Estimating Ocean Tidal Constituents Using SAR Interferometric Time Series over the Sulzberger Ice Shelf, W. Antarctica

백상호,Shum, C. K. 한국측량학회 2018 한국측량학회지 Vol.36 No.5

Ocean tides in Antarctica are not well constrained mostly due to the lack of tidal observations. Especially, tides underneath and around ice shelves are uncertain. InSAR (Interferometric Synthetic Aperture Radar) data has been used to observe ice shelf movements primarily caused by ocean tides. Here, we demonstrate that it is possible to estimate tidal constituents underneath the Sulzberger ice shelf, West Antarctica, solely using ERS-1/2 tandem mission DInSAR (differential InSAR) observations. In addition, the tidal constituents can be estimated in a high-resolution (~200 m) grid which is beyond any tidal model resolution. We assume that InSAR observed ocean tidal heights can be derived after correcting the InSAR data for the effect of atmospheric loading using the inverse barometric effect, solid earth tides, and ocean tide loading. The ERS (European Remote Sensing) tandem orbit configuration of a 1-day separation between SAR data takes diminishes the sensitivity to major tidal constituents including K1 and S2. Here, the dominant tidal constituent O1 is estimated using 8 differential interferograms underneath the Sulzberger ice shelf. The resulting tidal constituent is compared with a contemporary regional tide model (CATS2008a) and a global tide model (TPXO7.1). The InSAR estimated tidal amplitude agrees well with both models with RMS (root-mean-square) differences of < 2.2 cm and the phase estimate corroborating both tide models to within 8˚. We conclude that fine spatial scale (~200 m) Antarctic ice shelf ocean tide determination is feasible for dominant constituents using C-band ERS-1/2 tandem mission InSAR.

Spaceborne Gravity Sensors for Continental Hydrology and Geodynamic Studies

Shum C. K.,Han Shin-Chan,Braun Alexander The Korean Society of Remote Sensing 2005 大韓遠隔探査學會誌 Vol.21 No.1

The currently operating NASA/GFZ Gravity Recovery and Climate Experiment (GRACE) mission is designed to measure small mass changes over a large spatial scale, including the mapping of continental water storage changes and other geophysical signals in the form of monthly temporal gravity field. The European Space Agency's Gravity field and steady state Ocean Circulation Explorer (GOCE) space gravity gradiometer (SGG) mission is anticipated to determine the mean Earth gravity field with an unprecedented geoid accuracy of several cm (rms) with wavelength of 130km or longer. In this paper, we present a summary of present GRACE studies for the recovery of hydrological signals in the Amazon basin using alternative processing and filtering techniques, and local inversion to enhance the temporal and spatial resolutions by two-folds or better. Simulation studies for the potential GRACE detection of slow deformations due to Nazca-South America plate convergence and glacial isostatic adjustment (GIA) signals show that these signals are at present difficult to detect without long-term data averaging and further improvement of GRACE measurement accuracy.

Spaceborne Gravity Sensors for Continental Hydrology and Geodynamic Studies

C. K. Shum,Shin Chan Han,Alexander Braun 大韓遠隔探査學會 2005 大韓遠隔探査學會誌 Vol.21 No.1

The currently operating NASA/GFZ Gravity Recovery and Climate Experiment (GRACE) mission is designed to measure small mass changes over a large spatial scale, including the mapping of continental water storage changes and other geophysical signals in the form of monthly temporal gravity field. The European Space Agency`s Gravity field and steady state Ocean Circulation Explorer (GOCE) space gravity gradiometer (SGG) mission is anticipated to determine the mean Earth gravity field with an unprecedented geoid accuracy of several cm (rms) with wavelength of 130 km or longer. In this paper, we present a summary of present GRACE studies for the recovery of hydrological signals in the Amazon basin using alternative processing and filtering techniques, and local inversion to enhance the temporal and spatial resolutions by two-folds or better. Simulation studies for the potential GRACE detection of slow deformations due to Nazca-South America plate convergence and glacial isostatic adjustment (GIA) signals show that these signals are at present difficult to detect without long-term data averaging and further improvement of GRACE measurement accuracy.

Optimal wind-induced load combinations for structural design of tall buildings

C.M. Chan,F. Ding,K.T. Tse,M.F. Huang,K.M. Shum,K.C.S. Kwok 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.29 No.5

Wind tunnel testing technique has been established as a powerful experimental method for predicting wind-induced loads on high-rise buildings. Accurate assessment of the design wind load combinations for tall buildings on the basis of wind tunnel tests is an extremely important and complicated issue. The traditional design practice for determining wind load combinations relies partly on subjective judgments and lacks a systematic and reliable method of evaluating critical load cases. This paper presents a novel optimization-based framework for determining wind tunnel derived load cases for the structural design of wind sensitive tall buildings. The peak factor is used to predict the expected maximum resultant responses from the correlated three-dimensional wind loads measured at each wind angle. An optimized convex hull is further developed to serve as the design envelope in which the peak values of the resultant responses at any azimuth angle are enclosed to represent the critical wind load cases. Furthermore, the appropriate number of load cases used for design purposes can be predicted based on a set of Pareto solutions. One 30-story building example is used to illustrate the effectiveness and practical application of the proposed optimization-based technique for the evaluation of peak resultant wind-induced load cases.

티베트 암석권의 분리 습곡 구조 모델

신영홍(Younghong Shin),C.K. Shum,C. Braitenberg,나성호(Sungho Na),이상묵(Sangmook Lee),임무택(Mutaek Lim),C. Dai,C. Zhang 대한지질학회 2018 대한지질학회 학술대회 Vol.2018 No.10

Three-dimensional fold structure of the Tibetan Moho from GRACE gravity data

Shin, Young Hong,Shum, C.-K.,Braitenberg, Carla,Lee, Sang Mook,Xu, Houze,Choi, Kwang Sun,Baek, Jeong Ho,Park, Jong Uk American Geophysical Union 2009 Geophysical research letters Vol.36 No.1

Can bedside patient-reported numbness predict postoperative ambulation ability for total knee arthroplasty patients with nerve block catheters?

