Hybrid geoid model over peninsular Malaysia (PMHG2020) using two approaches

We describe the development of a hybrid geoid model for Peninsular Malaysia, based on two approaches. The first approach is utilising an ordinary method fitting the gravimetric geoid to the geometric undulation derived from GNSS-levelling data; the second approach directly fits the gravimetric geoid to the reference mean sea level derived from the tide measurements of Port Klang tide gauge station. The hybrid geoid model fitted to Port Klang (PMHGG2020_PK) is produced by adding an offset of 0.446 m to the gravimetric geoid, based on the comparison at the tide gauge benchmark. To calculate the gravimetric geoid, a new model for Peninsular Malaysia (PMGG2020) has been developed based on Least-Squares Modification of Stokes’ Formula with Additive correction (LSMSA). Three different sources of gravity data which are terrestrial, airborne, and satellite altimetry-derived gravity anomaly (DTU17) have been combined to construct the geoid model. The height information has been extracted from the newly released global digital elevation model, TanDEM-X DEM. GO_CONS_GCF_2_SPW_R4 model derived from GOCE data provides long-wavelengths gravity field up to maximum degree and order 130. The gravity datasets are gridded by 3D Least-Squares Collocation method. The PMGG2020 model is consistent with the geometric geoid heights from 173 GNSS-levelling measurements, with a standard deviation of ±5.8 cm. Evaluation of the hybrid geoid model constructed from the first approach shows a significant improvement over the two existing hybrid geoid models. The accuracy of ±4.6 cm has been achieved after evaluating by 20 GNSS-levelling points, externally. Hybrid geoid model fitted to Port Klang has also been evaluated via 173 GNSS-levelling points, and the result shows that 71% of the total data exhibit height differences lower than 10 cm. The overall results indicate that the hybrid geoid model developed in this study can be valuable as an alternative to the current modern height system in Peninsular Malaysia for surveying and mapping.