Measuring glacier surface roughness using plot-scale, close-range digital photogrammetry

Abstract

ABSTRACT. 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 plotscale (�25 m 2 ) 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 m 2 . 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.

Aerodynamic roughness of glacial ice surfaces derived from high‐resolution topographic data

“…Similar z 0 variability was also reported by Irvine‐Fynn et al . []. Second, while orthogonal profiles are often computed, the different frontal areas from two opposing wind directions cannot be resolved.…”

Evaluating morphological estimates of the aerodynamic roughness of debris covered glacier ice

“…Smith et al () reported good agreement between the three approaches, but only using smaller (2 m × 2 m) plots, at which scale our data also show good agreement even if they underestimate z 0 in each case. Our full dataset (Supplementary data S1) confirms that the profile‐based method produces highly variable results even within a single plot (as noted by Irvine‐Fynn et al, ), and is direction dependent. There is an argument for integrating profiles both parallel and perpendicular to flow so that frontal areas from opposing wind directions can be resolved (i.e.…”

Glacial Aerodynamic Roughness Estimates: Uncertainty, Sensitivity, and Precision in Field Measurements

“…These methods allow rapid data acquisition over much larger areas and shorter timescales than is feasible with more traditional manual surveys. Recent studies have used digital elevation models (DEMs) constructed from SfM (Irvine‐Fynn et al, ; Miles et al, ; Rounce et al, ) or TLS (Nield et al, ) data, from which transects can be extracted as the grid rows and columns. Smith, Quincey, et al () obtained terms for (3) from both DEMs and filtered point clouds, allowing the previous assumptions to be relaxed by accounting for the total exposed frontal area and giving a value for each cardinal wind direction.…”