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 Title
 A STUDY OF EQUATORIAL IONOPSHERIC VARIABILITY USING SIGNAL PROCESSING TECHNIQUES.
 Creator

wang, xiaoni, Eastes, Richard, University of Central Florida
 Abstract / Description

The dependence of equatorial ionosphere on solar irradiances and geomagnetic activity are studied in this dissertation using signal processing techniques. The statistical time series, digital signal processing and wavelet methods are applied to study the ionospheric variations. The ionospheric data used are the Total Electron Content (TEC) and the critical frequency of the F2 layer (foF2). Solar irradiance data are from recent satellites, the Student Nitric Oxide Explorer (SNOE) satellite and...
Show moreThe dependence of equatorial ionosphere on solar irradiances and geomagnetic activity are studied in this dissertation using signal processing techniques. The statistical time series, digital signal processing and wavelet methods are applied to study the ionospheric variations. The ionospheric data used are the Total Electron Content (TEC) and the critical frequency of the F2 layer (foF2). Solar irradiance data are from recent satellites, the Student Nitric Oxide Explorer (SNOE) satellite and the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite. The Disturbance StormTime (Dst) index is used as a proxy of geomagnetic activity in the equatorial region. The results are summarized as follows. (1) In the shortterm variations < 27days, the previous three days solar irradiances have significant correlation with the present day ionospheric data using TEC, which may contribute 18% of the total variations in the TEC. The 3day delay between solar irradiances and TEC suggests the effects of neutral densities on the ionosphere. The correlations between solar irradiances and TEC are significantly higher than those using the F10.7 flux, a conventional proxy for short wavelength band of solar irradiances. (2) For variations < 27 days, solar soft Xrays show similar or higher correlations with the ionosphere electron densities than the Extreme Ultraviolet (EUV). The correlations between solar irradiances and foF2 decrease from morning (0.5) to the afternoon (0.1). (3) Geomagnetic activity plays an important role in the ionosphere in shortterm variations < 10 days. The average correlation between TEC and Dst is 0.4 at 23, 35, 59 and 911 day scales, which is higher than those between foF2 and Dst. The correlations between TEC and Dst increase from morning to afternoon. The moderate/quiet geomagnetic activity plays a distinct role in these shortterm variations of the ionosphere (~0.3 correlation).
Show less  Date Issued
 2007
 Identifier
 CFE0001602, ucf:47188
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0001602
 Title
 MODELED AND OBSERVED N2 LYMANBIRGEHOPFIELD BAND EMISSIONS IN EARTH'S DAYGLOW: A COMPARISON.
 Creator

Murray, Donald, Eastes, Richard, University of Central Florida
 Abstract / Description

Ultraviolet (UV) spectra obtained from Earth's dayglow contain important information for understanding the thermosphere, and the N2 LymanBirgeHopfield (LBH) bands are possibly the most useful emission. To be useful, a thorough understanding of how the LBH band emission varies with altitude and latitude is essential to present and future use of this emission by spacebased remote sensors. Excited by photoelectron impact on N2 leading to transitions from the a 1Πg state to the ground...
Show moreUltraviolet (UV) spectra obtained from Earth's dayglow contain important information for understanding the thermosphere, and the N2 LymanBirgeHopfield (LBH) bands are possibly the most useful emission. To be useful, a thorough understanding of how the LBH band emission varies with altitude and latitude is essential to present and future use of this emission by spacebased remote sensors. Excited by photoelectron impact on N2 leading to transitions from the a 1Πg state to the ground state, the LBH emissions radiate between 1270 and 2400 Å. In addition to being populated by electron impact excitation, the a 1Πg state is populated by radiative and collisional cascading from adjacent singlet states a' 1Σu, and w 1Δu (Eastes, 2000). Ultimately, the intensity is most dependent on low energy electron flux (Ajello and Shemansky, 1985; Meier, 1991) because that is where the electron impact scattering cross sections of the singlet states are the largest. This dissertation presents modeled LBH profiles produced using the Intrasystem Cascade Excitation (ICE) model (Eastes, 2000) with photoelectron fluxes calculated using the Continuous Slowing Down (CSD) model (Jasperse, 1976). Both of these models implement the Mass Spectrometer and Incoherent Scatter (MSIS) to model an atmosphere. Modeled emissions are compared against observations by the High resolution Ionospheric and Thermospheric Spectrograph (HITS) on the Advanced Research and Global Observation Satellite (ARGOS). This dissertation will investigate the LBH emissions in detail and ultimately use them for remote sensing of thermospheric temperatures.
Show less  Date Issued
 2007
 Identifier
 CFE0001986, ucf:47422
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0001986
 Title
 DATA COMMUNICATION WITH A NANOSATELLITE USING SATELLITE PERSONAL COMMUNICATION NETWORKS (SPCNS).
 Creator

