Page:Ruppelt - The Report on Unidentified Flying Objects.djvu/131

 UFO’s while the camera stations were in operation because they realized that if the flight path of a UFO could be accurately plotted and timed it could be positively identified. But no more UFO’s showed up.

One day Lieutenant Cummings came over to my desk and dropped a stack of reports in front of me. “All radar reports,” he said, "and I’m getting more and more of them every day.”

Radar reports, I knew, had always been a controversial point in UFO history, and if more and more radar reports were coming in, there was no doubt that an already controversial issue was going to be compounded.

To understand why there is always some disagreement whenever a flying saucer is picked up on radar, it is necessary to know a little bit about how radar operates.

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