Repeating Pattern Illusion

The repeating pattern illusion occurs when an aircraft flies at very low altitude over a surface with a regular repeating visual pattern, such as ripples on water. If each eye lines up with a different part of the pattern instead of both eyes lining up on the same part, the pilot brain can badly misjudge the aircraft altitude, and any descent made under that misperception risks striking the surface, a danger that is particularly acute for helicopter pilots operating only a few metres above calm water. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/