Browsing by Subject "GPS"
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Item A Comparative Study of Kalman Filter Implementations for Relative GPS Navigation(2011-02-22) Fritz, Matthew PeytonRelative global positioning system (GPS) navigation is currently used for autonomous rendezvous and docking of two spacecraft as well as formation flying applications. GPS receivers deliver measurements to flight software that use this information to determine estimates of the current states of the spacecraft. The success of autonomous proximity operations in the presence of an uncertain environment and noisy measurements depends primarily on the navigation accuracy. This thesis presents the implementation and calibration of a spaceborne GPS receiver model, a visibility analysis for multiple GPS antenna cone angles, the implementation of four different extended Kalman filter architectures and a comparison of the advantages and disadvantages of each filter used for relative GPS navigation. A spaceborne GPS model is developed to generate simulated GPS measurements for a spacecraft located on any orbit around the Earth below the GPS constellation. Position and velocity estimation algorithms for GPS receivers are developed and implemented. A visibility analysis is performed to determine the number of visible satellites throughout the duration of the rendezvous. Multiple constant fields of view are analyzed and results compared to develop an understanding of how the GPS constellation evolves during the proximity operations. The comparison is used to choose a field of view with adequate satellite coverage. The advantages and disadvantages of the relative navigation architectures are evaluated based on a trade study involving several parameters. It is determined in this thesis that a reduced pseudorange filter provides the best overall performance in both relative and absolute navigation with less computational cost than the slightly more accurate pseudorange lter. A relative pseudorange architecture experiences complications due to multipath rich environments and performs well in only relative navigation. A position velocity architecture performs well in absolute state estimation but the worst of the four filters studied in relative state estimation.Item Analysis and synthesis of collaborative opportunistic navigation systems(2014-05) Kassas, Zaher; Humphreys, Todd Edwin; Arapostathis, Ari, 1954-Navigation is an invisible utility that is often taken for granted with considerable societal and economic impacts. Not only is navigation essential to our modern life, but the more it advances, the more possibilities are created. Navigation is at the heart of three emerging fields: autonomous vehicles, location-based services, and intelligent transportation systems. Global navigation satellite systems (GNSS) are insufficient for reliable anytime, anywhere navigation, particularly indoors, in deep urban canyons, and in environments under malicious attacks (e.g., jamming and spoofing). The conventional approach to overcome the limitations of GNSS-based navigation is to couple GNSS receivers with dead reckoning sensors. A new paradigm, termed opportunistic navigation (OpNav), is emerging. OpNav is analogous to how living creatures naturally navigate: by learning their environment. OpNav aims to exploit the plenitude of ambient radio frequency signals of opportunity (SOPs) in the environment. OpNav radio receivers, which may be handheld or vehicle-mounted, continuously search for opportune signals from which to draw position and timing information, employing on-the-fly signal characterization as necessary. In collaborative opportunistic navigation (COpNav), multiple receivers share information to construct and continuously refine a global signal landscape. For the sake of motivation, consider the following problem. A number of receivers with no a priori knowledge about their own states are dropped in an environment comprising multiple unknown terrestrial SOPs. The receivers draw pseudorange observations from the SOPs. The receivers' objective is to build a high-fidelity signal landscape map of the environment within which they localize themselves in space and time. We then ask: (i) Under what conditions is the environment fully observable? (ii) In cases where the environment is not fully observable, what are the observable states? (iii) How would receiver-controlled maneuvers affect observability? (iv) What is the degree of observability of the various states in the environment? (v) What motion planning strategy should the receivers employ for optimal information gathering? (vi) How effective are receding horizon strategies over greedy for receiver trajectory optimization, and what are their limitations? (vii) What level of collaboration between the receivers achieves a minimal price of anarchy? This dissertation addresses these fundamental questions and validates the theoretical conclusions numerically and experimentally.Item Arterial Performance and Evaluation using Bluetooth and GPS Data(2012-11-29) Shollar, Brian 1988-Accurate travel time data are necessary to monitor and evaluate traffic conditions effectively. In the past 20 years, the hours per year lost by the average driver have