How does IMU misalignment influence ENU position estimates, and what alignment corrections are typically performed?

• A. Misalignment rotates sensor axes relative to the navigation frame, causing cross-axis errors; corrections include initial and dynamic alignment, and calibration of misalignment angles.
• B. Misalignment has no effect if you use GNSS.
• C. Misalignment improves cross-axis coupling.
• D. Misalignment only affects altitude.

Answer: (A)

IMU misalignment is an orientation error between the IMU’s body-frame axes and the ENU navigation frame. When the axes are rotated relative to the world frame, the accelerations and angular rates measured by the IMU are interpreted in the wrong directions. This creates cross-axis coupling, so motion that should appear along one ENU axis leaks into the others. As the system integrates these measurements to compute velocity and then position, these small orientation errors accumulate into drift and misorientation of the ENU position estimates.

To address this, alignment corrections are routinely performed. Static initial alignment uses known references like gravity and Earth’s rotation to estimate the misalignment angles and biases at setup. Dynamic alignment refines attitude during operation by leveraging the vehicle’s motion and external references such as GNSS updates, effectively updating the misalignment estimates over time. Calibration of misalignment angles (the rotation between the IMU frame and the ENU frame, often represented as a small rotation matrix or Euler angles) is performed so those angles can be removed from the measurements, typically within the estimator as part of the state and updated with sensor data.