Knowra Earth orientation parameters Earth orientation parameters Earth orientation parameters quantify how Earth’s rotation and figure axis vary relative to celestial and terrestrial reference frames. They include polar motion, variations in rotation rate, and changes in the direction of the rotation axis.
International Terrestrial Reference System : A global reference system fixed to Earth, defining the origin, scale, orientation, and time evolution of terrestrial coordinates. Earth orientation links celestial directions to this Earth-fixed frame.
Polar motion : The motion of Earth’s rotation axis relative to its crust, described in terrestrial coordinates. Its coordinates form the most direct Earth-fixed component of orientation parameters.
International Polar Motion Service : An international service established in 1962 to coordinate observations and determine variations in the position of Earth’s pole. It was an early institutional source of systematic polar-motion estimates.
Precise Point Positioning : A satellite-navigation method that determines a position from precise orbit, clock, and signal corrections. Accurate terrestrial coordinates require Earth orientation corrections alongside satellite products.
Earth rotation prediction : The forecasting of future Earth orientation values from observations and models. Operational products must predict parameters before later measurements become available.
International Celestial Reference System : A quasi-inertial reference system whose axes are defined by distant celestial sources. Celestial pole coordinates express Earth’s orientation relative to this nearly inertial system.
Length of day : The duration of one rotation of Earth relative to a reference time scale. Its departures from the nominal day reveal changes in Earth’s rotation rate.
Bureau International de l’Heure : An international timekeeping bureau that coordinated time signals and Earth-rotation measurements from 1912 to 1987. Its rotation monitoring helped establish the continuous UT1 records underlying modern parameters.
Space geodesy : The measurement of Earth’s shape, rotation, gravity, and motion using observations to or from space. Earth orientation parameters are core products of space-geodetic measurement.
Chandler wobble : A roughly 433-day oscillation in the position of Earth’s rotation pole relative to its crust. Its changing amplitude and phase complicate forecasts of polar motion.
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