Alignment bias estimation improves navigation by

• A. Calibrating GNSS satellite clock biases.
• B. Adjusting magnetometer to Earth's field.
• C. Eliminating the need for INS.
• D. Providing better initial state estimates by reducing sensor biases during alignment.

Answer: (D)

During alignment, the navigation system estimates both the initial state and the biases of the inertial sensors. Sensor biases, especially gyro bias and accelerometer bias, directly affect how IMU measurements translate into attitude, velocity, and position. If these biases aren’t accounted for, integrating the measurements drifts and builds up errors even before useful external updates arrive. Estimating and compensating these biases during alignment gives you a more accurate initial attitude, velocity, and bias values, which in turn reduces early drift and improves overall navigation performance as the system continues to operate. Other options refer to calibration tasks that belong to different parts of the system (GNSS timing, magnetometer calibration) or to a concept (eliminating INS) that isn’t what alignment bias estimation accomplishes. In short, providing better initial state estimates by reducing sensor biases during alignment best describes the benefit.