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

摘要

This paper presents new methods of estimating the aerodynamic roughness (z(0)) of glacier ice directly from three-dimensional point clouds and digital elevation models (DEMs), examines temporal variability of z(0), and presents the first fully distributed map of z(0) estimates across the ablation zone of an Arctic glacier. The aerodynamic roughness of glacier ice surfaces is an important component of energy balance models and meltwater runoff estimates through its influence on turbulent fluxes of latent and sensible heat. In a warming climate these fluxes are predicted to become more significant in contributing to overall melt volumes. Ice z(0) is commonly estimated from measurements of ice surface microtopography, typically from topographic profiles taken perpendicular to the prevailing wind direction. Recent advances in surveying permit rapid acquisition of high-resolution topographic data allowing revision of assumptions underlying conventional z(0) measurement. Using Structure from Motion (SfM) photogrammetry with Multi-View Stereo (MVS) to survey ice surfaces with millimeter-scale accuracy, z(0) variation over 3 orders of magnitude was observed. Different surface types demonstrated different temporal trajectories in z(0) through 3 days of intense melt. A glacier-scale 2m resolution DEM was obtained through terrestrial laser scanning (TLS), and subgrid roughness was significantly related to plot-scale z(0). Thus, we show for the first time that glacier-scale TLS or SfM-MVS surveys can characterize z(0) variability over a glacier surface potentially leading to distributed representations of z(0) in surface energy balance models.