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URN	etd-0705113-104933
Author	Jing-zhong Ding
Author's Email Address	m995080005@student.nsysu.edu.tw
Statistics	This thesis had been viewed 5575 times. Download 338 times.
Department	IAMPUT
Year	2012
Semester	2
Degree	Master
Type of Document
Language	zh-TW.Big5 Chinese
Title	Effects of sound speed variation and measurement errors on the positioning of a seafloor transponder
Date of Defense	2013-06-19
Page Count	67
Keyword	bilinear model linear model sound-speed profile positioning seafloor transponder GPS/Acoustic geodesy
Abstract	Plate motions over the past few million years have averaged 110 centimeters per year. To monitor such slight deformations in the crust by the GPS/Acoustic geodesy, the accuracy on the order of a few centimeters in positioning seafloor transponders is required. Temporal and spatial variability of sound speed in the water column, however, as well as the measurement error of sound speed, is a main limiting factor in the production of accurate acoustic ranging even though frequent conductivity-temperature-depth (CTD) casts are made. Therefore, in this study, various geometrical options for acoustic ranging are designed in the numerical simulation of GPS/Acoustic geodesy and the effects of various sound-speed measurement errors on the accuracy of transponder positioning are evaluated. The simulation results show that observing slant-range measurements symmetrically around the transponder can nullify sound-speed errors in the horizontal but not vertical positioning of a seafloor transponder. Sound-speed errors produce the vertical positioning error although the slant-range observations are well geometrically balanced. For reducing the effect of sound-speed variation on the precision of GPS/Acoustic seafloor geodesy, this study proposes two synthetic sound-speed profiles of the water column, one linear and the other bilinear, to approximate acoustic travel-time measurements. The approximating sound-speed profile is used in combination with the tomographic estimation in GPS/Acoustic geodesy to estimate the sound speed variation, such that the effect of sound speed variation on the accuracy of transponder positioning is reduced. The performance of the two synthetic models is evaluated for different types of CTD-derived sound-speed profiles and for the acoustic ranging observations collected from a field GPS/Acoustic survey. The evaluation results demonstrate that both the linear and bilinear models can effectively reduce the effect of sound-speed variation on the precision of GPS/Acoustic positioning.
Advisory Committee	Chi-Cheng Cheng - chair Chau-Chang Wang - co-chair Hsin-Hung Chen - advisor
Files	etd-0705113-104933.pdf Indicate in-campus at 0 year and off-campus access at 1 year.
Date of Submission	2013-08-05

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