Browsing by Author "Lee, LH"

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Adjustment of relative gravity measurements using weighted and datum-free constraints
(2002-11-01)
Hwang, CW
;
Wang, CG
;
Lee, LH
;
土木工程學系
;
Department of Civil Engineering
A program in FORTRAN 90 is developed which can adjust relative gravity measurements and solve for gravimeter parameters using the weighted constraint and datum-free constraint models. The weighted constraint model is chosen when there exist reliable a priori gravity values for use as supplementary data, or when it is required that a gravity network be attached to an existing gravity network of a higher order. The datum-free model uniquely determines relative gravity values among all stations without the need of a fixed gravity value, thus it is suitable for detecting relative gravity change. The optional solve-for gravimeter parameters include drift coefficients, and coefficients of the long wavelength and periodic components of calibration function. The program can also detect outliers in observations using the T-test method. A set of relative gravity data in Taiwan was used to test this program using five different choices of command-line arguments. The results show that there are no outliers in these data and that the estimated reading accuracy of the LaCoste and Romberg G meter (serial number 838) is about 0.02 mgal and the gravimeter drift rate is 0.9 mgal/month. The coefficients of the long wavelength and periodic components of calibration function are statistically equal to zero. The result from the datum-free solution is used to detect gravity variation due to the 1999 Chi-Chi earthquake, concluding that only one station experiences a significant change. (C) 2002 Elsevier Science Ltd. All rights reserved.
Single- and multiepoch analyses of global positioning system baseline network: Application to coordinate and velocity determinations in Central Taiwan
(2004-05-01)
Hwang, CW
;
Lee, LH
;
Yu, SB
;
Chen, HY
;
土木工程學系
Theories and computer programs are developed for single- and multiepoch analyses of a global positioning system (GPS) baseline network using the datum-free and weighted constraint solutions. Single-epoch analysis is for evaluating data quality, removing outliers, examining network precision, and estimating coordinates. Multiepoch analysis is for simultaneously determining epoch coordinates and station velocities. The datum-free solution yields estimable data residuals and relative coordinates and is suitable for adjusting data only and for detecting changes of relative coordinates. The weighted constraint solution allows a lower-order network to be attached to an existing, higher-order network. The analysis methods are applied to a multiepoch GPS baseline network in central Taiwan, which was hit by the 1999 Chi-Chi earthquake measuring 7.3 on the Richter scale. The velocities computed by the methods developed in this study are consistent with those from the Bernese GPS software. The result of the multiepoch analysis indicates that, in the first year after the Chi-Chi earthquake, the crust east of the Chelungpu Fault moved northwestwards at a mean rate of about 10 cm/year, while the crust west of the Chelungpu Fault moved in the opposite direction at a much lower speed.