ANOMALOUS PROPAGATION (AP)

Non-standard atmospheric temperature or moisture gradients will cause all or part of the radar beam to propagate along a non-normal path. When non-standard index-of-refraction distributions prevail, "abnormal" or "anomalous" propagation occurs. When abnormal downward bending occurs, it is called "superrefraction." If the beam is refracted downward sufficiently, it will illuminate the ground and return signals to the radar from distances further than is normally associated with ground targets. The term "subrefraction" is applied when there is abnormal upward bending of the radar beam.

Abnormal propagation caused by fluctuations in the properties (such as density and refractive index) of the propagation medium. Note: AP may result in the reception of signals well beyond the distances usually expected.