Geoid of South East Sulawesi from airborne gravity using Hotine approach

Abstract

Abstract In the past, geoid was computed from gravity anomaly data using Stokes or Molodensky approaches. Obtaining gravity anomaly data is difficult because it needs some reductions of gravity from surface of the earth to the geoid using orthometric height from spirit level measurement. In the modern era, gravity anomaly data may be replaced by gravity disturbance data. It only required gravity and GNSS (Global Navigation Satellite System) measurement. This research aimed to determine geoid using Hotine’s approach. Disturbance data were generated from archived free air anomaly of airborne gravimetry in Sulawesi area. South East Sulawesi province was selected as a case study area. In this study, gravity observation was calculated at an altitude of 4000 m above the reference ellipsoid. Gravity estimation at the same height aims to increase the precision of the downward continuation process to the geoid. Hotine integral is calculated above the geoid, so that the gravity disturbance data is downwarded to the geoid. The geoid undulation is graded from north to south. Geoid from airborne gravity around Pegunugan Mekongga in the northern part of Southeast Sulawesi Province has the largest geoid undulation which reaches 63 m, while the geoid in the southern part of Buton Island reaches 52 m. Geoid validation of airborne gravity at 13 test points produces a standard deviation of ± 0.050 m. The standard deviation is much smaller than the results of geoid testing from airborne data in North Sulawesi, Central Sulawesi and Southeast Sulawesi. This fact indicates that the Hotine approach has the potential to produce a precise geoid if used in geoid-based airborne gravity calculations.