Laboratory Simulation of Inferior and Superior Mirages

Abstract

Mirages come in a wide variety of forms. For simplicity we divide them into two classes. Over a region of space where the air temperature decreases with height (as over a hot road or heated desert floor) light rays follow curved paths that are concave upwards. Such paths yield an upright image of a distant scene that appears to be below its actual position and hence is called an inferior mirage. Where the air temperature increases with height (as when warm air flows over a cold body of water) light-ray paths are concave downward. An upright image of a distant scene, in this case, appears above its real position, which we indicate by calling it a superior mirage. Of course, more complicated mirage effects can be observed when we look through a layered atmosphere which has a positive temperature gradient at some elevations and a negative gradient at others. Such complicated mirages may not fit neatly into our two classes. I will not discuss the elementary theory of the mirages here. Two Scientific American articles1,2 describe new ways to understand mirage phenomena, and the classical treatment can be found in a variety of texts; for example, see references 3-6.