Towards unification of vertical datum for Sabah and Sarawak using gravimetric geoid model

Abstract

Sabah and Sarawak have adopted various local vertical datums that tied to mean sea level referring to tide gauges. The use of various datums may implicate height inconsistencies in these two states. This study aims to evaluate the potential of gravimetric geoid model as uniform vertical datum for Sabah and Sarawak. The objectives of this study are to assess the existing geoid model and to compute vertical datum offset. East Malaysia Gravimetric Geoid (EMG03C) model and Global Positioning System (GPS) levelling are the primary data used in this study. The assessment of geoid models involved in this study are EMG03C model, fitted geoid model EMGEOID05 and EGM2008. These geoid models were evaluated with GPS levelling derived geoid height and the comparison were made in absolute and relative method. Meanwhile, the vertical datum offset value between Sabah 97 Datum and Pulau Lakei Datum was computed by comparing the mean bias of geoid height differences based on 108 GPS levelling points. Based on absolute geoid assessment, this study found that the fitted geoid model has good performance over Sabah which is 6 cm and the accuracy of geoid model is degraded over Sarawak of 30 cm. The possible reason of low accuracy of fitted geoid model in Sarawak due to the model has been fitted to the mean sea level at Sabah 97 Datum. Hence, for local application vertical datum offset need to be considered. Based on relative assessment, gravimetric model demonstrate the difference Root Mean Square (RMS) of 3 cm and 2 cm for 60 km baseline over Sabah and Sarawak respectively. This demonstrates the feasibility of relative GPS levelling and gravimetric geoid as alternative technique in height determination for engineering and construction project. In addition, the result also shows that vertical datum offset between Sabah 97 Datum and Pulau Lakei Datum using gravimetric geoid model and GPS levelling data is about 0.257 m. Therefore, gravimetric geoid is suggested as suitable unified vertical datum for Sabah and Sarawak. In conclusion, gravimetric geoid-based vertical datum has a potential for modernizing the height system in Sabah and SarawaK.