Khan, Khudeja, Eastes, Richard, University of Central Florida
 Abstract / Description

Satellites typically communicate with locations on the ground to receive commands and send data back. Establishing reliable communications generally requires dedicated ground stations, which in turn require hardware and expertise. Developers of nanosatellites, however, may not have the expertise or resources necessary for establishing a dedicated ground station. Therefore, the use of an existing communication system, such as the Satellite Personal Communication Networks (SPCNs), is...
Show moreSatellites typically communicate with locations on the ground to receive commands and send data back. Establishing reliable communications generally requires dedicated ground stations, which in turn require hardware and expertise. Developers of nanosatellites, however, may not have the expertise or resources necessary for establishing a dedicated ground station. Therefore, the use of an existing communication system, such as the Satellite Personal Communication Networks (SPCNs), is attractive. Another shortcoming of the fixed ground stations, already available, is that they are normally only able to communicate with Low Earth Orbit (LEO) nanosatellites four times per day (two10minute windows separated by 90 minutes, followed 12 hours later by two more such 10minute windows). This drawback is also overcome by the use of SPCNs which provide increased access times, smaller gaps in contact between the satellites and ground stations, and easier tracking of satellite health. In this thesis, the capabilities of SPCNs for communications with a nanosatellite are explored. Software simulation and analysis have been performed to assess system performance. Ground testing of the hardware is done to understand the use of such systems for small satellites.
Show less  Date Issued
 2008
 Identifier
 CFE0002488, ucf:47693
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0002488
 Title
 On Hall Magnetohydrodynamics: Xtype Neutral Point and Parker Problem.
 Creator

Reger, Kyle, Shivamoggi, Bhimsen, Rollins, David, Eastes, Richard, University of Central Florida
 Abstract / Description

The framework for the Hall magnetohydrodynamic (MHD) model for plasma physics is built up from kinetic theory and used to analytically solve problems of interest in the field. The Hall MHD model describes fast magnetic reconnection processes in space and laboratory plasmas. Specifically, the magnetic reconnection process at an Xtype neutral point, where current sheets form and store enormous amounts of magnetic energy which is later released as magnetic storms when the sheets break up, is...
Show moreThe framework for the Hall magnetohydrodynamic (MHD) model for plasma physics is built up from kinetic theory and used to analytically solve problems of interest in the field. The Hall MHD model describes fast magnetic reconnection processes in space and laboratory plasmas. Specifically, the magnetic reconnection process at an Xtype neutral point, where current sheets form and store enormous amounts of magnetic energy which is later released as magnetic storms when the sheets break up, is investigated. The phenomena of magnetic flux pileup driving the merging of antiparallel magnetic fields at an ion stagnationpoint flow in a thin current sheet, called the Parker problem, also receives rigorous mathematical analysis.
Show less  Date Issued
 2012
 Identifier
 CFE0004428, ucf:49345
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0004428
 Title
 Image degradation due to surface scattering in the presence of aberrations.
 Creator

Choi, Narak, Harvey, James, Zeldovich, Boris, Moharam, M., Eastes, Richard, University of Central Florida
 Abstract / Description

