Numerical modeling of displacements due to ocean tide loading: case study at GPS stations in Taiwan and western Pacific

Abstract

We model the horizontal and radial displacements due to ocean tidal loading (OTL) in a computer program DISOTL (DISplacements due to Ocean Tide Loading). Numerical modeling of OTL considers inner and outer zone contributions. A local tide model and shoreline defined by a GMT and Taiwan digital elevation model is used for the inner zone. OTL-induced displacements from DISOTL, GOTIC2, and BS computer programs differ at the millimeter level in amplitude, but the phase difference can be over 10 degrees. Such displacements at 13 IGS stations in the western Pacific can be up to 8.5 cm in amplitude (KWJ1, Marshall Islands). At stations around Taiwan, the radial displacements can be up to 5.5 cm (MZUM, Matzu Islands). This implies that such large OTL effects (over 1 cm) will have a profound influence on precise global positioning system (GPS) positioning. To establish a new GPS reference frame in Taiwan, the use of a precise computer program is critical. A case study of coastal and offshore-island GPS continuous stations suggests that DISOTL can model OTL corrections to a 1 mm accuracy and reduce coordinate variations by up to 35%.