Browsing by Author "Li, Yi-Shan"

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A Near-Real-Time Automatic Orbit Determination System for COSMIC and Its Follow-On Satellite Mission: Analysis of Orbit and Clock Errors on Radio Occultation
(2014-06-01)
Li, Yi-Shan
;
Hwang, Cheinway
;
Tseng, Tzu-Pang
;
Huang, Cheng-Yung
;
Bock, Heike
The COSMIC-2 mission is a follow-on mission of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) with an upgraded payload for improved radio occultation (RO) applications. The objective of this paper is to develop a near-real-time (NRT) orbit determination system, called NRT National Chiao Tung University (NCTU) system, to support COSMIC-2 in atmospheric applications and verify the orbit product of COSMIC. The system is capable of automatic determinations of the NRT GPS clocks and LEO orbit and clock. To assess the NRT (NCTU) system, we use eight days of COSMIC data (March 24-31, 2011), which contain a total of 331 GPS observation sessions and 12 393 RO observable files. The parallel scheduling for independent GPS and LEO estimations and automatic time matching improves the computational efficiency by 64% compared to the sequential scheduling. Orbit difference analyses suggest a 10-cm accuracy for the COSMIC orbits from the NRT (NCTU) system, and it is consistent as the NRT University Corporation for Atmospheric Research (UCAR) system. The mean velocity accuracy from the NRT orbits of COSMIC is 0.168 mm/s, corresponding to an error of about 0.051 mu rad in the bending angle. The rms differences in the NRT COSMIC clock and in GPS clocks between the NRT (NCTU) and the postprocessing products are 3.742 and 1.427 ns. The GPS clocks determined from a partial ground GPS network [from NRT (NCTU)] and a full one [from NRT (UCAR)] result in mean rms frequency stabilities of 6.1E-12 and 2.7E-12, respectively, corresponding to range fluctuations of 5.5 and 2.4 cm and bending angle errors of 3.75 and 1.66 mu rad.
Assessing antenna field of view and receiver clocks of COSMIC and GRACE satellites: lessons for COSMIC-2
(2014-04-01)
Tseng, Tzu-Pang
;
Zhang, Kefei
;
Hwang, Cheinway
;
Hugentobler, Urs
;
Wang, Chuan-Sheng
We provide suggestions for the approved COSMIC-2 satellite mission regarding the field of view (FOV) and the clock stability of its future GNSS receiver based on numerical analyses using COSMIC GPS data. While the GRACE GPS receiver is mounted on the zenith direction, the precise orbit determination (POD) antennas of COSMIC are not. The COSMIC antenna design results in a narrow FOV and a reduction in the number of GPS observations. To strengthen the GPS geometry, GPS data from two POD antennas of COSMIC are used to estimate its orbits. The phase residuals of COSMIC are at the centimeter level, compared to the millimeter level of GRACE. The receiver clock corrections of COSMIC and GRACE are at the microsecond and nanosecond levels, respectively. The clock spectra of COSMIC at the frequencies of 0-0.005 Hz contain significant powers, indicating potential systematic errors in its clock corrections. The clock stability, expressed by the Allan deviation, of COSMIC ranges from 10(-9) to 10(-11) over 1 to 10(4) s, compared to 10(-12) to 10(-14) for GRACE. Compared to USO-based clock of GRACE, the clock of COSMIC is degraded in its stability and is linked to the reduction of GPS data quality. Lessons for improvement of COSMIC-2 over COSMIC in FOV and receiver clock stability are given.
On paradox of transportation networks
(2007-01-01)
Cho, Hsun-Jung
;
Li, Yi-Shan
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
In transportation planning and network design, Braess paradox problem has been discussed for many decades. Those researches were originated from the simple network illustrated by Braess. Many works devoted to seek efficient methods to avoid the occurrence of paradox problem or find some rules for network designers to refer. Under arc-OD/path matrix is full column rank assumption i.e., the number of paths is less than the number of arcs plus origin/destination pairs, Dafermos and Nagurney derived the formulas to determine, whether Braess' paradox occurs in the network. In the large transportation networks, the number of path is larger than the number of arc, so their assumption is violated. The main purpose of this paper is to conquer the small network restriction. The generalized inverse method is used to relax the assumption presented by Dafermos and Nagurney.
On paradox of transportation networks
(2007)
Cho, Hsun-Jung
;
Li, Yi-Shan
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
In transportation planning and network design, Braess paradox problem has been discussed for many decades. Those researches were originated from the simple network illustrated by Braess. Many works devoted to seek efficient methods to avoid the occurrence of paradox problem or find some rules for network designers to refer. Under arc-OD/path matrix is full column rank assumption i.e., the number of paths is less than the number of arcs plus origin/destination pairs, Dafermos and Nagurney derived the formulas to determine, whether Braess' paradox occurs in the network. In the large transportation networks, the number of path is larger than the number of arc, so their assumption is violated. The main purpose of this paper is to conquer the small network restriction. The generalized inverse method is used to relax the assumption presented by Dafermos and Nagurney.
On paradox of transportation networks
(2007)
Cho, Hsun-Jung
;
Li, Yi-Shan
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
In transportation planning and network design, Braess paradox problem has been discussed for many decades. Those researches were originated from the simple network illustrated by Braess. Many works devoted to seek efficient methods to avoid the occurrence of paradox problem or find some rules for network designers to refer. Under arc-OD/path matrix is full column rank assumption i.e., the number of paths is less than the number of arcs plus origin/destination pairs, Dafermos and Nagurney derived the formulas to determine, whether Braess' paradox occurs in the network. In the large transportation networks, the number of path is larger than the number of arc, so their assumption is violated. The main purpose of this paper is to conquer the small network restriction. The generalized inverse method is used to relax the assumption presented by Dafermos and Nagurney.
Room temperature spin-polarized polariton lasers
(2013-01-01)
Hsu, Feng-Kuo
;
Li, Yi-Shan
;
Lin, Sheng-Di
;
Lai, Chih-Wei
;
電子工程學系及電子研究所
We report room temperature spin-polarize polariton lasing characteristics and dynamics of a planar InGaAs/GaAs microcavity under non-reasonant circularly polarized picosecond optical excitation. (C) 2013 Optical Society of America