Ryan Perroy, Professor of Geography and Environmental Science

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Professor Perroy’s areas of expertise and research are in remote sensing, high-resolution mapping, geospatial data analysis, and aerial robotics.

At left is aerial view of lava flow. At right is profile photo of Ryan Perroy.
Ryan Perroy. At left is an aerial photo captured by Perroy’s research team using a SwingletCAM over an advancing flow breakout heading toward Pāhoa, Hawaiʻi, on Oct. 22, 2014. (Courtesy photos from Ryan Perroy/SDAV Lab/UH Hilo)

Posted Oct. 9, 2024.

Ryan Perroy is a professor of geography and environmental science at the University of Hawaiʻi at Hilo. His areas of expertise and research are in remote sensing, high-resolution mapping, geospatial data analysis, and aerial robotics.

He received his master of arts (2004) and doctor of philosophy (2009), both in geography, from the University of California, Santa Barbara.

Professor Perroy was already at the leading edge of his field with his dissertation research using light detection and ranging (LIDAR) to study erosion on Santa Island, Calif. LIDAR is a remote sensing method used to examine the surface of Earth.

“My dissertation was one of the first studies to compare airborne and ground-based LIDAR for the purposes of quantifying erosion, and also integrated modern remote sensing tools with traditional soil science and archaeological evidence to reconstruct geomorphic processes and drivers in an island setting,” says Perroy.

Perroy has built on and expanded this type of research since his arrival at UH Hilo in 2013. He is principal investigator at the UH Hilo Spatial Data Analysis and Visualization Laboratory, a research unit applying geospatial tools to local environmental problems in Hawaiʻi and the Pacific region.

Professor Perroy’s geographic research activity in remote sensing has contributed greatly to local agriculture, coastal resource management, crisis management during natural disasters on Hawaiʻi Island, and to the battle against invasive species, notably contributing a much greater understanding of Rapid ʻŌhiʻa Death in Hawaiʻi’s forests. The work includes capturing images through remote sensing technology, processing that data, and creating 3-D maps and other visual media for greater scientific and public understanding.

The field part of the research also includes a strong engineering component, working with drones that carry attachments such as remote sensing equipment or chain saws, and developing a way to mount digital cameras on the undercarriage of helicopters for data collection.

From left, aeronautical scientist Roberto Rodriguez, geographer Ryan Perroy, and geography student Shawna Blackford assemble an attachment to a drone in 2020. The unmanned aerial vehicle above is named Kūkūau and has a small rotating chainsaw with a robotic gripper claw mounted beneath. It can cut and retrieve branches from an ʻōhiʻa canopy up to seven centimeters in diameter, saving researchers and forest managers from time-consuming and often challenging ground-based sample collection. (Photo: Courtesy of SDAV Lab/UH Hilo)

Here following are descriptions of several of Prof. Perroy’s research since arriving at UH Hilo, showing his development of geographic information systems (GIS) technology, remote sensing strategies, high resolution aerial imagery, 3-D mapping, and other leading-edge technologies to answer the needs of Hawaiʻi’s people and environment. A full catalog of his past and current projects can be viewed on the SDAV website.

Mapping agricultural land use in Hawaiʻi

Maps of Hawaiian islands with color-coded areas in agriculture.
A map from the study, Statewide Agricultural Land Use Baseline 2015, which provides a snapshot of information and maps on the locations of Hawaiʻi’s farms and ranches. Click to enlarge. (SDAV/UH Hilo)

In the first years after arriving at UH Hilo, Perroy was primary investigator on a study about agricultural land use in Hawaiʻi that provides information on the location of commercial agriculture activities statewide. The project used GIS technology and aerial imagery from several sources to digitally document the footprint of lands engaged in commercial scale agriculture statewide.

The Statewide Agricultural Land Use Baseline 2015 was done collaboratively between the Hawaiʻi Department of Agriculture and Perroy’s Spatial Data Analysis and Visualization Lab to update a 1980 state survey on the locations of Hawaiʻi’s farms and ranches.

The report provides a wide range of maps and graphics depicting the location of 15 crop categories with island-by-island summaries and regional descriptions of some of the factors that drive ongoing agricultural activity around the state. This baseline helps industry, government, and the local agricultural community in making decisions that affect agriculture land use in the state. The research team published a paper on their findings.

Finding invasive species

Bringing new technology to the fight against invasive plants species, Perroy and colleagues tested small unmanned aerial systems (sUAS) and their use for the early detection and management of invasive plants in Hawaiʻi’s forests. The research team published their findings in 2017.

The researchers set out on their field work looking for miconia (Miconia calvescens) plants, an aggressive invasive species, focusing on how overstory vegetation cover, imagery resolution, and camera look-angle impact aerial detection of individual miconia plants within the forest. Perroy’s co-researcher, UH Hilo aeronautical scientist Roberto Rodriguez, trained artificial intelligence software to recognize the miconia.

“While dense overstory canopy cover, limited flight times, and visual line of sight regulations present formidable obstacles for detecting miconia and other invasive plant species,” write the study’s authors, “we show that sUAS platforms carrying optical sensors can be an effective component of an integrated management plan within challenging subcanopy forest environments.”

Tracking lava flows

During the lava flows of 2014 and 2018 on Hawaiʻi Island, both of which impacted island communities, Perroy and his research team used drones equipped with cameras to collect high resolution stills later merged into aerial maps for use by Civil Defense emergency planners.

Perroy co-authored a paper about the 2014 work with Nicholas Turner, a geospacial analyst in the SDAV lab, and Ken Hon, then a UH Hilo geology professor and researcher who specializes in the study of active Hawaiian volcanoes.

