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Virginia Tech
1.
Glesner, Colin Christopher.
Development of Magnetic Nozzle Simulations for Space Propulsion Applications.
Degree: MS, Aerospace Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/74947 
► A means of space propulsion using the channeling of plasma by a divergent magnetic field, referred to as a magnetic nozzle has been explored by…
(more)
▼ A means of space propulsion using the channeling of plasma by a divergent magnetic field, referred to as a magnetic nozzle has been explored by a number of research groups. This research develops the capability to apply the high order accurate Runge-Kutta discontinuous Galerkin numerical method to the simulation of magnetic nozzles. The resistive magnetohydrodynamic model of plasma behavior is developed for these simulations. To facilitate this work, several modeling capabilities are developed, including the implementation of appropriate inflow and far-field boundary conditions, the application of a technique for correcting errors that develop in the divergence of the magnetic field, and a split formulation for the magnetic field between the applied and the perturbed component. This model is then applied to perform a scaling study of the performance of magnetic nozzles over a range of Bk and Rm. In addition, the effect of the choice of simulation domain size is
investigated. Finally, recommendations for future work are made.
Advisors/Committee Members: Srinivasan, Bhuvana (committeechair), Scales, Wayne A. (committeechair), Adams, Colin (committee member).
Subjects/Keywords: Plasma; Simulation
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APA (6th Edition):
Glesner, C. C. (2017). Development of Magnetic Nozzle Simulations for Space Propulsion Applications. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/74947
Chicago Manual of Style (16th Edition):
Glesner, Colin Christopher. “Development of Magnetic Nozzle Simulations for Space Propulsion Applications.” 2017. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/74947.
MLA Handbook (7th Edition):
Glesner, Colin Christopher. “Development of Magnetic Nozzle Simulations for Space Propulsion Applications.” 2017. Web. 10 Apr 2021.
Vancouver:
Glesner CC. Development of Magnetic Nozzle Simulations for Space Propulsion Applications. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/74947.
Council of Science Editors:
Glesner CC. Development of Magnetic Nozzle Simulations for Space Propulsion Applications. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/74947
Virginia Tech
2.
Cagas, Petr.
Continuum Kinetic Simulations of Plasma Sheaths and Instabilities.
Degree: PhD, Aerospace Engineering, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/84979
► A careful study of plasma-material interactions is essential to understand and improve the operation of devices where plasma contacts a wall such as plasma thrusters,…
(more)
▼ A careful study of plasma-material interactions is essential to understand and improve the operation of devices where plasma contacts a wall such as plasma thrusters, fusion devices, spacecraft-environment interactions, to name a few. This work aims to advance our understanding of fundamental plasma processes pertaining to plasma-material interactions, sheath physics, and kinetic instabilities through theory and novel numerical simulations. Key contributions of this work include (i) novel continuum kinetic algorithms with novel boundary conditions that directly discretize the Vlasov/Boltzmann equation using the discontinuous Galerkin method, (ii) fundamental studies of plasma sheath physics with collisions, ionization, and physics-based wall emission, and (iii) theoretical and numerical studies of the linear growth and nonlinear saturation of the kinetic Weibel instability, including its role in plasma sheaths.
The continuum kinetic algorithm has been shown to compare well with theoretical predictions of Landau damping of Langmuir waves and the two-stream instability. Benchmarks are also performed using the electromagnetic Weibel instability and excellent agreement is found between theory and simulation. The role of the electric field is significant during nonlinear saturation of the Weibel instability, something that was not noted in previous studies of the Weibel instability. For some plasma parameters, the electric field energy can approach magnitudes of the magnetic field energy during the nonlinear phase of the Weibel instability.
A significant focus is put on understanding plasma sheath physics which is essential for studying plasma-material interactions. Initial simulations are performed using a baseline collisionless kinetic model to match classical sheath theory and the Bohm criterion. Following this, a collision operator and volumetric physics-based source terms are introduced and effects of heat flux are briefly discussed. Novel boundary conditions are developed and included in a general manner with the continuum kinetic algorithm for bounded plasma simulations. A physics-based wall emission model based on first principles from quantum mechanics is self-consistently implemented and demonstrated to significantly impact sheath physics. These are the first continuum kinetic simulations using self-consistent, wall emission boundary conditions with broad applicability across a variety of regimes.
Advisors/Committee Members: Srinivasan, Bhuvana (committeechair), Adams, Colin (committee member), Scales, Wayne A. (committee member), Warburton, Timothy (committee member).
Subjects/Keywords: plasma sheath; discontinuous Galerkin; continuum kinetic method; plasma instabilities; plasma-material interactions
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APA (6th Edition):
Cagas, P. (2018). Continuum Kinetic Simulations of Plasma Sheaths and Instabilities. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/84979
Chicago Manual of Style (16th Edition):
Cagas, Petr. “Continuum Kinetic Simulations of Plasma Sheaths and Instabilities.” 2018. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/84979.
MLA Handbook (7th Edition):
Cagas, Petr. “Continuum Kinetic Simulations of Plasma Sheaths and Instabilities.” 2018. Web. 10 Apr 2021.
Vancouver:
Cagas P. Continuum Kinetic Simulations of Plasma Sheaths and Instabilities. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/84979.
Council of Science Editors:
Cagas P. Continuum Kinetic Simulations of Plasma Sheaths and Instabilities. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/84979
Virginia Tech
3.
Jean, Marc Henri.
Multi-Constellation GNSS Scintillation at Mid-Latitudes.
Degree: MS, Electrical Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/73704
► Scintillation of Global Positioning Systems (GPS) signals have been extensively studied at low and high latitude regions of the Earth. It has been shown in…
(more)
▼ Scintillation of Global Positioning Systems (GPS) signals have been extensively studied
at low and high latitude regions of the Earth. It has been shown in past studies that amplitude
scintillation is severe at low latitudes and phase scintillation is severe at high latitudes. Unlike
low and high latitude regions, mid-latitude scintillation has not been extensively studied. Further, it has been suggested that mid-latitude scintillation is negligible. The purpose of this research is to challenge this belief.
A multi-constellation and multi-frequency receiver, that tracks American, Russian, and
European satellites, was used to monitor scintillation activity at the
Virginia Tech Space Center.
Analysis was performed on collected data from various days and compared to past research done at high, mid, and low latitudes. The results are discussed in this thesis.
Advisors/Committee Members: Scales, Wayne A. (committeechair), Bailey, Scott M. (committee member), Sweeney, Dennis G. (committee member).
Subjects/Keywords: Mid-Latitude scintillation; amplitude scintillation; phase scintillation; Novatel GP6-Station receiver; Novatel Connect; spectral index; histogram distribution; GPS L1; GPS L2; GPS L5; GLONASS G1; GLONASS G2; Galileo E1; Galileo E5A; Galileo E5B; SP
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APA (6th Edition):
Jean, M. H. (2016). Multi-Constellation GNSS Scintillation at Mid-Latitudes. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/73704
Chicago Manual of Style (16th Edition):
Jean, Marc Henri. “Multi-Constellation GNSS Scintillation at Mid-Latitudes.” 2016. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/73704.
MLA Handbook (7th Edition):
Jean, Marc Henri. “Multi-Constellation GNSS Scintillation at Mid-Latitudes.” 2016. Web. 10 Apr 2021.
Vancouver:
Jean MH. Multi-Constellation GNSS Scintillation at Mid-Latitudes. [Internet] [Masters thesis]. Virginia Tech; 2016. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/73704.
Council of Science Editors:
Jean MH. Multi-Constellation GNSS Scintillation at Mid-Latitudes. [Masters Thesis]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/73704
Virginia Tech
4.
Williams, Jon A.
Enabling Validation of a CubeSat Compatible Wind Sensor.
Degree: MS, Electrical Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/78711
► The Ram Energy Distribution Detector (REDD) is a new CubeSat-compatible space science instrument that measures neutral wind characteristics in the upper atmosphere. Neutral gas interactions…
(more)
▼ The Ram Energy Distribution Detector (REDD) is a new CubeSat-compatible space science instrument that measures neutral wind characteristics in the upper atmosphere. Neutral gas interactions with plasma in the ionosphere/thermosphere are responsible for spacecraft drag, radio frequency disturbances such as scintillation, and other geophysical phenomena. REDD is designed to collect in-situ measurements within this region of the atmosphere where in-flight data collection using spacecraft has proven particularly challenging due to both the atmospheric density and the dominating presence of highly reactive atomic oxygen (AO). NASA Marshall Space Flight Center has a unique AO Facility (AOF) capable of simulating the conditions the sensor will encounter on orbit by creating a supersonic neutral beam of AO. Collimating the beam requires an intense magnetic field that creates significant interference for sensitive electronic devices. REDD is undergoing the final stages of validation testing in the AOF. In this presentation, we describe the LabVIEW-automated system design, the measured geometry and magnitude of the field and the specially designed mount and passive shielding that are utilized to mitigate the effects of the magnetic interference.
Advisors/Committee Members: Earle, Gregory D. (committeechair), Scales, Wayne A. (committee member), Bailey, Scott M. (committee member).
Subjects/Keywords: CubeSat; Retarding Potential Analyzer; Microchannel Plate Detector; Atomic Oxygen; Validation
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APA (6th Edition):
Williams, J. A. (2017). Enabling Validation of a CubeSat Compatible Wind Sensor. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/78711
Chicago Manual of Style (16th Edition):
Williams, Jon A. “Enabling Validation of a CubeSat Compatible Wind Sensor.” 2017. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/78711.
MLA Handbook (7th Edition):
Williams, Jon A. “Enabling Validation of a CubeSat Compatible Wind Sensor.” 2017. Web. 10 Apr 2021.
Vancouver:
Williams JA. Enabling Validation of a CubeSat Compatible Wind Sensor. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/78711.
Council of Science Editors:
Williams JA. Enabling Validation of a CubeSat Compatible Wind Sensor. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/78711
Virginia Tech
5.
Roback, Vincent Eric.
Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing.
Degree: MS, Electrical and Computer Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/76845
► Two flash lidars, integrated from a number of cutting-edge components from industry and NASA, are lab characterized and flight tested under the Autonomous Landing and…
(more)
▼ Two flash lidars, integrated from a number of cutting-edge components from industry and NASA, are lab characterized and flight tested under the Autonomous Landing and Hazard Avoidance (ALHAT) project (in its fourth development and field test cycle) which is seeking to develop a guidance, navigation, and control (GNC) and sensing system based on lidar technology capable of enabling safe, precise human-crewed or robotic landings in challenging terrain on planetary bodies under any ambient lighting conditions. The flash lidars incorporate pioneering 3-D imaging cameras based on Indium-Gallium-Arsenide Avalanche Photo Diode (InGaAs APD) and novel micro-electronic technology for a 128 x 128 pixel array operating at 30 Hz, high pulse-energy 1.06 ?m Nd:YAG lasers, and high performance transmitter and receiver fixed and zoom optics. The two flash lidars are characterized on the NASA-Langley Research Center (LaRC) Sensor Test Range, integrated with other portions of the ALHAT GNC system from around the country into an instrument pod at NASA-JPL, integrated onto an Erickson Aircrane Helicopter at NASA-Dryden, and flight tested at the Edwards AFB Rogers dry lakebed over a field of human-made geometric hazards. Results show that the maximum operational range goal of 1000m is met and exceeded up to a value of 1200m, that the range precision goal of 8 cm is marginally met, and that the transmitter zoom optics divergence needs to be extended another eight degrees to meet the zoom goal 6° to 24°. Several hazards are imaged at medium ranges to provide three-dimensional Digital Elevation Map (DEM) information.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Scales, Wayne A. (committee member), Henderson, Troy A. (committee member).
