A system and method for providing highly accurate measurements of the altitude above ground level (AGL) of an aircraft flying over local terrain. A current AGL altitude of the aircraft over local terrain is obtained by activating a radar altimeter on the aircraft for a single short duration or pulse. A mean sea level (MSL) elevation of the local terrain is determined by identifying the terrain from the then-current aircraft geographical position coordinates and utilizing known terrain topography data. The actual MSL altitude of the aircraft can then be determined. An uncorrected MSL altitude of the aircraft is then determined from conventional static air pressure measurements and the difference between the actual MSL altitude and the uncorrected MSL altitude of the aircraft yields a local barometric correction factor for use in determining MSL altitude measurements of the aircraft as the aircraft flies over and continues its flight away from the local terrain.