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Measuring (subglacial) bedform orientation, length, and longitudinal asymmetry - Method assessment
Marco G Jorge1, Tracy A Brennand1
1Department of Geography, Simon Fraser University, Burnaby, British Columbia, Canada.
Plos One
|March 21, 2017
Summary
The standard deviational ellipse method is recommended for measuring subglacial bedform morphometry. It accurately replicates manually derived data, especially for elongated features, unlike other tested geospatial analysis techniques.
Area of Science:
- Geomorphology
- Glaciology
- Geospatial Analysis
Background:
- Subglacial bedform morphometry is crucial for understanding ice sheet dynamics.
- Existing geospatial analysis methods for measuring bedform characteristics vary in accuracy.
- Defining a longitudinal axis is key for subglacial bedform morphometric analysis.
Purpose of the Study:
- To assess five different geospatial methods for measuring subglacial bedform morphometry.
- To compare the accuracy of these methods against a manually derived longitudinal axis.
- To identify the most reliable method for analyzing subglacial bedform orientation, length, and asymmetry.
Main Methods:
- Standard Deviational Ellipse (SDE)
- Longest Straight Line (LSL) fitting (two approaches)
- Minimum-size footprint-bounding rectangle
- Euler's approximation
- Comparison against manually mapped longitudinal axes for 100 subglacial bedforms.
Main Results:
- For highly elongated bedforms (elongation > 5), most methods showed negligible deviations, except Euler's approximation for length.
- For less elongated bedforms (elongation < 5), most methods yielded small errors (MAE, MAD), suitable for central tendency analysis.
- The LSL and Euler's approximation methods were found to be the least precise for statistical dispersion analysis.
Conclusions:
- The Standard Deviational Ellipse method is recommended for subglacial bedform morphometry due to its shape invariance and close replication of reference data.
- The study suggests potential applicability to negative-relief, fluvial, and aeolian bedforms.
- Care should be taken when using LSL and Euler's approximation for dispersion analysis of subglacial bedforms.
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