Thesis (M.S.C.I.T.)--Regis University, Denver, Colo., 2006. / Title from PDF title page (viewed on May 24, 2006). Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references and index.

Using observations from the Global Positioning System (GPS) satellites to determine a three dimensional (3-D) geodetic control network are considered. The repeatability of individual baselines and 3-D vector closures are examined, in order to investigate refraction effects on GPS networks. The effect on GPS baselines of a height bias in the reference point's coordinates is also investigated. A least squares adjustment program is developed and used to obtain a single consistent set of 3-D coordinates for the Tygerberg Test Network (TTN). The results of two GPS processing packages are compared by means of a conformal transformation. It is concluded that single frequency measurements produce better results than the ionospheric free observable on short baselines. Furthermore, a standard atmospheric model shows an improvement over the Marini model to account for tropospheric refraction.

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Includes bibliographical references / Global Navigation Satellite Systems (GNSS) are used to provide information on position, time and velocity all over the world at any time of the day. Currently there are four operational GNSS and one of them is GPS (Global Positioning System) that is developed and maintained by U.S Department of Defence (DoD), which is widely used and accessible all over the world. The accuracy of the output or even the availability of the navigation system depends on current space weather conditions, which can cause random fluctuations of the phase and amplitude of the received signal, called scintillation. Interference of GNSS signals that are reflected and refracted from stationary objects on the ground, with signals that travel along a direct path via the ionosphere to the antenna, cause errors in the measured amplitude and phase. These errors are known as multipath errors and can lead to cycle slip and loss of lock on the satellite or degradation in the accuracy of position determination. High elevation cut off angles used for filtering GNSS signals, usually 15-30°, can reduce non-ionospheric interference due to multipath signals coming from the horizon. Since a fixed-elevation threshold does not take into consideration the surrounding physical environment of each GPS station, it can result in a significant loss of valuable data. Alternatively, if the fixed-elevation threshold is not high enough we run the risk of including multipath data in the analysis. In this project we characterized the multipath environment of the GPS Ionospheric Scintillation and TEC (Total Electron Content) Monitor (GISTM) receivers installed by SANSA (South African National Space Agency) at Gough Island (40:34oS and 9:88° W), Marion Island (46:87° S and 37:86° E), Hermanus (34:42° S and19:22° E) and SANAE IV (71:73° S and 2:2° W) by plotting azimuth-elevation maps of scintillation indices averaged over one year. The azimuth-elevation maps were used to identify objects that regularly scatter signals and cause high scintillation resulting from multipath effects. After identifying the multipath area from the azimuth-elevation map, an azimuth-dependent elevation threshold was developed using the MATLAB curve fitting tool. Using this method we are able to reduce the multi-path errors without losing important data. Using the azimuth-dependent elevation threshold typically gives 5 to 28% more useful data than using a 20° fixed-elevation threshold.

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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.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / Several test programs have reported degraded Global Positioning System (GPS) performance when L-band (1435-1535 MHz) telemetry is used while other test programs have had acceptable GPS performance with L-band telemetry. Most test programs seem to have minimal problems with S-band telemetry interfering with GPS performance if a bandpass filter is used between the GPS antenna and the low noise amplifier (LNA). This paper will present measured data on GPS performance with L- and S-band telemetry and explain what must be done to minimize interference to GPS. The paper will present both GPS signal-to-noise ratio (S/N) values as well as measured spectra from telemetry transmitters. System design guidelines for compatible operation will be presented.

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.