A vibration correction method based on element searching applied in atomic-interferometry absolute gravimeter

Absolute gravimeter has played an important role in geophysics, metrology, geological exploration, etc. It is an instrument applying laser interferometry or atom interferometry for the measurement of gravitational acceleration g (approximately 9.8 m/s2). To achieve a high accuracy, vibration correction method is often employed to reduce the influence of the vibration of the reference object (a retro-reflector or a mirror) on the measurement results of absolute gravimeters. Specifically, in an atomic-interferometry absolute gravimeter, the phase noise caused by the vibration of the reference mirror, namely the vibration phase, can be calculated from the output signal of a sensor placed below or next to the mirror, either a seismometer or an accelerometer. Considering this vibration phase, the fringe signal of the atomic interferometer as a function of the phase shift set by the control system of the gravimeter can be corrected to approach an ideal sinusoidal curve, with the fitting residual to be decreased. Currently, the parameters in the algorithm of most vibration correction methods applied in atomic-interferometry absolute gravimeters are set to be constant. As a result, the performance of these methods may be limited when the practical transfer function between the real vibration of the reference mirror and the signal of the sensor has a variation due to the change of measurement environments. In this paper, based on a simplified model of the practical transfer function previously proposed in an algorithm used in laser-interferometry absolute gravimeter, a new vibration correction method for atomic-interferometry absolute gravimeter is presented. Firstly, a detailed description of its principle is introduced. With a searching algorithm, the time delay and the proportional element in the simplified model can be obtained from the fringe signal of the atomic interferometer and the output of the vibration sensor. In this way, the parameters used to calculate the vibration phase can be adjusted to approach their true values in different environments, causing the fitting residual of the corrected fringe to be decreased as much as possible. Then the measurement results of the homemade NIM-AGRb-1 atomic-interferometry absolute gravimeters applying this method is analyzed. It is indicated that, with the vibration correction algorithm, the standard deviation of the fitting residual of the measured fringe signal can be decreased by 58% at the best level in a quiet environment. In the future, the performance of this vibration correction algorithm will be further evaluated in other atomic-interferometry absolute gravimeters during their measurements in hostile environments.