The GWR iGravTM Superconducting Gravity Meter

Warburton, Richard J.
GWR Instruments, Inc., 6264 Ferris Sq. San Diego, CA, 92121 USA; warburton@gwrinstruments.com

It is generally know that Superconducting Gravimeters (SGs) are far superior to spring-type gravity meters when used for making continuous gravity measurements over periods of months to many years. Spring-type gravity meters suffer from large non-linear drifts, variation in scale factor, and respond to changes in temperature and pressure. As a result, it is not possible to separate instrumental effects from real gravity changes. In contrast, the SG drift is extremely small (< 6 µGal/year) and highly linear over decades; and its scale factor is constant to better than 0.01 percent. Therefore, using SGs to replace spring gravity meters would significantly improve geophysical data in many applications. As an example, recent publications have shown that the SG provides precise measurements of local water storage changes (WSC). As an integrative tool, the SG can be used to evaluate or calibrate hydrological models that are extremely difficult to test in any other way. We expect a similar improvement in understanding and interpreting other geophysical phenomena after SGs replace spring gravity meters in these areas. Possible applications include: volcano and geothermal monitoring, measurement of silent earthquakes, stability of CO2 geologic sequestration, and subsidence caused by oil, water, or gas extraction. Due to their high cost, the complexity of the equipment, and perceived and real difficulty of operating and maintenance, SGs are normally restricted to observatories sites chosen to minimize noise over the whole range of gravity signals from periods of decades to 100 seconds. This eliminates many sites of high geophysical interest. To overcome these obstacles and to increase the utility of the SG, GWR Instruments has been developing the new iGrav? Superconducting Gravity Meter. The iGrav? is designed specifically for geophysical applications that require much higher stability and precision than provided by mechanical spring-type gravity meters, but can be set up easily and quickly without the need for an expensive platform, housing or infrastructure. In this poster, we delineate the advantages of the iGrav? to previous SGs and show recent data comparing the two types of SGs.