Which wave propagation method uses the Earth’s surface for transmission?

The method of wave propagation that utilizes the Earth's surface for transmission is known as ground wave propagation. This type of propagation occurs primarily at low frequencies, where radio waves can travel along the surface of the Earth. As the waves travel, they hug the ground, which allows them to cover distances beyond the horizon. Ground wave propagation is particularly useful for medium-wave and low-frequency broadcasting, such as AM radio, because these lower frequencies can diffract around obstacles and follow the curvature of the Earth.

In contrast, sky wave propagation involves waves reflecting off the ionosphere back to Earth, which is more suitable for high-frequency signals. Tropospheric scattering refers to waves that are scattered in the troposphere, allowing radio signals to propagate beyond the horizon but doesn’t specifically make use of the Earth’s surface like ground waves do. Satellite wave propagation depends on signals being transmitted to and from satellites in orbit, which does not involve utilization of the Earth's surface in the same direct manner as ground waves.