EXCERPT FROM SECTION XV, RADAR CASES (FORM 9)

by Chyck Pine and Ron Johnson

15.1 PURPOSE

This section is devoted to familiarizing the field investigator with the nomenclature of different types of radar equipment, their use and limitations. It offers suggestions to help in communicating with Air Traffic Control operators as a means of identifying visual UFO sightings that may have been detected simultaneously on nearby radar installations.

From the field investigator's viewpoint, one needs to be familiar with radar in general, with emphasis on the Air Traffic Control standpoint, both FAA and military. Both utilize the same basic technology, but the military has more applications.

15.2 RADAR THEORY

Pulse radar is the type that we use for aviation purposes. This means that a signal is transmitted in the microwave range for a very short time frame (microseconds), after which the antenna and receiver "listen" for echo returns from the aircraft targets. For example, the FAA ASR-8 approach radar (also known as "terminal radar") at Air Traffic Control facilities will transmit a signal for 0.6 microseconds. This is commonly referred to as the pulse width, or length of time of the transmitted signal. Following this, the receiving equipment in the ASR-8 spends 961.5 microseconds listening for the reflected return signal. The time that the return takes is measured and converted into the distance to the object. The azimuth (horizontal direction) in degrees of the rotating antenna is registered, and the two (distance and azimuth) are combined, displaying a target on the video indicator (plan position indicator, or PPI).

At times, a "false target" can be observed when the microwave signal hits an aircraft beyond the range of the indicator. That target may be many hundreds of miles away, but electronically, due to antenna sweep and timing, the target appears to be in your area of view. This is commonly referred to as a "second time around target." This is why most controllers do not report targets that jump across their indicators. Without a visual confirmation it could be anything. Thus real, solid targets, traveling at speeds well in excess of the expected aircraft types, may appear on a controller's PPI scope and be deliberately ignored.