Erdrotationsparameter

Erdrotationsparameter, in English Earth rotation parameter (ERP), is a set of quantities used in geodesy and astronomy to describe the irregular rotation of the Earth relative to a fixed celestial reference frame. They quantify how the orientation of the terrestrial reference frame must be adjusted to maintain alignment with the celestial frame as the Earth wobbles and its rotation rate varies. ERP are a component of the broader Earth Orientation Parameters (EOP), which are essential for transforming coordinates between the International Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF).

An ERP typically comprises three quantities: two polar motion parameters, x_p and y_p, which describe the rotation of the terrestrial frame about its X and Y axes, expressed in arcseconds (commonly in milliarcseconds). The third parameter, dUT1 (UT1 minus UTC), accounts for variations in the Earth's rotation rate and is expressed in seconds. Together, x_p, y_p, and dUT1 capture both short-term fluctuations and longer-term trends in Earth's rotation and its orientation in space.

Measurement and use: ERP values are derived from multiple observation techniques, with very-long-baseline interferometry (VLBI) as the primary source, complemented by satellite laser ranging (SLR) and, to a lesser extent, GNSS data. The IERS (International Earth Rotation and Reference Systems Service) publishes ERP estimates in its EOP bulletins and the C04 series, following standardized conventions that link ITRF to ICRF. Applications include precise astronomical ephemerides, satellite and spacecraft navigation, timekeeping, and geodetic research.