Abstract
ABSTRACTFine resolution topographic data derived from methods such as Structure from Motion (SfM) and Multi-View Stereo (MVS) have the potential to provide detailed observations of geomorphological change, but have thus far been limited by the logistical constraints of conducting repeat surveys in the field. Here, we present the results from an automated time-lapse camera array, deployed around an ice-marginal lake on the western margin of the Greenland ice sheet. Fifteen cameras acquired imagery three-times per day over a 426 day period, yielding a dataset of ~19 000 images. From these data we derived 18 point clouds of the ice-margin across a range of seasons and successfully identified calving events (ranging from 234 to 1475 m2 in area and 815–8725 m3 in volume) induced by ice cliff undercutting at the waterline and the collapse of spalling flakes. Low ambient light levels, locally reflective surfaces and the large survey range hindered analysis of smaller scale ice-margin dynamics. Nevertheless, this study demonstrates that an integrated SfM-MVS and time-lapse approach can be employed to generate long-term 3-D topographic datasets and thus quantify ice-margin dynamics at a fine spatio-temporal scale. This approach provides a template for future studies of geomorphological change.
Highlights
The number and area of ice-marginal lakes are increasing globally in response to contemporary deglaciation (Carrivick and Tweed, 2013)
Analysis of the image dataset illustrates the capacity of the automated camera array setup for capturing long-term (> annual) records of ice-margin change
Analysis of the keypoint matching stage of the workflow revealed that cameras A1–A4 contributed significantly fewer matches to the final point cloud, a problem later exacerbated by the loss of camera A2
Summary
The number and area of ice-marginal lakes are increasing globally in response to contemporary deglaciation (Carrivick and Tweed, 2013). Naruse and Skvarca, 2000; Mayer and others, 2008; Tsutaki and others, 2013); and perhaps most importantly, the initiation of calving (Warren and others, 2001; van der Veen, 2002) Their development often leads to the formation of a positive feedback mechanism whereby icemargin recession promotes lake expansion, which further accelerates glacier mass loss Repeat optical or dGPS surveys of stakes installed on glacier termini are commonly employed to measure changes in ice-margin extent, elevation and velocity (e.g. Anderson and others, 2005; Sugiyama and others, 2007; Tsutaki and others, 2011). Such surveys necessarily possess a coarse spatial resolution and may only be resurveyed weekly or seasonally. The spatial coverage of physical surveys at ice margins is often restricted by zones of deep crevassing and extensive calving activity
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