Doctor of Philosophy

dissertationSnow and ice cover exhibits a high degree of spatial and temporal variability. Data from multispectral optical remote sensing instruments such as Landsat are an underutilized resource that can extend our ability for mapping these phenomena. High resolution imagery is used to demonstrate that even at finer spatial resolutions (below 100 m), pixels with partial snow cover are common throughout the year and nearly ubiquitous during the meltout period. This underscores the importance of higher spatial resolution datasets for snow cover monitoring as well as the utility of fractional snow covered area (fSCA) monitoring approaches. Landsat data are used to develop a fully automated approach for mapping persistent ice and snow cover (PISC). This approach relies on the availability of numerous Landsat scenes, an improved technique for automated cloud cover mapping, and a series of automated postprocessing routines. Validation at 12 test sites suggest that the automated PISC mapping approach provides a good approximation of debris-free glacier extent across the Arctic. The PISC mapping approach is then used to produce the first single-source, temporally well-constrained (2010-2014) map of PISC across the conterminous western U.S. The Landsat-derived PISC map is more accurate than both a previously published dataset based on aerial photography acquired during the 1960s, 1970s and 1980s and the National Land Cover Database (NLCD) 2011 extent of perennial snow and ice cover. Further analysis indicates differences between the newly developed Landsat-derived PISC dataset and the previously published glacier dataset can likely be attributed to changes in the extent of PISC over time. Finally, in order to map mean annual snow cover persistence across the entire landscape, we implement a novel canopy adjustment approach designed to improve the accuracy of Landsat-derived fSCA in forested areas. In situ observations indicate canopy-adjusted snow covered area calculated from all available Landsat scenes can provide an accurate estimate of mean annual snow cover duration. The work presented here lays the groundwork for addressing scientific questions regarding the spatial and temporal variability of snow cover, snow accumulation and ablation processes, and the impact of changes in snow cover on physical and ecological systems

The shock reprocessing model of electron acceleration in impulsive solar flares

We propose a new two-stage model for acceleration of electrons in solar flares. In the first stage, electrons are accelerated stochastically in a post-reconnection turbulent downflow. The second stage is the reprocessing of a subset of these electrons as they pass through a weakly compressive fast shock above the apex of the closed flare loop on their way to the chromosphere. We call this the "shock reprocessing" model. The model reproduces the energy dependent arrival time delays observed for both the pulsed and smooth components of impulsive solar flare x-rays with physically reasonable parameters for the downflow region. The model also predicts an emission site above the loop-top, as seen in the Masuda flare. The loop-top source distinguishes the shock reprocessing model from previous models. The model makes testable predictions for the energy dependence of footpoint pulse strengths and the location and spectrum of the loop-top emission, and can account for the observed soft-hard-soft trend in the spectral evolution of footpoint emission. Our model highlights the concept that reconnection is an acceleration environment rather than a single process. Which combination of processes operate may depend on the initial conditions that determine, for example, whether the reconnection downflow is turbulent. The shock reprocessing model comprises one such combination.Comment: submitted to MNRA

Prevalence of pure versus mixed snow cover pixels across spatial resolutions in alpine environments

pre-printRemote sensing of snow-covered area (SCA) can be binary (indicating the presence/absence of snow cover at each pixel) or fractional (indicating the fraction of each pixel covered by snow). Fractional SCA mapping provides more information than binary SCA, but is more difficult to implement and may not be feasible with all types of remote sensing data. The utility of fractional SCA mapping relative to binary SCA mapping varies with the intended application as well as by spatial resolution, temporal resolution and period of interest, and climate. We quantified the frequency of occurrence of partially snow-covered (mixed) pixels at spatial resolutions between 1 m and 500 m over five dates at two study areas in the western U.S., using 0.5 m binary SCA maps derived from high spatial resolution imagery aggregated to fractional SCA at coarser spatial resolutions. In addition, we used in situ monitoring to estimate the frequency of partially snow-covered conditions for the period September 2013-August 2014 at 10 60-m grid cell footprints at two study areas with continental snow climates. Results from the image analysis indicate that at 40 m, slightly above the nominal spatial resolution of Landsat, mixed pixels accounted for 25%-93% of total pixels, while at 500 m, the nominal spatial resolution of MODIS bands used for snow cover mapping, mixed pixels accounted for 67%-100% of total pixels. Mixed pixels occurred more commonly at the continental snow climate site than at the maritime snow climate site. The in situ data indicate that some snow cover was present between 186 and 303 days, and partial snow cover conditions occurred on 10%-98% of days with snow cover. Four sites remained partially snow-free throughout most of the winter and spring, while six sites were entirely snow covered throughout most or all of the winter and spring. Within 60 m grid cells, the late spring/summer transition from snow-covered to snow-free conditions lasted 17-56 days and averaged 37 days. Our results suggest that mixed snow-covered snow-free pixels are common at the spatial resolutions imaged by both the Landsat and MODIS sensors. This highlights the additional information available from fractional SCA products and suggests fractional SCA can provide a major advantage for hydrological and climatological monitoring and modeling, particularly when accurate representation of the spatial distribution of snow cover is critical

