Strategy for the realisation of the International Height Reference System (IHRS)

Abstract

In 2015, the International Association of Geodesy defined the International Height Reference System (IHRS) as the conventional gravity field-related global height system. The IHRS is a geopotential reference system co-rotating with the Earth. Coordinates of points or objects close to or on the Earth’s surface are given by geopotential numbers C(P) referring to an equipotential surface defined by the conventional value W0 = 62,636,853.4 m2 s−2, and geocentric Cartesian coordinates X referring to the International Terrestrial Reference System (ITRS). Current efforts concentrate on an accurate, consistent, and well-defined realisation of the IHRS to provide an international standard for the precise determination of physical coordinates worldwide. Accordingly, this study focuses on the strategy for the realisation of the IHRS; i.e. the establishment of the International Height Reference Frame (IHRF). Four main aspects are considered: (1) methods for the determination of IHRF physical coordinates; (2) standards and conventions needed to ensure consistency between the definition and the realisation of the reference system; (3) criteria for the IHRF reference network design and station selection; and (4) operational infrastructure to guarantee a reliable and long-term sustainability of the IHRF. A highlight of this work is the evaluation of different approaches for the determination and accuracy assessment of IHRF coordinates based on the existing resources, namely (1) global gravity models of high resolution, (2) precise regional gravity field modelling, and (3) vertical datum unification of the local height systems into the IHRF. After a detailed discussion of the advantages, current limitations, and possibilities of improvement in the coordinate determination using these options, we define a strategy for the establishment of the IHRF including data requirements, a set of minimum standards/conventions for the determination of potential coordinates, a first IHRF reference network configuration, and a proposal to create a component of the International Gravity Field Service (IGFS) dedicated to the maintenance and servicing of the IHRS/IHRF.

Can an Earth Gravitational Model Augmented by a Topographic Gravity Field Model Realize the International Height Reference System Accurately?

“…For the two hybrid models, the RMS error of W p is 0.3 m 2 s 2 assuming the equal error between them. This is three times the magnitude of the targeted accuracy of 0.1 m 2 s 2 stated for the IHRF (Sánchez et al 2021).…”

“…In principle, either an EGMe or a regional (quasi-) geoid model can realize the IHRS (Sánchez et al 2021). Either approach has its advantages and disadvantages.…”

GGOS Bureau of Products and Standards: Description and Promotion of Geodetic Products

“…This includes the geometry (size and shape of a reference ellipsoid), the gravity field (normal gravity field of this ellipsoid), terrestrial time and Earth rotation. More background information is provided in, e.g., Angermann et al (2020), Ihde et al (2017), Sánchez et al (2021). This new definition becomes necessary because, since the introduction of the GRS80 (Moritz 2000), the knowledge in geodesy has improved a lot (e.g.…”

Topographic Gravity Field Modelling for Improving High-Resolution Global Gravity Field Models

“…This application area is one of the focus topics of the Global Geodetic Observing System (GGOS, https:// ggos.org) of the International Association of Geodesy (IAG) which is on the unification of height systems and realization of the International Height Reference System (IHRS). Such a reference system can only be achieved via the contribution of high-resolution topographic gravity field models especially over the areas that are lacking gravity observations (Sánchez et al 2021).…”