Subjects/Keywords: Precision Landing; Safe Landing; 3-D Imaging; Flash Lidar; Laser Remote Sensing; Hazard Detection; ALHAT; Flight Test; Planetary Landing; Lunar Landing
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APA (6th Edition):
Roback, V. E. (2012). Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/76845
Chicago Manual of Style (16th Edition):
Roback, Vincent Eric. “Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing.” 2012. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/76845.
MLA Handbook (7th Edition):
Roback, Vincent Eric. “Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing.” 2012. Web. 10 Apr 2021.
Vancouver:
Roback VE. Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing. [Internet] [Masters thesis]. Virginia Tech; 2012. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/76845.
Council of Science Editors:
Roback VE. Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing. [Masters Thesis]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/76845
Virginia Tech
6.
Venkataramani, Karthik.
Simulating Nitric Oxide in the lower thermosphere using a 3D model.
Degree: MS, Electrical and Computer Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/46171
► Nitric oxide (NO), despite being a minor species, influences the chemistry, composition and energy balance of the earth's atmosphere above 90 kilometers. Variations in its…
(more)
▼ Nitric oxide (NO), despite being a minor species, influences the chemistry, composition and energy balance of the earth's atmosphere above 90 kilometers. Variations in its density have been shown to strongly correlate with solar x-ray irradiance at lower latitudes and precipitating energetic particles at higher latitudes. Though the broad variations in NO densities with altitude and latitude are well known, there are still uncertainties associated with its chemistry. It is important to accurately model NO and its associated chemistry in an atmospheric model in order to obtain an accurate representation of the thermosphere.
The NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) is a three dimensional first principles based model which includes a self consistent aeronomic scheme that solves for winds, temperatures and densities of various neutral and charged species in the earth's upper atmosphere. Using a combination of the solar irradiance spectrum and solar indices as inputs, the model computes these outputs at every time step.
The ability of the TIEGCM to predict NO densities in the thermosphere is examined by comparing results from the model with data obtained from the Student Nitric Oxide Explorer (SNOE). The comparisons are made for the year 1999 at 110 km and 150 km at the equator. Changes are made to the NO chemistry present in the model to reflect recent results obtained from laboratory data. Paricularly, the reaction of atomic oxygen with the first excited electronic state of nitrogen, N
2 (A) has been shown to play an important role in the production of NO. These changes are introduced to the model and their effect on NO densities is studied.
Overall, it is seen that the updated chemistry scheme reduces the model agreement with the SNOE data at 110 km while slightly improving the agreement at a 150 km. The loss of agreement at 110 km is attributed to the fact that the neutral temperatures and atomic oxygen densities calculated by the TIEGCM are in sharp disagreement to the temperatures predicted by the NRL-MSIS at a 110 km, on which the new chemistry scheme is based.
While the chemistry scheme used in this thesis is a step in the right direction for modelling NO using the TIEGCM, the parameters used were determined from the best fit obtained from the 1-D NO model. In the light of the differences between the NRL-MSIS and TIEGCM, it is necessary to return to the laboratory data and modify the parameters used here to achieve a better agreement with the data.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Earle, Gregory D. (committee member), Scales, Wayne A. (committeecochair).
Subjects/Keywords: Simulating NO; Thermospheric Modelling; N2(A); TIEGCM; Nitric Oxide
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APA (6th Edition):
Venkataramani, K. (2012). Simulating Nitric Oxide in the lower thermosphere using a 3D model. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/46171
Chicago Manual of Style (16th Edition):
Venkataramani, Karthik. “Simulating Nitric Oxide in the lower thermosphere using a 3D model.” 2012. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/46171.
MLA Handbook (7th Edition):
Venkataramani, Karthik. “Simulating Nitric Oxide in the lower thermosphere using a 3D model.” 2012. Web. 10 Apr 2021.
Vancouver:
Venkataramani K. Simulating Nitric Oxide in the lower thermosphere using a 3D model. [Internet] [Masters thesis]. Virginia Tech; 2012. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/46171.
Council of Science Editors:
Venkataramani K. Simulating Nitric Oxide in the lower thermosphere using a 3D model. [Masters Thesis]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/46171
Virginia Tech
7.
Kim, Alexander.
Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems.
Degree: MS, Electrical and Computer Engineering, 2011, Virginia Tech
URL: http://hdl.handle.net/10919/34568
► The ultimate goal for power electronics is to convert one form of raw electrical energy into a usable power source with the lowest amount of…
(more)
▼ The ultimate goal for power electronics is to convert one form of raw electrical energy into a usable power source with the lowest amount of loss. A considerable portion of these losses are due to the use of switching devices themselves. Device losses can be apportioned to conduction loss and switching loss. It is commonly known and practiced that conduction loss can be reduced by driving MOSFETs and IGBTs harder with gate voltages closer to the maximum rating. This lowers the voltage across the device in the path of the amplified current and ultimately reduces power dissipated by the device. However, switching losses of these devices are not as easily characterized or intuitive for power electronics designers. This is mainly due to the fact that the parasitic reactive elements are nonlinear and not as readily documented as I-V characteristics of a given power device. For example, non-linear parasitic capacitances in the device are given for a fixed frequency across a voltage sweep. Parasitic inductance is typically not even mentioned in the datasheet. The switching losses of these devices depend on these mysterious reactances. A functional way to obtain estimates
of switching loss is to test the device under the conditions the device will be used. However, this task must be approached carefully in order to accurately measure the voltage and current of the device. Measurement devices also have parasitic impedances of their own that can add or subtract to switching energy during turn on or turn off and create misleading results. Preliminary testing was performed on multiple devices. After preliminary testing and deliberation, a device-measurement printed circuit board was made to easily replace switching devices of the same package.
This thesis presents switching loss measurements of medium-power capable devices in the tens of kW range. It also aims to attribute characteristics of switching voltage and current waveforms to the internal structure of the devices. The device tester designed is versatile since the output buffer of the gate drive is comprised of D-PAK totem pole BJTs. This is able to drive both current and voltage driven devices, i.e. SiC J-FETs (current-driven) and other voltage-driven devices (i.e. MOSFETs and IGBTs). It also allows for TO-220 and TO-247 packaged power diodes.
Advisors/Committee Members: Lai, Jih-Sheng Jason (committeechair), Meehan, Kathleen (committee member), Scales, Wayne A. (committee member).
Subjects/Keywords: SupreMOS; CoolMOS; Switching Loss; Z-FET; Device Testing; MDMesh
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APA (6th Edition):
Kim, A. (2011). Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/34568
Chicago Manual of Style (16th Edition):
Kim, Alexander. “Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems.” 2011. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/34568.
MLA Handbook (7th Edition):
Kim, Alexander. “Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems.” 2011. Web. 10 Apr 2021.
Vancouver:
Kim A. Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems. [Internet] [Masters thesis]. Virginia Tech; 2011. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/34568.
Council of Science Editors:
Kim A. Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems. [Masters Thesis]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/34568
Virginia Tech
8.
Thirukoveluri, Padma Latha.
Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation.
Degree: MS, Electrical Engineering, 2011, Virginia Tech
URL: http://hdl.handle.net/10919/32969
► The objective of this thesis was to select a star for observation and determine the error in the retrieval technique for a rocket experiment to…
(more)
▼ The objective of this thesis was to select a star for observation and determine the error in the retrieval technique for a rocket experiment to measure lower thermospheric Nitric Oxide in the polar night using stellar occultation technique. These objectives are accomplished by planning the geometry, determining the requirements for observations, window for launch and discussing the retrieval technique. The planning is carried out using an approximated (no drag) and simulated rocket trajectory (provided by NSROC: NASA Rocket Operations Contract). The simulation for the retrievals is done using data from Student Nitric Oxide Explorer. Stars were taken from a catalogue called TD1. Launch times were obtained from the geometry planned resulting from selecting a zenith angle after choosing a maximum occultation height and determining rocket apogee. Window for observing Spica was found to be 20 minutes. The retrieval technique and simulations showed that column densities and volume densities should be retrievable to less than 5% and 20% respectively observing occultation heights 90-120km. The study suggests that choosing a star positioned north w.r.t the observation location gives us more poleward latitudes and larger launch window. Future research can be carried out applying the stellar occultation and retrieval technique to a satellite.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Scales, Wayne A. (committee member), Henderson, Troy A. (committee member).
Subjects/Keywords: launch time selection; star selection; rocket experiment; rocket experiment simulation; density retrieval techniques; stellar occultation technique; rocket geometry planning; rocket observation planning
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APA (6th Edition):
Thirukoveluri, P. L. (2011). Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/32969
Chicago Manual of Style (16th Edition):
Thirukoveluri, Padma Latha. “Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation.” 2011. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/32969.
MLA Handbook (7th Edition):
Thirukoveluri, Padma Latha. “Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation.” 2011. Web. 10 Apr 2021.
Vancouver:
Thirukoveluri PL. Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation. [Internet] [Masters thesis]. Virginia Tech; 2011. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/32969.
Council of Science Editors:
Thirukoveluri PL. Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation. [Masters Thesis]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/32969
Virginia Tech
9.
Peng, Yuxiang.
GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications.
Degree: MS, Electrical and Computer Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/79594
► The Global Navigation Satellite System (GNSS) is significantly advantageous to absolute and relative navigation for spacecraft formation flying. Ionospheric remote sensing, such as Total Electron…
(more)
▼ The Global Navigation Satellite System (GNSS) is significantly advantageous to absolute and relative navigation for spacecraft formation flying. Ionospheric remote sensing, such as Total Electron Content (TEC) measurements or ionospheric irregularity studies are important potential Low Earth Orbit (LEO) applications. A GNSS-based Hardware-in-the-loop (HIL) simulation testbed for LEO spacecraft formation flying has been developed and evaluated. The testbed infrastructure is composed of GNSS simulators, multi-constellation GNSS receiver(s), the Navigation & Control system and the Systems Tool Kit (STK) visualization system. A reference scenario of two LEO spacecraft is simulated with the initial in-track separation of 1000-m and targeted leader-follower configuration of 100-m along-track offset. Therefore, the feasibility and performance of the testbed have been demonstrated by benchmarking the simulation results with past work.
For ionospheric remote sensing, multi-constellation multi-frequency GNSS receivers are used to develop the GNSS TEC measurement and model evaluation system. GPS, GLONASS, Galileo and Beidou constellations are considered in this work. Multi-constellation GNSS TEC measurements and the GNSS-based HIL simulation testbed were integrated and applied to design a LEO satellite formation flying mission for ionospheric remote sensing. A scenario of observing sporadic E is illustrated and adopted to demonstrate how to apply GNSS-based spacecraft formation flying to study the ionospheric irregularities using the HIL simulation testbed. The entire infrastructure of GNSS-based spacecraft formation flying simulation and ionospheric remote sensing developed at
Virginia Tech is capable of supporting future ionospheric remote sensing mission design and validation.
