A PRIORI AND REAL TIME USE OF A GRAVITY GRADIOMETER TO IMPROVE INERTIAL NAVIGATION SYSTEM ACCURACY

As inertial navigation instrumentation has become more advanced, the errors associated with imprecise knowledge of the true gravity vector have become significant. With the development of the moving base gravity gradiometer, ongoing for the past ten years, a means for detecting the true gravity vector is available. This research explores both real time and a priori schemes for using the gradiometer information to reduce the position and velocity error associated with an inertial navigation system.; In the real time application, information derived from the gradiometer is filtered to produce estimates of position and velocity error. The problem is to derive accurate filters in the presence of an inherently transcendental gravity field. Conventional Kalman filters are very cumbersome to apply in this instance. However, the sensitivity of inertial navigation systems at Schuler frequency makes it possible to neglect errors outside of a narrow band of frequencies centered at Schuler frequency. This approximation leads to low order filters which may be applied with surprising accuracy.; For the a priori application the gradiometer is used in a survey mode to establish a reference gravity model to be used in open loop inertial navigation system operation. By determining the root mean squared values of the resulting position and velocity errors it is possible to evaluate the effectiveness of the survey scheme and to compare the survey application with the real time gradiometer application. Again, analytic and numeric covariance methods are used to do these analyses.