What degrades ground wave propagation?

Ground wave propagation refers to the way radio waves travel along the surface of the Earth. It is primarily influenced by factors such as frequency and the physical environment.

The correct choice highlights that ground wave propagation can be significantly degraded by terrain, vegetation, manmade structures, and severe weather. These elements can obstruct, reflect, or scatter radio waves, thus weakening the signal as it attempts to travel over the surface. For instance, mountainous regions can create shadow zones where signals are weaker, while dense forests can absorb high-frequency signals and hinder their ability to propagate effectively. Similarly, manmade structures such as buildings can cause reflections and multipath propagation, leading to a further degradation of the signal.

In contrast, higher altitudes and longer wavelengths generally have less direct impact on ground wave propagation. Increased frequency can actually lead to a phenomenon known as 'skip propagation,' where the waves reflect off the ionosphere, potentially improving long-distance communication but not necessarily affecting ground-level propagation negatively. Understanding these factors is crucial for effective communication system design and implementation.