increased by 300% in the 85 largest U.S. cities, which translates into lost productivity and increased costs. State department of transportation (DOT) agencies and other government organizations need accurate travel time and speed information to better combat this congestion faced by motorists. In the past, ground truth travel time information was typically collected with probe vehicles using the ?floating car? method. However, new methods using data collected from global positioning systems by private companies such as INRIX?, Navteq?, and TomTom? have emerged that allow travel time data to be obtained more cheaply and quickly. The Urban Mobility Report (UMR) has turned to these companies, specifically INRIX?, for calculating congestion indices across the United States. This is done by analyzing average speeds and reference speeds supplied by INRIX. The UMR analysis relies on INRIX-supplied reference speeds to calculate delay, which produces artificially high delay on many suburban arterials. Currently, these reference speeds are determined by taking the 85th percentile of weekly speeds (typically overnight hours [10PM to 6AM]). There is a need to refine the reference speeds on arterials in order to account for signal operations, particularly during the daytime hours, so that the UMR more accurately reflects arterial congestion across the nation. Using Bluetooth and INRIX speed data, this thesis develops a new reference speed methodology that accurately reflects arterial delay during daytime hours. This study found that a 60% daytime free-flow reference speed best represents arterial congestion. Using Highway Capacity Manual (HCM) guidelines, this thesis also explores the use of Bluetooth data for arterial and intersection level of service (LOS) analysis under both HCM 2000 and HCM 2010 methodologies. Through analysis, it was found that Bluetooth data capture more of the high and low LOS values compared to the HCM methodology based on segment speed calculations. These high and low LOS values, as well as the rapidly changing LOS between 15-minute intervals, could be attributed to an insufficient sample size.Item Assessing the Effectiveness of Water Quality Best Management Practices for Grazing-Lands(2013-12-10) Clary, Calvin RussellBest management practices (BMPs) aim to reduce bacterial loading caused by grazing cattle. Relatively little is known about the effectiveness of alternative shade, alternative water, rip-rap, and prescribed grazing as potential BMPs. Prescribed grazing evaluated how stocking rate affected bacterial loading. E. coli concentrations in runoff samples were compared between plots with various stocking rates. GPS collars were used to determine how a shade pavilion, water source, or rip-rap effected cattle distribution within a stream and riparian pasture by comparing time cattle spent at a location before and after implementing the BMPs. While plots were stocked or within 14 days of being destocked, E. coli concentrations were significantly higher than destocked pastures. No significant differences were observed between E. coli concentrations in runoff from heavily stocked, moderately stocked, or non-grazed pastures when pastures had been destocked for greater than 14 days. On average, the shade structure reduced cattle's dependence on riparian shade by 30%. The alternative water BMP did not reduce the amount of time cattle spent within the riparian zone; however, the study was limited to one trial. Riparian rip-rap trials were inconclusive; however, preliminary rip-rap trials showed 20 to 40 cm diameter rip-rap was effective at modifying cattle trough preference. Advances in microbial source tracking, specifically Bacteroides, have allowed better identification of bacterial sources. However, genetic variability within some Bacteroides sequences may undermine the accuracy of these molecular markers. Localized gene-copy curves were created from 12 bovine fecal samples from a single herd, and qPCR assays were used to determine if they better correlated Bacteroides and E. coli populations. Sequences were pyro-sequenced to see if mismatches occurred within primer/probe regions. Base-pair mismatches occurred, and affected qPCR efficiencies. Fecal pollution load estimations were overestimated by using sequences with more mismatches. Genetic diversity was observed within samples from all locations, and indicated genetic variability within Bacteroides populations occurs within a single location as much as between locations. Thus, creating standard curves for individual watersheds would not necessarily improve pollution load estimations.Item An assessment of the GPS L5 signal based on multiple vendor receivers(2011-12) Smyers, Serena Ashley; Schutz, Bob E.; Kerkhoff, AaronThe L5 signal of the Global Positioning System (GPS) is becoming available on an increasing number of Block IIF satellites. As the third civilian signal, L5 is superior in signal design to the L1 C/A and L2C civilian signals. This new signal has been marked healthy for use on selected satellites since 2010, yet the hardware capable of tracking the L5 signal is still in the early stages of development. This work investigates the characteristics of the new signal and the quality of