Initial coarse attitude can be obtained through a coarse alignment in the Inertial Navigation System (INS). Initial attitude is required in the GF-INS which contains only accelerometers. In this paper, a coarse alignment of GF-INS with gyroscope is investigated. For the GF-INS, levelling is performed after neglecting the Euler force term. Yaw estimation from accelerometer outputs of the GF-INS for gyro compassing is derived. It is shown that the gyro compassing is not feasible in a GF-INS. The yaw estimation and yaw estimation error are investigated when gyroscopes are additionally fixed to the GF-INS. The results show that the gyroscopes should be fixed to roll and pitch axes in order to have feasible results.

Keywords: distributed accelerometers, gyroscope, inertial navigation system, coarse alignment