Development of a nonlinear psi-angle model for large misalignment errors and its application in INS alignment and calibration

This work presents a general nonlinear psi-angle approach that does not require coarse alignment. In this psi-angle model, the three misalignment angles are assumed all large. Three states are used to describe three psi-angles rather than the four used in previous works. The approach is identical to the standard small error methods when the process errors diminish to small angles. The position and velocity error models are also presented. Standard extended Kalman filter techniques are used to solve the nonlinear data fusion problem. Experimental results of in-flight inertial navigation systems (INS) alignment and calibration are presented considering total uncertainty in azimuth orientation using a low cost inertial measurement unit aided with a differential global positioning system.