data produced by L5-tracking receivers. Commonly used receiver models chosen for this study are the Leica GRX1200+GNSS, the Trimble NetR8, and the Javad Delta TRE-G3TH. The metrics used in this analysis to assess the quality of data produced by these receivers are signal strength, receiver phase noise, receiver code noise, and multipath. The data used in these analyses were obtained from the International GNSS Service for the days of the year 275 to 281 in 2011. Metrics averaged over the GPS week 1656 provide a good indication of the overall performance of the receivers.Item Development and testing of a miniaturized, dual-frequency, software-defined gps receiver for space applications(2011-12) Joplin, Andrew Jonathan; Lightsey, E. Glenn; Humphreys, ToddWhile dual-frequency GPS receivers have been used in space for more than two decades, the size, power, and cost of this technology is an important driver for future space missions. The growing availability of launch opportunities for very small satellites known as nanosatellites and CubeSats raises the possibility of more affordable access to space measurements if the observation quality is sufficient to support the user's needs. This thesis presents the initial development and testing of the Fast, Orbital, TEC, Observables, and Navigation (FOTON) receiver: a small, reconfigurable, dual-frequency, space-based GPS receiver. Originally developed as a science-grade software receiver for monitoring ionospheric scintillation and total electron content (TEC), this receiver was designed to provide high-quality GPS signal observations. The original receiver hardware was miniaturized and the software has been adapted for low earth orbit (LEO) operations. FOTON now fits within a 0.5U CubeSat form factor (8.3 x 9.6 x 3.8 cm), weighs 326 g, and consumes 4.5 W of instantaneous power, which can be reduced to <1 W orbit average power with on-off duty cycling. The receiver has been designed with commercial parts to keep manufacturing costs low. Significant testing of FOTON has been performed with live signals and with signals generated by a Spirent GPS signal simulator. Initial terrestrial tests demonstrate behavioral consistency with the original heritage high-performance receiver. Several LEO simulations are presented, demonstrating FOTON's single-frequency and dual-frequency-enhanced positioning down to 0.5 m and 1.5 m, respectively, which can be improved using Kalman filter based POD. FOTON's potential for GPS radio occultation observation is also demonstrated. In addition, its acquisition and reacquisition performance is presented; on average, FOTON's time to first fix is approximately 45 seconds. Finally, navigation in geostationary orbit (GEO), a challenging application for space-based GPS receivers, is demonstrated. Extensive testing demonstrates that FOTON is a robust, versatile, high-precision dual-frequency space receiver. Its low cost, size, weight, and power requirements are key enablers for future small-satellite missions.Item Field location & marking of no-passing zones due to vertical alignments using the global positioning system(Texas A&M University, 2008-10-10) Williams, Cameron LeePassing on two-lane roadways is one of the most difficult movements a driver may perform and guidance on where passing maneuvers are prohibited is given by the location of no-passing zones. Currently the processes for identifying no-passing zone locations can be daunting and many practices require work crews to operate in the roadway creating potentially hazardous situations. Due to these challenges new alternatives need to be developed for the safe, accurate, and efficient location of nopassing zones on two-lane roadways. This thesis addresses the use of Global Positioning System (GPS) coordinates to evaluate sight distance along the vertical profile of roadways to provide an alternative for an automated no-passing zone location system. A system was developed that processes GPS coordinates and converts them into easting and northing values, smoothes inaccurate vertical elevation data, and evaluates roadway profiles for possible sight restrictions which indicate where no-passing zones should be located. The developed automated no-passing zone program shows potential in that it identifies the general location of no-passing zones as compared to existing roadway markings.; however, as concluded by the researcher, further evaluation and refinement is needed before the program can be used effectively in the field for the safe, accurate, and efficient location of no-passing zones.Item Fusion of carrier-phase differential GPS, bundle-adjustment-based visual SLAM, and inertial navigation for precisely and globally-registered augmented reality(2013-05) Shepard, Daniel Phillip; Humphreys, Todd EdwinMethodologies are proposed for combining carrier-phase differential GPS (CDGPS), visual simultaneous localization and mapping (SLAM), and inertial measurements to obtain precise and globally-referenced position and attitude estimates of a rigid structure connecting a GPS receiver, a camera, and an inertial measurement unit (IMU). As part of developing these methodologies, observability of globally-referenced attitude based solely on GPS-based position