PRELIMINARY SPECTRAL-ANALYSIS OF THE RESIDUAL SIGNAL OF A SUPERCONDUCTING GRAVIMETER FOR PERIODS SHORTER THAN ONE DAY

We show for the first time an analysis of a 1.5 year data set from the superconducting gravimeter in Strasbourg. For periods between 7 and 24 h, a residual gravity signal is first generated by removal of the main tidal components by a standard least squares fit; this signal is then treated to suppress any remaining transient signals (de-spiking). At shorter periods, between 7 h and 10 min, a simple high-pass filter is applied before de-spiking. In both cases, the noise level is estimated in different frequency bands; spectra of the gravity residuals are shown. We also analysed by two different methods the local barometric pressure, which contains harmonic components of the S1 wave related to air pressure changes - driven by diurnal solar heating - superimposed on the frequency-dependent meteorological noise. After removal of the daily harmonics which are also present in the gravity residual spectrum, a few remaining spectral lines of possible geophysical interest are discussed.