A Drone of Our Own: NEON Adds Drone-Based Leaf Sampling Protocol

Treetop leaf sampling (canopy foliar sampling) at forested NEON field sites just got a whole lot easier. We've added a new tool to our kit: an unmanned aerial vehicle (UAV), or drone. Drone-based foliar sampling has been added as an official NEON protocol for forested sites. The UAV will also be available for use in the Assignable Assets program.

Faster, Safer Canopy Sampling with UAVs

The NEON program has been experimenting with drone-based foliar sampling since 2019, when we conducted a pilot program with Outreach Robotics, the creators of the DeLeaves tree sampling tool. Since then, DeLeaves has made significant improvements in range, portability, and ease of use for the system. After training additional pilots in 2021, we decided to invest in a UAV of our own. The Matrice 300 RTK commercial drone is about 2' by 2.5' and has a payload capacity of ~3 kg, enough to support the DeLeaves sampling arm, camera, and a foliar sample. It can also be outfitted with other types of equipment, such as a lidar system or spectrometer. This is the first UAV purchased by the NEON project, though previous flights have been performed at NEON sites using Battelle-owned drones as part of a series of internal research and development (IRAD) grants aimed at improving drone research capabilities across the organization. Battelle operates the NEON program on behalf of the National Science Foundation (NSF).

Tree foliar sampling is the first drone-based protocol to be added to NEON's sampling design. NEON collects foliar samples from as close to the canopy top as possible, and does chemical analyses of these samples, to provide ground-truthing for the hyperspectral data from the Airborne Observation Platform (AOP). Previously, field staff used line launchers to collect leaf samples from the tree canopy—a process that is both time-consuming and imprecise. The line launchers collect leaf samples from the sides of the tree instead of the top of the canopy. This matters because leaves from lower in the canopy do not get as much sunlight as leaves at the top, resulting in different chemical makeup and growth patterns. As a result, it is harder to correlate hyperspectral data from with chemical analysis of foliar samples for ground truthing.

The DJI M300 drone equipped with the DeLeaves tool while bringing back a tree sample collected 150m away from the takeoff point, with Rhode River in the background. Photo credit: Hughes La Vigne, DeLeaves, captured with a DJI Mavic 2 Pro.

Using drones to collect samples from the canopy tops is safer, faster, and easier than other methods. Using a UAV and the DeLeaves sampling tool, it is possible to precisely target samples from the very top of the canopy—the part of the canopy viewed by the AOP—for better ground truthing data. In addition, the drone protocol saves considerable time in the field. Dave Durden, a senior research scientist for the NEON program and the primary investigator for the drone project, says, "Canopy sampling is conducted at peak greenness for each site, which is already a tremendously busy time for our field scientists. Anything that gives our field science team some time back is a big win. This has greatly reduced the time needed for canopy sampling." Using the drone, the team was able to cut time for canopy sampling at mixed forest sites from 3-4 weeks per site to just 1-1.5 weeks per site.

The new drone sampling protocol will be used for nearly all forested NEON field sites moving forward. (Drones are prohibited at a few forested sites due to security or permitting concerns.) Foliar canopy sampling is conducted concurrently with the AOP flyovers for each site on a rotating schedule, with sites sampled every five years. So far, five field sites have been sampled using the DeLeaves tool. Durden and other NEON field staffers partnered with Outreach Robotics for pilot programs at Wind River Experimental Forest (WREF) and Smithsonian Environmental Research Center (SERC) in 2019 and 2021. In 2022, NEON teams sampled three additional sites independently using the new NEON-owned equipment: Bartlett Experimental Forest (BART), Guanica Forest (GUAN), and Smithsonian Conservation Biology Institute (SCBI).

What's Next for Drones at NEON?

So far, Durden and Skyler Hackley – a technician specialist with NEON – have been specifically trained to operate the drone and DeLeaves sampling tool. However, NEON has five total licensed drone pilots; some have gained experience flying other missions for the EPA, NEON site characterization, and other Battelle IRAD projects. The team is already making improvements to the process. A second drone controller allows them to reach areas that were previously inaccessible; one team member can launch the drone from a safe takeoff location and then pass control to a second person located near the sampling site to take the sample. This allows them to reach trees in locations that are not close enough to a safe takeoff and landing location for transmission of images to guide sampling. (Camera transmission range is limited to ~200-250 m in dense forest.)

Take-off from a narrow opening in the natural forest, piloted by David Durden (NEON). Photo credit: Hughes La Vigne, DeLeaves, captured with a DJI Mavic 2 Pro.

Moving forward, Durden expects to see additional people trained on the technology. And there could be other uses for the UAV beyond canopy sampling. "Drones are becoming more common in field ecology to replace things that are dull, dirty or dangerous—or really, anything where field staff time could be better used for something else." For example, drones could be used to supplement the AOP data for remote sensing products such as Leaf Area Index (LAI) or canopy water, nitrogen, or lignin content. They could also be added to the plant phenology protocol, allowing close-up views of leaf budding or cone formation on tall trees, for example. Durden also sees potential for certain aquatic protocols, such as calculating stream velocity or discharge rates.

The UAV is also an exciting addition to the Assignable Assets program. This program allows individual researchers or organizations to tap into NEON infrastructure for their own research programs, which may be self-funded or funded by NSF or other grant-providing organizations. The drone team also has access to additional Battelle drones; these drones have been used for a variety of Battelle IRAD projects as well as client work, including site monitoring for the EPA. The UAVs can be equipped with a variety of different sensors and tools—including lidar, RGB cameras and hyperspectral imaging spectrometers—to address a wide range of scientific questions.

In the future, drones could be combined with other emerging technologies, such as edge computing, to enable new methods such as reactive sampling (that is, automated sampling or observations made when certain conditions are met). Durden says, "It's important for us to keep up with the current state of technology. We have seen drones take off in recent years, and their capabilities are growing exponentially. Along with other technologies, there is an opportunity for us to augment what we are doing and change the ways in which we collect data. We are always working to provide the very highest quality data to our end users and expand the range of services we are able to offer through the Assignable Assets program."

What would you do with a drone through the Assignable Assets program? Tell us !