18 years continuous gravity time series at station Medicina: A benchmark for tidal analysis

The gravity station Medicina in Northern Italy was established in October 1996 by deploying the superconducting gravimeter CD-023. Since then the gravimeter was recording continuously and the long term stability is supported by regular absolute gravity measurements. Since end of 1997, the registration is almost undisturbed and will be analyzed using the extended capabilities of the recently updated Eterna V50 tidal analysis package after correcting various effects, like atmospheric and water storage changes or monument stability. A parallel registration with two different low pass filters over a period of almost 2 years is used to check the impact of the different transfer functions and on the sensors scale factor. After removing seasonal variations in the residual time series using a global hydrology model, stacking and singular spectrum analysis, the long term characteristics is analyzed and compared with vertical velocities of station position from ITRF (VLBI, GNSS) and finally an attempt to identify the 18.6-year period lunar nodal tidal cycle will be made.