Advisors/Committee Members: Scales, Wayne A. (committeechair), Sweeney, Dennis G. (committee member), Black, Jonathan T. (committee member).
Subjects/Keywords: HIL Simulation; Remote Sensing; Spacecraft Formation Flying; GPS; GNSS; TEC; Ionospheric Irregularity; Scintillation
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APA (6th Edition):
Peng, Y. (2017). GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/79594
Chicago Manual of Style (16th Edition):
Peng, Yuxiang. “GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications.” 2017. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/79594.
MLA Handbook (7th Edition):
Peng, Yuxiang. “GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications.” 2017. Web. 10 Apr 2021.
Vancouver:
Peng Y. GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/79594.
Council of Science Editors:
Peng Y. GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/79594
Virginia Tech
10.
Harris Jr, Frederick Bernard.
GNSS Hardware-In-The-Loop Formation and Tracking Control.
Degree: MS, Electrical Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/71380
► Formation and tracking control are critical for of today's vehicle applications in and this will be true for future vehicle technologies as well. Although the…
(more)
▼ Formation and tracking control are critical for of today's vehicle applications in and this will be true for future vehicle technologies as well. Although the general function of these controls is for data collection and military applications, formation and tracking control may be applied to automobiles, drones, submarines, and spacecraft. The primary application here is the investigation of formation keeping and tracking solutions for realistic, real-time, and multi-vehicle simulations. This research explores the creation of a predictive navigation and control algorithm for formation keeping and tracking, raw measurement data collection, and building a real-time GNSS closed HWIL testbed for simulations of different vehicles. The L1 frequency band of the Global Positioning System (GPS) constellation is used to observe and generate raw measurement data that encompasses range, pseudo-range, and Doppler frequency. The closed HWIL simulations are implemented using Spirent's Communication Global Navigation Satellite system (GNSS) 6560 and 8000 hardware simulators along with Ashtech, G-12 and DG-14, and Novetel OEM 628 receivers. The predictive navigation control is similar to other vision-based tracking techniques, but relies mainly on vector projections that are controlled by acceleration, velocity magnitude, and direction constraints to generate realistic motion.
The current state of the testbed is capable of handling one or more vehicle applications. The testbed can model simulations up to 24 hours. The vehicle performance during simulations can be customized for any required precision by setting a variety of vehicle parameters. The testbed is built from basic principles and is easily upgradable for future expansions or upgrades.
Advisors/Committee Members: Scales, Wayne A. (committeechair), Baker, Joseph B. H. (committee member), Ellingson, Steven W. (committee member).
Subjects/Keywords: Hardware-In-The-Loop; Formation Flying; Formation Travel; Tracking Control; Linear Navigation; Ashtech G-12; Spirent; GNSS 8000; GNSS 6560; Real-Time; Predictive Navigation Algorithm; GPS; Global Positioning System
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APA (6th Edition):
Harris Jr, F. B. (2016). GNSS Hardware-In-The-Loop Formation and Tracking Control. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/71380
Chicago Manual of Style (16th Edition):
Harris Jr, Frederick Bernard. “GNSS Hardware-In-The-Loop Formation and Tracking Control.” 2016. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/71380.
MLA Handbook (7th Edition):
Harris Jr, Frederick Bernard. “GNSS Hardware-In-The-Loop Formation and Tracking Control.” 2016. Web. 10 Apr 2021.
Vancouver:
Harris Jr FB. GNSS Hardware-In-The-Loop Formation and Tracking Control. [Internet] [Masters thesis]. Virginia Tech; 2016. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/71380.
Council of Science Editors:
Harris Jr FB. GNSS Hardware-In-The-Loop Formation and Tracking Control. [Masters Thesis]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/71380
11.
Nikrant, Alex Warner.
Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode.
Degree: MS, Aerospace Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/93959
► In recent years, the space industry has seen rapidly accelerating growth due to the continuing advancement of technology. A critical area of spacecraft technology is…
(more)
▼ In recent years, the space industry has seen rapidly accelerating growth due to the continuing advancement of technology. A critical area of spacecraft technology is the spacecraft’s propulsion system, which allows the vehicle to achieve and maintain its desired orbit or trajectory through space. One class of propulsion systems known as “electric propulsion” uses electrical power to accelerate the fuel of the spacecraft. These types of propulsion systems are far more efficient than traditional propulsion systems, which use chemical reactions to create thrust. One of the main components of certain types of electric propulsion systems is the hollow cathode, which initiates and sustains the thruster operation. In this research, a hollow cathode with several non-conventional characteristics is developed and tested. First of all, standard hollow cathodes use a heater to bring the cathode up to operational temperature, but this design is heaterless which offers several benefits to the cathode and electrical power system designs. Secondly, the cathode uses a non-conventional choice of material for the “emitter”, which emits electrons when heated and allows the cathode to operate. Lastly, while typical electric propulsion systems use xenon for fuel, this cathode uses argon which has several benefits over xenon including cost. An overview of electric propulsion is presented, as well as a new physics-based model of this type of cathode that allows useful calculations based on simple measurements. The design and test results of the cathode are discussed in detail, with several interesting and insightful behaviors that were noted during testing. Heaterless cathodes have the potential to improve the efficiency, cost, and weight of electric propulsion systems, and this research therefore contributes to an important field for the future of space exploration.
Advisors/Committee Members: Adams, Colin (committeechair), Scales, Wayne A. (committee member), Srinivasan, Bhuvana (committee member).
Subjects/Keywords: heaterless hollow cathode; electric propulsion; plasma dynamics; plume mode
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APA (6th Edition):
Nikrant, A. W. (2019). Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/93959
Chicago Manual of Style (16th Edition):
Nikrant, Alex Warner. “Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode.” 2019. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/93959.
MLA Handbook (7th Edition):
Nikrant, Alex Warner. “Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode.” 2019. Web. 10 Apr 2021.
Vancouver:
Nikrant AW. Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode. [Internet] [Masters thesis]. Virginia Tech; 2019. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/93959.
Council of Science Editors:
Nikrant AW. Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode. [Masters Thesis]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/93959
Virginia Tech
12.
Robertson, Ellen Faith.
Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments.
Degree: PhD, Electrical Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/94631
► This dissertation explores ways to improve autonomous navigation in unstructured terrain conditions, with specific applications to unmanned casualty extraction in disaster scenarios. Search and rescue…
(more)
▼ This dissertation explores ways to improve autonomous navigation in unstructured terrain conditions, with specific applications to unmanned casualty extraction in disaster scenarios. Search and rescue applications often put the lives of first responders at risk. Using robotic systems for human rescue in disaster scenarios can keep first responders out of danger. To enable safe robotic casualty extraction, this dissertation proposes a novel rescue robot design concept named SAVER. The proposed design concept consists of several subsystems including a declining stretcher bed, head and neck support system, and robotic arms that conceptually enable safe casualty manipulation and extraction based on high-level commands issued by a remote operator. In order to enable autonomous navigation of the proposed conceptual system in challenging outdoor terrain conditions, this dissertation proposes improvements in planning, trajectory tracking control and terrain estimation. The proposed techniques are able to take into account the dynamic effects of robot-terrain interaction including slip experienced by the vehicle, slope of the terrain and actuator limitations. The proposed techniques have been validated through simulations and experiments in indoor and simple outdoor terrain conditions. The applicability of the above techniques in improving tele-operation of rescue robotic systems in unstructured terrain is also discussed at the end of this dissertation.
Advisors/Committee Members: Earle, Gregory D. (committeechair), Tront, Joseph G. (committee member), Srinivasan, Bhuvana (committee member), Scales, Wayne A. (committee member), Bailey, Scott M. (committee member).
Subjects/Keywords: Space Science; Ion source; Simulations; Plasma; Vacuum Testing; Satellite Instrumentation
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APA (6th Edition):
Robertson, E. F. (2019). Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/94631
Chicago Manual of Style (16th Edition):
Robertson, Ellen Faith. “Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments.” 2019. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/94631.
MLA Handbook (7th Edition):
Robertson, Ellen Faith. “Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments.” 2019. Web. 10 Apr 2021.
Vancouver:
Robertson EF. Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/94631.
Council of Science Editors:
Robertson EF. Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/94631
Virginia Tech
13.
Malhotra, Garima.
HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds.
Degree: MS, Electrical and Computer Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/78084
► The equatorial Quasi Biennial Oscillation (QBO) is known to be an important source of inter-annual variability at mid and high latitudes in both hemispheres. Coupling…
(more)
▼ The equatorial Quasi Biennial Oscillation (QBO) is known to be an important source of inter-annual variability at mid and high latitudes in both hemispheres. Coupling between QBO and the polar vortex has been extensively studied over the past few decades, however, less is known about QBO influences in the mid-latitude mesosphere. One reason for this is the relative lack of instrumentation available to study mesospheric dynamics at mid-latitudes. In this study, we have used the mid-latitude SuperDARN HF radar at Saskatoon (52.16 N, -106.53 E) to study inter-annual variation in mesospheric winds. The specific aim was to determine whether or not a Quasi Biennial signature could be identified in the Saskatoon mesosphere, and if so, to understand its relationship with the equatorial stratospheric QBO. To achieve this goal, a technique has been developed which extracts meteor echoes from SuperDARN near-range gates and then applies least-squares fitting across all radar beam directions to calculate hourly averages of the zonal and meridional components of the mesospheric neutral wind. Subsequent analysis of 13 years (2002-2014) of zonal wind data produced using this technique indicates that there is indeed a significant QBO signature present in Saskatoon mesospheric winds during late winter (Jan-Feb). This mesospheric QBO signature is in opposite phase with the equatorial stratospheric QBO, such that when QBO (at 50 hPa) is in its easterly (westerly) phase, the late winter winds in Saskatoon mesosphere become more (less) westerly. To further examine the source of the signature, we also analyzed winds in the Saskatoon stratosphere between 5 hPa and 70 hPa using the ECMWF ERA-Interim reanalysis data set, and found that the late winter stratospheric winds become less (more) westerly when QBO is easterly (westerly). This QBO signature in the mid-latitude stratospheric winds is essentially the same as that observed for the polar vortex in previous studies but it is opposite in phase to the mid-latitude mesospheric QBO. We therefore conclude that filtering of gravity waves through QBO-modulated stratospheric winds plays a major role in generating the mesospheric QBO signature we have identified in the Saskatoon HF radar data. When the Saskatoon stratospheric winds are anomalously westward during easterly QBO, the gravity waves having westward momentum might be filtered out, depositing a net eastward momentum in the mesosphere as they propagate upwards. This would result in increased westerly mesospheric winds at Saskatoon. The opposite would happen when the equatorial QBO is westerly.
Advisors/Committee Members: Scales, Wayne A. (committee member), Clauer, Robert C. (committee member), Baker, Joseph B. H. (committeecochair), Ruohoniemi, J. Michael (committeecochair).