estimates and visual feature measurements is proven. Determination of attitude in this manner eliminates the need for attitude estimates based on magnetometer and accelerometer measurements, which are notoriously susceptible to magnetic disturbances. This combination of navigation techniques, if coupled properly, is capable of attaining centimeter-level or better absolute positioning and degree-level or better absolute attitude accuracies in any space, both indoors and out. Such a navigation system is ideally suited for application to augmented reality (AR), which often employs a GPS receiver, a camera, and an IMU, and would result in tight registration of virtual elements to the real world. A prototype AR system is presented that represents a first step towards coupling CDGPS, visual SLAM, and inertial navigation. While this prototype AR system does not couple CDGPS and visual SLAM tightly enough to obtain some of the benefit of the proposed methodologies, the system is capable of demonstrating an upper bound on the precision that such a combination of navigation techniques could attain. Test results for the prototype AR system are presented for a dynamic scenario that demonstrate sub-centimeter-level positioning precision and sub-degree-level attitude precision. This level of precision would enable convincing augmented visuals.Item GPS L2 C signal survey and the development of the emergent MATLAB L2 C (EMAL2) receiver(2012-12) Bright, Marlon Wayne; Humphreys, Todd Edwin; Schutz, BobThe United States Department of Defense has introduced two new GPS civilian signals on its “Link 2” (L2) and “Link 5” (L5) center frequencies. The first of these new civilian signals to reach full operational capability in the GPS constellation will be the L2 C signal. The L2 C signal boasts new signal structure features aimed at better tracking performance in comparison to the legacy L1 C/A signal. Amongst these are two new chip-by-chip interleaved spreading code sequences, Civilian Moderate (CM) and Civilian Long (CL), and a new, higher resolution navigation message, CNAV. The two new C codes are longer than the legacy C/A code and feature a data less pilot signal (CL) for improved tracking performance in weak signal environments. This work investigates L2 C acquisition and tracking considerations and implements algorithms for acquiring and tracking the signal in a software-defined receiver developed in MATLAB. The Emergent MATLAB L2 C (EMAL2) receiver was developed for the purpose of GPS signal simulator testing. This software-defined receiver differs from legacy receivers containing application specific integrated circuits (ASICs) in that all of EMAL2’s digital signal processing is done in software able to run on a general purpose processor. This approach offers greater flexibility and ease in configuration over ASICs for tracking a number of different types of signal structures in the receiver. The EMAL2 receiver’s design and implementation is described here-in. Initial testing of the EMAL2 receiver was conducted with live-sky signal data captured by antennas and front-ends at the University of Texas Radionavigation Laboratory (UT RNL). The data was processed by the GRID receiver (also at the UT RNL) to provide EMAL2 baseline received signal characteristics.Item GPS receiver self survey and attitude determination using pseudolite signals(Texas A&M University, 2004-11-15) Park, Keun JooThis dissertation explores both the estimation of various parameters from a multiple antenna GPS receiver, which is used as an attitude sensor, and attitude determination using GPS-like Pseudolite signals. To use a multiple antenna GPS receiver as an attitude sensor, parameters such as baselines, integer ambiguities, line biases, and attitude, should be resolved beforehand. Also, due to a cycle slip problem a subsystem to correct this problem should be implemented. All of these tasks are called a self survey. A new algorithm to estimate these parameters from a GPS receiver is developed usingnonlinear batch ?lteringmethods.For convergence issues, both the nolinear least squares (NLS) and Levenberg-Marquardt (LM) methods are applied in the estimation.Acomparison ofthe NLSand LMmethods shows that the convergence of the LM method for the large initial errors is more robust than that of the NLS. In the proximity of the International Space Station (ISS), Pseudolite signals replace the GPSsignals since almostallsignals are blocked.Since the Pseudolite signals have spherical wavefronts, a new observation model should be applied. A nonlinear predictive ?lter, an extended Kalman ?lter (EKF), and an unscented ?lter (UF) are developed and compared using Pseudolite signals. A nonlinear predictive ?lter can provide a deterministic solution; however, it cannot be used for the moving case. Instead, the EKF or the UF can be used with the angular rate measurements. A comparison of EKF and UF shows that the convergence of the UF for the large initial errors is more robust than that of the EKF. Also, an alternative global navigation constellation is presented by using the Flower Constellation (FC) scheme. A comparison of FC global navigation constellation and other GPS constellations, U.S. GPS, Galileo, and GLONASS, shows that position and attitude errors of the FC constellation are smaller that those of the others.Item Habitat selection and movement patterns of cattle and white-tailed deer in a temperate savanna(Texas A&M University, 2005-11-01) Depew, Jarrod JasonThis study investigated the use of high resolution satellite imagery in research involving habitat selection, and movement patterns of white-tailed deer and cattle in a semi-arid landscape. Vegetation classification was developed based on Ikonos satellite imagery that was then used to define habitat selection and characterize movement paths of deer and cattle to allow a better understanding of these 2 species. Pasture attributes were also measured to determine animal distribution throughout the study area in relation to roads, fences, water location, and supplemental feeders. Three cattle and 3 free ranging white-tailed deer were used during 3 trials to test seasonal differences in habitat selection and spatial distribution across the pasture. Ikonos satellite imagery was classified to a final classification accuracy of 83.6%. Seven vegetation classes were defined in the classification with 1 class of bare ground/ herbaceous that represents interspaces between shrub vegetation. Classification accuracy was obtained using a ?? meter buffer to all ground control points increasing the accuracy from 71.29%. All physical pasture attributes were significant to animal distributions in the study area when compared to the random distribution. Roads and water location were most important to cattle during the spring and summer. White tailed deer use of the pasture was more dependent on vegetation characteristics than physical attributes. Both cattle and deer selected habitat patches with a proportionately large percentage of bare-ground/interspaces (>40%). Deer were predominately found in areas containing higher percentages of shrub species, while cattle were found in areas containing a mixture of larger tree species in addition to shrub complexes. Travel velocity and path tortuosity were measured to determine effects of vegetation attributes on animal movements. Both cattle and deer followed fairly linear paths (Fractal Dimension<1.2). Factors contributing to path tortuosity included mean patch size, number patches, and patch fractal dimension. Travel velocity was also measured and compared to vegetation association attributes. Travel velocity was significantly different between seasons for white-tailed deer however cattle and deer comparisons were not significant across the 3 trials. Number of patches, patch fractal dimension, mean patch size, and patch area were significant in the travel velocity model.Item iTrak : a social mobile diary and web blogging utility for travelers(2013-05) Dao, Tung Thanh, active 2013; Aziz, AdnaniTrak is a combined mobile and web application that takes advantage of the GPS to allow travelers to share their experience while travelling. The application gathers GPS data and broadcasts it via a web interface or social networks such as Facebook to update user’s status during a trip. iTrak is also equipped with other features such as writing notes or recording video journals to offer a rich experience and provide an interactive diary, along with a real-time tracking ability, for travelers.Item Location-based information system for open spaces(Texas A&M University, 2004-11-15) Tejavanija, KampanartProblem solving for location is one of the most critical cognitive skills that can be utilized in deriving a naive location and/or finding a primed location in large open spaces of the built environment. Wayfinding or locating objects in large open spaces is not often easy for individuals due their limitations in building effective mental models of the open space or their lack of a correct procedure for determining the grid coordinates of an object within that space. With the success of the global positioning system (GPS) in providing location information, it is expected that this technology could be utilized to control and improve building construction and facility management productivity within building interior spaces as well. However, GPS cannot perform robustly inside buildings due to the exterior walls or roofs, which weaken the signal. The Cricket indoor location support technology has been developed to respond to this limitation. Cricket uses a combination of radio frequency (RF), ultrasonic sound signals, and the triangular rule to calculate a user's current location. This research investigated performances within the context of a work order system between a human-based system and a computer-based system. Thirty subjects participated in this study. The subjects were asked to derive, find and verify a target box's location. Locating time-on-task, accuracy, and attitudes were measured. The overwhelming results demonstrated the speed and accuracy of the computer-based system over the human-based system. In addition to longer procedural processing times, subject errors included: 1) an incorrect estimation of distance, 2) an inability to correctly locate and/or project the X-axis and Y-axis grid lines, and 3) an incorrect treatment of the positive and negative characteristics of these coordinates. Even