Sun He-ping

European Tidal Gravity Observations: Comparison With Earth Tide Models And Estimation Of The Free Core Nutation (Fcn) Parameters

The data of sixteen West European tidal gravity stations have been reprocessed. The tidal gravity factors have been corrected for ocean loading effect using the mean of 9 different ocean tides models with different grid size (0.5 ◦ ,0 .25 ◦ and 0.125 ◦ ). For the principal tidal waves O1 and M2 the standard deviation of the corrected amplitude factors δc is lower than 0.1%. For O1 the value δc = 1.15340 ± 0.00023 lies between the Dehant, Defraigne and Wahr, 1999 (DDW99) elastic model and the Mathews, 2001 (MAT01) inelastic model. For M2 the value δc = 1.16211 ± 0.00020 fits very well the DDW99 and the MAT01 inelastic models. For K1 the mean result δc = 1.13525 ± 0.00032 (7 Global Geodynamics Project stations and Pecny) fits the MAT01 model to better than 0.05%. We determine the FCN parameters using either generalized least-squares or a Bayesian approach and find values between 428 and 432 sidereal days for the eigenperiod and quality factor Q values around 15,000.

Accurate determination of calibration factor for tidal gravity observation of a GWR-superconducting gravimeter

It is recognized widely nowadays that the superconducting gravimeter (SG) is a kind of best relative gravimeter with high observing precision, good continuity and stability. However, it is necessary to calibrate the direct output (change in voltage) by using scale value (calibration factor) before getting the change of the real gravity field. Studies show that the accuracy of the scale value will influence the late analysis and explanation of the observations. By using absolute gravity measurements of a FG5 absolute gravimeter (AG) at Wuhan international tidal gravity fundamental station (two campaigns each for 3 days) and by using known tidal parameters at the same station, the calibration factors of the SG and their precision are studied in detail in this paper.

Check of Earth’s free oscillations excited by Sumatra-Andaman Large Earthquake and discussions on the anisotropy of inner core

Sumatra-Andaman Large Earthquake on Dec. 26, 2004 generated not only the Indian Ocean Tsunami but also the Earth’s free oscillations (EFO). The signals of Earth’s free oscillations were perfectly recorded by the superconducting gravimeter C0-32 at Wuhan station in China. After the pre-treatment and spectral analysis on the observational data from Wuhan station, we obtained more than ninety EFO modes including 42 fundamental modes, 2 radial modes and 49 harmonic modes. On the basis of the discussions on some observed harmonic modes and abnormal splitting phenomena, we considered that the real rigidity might be lower than the theoretical prediction of PREM model in the inner core and however the anisotropy of compressive wave was brightly higher than the present estimations in the inner core. This suggested that the anisotropy of the inner core could be much more complicated than our present understanding, and there might be some new geophysical phenomena in the formation process of the inner core.

Analysis and comparison of the tidal gravity observations obtained with LCR-ET20 spring gravimeter

Based on the tidal gravity observations recorded with LCR-ET20 spring gravimeter at Wuhan international fundamental tidal gravity station, the characteristics of the ET20 and the atmospheric and oceanic gravity signals are studied systematically by using international standard data pre-processing and analysis methods, and by comparing the results with those obtained using superconducting gravimeter (SG) at same station. The numerical results indicate that the identical tidal gravity parameters same as those with the SG are obtained, the instrument can be used effectively to record temporal change of the gravity field, though the accuracy of the ET20 is one order lower than that of the SG, and has also the large drift induced by the spring creep character.