New method of digital fringe signal processing in an absolute gravimeter

This paper describes a digital fringe signal processing method realized in the new Tsubokawa-type transportable absolute gravimeter at the National Astronomical Observatory, Mizusawa (NAOM), Japan. A data processing algorithm is based on the second-differences method that uses neither the nonlinear least-squares approximation nor the commonly adopted fringe counting. An estimated uncertainty shows that it is possible to achieve a resolution of the measured falling distance intervals of order 0.04 nm over the operating fringe frequency range 1.2 MHz to 7.4 MHz. Finally, the relative combined standard uncertainty of the method is about 0.2×10^-9 of an absolute gravity value