of the return on the scope tells
him the location of the object that was causing the echo. As the
object moves through the sky, the radar operator sees a series of
bright dots on his scope that make a track. On some radar sets the
altitude of the target, the object causing the echo, can also be
measured.

Under normal conditions the path that the radar waves take as they
travel through the air is known. Normal conditions are when the
temperature and relative humidity of the air decrease with an
increase in altitude. But sometimes a condition will occur where at
some level, instead of the temperature and/or relative humidity
decreasing with altitude, it will begin to increase. This layer of
warm, moist air is known as an inversion layer, and it can do all
kinds of crazy things to a radar wave. It can cause part of the radar
wave to travel in a big arc and actually pick up the ground many
miles away. Or it can cause the wave to bend down just enough to pick
up trucks, cars, houses, or anything that has a surface perpendicular
to the ground level.

One would immediately think that since the ground or a house isn't
moving, and a car or truck is moving only 40, 50, or 60 miles an
hour, a radar operator should be able to pick these objects out from
a fast-moving target. But it isn't as simple as that. The inversion
layer shimmers and moves, and one second the radar may be picking up
the ground or a truck in one spot and the next second it may be
picking up something in a different spot. This causes a series of
returns on the scope and can give the illusion of extremely fast or
slow speeds.

These are but a few of the effects of an inversion layer on radar.
Some of the effects are well known, but others aren't. The 3rd
Weather Group at Air Defense Command Headquarters in Colorado Springs
has done a lot of work on the effects of weather on radar, and they
have developed mathematical formulas for telling how favorable
weather conditions are for "anomalous propagation," the two-bit words
for false radar targets caused by weather.

The first problem in analyzing reports of UFO's being picked up on
radar is to determine if the weather conditions are right to give
anomalous propagation. This can be determined by putting weather data
into a formula. If they are, then it is necessary to determine
whether the radar targets were real or caused by the weather. This is
the difficult job. In most cases the only answer is the appearan