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Date Permissions Signed

5-30-2019

Date of Award

Fall 2019

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Rice, Melissa S.

Second Advisor

Kraft, Michael

Third Advisor

Mulcahy, Sean

Abstract

Reflectance spectroscopy is a major technique for characterizing the composition of planetary surfaces, and has led to many key findings in planetary geology. In laboratory measurements, reflectance spectrometers typically acquire data using a standard, fixed viewing geometry. Measurements from spacecraft, however, may be acquired at a wide range of viewing geometries, depending on the orientation of the instrument relative to the target surface and the Sun. For many materials, the impact of viewing geometry on reflectance is minor; however, some materials’ spectral signatures can be influenced by these photometric effects. In particular, spectra of weathering rinds and rock coatings are likely to show photometric variability. In this work, our goal is to better constrain how photometric properties of Mars-analog surfaces vary as a function of the composition and microtexture of weathering rinds and coatings. We developed a new automated goniometer to enable the collection of reflectance spectra across a range of viewing geometries similar to those of spacecraft observations. We acquired spectrogoniometric measurements for synthetically-coated and naturally-weathered Mars analog samples, which we further characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). Our results show that thin silica coatings on basalt substrates are not detectable at standard viewing geometries but exhibit diagnostic photometric effects in the visible and near-infrared. Additionally, we find that weathering processes may influence the shapes of scattering lobes, with some weathered samples found to change from forward scattering to backscattering depending on the degree and nature of sample weathering.

Type

Text

Keywords

Reflectance spectroscopy, photometry, weathering, Mars, Columbia River Basalt, rock coatings, silica, habitability, paleoenvironment

Publisher

Western Washington University

OCLC Number

1130713122

Subject – LCSH

Photometry; Reflectance spectroscopy; Basalt; Chemical weathering

Geographic Coverage

Mars (Planet)--Geology; Mars (Planet)--Surface

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Rights Statement

http://rightsstatements.org/vocab/NKC/1.0/

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