Mental Rotation: Can Familiarity Alleviate the Effects of Complex Backgrounds?

This dissertation investigated the effects of complex backgrounds on mental rotation. Stimulus familiarity and background familiarity were manipulated. It systematically explored how familiarizing participants to objects and complex backgrounds affects their performance on a mental rotation task involving complex backgrounds. This study had 113 participants recruited through the UCF Psychology SONA system. Participants were familiarized with a stimulus in a task where they were told to distinguish the stimulus from 3 other stimuli. A similar procedure was used to familiarize the backgrounds. The research design was a 2 stimulus familiarity (Familiarized with the Target Stimulus, not familiarized with the Target Stimulus) by 2 background familiarity (Familiarized with Target Background, not familiarized with Target Background 1) by 2 stimulus response condition (Target Stimulus, Non-Target Stimulus) by 3 background response condition (Target Background, Non-Target Background, Blank Background) by 12 degree of rotation (0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330) mixed design. The study utilized target stimulus and target background familiarity conditions as the between-subjects variables. Background, stimulus, and degree of rotation were within-subjects variables. The participants\u27 performance was measured using reaction time and percent of errors. Reaction time was computed using only the correct responses. After the familiarization task, participants engaged in a mental rotation task featuring stimuli and backgrounds that were present or not present in the familiarization task. A 2 (stimulus familiarization condition) by 2 (background familiarization condition) by 2 (stimulus response condition) by 3 (background response condition) by 12 (degree of rotation) mixed ANOVA was computed utilizing reaction time and percent of errors. Results suggest that familiarity with the Target Background had the largest effect on improving performance across response conditions. The results also suggest that familiarity with both the Target Stimulus and Target Background promoted inefficient mental rotation strategies which resulted in no significant differences between participants familiarized with neither the Target Stimulus nor the Target Background. Theoretical conclusions are drawn about stimulus familiarity and background familiarity. Future studies should investigate the effects of long term familiarity practice on mental rotation and complex backgrounds

On the role of stochastic Fermi acceleration in setting the dissipation scale of turbulence in the interstellar medium

We consider the dissipation by Fermi acceleration of magnetosonic turbulence in the Reynolds Layer of the interstellar medium. The scale in the cascade at which electron acceleration via stochastic Fermi acceleration (STFA) becomes comparable to further cascade of the turbulence defines the inner scale. For any magnetic turbulent spectra equal to or shallower than Goldreich-Sridhar this turns out to be $\ge 10^{12}$cm, which is much larger than the shortest length scales observed in radio scintillation measurements. While STFA for such spectra then contradict models of scintillation which appeal directly to an extended, continuous turbulent cascade, such a separation of scales is consistent with the recent work of \citet{Boldyrev2} and \citet{Boldyrev3} suggesting that interstellar scintillation may result from the passage of radio waves through the galactic distribution of thin ionized boundary surfaces of HII regions, rather than density variations from cascading turbulence. The presence of STFA dissipation also provides a mechanism for the non-ionizing heat source observed in the Reynolds Layer of the interstellar medium \citep{Reynolds}. STFA accommodates the proper heating power, and the input energy is rapidly thermalized within the low density Reynolds layer plasma.Comment: 12 Pages, no figures. Accepted for publication in MNRA

THE DAYLIGHTING SOLUTION

The topic of daylighting, particularly in commercial buildings, is discussed, including economic aspects, control of daylight, fenestration functions, data gathering, design tools and methods, and lighting controls