• Login
    View Item 
    •   Home
    • University of Alaska Fairbanks
    • UAF Graduate School
    • Geosciences
    • View Item
    •   Home
    • University of Alaska Fairbanks
    • UAF Graduate School
    • Geosciences
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of Scholarworks@UACommunitiesPublication DateAuthorsTitlesSubjectsTypeThis CollectionPublication DateAuthorsTitlesSubjectsType

    My Account

    Login

    First Time Submitters, Register Here

    Register

    Statistics

    Display statistics

    Basal shear strength inversions for ice sheets with an application to Jakobshavn Isbræ, Greenland

    • CSV
    • RefMan
    • EndNote
    • BibTex
    • RefWorks
    Thumbnail
    Name:
    Habermann_uaf_0006E_10066.pdf
    Size:
    29.70Mb
    Format:
    PDF
    Download
    Author
    Habermann, Marijke
    Chair
    Truffer, Martin
    Committee
    Maxwell, David
    Freymueller, Jeff
    Pettit, Erin
    Tape, Carl
    Metadata
    Show full item record
    URI
    http://hdl.handle.net/11122/4628
    Abstract
    Satellite and in situ observations of ice sheet outlet glaciers around the turn of the 21st century showed that rapid changes in ice dynamics are possible and important for the evolution of ice sheets. When attempting to model these dynamic changes the conditions at the ice-bed interface are crucial. Inverse methods can be used to infer basal properties, such as the basal yield stress, from abundant surface velocity observations by using a physical model of ice flow. Inverse methods are very powerful, but they need to be applied with care, otherwise errors can dominate the solution. In this study we investigate the potentials and caveats of inverse methods. Synthetic experiments can be designed where basal conditions are assumed and an ice flow model is used to produce a set of 'synthetic' surface velocities. These can then be used to examine and evaluate inverse methods. We find that in iterative inverse methods it is essential to use a stopping criterion that will prevent overfitting the data. We introduce a new and rapidly-converging iterative inverse method called Incomplete Gauss Newton method, where the linearized problem is partly minimized in each step.In a practical application of inverse methods to the terminus region of Jakobshavn Isbræ, Greenland we investigate changes in basal conditions over time by performing inversions for different years of available surface velocity data. We find a decrease in basal yield stress in the lower areas of the glacier that agrees with effective pressure changes due to the changes in ice geometry. This supports an ocean and terminus driven system. The difference between the modeled and observed velocity fields, called residual, contains information about the ability to reproduce the velocities when only adjustment of the basal condition is allowed. With a properly regularized inversion the residual patterns can be used to investigate sources of error in the system. We find that the ice geometry and the model simplifications influence the ability to reproduce observed velocity fields more than the error in observed velocity does. This indicates that further progress must come from model improvements and improved capabilities to measure bedrock geometry.
    Description
    Dissertation (Ph.D.) University of Alaska Fairbanks, 2013
    Date
    2013-12
    Type
    Dissertation
    Collections
    Geosciences

    entitlement

     
    ABOUT US|HELP|BROWSE|ADVANCED SEARCH

    The University of Alaska is an affirmative action/equal opportunity employer, educational institution and provider and prohibits illegal discrimination against any individual.

    Learn more about UA’s notice of nondiscrimination.

    Open Repository is a service operated by 
    Atmire NV
     

    Export search results

    The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

    By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.

    To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

    After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.