Browsing by Author "Wang, CG"

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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.
Terrain correction computation using Gaussian quadrature
(2003-12-01)
Hwang, CW
;
Wang, CG
;
Hsiao, YS
;
土木工程學系
;
Department of Civil Engineering
A method and a program (tcq) in FORTRAN 90 based on Gaussian quadrature are developed to compute the terrain correction (TC). TCs were determined on 1010 benchmarks using the Gaussian quadrature, prism and FFT methods using a 3" x 3" elevation grid for the inner zone and a 30" x 30" elevation grid for the outer zone. In order to achieve a 0.1 mgal accuracy in TC while reducing the computing time, the best inner and outer radii for TC computation are 20 and 200 km, respectively. The Gaussian quadrature is a highly accurate numerical integrator and yields results that outperform those from the prism method and the FFT method. The singular problem of the kernel function in TC is treated by considering the innermost zone effect, which can be expressed as a complete elliptic integral of the first kind. The innermost zone effect must be taken into account if the required accuracy of TC is at a 1-mgal level. (C) 2003 Elsevier Ltd. All rights reserved.