National datum uncertainty due to reference frame transformation: Case study for the geodetic datum of Taiwan

With the advent of global navigation satellite systems (GNSSs), many national geodetic datums have been established with modern technology and referenced to a specific epoch of the international terrestrial reference frame (ITRF) definition. Following the static datum concept, the datum remains unchanged after its publication, which consequently creates problems in datum maintenance. In the recent update of TWD97, the national datum presently used in Taiwan, the resurvey coordinates are transformed back to the original frame but expressed in a recent epoch. In this study, the uncertainties resulting from the transformation between ITRF definitions in the region of Taiwan were investigated. Based on error propagation, a standard error of ±7 cm was estimated due to the transformation of the TWD97 coordinates between ITRF2005(2010.0) and ITRF94(2010.0). The uncertainties propagated from transformation parameters are more significant than those from station coordinates and velocities, and the uncertainty expands with the time interval. The SD is ±1.1 cm for the transformation between ITRF2005 and ITRF2000. Considering that the uncertainty between later definitions is much smaller than transforming to ITRF94, it may be preferable to replace the ITRF94 with a modern ITRF definition, at least ITRF2000, for the next TWD97 datum maintenance.