Almost every ENG truck operator has experienced unexplained microwave link failures. Perfect ENG links that are set up an hour before the newscast can mysteriously fade before air time. A truck dispatched to a known good site can experience difficulty in establishing a link. In Buffalo, NY, WIVB-TV's ENG truck operators and meteorologists have found a definite correlation between lost ENG signals and the presence of thermoclines and inversion layers in the lower atmosphere. Thermoclines are narrow boundaries between two air layers of different temperatures.
Inversion layers are a type of thermocline that forms when air layers are cooled at different rates.
These layers of warm and cold air can cause signal degradation or complete loss of signal by bending the ENG signal down into the ground or up into space. Refraction happens The bending of microwave signals passing through thermal layers of air is similar to the bending of light as it passes from air to glass. There is a point, as the angle of the light striking the glass decreases, where all the light is reflected away from the glass. The angle at which this occurs is called the critical angle. As air density decreases, the index of refraction increases.