though half of the subjects liked the human-based system more, they significantly believe the computer-based system to be more accurate. All but one subject preferred that the computer-based system be used in his or her own future business. Finally, results indicate that the computer-based system does relieve humans of cognitive dependency, which may be further evidence that the computer-based system developed and tested in this study achieved its purpose.Item Logistic regression models for predicting trip reporting accuracy in GPS-enhanced household travel surveys(Texas A&M University, 2007-04-25) Forrest, Timothy LeeThis thesis presents a methodology for conducting logistic regression modeling of trip and household information obtained from household travel surveys and vehicle trip information obtained from global positioning systems (GPS) to better understand the trip underreporting that occurs. The methodology presented here builds on previous research by adding additional variables to the logistic regression model that might be significant in contributing to underreporting, specifically, trip purpose. Understanding the trip purpose is crucial in transportation planning because many of the transportation models used today are based on the number of trips in a given area by the purpose of a trip. The methodology used here was applied to two study areas in Texas, Laredo and Tyler-Longview. In these two study areas, household travel survey data and GPS-based vehicle tracking data was collected over a 24-hour period for 254 households and 388 vehicles. From these 254 households, a total of 2,795 trips were made, averaging 11.0 trips per household. By comparing the trips reported in the household travel survey with those recorded by the GPS unit, trips not reported in the household travel survey were identified. Logistic regression was shown to be effective in determining which household- and trip-related variables significantly contributed to the likelihood of a trip being reported. Although different variables were identified as significant in each of the models tested, one variable was found to be significant in all of them - trip purpose. It was also found that the household residence type and the use of household vehicles for commercial purposes did not significantly affect reporting rates in any of the models tested. The results shown here support the need for modeling trips by trip purpose, but also indicate that, from urban area to urban area, there are different factors contributing to the level of underreporting that occurs. An analysis of additional significant variables in each urban area found combinations that yielded trip reporting rates of 0%. Similar to the results of Zmud and Wolf (2003), trip duration and the number of vehicles available were also found to be significant in a full model encompassing both study areas.Item Motion and evolution of the Chaochou Fault, Southern Taiwan(Texas A&M University, 2005-11-01) Hassler, Lauren E.The Chaochou Fault (CCF) is both an important lithologic boundary and a significant topographic feature in the Taiwan orogenic belt. It is the geologic boundary between the Slate Belt to the east, and the Western Foothills to the west. Although the fault is known to be a high angle oblique sinistral thrust fault in places, both its kinematic history and its current role in the development of the orogen are poorly understood. Field fabric data suggest that structural orientations vary along strike, particularly in the middle segment, the suspected location of the intersection of the on-land Eurasian continent-ocean boundary and the Luzon Island Arc. Foliation/solution cleavage is oriented NE-SW and in the northern and southern sections, but ESE-WNW in the middle segment. Slip lineations also reveal a change in fault motion from dip-parallel in the north to a more scattered pattern in the south. This correlates somewhat with recent GPS results, which indicate that the direction of current horizontal surface motion changes along strike from nearly perpendicular to the fault in the northern field area, to oblique and nearly parallel to the fault in the southern field area. The magnitude of vertical surface motion vectors, relative to Lanyu Island, decreases to the south. Surface morphology parameters, including mountain front sinuosity and valley floor width/valley height ratio indicate higher activity and uplift in the north. These observations correlate well with published apatite/zircon fission track data that indicate un-reset ages in the south, and reset ages in the northern segment. Geodetic and geomorphic data indicate that the northern segment of the CCF and Slate Belt are currently undergoing rapid uplift related to oblique arc-continent collision between the Eurasian continent and the Luzon arc. The southern segment is significantly less active perhaps because the orogen is not yet involved in direct arc-continent collision.Item Navigation solution for the Texas A&M autonomous ground vehicle(Texas A&M University, 2006-10-30) Odom, Craig AllenThe need addressed in this thesis is to provide an Autonomous Ground Vehicle (AGV) with accurate information regarding its position, velocity, and orientation. The system