TABLE OF CONTENTS Errors in the navigation solution of position and velocity can build up due to unaccounted for sensor noise and error sources. Chief amongst them are gyro drifts and accelerometer biases. The g-slaving method was used with AHRS to estimate these errors, however this method can not be used when the craft maneuvers or can it reestablish any reference point after the craft ends the maneuver. An extra navigation aid is needed to establish the reference points and estimate the inertial errors.
The Global Positioning System (GPS) is one helpful aid for estimating these error sources. It provides, with a reasonable degree of accuracy, the position, the velocity and the heading of the craft. Thus it can establish a reference navigation point after the period in which the inertial navigation system (INS) has been acting alone. To employ such aiding tool, a GPS receiver is installed and a Kalman filter (KF) is designed to estimate the navigational error parameters. A processor on board receives and compares the position and velocity data from both the INS and the GPS. The residual the difference between the INS and GPS navigation data is weighted by the KF gain to correct the error in the INS estimates. Among the many approaches for implementing the KF, we herein select for our discussion the loosely coupled algorithm. This approach is selected for its simplicity in that it does not need to access GPS receiver internal raw data and the processing of the INS...
