A radio wave that travels along the surface of the earth.
A radio wave that follows the curvature of the earth near the ground.
A radio wave that hugs the ground, following the curvature of the Earth rather than traveling in a straight line.The Earth is an electromagnetic conductor, although certainly not a perfect one. At the low end of the electromagnetic spectrum, signals propagate close to, are coupled to, interact with, and even travel through the Earth. A ground wave also is attenuated by the Earth, with the effect increasing as the frequency of the signal increases. Signals in the extremely low frequency (ELF), very low frequency (VLF), low frequency (LF), and medium frequency (MF) ranges are characterized as ground waves. See also conductor, electromagnetic spectrum, ELF, LF, MF, propagation, skywave, surface wave, and VLF.