Subjects/Keywords: HF Radar Meteor echoes; SuperDARN radar; Gravity wave filtering; Mesospheric QBO; Mid-Latitude QBO; Holton Tan; SuperDARN Radar Mesospheric winds
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APA (6th Edition):
Malhotra, G. (2016). HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/78084
Chicago Manual of Style (16th Edition):
Malhotra, Garima. “HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds.” 2016. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/78084.
MLA Handbook (7th Edition):
Malhotra, Garima. “HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds.” 2016. Web. 10 Apr 2021.
Vancouver:
Malhotra G. HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds. [Internet] [Masters thesis]. Virginia Tech; 2016. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/78084.
Council of Science Editors:
Malhotra G. HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds. [Masters Thesis]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/78084
Virginia Tech
14.
Thurber, Andrew.
Investigations of Hypervelocity Impact Physics.
Degree: PhD, Mechanical Engineering, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/95298
► Spacecraft and satellites in orbit are under an increasing threat of impact from orbital debris and naturally occurring meteoroids. While objects larger than 10 cm…
(more)
▼ Spacecraft and satellites in orbit are under an increasing threat of impact from orbital debris and naturally occurring meteoroids. While objects larger than 10 cm are routinely tracked and avoided, collisions inevitably occur with smaller objects at relative velocities exceeding 10 km/s. Such hypervelocity impacts (HVI) create immense shock pressures and can melt or vaporize aerospace materials, even inducing brief plasmas at higher speeds. Sacrificial shields have been developed to protect critical components from damage under these conditions, but the response of many materials in such an extreme event is still poorly understood.
This work presents the summary of computational analysis methods to quantify the relevant physical mechanisms at play in a hypervelocity impact. Strain rate-dependent behavior was investigated using several models, and fluid material descriptions were used to draw parallels under high shear rate loading. The production and expansion of impact plasmas were modeled and compared to experimental evidence. Additionally, a parametric study was performed on a multitude of possible material candidates for sacrificial shield design, and new shielding configurations were proposed.
A comparison of material models indicated that the Johnson-Cook and Steinberg-Cochran-Guinan-Lund metallic formulations yielded the most consistent results with the lowest deviation from experimental measures in the strain rate regime of interest. Both meshless Lagrangian and quasi-Eulerian meshed schemes approximated the qualitative and quantitative characteristics of HVI debris clouds with average measurable errors under 5%. While the meshless methods showed better resolution of interfaces and small details, the meshed methods were shown to converge faster under several metrics with fewer regions of spurious instability.
Additionally, a new technique was introduced using hypothetical viscous fluids to approximate debris cloud behavior, which showed good correlation to experimental results when such models were constructed using the shear rates seen in hypervelocity impacts. Formulations using non-Newtonian fluids showed additional capability in approximating solid behavior, both quantitatively and qualitatively. Such fluid models are significant, in that they reproduced the qualitative and quantitative characteristics of evolving debris clouds with better fidelity than purely hydrodynamic models using inviscid fluids. This indicates that while inertial effects can dominate overdriven shock phenomena, neglecting shear forces invariably introduces errors; such forces can instead be simplistically approximated via viscous models. The viscous approximation also allowed for a successful scaling analysis using dimensionless Pi terms, which was unfeasible using solid constitutive relations.
Attempts to model plasma dynamics saw success in the simulation of a laser ablation-driven flyer plate by using a hot gas with solid initial conditions; similar strategies were used to analyze plasma production in hypervelocity…
Advisors/Committee Members: Bayandor, Javid (committeechair), Battaglia, Francine (committee member), O'Brien, Walter F. Jr. (committee member), Scales, Wayne A. (committee member), Samareh, Jamshid A. (committee member).
Subjects/Keywords: impact; orbital debris; finite element; shock physics
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APA (6th Edition):
Thurber, A. (2014). Investigations of Hypervelocity Impact Physics. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/95298
Chicago Manual of Style (16th Edition):
Thurber, Andrew. “Investigations of Hypervelocity Impact Physics.” 2014. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/95298.
MLA Handbook (7th Edition):
Thurber, Andrew. “Investigations of Hypervelocity Impact Physics.” 2014. Web. 10 Apr 2021.
Vancouver:
Thurber A. Investigations of Hypervelocity Impact Physics. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/95298.
Council of Science Editors:
Thurber A. Investigations of Hypervelocity Impact Physics. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/95298
Virginia Tech
15.
Schneider, Maximilian Kurt.
Characterization of Collisional Shock Structures Induced by the Stagnation of Railgun-driven Multi-ion-species Plasma-jets.
Degree: PhD, Aerospace Engineering, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/96551
► Plasma, the so-called fourth state of matter, is an ionized gas that often behaves like a fluid but can also become magnetized and carry an…
(more)
▼ Plasma, the so-called fourth state of matter, is an ionized gas that often behaves like a fluid but can also become magnetized and carry an electric current. This combination leads to a lot of interesting yet often un-intuitive physics, the study of which is very important for understanding a wide array of topics. One subset of this field is the study of shock-wave induced species separation. Just like the shock-wave a jet aircraft produces when it moves through the air at a speed greater than the speed of sound, a plasma shock is characterized by a large change in parameters like density, temperature, and pressure across a very small region. A shock-wave propagating through a plasma can cause different ion species present to separate out, a phenomenon that is driven by the gradients that are present across a shock front. Understanding how these mechanisms work is important to a number of applications, including fusion energy research and astrophysical events. The first section of this work discusses the design and development of a plasma-armature railgun, a device that can produce and accelerate jets of plasma to high-Mach-number within a vacuum chamber. The next and most substantive section of the work presents results from experimental campaigns to characterize the accelerated plasma jets and then to induce plasma-jet collisions with the hope of producing shock-waves that exist on time and spatial
scales that can be readily measured in a laboratory setting. This work is a foundation for future experimental attempts to measure separation induced by a shock-wave in order to better understand these complex phenomena.
Advisors/Committee Members: Adams, Colin (committeechair), Scales, Wayne A. (committee member), Lowe, Kevin T. (committee member), Srinivasan, Bhuvana (committee member).
Subjects/Keywords: plasma-jet; shock-wave; plasma railgun; multi-ion-species plasma
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APA (6th Edition):
Schneider, M. K. (2020). Characterization of Collisional Shock Structures Induced by the Stagnation of Railgun-driven Multi-ion-species Plasma-jets. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/96551
Chicago Manual of Style (16th Edition):
Schneider, Maximilian Kurt. “Characterization of Collisional Shock Structures Induced by the Stagnation of Railgun-driven Multi-ion-species Plasma-jets.” 2020. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/96551.
MLA Handbook (7th Edition):
Schneider, Maximilian Kurt. “Characterization of Collisional Shock Structures Induced by the Stagnation of Railgun-driven Multi-ion-species Plasma-jets.” 2020. Web. 10 Apr 2021.
Vancouver:
Schneider MK. Characterization of Collisional Shock Structures Induced by the Stagnation of Railgun-driven Multi-ion-species Plasma-jets. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/96551.
Council of Science Editors:
Schneider MK. Characterization of Collisional Shock Structures Induced by the Stagnation of Railgun-driven Multi-ion-species Plasma-jets. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/96551
Virginia Tech
16.
Janeski, John.
Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment.
Degree: PhD, Aerospace Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/23922
► Electrodynamic tethers have a wide range of proposed applications in the fields of satellite propulsion and space plasma research. The fundamental purpose of this dissertation…
(more)
▼ Electrodynamic tethers have a wide range of proposed applications in the fields of satellite propulsion and space plasma research. The fundamental purpose of this dissertation is to improve the understanding of the behavior of an electrodynamic tether (EDT) system in Earth's ionosphere. An electrodynamic tether system consists of two satellites connected by a long tether that generates current to produce either power or thrust via the system's electromagnetic interaction with the space environment. Previous electrodynamic tether investigations decouple the interaction between the tether and the constantly changing plasma environment. The limiting factor inhibiting the development of a full system model that has an accurate characterization of the tether/plasma interaction is that the understanding of that interaction is not well developed over a wide range of system parameters. The EDT system model developed in this study uses a high fidelity dynamics model that includes a tether current described by an analytical current collection model whose plasma parameters are determine by the International Reference Ionosphere. It is first shown that new instabilities are induced in the system dynamics under a basic analytical current model versus a constant current model.
A 2-D3v Particle-in-Cell (PIC) code has been developed to study the plasma dynamics near a positively charged EDT system end-body and their impact on the current collected. Simulations are run over a range of system parameters that occur throughout a LEO orbit. The azimuthal current structures observed during the TSS-1R mission are found to enhance the current collected by the satellite when the magnetic field is slightly off of perpendicular to the orbital velocity. When the in-plane component of the magnetic field becomes large, the electrons are not able to easily cross the field lines causing plasma lobes form above and below the satellite. The lobes limit the current arriving to the satellite and also cause an enhanced wake to develop. A high satellite bias causes a stable bow-shock structure to form in the ram region of the satellite, which limits the number of electrons entering the sheath region and thus limiting the current collected. Electron-neutral collisions are found to destabilize the bow-shock structure and remove its current limiting effects. Additionally, as the magnetization of the plasma is increased, the current becomes limited by the charged particle's inability to cross magnetic field lines. Analytical curve fits based on the simulation results are presented that characterize the dependence of the average current collected on the local magnetic field orientations, space plasma magnetization and satellite potential.
The results from the PIC simulations characterizing the magnetic field's influence on the tether's current are incorporated into the system dynamics model to study the behavior of the EDT system over a range of inclinations. The magnetic field is found to limit the diurnal variations in the current collected by the…
Advisors/Committee Members: Hall, Christopher D. (committeechair), Scales, Wayne A. (committeechair), Woolsey, Craig A. (committee member), Earle, Gregory D. (committee member).
Subjects/Keywords: Electrodynamic Tether; Current Collection; Spacecraft Charging; Particle-In-Cell Simulations
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APA (6th Edition):
Janeski, J. (2013). Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/23922
Chicago Manual of Style (16th Edition):
Janeski, John. “Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment.” 2013. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/23922.
MLA Handbook (7th Edition):
Janeski, John. “Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment.” 2013. Web. 10 Apr 2021.
Vancouver:
Janeski J. Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/23922.
Council of Science Editors:
Janeski J. Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/23922
Virginia Tech
17.
Esmond, Micah Jeshurun.
Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges.
Degree: PhD, Mechanical Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/81447
► A two-dimensional, time-dependent model and code have been developed to model electrothermal (ET) plasma discharges. ET plasma discharges are capillary discharges that draw tens of…
(more)
▼ A two-dimensional, time-dependent model and code have been developed to model electrothermal (ET) plasma discharges. ET plasma discharges are capillary discharges that draw tens of kA of electric current. The current heats the plasma, and the plasma radiates energy to the capillary walls. The capillary walls ablate by melting and vaporizing and by sublimation. The newly developed model and code is called the Three-fluid, 2D Electrothermal Plasma Flow Simulator (THOR). THOR simulates the electron, ion, and neutral species as separate fluids coupled through interaction terms. The two-dimensional modeling capabilities made available in this new code represent a tool for the exploration and analysis of the physics involved in ET plasma discharges that has never before been available.
