TERRAIN REFERENCED NAVIGATION SYSTEM

A navigation system for an aircraft includes a microelectromechanical systems inertial measurement unit (MEMS-IMU), a camera that captures, over time, a series of images of the terrain below the aircraft, a terrain map comprising terrain elevation data, an inertial navigation system (INS) and an optical terrain-referenced navigation unit (O-TRN). The INS generates a first position estimate based on one or more signals output by the MEMS-IMU. The O-TRN identifies a terrain feature in an image captured by the camera, derives a terrain height estimate of the terrain feature, and generates a second position estimate based on a comparison between the terrain height estimate and terrain elevation data extracted from the terrain map. The navigation system generates a third position estimate based on the first position estimate and the second position estimate.