Height system of Taiwan from satellite and terrestrial data

The global positioning system (GPS), satellite altimetry, tide records, differential leveling, and a geoid model have been used to study the height system of Taiwan, Republic of China. Using the International GPS Service (IGS) orbit, the geocentric coordinates in International Terrestrial Reference Frame (ITRF) and the mean sea levels at six key tide stations around Taiwan were determined by GPS, and this result will contribute data to the permanent service of mean sea level. It is found by detailed field work and calibration that the vertical datum of Taiwan is defined to be the mean sea level of Keelung located at northern Taiwan. The vertical datum undergoes a secular rise at 1.28 mm/year which must be considered in defining future benchmark heights. It is shown that a good geoid model can be of many uses such as GPS leveling, detecting systematic errors in a leveling net and changes of benchmark heights. The relative sea surface topography (SST) values at tide stations were determined from satellite altimetry and GPS data, and their standard errors are mostly below 10 cm. The SST values are recommended to be used as weighted constraints in the adjustment of a leveling net. A preliminary connection of Taiwan's vertical datum to other regional datums has been examined by computing a global SST at a 600-km wavelength using the EGM96 geopotential model and TOPEX/POSEIDON altimetry.