Visualizing and Monitoring Bluff Retreat Using Sentinel 1 Radar Interferometry and UAV Imagery.

The main focus of this research project is to apply radar interferometric techniques to Sentinel-1 SAR data to detect and monitor unstable bluffs along the Lake Michigan coastline at St. Joseph City, Michigan where failures along the bluff have been recently reported. Using a stack of 56 Sentinel 1A radar imagery in ascending acquisition geometry acquired between 2017 and 2019, and applying two popular radar interferometric methods (Persistent Scatter Interferometry [PSI] and Small Baseline Subset [SBAS]), we investigated the spatial and temporal displacement patterns in the study area. A high resolution DEM and orthophoto was extracted from structure-from-motion photogrammetry using a set of UAV imagery acquired on July 8, 2019 by the Michigan coastal project group (USGS, Michigan Geological Survey [MGS]) Lake Michigan coastal project group. The extracted radar-based Line of Sight (LOI) velocities using both methods (SBAS and PSI) were plotted over the high resolution UAV orthophoto and DEM to visualize and identify the locations where bluff movement has been occurring and to identify the lithological and geomorphologic features that promote slope failure. Initial findings include: (1) SBAS and PSI methods both identify similar displacement patterns along the bluff, yet SBAS yielded a greater coverage, especially over vegetated areas; (2) the locations of areas witnessing high rates of LOS displacement (up to 9 mm/year) that were detected along the bluff were verified from field data and from observations extracted from UAV imagery, and (3) the apparent acceleration of the observed deformation and slope failure during the investigated period is caused by the rise in ground water levels that was induced by increased precipitation (rain and snow fall), and surface and groundwater flows, all of which increased infiltration and aquifer recharge. The local geology (e.g., glacial aquifer thickness, lithology, and structure) provided additional controls on the location and rates of slope failures along the bluff.