Basically radar is nothing but a piece of electronic equipment that "shouts" out a radio wave and "listens" for the echo. By "knowing" how fast the radio, or radar, wave travels and from which direction the echo is coming, the radar tells the direction and distance of the object that is causing the echo. Any "solid" object like an airplane, bird, ship, or even a moisture-laden cloud can cause a radar echo. When the echo comes back to the radar set, the radar operator doesn't have to listen for it and time it because this is all done for him by the radar set and he sees the "answer" on his radarscope--a kind of a round TV screen. What the radar operator sees is a bright dot, called a "blip" or a "return." The location 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.