Establishment of a Geopotential-based World Height System – The International Height Reference System (IHRS) and its Realisation, the International Height Reference Frame (IHRF)

The International Height Reference System (IHRS) was introduced in 2015 by the International Association of Geodesy (IAG) as an international standard for the precise determination of physical heights worldwide. Primary vertical coordinates are gravity potential differences with respect to a conventional W0 value, which defines the potential of the geoid. The realisation of the IHRS is the International Height Reference Frame (IHRF), which corresponds to a global network of reference stations with precise reference coordinates specified in the IHRS. The spatial position of the stations at which the geopotential numbers are calculated is defined by their respective geocentric Cartesian coordinates in the International Terrestrial Reference Frame (ITRF). The implementation of the IHRS is thus based on the combination of a geometric component, given by the positions of the stations in the ITRF, and a physical component, given by the determination of the potential differences with respect to W0 at these positions. Through a strong international collaboration framed by the IAG, it has been possible in recent years to lay the scientific foundations of the IHRS, to compute a first solution of the IHRF, and to identify the key requirements for the long-term sustainability of the IHRF. This paper summarises the main features of the IHRF and the achievements in its implementation.