Ground Alignment Error Bounds for Inertial Navigation Initialization
Ground alignment error bounds depend on accelerometer turn-on bias for leveling and East gyro bias stability divided by cosine latitude for heading accuracy.
Earth Rotation Rate
Angular Velocity
Angular velocity at which the planet spins around its polar axis relative to inertial space. This earth rotation rate provides the fundamental reference for gyrocompassing and inertial navigation systems. The value is approximately fifteen degrees per hour and its horizontal and vertical components vary according to the latitude of the sensor.
Rotational Influence
Stationary gyroscopes detect this motion as a constant input signal. Calculations involving the earth rotation rate allow a navigation computer to distinguish between the actual movement of a vehicle and the underlying rotation of the globe. Any error in the measurement of this rate leads to a gradual drift in the calculated heading of the system.
Latitude Dependence
Magnitude of the detected signal changes as the sensor moves from the equator toward the poles. At the equator, the horizontal component of the earth rotation rate is at its maximum while the vertical component is zero. This relationship reverses at the poles, creating a challenge for systems that rely on the horizontal signal for north-seeking operations.
Designers must account for these geometric variations to maintain a consistent navigational performance across different geographic regions.
Metrological Standard
Precise determination of this value is essential for the calibration of high-accuracy inertial sensors. Laboratories use the earth rotation rate as a known stimulus to verify the scale factor and bias of navigation-grade gyroscopes.