A 2-YEAR COMPARISON BETWEEN THE FRENCH AND CANADIAN SUPERCONDUCTING GRAVIMETER DATA

This study is devoted to a preliminary comparison of the gravity recor ds provided by two geographically well-separated superconducting gravi meters over a common two-year observing period. The data sets are proc essed for the first time following exactly the same numerical steps. A fter a brief description of the observed gravity and pressure signals, we perform a classical least-squares fit to tides, taking into accoun t a single coefficient for the effect of the local barometric pressure fluctuations and a second-order polynomial approximation for the inst rumental drift. The results show a totally different drift behaviour b etween the two instruments. The time fluctuation of the resulting resi dual gravity signals is shown, as well as the corresponding power spec tral density. In particular, we provide detailed statistics on the spe ctral content of the residual gravity signals. In a subsequent step, w e first high-pass filter the observed gravity and pressure signals and then apply an automatic method to detect and remove obvious spikes. A new least-squares fit then provides new residual gravity signals, the power spectral density of which is reduced in all frequency bands, es pecially in the subtidal band. We finally provide cross-spectral estim ates of these two residual gravity sets indicating a further reduction in the power spectral density level.