Operational Infrastructure to Ensure the Long-Term Sustainability of the International Height Reference System and Frame (IHRS/IHRF)

Abstract

AbstractThe International Association of Geodesy (IAG) introduced the International Height Reference System (IHRS) in 2015 as an international standard for the accurate determination of physical heights worldwide. Primary vertical coordinates are geopotential numbers referenced to a conventional W0 value. 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 coordinates (X, Y, Z) in the International Terrestrial Reference Frame (ITRF). The realisation 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 values W at these positions. Through a strong international collaboration, framed by the IAG, it has been possible in recent years to pave the scientific foundations of the IHRS, to compute a first solution of the IHRF, and to identify the key requirements for a long-term sustainability of the IHRF. Much progress has been made and continuity is needed to ensure the maintenance and availability of the IHRF in the future. Following IAG practice, the development of theory and methods for the continuous improvement of the IHRS/IHRF should be promoted by the IAG Commissions and the Inter-Commission Committee on Theory (ICCT), while the operational performance should be ensured by the IAG Services. In this paper, we highlight the organisational challenges in maintaining the IHRS/IHRF, discuss how the existing gravity field related IAG Services could contribute to the IHRS/IHRF, and identify the elements needed to establish an operational infrastructure for the IHRS/IHRF that addresses the organisational challenges. Our proposal is to establish a central coordinating body under the responsibility of the International Gravity Field Service (IGFS), composed of individual modules taking care of the main components of the IHRS/IHRF. The central management body is the IHRF Coordination Centre and its modules are the IHRF Reference Network Coordination, the IHRF Conventions’ Coordination, the IHRF Associate Analysis Centres, and the IHRF Combination Coordination. The IGFS presented this proposal to the IAG Executive Committee at its meeting on 10 December 2023 and it was unanimously approved. Thus, a new component of the IGFS dedicated to the IHRF has been created and will ensure the long-term availability and reliability of the IHRF.