Multi-Method Topographic Survey at Lake Agnes Rock Glacier, Colorado

• Principal Investigator(s): Daniel McGrath, Colorado State University
• UNAVCO Staff: Spencer Niebuhr and Keith Williams
• Dates: Aug 30, 2019
• Location: Lake Agnes Rock Glacier near Cameron Pass, northern Colorado
• Funding Source: University funds

Written by Keith Williams
14 January 2020

The Lake Agnes rock glacier dominates the Lake Agnes cirque, near Cameron Pass in northern Colorado, however, little is known about its kinematics or dynamics. To determine the motion of the rock glacier, UNAVCO supported Colorado State University researchers with two sets of tools that were used simultaneously: terrestrial laser scanning (TLS) and an uncrewed aircraft system (UAS). The UAS was used to take sets of overlapping photos to be used for structure from motion (SfM) photogrammetry. For this first survey, TLS was used as the primary instrument with UAS SfM filling in the gaps. These gaps are the result of surveying from a ground-based platform, which is unable to image over the undulations of, and down into, the deepest depressions of the rock glacier.

Using these two methods simultaneously also allowed for a comparison. Initial analysis indicates that the accuracy of the UAS SfM could be very similar to the accuracy of the TLS, with many additional benefits. These benefits include:

• Nearly 100% coverage of the glacier (UAS) vs 60-70% (TLS)
• Imaging is always near nadir (vertical) looking at the glacier surface (UAS) vs oblique and from limited scan positions (TLS)
• Surface colors are true and accurate (UAS) vs overlaid and subject to misalignment (TLS)
• ~20 lbs of gear that needed to be hiked in (UAS) vs ~150 lbs (TLS)
• Survey time of ~30 minutes (UAS) vs ~6 hours (TLS)