Previous simulation models of ET plasma discharges have relied primarily on a 1D description of the plasma. These models have often had to include a tunable correction factor to account for the vapor shield layer - a layer of cold ablated vapor separating the plasma core from the ablating surface and limiting the radiation heat flux to the capillary wall. Some studies have incorporated a 2D description of the plasma boundary layer and shown that the effects of a vapor shield layer can be modeled using this 2D description. However, these 2D modeling abilities have not been extended to the simulation of pulsed ET plasma discharges. The development of a fully-2D and time-dependent simulation model of an entire ET plasma source has enabled the investigation of the 2D development of the vapor shield layer and direct comparison with experiments. In addition, this model has provided novel insight into the inherently 2D nature of the internal flow characteristics involved within the plasma channel in an ET plasma discharge. The model is also able to capture the effects of inter-species interactions.
This work focuses on the development of the THOR model. The model has been implemented using C++ and takes advantage of modern supercomputing resources. The THOR model couples the 2D hydrodynamics and the interactions of the plasma species through joule heating, ionization, recombination, and elastic collisions. The analysis of simulation results focuses on emergent internal flow characteristics, direct simulation of the vapor shield layer, and the investigation of source geometry effects on simulated plasma parameters. The effect of elastic collisions between electrons and heavy species are shown to affect internal flow characteristics and cause the development of back-flow inside the ET plasma source. The development of the vapor shield layer has been captured using the diffusion approximation for radiation heat transfer within the ET plasma source with simulated results matching experimental measurements. The relationship between source radius and peak current density inside ET plasma discharges has also been explored, and the transition away from the ablation-controlled operation of ET plasma discharges has been observed.
Advisors/Committee Members: Battaglia, Francine (committeechair), Winfrey, Leigh (committeechair), Scales, Wayne A. (committee member), Liu, Yang (committee member), Vick, Brian (committee member).
Subjects/Keywords: Electrothermal plasma; capillary discharge; plasma simulation
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APA (6th Edition):
Esmond, M. J. (2016). Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/81447
Chicago Manual of Style (16th Edition):
Esmond, Micah Jeshurun. “Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges.” 2016. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/81447.
MLA Handbook (7th Edition):
Esmond, Micah Jeshurun. “Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges.” 2016. Web. 10 Apr 2021.
Vancouver:
Esmond MJ. Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/81447.
Council of Science Editors:
Esmond MJ. Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/81447
Virginia Tech
18.
Peng, Senlin.
A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies.
Degree: PhD, Electrical and Computer Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/28605
► Ionospheric scintillations can cause significant amplitude and/or phase fluctuations of GNSS signals. This work presents analysis results of scintillation effects on the new GPS L5…
(more)
▼ Ionospheric scintillations can cause significant amplitude and/or phase fluctuations of GNSS signals. This work presents analysis results of scintillation effects on the new GPS L5 signal based on data collected using a real-time scintillation monitoring and data collection system at HAARP, Alaska. The data collection setup includes a custom narrow band front end that collects GPS L1, L2 IF samples and two reconfigurable USRP2 based RF front ends to collect wideband GPS L5 and GLONASS L1 and L2 signals. The results confirm that scintillation has a stronger impact on GPS L2 and L5 signals than on the L1 signal. Our preliminary results also show that carrier phase and amplitude scintillations on each signal are highly correlated. The amplitude and carrier phase scintillation are also correlated among the three signals.
In this study, a multi-constellation multi-band GNSS software receiver has been developed based on USRP2, a general purpose radio platform. The C++ class-based software receiver were developed to process the IF data for GPS L1, L2C, and L5 and GLONASS L1 and L2 signals collected by the USRP2 front end. The front end performance is evaluated against the outputs of a high end custom front end driven by the same local oscillator and two commercial receivers, all using the same real signal sources. These results demonstrate that the USRP2 is a suitable front end for applications, such as ionosphere scintillation studies.
Another major contribution of this work is the implementation of a Vector tracking loop (VTL) for robust carrier tracking. The VTL is developed based on the extended Kalman filter (EKF) with adaptive covariance matrices. Both scalar tracking loop (STL) and VTL are implemented. Once an error in the scalar loop is detected, the results from the VTL are used to assist the STL. The performance of the VTL is compared with the traditional STL with three different data sets: raw GPS RF data with short signal outages, RF data with strong scintillation impacts collected during the last solar maximum, and high dynamic data with long interval signal outages from a GPS simulator. The results confirm the performance improvement of the VTL over scintillation impacts and show that the VTL can maintain signal lock during long intervals of signal outage if the satellite ephemerides are available and the pseudorange estimation is within one code chip accuracy. The dynamic performance improvement of the VTL is verified as well. The results show the potential of robust tracking based on VTL during scintillation and interference.
Advisors/Committee Members: Scales, Wayne A. (committeechair), Farhood, Mazen (committee member), Bose, Tamal (committee member), Reed, Jeffrey Hugh (committee member), Morton, Jade Yu (committee member).
Subjects/Keywords: GNSS; Ionosphere scintillation; Software receiver; Vector tracking loop
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APA (6th Edition):
Peng, S. (2012). A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/28605
Chicago Manual of Style (16th Edition):
Peng, Senlin. “A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies.” 2012. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/28605.
MLA Handbook (7th Edition):
Peng, Senlin. “A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies.” 2012. Web. 10 Apr 2021.
Vancouver:
Peng S. A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/28605.
Council of Science Editors:
Peng S. A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/28605
Virginia Tech
19.
Song, Yang.
Unstructured Nodal Discontinuous Galerkin Method for Convection-Diffusion Equations Applied to Neutral Fluids and Plasmas.
Degree: PhD, Aerospace Engineering, 2020, Virginia Tech
URL: http://hdl.handle.net/10919/99291
► High-energy density (HED) plasma science is an important area in studying astrophysical phenomena as well as laboratory phenomena such as those applicable to inertial confinement…
(more)
▼ High-energy density (HED) plasma science is an important area in studying astrophysical phenomena as well as laboratory phenomena such as those applicable to inertial confinement fusion (ICF). ICF plasmas undergo radial compression, with an aim of achieving fusion ignition, and are subject to a number of hydrodynamic instabilities that can significantly alter the implosion and prevent sufficient fusion reactions. An understanding of these instabilities and their mitigation mechanisms is important allow for a stable implosion in ICF experiments. This work aims to provide a high order accurate and robust numerical framework that can be used to study these instabilities through simulations.
The first half of this work aims to provide a detailed description of the numerical framework, texttt{PHORCE}. texttt{PHORCE} is a high order numerical package that can be used in solving convection-diffusion problems in neutral fluids and plasmas. Outstanding challenges exist in simulating high energy density (HED) hydrodynamics, where very large gradients exist in density, temperature, and transport coefficients (such as viscosity), and numerical instabilities arise from these region if there is no intervention. These instabilities may lead to inaccurate results or cause simulations to fail, especially for high-order numerical methods. Substantial work has been done in texttt{PHORCE} to improve its robustness in dealing with numerical instabilities. This includes the implementation and design of several high-order limiters. An novel algorithm is also proposed in this work to solve the diffusion term accurately and efficiently, which further enriches the physics that texttt{PHORCE} can investigate.
The second half of this work involves rigorous benchmarks and experimentally relevant simulations of hydrodynamic instabilities. Both advection and diffusion solvers are well verified through convergence studies. Hydrodynamic and plasma models implemented are also validated against results in existing literature. Rayleigh-Taylor instability growth with experimentally relevant parameters are performed on both planar and radially converging domains. Although this work is motivated by physics in HED hydrodynamics, the emphasis is placed on numerical models that are generally applicable across a wide variety of fields and disciplines.
Advisors/Committee Members: Srinivasan, Bhuvana (committeechair), Roy, Christopher John (committee member), Adams, Colin (committee member), Scales, Wayne A. (committee member).
Subjects/Keywords: Nodal Discontinuous Galerkin; Magnetohydrodynamics; Two-Fluid Plasma Model; Plasma Instabilities; Convection-Diffusion; Reconstruction; Mass of Fluid
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APA (6th Edition):
Song, Y. (2020). Unstructured Nodal Discontinuous Galerkin Method for Convection-Diffusion Equations Applied to Neutral Fluids and Plasmas. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/99291
Chicago Manual of Style (16th Edition):
Song, Yang. “Unstructured Nodal Discontinuous Galerkin Method for Convection-Diffusion Equations Applied to Neutral Fluids and Plasmas.” 2020. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/99291.
MLA Handbook (7th Edition):
Song, Yang. “Unstructured Nodal Discontinuous Galerkin Method for Convection-Diffusion Equations Applied to Neutral Fluids and Plasmas.” 2020. Web. 10 Apr 2021.
Vancouver:
Song Y. Unstructured Nodal Discontinuous Galerkin Method for Convection-Diffusion Equations Applied to Neutral Fluids and Plasmas. [Internet] [Doctoral dissertation]. Virginia Tech; 2020. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/99291.
Council of Science Editors:
Song Y. Unstructured Nodal Discontinuous Galerkin Method for Convection-Diffusion Equations Applied to Neutral Fluids and Plasmas. [Doctoral Dissertation]. Virginia Tech; 2020. Available from: http://hdl.handle.net/10919/99291
Virginia Tech
20.
Zheng, Yi.
Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System.
Degree: PhD, Computer Engineering, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/48892
► Fast and accurate diagnosis is always in demand by modern medical professionals and in the area of national defense. At present, limitations of testing speed,…
(more)
▼ Fast and accurate diagnosis is always in demand by modern medical professionals and in the area of national defense. At present, limitations of testing speed, sample conditions, and levels of precision exist under current technologies, which are usually slow and involve testing the specimen under laboratory conditions. Typically, these methods also involve several biochemical processing steps and subsequent detection of low energy luminescence or electrical changes, all of which reduce the speed of the test as well as limit the precision. In order to solve these problems and improve the sensing performance, this project proposes an innovative CMOS magnetic biological sensor system for rapidly testing the presence of potential pathogens and bioterrorism agents (zoonotic microorganisms) both in specimens and especially in the environment. The sensor uses an electromagnetic detection mechanism to measure changes in the number of microorganisms – tagged by iron nanoparticles – that are placed on the surface of an integrated circuit (IC) chip. Measured magnetic effects are transformed into electronic signals that count the number and type of organisms present. This biosensor introduces a novel design of a conical-shaped inductor, which achieves ultra-accuracy of sensing biological pathogens. The whole system is integrated on a single chip based on the fabrication process of IBM 180 nm (CMOS_IBM_7RF), which makes the sensor small-sized, portable, high speed, and low cost. The results of designing, simulating, and fabricating the sensor are reported in this dissertation.
Advisors/Committee Members: Tront, Joseph G. (committeechair), Scales, Wayne A. (committee member), Ha, Dong S. (committee member), Sriranganathan, Nammalwar (committee member), Schaumont, Patrick Robert (committee member).
Subjects/Keywords: Biohazard; Antibody and antigen; Pathogen; Iron nanoparticle; CMOS; Integrated circuit; Conical-shaped inductor; Uniform magnetic field; Magnetic sensor; LC oscillator; Frequency counter; Prototype; Antenna effect
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APA (6th Edition):
Zheng, Y. (2014). Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/48892
Chicago Manual of Style (16th Edition):
Zheng, Yi. “Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System.” 2014. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/48892.
