Gravity Calibration Baseline Between Jeddah and Taif in the Kingdom of Saudi Arabia

Relative gravimeters are calibrated for calibration factors relating observable units to gravity. The calibration correction factors with respect to the instrument calibration factors are estimated by measurements at gravity calibration baseline (GCB) stations. GCB is a gravity network where known gravity differences are compared to those measured by relative gravimeters. The GCB in the Kingdom of Saudi Arabia has endpoints in Jeddah and Taif. The endpoints were observed by FG5 (#111) and A10 (#029) absolute gravimeters in 2013–2014. Twelve new sites in between the endpoints were installed in the late 2014. There are two stations (center/inside and ex-center/outside) at each GCB sites, hence the GCB includes 28 stations. Absolute gravity (AG) at the GCB stations were observed simultaneously by two A10X (#021, #023) absolute gravimeters. The stations were also tied simultaneously by four CG5 relative gravimeters. Besides gravity gradient at each of the stations was measured by two CG5s. The gravity measurements were completed from December 2014 to January 2015. The total uncertainty of A10X is smaller than 6 μGal. The uncertainties of gravity gradient and tie measurements are smaller than 2 μGal/m and 5.4 μGal, respectively. Comparisons of ties observed by CG5 and A10X result in differences less than 9 μGal. The GCB network is adjusted by weighted constraint least squares. Estimated uncertainty of the gravity differences is 1–2 μGal. The gravity differences between the endpoints of the calibration line at Jeddah and Taif is 430.678 ± 0.002 mGal.