NAVIGATION SYSTEM

Apparatus for determining the position and velocity of a vehicle over a given area as represented by stored data includes a radar terrain sensor responding to radar pulse returns and generating video signals to a terrain clearance estimator. Also input to the terrain clearance estimator are vehicle vertical position data and vertical speed data which along with the video output of the terrain sensor generates by means of a time of arrival estimator observed clearance signals which are sampled and input to a buffer. Also stored in the buffer are vehicle position and velocity signals from an inertial navigation system with the buffer data accessed by an error correction estimator. The error correction estimator responds to stored data to generate a sequence of position and velocity error correction signals each comprising three components. These error correction estimates of vehicle position and vehicle velocity are input to a data register which is accessed by the inertial navigation system to provide update information on the position and velocity of a vehicle.