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Date Permissions Signed

4-17-2020

Date of Award

Spring 2020

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Clark, Douglas H., 1961-

Second Advisor

Mitchell, Robert J., (Geologist)

Third Advisor

Riedel, Jon L. (Geologist)

Abstract

The traditional glaciological method of measuring glacier mass balance is labor-intensive and relies on broad extrapolation of sparse ablation stake data collected in the field to assess mass change across the glacier. In contrast, digital elevation models (DEMs) obtained from unmanned aerial vehicle (UAV) imagery and Structure-from-Motion (SfM) photogrammetry resolve a spatially distributed data set of surface elevation change. In this study, I compare seasonal mass balance estimated by field-based glaciological methods and UAV-SfM methods during summer 2018 on the Easton Glacier, Mount Baker, WA. Total snow and ice surface melt was measured at five ablation stakes between May 20th and September 17th, 2018. A research team at the University of Washington conducted UAV surveys on October 5th, 2017, June 6th, 2018, and October 6th, 2018 and used SfM software to generate DEMs of the Easton glacier’s surface for each date. Change detection maps were created by differencing the DEMs, and surface elevation changes across each differenced DEM were used as proxies for winter accumulation and summer ablation. I used a positive degree day model to adjust the glaciological data to span the SfM survey interval for summer ablation (June 6th - October 6th, 2018). Glacier thickness changes estimated by both methods were converted to water equivalent based on the density of the material lost (snow versus ice). Altitudinal swaths centered on each ablation stake were modified to fit the extent of the UAV imagery, and mass balance was estimated by extrapolating the discrete stake measurements and SfM averages across their respective swaths. SfM methods yield 4.3% less volume loss and 11.4% less mass loss in volume of water across the study area compared to the glaciological method. This discrepancy is likely explained by vertical ice flow related to emergence velocity during the study interval. After adjusting for emergence, SfM estimates overestimate mass balance, likely because of upper limit estimates of the emergence velocity. Uncertainties related to mass balance in crevasses, challenges with horizontal ice flux, and density assumptions are discussed. My study concludes that the influence of secondary processes, particularly emergence/submergence, must be more thoroughly constrained and integrated before SfM-UAV techniques can altogether replace the glaciological method.

Type

Text

Keywords

Glacier, mass balance, Structure-from-Motion, photogrammetry, Mount Baker

Publisher

Western Washington University

OCLC Number

1156321317

Subject – LCSH

Glaciers--Washington (State)--Baker, Mount; Photogrammetry--Washington (State)--Baker, Mount; Mass budget (Geophysics)--Measurement

Geographic Coverage

Baker, Mount (Wash.)

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/InC/1.0/

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