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Quantification and Analysis of Icebergs in a Tidewater Glacier Fjord Using an Object-Based Approach

Tidewater glaciers are glaciers that terminate in, and calve icebergs into, the ocean. In addition to the influence that tidewater glaciers have on physical and chemical oceanography, floating icebergs serve as habitat for marine animals such as harbor seals (Phoca vitulina richardii). The availability and spatial distribution of glacier ice in the fjords is likely a key environmental variable that influences the abundance and distribution of selected marine mammals; however, the amount of ice and the fine-scale characteristics of ice in fjords have not been systematically quantified. Given the predicted changes in glacier habitat, there is a need for the development of methods that could be broadly applied to quantify changes in available ice habitat in tidewater glacier fjords. We present a case study to describe a novel method that uses object-based image analysis (OBIA) to classify floating glacier ice in a tidewater glacier fjord from high-resolution aerial digital imagery. Our objectives were to (i) develop workflows and rule sets to classify high spatial resolution airborne imagery of floating glacier ice; (ii) quantify the amount and fine-scale characteristics of floating glacier ice; (iii) and develop processes for automating the object-based analysis of floating glacier ice for large number of images from a representative survey day during June 2007 in Johns Hopkins Inlet (JHI), a tidewater glacier fjord in Glacier Bay National Park, southeastern Alaska. On 18 June 2007, JHI was comprised of brash ice ( = 45.2%, SD = 41.5%), water ( = 52.7%, SD = 42.3%), and icebergs ( = 2.1%, SD = 1.4%). Average iceberg size per scene was 5.7 m2 (SD = 2.6 m2). We estimate the total area (± uncertainty) of iceberg habitat in the fjord to be 455,400 ± 123,000 m2. The method works well for classifying icebergs across scenes (classification accuracy of 75.6%); the largest classification errors occur in areas with densely-packed ice, low contrast between neighboring ice cover, or dark or sediment-covered ice, where icebergs may be misclassified as brash ice about 20% of the time. OBIA is a powerful image classification tool, and the method we present could be adapted and applied to other ice habitats, such as sea ice, to assess changes in ice characteristics and availability.

Data and Resources

  • View website
    Website :: Aerial Image Download

    http://www.harborseals.alaska.edu/data/index.html

  • View website
    Website :: Publisher's website

    http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0164444

Status: Complete
Type: Data
Data Types: Image, GIS
Primary Contact
Prakash, Anupma
Email: aprakash@alaska.edu
Primary Agency
National Park Service
Type
Federal

Funding Agency
National Science Foundation
Type
Federal

Other Agencies
EPSCoR - Alaska Adapting to Changing Environments

ISO Topics
biota, geoscientificInformation

Geo-keywords
Alaska, Southeast

Direct Record Link
http://epscor.portal.gina.alaska.edu/catalogs/11808-quantification-and-analysis-of-icebergs-in-a-ti
  • 01c8ceef3d596f40f05bf496ca00d929
    Updated by Lisa
    2016-11-21 09:55:10 -0900
  • 01c8ceef3d596f40f05bf496ca00d929
    Published by Lisa
    2016-11-21 09:54:34 -0900
  • 01c8ceef3d596f40f05bf496ca00d929
    Updated by Lisa
    2016-11-21 09:54:23 -0900
  • 01c8ceef3d596f40f05bf496ca00d929
    Updated by Lisa
    2016-11-21 09:46:57 -0900
  • 01c8ceef3d596f40f05bf496ca00d929
    New record created
    2016-11-21 09:32:21 -0900
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