chosen to meet these needs incorporates (1) a differential Global Positioning System, (2) an Inertial Measurement Unit consisting of accelerometers and angular-rate sensors, and (3) a Kalman Filter (KF) to fuse the sensor data. The obstacle avoidance software requires position and orientation to build a global map of obstacles based on the returns of a scanning laser rangefinder. The path control software requires position and velocity. The development of the KF is the major contribution of this thesis. This technology can either be purchased or developed, and, for educational and financial reasons, it was decided to develop instead of purchasing the KF software. This thesis analyzes three different cases of navigation: one-dimensional, two dimensional and three-dimensional (general). Each becomes more complex, and separating them allows a three step progression to reach the general motion solution. Three tests were conducted at the Texas A&M University Riverside campus that demonstrated the accuracy of the solution. Starting from a designated origin, the AGV traveled along the runway and then returned to the same origin within 11 cm along the North axis, 19 cm along the East axis and 8 cm along the Down axis. Also, the vehicle traveled along runway 35R which runs North-South within 0.1????, with the yaw solution consistently within 1???? of North or South. The final test was mapping a box onto the origin of the global map, which requires accurate linear and angular position estimates and a correct mapping transformation.Item Secure navigation and timing without local storage of secret keys(2014-05) Wesson, Kyle D.; Humphreys, Todd Edwin; Evans, Brian L. (Brian Lawrence), 1965-Civil Global Navigation Satellite System (GNSS) signals are broadcast unencrypted worldwide according to an open-access standard. The virtues of open-access and global availability have made GNSS a huge success. Yet the transparency and predictability of these signals renders them easy to counterfeit, or spoof. During a spoofing attack, a malefactor broadcasts counterfeit GNSS signals that deceive a victim receiver into reporting the spoofer-controlled position or time. Given the extensive integration of civil GNSS into critical national infrastructure and safety-of-life applications, a successful spoofing attack could have serious and significant consequences. Unlike civil GNSS signals, military GNSS signals employ symmetric-key encryption, which serves as a defense against spoofing attacks and as a barrier to unauthorized access. Despite the effectiveness of the symmetric-key approach, it has significant drawbacks and is impractical for civil applications. First, symmetric-key encryption requires tamper-resistant receivers to protect the secret keys from unauthorized discovery and dissemination. Manufacturing a tamper-resistant receiver increases cost and limits manufacturing to trusted foundries. Second, key management is problematic and burdensome despite the recent introduction of over-the-air keying. Third, even symmetric-key encryption remains somewhat vulnerable to specialized spoofing attacks. I propose an entirely new approach to navigation and timing security that avoids the shortcomings of the symmetric-key approach while maintaining a high resistance to spoofing. My first contribution is a probabilistic framework that develops necessary components of signal authentication. Based on the framework, I develop an asymmetric-key cryptographic signal authentication technique and a non-cryptographic spoofing detection technique, both of which operate without a secret key stored locally in a secure receiver. These anti-spoofing techniques constitute the remaining two contributions of this dissertation. They stand as viable spoofing defenses for civil users and could augment---or even replace---current and planned military anti-spoofing measures. Finally, I offer an in-depth case study of the security vulnerabilities and possible cryptographic enhancements of a modern GNSS-based aviation surveillance technology in the context of the technical and regulatory aviation environment.Item Spatio-temporal distribution of white-tailed deer (Odocoileus virginianus) relative to prescribed burns on rangeland in South Texas(2009-05-15) Meek, Michael GlennOvergrazing and fire suppression has left much rangeland in poor condition for various wildlife species. Prescribed fire is one range improvement practice used to restore degraded wildlife habitat. I determined the effect of prescribed fire on whitetailed deer (Odocoileus virginianus) spatial and temporal distribution, in the presence of cattle grazing. Three 40 ha patches, constituting 10% and 6% of the land area in the lesser and greater Yellow Bluff pasture, respectively, were burned in September 2005. To determine habitat use and distribution of deer relative to these burns 3 bucks and 3 does were netted from a helicopter and fitted with Global Positioning System (GPS) telemetry collars (Lotek? GPS_3300S) for a period of 30 days during each season. For estimation of spatial distribution of deer, the collars were programmed to take a position fix every hour to reduce problems associated with spatial autocorrelation. For 12 days within this period