Anomalous propagation

Anomalous propagation can cause interference to VHF and UHF radio communications if distant stations are using the same frequency as local services.

Over-the-air analog television broadcasting, for example, may be disrupted by distant stations on the same channel, or experience distortion of transmitted signals ghosting).

The first assumption of the prediction of propagation of a radio wave is that it is moving through air with temperature that declines at a standard rate with height in the troposphere.

[2] Changes to the path can be separated into super and under refraction:[3] It is very common to have temperature inversions forming near the ground, for instance air cooling at night while remaining warm aloft.

In surface-based ducting, the beam will hit the ground many times, causing return echoes at regular distances toward the emitter.

On the other hand, if the air is unstable and cools faster than the standard atmosphere with height, the wave is higher than expected and can miss the intended receiver.

Since precipitation exists in those circumstances, the abnormal propagation echoes are then mixed with real rain and/or targets of interest, which make them more difficult to separate.

Since anomalous propagation comes from stable targets, it is possible to subtract the reflectivity data having a null speed and clean the radar images.