Measuring glacier surface roughness using plot-scale, close-range digital photogrammetry
journal contributionposted on 2014-12-22, 16:18 authored by Tristam D.L. Irvine-Fynn, Enoc Sanz-Ablanedo, Nick Rutter, Mark W. Smith, Jim Chandler
Glacier roughness at sub-metre scales is an important control on the ice surface energy balance and has implications for scattering energy measured by remote-sensing instruments. Ice surface roughness is dynamic as a consequence of spatial and temporal variation in ablation. To date, studies relying on singular and/or spatially discrete two-dimensional profiles to describe ice surface roughness have failed to resolve common patterns or causes of variation in glacier surface morphology. Here we demonstrate the potential of close-range digital photogrammetry as a rapid and cost-effective method to retrieve three-dimensional data detailing plot-scale supraglacial topography. The photogrammetric approach here employed a calibrated, consumer-grade 5 Mpix digital camera repeatedly imaging a plot-scale (≤25 m2) ice surface area on Midtre Lovénbreen, Svalbard. From stereo-pair images, digital surface models (DSMs) with sub-centimetre horizontal resolution and 3 mm vertical precision were achieved at plot scales ≤4 m2. Extraction of roughness metrics including estimates of aerodynamic roughness length (z 0) was readily achievable, and temporal variations in the glacier surface topography were captured. Close-range photogrammetry, with appropriate camera calibration and image acquisition geometry, is shown to be a robust method to record sub-centimetre variations in ablating ice topography. While the DSM plot area may be limited through use of stereo-pair images and issues of obliquity, emerging photogrammetric packages are likely to overcome such limitations.
T.D.I.-F. acknowledges UK Natural Environment Research Council (NERC) [grant number NE/G006253/1] (principal investigator A.J. Hodson, University of Sheffield) for enabling data collection at Midtre Lovénbreen, and the Climate Change Consortium of Wales (C3W) for facilitating the completion of this work. Logistical support in Svalbard from Nick Cox (NERC Arctic Research Station), and field assistance from Aga Nowak and Jon Bridge, was gratefully received. E S.-A. and J.H.C. thank Eos Systems Inc. for providing access to PhotoModeler software at reduced academic rates.
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