Dune Reclamation with Drones

Over the summer, Geomatix  completed two small proof-of-concept projects in cooperation with the City of Ventnor, NJ to demonstrate the mapping and remote sensing technologies we use every day and how they can be used in support of dune reclamation and monitoring.

The first project was a fairly straight forward topography demo. We produced a topographic map and 3-D surface model for a two-block length of fully replenished dunes. We placed GPS ground control,  collected a few hundred high definition photos, and processed everything together using standard Structure-from-Motion (SfM) photogrammetry tools and techniques. In the image below you can see the contour data and digital elevation map (DEM) we generated for the city.

A big part of dune reclamation, following big storm events like Hurricane Sandy, is ensuring that not only are the dunes built back up, but that there is sufficient dune grass to hold everything in place. The City devotes precious resources to planting and maintaining these grasses, as they play a critical role in preventing erosion. Having a non-invasive tool to identify and prioritize areas of vegetative distress is a game-changer.

To accurately measure the health and coverage of planted beach grass, we suggested the use of a Multispectral Sensor and the Normalized Differential Vegetative Index (NDVI). The Inspire 2 was fitted with a MicaSense RedEdge Multispectral Sensor for these flights. After a short ten minutes in the air, we left the site with about 900 MSS images. We stitched these photos together into a collection of georeferenced raster data with the same workflows from the topographic mapping efforts. Below is an image of the final subject area.

The NDVI is a great tool assessing whether the target being observed contains live green vegetation. Using some in-house GIS expertise, we quickly filtered out all the NDVI values below a certain threshold, so that the only thing left were areas with a high enough NDVI score to indicate healthy, living beach grass. In the image below, the red areas are part of the NDVI mask we used to measure dune grass coverage.

We also generated a simple table indicating the total percentage cover for the area:

Description Min NDVI Max NDVI Area (Acres) Area (%)
Vegetative Cover 0.4 0.8 1.16 15.24
No Cover 0.0 0.4 6.47 84.76

These two technologies ended up offering both novel and cost-effective ways to support ongoing dune reclamation efforts. The topographic map and the 3-D model provide an excellent baseline to measure changes in the geomorphology of the dunes over time in response to natural forces such as wind and tide. From the standpoint of anthropogenic impacts, the photographic resolution is of sufficient detail to identify individual footprints on the dune slopes. Combined with the ability to quickly quantify beach grass coverage, we were able to generate a complete picture of dune health. Performing these studies over an extended period of time can be used to assess both the health of the dunes as well as the effectiveness of the reclamation program, helping shape and improve reclamation strategies over time.

If you have any questions about our process, techniques or how you might be able to leverage these exciting new remote sensing technologies please don't hesitate to reach out. We're always available for a call, consult or even a short presentation.