dry or dense layers. Figure 5-23 depicts two conditions of anomalous propagation: the
atmosphere causing a downward bending of RADAR beams and the atmosphere
causing an upward bending of RADAR beams.
Figure 5-23 -- Anomalous propagation.
Because of anomalous propagation, targets hundreds of miles away may be detected
even though they are far below the horizon. Conversely, relatively close targets may not
be detected.
False Targets
A proficient RADAR controller is quick to recognize a temperature inversion as a false
target. Such indications are often secondary reflections of RADAR energy from isolated
refracting areas in a temperature inversion level. Correlation of RADAR reports with the
National Weather Service records indicates that a temperature inversion is usually
present when unidentified flying objects appear on the scope. These inversions often
travel across the RADAR at tremendous speeds and in changing directions. Apparently
this phenomenon is produced by isolated refracting areas traveling with the wind at or
near temperature inversion levels. The exact size, shape, and composition of these
isolated areas are not known. It is believed that they may be atmospheric eddies
produced by a shearing action of dissimilar air strata. It appears that such eddies may
reflect and focus the RADAR energy with a lens effect. This produces a small
concentration of ground return with sufficient strength to show up on the RADAR
display.
RADAR Jamming
Jamming, as used in conjunction with RADAR, is defined as an introduction of false
radiation into RADAR and RADAR devices. False targets produced by jamming may
appear on the scope at varying ranges and bearings. In some cases, they may clutter
large portions of the scope.
5-47
