High-precision gravity measurements using absolute and relative

Accurate detection of time gravity changes attributable to the dynamics of
volcanoes requires high-precision gravity measurements. With the aim of
improving the quality of data from the Mount Etna gravity network, we
used both absolute and relative gravimeters in a hybrid method. In this
report, some of the techniques for gravity surveys are reviewed, and the
results related to each method are compared. We show how the total
uncertainty estimated for the gravity measurements performed with this
combined use of absolute and relative gravimeters is roughly comparable
to that calculated when the measurements are acquired using only relative
gravimeters (the traditional method). However, the data highlight how
the hybrid approach improves the measurement capabilities for surveying
the Mount Etna volcanic area. This approach enhances the accuracy of
the data, and then of the four-dimensional surveying, which minimizes
ambiguities inherent in the gravity measurements. As a case study, we
refer to two gravity datasets acquired in 2005 and 2010 from the western
part of the Etna volcano, which included five absolute and 13 relative
stations of the Etna gravity network.