Connecting a Quanterra Data Logger Q330 on the GWR C021 Superconducting Gravimeter for low Frequency Seismology

Below 1.5 mHz the superconducting gravimeters (SGs; Figure 1) are competitive with the best spring gravimeters and seismometers and can achieve the lowest noise level at frequencies lower than ∼1.0 mHz (Van Camp 1999; Rosat et al. 2003; Widmer-Schnidrig 2003; Park et al. 2005). SGs can therefore make a significant contribution to the illumination of long-wavelength density heterogeneities in the Earth's mantle (Widmer-Schnidrig 2003). For reasons of price and complexity, the number of SGs is small compared to the number of sensors deployed in the Global Seismic Network (GSN). However, the potential of a sparse network of gravimeters for normal-mode research has been demonstrated by the International Deployment of Accelerometers (IDA) network (Agnew et al. 1986). Another point worth noting is the stability and accuracy (∼0.1% level) of the calibration factor of SGs (Francis et al. 1998) requested to validate Earth and ocean tide models using tidal gravity measurements (Baker and Bos 2003). This compares well with seismic networks, where results are barely better than 1% (http://ida.ucsd.edu/pdf/DMSSC\_2005\_10.pdf; Park et al. 2005; Davis et al. 2005). Such accuracy is quite unacceptable for geodesy. Since 1997, most of the SG data have been collected under the framework of the Global Geodynamics Project (GGP) global network (Crossley et al. 1999) that presently includes about 25 instruments. The GGP aims to look at seismic normal modes, the Slichter triplet, tidal gravity, ocean tidal loading, core nutations, core modes, and hydrology. Up to now the data have been gathered in an ad hoc database, using the ASCII PRETERNA format, which acts as a standard for tidal analysis (Wenzel 1996). These data are available to non-GGP members after a six-month delay. In order to promote the SG data among the seismic community, contacts between the Royal Observatory of Belgium and the …