This dissertation focuses on the scattering phenomena by wellpolished optical mirror surfaces. Specifically, predicting image degradation by surface scatter from rough mirror surfaces for a twomirror telescope operating at extremely short wavelengths (9nm~30nm) is performed. To evaluate image quality, surface scatter is predicted from the surface metrology data and the point spread function in the presence of both surface scatter and aberrations is calculated.For predicting the scattering...
Show moreThis dissertation focuses on the scattering phenomena by wellpolished optical mirror surfaces. Specifically, predicting image degradation by surface scatter from rough mirror surfaces for a twomirror telescope operating at extremely short wavelengths (9nm~30nm) is performed. To evaluate image quality, surface scatter is predicted from the surface metrology data and the point spread function in the presence of both surface scatter and aberrations is calculated.For predicting the scattering intensity distribution, both numerical and analytic methods are considered. Among the numerous analytic methods, the small perturbation method (classical RayleighRice surface scatter theory), the Kirchhoff approximation method (classical BeckmanKirchhoff surface scatter theory), and the generalized HarveyShack surface scatter theory are adopted. As a numerical method, the integral equation method (method of moments) known as a rigorous solution is discussed. Since the numerical method is computationally too intensive to obtain the scattering prediction directly for the two mirror telescope, it is used for validating the three analytic approximate methods in special cases. In our numerical comparison work, among the three approximate methods, the generalized HarveyShack model shows excellent agreement to the rigorous solution and it is used to predict surface scattering from the mirror surfaces.Regarding image degradation due to surface scatter in the presence of aberrations, it is shown that the composite point spread function is obtained in explicit form in terms of convolutions of the geometrical point spread function and scaled bidirectional scattering distribution functions of the individual surfaces of the imaging system. The approximations and assumptions in this formulation are discussed. The result is compared to the irradiance distribution obtained using commercial nonsequential ray tracing software for the case of a twomirror telescope operating at the extreme ultraviolet wavelengths and the two results are virtually identical. Finally, the image degradation due to the surface scatter from the mirror surfaces and the aberration of the telescope is evaluated in terms of the fractional ensquared energy (for different wavelengths and field angles) which is commonly used as an image quality requirement on many NASA astronomy programs.
Show less  Date Issued
 2012
 Identifier
 CFE0004289, ucf:49492
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0004289
 Title
 Dynamical Invariants and the Fluid Impulse in Plasma Models.
 Creator

Michalak, Martin, Shivamoggi, Bhimsen, Mohapatra, Ram, Brennan, Joseph, Eastes, Richard, University of Central Florida
 Abstract / Description

Much progress has been made in understanding of plasmas through the use of the MHD equations and newer models such as Hall MHD and electron MHD. As with most equations of fluid behavior, these equations are nonlinear, and no general solutions can be found. The use of invariant structures allows limited predictions of fluid behavior without requiring a full solution of the underlying equations. The use of gauge transformation can allow the creation of new invariants, while differential...
Show moreMuch progress has been made in understanding of plasmas through the use of the MHD equations and newer models such as Hall MHD and electron MHD. As with most equations of fluid behavior, these equations are nonlinear, and no general solutions can be found. The use of invariant structures allows limited predictions of fluid behavior without requiring a full solution of the underlying equations. The use of gauge transformation can allow the creation of new invariants, while differential geometry offers useful tools for constructing additional invariants from those that are already known. Using these techniques, new geometric, integral and topological invariants are constructed for Hall and electron MHD models. Both compressible and incompressible models are considered, where applicable. An application of topological invariants to magnetic reconnection is provided. Finally, a particular geometric invariant, which can be interpreted as the fluid impulse density, is studied in greater detail, its nature and invariance in plasma models is demonstrated, and its behavior is predicted in particular geometries under different models.
Show less  Date Issued
 2013
 Identifier
 CFE0005382, ucf:50442
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005382