What are Zero-Velocity Updates (ZUPTs) and how do they aid inertial navigation?

• A. Updates performed when the platform is stationary to reset velocity and partially correct biases, reducing drift.
• B. Updates performed when the platform is moving to reset velocity.
• C. Updates used to recalibrate magnetometer during motion.
• D. Updates used to reset clock bias only.

Answer: (A)

Zero-velocity updates use moments when the platform is known to be at rest to anchor the inertial navigation solution. In an inertial system, velocity is obtained by integrating accelerations, and small biases in the accelerometer and gyroscope gradually cause drift in velocity and position estimates. When the true velocity is zero, as the platform stands still, a zero-velocity observation provides a reliable constraint. By injecting this constraint into the estimator (often an EKF or similar filter), the system corrects the velocity estimate toward zero and also reduces the estimated biases. This partial bias correction helps reduce long-term drift, improving position accuracy once motion resumes. ZUPTs are especially useful in pedestrian navigation, where stationary periods occur naturally and can repeatedly reset the solution.

They’re not applied during motion to reset velocity, they don’t recalibrate the magnetometer, and they don’t target clock bias alone.