GGOS Focus Area

Unified Height System


  • Refinement of standards and conventions for the definition and realization of the IHRS, including unification of standards and conventions that are used by the geometric and gravity Services of the IAG.
  • Develop of GGOS products for the realization of the IHRS.
  • Recommendation for a global vertical reference frame; i.e. the IHRF.
  • Guidelines/procedures for height system unification.
  • Development of a registry (metadata) containing the existing local/regional height systems and their connections to the global one.
  • Strategies for the maintenance and use in practice of the IHRS.
  • Determination and modelling of the temporal changes of the IHRF.
  • Update the IHRS definition and realization as needed, based on future improvements in geodetic theory and observations.
  • Servicing the vertical datum needs of other geosciences such as, e.g., hydrography and oceanography

The GGOS-FA-UHS activities are performed by dedicated working groups with the contribution of the IAG components. Since 2011, following working groups have been active:

  • Vertical Datum Standardization: determination of a conventional W0 value as vertical datum for the IHRS (read more).
  • Strategy for the Realization of the International Height Reference System (IHRS): station selection for the IHRF reference network and evaluation of methodologies for the computation of IHRF potential coordinates (read more).
  • Implementation of the International Height Reference Frame (IHRF): computation of the first static solution for the IHRF and the implementation of a IHRF operational infrastructure (read more).