Measuring Change in Arctic Coastal Environments Using Repeat Aerial Photography and SfM Elevation Models

Abstract:

Aerial- and ground-based photography can provide valuable information about coastal environments in space and time including the presence or absence of shorefast ice, beach characteristics and morphology, high-water indicators produced during storm surge events, bluff failure mechanisms, and habitat identification. Recent advances in digital photogrammetry and construction of Digital Elevation Models (DEM) using Structure-from-Motion (SfM) algorithms allow for improved mapping and analysis of coastal change in 3-dimensions at a relatively low cost. For example, analyses can include delineating shorelines based on a tidal datum, mapping inundation extent based on a known or modeled flood level, or quantifying volumetric change. Repeat aerial surveys and associated orthophoto and DEM construction serve as a powerful monitoring tool that can provide insights into the mechanisms responsible for coastal change.

Along the extensive and remote coast of Alaska, high-quality imagery and elevation data are rare, in part because traditional methods of acquiring the data are cost prohibitive. Here we evaluate the usefulness of data sets acquired using small aircraft and SfM techniques for evaluating seasonal change to the beach and permafrost bluffs at Barter Island, Alaska during the summer of 2014. Considerable bluff retreat and morphological change were measured along a 2.7 km stretch of coast with net mean volume loss of approximately 28,000 ± 540 m³ between the top and the base of the bluffs. The pattern of change was dominantly landward retreat of the top of the bluffs and removal of the debris fan at the base of the bluffs. Barrier-spit overwash and migration and deposition of storm berms were also observed and accurately measured. Our results suggest that this is a cost-effective method for mapping coastal change in remote environments leading to a similar data acquisition effort for the State of Alaska, primarily for shoreline and coastal hazard mapping purposes, along a major section of the western coast of Alaska in 2015.