Award Date

12-15-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geoscience

First Committee Member

Pamela Burnley

Second Committee Member

David Kreamer

Third Committee Member

Elisabeth Hausrath

Fourth Committee Member

Christopher Adcock

Fifth Committee Member

Alexander Barzilov

Number of Pages

143

Abstract

Aerial gamma-ray surveying (AGRS) is used in geologic and environmental contexts to provide data on the surface spatial distribution of naturally occurring radioactive material (NORM) or other gamma-ray-emitting isotopes. The standard data reduction workflow for AGRS data involves a process whereby pointwise gamma-ray spectral data are denoised, corrected for numerous sources of background radiation and aircraft height, and are finally converted to physical values by empirical conversion factors. The reduced pointwise data are then typically spatially interpolated to form a continuous surface map.

This dissertation introduces and explores a novel spatial inversion method for reduced AGRS data that considers aircraft height, terrain elevation, the directional sensitivity of the detectors, and is weighted against propagated uncertainty. First, a comprehensive analysis of empirical calibration data from calibration pads located in Grand Junction, CO, establishes physical calibration coefficients. Then, the novel method for spatial inversion of AGRS is introduced, benchmarked against synthetic data, and finally applied to a study area called Government Wash with ground truth geochemistry. The results show the spatial inversion method is able to preserve sharp geologic features in the data that are denuded in traditional pointwise interpolation, while matching the geochemistry.

Next, AGRS survey data over a study area called Sweeney Granite Mountains Desert Research Center (GMDR), characterized by complex terrain, is inverted to test the sensitivity of the method to terrain. The GMDR study area is homogeneous in terms of the geology and a high resolution terrain model is available for undersampling. Core samples have been collected and provide geochemical data for the GMDR study area. The inversion method is shown to reproduce the core sample results, and terrain influences are shown to be less important than the interrelationship between adjacent points during the inversion procedure. Finally, an AGRS survey over the Pinyon Plane Mine, an active uranium (U) mine, shows the inversion method is able to accurately localize the position and concentration of U ore stored on the surface of the mine site.

The spatial inversion method introduced and explored in this dissertation represents a shift away from conventional interpolation techniques by providing a powerful new physics based tool for interpretation of AGRS data.

Controlled Subject

Gamma rays; Isotopes; Geochemistry

Disciplines

Geophysics and Seismology | Other Physics | Physics | Remote Sensing

File Format

PDF

File Size

22400 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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