SGOTL: A Computer Program for Modeling High-Resolution, Height-Dependent Gravity Effect of Ocean Tide Loading

Hwang, Cheinway; Huang, Jen-Wei

doi:10.3319/tao.2011.10.06.02(oc)

Cited by 11 publications

(10 citation statements)

References 19 publications

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“…The improved accuracies are most pronounced at the sites with elevations > 1000 m, suggesting that the altitude of a gravity site should be considered when computing the OTL effect. This conclusion is consistent with that made in Hwang and Huang (2012).…”

Section: Adjustments Of Relative Gravity Measurementssupporting

confidence: 93%

“…The temporal gravity effects due to solid earth tide in all gravity measurements were removed using the model values of ETGAB (Wenzel, 2002;Dehant et al, 1999). The Newtonian effect and the loading effect of ocean tides (called OTL correction) were removed using the FES2004 tide model (Letellier et al, 2004) and the SGOTL software (Hwang and Huang, 2012), which considers the elevation of a gravity site. We also removed the effects of barometric pressure and polar motions using a SG-based gravity-atmosphere admittance coe cient (see below) and the earth rotation parameters from the International Earth Rotation Service and Reference Systems.…”

Section: Gravity Data Collections and Correctionsmentioning

confidence: 99%

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Delineating a Volcanic Aquifer Using Groundwater-induced Gravity Changes in the Tatun Volcano Group, Taiwan

Lien

Chang

Hwang

et al. 2021

Preprint

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The Tatun Volcanic Group (TVG) is an active volcano that could cause volcanic hazards in northern Taiwan. The latest phreatic eruption of the TVG occurred some 6000 years ago. Understanding the state of groundwater around the TVG can be a crucial step towards effectively assessing the risk of phreatic explosion by providing information about the sources of groundwater and the media it flows. We measured gravity changes at a superconducting gravity station and several groundwater-sensitive sites to examine the way the groundwater altered the gravity values around the TVG. Groundwater-induced gravity changes are simulated by two hydrological models (A and B). Both models show coherent seasonal variations in groundwater level and gravity value in the center of the TVG (Chintiengang). This coherence indicates inter-connected porous media for free groundwater flows below Chintiengang. However, inconsistencies between the modeled and observed gravity changes occurred in the eastern part of the TVG, suggesting here highly heterogeneous formations with fractures and barriers may exist below Chihsinshan and Dayoukeng. The gravity consistencies and inconsistencies between the observations and the models are used to delineate a volcanic aquifer, which can provide additional information for assessing the probability of a potential phreatic eruption over the TVG.

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Section: Adjustments Of Relative Gravity Measurementssupporting

confidence: 93%

Section: Gravity Data Collections and Correctionsmentioning

confidence: 99%

Delineating a Volcanic Aquifer Using Groundwater-induced Gravity Changes in the Tatun Volcano Group, Taiwan

Lien

Chang

Hwang

et al. 2021

Preprint

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“…It has been suggested that station elevation also affects the calculation results of tidal gravity loading effect (Hwang and Huang, 2012). Some of the stations used in this study have large elevations; CBS and MDJ are at > 1000 m. If a uniform elevation is used to calculate tidal loading, the accuracy of the calculation results will have an error of ~1.7× 10 −8 ms −2 .…”

Section: Ocean Tide Modelsmentioning

confidence: 95%

Influence of ocean tidal loading on continuous gravity observations in eastern China

Zhao

Jin

et al. 2022

Preprint

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Global and regional ocean tidal models were used to analyze the gravity effects of ocean tidal loading on continuous gravity observations in eastern China. The accuracies of tidal loading gravity correction results for 21 gPhone and superconducting gravity stations were evaluated. The global ocean tidal model was most effective for gravity correction at inland stations (up to 90%), but less effective at coastal stations (only 60%). Taking into account regional ocean tidal models, the effectiveness of tidal loading correction increased to 80%, and the root sum square of the residual gravity series was 0.7450 ~ 0.9733\({\times 10}^{-8}\text{m}{\text{s}}^{-2}\). The best tidal loading gravity correction was obtained by combing the global FES2004 model and regional OSU.chinasea.2010 model (root sum square of 0.7450\({\times 10}^{-8}\text{m}{\text{s}}^{-2}\)). Using this combination, the tidal loading gravity amplitude in the China Sea and adjacent areas was calculated; tidal loading gravity was. Very low gravity effects were obtained inland and for island interiors; however, tide loading gravity was relatively larger along the coast, especially the southeast coast and Bohai Bay. Moreover, the amplitude changed drastically possibly owing to offshore topography. Our results provide a reference for selecting ocean tidal models for high-precision analysis of continuous gravity observations in China.

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“…The observed gravity changes in April, July, September, and November 2012. The stations Y20 (Chishinshan), YMSG (Chintiengang), Y08 (Dayoukeng), and Y03, at the different geological backgrounds, are denoted Lien et al Terrestrial, Atmospheric and Oceanic Sciences (2022) 33:31 2004) and the SGOTL software (Hwang and Huang 2012), which takes the elevation of the gravity site into account. The OTL correction preformed using SGOTL improved the point gravity accuracies in the adjustments by 1.4% to 6.2% compared to the cases where OTL correction was not applied.…”

Section: Figmentioning

confidence: 99%

Delineating a volcanic aquifer using groundwater-induced gravity changes in the Tatun Volcano Group, Taiwan

Lien

Chang

Hwang

et al. 2022

Terr Atmos Ocean Sci

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The Tatun Volcanic Group (TVG) is an active volcanic system that poses potential volcanic hazards to northern Taiwan. Groundwater migration can be sensitive to volcanic activities and can induce temporal gravity changes. Here we conducted four gravity measurement campaigns in 2012 with two CG5 relative gravimeters at a total of 31 gravity monitoring sites to probe the spatiotemporal groundwater variability in the TVG area. With careful adjustments to the gravity measurements, the standard point gravity error was approximately 8 μGal on average. The observed gravity changes were compared with the groundwater-induced gravity variations derived from two hydrological models: the continuous flow model that consisted of one permeable layer (Model A) and a dynamic groundwater flow model that used the hydrological solver MODFLOW (Model B). The results show that only gravity observations in the central TVG match the simulated gravity pattern, i.e., the hydrology in the central TVG follows free groundwater flows within the interconnected and porous strata. On the other hand, inconsistencies between simulated and observed gravity changes range from + 40 to – 80 μGal. The discrepancies were located at the eastern and western areas in the TVG and showed opposite variations over time. This pattern of temporal variability cannot be attributed to the use of shallow aquifer models that merely reflect the surface recharges and discharges. We infer that the pattern stems from deep flows, such as hydrothermal fluids alternately replenishing aquifers to the east and west of the TVG, i.e., deep fluid conduits may have developed to the east and west of the TVG and bypassed the central area.

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SGOTL: A Computer Program for Modeling High-Resolution, Height-Dependent Gravity Effect of Ocean Tide Loading

Cited by 11 publications

References 19 publications

Delineating a Volcanic Aquifer Using Groundwater-induced Gravity Changes in the Tatun Volcano Group, Taiwan

Delineating a Volcanic Aquifer Using Groundwater-induced Gravity Changes in the Tatun Volcano Group, Taiwan

Influence of ocean tidal loading on continuous gravity observations in eastern China

Delineating a volcanic aquifer using groundwater-induced gravity changes in the Tatun Volcano Group, Taiwan

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