Initial Calibration
The process of determining the initial attitude and position of a navigation platform occurs while the vehicle remains at rest on a stable foundation. A stationary inertial system alignment uses the gravity vector and the Earth’s rotation rate to compute the initial tilt and heading angles of the platform. This initialization must be executed with high precision before any navigation calculations can begin.
It establishes the reference frame for all subsequent acceleration and velocity integration.
Physical Mechanism
Accelerometers measure the local gravity vector to determine the roll and pitch of the platform. Gyroscopes measure the horizontal component of the Earth’s spin to calculate the true north heading, a process known as gyrocompassing. Because the Earth rotates slowly, these gyroscopes must feature low noise and drift to resolve the heading accurately.
Error Propagation
Any error in the initial alignment causes rapid drift in the calculated position over time. An incorrect heading angle, for instance, leads to a cross-track velocity error that grows quadratically during subsequent motion. This drift can render the navigation data useless in autonomous vehicles or mapping platforms.
Verification Procedure
Alignment quality is verified by monitoring the convergence of the covariance matrix in the system’s Kalman filter. A successful alignment occurs when the estimated errors fall below the predefined threshold specified by the design requirements. This condition is typically tested over a run of ten minutes.
