Aerial images from a drone are being evaluated as a method to survey seagrasses scarred by boat propellers.
The Texas Parks & Wildlife Department (TPWD) has partnered with Texas A&M University-Corpus Christi to determine if using unmanned aircraft systems is as effective as using planes.
Seagrasses serve as a refuge and nursery ground for fish, shrimp and crabs. They provide oxygen to the water column and serve as an area for growth of drift algae, a food source for shrimp, fish and crabs.
A law prohibiting the uprooting of seagrasses coast-wide was passed by the Texas Legislature during the 83rd legislative session and has been in effect since September 2013. Motorboats cause propeller scarring when they drift into shallow waters and tear a trough in the bay bottom.
Michael Starek, assistant professor of engineering, has been analyzing the images and data collected from flights in December of a small UAS about 450 feet above Redfish Bay’s seagrasses.
TPWD has conducted aerial surveys since 2007 using piloted aircraft flying at an altitude of about 2,000 feet, said Faye Grubbs, Upper Laguna Madre ecosystem leader with TPWD.
The project will compare the output from each method, and analyze costs of processing and ease of mobilization.
TPWD continues to collect aerial imagery in four areas along the Texas coast to evaluate the effects of the regulation. Based on the outcome of this project, Grubbs said the department may use drones for not only monitoring changes in propeller scarring, but possibly for mapping other habitats as well.
“We are comparing the accuracies of the different imagery sets — manned versus unmanned — and how well we are able to map scar features observed in the imagery,” she said.
UAS-collected imagery has the potential to change environmental monitoring at many scales, not just in coastal regions, Starek said.
The first step is to show drone-captured data is comparable to that collected from manned planes. University researchers have been doing just that for several years, flying along the coast and comparing drone-captured images to data from on-the-ground and in-the-water surveying by traditional means.
One of the biggest challenges with aerial imaging of the sea floor is weather and water clarity, Starek said.
“This experiment showed that with proper flight planning for weather conditions, mapping of prop scars with a small UAS can be a viable alternative to more costly, piloted airborne surveys,” Starek said. “Results from the flights show impressive spatial fidelity in the UAS-collected imagery. Pixel resolutions down to one inch will allow mapping of seagrass impacted by prop scaring at very fine spatial detail previously unattainable.”
Although the results show the capabilities, Starek said UAS technology still has to evolve both in platform endurance and in regulations to allow these systems to fly autonomously over much larger areas, such as an entire bay system. This latter component will evolve as the technology and confidence in its use matures.
“In the not too distant future, I can foresee the day when a fleet of small UAS equipped with cameras can routinely map an entire bay system at a fraction of the cost for traditional piloted airborne surveys,” he said. “The potential for UAS technology is immense.”
