What is RAIM and how can it help detect GNSS spoofing or jamming?

• A. A method to map satellite geometry for integrity checks
• B. A terrestrial surveillance technique
• C. RAIM stands for Receiver Autonomous Integrity Monitoring; uses redundant satellites to check pseudorange measurements
• D. A method for calibrating antennas

Answer: (C)

RAIM, or Receiver Autonomous Integrity Monitoring, is about keeping GNSS navigation trustworthy by using the redundancy in satellite signals. The receiver checks the pseudorange measurements from multiple satellites against the expected geometry to see if all the ranges fit together in a consistent solution. If one satellite’s measurement is off—perhaps due to a spoofed signal or localized jamming—the inconsistency appears as an outlier in the residuals. Because there are more measurements than unknowns, the system can test each satellite’s contribution and, if one is bad, exclude it and still produce a reliable position, or flag the navigation as potentially unsafe. This integrity check improves reliability in hostile environments where spoofing or jamming might distort some signals. It’s not about mapping satellite geometry for checks, nor about terrestrial surveillance or antenna calibration, which is why RAIM is the appropriate concept here.