EVALUASI MODEL GEOID LOKAL WILAYAH KERJA PERTAMINA: Studi Kasus : Bekasi dan Cirebon

Geoid is an equipotential gravity field coincide with the undisturbed mean sea level. Precise Local geoid modelling requires component of the Global Geopotential Models (GGM), terrain data and gravity data. The gravity measurement done over the PT.Pertamina�s working area, usually covered a narrow area with detailed data distribution, for example in Bekasi and Cirebon. The area is not more than 30 km x 30 km and the data distribution reach about 0,1 km to 0,6 km. The objective of this study was to evaluate the geoid modelling using gravity data of PT.Pertamina measurement in both areas. The gravity anomaly contain of 251 points in Bekasi and 1.649 points in Cirebon. The GGM that was used is EGM2008 with degree of 160. Terrain data derived from contours of RBI map 1:25.000. Geoid undulation was calculated using the Two Dimension Fast Fourier Transform (2D FFT). The evaluation was done by comparing the results with the local geoid model of Java Island and one point GPS-levelling data. Local geoid model of Java Island is assumed to have the correct value with the precision as much as 0,655 m. The results show that value of Bekasi undulation is range from 19,1 m to 19,76 m with mean value of 19,46m. The Cirebon undulation is range from 21,85 m to 22,9 m with mean value of 22,31 m. The comparison of Bekasi and Cirebon local geoid models with Java Island geoid model is obtained the mean of deviation is 0,477 m for Bekasi region with range from 0,37 m to 0,547 m and and 2,282 m for Cirebon region with range -4,255 m to -0,688 m. The comparison with one point GPS-levelling is obtained the accuracy 0,147 m for local geoid model of Cirebon and 2,019 m for local geoid model of Jawa Island. Based on limited data, the conclusions are the local geoid models on norrow area more precision than local geoid model of Java Island. Keywords: narrow areas, gravity, undulations, geoid