What does ducting in radio communication refer to?

Ducting in radio communication specifically refers to the phenomenon where radio frequency (RF) signals are trapped within layers of warm air, which can significantly enhance the propagation of signals over long distances. This occurs because the warm air acts as a barrier, effectively guiding the signals through the atmosphere. When conditions are right, such as a temperature inversion, ducting can lead to unusually long-range communication, allowing signals to travel much farther than they normally would due to the structure created by these warm air pockets.

In contrast, the other options represent different phenomena that affect radio signal propagation but do not capture the essence of ducting. For example, signal absorption by water refers to how certain frequencies can be weakened or absorbed when passing through water, which is not related to the trapping of signals. Additionally, the reflection off the Earth's surface describes a different propagation mechanism utilized in radio communication, while the diversion of signals through interference relates to unwanted disruptions in the signal path rather than the trapping of signals in air layers. Each of these options indicates different factors that can influence radio communication but does not describe the specific capturing effect seen with ducting.