Mirage

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Mirage

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1. (Optics) definition submitted by Andy Young, June 30, 1997
An apparently reflected image of an object, caused by abnormal atmospheric refraction. The most commonly seen is the inferior mirage over heated surfaces, which often looks like a pool of water because it reflects the sky. Superior mirages, which appear above the direct image of the object, are due to strong thermal inversions above eye level. Other mirage-like images can be produced by thermal inversions below eye level, and by hot air adjacent to a wall heated by the Sun (lateral mirage). </dd>
2. (Radar) A refraction phenomenon in the atmosphere wherein an image of some object is made to appear displaced from its true position. See radio duct, note.
Simple mirages may be any one of three types, the inferior mirage, the superior mirage, or the lateral mirage, depending, respectively, on whether the spurious image appears below, above, or to one side of the true position of the object. Of the three, the inferior mirage is the most common, being usually discernible over any heated street in daytime during summer. The abnormal refraction responsible for mirages is invariably associated with abnormal temperature distributions that yield abnormal spatial variations in the refractive index. [[/a>|/a> ]]

References

This article is based on NASA's Dictionary of Technical Terms for Aerospace Use