Amplification of Surface Topography during Surges of Tweedsmuir Glacier
Date
2021-09
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The recent development and improvement of remote sensing sensor technology and processing techniques has expanded the spatiotemporal basis of glacier monitoring, where in situ measurements are limited. With these developments, this thesis aims to identify periods of enhanced basal sliding from glacier surface digital elevation models (DEMs) of Tweedsmuir Glacier, a surge-type glacier in the St. Elias Mountains, Canada. We divide this problem into two study objectives: 1) reconstruct surface elevations on a multidecadal timescale, and 2) identify signatures of surges in the surface topography of Tweedsmuir Glacier. Structure-from-Motion with Multiview Stereo photogrammetry, an emerging technique in glaciology, was employed to reconstruct surface DEMs using historical imagery from 1950 to 1987. The photogrammetric DEMs were combined with more recent satellite DEMs acquired between 2000 and 2018 to calculate surface elevation changes throughout two complete surge cycles. An increase in surface elevation is observed in the terminus region between 1950 and 1969, which is interpreted to represent a previously undocumented surge in the early years of the interval. In addition, surface-elevation lowering along longitudinal profiles between surge cycles indicates that Tweedsmuir Glacier has sustained a net negative mass balance on an inter-surge timescale. To address the second objective, variations in surface topography along nine longitudinal profiles were quantified using a one-dimensional Fourier transform and continuous wavelet transform. The glacier surface following known surges (1974, 2010) and within an active surge phase (2007) exhibits an increase in amplitude of surface features with longitudinal wavelengths between 3 to 8 ice thicknesses. Subsequently, the amplitude of surface topography decreased during both quiescent phases (1987-2000, 2010-2018). The amplified wavelengths are in agreement with previous theoretical work that suggests that these features may represent spatial variability in basal topography or the basal slip ratio. Overall, spectral analysis of glacier surface DEMs may be developed to estimate basal slip ratios remotely, which are inherently difficult to measure directly and a poorly constrained parameter in modern ice flow models.
Description
Keywords
Glacier, Wavelet Transform, Fourier Transform, Photogrammetry, Structure from Motion
Citation
Sharp, M. (2021). Amplification of surface topography during surges of Tweedsmuir Glacier (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.