Wildfire season isn’t just a season, it’s a year-round concern for communities around the world. Exacerbated by climate change, fires are growing faster and more destructive. Photonics could help reduce the risks to first responders and communities by detecting smoke in the atmosphere long before we ever see flames.
The 2025 Los Angeles, California, wildfires, which began in January, racked up property losses and other damage costs totaling more than $164 billion, according to one report. