Under what condition are Zero-Velocity Updates (ZUPTs) applied in inertial navigation?

• A. When the platform is stationary.
• B. When the platform is moving to reset velocity.
• C. After satellite outage.
• D. At fixed time intervals regardless of motion.

Answer: (B)

Zero-velocity updates use moments when the platform is at rest to correct drift in the velocity estimate. When the device is known to be stationary, the navigation filter adds a measurement that the velocity equals zero (with some uncertainty). This constraint pulls the estimated velocity and sensor biases back toward their true values, dramatically reducing long-term drift that comes from integrating noisy accelerometer data.

So this update is applied during rest periods, not while the platform is moving, not after a satellite outage, and not at fixed times regardless of motion. The key is detecting and exploiting a genuine zero-velocity event to reset the velocity state.