Description: An objective of the International Height Reference System (IHRS) and its realization (the IHRF) is to support the monitoring and analysis of Earth’s system changes. The more accurate the IHRS/IHRF is, the more phenomena can be identified and modelled. Thus, the IHRS/IHRF must provide vertical coordinates and their changes with time as accurately as possible. As many global change phenomena occur at different scales, the global frame should be extended to regional and local levels to guarantee consistency in the observation, detection, and modelling of their effects. From this perspective, an operational infrastructure is needed to ensure the long-term sustainability of the IHRS/IHRF. In this contribution, we present a proposal to establish such as infrastructure within the International Association of Geodesy (IAG) and its International Gravity Field Service (IGFS). Some aspects to be considered are:- Improvements in the IHRS definition and realization following future developments in geodetic theory, observations and modelling.- Refinement of the IHRS/IHRF standards/conventions based on the unification of the standards/conventions used by the geometric and gravity IAG Services.- Development of strategies for collocation of IHRF stations with existing gravity and geometrical reference stations at different densification levels.- Identification of the geodetic products associated with the IHRF and description of the elements to be considered in the corresponding metadata.- Servicing the vertical datum needs of other geosciences such as, e.g., hydrography and oceanography.Implementation of a registry containing the existing local/regional height systems and their connections to the global IHRS/IHRF.

Description: The complex geophysical structures in the Italian region make it even more difficult to invert gravimetric data for determining the depths of the Moho. However, a revised computation approach based on windowed Least Square Collocation has been set up to deal with local features like Ivrea Body, important sedimental basins, tectonics and orogenic activities. The Italian ground-based gravity dataset has been used to determine the Moho depths over land and sea areas and the gravimetric model have been compared with the Moho depth values obtained by different techniques as the seismic reflection and refraction profiles, receiver functions and seismic surface waves. Nowadays different solutions are available for some areas, as the Alpine Region, however the Moho depths can differ for several km, so the gravimetric Moho validation represents also a validation of the seismic models, because the gravimetric inversion represent an independent estimate with respect to the seismic solutions.

Description: The International Service for the Geoid (ISG), hosted by Politecnico di Milano in Italy, is an official service of the International Association of Geodesy (IAG). Its activities are coordinated by the International Gravity Field Service (IGFS) and are related to the IAG Commission 2 on Gravity Field. The ISG provides access to a comprehensive repository of geoid models through its website, most of them with an open access. In this archive, the latest releases of the most important and well-known geoid models, as well as less recent or less known models are available. In this work, the current status of the repository is described and the ad-hoc developed web-services for its exploitation are presented. All the models contained in the repository are indexed by WoS Data Citation Index. Moreover, under author request, the models can be labelled with a Digital Object Identifier (DOI) assigned to univocally identify data files and to improve interoperability and reusability. This service is currently running in cooperation with GFZ Data Services. To allow a direct access to all the publicly available models, three web-services are developed. The first one performs height conversions, and it is an updated version of the existing service. The second one is dedicated to file format conversion and sub-model extraction, improving interoperability and allowing an easier usage of the distributed models by commercial GNSS receivers and software. Finally, the last service is devised to merge different geoid models by removing discontinuities at borders and thus unifying their height reference system.

Description: ETRS89 has become the common standard for harmonized horizontal coordinates in the European countries. In contrast, the national height networks are still determined by leveling with respect to different tide gauges and standards (height types, tide systems). The differences in the definitions cause height discrepancies up to a few decimeters along the borders. National geoid models are defined accordingly. Nowadays, GNSS-based height determination is widely used, which also increases the demand for geoid models as a height reference across borders. For large parts of the continent, the United European Leveling Network provides harmonized heights based on the standards of the EVRS. However, EUREF has yet to adopt a corresponding height reference surface officially. Thus, the EUREF Working Group “Unified European Height Reference” was formed by resolution in 2021 with the objective to enhance the usability of European heights for practical applications such as civil engineering, digital elevation models, etc. The main goal is to establish a European Height Reference Surface (EHRS) which is tailored to a consistent dataset of GNSS-leveling control points (EHRS_CP) referring to the latest ETRS89 and EVRS realizations. Furthermore, comprehensive information about the national integrated spatial reference systems, including heights and geoid models, shall be made available through the Information and Service System for European Coordinate Reference Systems (CRS-EU). The paper gives an overview of the rationale and current activities of the working group. Preliminary comparisons with selected gravimetric quasigeoid models provide an outlook on the increased accuracy of the new GNSS-leveling dataset.