Dynamic adaptability of digital fringe processing for the laser interference absolute gravimeter and its shipboard applications evaluation

The dynamic adaptability of digital fringe processing is a fundamental prerequisite for dynamic absolute gravity measurements. We have developed a dynamic restriction based on physical parameters of the background vibration according to the instantaneous phase methods, i.e., the reverse vibration velocity cannot exceed the falling velocity of the falling drop. This method involves the Hilbert transform, the direct quadrature, and the zero-crossing method. We have conducted simulation experiments with different vibration intensities and frequencies. The results show that this dynamic restriction is reasonable. The precision of the Hilbert transform method is better than 10⁻¹³ m/s², the precision of the zero-crossing method is better than 10⁻⁹ m/s², and the precision of the direct quadrature method is approximately （−7.9±2.0）×10⁻⁸ m/s² at a 60 MHz sampling rate when the dynamic restriction is satisfied. Furthermore, we conducted absolute gravity measurements on a wave simulator, and obtained results with a standard deviation of 4.6×10⁻⁵ m/s² . This verifies that the instantaneous phase methods apply to the dynamic environment when the restriction is satisfied. Based on the dynamic adaptability conclusion, we further evaluated the mooring system and the sea surface shipboard dynamic environment on the vessel. The evaluation revealed that the measurement vessel can conduct absolute gravity measurements with an accuracy of 10⁻⁵ m/s² under sea conditions of grade 3 or below. Under sea conditions of grade 3−4, the measurement results need to be screened based on vibration signals to obtain absolute gravity measurements at the 10⁻⁵ m/s² level. However, conducting dynamic absolute gravity measurements is not recommended under sea conditions above grade 4.