Absolute Measurement of Free-Fall Acceleration as Reference for Selenodesy Studies and Applications

Studies in gravimetry for the earth and celestial bodies insert in a more large context of our institute space applications. In particular, the aim is to realize an easy of use, rugged and completely automated absolute gravity meter for space applications through the huge knowledge obtained in gravity research. In fact, the Gravimetry Group of the Institute of Metrology “G. Colonnetti” (IMGC-CNR), nowadays National Institute of Metrological Research (INRIM), developed a new version of a transportable absolute gravimeter, the IMGC-02. The instrument has several improvements mainly concerning the transportability, the measurement automation and the userinterface programs. According to the Guide to the Expression of Uncertainty in Measurements (ISOGUM), an extensive analysis concerning the contributors to the uncertainty budget detects an instrumental expanded uncertainty (p = 95 %) of about 8 parts in 109 of the surface gravity value. Interest in absolute gravity measurements for applications in geophysics and volcanology is increasing and gives rise for the necessity of an instrument available to any kind of measurers and employable for investigating geological strata, phreatic surface, geological, tectonic and magmatic dynamics and gravimetric tides. Hence a new absolute transportable country gravity meter is under study. It should be of simple assembly and installation, low weight and size, low power consumption, full automated control, measurement and processing. IMGC-02 performances joint to the flexibility derived from the study of the new outdoor absolute gravimeter, under development at this time, will be the starting point for the space gravimeter project.