Sequence Operation
Initial sequence of operations performed while a vehicle is stationary to establish the relationship between the inertial sensor frame and the local geographic frame. This ground alignment allows the navigation system to determine its initial attitude and heading before the commencement of movement. The process relies on the detection of the gravity vector and the earth rotation rate to define the vertical and north directions.
Initialization Period
Duration of the process depends on the grade of the sensors and the required precision of the navigational solution. During ground alignment, the system filters out local vibrations and electronic noise to obtain a stable estimate of the starting orientation. Any movement of the platform during this phase introduces large errors that will persist throughout the mission.
Longer durations generally lead to better convergence of the heading estimate as more samples of the rotation of the earth are collected.
Mathematical Integration
Onboard computers solve complex equations to transform raw sensor data into a useful coordinate system. The accuracy of ground alignment determines the drift rate of the position estimate once the vehicle is in motion. Modern systems use advanced filtering techniques to refine the initial estimates of tilt and heading based on repeated measurements.
Environmental Constraint
High winds or seismic activity can interfere with the stability of the platform. Successful ground alignment requires a stable surface to ensure that the sensors only respond to the constant forces of the earth.
