Abstract
Abstract. The International Service for the Geoid (ISG, https://www.isgeoid.polimi.it/, last access: 31 March 2021) provides free access to a dedicated and comprehensive repository of geoid models through its website. In the archive, both the latest releases of the most important and well-known geoid models, as well as less recent or less known ones, are freely available, giving to the users a wide range of possible applications to perform analyses on the evolution of the geoid computation research field. The ISG is an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). Its main tasks are collecting, analysing, and redistributing local, regional, and continental geoid models and providing technical support to people involved in geoid-related topics for both educational and research purposes. In the framework of its activities, the ISG performs research taking advantage of its archive and organizes seminars and specific training courses on geoid determination, supporting students and researchers in geodesy as well as distributing training material on the use of the most common algorithms for geoid estimation. This paper aims at describing the data and services, including the newly implemented DOI Service for geoid models (https://dataservices.gfz-potsdam.de/portal/?fq=subject:isg, last access: 31 March 2021), and showing the added value of the ISG archive of geoid models for the scientific community and technicians, like engineers and surveyors (https://www.isgeoid.polimi.it/Geoid/reg_list.html, last access: 31 March 2021).
Highlights
The geoid, an equipotential surface of the Earth gravity field (Heiskanen and Moritz, 1967; Sansò and Sideris, 2013), has important applications in engineering for the definition of physical heights (Sansò et al, 2019), for example to compute them from ellipsoidal heights observed by Global Navigation Satellite System (GNSS) techniques, and in geosciences, for example to determine the ocean geostrophic currents (Bingham et al, 2008; Knudsen et al, 2011)
Since the model ColWLSC2020 compared against GSVS17 GPS/levelling has residuals of about 2.5 cm standard deviation, it might be that the global models suffer from missing information in the Colorado area, making the local geoid model more reliable for investigations requiring a high level of accuracy
The International Service for the Geoid (ISG) is an official worldwide International Association of Geodesy (IAG) service hosted at Politecnico di Milano aiming at supporting the geodetic community
Summary
The geoid, an equipotential surface of the Earth gravity field (Heiskanen and Moritz, 1967; Sansò and Sideris, 2013), has important applications in engineering for the definition of physical heights (Sansò et al, 2019), for example to compute them from ellipsoidal heights observed by Global Navigation Satellite System (GNSS) techniques, and in geosciences, for example to determine the ocean geostrophic currents (Bingham et al, 2008; Knudsen et al, 2011). Biases are typically present between geoids of neighbouring countries, accounting for the different used conventions, e.g. the different reference tide gauge (Rummel and Teunissen, 1988; Sansò and Usai, 1995; Barzaghi et al, 2015b) These regional/local geoids can describe high-frequency features that are not generally included in global models, unless considering an ultra-high maximum spherical harmonic degree. The models stored in the geoid repository can be further used for crossvalidation, for comparison with global models, and, in general, for providing alternative solutions to the scientific community, different from the official ones that are typically released by national agencies To reach these objectives, the ISG developed a specific website with a geographic database. Like global gravity models, useful for the geoid determination, may be collected by the ISG, without redistributing them if they are already provided by other IAG services. – Provide users with online services through the website, like the height conversion service exploiting any of the publicly available geoid models in the geoid repository (see Sect. 3.2)
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