation satellite system (GNSS) to support aircraft precision approach and landing.

GBAS works by augmenting the information obtained from satellite navigation systems, such as GPS, with correction data, along with integrity information, transmitted from a  ground station. This information used by an airborne GNSS receiver improves the performance of the position information provided to the aircraft.

A typical GBAS system consists of ground-based reference receivers (with their reference antennas), a central processing facility (CPF), and a VHF Data Broadcast (VDB) transmitter. The reference receivers acquire and process the signals from the GNSS satellites to measure the distances to the satellites (measurements), which are then sent to the CPF for processing and computation of corrections to these measurements and of integrity data, and broadcast them to the aircraft. A GBAS onboard receiver (usually integrated in a Multi-Mode Receiver called MMR) applies these corrections to its own GNSS measurements to output an augmented GNSS position solution. 

GBAS is primarily used in aviation for precision approach and landing procedures, being an alternative to the Instrument Landing System (ILS).

GBAS offers several benefits, including increased landing capacity at airports, improved safety through enhanced navigation accuracy, reduced weather-related delays, and enhanced operational efficiency for airlines.

While both GBAS and ILS are used for precision approaches, they are different technologies. ILS relies on ground-based radio signals, while GBAS utilizes satellite-based navigation signals augmented with ground-based computed corrections.

GBAS is deployed at various airports around the world, including major hubs and busy international airports. Some countries, such as the United States, Germany, and Australia, have a few GBAS stations.

GBAS is compatible with most modern commercial and general aviation aircraft equipped with the necessary avionics. However, retrofitting older aircraft with GBAS capability may require modifications or upgrades.

The future of GBAS technology includes further advancements in accuracy, integrity, and availability, as well as potential integration with other navigation systems. Research and development efforts are ongoing to enhance GBAS performance and expand its capabilities.

GBAS plays a crucial role in airspace modernization efforts, such as the FAA's NextGen program in the United States. By improving navigation accuracy and efficiency, GBAS helps optimize airspace capacity, reduce congestion, and enhance overall aviation safety and performance.