Initial and Final Alignment of a Strapdown Airborne Gravimeter and Accelerometer Bias Determination

In strapdown airborne gravimetry, initial alignment of a strapdown inertial measurement unit (IMU) of the gravimeter is of great importance. It is performed to determine the IMU attitude angles by the measurements during the aircraft standstill before the flight. This information, in its turn, helps determine the bias of the gravimeter vertical accelerometer. After the flight the bias is determined again and the linear drift over the entire flight can be removed from the vertical accelerometer measurements. However, the measurements of inertial sensors are disturbed by uncontrolled angular motions of the IMU due to external mechanical actions on the gravimeter body during the aircraft standstill. The paper proposes an algorithm for the gravimeter IMU initial and final alignments with the determination of IMU attitude angles and biases of all three accelerometers during the standstills before and after the flight. It has been shown in the paper that the accelerometer scale factor errors can also be determined by the algorithm. The algorithm performance under the angular motions of the gravimeter has been demonstrated on experimental data. The accelerometers calibration accuracy has been evaluated by comparing with the results of another calibration algorithm and by analyzing the errors in IMU autonomous dead-reckoning.