MLA Handbook (7th Edition):
Zheng, Yi. “Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System.” 2014. Web. 10 Apr 2021.
Vancouver:
Zheng Y. Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/48892.
Council of Science Editors:
Zheng Y. Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/48892
Virginia Tech
21.
Pramodkumar, Neeraj.
Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars.
Degree: MS, Electrical Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/23845
► The Sub-Auroral Polarization Stream (SAPS) is a narrow, intense and persistent westward (sunward) ionospheric convection flow channel observed equatorward of the auroral electron precipitation boundary,…
(more)
▼ The Sub-Auroral Polarization Stream (SAPS) is a narrow, intense and persistent westward (sunward) ionospheric convection flow channel observed equatorward of the auroral electron precipitation boundary, predominantly on the nightside. Previous studies have identified disturbed-time SAPS to be a geomagnetic activity dependent phenomenon, which exhibits average pre-midnight and post-midnight velocities of 1000 m/s and 400 m/s respectively. Numerous studies have reported even narrower and more intense westward plasma flows called SAIDs to be embedded within SAPS channels, especially during substorm recovery phases. Quiet-time SAPS studies, although relatively few, have shown these SAPS to be associated with much weaker velocities and to be influenced by substorm intensifications. However, these studies have been limited in their ability to make simultaneous measurements of SAPS flow velocities over many hours of MLT. The recent expansion of SuperDARN radars to middle latitudes facilitates unprecedented large-scale observations of SAPS over 10 hours of MLT with high temporal and spatial resolution. In this thesis, we first examine the spatial and temporal dynamics of one quiet-time SAPS event, using the mid-latitude SuperDARN radars. The SAPS was identified as elevated flows lying equatorward of the auroral electron precipitation boundary specified by the NOAA POES satellites. We demonstrate the L-shell fitting technique to analyze the dynamics in the strength and direction of the two-dimensional SAPS flow velocities at three separate magnetic longitudes. The quiet-time SAPS event thus examined lasted for over 4 hours in UT and extended over 10 hours of MLT, as is commonly observed for disturbed-time SAPS.
However, the decrease in SAPS peak latitudes and peak velocities with MLT and MLon respectively, observed for disturbed-time SAPS, was not observed for this event. We also find the dynamics of the enhancements in the quiet-time SAPS peak velocities, to correlate well with that of substorm intensifications identified using the CARISMA magnetometers. We then identify numerous such conjunctions between quiet-time SAPS and substorms to infer that quiettime SAPS were almost always associated with substorms and their durations were well bounded by that of the substorms for most cases. Next, we extend this analysis over to a statistical study of quiet-time and disturbed-time SAPS events identified over two years. From this study, we find quiet-time SAPS to occur between the relatively narrow nightside MLT range of [18, 4] whereas disturbed-time SAPS was found to occur between the broader nightside MLT range of [15, 5]. We also find the occurrence percentage of quiet-time SAPS to be at its highest between the narrow latitude range of 60-66⁰, while disturbed-time SAPS was observed to occur within a much broader latitude range of 55-66⁰. Finally, the calibration and validation of a control card used in the SuperDARN radar transmitters, is discussed.
Advisors/Committee Members: Ruohoniemi, John Michael (committeechair), Baker, Joseph B. H. (committeechair), Pratt, Timothy J. (committee member), Scales, Wayne A. (committee member).
Subjects/Keywords: SuperDARN; SAPS; mid-latitude; substorm; ionosphere
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APA (6th Edition):
Pramodkumar, N. (2013). Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/23845
Chicago Manual of Style (16th Edition):
Pramodkumar, Neeraj. “Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars.” 2013. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/23845.
MLA Handbook (7th Edition):
Pramodkumar, Neeraj. “Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars.” 2013. Web. 10 Apr 2021.
Vancouver:
Pramodkumar N. Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars. [Internet] [Masters thesis]. Virginia Tech; 2013. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/23845.
Council of Science Editors:
Pramodkumar N. Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars. [Masters Thesis]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/23845
Virginia Tech
22.
Thomas, Evan Grier.
Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars.
Degree: MS, Electrical Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/19207
► Total electron content (TEC) data measured from ground-based GPS receivers is compared to HF backscatter from ionospheric irregularities obtained by Super Dual Auroral Radar Network…
(more)
▼ Total electron content (TEC) data measured from ground-based GPS receivers is compared to HF backscatter from ionospheric irregularities obtained by Super Dual Auroral Radar Network (SuperDARN) radars. We present the first observations of a recurrent region of anomalous enhanced TEC at mid-latitudes over North America and attempt to characterize its frequency of occurrence. Next, we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization (TOI) from mid-latitude plumes of storm enhanced density (SED) during a geomagnetic storm on 26 September 2011. A channel of high density F region plasma was transported from the dayside ionosphere and into the polar cap by enhanced convection electric fields extending to mid-latitudes. After the solar wind IMF conditions quieted and the dayside convection electric fields retreated to higher latitudes, an SED was observed extending to, but not entering, the dayside cusp region. The source mechanism (enhanced electric fields) previously drawing the plasma from mid-latitudes and into the polar cap was no longer active, resulting in a fossil feature which persisted for several hours as it elongated in magnetic local time. Finally, we discuss ground surface effects on the HF backscatter observed by four SuperDARN radars. Monthly ground scatter occurrence rates are calculated for comparison with Arctic sea ice boundaries derived from satellite observations, showing reduced backscatter from regions covered by ice.
Advisors/Committee Members: Ruohoniemi, John Michael (committeechair), Baker, Joseph B. H. (committeechair), Scales, Wayne A. (committee member), Pratt, Timothy J. (committee member).
Subjects/Keywords: SuperDARN; GPS; mid-latitude; ionosphere
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APA (6th Edition):
Thomas, E. G. (2012). Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/19207
Chicago Manual of Style (16th Edition):
Thomas, Evan Grier. “Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars.” 2012. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/19207.
MLA Handbook (7th Edition):
Thomas, Evan Grier. “Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars.” 2012. Web. 10 Apr 2021.
Vancouver:
Thomas EG. Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars. [Internet] [Masters thesis]. Virginia Tech; 2012. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/19207.
Council of Science Editors:
Thomas EG. Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars. [Masters Thesis]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/19207
23.
Brosie, Kayla Nicole.
Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse.
Degree: MS, Electrical Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/78710
► A full solar eclipse is going to be visible from a range of states in the contiguous United States on August 21, 2017. Since the…
(more)
▼ A full solar eclipse is going to be visible from a range of states in the contiguous United States on August 21, 2017. Since the atmosphere of the Earth is charged by the sun, the blocking of the sunlight by the moon may cause short term changes to the atmosphere, such as density and temperature alterations. There are many ways to measure these changes, one of these being ionospheric scintillation. Ionospheric scintillation is rapid amplitude and phase fluctuations of signals passing through the ionosphere caused by electron density irregularities in the ionosphere. At mid-latitudes, scintillation is not as common of an occurrence as it is in equatorial or high-altitude regions. One of the theories that this paper looks into is the possibility of the solar eclipse producing an instability in the ionosphere that will cause the mid-latitude region to experience scintillations that would not normally be present. Instabilities that could produce scintillation are reviewed and altered further to model similar conditions to those that might occur during the solar eclipse. From this, the satellites that are being used are discuses, as is hardware and software tools were developed to record the scintillation measurements. Although this work was accomplished before the eclipse occurred, measurement tools were developed and verified along with generating a model that predicted if the solar eclipse will produce an instability large enough to cause scintillation for high frequency satellite downlinks.
Advisors/Committee Members: McGwier, Robert W. (committeechair), Earle, Gregory D. (committeechair), Buehrer, R. Michael (committee member), Scales, Wayne A. (committee member).
Subjects/Keywords: ionospheric scintillation; solar eclipse; temperature gradient instability; ionospheric instabilities
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APA (6th Edition):
Brosie, K. N. (2017). Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/78710
Chicago Manual of Style (16th Edition):
Brosie, Kayla Nicole. “Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse.” 2017. Masters Thesis, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/78710.
MLA Handbook (7th Edition):
Brosie, Kayla Nicole. “Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse.” 2017. Web. 10 Apr 2021.
Vancouver:
Brosie KN. Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/78710.
Council of Science Editors:
Brosie KN. Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/78710
Virginia Tech
24.
Samimi, Alireza.
Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating.
Degree: PhD, Electrical Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/51833
► Stimulated Electromagnetic Emissions SEEs may provide important diagnostic information about space plasma composition, energetics, and dynamics during active experiments in which ground-based high powered radio…
(more)
▼ Stimulated Electromagnetic Emissions SEEs may provide important diagnostic information about space plasma composition, energetics, and dynamics during active experiments in which ground-based high powered radio waves are transmitted into the ionosphere. The nonlinear plasma processes producing this secondary radiation are not well understood particularly for some recent observations where the transmitter (pump) frequency is near the second harmonic of the electron gyro-frequency. New, more comprehensive, experimental observations of spectral features within 1kHz of the pump wave frequency are reported here in order to begin more careful comparisons of the experimental observations and a possible theoretical underpinning which is also provided. The experimental observations typically show two distinct types of secondary radiation spectra which are a) discrete narrowband harmonic spectral structures ordered by the ion gyro-frequency, so-called stimulated ion Bernstein Scatter (SIBS) and, b) broadband spectral structure with center frequency near 500 Hz and similar spectral bandwidth named ion acoustic parametric decay (IAPD). A theoretical model is provided that interprets these spectral features as resulting from parametric decay instabilities in which the pump field ultimately decays into high frequency upper hybrid/electron Bernstein and low frequency neutralized ion Bernstein and/or obliquely propagating ion acoustic waves at the upper hybrid interaction altitude. Detailed calculations of the threshold level, growth rate, unstable wavenumber and frequency bandwidth of the instabilities are provided for comparisons with experimental observations. An assessment of the effect of the critical instability parameters are provided including pump electric field strength, proximity of the pump frequency to the electron gyro-frequency and pump electric field geometry. The model shows quite reasonable agreement with the experimental observations.
Next, a two dimensional Particle-In-Cell Monte-Carlo Collision computational model (PIC-MCC) is employed in order to consider nonlinear aspects such as 1) electron acceleration through wave-particle heating, 2) more complex nonlinear wave-wave processes and 3) temporal evolution of electron irregularities through nonlinear saturation. The simulation results show that the IB associated parametric decay is primarily associated with electron acceleration perpendicular to the geomagnetic field. More gyro-harmonic lines are typically associated with more intense heating. Heating is reduced when the pump frequency is sufficiently close to 2fce. The IA associated parametric decay instability is primarily associated with electron tail heating along the magnetic field and heating is reduced when the pump frequency is sufficiently close to 2fce. Characteristics of caviton collapse behavior become prevalent in this case. Results are discussed within the context of some recent experimental observations. Further discussions are provided of connections with past observed SEE spectral features…
Advisors/Committee Members: Scales, Wayne A. (committeechair), Ruohoniemi, John Michael (committee member), Sharpe, Eric R. (committee member), Bailey, Scott M. (committee member), Pratt, Timothy J. (committee member).
