Report (M.S.)--Virginia Polytechnic Institute and State University. M.S. 1993. / Abstract. Includes bibliographical references (leaves 81-84). Also available via the Internet.

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International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Quartz crystal is an important electronic element in the field of communication systems, computer systems, etc. It is important to precisely measure the frequency of quartz crystal unit for manufacturing. The Pi-network transmission system recommended by International Electrotechnical Commission (IEC) is generally acknowledged as a measurement technique. However it needs a precise frequency source. The frequency source must be calibrated within a regular period in the process of manufacturing. Frequency counters, time internal counters, phase comparisons, which are the most common frequency calibrations, are introduced in the paper. Nowadays GPS has also become the primary system for frequency calibration. GPS receivers provide 1 PPS (Pulse Per Second) with accuracy < 100 nanoseconds to UTC under normal conditions. Motorola UT Oncore timing GPS with time accuracy < 50ns (1 sigma) uses time RAIM algorithm to ensure the validity and reliability of measurements. The comparison between the precise 1PPS and local reference is implemented. And the phase differences are logged and read by computer. According to the values, the frequency output of DDS is coordinated. In order to reduce the phase ambiguity, local reference is divided before comparison. The calibration can be implemented at any time by GPS. Block diagrams of calibration are presented in this paper.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Background and advantages of GPS based Remote Sensing are introduced, characteristics of forward scattered GPS signal such as polarization change, cross-correlation power variation, code delay due to the wave travel distance difference between direct and scattered signal, and cross-correlation power expansion due to sea surface roughness are discussed in detail. Working principle of the self-developed delay-mapping receiver is also presented. First data collection campaign is done at Inshore of BOHAI ocean with the delay-mapping receiver mounted on an airplane. Results show that the reflected signals has much variation than the direct signals, the code delay of the reflected signals varies as the receiver height and satellite elevation angle changes and expansion of the cross-correlation due to the wind driven surface was also demonstrated.

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Approved for public release; distribution is unlimited / Measurements of a 1230-km baseline were made during an eight-week period in the fall of 1987 using Trimble 4000SX single-frequency, five channel Global Positioning System (GPS) receivers. Twenty-eight days of carrier phase data were processed using correlated triple differences with fixed satellite orbits, the broadcast ephemerides, a modified Hopfield tropospheric model, and without ionospheric correction to determine the accuracies and precisions of the slope distance and baseline components. The data were processed in ever increasing observing sessions to determine the optimized observation periods required to achieve various orders of geodetic accuracies. The accuracies of the slope distances were better than 1.0 ppm for any observing period. The day-to-day repeatabilities of the slope distance measurements were better than 1.0 ppm (2) sigma after 20 minutes of observations. Accuracies and repeat-abilities (2 sigma) of the baseline components were better than 10.0 ppm after 20 minutes of observations. The correlated triple difference results were on the order of previous GPS surveys that used higher resolution differencing or external timing aids. Discussions include the effect of ephemeris, tropospheric and ionospheric errors, and dilution of precision. Observation periods and mean slope distance errors were reduced when observations started close to and included the infinite peak of the Position Dilution of Precision (PDOP). The smallest variances were associated with observations about the infinite PDOP peak / http://archive.org/details/optimizedobserva00bouc / Lieutenant, United States Navy

Thesis (S.M. in Transportation)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 101-103). / The pervasive location-based technologies, such as GPS and cell phone, help us find the pattern of geographical information of human behavior and also help dig opportunities in real world. In transportation field, they help people better understand the transportation behavior and at the same time collect necessary information for us. One important aspect of its application is how people choose the route given the existing urban network. However, dealing with the excessive amount of data and the modeling of route choice behavior are two major challenges in the route choice analysis.This thesis discusses the general process in the route choice analysis, from GPS data processing, map matching to the generation of route choice sets. Besides, the Path-Size logit model is implemented to address the modeling issue. In this thesis, I develop a new effective method, which I called Point-Based Local Search Map Matching, to match the consecutive GPS data to the network data. Also, I develop a new model, which I called Random Weight Choice Set Generation Model to deal with the choice set generation problem in the route choice analysis. The data comes from two major sources. One is the Boston car GPS data. It tells when and where a specific car is. The other is the Boston urban network data, which contains all types of roads in GIS format. / by Anyang Hou. / S.M.in Transportation