Gravity Calibration Baseline Between Jeddah and Taif in Kingdom of Saudi Arabia
21/09/2016 | 09:45 | Session 4: On the ground and airborne gravimetry
Author(s): Gokhan Arslan, Mehmet Emin Ayhan, Bandar Saleh Abdulkareem Al-Muslmani, Meshal Al-Qulaity and Sultan Falah Al-Shahrani
Gokhan Arslan, Mehmet Emin Ayhan, Bandar Saleh Abdulkareem Al-Muslmani, Meshal Al-Qulaity and Sultan Falah Al-Shahrani
Relative gravimeters are calibrated for calibration constant(s) relating observable units to µGal. The calibration correction factor(s) with respect to the instrument calibration constant(s) are constrained by measurements at gravity calibration baseline (GCB) stations. GCB is a gravity network where known gravity differences are compared to those measured by relative gravimeter. Start and end sites of the GCB in the Kingdom of Saudi Arabia were installed at Jeddah and Taif. GCB sites include two stations: center and ex-center. The GCB is extended with 12 sites between those two sites in the late 2014. Absolute gravity (AG) at the GCB 28 stations were observed simultaneously by two A10X (#021, #023) absolute gravimeters. Ties between the stations are also measured simultaneously by four CG5 relative gravimeters. Two CG5s were used in gravity gradient measurements at the stations. AG, gradient and tie measurements were completed from December 2014 to January 2015. A10X provided total uncertainty of less than 6 μGal. The uncertainty of gravity gradient and tie measurements are less than 2 µGal and 5.4 µGal respectively. Comparison of ties observed by CG5 and A10X results in differences less than 9 µGal.
In order to screen the CG5 tie measurements, first the GCB network, includes 112 CG5 ties only is adjusted datum free. Outliers (15 ties) detected by Pope’s Tau-test are excluded. Then the network consists of A10X absolute gravity (total 56) and CG5 tie (total 97 ties) measurements are adjusted by weighted constraint. At this step we basically screen the AG measurements. Finally the AG at each of the stations is estimated with their uncertainty. The uncertainty for absolute gravity at each station and gravity differences between stations are less than 2.3 μGal and 2.6 μGal respectively. The gravity differences between the center stations at Jeddah and Taif is 430796.3 ± 1.92 µGal. Considering the height difference of 1521 m between Jeddah and Taif sites, average rate of gravity with height along the baseline is about 283 µGal per meter.