What is a Fresnel Zone?
(pronounced ‘fre-nel’ the “s” is silent) A frequency and range-dependent area of a reflector from which most of the energy of a reflection is returned and arrival times differ by less than half a period from the first break, named for French physicist Augustin-Jean Fresnel (1788 to 1827). Waves with such arrival times will interfere constructively and will be detected as a single arrival. Subsurface features smaller than the Fresnel zone usually cannot be detected using seismic waves. In radio communications, one of a (theoretically infinite) number of a concentric ellipsoids of revolution which define volumes in the radiation pattern of a (usually) circular aperture. The area around the visual line-of-sight that radio waves spread out into after they leave the antenna. This area must be clear or else signal strength will weaken.