Subjects/Keywords: Stimulated Electromagnetic Emission (SEE); Parametric decay instability (PDI); Oscillating two stream instability (OTSI)
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APA (6th Edition):
Samimi, A. (2013). Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/51833
Chicago Manual of Style (16th Edition):
Samimi, Alireza. “Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating.” 2013. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/51833.
MLA Handbook (7th Edition):
Samimi, Alireza. “Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating.” 2013. Web. 10 Apr 2021.
Vancouver:
Samimi A. Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/51833.
Council of Science Editors:
Samimi A. Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/51833
Virginia Tech
25.
Deshpande, Kshitija Bharat.
Investigation of High Latitude Ionospheric Irregularities utilizing Modeling and GPS Observations.
Degree: PhD, Electrical Engineering, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/49507
► Complex magnetosphere-ionosphere coupling mechanisms result in high latitude irregularities that are difficult to characterize. Until recently, the polar and auroral irregularities remained largely unexplored. Inadequate…
(more)
▼ Complex magnetosphere-ionosphere coupling mechanisms result in high latitude irregularities that are difficult to characterize. Until recently, the polar and auroral irregularities remained largely unexplored. Inadequate infrastructures to deploy and maintain advanced dual frequency Global Navigation Satellite System (GNSS) receivers at high latitudes, especially in the Southern hemisphere, makes such an investigation a formidable task. Additionally, the complicated geometry of the magnetic field lines in these regions pose challenges in designing global scintillation models. This dissertation takes some steps towards bridging these gaps while advancing the state-of-the-art high latitude irregularity studies.
In the first part of this dissertation, we briefly describe the Autonomous Adaptive Low-Power Instrument Platforms (AAL-PIP) experimental setup. These space science instrument platforms are being deployed in remote locations in Antarctica, improving the coverage of GNSS data availability. We explain in detail the method developed for analyzing high rate (typically 50 Hz) data from a novel dual-frequency Global Positioning System (GPS) receiver called Connected Autonomous Space Environment Sensor (CASES). We also report first observations from CASES at high latitudes. From this study, we established that CASES can be reliably used as a science grade GPS scintillation monitor.
Following this, a novel three dimensional (3D) electromagnetic (EM) wave propagation model called "Satellite-beacon Ionospheric-scintillation Global Model of the upper Atmosphere" (SIGMA) was developed to simulate GNSS scintillations on ground. GPS scintillation simulations of significantly high fidelity are now possible with this model. While the model is global, it is the first such model which accounts for the complicated geometry of magnetic field lines at high latitudes. Using SIGMA, a sensitivity study is presented to understand the effect of geographical, propagation and irregularity parameters on the phase scintillations. This allows us to reduce the dimensionality of the design space while solving the inverse problem described next.
In the final part, we utilize the tools developed for GPS measurement analysis and SIGMA to characterize the high latitude irregularities. We propose an inverse modeling technique to derive irregularity parameters by comparing the high rate (50 Hz) GNSS observations to the modeled outputs. We consider interhemispheric high latitude datasets for this investigation. We also implement SIGMA for analyzing a substorm event observed by AAL-PIP stations. One of the unique contributions of this research is to demonstrate that such an inverse modeling technique can form a basis in the investigation of the ionospheric irregularities. Moreover, availability of ample auxiliary data from multi-instrument observations can assist in this quest of understanding the physics of high latitude irregularities and their generation mechanisms.
Advisors/Committee Members: Clauer, C. Robert (committeechair), Pratt, Timothy J. (committee member), Bust, Gary (committee member), Brown, Gary S. (committee member), Scales, Wayne A. (committee member), Simonetti, John H. (committee member).
Subjects/Keywords: Ionosphere; Irregularities; High Latitude; GPS; Modeling; SIGMA
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APA (6th Edition):
Deshpande, K. B. (2014). Investigation of High Latitude Ionospheric Irregularities utilizing Modeling and GPS Observations. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/49507
Chicago Manual of Style (16th Edition):
Deshpande, Kshitija Bharat. “Investigation of High Latitude Ionospheric Irregularities utilizing Modeling and GPS Observations.” 2014. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/49507.
MLA Handbook (7th Edition):
Deshpande, Kshitija Bharat. “Investigation of High Latitude Ionospheric Irregularities utilizing Modeling and GPS Observations.” 2014. Web. 10 Apr 2021.
Vancouver:
Deshpande KB. Investigation of High Latitude Ionospheric Irregularities utilizing Modeling and GPS Observations. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/49507.
Council of Science Editors:
Deshpande KB. Investigation of High Latitude Ionospheric Irregularities utilizing Modeling and GPS Observations. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/49507
Virginia Tech
26.
Mahmoudian, Alireza.
New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities.
Degree: PhD, Electrical Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/19239
► Recently, experimental observations have shown that radar echoes from the irregularity source region associated with mesospheric dusty space plasmas may be modulated by radio wave…
(more)
▼ Recently, experimental observations have shown that radar echoes from the irregularity source region associated with mesospheric dusty space plasmas may be modulated by radio wave heating with ground-based ionospheric heating facilities. These experiments show great promise as a diagnostic for the associated dusty plasma in the Near-Earth Space Environment which is believed to have links to global change. This provides an alternative to more complicated and costly space-based observational approaches to investigating these layers. This dissertation seeks to develop new analytical and computational models to investigate fundamental physics of the associated dusty plasmas as well as utilize experimental observations during High Frequency HF ground-based heating experiments to develop practical techniques for diagnosing these dusty plasma layers. The dependency of the backscattered signal strength (i.e. Polar Mesospheric Summer Echoes PMSEs) after the turn-on and turn-off of the radio wave heating on the radar frequency is an unique phenomenon that can shed light on the unresolved issues associated with the basic physics of the natural charged mesospheric dust layer. The physical process after turn-on and turn-off of radio wave heating is explained by competing ambipolar diffusion and dust charging processes. The threshold radar frequency and dust parameters for the enhancement or suppression of radar echoes after radio wave heating turn-on are investigated for measured mesospheric plasma parameters. The effect of parameters such as the electron temperature enhancement during radiowave heating, dust density, dust charge polarity, ion-neutral collision frequency, electron density and dust radius on the temporal evolution of electron irregularities associated with PMSE is investigated. The possibility of observing the turn-on overshoot (enhancement of radar echoes after the radiowave turn-on) in the high frequency HF radar band is discussed based on typical mesospheric parameters. It has been shown that predicted enhancement of electron irregularity amplitude after heater turn-on at HF band is the direct manifestation of the dust charging process in the space. Therefore further active experiments of PMSEs should be pursued at HF band to illuminate the fundamental charging physics in the space environment to provide more insight on this unique medium. Preliminary observation results of HF PMSE heating experiment with the new 7.9 MHz radar at the European Incoherent Scatter EISCAT facility appear promising for the existence of PMSE turn-on overshoot. Therefore, future experimental campaigns are planned to validate these predictions. Computational results are used to make predictions for PMSE active modification experiments at 7.9, 56, 139, 224 and 930MHz corresponding to existing ionospheric heating facilities. Data from a 2009 very high frequency VHF (224 MHz) experiment at EISCAT is compared with the computational model to obtain dust parameters in…
Advisors/Committee Members: Scales, Wayne A. (committeechair), Pratt, Timothy J. (committee member), Earle, Gregory D. (committee member), Roy, Christopher John (committee member), Bailey, Scott M. (committee member).
Subjects/Keywords: Ionospheric Modification; Plasma; Numerical Simulations; Analytical model
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APA (6th Edition):
Mahmoudian, A. (2013). New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/19239
Chicago Manual of Style (16th Edition):
Mahmoudian, Alireza. “New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities.” 2013. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/19239.
MLA Handbook (7th Edition):
Mahmoudian, Alireza. “New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities.” 2013. Web. 10 Apr 2021.
Vancouver:
Mahmoudian A. New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/19239.
Council of Science Editors:
Mahmoudian A. New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/19239
Virginia Tech
27.
Lin, Ying-Tsen.
Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor.
Degree: PhD, Electrical Engineering, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/64980
► On-board the International Space Station (ISS), the Remote Atmospheric and Ionospheric Detection System (RAIDS) is a suite of limb-scanning monitors taking measurements from the extreme…
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▼ On-board the International Space Station (ISS), the Remote Atmospheric and Ionospheric Detection System (RAIDS) is a suite of limb-scanning monitors taking measurements from the extreme ultraviolet (EUV) to the near infrared (NIR). A single-scattering Rayleigh model is developed to eliminate the scattered brightness below 90 km and an inversion technique is applied on limb-scanned radiance profiles at 236.5 nm, NO (0,1) gamma band. The ISS orbit allows observations from 7:00 to 16:00 local hours over a one-month period from mid-June to mid-July of 2010 and observation of the local-time variation of NO abundance in the lower thermosphere is derived. The uniquely stable solar activity during 2010 allows the local time variation of NO to be observed with limited influence of solar variability. The comparison with a 1D model shows good agreement at altitude above 120 km, suggesting that most of the local time variation of NO is due to solar illumination, radiation, chemistry, and vertical diffusion.
Solar soft X-ray is the major driver of the variability observed in the ionospheric and thermospheric constituents at the equatorial region. Over the years measurements in these wavelengths are scarce and discrepancies lie among the existing data. The Solar Aspect Monitor (SAM) is a pinhole camera on the Extreme-ultraviolet Variability Experiment (EVE) flying on the Solar Dynamics Observatory (SDO). Every 10 seconds SAM projects the solar disk onto the CCD through a metallic filter designed to allow only solar photons shortward of 7 nm to pass. Contamination from energetic particles and out-of-band irradiance is, however, present. The broadband (BB) technique is developed for isolating the 0.1 to 7 nm integrated irradiance to produce broadband irradiance. The results agree with the zeroth-order product from the EUV SpectroPhotometer (ESP) with 25% regardless of solar activity level. Active regions in the solar atmosphere are tracked by the Apertural Progression Procedure for Light Estimate (APPLE). The photon event detection (PED) algorithm takes both BB and APPLE results as prior information to extract in-band photons. Applications of the PED products, including solar feature studies and spectral resolved irradiance, are demonstrated.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Minschwaner, Kenneth R. (committee member), Hsiao, Michael S. (committee member), Scales, Wayne A. (committee member), Earle, Gregory D. (committee member).
Subjects/Keywords: solar irradiance; soft X-ray; image processing; nitric oxide; thermosphere
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APA ·
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Export
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APA (6th Edition):
Lin, Y. (2014). Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/64980
Chicago Manual of Style (16th Edition):
Lin, Ying-Tsen. “Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor.” 2014. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/64980.
MLA Handbook (7th Edition):
Lin, Ying-Tsen. “Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor.” 2014. Web. 10 Apr 2021.
Vancouver:
Lin Y. Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/64980.
Council of Science Editors:
Lin Y. Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/64980
Virginia Tech
28.
Eltrass, Ahmed Said Hassan Ahmed.
The Mid-Latitude Ionosphere: Modeling and Analysis of Plasma Wave Irregularities and the Potential Impact on GPS Signals.
