Ultra-Shallow Imaging Using 2D & 3D Seismic Reflection Methods

The research presented in this dissertation focuses on the survey design, acquisition, processing, and interpretation of ultra-shallow seismic reflection (USR) data in two and three dimensions. The application of 3D USR methods to image multiple reflectors less than 20 m deep, including the top of the saturated zone (TSZ), a paleo-channel, and bedrock, are presented using conventional acquisition methods and a new automated method of acquiring 3D data using hydraulically planted geophones. Processing techniques that focus on near-surface problems, such as intersecting reflection hyperbolae caused by large vertical velocity changes and processing pitfalls, are also discussed. The application of AVO analysis of 2D USR data collected during a pumping test yielded amplitude variations related to the thickness of the partially saturated zone that correlated spatially and with changes in pumping. USR methods were also used to image the TSZ less than one meter deep, the shallowest TSZ reflection to date

Allozyrne Variation Within and Between Populations of Ruth\u27s Golden Aster, \u3cem\u3ePityopsis ruthii\u3c/em\u3e (Small) Small

Genetic structure of the two known populations of Ruth\u27s golden aster, Pityopsis ruthii (Small) Small, was determined. Pityopsis ruthii is a rare, endemic plant species restricted to exposed phyllite and graywacke rock outcrops in the flooding zones of the Hiwassee and Ocoee River drainages in Polk County, Tennessee. There are an estimated 10,000 to 15,000 P. ruthii plants on the Hiwassee and ~600 on the Ocoee River. Patterns of variation at three enzyme loci were examined. Two loci, Pgm-2 and Prx-1, were polymorphic in both river populations. Despite limited habitat and subsequent restricted ranges (~ 5 kmalong each river), populations of this obligately outcrossed species were moderately substructured (mean FST = 0.163). Although river populations were separated by ~ 20 kmof mountainous terrain, only 1.05% of the gene diversity was attributable to differences between river populations, while 15.16% was attributable to differences among subpopulations within respective river gorges, and 83.79% was attributable to within subpopulation variation. The low mean FIS value for P. ruthii (0.062) may indicate that this species is avoiding inbreeding by predominantly reproducing vegetatively. What has been traditionally considered two separate, breeding river populations of P. ruthii was demonstrated, on the basis of two polymorphic loci, to be many separate rock populations within each river population. To determine how many separate breeding groups exist, further allozyrne analyses of more rock populations and subsampling within rock populations needs to be conducted. Based on these data each rock outcrop should, unless demonstrated to be the contrary, be considered a breeding population

Looks Can Be Deceiving: Reconsidering the Evidence for Gliotransmission

Gliotransmission, a process involving active vesicular release of glutamate and other neurotransmitters by astrocytes, is thought to play a critical role in many brain functions. A new paper by Nedergaard et al. (2014) identifies an experimental flaw in these previous studies suggesting that astrocytes may not perform active vesicular release after all

Setting an OFHEO Plan, But Wishing Otherwise

Discussing the potential of future plans for OFHEO involvement with Fannie Mae and Freddie Mac

Time Critical Lumigraph Rendering

It was illustrated in 1996 that the light leaving the convex hull of an object (or entering a convex region of empty space) can be fully characterized by a 4D function over the space of rays crossing a surface surrounding the object (or surrounding the empty space). Methods to represent this function and quickly render individual images from this representation given an arbitrary cameras were also described. This paper extends the work outlined by (Gortler et al) by demonstrating a taxonomy of methods to accelerate the rendering process by trading off quality for time. Given the specific limitation of a given hardware configuration, we discuss methods to tailor a critical time rendering strategy using these methods.Engineering and Applied Science

Shallow seismic AVO variations related to partial water saturation during a pumping test

This is the published version. Copyright 2007 by the American Geophysical Union. All Rights Reserved.High-resolution shallow seismic reflection experiments were conducted during and after a pumping test of an agricultural irrigation well to image the cone of depression. Although variations in the reflection time from the top of the saturated zone were not observed, amplitude-versus-offset (AVO) analysis revealed changes in reflection amplitude responses that correlate temporally and spatially to expected changes to the partially saturated zone induced by the pumping and recovery of the aquifer. The AVO responses exhibit dependence on aquifer drawdown and recovery cycles and the distance from the pumping well. We propose that near-surface soil heterogeneity and relatively rapid changes in the water table elevation during irrigation cycles caused a thickening of the partially saturated zone above the water table, which resulted in detectable changes in seismic reflection amplitudes. This study offers insights about the response of shallow seismic reflections to changes in subsurface water saturation and the potential application of seismic techniques to hydrogeophysical problems

Ultra-shallow seismic imaging of the top of the saturated zone

This is the published version. Copyright 2010 by the American Geophysical Union. All Rights Reserved.We collected ultra-shallow seismic-reflection data to image the near-surface stratigraphy of a Kansas River point bar. We were successful in identifying a discontinuous clay layer and the top of the saturated zone at depths of 0.95 and 1.4 m. Seismic walkaway data collected using various .22-caliber ammunition show that decreased source energy is necessary to generate higher frequencies and prevent clipping of critical near-offset traces needed to identify ultra-shallow reflections. The seismic reflections exhibited average normal moveout velocities of 180–195 m/s with dominant frequencies of 200–450 Hz. Coincident subsurface features were also imaged using 200-MHz ground-penetrating radar. This study presents the shallowest seismic reflection from the top of the saturated zone reported in the literature to date and further demonstrates the potential of using seismic-reflection methods for ultra-shallow imaging of the subsurface as a stand-alone tool or in conjunction with other high-resolution geophysical techniques