Use of geoid for assessing trigonometric height accuracy and detecting vertical land motion

An improved geoid model for Taiwan was developed using land and sea gravity anomalies and altimeter-derived geoid gradients by least-squares collocation. The estimated model accuracy ranges from 2 cm in the flat area to 10 cm in the mountainous area. This geoid model, along with GPS ellipsoidal heights, is used to determine the errors of the "orthometric heights" at Taiwan's first-order triangulation stations, yielding an RMS error of 0.97 m. Yushan, east Asia's highest peak, is now estimated to be 3, 950.50 m above the mean level at Keelung from this geoid model and GPS measurements. With recent measured ellipsoidal heights at 33 benchmarks in eastern Taiwan, an average uplift rate of 4.46 cm/year is found along the Longitudinal Valley, and 3.02 cm/year along the coastal highway. This uplift is the result of the collision between the Philippine Sea plate and the Eurasian plate, and the rates are consistent with those derived from terrestrial measurements and tide gauge records.