DUNEX Aerial Imagery of the Outer Banks

USGS DUNEX Operations on the Outer Banks

USGS DUNEX Operations on the Outer Banks

DUring Nearshore Event eXperiment (DUNEX) is a multi-agency, academic, and non-governmental organization (NGO) collaborative community experiment designed to study nearshore coastal processes during storm events. 

DUNEX Home Page

DUNEX Research and Experiments

USGS participation in DUNEX will contribute new measurements and models that will increase our understanding of storm impacts to coastal environments, including hazards to humans and infrastructure and changes in landscape and natural habitats.

Pea Island Experiment

Nearshore Geology

Numerical Models

Science Center Objects

The During Nearshore Event Experiment (DUNEX) project is a large collaborative scientific study focusing on understanding the consequences of coastal storms on the morphology of coastal ecosystems.  By flying large sections of the coast and collecting still images using structure from motion (SfM) techniques, we hope to contribute high resolution (20cm) elevation maps for time series comparisons. Coastal landscapes change quickly during storm events, but our ability to measure these changes is often compromised by delayed disaster relief responses and operational challenges to mobilizing field crews. Rapid assessments of ground conditions immediately after these events can provide important information about the extent and magnitude of coastal erosion, the location and elevation of flooding high water marks, and the extent of damage to natural resources, infrastructure, and private property.  Additionally, because storms can cause widespread changes to the landscape and can be followed by subsequent storms, it is valuable to rapidly update our topographic maps as input for coastal change and flooding models, such as the USGS Total Water Level forecasts.  

The Outer Banks of North Carolina, where DUNEX is being held, comprise around 175 miles of barrier island, separated from the mainland by up to 30 miles. Long stretches of coast are uninhabited and remain only accessible by boat. While small scale mapping of sections is feasible with Unoccupied Aerial Systems (UAS), such as drones and kites, or by foot, these endeavors can be dangerous or hard to achieve under or after storm conditions. The solution to safer, faster, and greater coverage of the coast is achieved with piloted fixed wing aircraft taking photos and modern photogrammetry workflows.

A basic map of Pea Island with cartographic symbols and labels

Aerial Imagery is collected along the entire Outer Banks using a fixed wing plane making several passes up and down the coast. The imagery along with ground control points in the area are used to make structure-from-motion products. Aerial imagery is from USGS flight on 2021-09-28. (Credit: Jin-Si Over, Woods Hole Coastal and Marine Science Center. Public domain.)

As a hurricane approaches the study site, a pilot is contracted to fly over the coast and take overlapping images with highly accurate GPS (x,y,z) information to establish baseline conditions. The overlapping imagery is used in a process known as Structure from Motion (SfM) that can take 2D images to produce 3D products that contain elevation information. These SfM digital elevation models (DEMs) are similar to elevational data derived from lidar, but have difficulty resolving through water, tall structures, and vegetation and could be more accurately described as digital surface models as compared to bare earth or digital terrain models. Currently, the relative cost of SfM with the aerial imagery is pointedly cheaper than lidar. The SfM workflow also returns orthomosaics, the stitched together imagery, which can be used to visually identify coastal features and damage. After the baseline imagery and elevations have been established, the process can be repeated as soon as it is safe to do so after the storm. By comparing pre and post storm DEM’s, the elevation differences can be used to evaluate the volumetric changes in the coastal morphology.  Imagery collected between storms can also be used to evaluate the recovery process, but even without pre-storm data to detect change, profiles can be extracted from post-storm DEMs to update numerical models to provide more accurate forecasts. 

This process, with varying types of aerial imagery, has been actively used by the USGS Remote Sensing Coastal Change group from past hurricanes, including Hurricane Matthew (2016), Hurricane Irma (2017), Hurricane Florence (2018), and Hurricane Dorian (2019) to provide rapid response SfM products to a wide audience that includes the National Park Service, local and state government authorities, and other researchers in the coastal hazards community. Aerial Imagery of Pea Island and the Duck Field Research Facility, the two main study areas for DUNEX, has been collected ten times since August 2019 and will provide a time series leading up to the experiment. 

The goal for DUNEX is to obtain aerial imagery along the Outer Banks on a semi-regular (approximately monthly) basis and also include additional post-storm flights. Imagery and navigation will be used to produce decimeter-scale DEMs and orthophotos using SfM in support of the other projects. All data will be published and made available to the public. From these products the orthomosaics can be used to identify, label, and characterize features in the beach-dune system such as vegetation, substrate, storm-induced flow features with machine learning techniques or other processes. The results may help identify nesting habitat and landcover changes.  DEMs can also be used to extract elevation metrics such as dune height, shoreline positions, and beach slope for updating models and long term records of change.