A Atmospheric Correction of FG5 Absolute Gravimetry Data using Measured Air Pressure

Abstract

Changes in atmospheric density affect atmospheric pressure, which is a key factor affecting high-precision gravity measurement. Currently, atmospheric correction of absolute gravity measurements uses the empirical admittance value recommended by the International Association of Geodesy (−0.3 μGal/mbar); however, the actual admittance value changes with atmospheric mass and time.  In this study, we determine the effect of using measured admittance values for absolute gravity correction. First, high-precision relative gravimeters (GWR OSG-057, Scintrex CG5) are used for continuous gravity measurements. Then, air pressure measured by the pressure sensor equipped by FG5 absolute gravimeter is used to obtain the atmospheric admittance using the iterative least squares method, which is compared with the theoretical atmospheric admittance. Taking FG5-257 as an example, we use the measured admittance for atmospheric correction of absolute gravity at four different elevations (Lhasa, Nagqu, Gar, and Suining, China). The results are as follows: 1) According to co-location measurements in Lhasa, CG5 and OSG gravimeter measured admittance values exhibit comparable precision (–0.332 ± 0.003 μGal/mbar and –0.332 ± 0.001 μGal/mbar, respectively), though  the CG5 has larger standard deviation. 2) After correction using the measured admittance, changes in set standard deviation and measurement precision are approximately 0.01 μGal; however, the effect on the measurement results does not exceed 1 μGal, which is equivalent to the measurement  precision of FG5. Therefore, measured admittance values are only recommended for atmospheric correction of high-precision absolute gravity measurements.