The new IMGC-02 transportable absolute gravimeter: measurement apparatus and applications in geophysics and volcanology

Abstract

The research carried out at the Istituto Nazionale di Ricerca Metrologica (formerly Istituto di Metrologia «G.
Colonnetti») aiming to develop a transportable ballistic absolute gravimeter ended with a new version of the instrument,
called the IMGC-02. It uses laser interferometry to measure the symmetrical free rising and falling
motion of a test mass in the gravity field. Providing the same accuracy achieved with previous versions, the instrumental
improvements mainly concern size, weight, data processing algorithms and operational simplicity.
An uncertainty of 9 ?Gal (1 ?Gal=1×108 m·s?2) can be achieved within a single observation session, lasting
about 12 h, while the time series of several observation sessions show a reproducibility of 4 ?Gal. At this level,
gravity measurements provide useful information in Geophysics and Volcanology. A wide set of dynamic
phenomena, i.e. seismicity and volcanic activity, can produce temporal gravity changes, often quite small, with
an amplitude ranging from a few to hundreds of microgals. Therefore the IMGC absolute gravimeter has been
employed since 1986 in surveying the Italian active volcanoes. A brief history of the gravimeter and the description
of the new apparatus, together with the main results of ongoing applications in Geophysics and Volcanology
are presented.