抄録
The Canadian Superconducting Gravimeter Installation (CSGI) operates a GWR TT70 superconducting gravimeter at a site near Cantley, Quebec. An adjacent pier is the reference point for the Canadian Absolute Gravity Station (LAGS) JILA-2 absolute gravimeter. The co-location of the two instruments provides an opportunity to examine the drift of the superconducting gravimeter and to search for spurious signals in either instrument. It is known that the superconducting gravimeter suffers from occasional tares, but the extent to which there are spurious signals on any time-scale is unknown. Nine separate experiments have been conducted since February 1998, in which the absolute gravimeter was dedicated to rapid sampling of gravity for about a week. From these we have calibrated the superconducting gravimeter, established the drift, and assessed the level of spurious gravity signals in both instruments. The calibration factor recovered from these experiments is -78.3 f 0.1 ugal/V. During the period from early 1998 to late 1999, the superconducting gravimeter maintained a constant reference level to better than three microgals. However, in early 2000, the level of the absolute gravimeter rapidly diverged from that of the superconducting gravime ter achieving a maximum recorded difference of fourteen microgal during April 12-13 2000. As of June 2000 the absolute gravimeter had recovered and the offset between the two is again only two microgal. There is occasionally a rough correlation between the (tide and pressure corrected) residuals of the two gravimeters at the microgal or better level on time-scales down to about a day. However, in several experiments no correlation was apparent and excursions of the absolute gravimeter of several microgal persisting for several hours were noted. Most of the variance of the absolute gravimeter residuals seems to be at periods of hours to a day, and there are occasionally episodes of several hours duration when the instrument reads low by several microgal.
