The accuracy of modern multisensor integrated inertial navigation systems (INS) is affected by various noise sources, such as accelerometer and gyro instabilities. These error sources are often modeled as Gauss-Markov random processes and their effects on navigation system accuracy are determined by covariance simulation. Environmental error sources such as gravity uncertainties have been treated similarly. In this paper, the error equations for a local-level INS are derived. In order to apply covariance error analysis to the system, the linear dynamic error equations in their state-space representation are presented. The error sources considered are gyro drift, accelerometer error, and gravity uncertainties.
We have obtained finally a general case model representing error propaga-tion equations including three dimensional free vehicle motion .