Measuring the free-fall acceleration with the IMGC-02 transportable absolute gravimeter

The knowledge of the acceleration g due to gravity plays an important role in force metrology in calibration of mechanical standards and, recently, in mass metrology in realizing new mass standards based on electrical references for the redefinition of kilogram. Moreover gravimetric surveys are carried on for applications in Geophysics and Geodesy. Over the past thirty years the development of transportable ballistic absolute gravimeters has dramatically pushed up the ability to measure the g value. The application of new technological advances and the deep study of the physical phenomena influencing the gravity measurement allowed a significant reduction of the uncertainty, estimated to be some parts in 109. Nowadays the future progresses are expected to reduce instrumental size, weight, costs and operational simplicity. The Istituto Nazionale di Ricerca Metrologica (INRIM) developed a transportable absolute gravimeter, called IMGC-02 [1-2-3]. It uses laser interferometry to measure, from an inertial reference point, the symmetrical free rise and falling motion of a test-body in the gravity field. The local g value is extracted from the trajectory by fitting a suitable motion model to the space-time coordinates. The description of the instrument, the measurement principle, the reconstruction of the test-body trajectory, the user interface of the software and the results obtained during the last International Comparison of Absolute Gravimeters (ICAG-2005) are shown.