Abstract: On-board, computer-based systems and methods compute continuously updated, real-time state estimates for an aerial vehicle by appropriately combining, by a suitable Kalman filter, local, relative, continuous state estimates with global, absolute, noncontinuous state estimates. The local, relative, continuous state estimates can be provided by visual odometry (VO) and/or an inertial measurement unit (IMU). The global, absolute, noncontinuous state estimates can be provided by terrain-referenced navigation, such as map-matching, and GNSS. The systems and methods can provide the real-time, continuous estimates even when reliable GNSS coordinate data is not available.