A Transportable Absolute Gravimeter for Determining the Acceleration due to the Earth's Gravity

A transportable absolute gravimeter has been constructed at the National Institute of Metrology (NIM), which is based upon the principle of free fall through three stations. A cube-corner reflector dropped in a vacuum chamber forms an arm of an optical interferometer. The interference pattern produced by the motion of the falling object is converted to an electric signal. This is then processed by a special electronics system, so that the distances and the respective time intervals of the falling reflector as it passes each of the three stations are measured. The light source of the interferometer is a stabilized He-Ne laser. The time base is a rubidium frequency standard. The sources of error of the measurement and the uncertainty of the results are given. The effect of non-verticality of the laser beam is discussed. Some of the recent results including the comparison with A. Sakuma's gravimeter at the Bureau International des Poids et Mesures (BIPM) are presented. The accuracy achieved with this gravimeter is about 2 × 10-8.