Edward R. Mariano,Seshadri C. Mudumbai,Toni Ganaway,T. Edward Kim,Steven K. Howard,Nicholas J. Giori,Cynthia Shum 대한마취통증의학회 2016 Korean Journal of Anesthesiology Vol.69 No.1

Background: Adductor canal catheters offer advantages over femoral nerve catheters for knee replacement patients because they produce less quadriceps muscle weakness; however, applying adductor canal catheters in bedside clinical practice remains challenging. There is currently no patient-reported outcome that accurately predicts patients’ physical function after knee replacement. The present study evaluates the validity of a relatively new patient-reported outcome, i.e., a numbness score obtained using a numeric rating scale, and assesses its predictive value on postoperative ambulation. Methods: We conducted a retrospective cohort study pooling data from two previously-published clinical trials using identical research methodologies. Both studies recruited patients undergoing knee replacement; one studied adductor canal catheters while the other studied femoral nerve catheters. Our primary outcome was patient-reported numbness scores on postoperative day 1. We also examined postoperative day 1 ambulation distance and its association with postoperative numbness using linear regression, adjusting for age, body mass index, and physical status. Results: Data from 94 subjects were included (femoral subjects, n = 46; adductor canal subjects, n = 48). Adductor canal patients reported decreased numbness (median [10th–90th percentiles]) compared to femoral patients (0 [0–5] vs. 4 [0–10], P = 0.001). Adductor canal patients also ambulated seven times further on postoperative day 1 relative to femoral patients. There was a significant association between postoperative day 1 total ambulation distance and numbness (Beta = −2.6; 95% CI: −4.5, −0.8, P = 0.01) with R2 = 0.1. Conclusions: Adductor canal catheters facilitate improved early ambulation and produce less patient-reported numbness after knee replacement, but the correlation between these two variables is weak.

The effects of topography on local wind-induced pressures of a medium-rise building

Hitchcock, P.A.,Kwok, K.C.S.,Wong, K.S.,Shum, K.M. Techno-Press 2010 Wind and Structures, An International Journal (WAS Vol.13 No.5

Wind tunnel model tests were conducted for a residential apartment block located within the complex terrain of The Hong Kong University of Science and Technology (HKUST). The test building is typical of medium-rise residential buildings in Hong Kong. The model study was conducted using modelling techniques and assumptions that are commonly used to predict design wind loads and pressures for buildings sited in regions of significant topography. Results for the building model with and without the surrounding topography were compared to investigate the effects of far-field and near-field topography on wind characteristics at the test building site and wind-induced external pressure coefficients at key locations on the building facade. The study also compared the wind tunnel test results to topographic multipliers and external pressure coefficients determined from nine international design standards. Differences between the external pressure coefficients stipulated in the various standards will be exacerbated when they are combined with the respective topographic multipliers.

The effects of topography on local wind-induced pressures of a medium-rise building

P.A. Hitchcock,K.C.S. Kwok,K.S. Wong,K.M. Shum 한국풍공학회 2010 Wind and Structures, An International Journal (WAS Vol.13 No.5

Wind tunnel model tests were conducted for a residential apartment block located within the complex terrain of The Hong Kong University of Science and Technology (HKUST). The test building is typical of medium-rise residential buildings in Hong Kong. The model study was conducted using modelling techniques and assumptions that are commonly used to predict design wind loads and pressures for buildings sited in regions of significant topography. Results for the building model with and without the surrounding topography were compared to investigate the effects of far-field and near-field topography on wind characteristics at the test building site and wind-induced external pressure coefficients at key locations on the building façade. The study also compared the wind tunnel test results to topographic multipliers and external pressure coefficients determined from nine international design standards. Differences between the external pressure coefficients stipulated in the various standards will be exacerbated when they are combined with the respective topographic multipliers.

Topography, Vertical and Horizontal Deformation In the Sulzberger Ice Shelf, West Antarctica Using InSAR

Kwoun Oh-Ig,Baek Sangho,Lee Hyongki,Sohn Hong-Gyoo,Han Uk,Shum C. K. The Korean Society of Remote Sensing 2005 大韓遠隔探査學會誌 Vol.21 No.1

We construct improved geocentric digital elevation model (DEM), estimate tidal dynamics and ice stream velocity over Sulzberger Ice Shelf, West Antarctica employing differential interferograms from 12 ERS tandem mission Synthetic Aperture Radar (SAR) images acquired in austral fall of 1996. Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry profiles acquired in the same season as the SAR scenes in 2004 are used as ground control points (GCPs) for Interferometric SAR (InSAR) DEM generation. 20 additional ICESat profiles acquired in 2003-2004 are then used to assess the accuracy of the DEM. The vertical accuracy of the OEM is estimated by comparing elevations with laser altimetry data from ICESat. The mean height difference between all ICESat data and DEM is -0.57m with a standard deviation of 5.88m. We demonstrate that ICESat elevations can be successfully used as GCPs to improve the accuracy of an InSAR derived DEM. In addition, the magnitude and the direction of tidal changes estimated from interferogram are compared with those predicted tidal differences from four ocean tide models. Tidal deformation measured in InSAR is -16.7cm and it agrees well within 3cm with predicted ones from tide models. Lastly, ice surface velocity is estimated by combining speckle matching technique and InSAR line-of-sight measurement. This study shows that the maximum speed and mean speed are 509 m/yr and 131 m/yr, respectively. Our results can be useful for the mass balance study in this area and sea level change.