An optical pattern consisting of discrete steps or shades of gray between black and white.

A circle defined by the intersection of the surface of the Earth and any plane that passes through the center of the Earth.
Note: On the idealized surface of the Earth, the shortest distance between two points lies along a great circle.

Synonym Greenwich Mean Time (GMT). Obsolete term. See Coordinated Universal Time.

Mean solar time at the meridian of Greenwich, England, formerly used as a basis for standard time throughout the world. Obsolete term. Synonym Greenwich Civil Time. See Coordinated Universal Time.

1. An electrical connection to earth through an earth-electrode subsystem.
2. In an electrical circuit, a common return path that usually (a) is connected to an earth-electrode subsystem and (b) is extended throughout a facility via a facility ground system consisting of the signal reference subsystem, the fault protection subsystem, and the lightning protection subsystem.
3. In an electrical circuit,… (Read More →)

The dissipation of rf energy by the earth.

The electrical parameters of earth, such as conductivity, permittivity, and magnetic permeability.
Note 1: The values of these parameters vary with the local chemical composition and density of the earth.
Note 2: For a propagating electromagnetic wave, such as a surface wave propagating along the surface of the Earth, these parameters vary with frequency and direction.

In the presence of an electrical fault, the current that flows in the protective ground wire of a power distribution system.

In an electrical system, an unwanted current that flows in a conductor connecting two points that are nominally at the same potential, i.e., ground, but are actually at different potentials.
Note 1: For example, the electrical potential at different points on the surface of the Earth can vary by hundreds of volts, primarily from the influence of the solar wind.… (Read More →)

An electrically conductive surface that serves as the near-field reflection point for an antenna.
Note: A ground plane may consist of a natural (e.g., Earth or sea) surface, an artificial surface of opportunity (e.g., the roof of a motor vehicle), or a specially designed artificial surface (e.g., the disc of a discone antenna).