Embodiments of the system provide for processing non-continuous atom interferometer inertial instrument measurements and continuous wide bandwidth instrument measurements with a gravity database. An embodiment may have: a gravity disturbance vector database having gradients; a comparator that compares real-time gravity gradiometer gradient measurements with gradients from the database to provide an observation; and a Kalman filter that receives the observation on an input thereof, the Kalman filter outputting a modeled error state vector; wherein the gravity disturbance vector from the gravity database is used to remove a known portion of an actual gravity disturbance vector from specific force measurements of high bandwidth conventional inertial accelerometers to thereby form navigation data. An embodiment of the method that may have the steps of: providing a gravity disturbance vector database having stored gradients; providing real-time measurements of gravity gradients; and processing the stored gradients and the gravity gradients to form navigational data.