Define velocity aiding in GNSS/INS integration and how it improves performance during updates.

• A. Velocity aiding uses IMU angular rates to correct GNSS velocities.
• B. Velocity aiding uses GNSS-derived velocity to constrain INS drift, improving velocity accuracy and stabilizing attitude estimates during updates.
• C. Velocity aiding ignores GNSS data.
• D. Velocity aiding only applies during initial alignment.

Answer: (B)

Velocity aiding uses GNSS measurements of velocity as a reference to constrain the drift of the INS. An INS continuously integrates accelerations and gyro rates, which accumulates error over time due to biases and noise. When a GNSS velocity update arrives, the estimator blends that GNSS velocity with the current INS velocity estimate, pulling the INS drift back toward the true value. This correction reduces velocity error and, because velocity is connected to the attitude through the navigation frame, it also helps stabilize the attitude estimate during the update.

So, the key benefit is clearer, more accurate velocity information and steadier attitude estimates when GNSS updates occur. This approach relies on GNSS velocity data to correct the INS, rather than using IMU angular rates to fix GNSS velocity, and it operates during regular updates rather than being limited to initial alignment.