Research into GNSS levelling using network RTK in Taiwan

Abstract

Modern height surveying obtains orthometric heights through geoid undulations and ellipsoidal heights derived from global navigation satellite system (GNSS), a process referred to as ‘GNSS levelling’. In this study, an efficient survey technology, the e-global navigation satellite system (e-GNSS), was used instead of static satellite surveying to execute GNSS levelling. The e-GNSS in Taiwan is based on Virtual Reference Station-Real-Time Kinematic technology and networks. The orthometric heights were calculated by subtracting the geoid undulations, derived from three geoid models (gravimetric, hybrid, and geometric models), from the ellipsoidal heights, derived from the e-GNSS. Additionally, two corrector methods, namely the difference and the corrector surface method, were adopted to improve the accuracies and the systematic errors. The experiment showed that the two corrector methods improved the accuracies of the orthometric heights in the gravimetric model by approximately 66.3 and 80.0% and mitigated the systematic errors in the gravity model by approximately 96.2 and 99.9%.