Status of the International Gravity Reference System and Frame

Abstract

The increasing importance of terrestrial gravimetry in monitoring global change processes, in providing a reference for satellite measurements and in applications in metrology necessitates a stable reference system reflecting the measurement accuracy achievable by modern gravimeters. Therefore, over the last decade, the International Association of Geodesy (IAG) has developed a system to achieve accurate, homogeneous, long-term global recording of Earth’s gravity, while taking advantage of the potential of today’s absolute gravity measurements. The current status of the International Gravity Reference System and Frame is presented as worked out by the IAG Joint Working Group 2.1.1 “Establishment of a global absolute gravity reference system” during the period 2015–2019. Here, the system is defined by the instantaneous acceleration of free-fall, expressed in the International System of Units (SI) and a set of conventional corrections for the time-independent components of gravity effects. The frame as the systems realization includes a set of conventional temporal gravity corrections which represent a uniform set of minimum requirements. Measurements with absolute gravimeters, the traceability of which is ensured by comparisons and monitoring at reference stations, provide the basis of the frame. A global set of such stations providing absolute gravity values at the microgal level is the backbone of the frame. Core stations with at least one available space geodetic technique will provide a link to the terrestrial reference frame. Expanded facilities enabling instrumental verification as well as repeated regional and additional comparisons will complement key comparisons at the level of the International Committee for Weights and Measures (CIPM) and ensure a common reference and the traceability to the SI. To make the gravity reference system accessible to any user and to replace the previous IGSN71 network, an infrastructure based on absolute gravity observations needs to be built up. This requires the support of national agencies, which are encouraged to establish compatible first order gravity networks and to provide information about existing absolute gravity observations.

A compact differential gravimeter at the quantum projection noise limit

“…3 a 63 h-long differential gravity measurement obtained in laboratory conditions. We calculate gravity residuals g − g by correcting the raw gravity signal for tilt [32], atmospheric pressure and tidal fluctuations using a bespoke model for our measurement site [33]. The residuals reveal no significant drift which is confirmed by the total deviation that continuously decreases with averaging times down to 5 nm s −2 at 10 000 s. From the slope of the total deviation we estimate the sensitivity of the gravity measurement at 750 nm/s 2 / √ τ .…”

Forty-three years of absolute gravity observations of the Fennoscandian postglacial rebound in Finland

“…The absolute gravity stations and the measurements on them that are described here are the contribution of the Finnish Geospatial Research Institute, National Land Survey of Finland, to the International Gravity Reference Frame of the International Association of Geodesy. The Metsähovi Geodetic Research Station is a GGOS Core Station and has the qualifications to become both a Reference Station and a Comparison Station of the IGRF (Wziontek et al 2021). The other absolute stations provide a highquality network at national level.…”

“…The International Gravity Reference System (IGRS) will be realized by absolute gravity observations and the comparisons between the absolute gravimeters that make the observations (Wilmes et al 2016;Wziontek et al 2021). The system will provide an accurate and unified global gravity reference, but the long-term stability of reference stations in the system must be studied, and in areas where the gravity field is not stable and its changes in time must be investigated.…”

Geodetic-Gravimetric Monitoring of Mountain Uplift and Hydrological Variations at Zugspitze and Wank Mountains (Bavarian Alps, Germany)

“…The gravimetric effect of atmospheric mass variations on the absolute measurements were reduced using local barometric readings and applying the factor −3.0 nm/s 2 per hPa to the pressure differences compared to a standard atmosphere which is recommended in the IGRS Conventions 2020 [28]. Table A1 in the Appendix A compiles the Earth tide parameters for the tidal reduction.…”