Browsing by Author "Liu, Ya-Chi"

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Geocenter motion estimated from GRACE orbits: The impact of F10.7 solar flux
(2017-06-01)
Tseng, Tzu-Pang
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Hwang, Cheinway
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Sosnica, Krzysztof
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Kuo, Chung-Yen
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Liu, Ya-Chi
We assess the impact of orbit modeling on the origin offsets between GRACE kinematic and reduced-dynamic orbits. The origin of the kinematic orbit is the center of IGS network (CN), whereas the origin of the reduced-dynamic orbit is assumed to be the center of mass of the Earth (CM). Theoretically, the origin offset between these two orbits is associated with the geocenter motion. However, the dynamic property of the reduced-dynamic orbit is highly related to orbit parameterizations. The assessment of the F10.7 impact on the geocenter motion is implemented by using different orbit parameterization setups in the reduced-dynamic method. We generate two types of reduced-dynamic orbits using 15 and 240 empirical parameters per day from 2005 to 2012. The empirical parameter used in Bernese GNSS Software is called piece-wise constant empirical acceleration (PCA) and is mainly to absorb the non-gravitational forces mostly related to the atmospheric drag and solar radiation pressure. The differences between kinematic and dynamic orbits can serve as a measurement for geocenter. The RMS value of the geocenter measurement in the 15-PCA case is approximately 3.5 cm and approximately 2 cm in the 240-PCA case. The correlation between the orbit difference and F10.7 is about 0.90 in the 15-PCA case and -0.10 to 0 in the 240-PCA case. This implies that the reduced-dynamic orbit modeled with 240 PCAs absorbs the F10.7 variation, which aliases to the 15-PCA orbit solution. The annual amplitudes of the geocenter motion are 3.1, 3.1 and 2.5 mm in the 15-PCA case, compared to 0.9, 2.0 and 1.3 mm in the 240-PCA case in the X, Y and Z components, respectively. The 15-PCA solution is thus closer to the geocenter motions derived from other space-geodetic techniques. The proposed method is limited to the parameterizations in the reduced-dynamic approach. (C) 2016 COSPAR. Published by Elsevier Ltd. All rights reserved.
High-resolution depth and coastline over major atolls of South China Sea from satellite altimetry and imagery
(2016-04)
Hsiao, Yu-Shen
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Hwang, Cheinway
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Cheng, Yung-Sheng
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Chen, Liang-Chien
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Hsu, Hung-Jui
Current bathymetric models for the South China Sea (SCS) are largely based on predicted depths from gravity and sparse single-beam echo-sounder measurements. Such models lack high-resolution coastlines and shallow water bottom features around atolls and islands. This study refines the gravity field of the SCS using sea surface heights from measurements of satellite altimeter Geosat/GM, ERS-1/GM, Jason-1/GM and the original Cryosat-2. A new one-minute gravity anomaly grid is determined. The modeled gravity anomalies show a 6-mgal RMS discrepancy with shipborne measurements in shallow waters. An altimeter-only bathymetric model is derived from the new gravity grid by the gravity-geological method that uses the latest global and regional models of the ocean depth and marine gravity as a priori knowledge. The new model outperforms current SCS bathymetric models and is accurate to 100 m, based on comparison with multi-beam depth measurements. Optical images from IKONOS-2, QuickBird-2, GeoEye-1, WorldView-1-2 and -3, are rectified and digitized to derive the zero (coastline) and 20-m depth contours (reef lines) around 44 atolls, which are integrated with the altimeter-only depths, giving significantly improved accuracies and spatial resolutions in modeled depths. The improvement percentages of coastlines by the satellite imagery range from 50% to 97% at 41 of the 44 atolls. We establish a webpage for free access to the optical and depth images, and the depth and gravity grids. We will continue to update satellite images, altimeter-derived gravity grids and bathymetric models over major atolls of the SCS. (C) 2016 Elsevier Inc. All rights reserved.
Root Cause Analysis and Correction of Single Metal Contact Open-Induced Scan Chain Failure in 90nm node VLSI
(2017-01-01)
Ting, Chao-Cheng
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Liu, Ya-Chi
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Chen, Hsuan-Hsien
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Tsai, Chung-Ching
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Shih, Liwen
In this paper, the localization of open metal contact for 90nm node SOC is reported based on Electron Beam Absorbed Current (EBAC) technique and scan diagnosis for the first time. According to the detected excess carbon, silicon and oxygen signals obtained from X-ray energy dispersive spectroscopy (EDX), the failure was deemed to be caused by the incomplete removal of silicate photoresist polymer formed during the O-2 plasma dry clean before copper plating. Based on this, we proposed to replace the dry clean with diluted HF clean prior to the copper plating, which can significantly remove the silicate polymers and increase the yield.
Sediment-Mass Accumulation Rate and Variability in the East China Sea Detected by GRACE
(2016-09-01)
Liu, Ya-Chi
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Hwang, Cheinway
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Han, Jiancheng
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Kao, Ricky
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Wu, Chau-Ron
The East China Sea (ECS) is a region with shallow continental shelves and a mixed oceanic circulation system allowing sediments to deposit on its inner shelf, particularly near the estuary of the Yangtze River. The seasonal northward-flowing Taiwan Warm Current and southward-flowing China Coastal Current trap sediments from the Yangtze River, which are accumulated over time at rates of up to a few mm/year in equivalent water height. Here, we use the Gravity Recovery and Climate Experiment (GRACE) gravity products from three data centres to determine sediment mass accumulation rates (MARs) and variability on the ECS inner shelf. We restore the atmospheric and oceanic effects to avoid model contaminations on gravity signals associated with sediment masses. We apply destriping and spatial filters to improve the gravity signals from GRACE and use the Global Land Data Assimilation System to reduce land leakage. The GRACE-derived MARs over April 2002-March 2015 on the ECS inner shelf are about 6 mm/year and have magnitudes and spatial patterns consistent with those from sediment-core measurements. The GRACE-derived monthly sediment depositions show variations at time scales ranging from six months to more than two years. Typically, a positive mass balance of sediment deposition occurs in late fall to early winter when the southward coastal currents prevail. A negative mass balance happens in summer when the coastal currents are northward. We identify quasi-biennial sediment variations, which are likely to be caused by quasi-biennial variations in rain and erosion in the Yangtze River basin. We briefly explain the mechanisms of such frequency-dependent variations in the GRACE-derived ECS sediment deposition. There is no clear perturbation on sediment deposition over the ECS inner shelf induced by the Three Gorges Dam. The limitations of GRACE in resolving sediment deposition are its low spatial resolution (about 250 km) and possible contaminations by land hydrological and oceanic signals. Potential GRACE-derived sediment depositions in six major estuaries are presented.
The development of low-temperature atomic layer deposition of HfO2 for TEM sample preparation on soft photo-resist substrate
(2018-01-01)
Peng, Kang-Ping
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Liu, Ya-Chi
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Lin, I-Feng
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Lin, Chih-Chien
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Huang, Shu-Wei
In this study, the method of low-temperature atomic layer deposition (ALD), which is applied on the soft photo-resist (PR) substrate forming hafnium dioxide (HfO2) at 40 degrees C to 85 degrees C, is reported for the first time. This reveals the potential application in the TEM sample preparation. The thickness, refractive index, band gap, and depth profiling chemical state of the thin film are analyzed by ellipsometry, X-ray diffraction, and photoelectron spectroscopy respectively. Our TEM image shows a clear boundary between the photo-resist and hafnium dioxide deposited on PR, which indicates the low-temperature atomic layer deposition (ALD) may lead a new way for TEM sample preparation in advanced technology node.