RAIM stands for which concept?

• A. A technique for calibrating GPS receivers.
• B. Receiver Autonomous Integrity Monitoring.
• C. A method for adjusting radar altimeter sensitivity.
• D. An instrument to determine wind shear.

Answer: (B)

RAIM is a GPS integrity-monitoring capability used by receivers to ensure the navigation solution is trustworthy. It relies on the redundancy of multiple satellite measurements to check for inconsistencies. By comparing the pseudorange data from several satellites, the receiver can detect when one satellite (or its signal path) is faulty or anomalous. When a fault is suspected, the receiver can exclude the suspect satellite and recompute the position using the remaining satellites. This is crucial for aviation, where GPS navigation must be reliable for IFR operations; RAIM helps determine whether the GPS solution is valid or whether alternative navigation methods should be used. In practice, certain satellite counts are needed to perform these checks: with a sufficient number of satellites, the system can perform fault-detection tests, and with even more satellites it can perform fault-exclusion if a fault is identified. In short, RAIM stands for Receiver Autonomous Integrity Monitoring.