Static Accelerometer Orientation Tumble Calibration Procedures
Static tumble calibration calculates accelerometer bias, scale factor, and cross-axis matrices by optimizing spatial vector residuals against local gravity.
WGS-84
Geodetic Reference
Standard geodetic models established by international defense and intelligence agencies define the reference ellipsoid and coordinate frame for global positioning. In inertial navigation, WGS-84 provides the mathematical model used to calculate the local gravity vector based on the receiver’s latitude and altitude. This reference defines the shape of the Earth and the behavior of the gravitational field.
The model is utilized by navigation algorithms to correct for gravity during long-range flights.
Gravity Modeling
Calculating the correct gravity vector at the current position of the vehicle is necessary to prevent drift in the inertial navigation solution. Since the Earth is not a perfect sphere, the gravity model in WGS-84 accounts for the flattening of the poles and the centrifugal force of the Earth’s rotation. This calculation provides the nominal gravity value that is subtracted from the accelerometer readings.
The model ensures that the calculated velocity remains stable over time.
Coordinate Mapping
Transforming the raw sensor measurements into a global coordinate frame requires a consistent datum for the position calculations. In systems utilizing WGS-84, the position coordinates are represented as latitude, longitude and ellipsoidal height. The navigation processor executes real-time coordinate transformations to convert the acceleration data into these global coordinates.
If the coordinate system is not aligned, the calculated position will diverge from the true path. This alignment is verified during system integration by comparing the navigation solution against known reference points on the surface of the Earth. The verification is repeated under dynamic test scenarios to ensure consistency.
Receiver Validation
Sourcing global positioning receivers requires verifying that their internal coordinate calculations match the standard model. For a device tracking positions in WGS-84, the output is compared against standard test datasets to ensure the mathematical algorithms are implemented correctly. This validation prevents coordinate transformation errors from skewing the final position output.