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Drones on Nantucket; Spying on our non-native invasive plants

The Phragmited on the right is clearly distinguished from the other vegetation on the left.
A snapshot of the full orthomosaic of the south portion of Long Pond.
The drone; a DJI Inspire 1.
A close up of the non-native invasive plant in question, Phragmites australis.

We’ve all heard of them. Many of us on Nantucket have seen them hovering over our coastlines and possibly in our backyards. And then there is that buzzing sound. We’re talking about drones. Sure, Doc Hinson’s videos are great and many a real estate agent has been able to showcase a property or two with this amazing technology. However, there are many applications for this tech beyond tourism and real estate. A group of Nantucket scientists, conservationists, non-profits, and educators have now delved into using unmanned aircraft systems to map and monitor invasive plants.

The Nantucket Pond Coalition, the Nantucket Land Council, and the Linda Loring Nature Foundation have teamed up with off-island consultant, Ron Fortunato of Trillium Learning, to use drone technology to map non-native invasive plants on some of Nantucket’s major ponds. Researchers from the University of Massachusetts Amherst also helped with mission planning and technical assistance for this project. This is a first for Nantucket collaboration, opening the door for a multitude of scientific applications.

Discussions about this recent project began at the end of summer 2016 when Seth Engelbourg of the Linda Loring Nature Foundation gave a talk about his master’s thesis work using drone technology. Audience members later relayed information about the presentation to Bob Williams of the Nantucket Pond Coalition and then the lightbulb went off. The group that resulted from these discussion fast-tracked the idea and moved forward to get surveys completed this fall. Bad weather hampered the first efforts in October, but by November, everything fell into place for the surveys and educational components to take place.

Surveys were conducted over two days in November covering Long Pond, Hummock Pond, and Miacomet Pond. These surveys were targeted at mapping the non-native invasive Phragmites australis (Giant Reed). Because Phragmites causes large monoculture stands along pond edges, this system is a good test of the resolution of the drone technology and imaging.

The drone used for this survey was a DJI Inspire 1 (See image right). The Zenmuse X5 camera is a separate component which captures 16 MP full HD images and records video in 4K resolution. Even in winds, the images are crystal clear; a 3-axis gimbal system stabilizes the camera to respond to different flight and weather conditions (this gimbal is capable of maintaining stability even in 20mph winds). Another integral part of the equipment is the GPS, which provides accurate coordinate positioning so that the drone knows exactly where to fly. When flying for ecological purposes, the drone needs to fly along a precise route which is preprogrammed. To conduct the surveys, the drone is programmed to fly over the pond edges taking a picture every few seconds. In this survey the drone was programmed to take pictures with 70% horizontal and vertical overlap of the surrounding images, in order to ensure that there would be no holes in the area photographed. When the drone’s battery falls to 30% the operator receives an initial low battery warning, indicating that it is time to begin wrapping up the survey. At 20%, the pilot will receive a second warning. If the survey segment has not been completed by this time, the drone will trigger an automatic return to home and for safety reasons will land itself, even if the survey is not yet finished. If the survey has been completed before the 20% warning, then the operator can choose to have the drone land itself, or steer it down manually. During mission planning, operators use software to determine the feasible area that the drone can fly on each battery, however heavy winds or other contingencies may prevent the drone from completing its assigned section on one battery. In this case, the operator simply switches the battery out and restarts the survey from where the drone stopped. Since on average each battery only last for 20 minutes, multiple segments had to be flown to survey each pond. At the end of all the flights is when the magic really happens and post-processing begins. The individual photos are seamlessly meshed together using computer software to create a high definition image of the pond (See image right). This image is georeferenced and is ready to use in any GIS software.

The tech is ideal for ecological surveys as the starting and ending points of survey transects as well as the altitude can be programmed into the drone. This makes for systematic and constant surveys throughout.

Based on the image results from the November surveys, you can clearly see differences in vegetation and identify the phragmites stands. The works that resulted from the drone survey saved the Nantucket Pond Coalition a considerable amount of money, time, and effort in surveying the pond edges. If done with more traditional methods, a field person would use a hand-held GPS device to walk the perimeter of each phragmites stand. Generally, that would take several 8 hour days per pond, plus the need to use a boat for the pond-side of the surveys. In contrast, all three ponds, Long, Hummock, and Miacomet, were able to be surveyed by drone in a mere day and a half.

Although analysis of the survey maps has yet to be done, the data will be used to calculate the total area and volume of phragmites for each pond. These images will also be used as a baseline to compare with future surveys in order to document expansion of populations and/or the results of management.

In addition to the surveys, Trillium Learning and local partners are using these surveys as an educational opportunity for the Nantucket School systems. Seth Engelbourg of the Linda Loring Nature Foundation and Emily Molden of the Nantucket Land Council worked with the Nantucket New School 7th and 8th graders, 5th and 6th graders from the Lighthouse School, and  the Nantucket High School AP Environmental Science classes to learn about using modern technology in ecology. The students learned about invasive species, technology applications, and drone logistics. Having multiple partner organizations is also a good example of collaborative research.

After this first-of-its-kind survey for Nantucket, we can easily see the potential for many future applications.