Absolute gravity measurements by using FG5 and A10 absolute gravimeters in the Kingdom of Saudi Arabia

Abstract

In order to define gravity datum and gravity scale in the Kingdom of Saudi Arabia (KSA), an absolute gravity network, called KSA Absolute Gravity Network (KSA-AGN), comprising of 25 sites distributed countrywide was observed from January 2013 to February 2013. Two stations were installed at each network site: one inside the building and one outside. Micro-g A10 (#029) portable absolute gravimeter was used for data acquisition of two setups of ten sets each at both inside and outside stations. Set scatters for A10 setups are usually less than ±3 μGal, and the differences between two setups vary in the range of −8 to 5 μGal. The weighted mean of the two setups were calculated as unique absolute gravity value and its uncertainty at the stations. Seven of the stations (five inside and two outside) were collocated by Micro-g FG5 (#111) absolute gravimeter having 24 sets for each setup. Set scatters for FG5 setups are less than ±4 μGal almost like A10 setups. However, we obtained the total uncertainty of FG5 and A10 measurement about ±2 and ±6 μGal, respectively. Furthermore, to reduce measured absolute gravity from the reference height to any height, gravity gradients over both inside and outside stations were measured by using two Scintrex CG5 (#922 and #924) relative gravimeters. Average CG5 gradient at the outside stations is about 3.1 μGal/cm, satisfying the free air gradient in the country. Differences between A10 and FG5 absolute gravities at 72 cm vary between −3.8 and 9.5 μGal at seven stations. Excluding the outside stations, we obtained the differences from −3.8 to 5.5 μGal at inside stations.