Transferring the Bearing Using a Strapdown Inertial Measurement Unit

Of all the various possibilities of using an inertial measurement unit (IMU) in surveying engineering only the determination of a reference bearing and its transfer is focussed upon in this paper. Strapdown-systems differ from the conventional gimballed platform-configuration by the use of the sensors which are sensitive to a rotation of the IMU. The gyroscopes, usually three Ringlasergyros or two Dynamical Tuned Gyros are, in addition to the accelerometer triad, fixed to the carrier. Thus the gyros serve as rate sensors and not as stabilizing elements as in the case of gimballed platform-systems. The advantage of fewer hardware components and thus lower hardware purchase and maintenance costs is opposed by the exposition of the sensors to the whole dynamical environment of the carrier. After an initial alignment with respect to the local horizontal frame the determined alignment-angles can be transferred to another control point by a proper evaluation of the sensor output without the necessity of a direct line of sight between the two points. In this paper the potential of the determination of the alignment and its transfer is discussed. In addition some simulation results of corresponding scenarios are presented.