Park brings in drones to survey trees
PU‘UHONUA O HONAUNAU — It takes a serious threat to convince the National Park Service to allow drones in its airspace, and for Puuhonua O Honaunau that was the death of palm trees.
The park has lost about 65 palms during the last several years, said Adam Johnson, chief of integrated resources management and supervisory archaeologist for the park.
That led him to bring in the unmanned aerial devices to give him an idea of what was going on. The service workers think there are at least two, possibly three, fungi attacking the trees and potentially insects as well.
Thankfully, Johnson said, the trees are not suffering from the coconut rhinoceros beetle that savaged Oahu’s palm trees.
Many of the trees in the park were planted more than 100 years ago, he said, so some deaths were expected.
But the number was excessive, and other trees are in poor shape — with weak new leaves and thinning crowns. At that point, the tree’s already dying, Johnson said.
The plan is to help determine what is going on and give a baseline image of what’s happening, said Ryan Perroy, assistant professor of the University of Hawaii at Hilo geography and environmental science department. He uses drone technology in much of his research.
Drones are less disruptive than other options, Perroy said, which would include surveying each tree from a bucket truck or a helicopter, he said.
A bucket truck could also lead to damage of the site, he said.
Following the NPS procedures to get the drones into the park took a lot of effort, Johnson said, but it was worth it for the efficiency in surveying the park’s hundreds of trees.
Beyond convincing his boss, he said there were an additional eight months of work and five levels of approval to go through.
“This had to go up to the Washington offices,” Johnson said.
The drone equipment on Monday took the form of three units, all using four rotors. One carried a high-quality camera for visible light, while another had a hyper-spectral system that allowed photos into near-infrared, Perroy said.
Monday’s flights were under cloud cover, which Perroy said made it a lesser option for the hyper-spectral system. The clouds interfere with the various types of radiation, he said, making it less useful than a bright sunny day.
The drone flew a pattern “like a lawnmower,” Perroy said, as it followed a series of even passes over the area of interest.
That route was programmed into the machine, which largely flew on its own, while someone holding the control panel watched it in case it should begin to act up.
The first area surveyed was the southern beach section of the park, an area excluded by the great wall on the site.
It landed, giving park workers time to offload the high-resolution images and recharge the batteries.
During that time, park staff moved to clear the royal area, the region enclosed by the great wall, dominated by heiau and featuring most of the park’s historical sites.
The staff tried to minimize the trouble of clearing people out during the survey time by scheduling flights on days with lowest attendance, Johnson said.
When the drones went up, they sounded like a swarm of bees sweeping the site, with Sean Headrick of Aerotestra, Inc. holding the controls.
The park has begun to recover from the tree deaths in one way.
They replanted some of the lost palms, placing them inside the trunks of their predecessors. This will reduce the disturbance of the historic sites, Johnson said.
Email Graham Milldrum at firstname.lastname@example.org.
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