Lidar and Geomorphic Change Detection: Useful Tools for River Ecosystem Assessment and Restoration Monitoring
Anthony Brais, PE
Resource Environmental Solutions (RES)
Brentwood, TN
High quality prosumer drones make aerial photogrammetry accessible at a relatively low cost (ca. 2,000 USD). Drone aerial photogrammetry can be used for post-construction monitoring as an alternative to conventional survey methods saving time and money. At a stream restoration site in east Tennessee, we collected drone imagery to document as-built conditions. A twenty-five acre site was mapped at 310 feet during an automated mapping mission. Four aerial targets were placed pre-flight in the center of the stream corridor and surveyed into a state plane coordinate system. Individual images captured were merged and georeferenced during post-processing. The final product, a georeferenced aerial image and digital surface model of the site, can be utilized in CAD or GIS environments to evaluate construction efforts. Horizontal and vertical accuracy of photogrammetric products to the surveyed targets was less than a tenth of an inch.
The site and equipment used presented several challenges. Restoration sites even recently after construction can be densely vegetated which requires selecting a higher flight altitude to ensure sufficient matching features in adjacent images. Forested conditions and active agriculture prevented placement of targets around the project perimeter. Horizontal / vertical georeferencing accuracy to control targets was excellent however the digital surface model was not accurate to topographic check shots. Lastly, our drone’s camera utilized a non-global shutter. Images are not geotagged at the precise location data is recorded during automated mapping missions. A camera with a global shutter provides better raw imagery for photogrammetric processing.
About Anthony Brais, PE
Anthony Brais, PE is a restoration design engineer at Resource Environmental Solutions based out of Nashville, Tennessee. He is responsible for fifteen stream and wetland restoration projects across Tennessee and Georgia including the design of over 40,000 feet of stream restoration. He is also an FAA Part 107 Remote Pilot and has worked on projects from 10 to 500 acres collecting and processing aerial imagery and topography. When not working, he enjoys field herpetology and traveling with his wife Chandler and their Australian Shepherd, Waffle.