What do ground waves in radio propagation refer to?

Ground waves in radio propagation refer to signals that propagate along the surface of the Earth. This phenomenon occurs primarily at low frequencies where the radio waves can follow the curvature of the Earth. Ground waves are affected by the nature of the terrain they travel over; for example, they can diffract around obstacles and can propagate over large distances, especially if the ground is conductive, such as in coastal areas where the sea enhances the propagation effects.

This type of wave propagation is particularly useful for AM broadcasting and marine communications, as it allows signals to reach receivers that are not in the direct line of sight of the transmitter. Ground waves typically have a lower frequency range, and their ability to travel over the ground makes them distinct from other propagation methods, such as skywaves, which involve signals that are reflected off the ionosphere, or satellite communications, which rely on signals transmitted directly to and from satellites in orbit.