Abstract This paper summarizes the main instrumental and methodological points of
the tidal research which was performed in the framework of the National Scientific
Research Fund Project K101603. Since the project is still running the tidal analysis
results published here are only preliminary. Unmodelled tidal effects have been highlighted
in some recent absolute gravity measurements carried out in the Pannonian basin resulting
in a periodic modulation exceeding the typical standard deviations (±1microGal) of
the drop sets. Since the most dominant source of the daily gravity variation is the
bulk tidal effect, the goal of the project is to check its location dependency at
μGal level. Unfortunately Hungary has had no dedicated instrumentation, so an effort
was made to make the available LaCoste-Romberg spring G meters capable for continuous
recording. As a reference instrument the GWR SG025 operated in the Conrad Observatory,
Austria was also used and in the mean time of the project, a Scintrex CG-5 became
also available. Eventually 6 instruments at 5 different locations were operated for
3–9 months mainly in co-located configuration. Although many experiments (moving mass
calibrations) were done to determine the scale factors and scale functions of the
instruments, the direct comparison of the tidal parameters obtained from the observations
is still questionable. Therefore the ratio of the delta factors of O1 and M2 tidal
constituents was investigated supposing that M2 is much more influenced by the ocean
loading effect than O1. The slight detected increase of δ(O1)/δ(M2) (≈0.2%) toward
east does not contradict to theory. This result has to be validated in the near future
by analyzing available ocean loading models.
