A New Height Reference Network in Taiwan

The island of Taiwan is located in an active tectonic zone on the boundary of the Eurasian and Philippine Sea plates. Due to the continuous mountain building process in association with the collision of the two plates, it is very important for Taiwan to periodically re-survey the island so as to maintain the intrinsic accuracy requirement of its vertical reference network. The existing height network was created in 1979 by means of the spirit levelling technique with theoretical surface gravity quantities derived from the Geodetic Reference System 1967 (GRS67) normal gravity field. Because of the lack of use of actual gravity measurements in its creation, the existing network has been found to suffer from severe systematic errors in the central mountainous areas.In this paper, we present the design and implementation of a new national vertical datum in Taiwan, Taiwan Vertical Datum 2001 (TWVD2001). The new datum was developed by optimally combining geodetic levelling and surface gravity observations collected at 1010 newly established benchmarks within a network of 2200-km first-order levelling lines. The data analyses and adjustment computation were based on geopotential numbers. Both orthometric and normal heights were computed for the new vertical reference network.