The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), taking care of providing a precise geodetic infrastructure for monitoring the System Earth, promotes the standardization of height systems worldwide. With the purpose to bring together existing initiatives and to address the activities to be faced, the GGOS Focus Area "Unified Height System" (formerly GGOS Theme 1) was established during the GGOS Planning Meeting 2010 (February 1 - 3, Miami/Florida, USA). Starting point were the results delivered by the IAG Inter-Commission Project 1.2 "Vertical Reference Frames" (IAG ICP1.2 VRF), which was operative from 2003 to 2011.
During the term 2011-2015, the GGOS Focus Area Unified Height System was chaired by Michael Sideris (University of Calgary, Canada) and Johannes Ihde (Bundesamt für Kartographie und Geodäsie, Germany). The main result is the compilation of the IAG resolution for the "Definition and realization of an International Height Reference System (IHRS)" approved during the 2015 General Assembly of the International Union of Geodesy and Geophysics (IUGG) in Prague, Czech Republic.
The immediate objectives of the GGOS Focus Area 1 are (1) the outlining of detailed standards, conventions, and guidelines to make the IAG Resolution applicable, and (2) to establish the realization of the IHRS, i.e. the International Height Reference Frame (IHRF). For the term 2015-2019, this Area is chaired by Laura Sánchez, Deutsches Geodätisches Forschungsinstitut, Technische Universität München, Germany.