Robert Stewart: Mapping risk, advancing human security

As a teenager in Wartburg, Tennessee, Robert Stewart's bedroom reflected two defining interests: On one wall, he had pinned hand-drawn maps of the scarred hills and winding streams left behind by the nearby strip mines he explored in his free time. Below the maps, his desk held a beige Commodore VIC-20 - an expensive purchase his father had made, convinced that computers would be an important part of peoples' lives in the future, even if neither of them fully understood the technology at the time.

Between those maps and that computer sat a future the Department of Energy' s Oak Ridge National Laboratory scientist. Today, Stewart leads the Human Dynamics section in the lab's Geospatial Science and Engineering Division, where his work helps translate complex data into decisions that affect people, places and security.

But even as a kid growing up in the shadow of "the plants"-Y-12, X-10, and K-25, Stewart understood that something world-defining was happening just down the road, and he wanted to be part of it. He was a motivated student, teaching himself to code and eventually teaching fellow middle schoolers in a repurposed side room of his school, where no instructors were yet qualified to teach programming. He would not describe himself as a prodigy, but he had the patience and curiosity to sit with difficult material until it stuck.

"If you are willing to work patiently for it, you understand things more deeply and remember them much better when you really need them," Stewart said. "It gets in your DNA that way."

Stewart went on to study mathematics and statistics at the University of Tennessee and landed his first ORNL undergraduate internship in the Environmental Sciences Division.

"It seemed unbelievable that I could be there," he said. "I played a very small role on a team studying the effects of acid rain on trees in the Smokies."

He fondly recalls hiking in the Smokies with a CO₂ monitor strapped to his back, measuring off-gassing from leaves to help assess how remediation strategies for acid rain effects were progressing.

"I felt immediately like I was part of something bigger, and I knew I had to get back as soon as possible," Stewart said.

An opportunity for big science and big impact

As his education progressed, Stewart began building the mix of mathematics, statistics and computing expertise that would shape much of his career. After earning a master's degree in mathematics from UT, he returned to ORNL through an opportunity in the Environmental Sciences Division.

At the time, environmental restoration programs struggled to translate tabular regulatory limits into site level decision making which was inherently spatial, and Stewart was asked whether geostatistics could help.

His boss gave him $20,000 in funding and a problem to solve: How might you map and link environmental pollution, human exposure, and spatial decision uncertainty to improve remedial decisions?

"He asked me to compile something on it," Stewart said. "I learned later that he meant compile a literature review, but I was so naïve that I thought he meant compile code. So I did both, and I developed a software tool that mapped and integrated spatial modeling and decision frameworks under uncertainty."

The software tool became SADA- the Spatial Analysis and Decision Assistance software package. Over the next 15 years, SADA was funded by multiple federal agencies, used in training across the United States and abroad, and helped advance regulatory approaches for spatial decision-making under uncertainty.

"We'd hear from people all over the world, often in places with far fewer resources, who were using SADA to make decisions they simply couldn't make before," he recalled. "That was the most important thing to me, to feel I had made a real impact somewhere."

As a result of his work on SADA, Stewart was asked to support the Nuclear Regulatory Commission in adopting geostatistical methods into cleanup guidance - a lasting contribution to how nuclear site remediation is approached.

"At the time, it felt unbelievable to be helping to define a guidance approach that didn't really exist anywhere in the world," Stewart said. "We were always asking questions like, 'Would you build your kids' playground there?' That kind of thinking guided how I approached risk and decision-making."

From environmental cleanup to human security

By the late 2000s, Stewart felt he had pushed his contributions to environmental restoration as far as he could, and he was ready for a change. During this time, he met Dr. Budhu Bhaduri - now the lab's chief data officer - and found him "simply compelling."

Stewart joined Bhaduri's Geospatial Information Science and Technology Group in 2009, where he advanced a blend of spatial modeling, statistics, AI, and computing to address human security challenges within operational environments. As team leader, Stewart grew a small Geographic Data Science team of 5 into two large groups (GeoAI, Remote Sensing) that would anchor a new Geographic Data Science Section.

In 2019, Stewart and colleagues were invited to the Pentagon to hear firsthand how their work had been used. A letter of appreciation they received, personalized to each researcher's contribution, left a deep impression.

"It said that the mathematics our team built had resulted in saving countless lives," Stewart said. "They told us they weren't allowed to use that phrase lightly. The wording went through a formal review process by the Pentagon before it was written. Hearing those stories from the people using these systems in the field was one of the most impactful and emotional moments of my career."

From scientist to leader

Stewart is both humble and deeply reflective about his time at ORNL and the lasting impact of his work.

"When the number of years until retirement drops into single digits, you start thinking differently," he said. "For me, that means focusing on service and making sure the people who come after me have what they need to succeed."

Inside the lab, Stewart co-chairs the Distinguished Staff Fellowships Committee, which helps recruit some of the nation's most promising early-career scientists. He helps shape the lab plan on decision science and is excited about advancing his geospatial data center concept, which is now becoming part of a broader initiative to build a lab-wide ecosystem strategy for data.

Outside ORNL, Stewart holds leadership roles in several professional organizations, including IEEE's Computational Intelligence Society, the American Association of Geographers and the GIS Certification Institute. He has also served as an AAAS representative, an OECD delegate in nuclear decommissioning, and a contributor to editorial boards and advisory panels.

Stewart's life outside the lab has also helped shape his perspective. For more than 25 years, he has played live music with current and former ORNL colleagues, including in the Shelter Road Band. He says music has helped him maintain balance and stay energized for his scientific work.

"Having a great hobby like music has been very important in helping me maintain work-life balance," Stewart said. "I am better at my day job when I'm playing music at night."

Reflecting on his time at ORNL, Stewart emphasizes the pivotal role that his own sense of awe about the lab has had on his life and work.

"I'd like people to come in with a sense of awe and respect for what this place is and has been. If I'd never shown up, ORNL would have been fine," he said. "But because I did, I can point to the places where there's a little fingerprint of my effort. That's what I want for the people coming in now, to leave their own fingerprints on a national institution that has impacted the world since 1945 and is still helping define the future today."

UT-Battelle manages ORNL for the Department of Energy's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science. - Galen Fader