IERS Conventions that play a fundamental role for creating all IERS products.
The estimation of coordinates, performed by the IERS, is based on individual frames contributed by the IERS Analysis Centers.
Within IERS, each Terrestrial Reference Frame is either directly or after transformation expressed as a realization of the ITRS.
Realizations of the ITRS are produced by the IERS under the name International Terrestrial Reference Frames (ITRF).
Their values and accuracy are available on IERS website (www.
The combination of these results with the IERS results of space techniques is depicted in Fig.
This paper is a summary based on the technical details concerning the different ITRF realizations as available in various IERS technical notes and related papers.
The orientation is defined by adopting IERS Earth Orientation Parameters (ERP) at a "reference" epoch.
The orientation of the IERS Reference Pole (IRP) and Reference Meridian (IRM) were initially based on the BIH Terrestrial System (BTS) 1984.
Since BIH was replaced by IERS from 1988, it is interpreted that the orientations for the ITRF94, ITRF96, and combined ITRF96 and ITRF97 have to be based on independent IERS realized solutions.
According to Montag (1997), the IRP and IRM were defined by IERS on the basis of the Conventional International Origin (CIO).
The scale is obtained by relativistic modeling and is consistent with the Geocentric Coordinate Time (TCG) for a geocentric local frame (Chapter 11, IERS Tech.