Transportable spring gravimeters have many applications besides exploration geophysics and potential field determination, such as time-lapse measurements in hydrology and volcanology. For maximum accuracy, the time-dependent scale factor of each gravimeter must be determined before and after use. The required scale uncertainty depends on the target signals, the maximum gravity difference in the network, and the desired level of accuracy. In high alpine regions, large height differences can result in gravity differences of more than 1⋅10^6 nm/s^2. For a target uncertainty of 30 nm/s^2, the scale factor must be determined with an uncertainty below 1⋅10^(-5).
The Zugspitze Calibration System, near Garmisch-Partenkirchen in the German Alps, consists of three absolute gravity (AG) stations that cover an elevation range of 2,200 m and a gravity range of 5,220 µm/s^2: W200 at Wank valley station (735 m a.s.l.) and W100 at Wank mountain station (1,738 m a.s.l.) at the cable car leading to Wank mountain, as well as the Zugspitze Geodynamic Observatory Germany (ZUGOG) at Zugspitze (2,939 m a.s.l.), where the OSG 052 superconducting gravimeter continuously measures gravity acceleration with the highest precision (1 nm/s^2) and long-term stability. Due to unmodeled temporary gravity changes, primarily caused by variations in snow water equivalent and groundwater, the system has a relative stability of approximately 5⋅10^(-5).
To obtain gravimeter scale factors with an uncertainty below 1⋅10^(-5) in the Zugspitze Calibration System, we increase the precision by taking many measurements and improve the systematic uncertainty by modeling. From December 2023 to April 2026, a total of 73 difference measurements were taken between W200 and W100 using the relative gravimeters Scintrex CG6#362 from GFZ and CG6#171 from project partner LUH. Additionally, 18 difference measurements were carried out between W200 and ZUGOG. The CG6 measurements employed gravity gradients from Timmen et al. (2021) and tidal parameters from six years of SG measurements at Zugspitze. To correct for atmospheric variations, an air pressure admittance factor of -3 nm/s^2/hPa was used.
The attached data have been calibrated using the initial scale factor specified by the manufacturer, and corrected for gravity gradients, tides, and atmospheric pressure variations.
The International Geodynamics and Earth Tide Service (IGETS) was established in 2015 by the International Association of Geodesy (IAG). IGETS continues the activities of the Global Geodynamics Project (GGP, 1997-2015) to provide support to geodetic and geophysical research activities using superconducting gravimeter (SG) data within the context of an international network.
The Hurbanovo gravimetric observatory in southern Slovakia was established in 2019 as a part of the integrated station HUVO (GNSS permanent station and seismic station). HUVO is located on a ground floor in a small building in the vicinity of the Hurbanovo Geomagnetic Observatory, which was founded on September 30, 1900. Integration of InSAR transponder into current station architecture is also planned in 2022.
The gravimetric observatory equipped with the spring gravimeter gPhoneX #108 provides continuous time-varying gravity and atmospheric pressure data. The spring gravimeter gPhoneX #108 is installed on a concrete block isolated from the rest of the building grounding. The room containing gravimeter is thermally stabilized at around 22 ± 1°C using an air conditioning unit. An additional thermal polystyrene insulation is placed around the instrument further decreasing temperature variations on its surface. Concerning signal to noise ratio, the HUVO station can be characterized as moderately noisy.
The operation and maintenance of the HUVO gravimetric instrumentation is done mainly by the staff of the Slovak University of Technology. HUVO gravimetric observatory is also equipped with the accelerometer Raspberry Shake (4D) installed on the same concrete block as the spring gravimeter, operated by the staff of the Slovak Academy of Sciences. Several other meteorological sensors are also present at the site in the close vicinity of the gPhoneX #108: the meteorological station MWS 9-5, a well equipped with the ground-water level sensor and a total number of 16 sensors measuring the soil moisture. These sensors provide information necessary for modelling the gravity response associated with the variation of local hydrological masses.