The Path to an Up-to-date Absolute Gravity Reference System
Abstract:The determination of precise gravity field parameters is of great importance in a period in which earth sciences are achieving the necessary accuracy to monitor and document global change processes. This is the reason why experts from geodesy and metrology joined in a successful cooperation to make absolute gravity observations traceable to SI quantities, to improve the metrological kilogram definition and to monitor mass movements and smallest height changes for geodetic and geophysical applications.
How can we determine such a gravity reference system and secure it over multiple decades? Precise knowledge of the gravity acceleration and definition of standards, models and corrections are an important prerequisite to the definition of the gravity system. Over more than three decades, the absolute gravity community cooperated successfully to obtain the gravity reference in comparisons at intervals of 4 years and to certify metrological equivalence between National Metrology Institutes.
With increasing resolution of the absolute gravimeter sensors and new measurement principles it becomes obvious that such comparisons are not sufficient for all applications. Mainly for geodetic purposes it is necessary to sub-divide comparison intervals and maintain a connected network of gravity reference sites where compared absolute gravimeters operate together with superconducting gravimeters to derive a continuous gravity reference function.
By means of this distributed monitoring of the gravity reference it will also be possible to relate observations of earlier absolute gravimeters to the present-day and to future instruments. It will be possible to include new sensors like atom interferometers and in future to relate the results of precise optical clocks. With co-located space geodetic sensors like GNSS, SLR and VLBI, these reference sites fulfill the conditions of a geodetic fundamental station as a component of IAG’s Global Geodetic Observing System.