The International Centre for Global Earth Models (ICGEM, http://icgem.gfz-potsdam.de/, last access: 6 May 2019) hosted at the GFZ German Research Centre for Geosciences (GFZ) is one of the five services coordinated by the International Gravity Field Service (IGFS) of the International Association of Geodesy (IAG). The goal of the ICGEM service is to provide the scientific community with a state-of-the-art archive of static and temporal global gravity field models of the Earth, and develop and operate interactive calculation and visualization services of gravity field functionals on user-defined grids or at a list of particular points via its website. ICGEM offers the largest collection of global gravity field models, including those from the 1960s to the 1990s, as well as the most recent ones, which have been developed using data from dedicated satellite gravity missions, CHAMP, GRACE, GOCE, advanced processing methodologies, and additional data sources such as satellite altimetry and terrestrial gravity. The global gravity field models have been collected from different institutions at international level and after a validation process made publicly available in a standardized format with DOI numbers assigned through GFZ Data Services. The development and maintenance of such a unique platform is crucial for the scientific community in geodesy, geophysics, oceanography, and climate research. In this article, we present the development history and future plans of ICGEM and its current products and essential services. We present the ICGEM's data by means of Earth's static, temporal, and topographic gravity field models as well as the gravity field models of other celestial bodies together with examples produced by the ICGEM's calculation and 3-D visualization services and give an insight into how the ICGEM service can additionally contribute to the needs of research and society.

During the last few years, the determination of high-resolution global gravity field has gained momentum due to high-accuracy satellite-derived observations and development of forward gravity modelling. Forward modelling computes the global gravitational field from mass distribution sources instead of actual gravity measurements and helps improving and complementing the medium to high-frequency components of the global gravity field models. In this study, we approximate the global gravity potential of the Earth’s upper crust based on ellipsoidal approximation and a mass layer concept. Such an approach has an advantage of spectral methods and also avoids possible instabilities due to the use of a sequence of thin ellipsoidal shells. Lateral density within these volumetric shells bounded by confocal lower and upper shell ellipsoids is used in the computation of the ellipsoidal harmonic coefficients which are then transformed into spherical harmonic coefficients on the Earth’s surface in the final step. The main outcome of this research is a spectral representation of the gravitatioal potential of the Earth’s upper crust, computed up to degree and order 3660 in terms of spherical harmonic coefficients (ROLI_EllApprox_SphN_3660). We evaluate our methodology by comparing this model with other similar forward models in the literature which show sub-cm agreement in terms of geoid undulations. Finally, EIGEN-6C4 is augmented by ROLI_EllApprox_SphN_3660 and the gravity field functionals computed from the expanded model which has about 5 km half-wavelength spatial resolution are compared w.r.t. ground-truth data in different regions worldwide. Our investigations show that the contribution of the topographic model increases the agreement up to ~ 20% in the gravity value comparisons.

In 2017 and 2018 GFZ performed two gravimetry campaigns on commercial ferries in the Baltic Sea. The nature of such “non-dedicated” campaigns is different from “dedicated” campaigns that are performed on research vessels with tracks planned according to gravity measurement needs. The non-dedicated campaigns use non-survey vessels or survey vessels running for other purposes such as hydrographic measurements, which may require additional corrections. To assess the usefulness of non-dedicated campaigns, we analysed gravity measurements collected on two commercial ferries as part of the EU funded FAMOS project. Besides the typical marine gravimetry corrections, we also investigated the corrections for the vertical accelerations due to the ship’s movement and the dynamical effect due to the cross-coupling between horizontal and vertical acceleration components. Taking the latter two corrections into account partly leads to slight improvements, but our results also demonstrate that the standard processing without the two corrections, as used in most of the dedicated campaigns, already delivers good quality end products that fulfil the requirements of a typical marine gravimetry survey with an uncertainty of about 1 mGal. Our findings suggest that gravimetry campaigns on commercial ferries can be used to complement dedicated marine gravimetry campaigns and contribute to geodetic purposes.

Various research topics in geosciences such as gravity modelling, terrain correction and ocean circulation, require high resolution and accuracy global elevations for land topography, bathymetry, and ice thickness that refer to a consistent vertical datum. Unfortunately, most of the existing DEMs do not provide such solutions for Earth relief layers with the same resolution globally. To overcome this deficiency, we merged various DEMs published in the recent years and compiled an up-to-date global solution. We provide 30 arcsecond grid suite for relief layers and land-type masks which have been substantially improved w.r.t. the grids in literature. The quality of the merged surface elevation is assessed against the GNSS heights at about globally distributed 22000 stations. The merged surface model shows a reduction in standard deviation of a factor of three compared to other commonly used DEMs. Other evaluations are performed over land-ice and oceans which supports the advancement of GDEMM2024. The improvements are due to the accuracy and coverage of the original input data, updated land-type masks and merging methodology.