the collars recorded animal location every 5 minutes to compare habitat use with 6?9 GPS collars (GPS_3300LR) placed on cattle. This allowed me to examine fine-scale movements of deer relative to cattle. Trials were conducted prior to the burn and in each season for one year after the burn. Areas to be burned were not favored by deer. A month after the burn in Fall 2005 there was an increase in use of the burned areas by deer. Deer preference for burned areas fell in Spring and Summer 2006, but in Fall 2006 females dramatically increased their use of the burns. This is possibly an artifact of small sample size and the random selection of individuals. Interaction between deer and cattle was minimal, as they inhabited different areas. When cattle moved within approximately 50 m of a stationary deer the deer was likely to move away. Vegetation measurements showed no significant change in shrub cover and density and a decline in available herbaceous forage on both treatment and control sites in the second year. The lack of vegetative response because of drought conditions was likely the cause of the lack of response by the deer to the burns.Item Spatio-temporal relationships between feral hogs and cattle with implicatons for disease transmission(Texas A&M University, 2007-09-17) Deck, Aubrey LynnIt is widely recognized that livestock industries are vulnerable to intentional or accidental introductions of Foreign Animal Diseases (FADs). Combating disease is difficult because of unknown wildlife-livestock interactions. Feral hogs (Sus scrofa) could harbor and shed disease in areas used by domestic livestock such as cattle (Bos taurus). Extent of risk logically depends on spatio-temporal interactions between species. I used Global Positioning System (GPS) collars on cattle and hogs in combination with a Geographic Information Systems (GIS) for detailed analysis on movement patterns of these 2 species on a ranch in southwestern Texas, USA. Motion-triggered video recorders were also utilized to determine interspecific activity patterns. I tested hypotheses that spatio-temporal distributions of domestic cattle and feral hogs on rangeland overlap and that interspecific contact occurs. If these posits are true, it is possible that introduced pathogens like foot-and-mouth disease (FMD) could be transmitted from feral hogs to cattle. Using a rate of 1 GPS fix/15 min (96 fixes/day), I found that spatial distribution of individual hogs and cattle overlapped on both the 95% and 50% kernel area use among 4 seasons. Both cows and feral hogs used Clay Flat, Clay Loam, and Rolling Hardland more so than other range sites. During Summer 2004, riparian zones were the most used feature, identified at 14% (2,760/19,365) of cattle and 70% (445/632) of hog fixes. Other than brush strips, cattle and feral hogs primarily interacted at riparian zones, fencelines, and roads. There were no direct interspecific contacts evident from GPS data, but 3 cases were recorded from video data. Indirect interspecific contacts that may be sufficient for disease transmission occurred much more frequently (GPS = 3.35 indirect contacts/day, video = cows follow hogs: 0.69 indirect contacts/day and hogs follow cows: 0.54 indirect contacts/day). Research results suggested that both species often travel along the same roads and fencelines to water and food sources, especially during extreme heat and low-precipitation conditions. This research provides basic information needed to improve models for management of FAD outbreaks in the U.S., based on specific knowledge of landscape usage and movement patterns of feral hogs and cattle.Item Synthetic Aperture Digital Beamsteering Array for Global Positioning System Interference Mitigation: A Study on Array Topology(2014-05-20) Harms, Joel KThe Global Positioning System (GPS) satellite navigation system is deeply intertwined with civilian everyday life. Unfortunately for the civilians that use the system, the GPS system is vulnerable to external interference. Antenna arrays with Direction of Arrival (DoA) signal identification and beamsteering provide a very effective technique for mitigating directional interference by moving the antenna gain toward the Signal of Interest (SOI) or away from the Signal not of Interest (SNOI), however, such systems are typically too large to integrate or require more processing capabilities than civilian devices are able to provide. Synthetic aperture arrays are a means to reduce the array size but provide a similar interference protection with a smaller processing capability overhead. This thesis assists in array selection by providing simulated gains of different switched antenna arrays. The Uniform Circular Array (UCA), rectangular array, random array, random full aperture, random sequential, ring (UCA random hybrid) topologies are evaluated. In a pure synthetic beamsteering system in the presence of continuous wave (CW) interference, it is determined that array topology has marginal impact on Signal to Interference Noise Ratio (SINR) as each array's results show very similar performance. With the two CW scenarios in the absence of null steering, the UCA maintains the highest performance using the smallest number of antenna elements.