Abbreviation Stands for Main usage Zero level Measuring devices AGL, HAGL Height Above Ground Level aviation, atmospheric science, broadcasting ground surface radar altimeter AMSL, HAMSL Height Above Mean Sea Level nautic, technics, geography sea level average barometric altimeter HAE Height Above Ellipsoid navigation, science math surface model WGS84 GPS receiver AAT, HAAT Height Above Average Terrain broadcasting, cellular networks average surrounding surface