During the 2018 flow in lower Puna, Civil Defense personnel were worried about pinpointing the exact locations of the advancing lava, so they contacted Perroy. “We can get that sort of overview, overhead shot, and relay that information very quickly to the incident commanders and fire responders,” Perroy says.

Large group of students and faculty gather for photo during survey work. Several hold drones and camera equipment.
UH Hilo Drone Team: Ryan Perroy, (back row, third from right) and students, researchers, and staff in the field during the lava flow of 2018. (Photo: Tracey Niimi)

The data provided to Civil Defense aided in a range of ways, such as helping residents to recoup losses. The same data also helped the team with other of its scientific endeavors.

  • Learn more: See Perroy’s presentations, “sUAS Operations Over Active Eruptions in Hawaiʻi,” Part I and Part II at the Geoscience and Remote Sensing Society’s YouTube channel.

Mapping Rapid ʻŌhiʻa Death

Professor Perroy’s work with aerial imagery has been instrumental in the fight against Rapid ʻŌhiʻa Death (ROD), a fungal disease decimating a keystone native tree in Hawaiian forests.

Perroy’s work on the problem uses high-resolution cameras and other sensors to improve early detection of ROD across forests, including areas where signs of the disease may not yet be visible to the naked eye. The imaging and correlated mapping gives forest managers precious time to respond to outbreaks, and gives scientists better information on how the disease spreads.

In 2019, Perroy won first place and a $70,000 prize in a competition co-sponsored by the National Park Service called The ʻŌhiʻa Challenge in recognition of his ROD work.

Another component to Perroy’s ROD research uses a drone equipped with a robotic gripper claw and chain saw, an engineering feat accomplished with the help of Assistant Professor Rodriguez (the aeronautical scientist who also worked on the miconia project) in collaboration with researchers at ETH Zürich, a public research university based in the city of Zürich, Switzerland, and R&R Machining/Welding in Hilo.

The remote controlled device, called Kūkūau (named after a type of crab), cuts branches from the canopy of suspect trees for laboratory analysis. This technique increases the chances of detecting the fungus and saves time and effort of crews sampling on the ground in often challenging environments.

Aerial map shows huge inundation of ROD in unfenced areas. The fenced area has only 1 infection point.
In the Kaʻū Forest Reserve, the researchers observed how Rapid ʻŌhiʻa Death can escalate very quickly. The magnitude of increased mortality is not nearly as large as within the fenced areas, where hooved animals are actively excluded. Click image to enlarge. (Image: SDAV StoryMap)

Further, additional studies on Rapid ʻŌhiʻa Death revealed significant differences in areas on Hawaiʻi Island with and without ungulates (hooved animals), suggesting that ungulate exclusion is an effective management tool to lessen the impacts of ROD in forested areas in Hawaiʻi. The group published their findings and recommendations in 2021.

Then in 2023, with the goal to widely share their findings about ungulates’ impact on the spread of ROD, the research team released a “story map,” an online visual medium that can help the general public understand complex and detail-rich scientific data. The story map shows the destructive role animals such as cattle and pigs can play in infecting ʻōhiʻa trees with the fatal fungus, Ceratocystis lukuohia, that causes ROD.

Perroy notes how striking the differences in ʻōhiʻa mortality are across forested areas with and without ungulates. “I wasn’t expecting those patterns to be so clear,” he says.

The data for the story map were produced from a collaborative study involving university, community, county, state and federal experts. Perroy credits Brian Tucker, a ROD data specialist at UH Mānoa’s Pacific Cooperative Studies Unit through the UH Research Corporation, with pushing the story map project forward to online publication.

“ROD continues to kill trees and negatively impact our native forests, and it’s important to make sure the public is aware of this ongoing issue,” says Perroy. “Publicly-accessible maps, like the ones produced as a result of this collaboration, are valuable for getting that message out and visualizing the differences measures like fencing and ungulate removal can have on forest health.”

Current research

Perroy’s research continues, each project answering the needs of island communities or the environment. Ongoing projects include surveys on the invasive plant species strawberry guava, shoreline change, and mapping the Puna ahupuaʻa (land division).

In the fall of 2024, Perroy worked on a project on Maui, dropping seed balls from a drone to help restore a recently burned area in Kula. He’s also working on the strawberry guava mapping and control, and species-specific carbon mapping for a National Science Foundation project. Graduate and undergraduate, as well as three UH Hilo alums are working with him on these projects.

Perroy also has a high-resolution digital documentation project underway of five coastal federal parks across the state of Hawaiʻi to assist with climate change adaptation planning and resilience modeling for identified natural resources. Co-principle investigator on the project is Seth Quintus, associate professor of anthropology at UH Mānoa. In fall of 2024, the researchers received a $1.15 million grant from the National Park Service to complete the study, “Inventory and Monitoring of Pacific Island Historic and Cultural Resources Impacted by Climate Change.”

Looking to the future: Diversity

When asked about future goals, Perroy says he hopes to one day be replaced by new faculty and researchers who are Native Hawaiian.

“For the goals, beyond continuing and expanding the work we’re doing, in the future it will be great to see local students, especially Hawaiian students, that have graduated from UH Hilo come back as faculty and researchers to help move things forward even more,” says Perroy.

“We see our graduates taking important roles in conservation and employed with a variety of state and local agencies, it will be wonderful to see some of those same folks eventually reflected in our faculty here at UH Hilo.”

By Susan Enright, a public information specialist for the Office of the Chancellor and editor of Keaohou and UH Hilo Stories. She received her bachelor of arts in English and certificate in women’s studies from UH Hilo.