Continuous landfast ice climatology from 1996-2023 and interferometric classification of landfast ice stability along the Outer Alaska Continental Shelf

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Author
Einhorn, Andrew H.
Chair
Mahoney, Andy
Committee
Meyer, Franz
Danielson, Seth
Keyword
Sea ice
Sea ice drift
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URI
http://hdl.handle.net/11122/15497
Abstract
Landfast ice in Alaska is experiencing rapid changes in extents and duration, impacting the safety and utility of the ice for Arctic coastal communities. This study presents findings from an updated landfast ice dataset spanning from 1996 to 2023, comprising 7797 Seaward Landfast Ice Edge (SLIE) images derived from a combination of sources including prior work by Mahoney et al. (2014) and new analysis of operational ice charts produced by the National Weather Service Alaska Sea Ice Program (ASIP) and National Ice Center (NIC). We referred to this new dataset as the EM2024 dataset. Analysis of the entire EM2024 dataset reveals a declining trend in landfast ice extent and season length across Alaska. To better understand the nature of these changes and explore options for more robust detection of landfast ice for future datasets, we compared the EM2024 data for the winter period of 2017-2021 with SLIE data derived from Interferometric Synthetic Aperture Radar (InSAR). We used coherence to identify areas of landfast ice and the interferograms to derive the phase gradient as a proxy for estimating the relative stability of the landfast ice. We built on a pervious study by Dammann et al. (2019) by assigning quantitative phase gradient values to identify 3 distinct stability regimes of landfast ice: Bottomfast (|▽ϕ| < 0.14 radians/pixel), Stabilized (0.14 ≤ |▽ϕ| ≤ 0.47 radians/pixel), and Nonstabilized (|▽ϕ| > 0.47 radians/pixel). The monthly average phase gradient decreases as the season progresses, achieving the maximum stability in April or May depending on the region. This study provides an updated assessment of landfast ice conditions in Alaska and introduces a novel approach to identify relatively stable areas of landfast ice using InSAR. These findings have implications for enhancing the safety and planning of activities on landfast ice for Arctic coastal communities.
Description
Thesis (M.S.) University of Alaska Fairbanks, 2024
Table of Contents
Chapter 1: Introduction -- 1.1 Landfast ice processes in Alaska -- 1.2 Recent changes of sea ice in the Arctic -- 1.3 M2014 landfast ice dataset -- 1.4 Application of InSAR over landfast sea ice. Chapter 2: Methods and data -- 2.1 Study region -- 2.2 Extending the M2014 dataset -- 2.2.1 U.S. National Ice Center (NIC) ice charts -- 2.2.2 Alaska Sea Ice Program (ASIP) ice charts -- 2.2.3 Rasterization of chart-defined landfast ice -- 2.2.4 Creation of coast vectors -- 2.2.5 Measurement of landfast ice width -- 2.2.6 Identification of annual events from landfast ice width measurements -- 2.2.7 Combination of datasets to form continuous landfast ice climatology (1996-2023) -- 2.3 InSAR-based detection of landfast ice -- 2.3.1 Identification of landfast ice by coherence thresholding -- 2.3.2 Assessment of landfast ice stability using interferometric phase gradient -- 2.3.3 Derivation of landfast ice stability thresholds. Chapter 3: Results -- 3.1 1996-2023 landfast ice climatology -- 3.1.1 Assessment of differences and bias between landfast ice data source -- 3.1.2 Regional landfast ice variability in the EM2024 dataset -- 3.1.3 Landfast ice occurrence probabilities -- 3.1.4 Monthly landfast ice extents -- 3.1.5 Timing of annual landfast ice events -- 3.2 InSAR-derived landfast ice extent and stability -- 3.2.1 Landfast ice extent from coherence masks -- 3.2.2 Monthly average phase gradients -- 3.2.3 Quantification of landfast ice stability categories. Chapter 4: Discussion -- 4.1 Recent changes in landfast ice in Alaska -- 4.1.1 Changes in landfast ice extent -- 4.1.2 Changes in timing of annual events in the landfat ice season -- 4.2 InSAR detection of landfast ice extent and stability -- 4.2.1 Suitability of InSAR for routine identification of landfast sea ice -- 4.2.2 Regional variability in landfast ice stability. Chapter 5: Conclusion. Chapter 6: References.
Date
2024-08
Type
Thesis
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