So far, the valid gravity reference system of the IAG is still the International Gravity Standardization Net 1971 (IGSN71) (Morelli et al. 1974). Although it is widely used, at an uncertainty level of it fulfils neither the requirements nor the accuracy for the understanding of the Earth’s System and applications in metrology.
Following IAG Resolution No. 2 “Establishment of a Global Absolute Gravity Reference System” adopted at the XXVI, General Assembly of the International Union of Geodesy and Geophysics (IUGG) in Prague 2015, the IAG Joint Working Group 2.1.1 “Establishment of a global absolute gravity reference system” has developed the basis of a new system and frame to achieve accurate, homogeneous, long-term global recording of Earth’s gravity, while taking advantage of the potential of today’s absolute gravity measurements. (Wilmes et al. 2016, Wziontek et al. 2021)
The International Gravity Reference System (IGRS) is defined by the instantaneous acceleration of free-fall, expressed in the International System of Units (SI). It is completed by a set of conventional models for the time-dependent corrections of this quantity comprising constant components which define the conventional quantity “acceleration of gravity”.
The International Gravity Reference Frame (IGRF) as the realization of the IGRS is represented by absolute gravity measurements traceable to the SI that contain conventional temporal gravity corrections (Fig. 1). Due to its principle, absolute gravity observations at individual stations are not linked to each other avoiding the need to build up classical observation networks. All absolute gravimeters (AG) have to be checked at comparisons, where the gravity reference is realized based on a set of measurements by a group of AGs and the functional model for their processing. The comparisons follow the “CCM – IAG Strategy for Metrology in Absolute Gravimetry”, which also describes the traceability chain in gravimetry. The reliability of all AGs used for the realization of the IGRF has to be ensured further by regular monitoring at reference stations.