Abstract

The present invention is directed to a system that has a first sensor assembly coupled to a mobile platform that traverses a predetermined subsurface path and has an axis of motion. The first sensor assembly obtains a gravity vector of the Earth relative to the mobile platform. A second sensor assembly is disposed in substantial alignment with a predetermined position relative to the axis of motion and is characterized by a sensitivity axis. The second sensor assembly provides a sensor signal substantially corresponding to a single vector component of the Earth's rotation vector. A control system is configured to derive the path direction relative to a known direction and an inclination angle of the mobile platform relative to the surface based on the gravity vector and the single vector component of the Earth's rotation vector.