High resolution mapping of supra‐glacial drainage pathways reveals link between micro‐channel drainage density, surface roughness and surface reflectance

Abstract

This paper reports on the use of a small unmanned aerial vehicle (sUAV) carrying a standard compact camera, to construct a high resolution orthomosaic (OM) and digital elevation model (DEM) over the lower reaches of the glacier Midtre Lovénbreen, Svalbard. Structure from Motion (SfM) techniques were used to build the OM and DEM, and together these reveal insights into the nature of supra‐glacial drainage. Major meandering supra‐glacial drainage pathways show clear dynamism, via meander cutoffs and abandoned channels. In addition, the imagery reveals a very extensive network of smaller channels that may well carry substantial amounts of water. This network of channels is in part controlled by the structure of the glacier, but in turn, these channels have a significant impact on the ice surface. Roughness of the ice surface is higher where channels are most extensive. In addition, we find a relationship between channel density and surface reflectance, such that greater channel density is associated with lower reflectance values. Given the role of surface reflectance and roughness in the energy balance of glaciers, it is therefore apparent that extensive networks of small supra‐glacial channels across such glaciers have the potential to have an important impact on energy exchanges between the atmosphere and the ice surface. Copyright © 2015 John Wiley & Sons, Ltd.

Flow Routing for Delineating Supraglacial Meltwater Channel Networks

“…DEMs are increasingly available at high resolution for ice surfaces [4,16,18,20], and reproducible, accurate methods of extracting surface meltwater channels are necessary for quantifying their temporal and spatial characteristics. Flow routing has numerous advantages for delineating meltwater channels; however, previous research by Yang et al (2015) [34] on the use of flow routing over moderate-resolution ice surface DEMs found that (1) automated sink preservation thresholds missed over half of mapped moulins and resulted in significantly overestimated drainage network extent; (2) mapped channel networks could be replicated by flow routing with match rates in excess of 85% when a 600 m buffer was applied; (3) less than 40% of the FR drainage network did not match the mapped drainage network, leading to the conclusion that these channels were miscoded.…”

“…Supraglacial meltwater channels are ubiquitous fluvial features in the ablation zones of glaciers and ice sheets (e.g., [1][2][3][4]). They are of intrinsic interest to researchers as unique fluvial systems as well as for the important roles they play in glacial hydrology.…”

“…Smith et al (2015) [2] and Yang et al (2015) [34] used multispectral methodologies on high-resolution (~2.0 m) WorldView-2 imagery of the southwest GrIS to produce the most extensive dataset to date, and [8] analyzed fluvial morphometry of these supraglacial river networks. With topographic data, Rippin et al (2015) [4] used drone imagery to produce high-resolution (0.01 m) surface Digital Elevation Models (DEMs) of an alpine glacier in Svalbard, and identified channels using an iterative elevation threshold. DEMs have also increasingly been used to delineate channels through flow routing methods modified for use on ice surfaces [10,[34][35][36][37].…”

“…This processing step is problematic in ice surfaces, however, where surface water drains via moulins (sinks on the ice surface) to the englacial hydrological system [39][40][41]. Yang et al (2015) [34] and Rippin et al (2015) [4] both concluded that flow routing overestimates hydrological network extent for this reason. Studies employing flow routing to delineate supraglacial meltwater drainage pathways have employed various approaches to this problem.…”

Biocryomorphology: Integrating Microbial Processes with Ice Surface Hydrology, Topography, and Roughness

“…Rippin et al (2015) shows that greater density of microscale channels is associated with rougher, darker ice. Since roughness is a key parameter in surface energy balance it likely influences hole morphology, which impacts cryoconite biogeochemistry (Cook et al, 2010) and reciprocally influences surface roughness.…”