What are the three systems used in aviation to confirm and improve GPS?

The three systems used in aviation to confirm and improve GPS accuracy are WAAS, GBAS, and RAIM.

WAAS, or Wide Area Augmentation System, enhances the performance of GPS by providing correction signals from ground stations to improve position accuracy for users in North America. It is particularly useful for precision approaches in aviation.

GBAS, or Ground-Based Augmentation System, operates similarly but is designed for more localized areas. It provides differential GPS corrections to allow for more precise landings, particularly in complex airport environments.

RAIM, or Receiver Autonomous Integrity Monitoring, is a critical function that allows a GPS receiver to monitor its own systems for integrity. It checks the reliability of the GPS signals being received, ensuring that pilots can trust the information provided for safe navigation.

Together, these systems significantly enhance the accuracy, reliability, and safety of GPS for aviation purposes, making option A the correct choice.