Degree: PhD, Electrical Engineering, 2015, Virginia Tech
URL: http://hdl.handle.net/10919/51804
► The mid-latitude ionosphere is more complicated than previously thought, as it includes many different scales of wave-like structures. Recent studies reveal that the mid-latitude ionospheric…
(more)
▼ The mid-latitude ionosphere is more complicated than previously thought, as it includes many different
scales of wave-like structures. Recent studies reveal that the mid-latitude ionospheric irregularities are less understood due to lack of models and observations that can explain the characteristics of the observed wave structures. Since temperature and density gradients are a persistent feature in the mid-latitude ionosphere near the plasmapause, the drift mode growth rate at short wavelengths may explain the mid-latitude decameter-scale ionospheric irregularities observed by the Super Dual Auroral Radar Network (SuperDARN). In the context of this dissertation, we focus on investigating the plasma waves responsible for the mid-latitude ionospheric irregularities and studying their influence on Global Positioning System (GPS) scintillations.
First, the physical mechanism of the Temperature Gradient Instability (TGI), which is a strong candidate for producing mid-latitude irregularities, is proposed. The electro- static dispersion relation for TGI is extended into the kinetic regime appropriate for High- Frequency (HF) radars by including Landau damping, finite gyro-radius effects, and tem- perature anisotropy. The kinetic dispersion relation of the Gradient Drift Instability (GDI) including finite ion gyro-radius effects is also solved to consider decameter-scale waves gen- eration. The TGI and GDI calculations are obtained over a broad set of parameter regimes to underscore limitations in fluid theory for short wavelengths and to provide perspective on the experimental observations.
Joint measurements by the Millstone Hill Incoherent Scatter Radar (ISR) and the Su- perDARN HF radar located at Wallops Island,
Virginia have identified the presence of decameter-scale electron density irregularities that have been proposed to be responsible for low-velocity Sub-Auroral Ionospheric Scatter (SAIS) observed by SuperDARN radars. In order to investigate the mechanism responsible for the growth of these irregularities, a time series for the growth rate of both TGI and GDI is developed. The time series is computed for both perpendicular and meridional density and temperature gradients. The growth rate comparison shows that the TGI is the most likely generation mechanism for the observed quiet-time irregularities and the GDI is expected to play a relatively minor role in irregular- ity generation. This is the first experimental confirmation that mid-latitude decameter-scale ionospheric irregularities are produced by the TGI or by turbulent cascade from primary irregularity structures produced from this instability. The quiet- and disturbed-times plasma wave irregularities are compared by investigating co-located experimental observations by the Blackstone SuperDARN radar and the Millstone Hill ISR under various sets of geomagnetic conditions. The radar observations in conjunction with growth rate calculations suggest that the TGI in association with the GDI or a cascade product from them may cause the observations of…
Advisors/Committee Members: Scales, Wayne A. (committeechair), Meehan, Kathleen (committee member), Riad, Sedki Mohamed (committee member), Winfrey, Leigh (committee member), Elkamchouchi, Hassan M. (committee member), Ruohoniemi, John Michael (committee member).
Subjects/Keywords: Ionospheric Irregularities; Plasma Instability; GPS; SuperDARN Radar; Computational Modeling
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APA (6th Edition):
Eltrass, A. S. H. A. (2015). The Mid-Latitude Ionosphere: Modeling and Analysis of Plasma Wave Irregularities and the Potential Impact on GPS Signals. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/51804
Chicago Manual of Style (16th Edition):
Eltrass, Ahmed Said Hassan Ahmed. “The Mid-Latitude Ionosphere: Modeling and Analysis of Plasma Wave Irregularities and the Potential Impact on GPS Signals.” 2015. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/51804.
MLA Handbook (7th Edition):
Eltrass, Ahmed Said Hassan Ahmed. “The Mid-Latitude Ionosphere: Modeling and Analysis of Plasma Wave Irregularities and the Potential Impact on GPS Signals.” 2015. Web. 10 Apr 2021.
Vancouver:
Eltrass ASHA. The Mid-Latitude Ionosphere: Modeling and Analysis of Plasma Wave Irregularities and the Potential Impact on GPS Signals. [Internet] [Doctoral dissertation]. Virginia Tech; 2015. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/51804.
Council of Science Editors:
Eltrass ASHA. The Mid-Latitude Ionosphere: Modeling and Analysis of Plasma Wave Irregularities and the Potential Impact on GPS Signals. [Doctoral Dissertation]. Virginia Tech; 2015. Available from: http://hdl.handle.net/10919/51804
Virginia Tech
29.
Westin, Benjamin Alexander.
Applications in Remote Sensing Using the Method of Ordered Multiple Interactions.
Degree: PhD, Electrical Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/19346
► The Method of Ordered Multiple Interactions provides a numerical solution to the integral equations describing surface scattering which is both computationally efficient and reliably convergent.…
(more)
▼ The Method of Ordered Multiple Interactions provides a numerical solution to the integral equations describing surface scattering which is both computationally efficient and reliably convergent. The method has been applied in a variety of ways to solving the electromagnetic scattering from perfectly-conducting rough surfaces. A desire to more accurately predict the scattering from natural terrain has led to the representation of the surface material as penetrable instead of conductive. For this purpose, the Method of Ordered Multiple Interactions is applied to numerically solve the electromagnetic scattering from randomly-rough dielectric surfaces. A primary consequence of the penetrable surface material is the introduction of a pair of coupled integral equations in place of the single integral equation used to solve the problem with a perfectly conducting surface. The method is tested and analyzed by developing independent scattering solutions for canonical cases in a transform domain and by comparing results with solutions from other techniques. The dielectric implementation of the Method of Ordered Multiple Interactions is used to solve the electromagnetic scattering from a class of randomly-rough dielectric surfaces. This allows for the characterization of the effect of a number of transmitter and surface parameters in the scattering problem, observing bistatically and also specifically in the backscatter direction. MOMI is then applied as a method to examine subsurface penetration characteristics from a similar family of rough surfaces. Characteristics of the environment parameters and the scattered field itself are examined, and the numerical challenges associated with observing beneath the surface are identified and addressed. The Method of Ordered Multiple Interactions is then incorporated as a major component of a larger solution which computes the total scattering when a dielectric object is buried just beneath the rough surface. This hyrid approach uses MOMI and the Method of Moments to iteratively account for multiple interactions between the target and the dielectric interface, enabling the study of scattering from the combined environment of a rough surface and the embedded object, as well as the individual scattering events which combine to form the steady-state solution.
Advisors/Committee Members: Brown, Gary S. (committeechair), Kohler, Werner E. (committee member), Davis, William A. (committee member), Scales, Wayne A. (committee member), Guido, Louis J. (committee member).
Subjects/Keywords: Computational Electromagnetics; Rough Surface Scattering; Microwave Remote Sensing; Method of Ordered Multiple Interactions
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APA ·
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Export
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APA (6th Edition):
Westin, B. A. (2013). Applications in Remote Sensing Using the Method of Ordered Multiple Interactions. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/19346
Chicago Manual of Style (16th Edition):
Westin, Benjamin Alexander. “Applications in Remote Sensing Using the Method of Ordered Multiple Interactions.” 2013. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/19346.
MLA Handbook (7th Edition):
Westin, Benjamin Alexander. “Applications in Remote Sensing Using the Method of Ordered Multiple Interactions.” 2013. Web. 10 Apr 2021.
Vancouver:
Westin BA. Applications in Remote Sensing Using the Method of Ordered Multiple Interactions. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/19346.
Council of Science Editors:
Westin BA. Applications in Remote Sensing Using the Method of Ordered Multiple Interactions. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/19346
Virginia Tech
30.
Carstens, Justin Neal.
Understanding Uncertainties for Polar Mesospheric Cloud Retrievals and Initial Gravity Wave Observations in the Stratopause from the Cloud Imaging and Particle Size Instrument.
Degree: PhD, Electrical and Computer Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/40089
► The Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere satellite images in the nadir at the UV wavelength…
(more)
▼ The Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere satellite images in the nadir at the UV wavelength of 265 nm. The camera array has an approximately 120° along track (2000 km) by 80° cross track (1000 km) field of view at a horizontal resolution of 1 by 2 km in the nadir. The satellite is in a sun synchronous orbit with an approximately noon local time equator crossing. The observed albedo is due to Rayleigh scattered sun light from an altitude of approximately 50 km and sunlight scattered from Polar Mesospheric Clouds (PMC) which occur in the summer mesosphere at 83 km.
The goal of the CIPS instrument is to retrieve high horizontal resolution maps of PMC albedo and the mode radius of the particle size distribution. The first manuscript analyzes the uncertainties involved in the retrieval. The ability to infer mode radius from the PMC signal is made significantly harder by the presence of the Rayleigh signal. Much of the difference between PMC signals of different mode radii is also consistent with possible changes in the Rayleigh signal. The signal is decomposed into components which isolate the portion of the PMC signalâ s dependence on radius which is not consistent with changes in the Rayleigh signal. This isolated component is compared with the measurement noise to estimate and understand the uncertainties in the CIPS retrieval.
The presence of the Rayleigh signal is a difficulty in the PMC retrieval, but it is also a valuable data product. The second manuscript highlights the initial findings of a new gravity wave data set developed by the author. The data set provides relative ozone variations at the stratopause with a horizontal resolution of 20 by 20 km. An abundance of gravity wave signatures can be seen in the data which appear to emanate from weather events like thunderstorms and hurricanes as well as orographic sources such as the Andes and the Antarctic Peninsula. The data set fills a gap that presently exists in our observational coverage of gravity waves, so the data set should help significantly in constraining Global Climate Models.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Scales, Wayne A. (committee member), Henderson, Troy A. (committee member), Brown, Gary S. (committee member), Earle, Gregory D. (committee member).
Subjects/Keywords: gravity waves; CIPS; AIM; retrieval uncertainties; polar mesospheric clouds
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APA ·
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MLA ·
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Export
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APA (6th Edition):
Carstens, J. N. (2012). Understanding Uncertainties for Polar Mesospheric Cloud Retrievals and Initial Gravity Wave Observations in the Stratopause from the Cloud Imaging and Particle Size Instrument. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/40089
Chicago Manual of Style (16th Edition):
Carstens, Justin Neal. “Understanding Uncertainties for Polar Mesospheric Cloud Retrievals and Initial Gravity Wave Observations in the Stratopause from the Cloud Imaging and Particle Size Instrument.” 2012. Doctoral Dissertation, Virginia Tech. Accessed April 10, 2021.
http://hdl.handle.net/10919/40089.
MLA Handbook (7th Edition):
Carstens, Justin Neal. “Understanding Uncertainties for Polar Mesospheric Cloud Retrievals and Initial Gravity Wave Observations in the Stratopause from the Cloud Imaging and Particle Size Instrument.” 2012. Web. 10 Apr 2021.
Vancouver:
Carstens JN. Understanding Uncertainties for Polar Mesospheric Cloud Retrievals and Initial Gravity Wave Observations in the Stratopause from the Cloud Imaging and Particle Size Instrument. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2021 Apr 10].
Available from: http://hdl.handle.net/10919/40089.
Council of Science Editors:
Carstens JN. Understanding Uncertainties for Polar Mesospheric Cloud Retrievals and Initial Gravity Wave Observations in the Stratopause from the Cloud Imaging and Particle Size Instrument. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/40089
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Open Access Theses and Dissertations
