Monday 22 August 2005

G4

PM0029
Estimation of horizontal movement function for geodetic - or mapping-oriented maintenance in the Taiwan area
Chang, Chia-Chyang¹, Huang, Huei-Chi²
1 Chung Cheng Institute Of Technology, Taiwan
2 Armaments Bureau, Taiwan
The concept of dynamic datum, in which the coordinates of control stations are time-varying, was the initiative to this study. The test area was selected for a deformation active island, i.e. Taiwan, and categorised into several regional groups depending on the similar pattern of the horizontal land movement. The velocity field consisting of 105 first-order control stations in the Taiwan area was computed using GPS measurements carried out in 1997 and 2000. The regional movement functions based on the information of velocity field can then be estimated with several mathematical models, e.g. the average, weighting mean, first and second order surface fitting. Moreover, the functions have been practically applied to estimate and examine the horizontal coordinate movement in different regions. It is expected to utilize the simplified mathematical function to predict the coordinate quality of the control station in a time span and determine a suitable period for geodetic- or mapping-oriented maintenance. Based on the internal precision of the function estimates, it is noted that the horizontal movement obtained using the second order surface fitting model is best agreed by ±1.2 cm. This set of function has also been tested with the GPS-based coordinates computed by an independent data set measured in 2002 for realising its external accuracy. The results show that the RMS differences are approximately ±6 cm for the estimates of horizontal movement over a time scale of 2 years. It is, hence, suggested that the coordinates of the first-order GPS control stations in the Taiwan area are able to maintain the quality for only 2-5 years. Moreover, the revision of 1/1,000 digital topographic map is estimated to be required for every 5-11 years in the test area.

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