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收集所有交通大學研究人員與學生個人或團體所發表之各項學術著作，涵蓋期刊論文、教師專書、學位論文等項。;;Collections of Publications of NCTU Researchers and Students Like Journal Papers and Thesis.

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🏛️國立陽明交通大學機構典藏

Author: search.filters.author.Hsiao, Yu-ShenSubject: search.filters.subject.Gravity anomaly

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Now showing 1 - 3 of 3
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    Topography-Assisted downward Continuation of Airborne Gravity: An Application for Geoid Determination in Taiwan
    (2010-08-01)
    Hsiao, Yu-Shen
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    Hwang, Cheinway
    ;
    土木工程學系
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    Department of Civil Engineering
    We investigated the Fourier transform-based downward continuation (DWC) of airborne gravity anomalies around Taiwan assisted by topographic information. The topographic data are from the latest collections of elevations and ocean depths. The DWC employs a remove-compute-restore (RCR) procedure in which the topography is removed prior to computation and then restored to achieve stable solutions. The topographic gravity effect is evaluated point-wise using the Gaussian quadrature. A Gaussian filter with an optimal smoothing parameter reduces the noise-amplifying effect of DWC. Use of topography in DWC leads to improvements of 3 to 6 mgal of gravity on land. Surface and downward continued gravity anomalies are used to determine geoidal heights by least squares collocation (LSC) in a similar RCR procedure through the same topographic data. The accuracy of the geoidal heights at Taiwan's first-order leveling benchmarks is improved by 1 to 2 cm due to inclusion of downward continued airborne gravity.
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    New free-air and Bouguer gravity fields of Taiwan from multiple platforms and sensors
    (2014-01-25)
    Hwang, Cheinway
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    Hsu, Hung-Jui
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    Chang, Emmy T. Y.
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    Featherstone, W. E.
    ;
    Tenzer, Robert
    We construct 1' x 1' grids of free-air and Bouguer gravity anomalies around Taiwan with well-defined error estimates for quality assessment. The grids are compiled from land, airborne and shipbome gravity measurements, augmented with altimeter gravity at sea. Three sets of relative land gravity measurements are network-adjusted and outlier-edited, yielding accuracies of 0.03-0.09 mGal. Three airborne gravity sets are collected at altitudes 5156 and 1620 m with accuracies of 2.57-2.79 mGal. Seven offshore shipborne gravity campaigns around Taiwan and its offshore islands yield shallow-water gravity values with 0.88-2.35 mGal accuracies. All data points are registered with GPS-derived geodetic coordinates at cm-dm accuracies, allowing for precise gravity reductions and computing gravity disturbances. The various datasets are combined by the band-limited least-squares collocation in a one-step procedure. In the eastern mountainous (or offshore) region, Bouguer anomalies and density contrasts without considering the oceanic (or land) topographic contribution are underestimated. The new grids show unprecedented tectonic features that can revise earlier results, and can be used in a broad range of applications. (C) 2013 Elsevier B.V. All rights reserved.
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    Analysis of Alabama Airborne Gravity at Three Altitudes: Expected Accuracy and Spatial Resolution from a Future Tibetan Airborne Gravity Survey
    (2013-08-01)
    Huang, Chi-Hsun
    ;
    Hwang, Cheinway
    ;
    Hsiao, Yu-Shen
    ;
    Wang, Yan Ming
    ;
    Roman, Daniel R.
    In situ airborne gravity data at altitudes of 11, 6.3, and 1.7 km over a smooth area of Alabama are used to assess gravity accuracy and errors in upward and downward continuations. Analysis of the Alabama free-air anomaly gravity data at crossover points at the three altitudes suggests 1 - 2 mgal accuracy for the dataset. Gravity data at each altitude are then expanded into local 3D Fourier series, to prepare for continuation. This Fourier representation results in continuation errors at few-mgal level in Alabama, even in the extreme case of downward continuation from 11 km to sea level. The result in Alabama inspires an airborne gravity survey over the rough, inaccessible terrain of Tibet. Similar investigations as in Alabama are made in Tibet using EGM08-derived airborne gravity data at flight altitudes of 10, 5, and 0 km. Bouguer anomalies at the 10-km altitude preserve the major tectonic features of Tibet. Downward continuation errors increase with terrain roughness, but the survey can enhance local tectonic features. This study highlights the value of a future Tibetan airborne gravity survey and points out the expected gravity accuracy and spatial resolution from this survey.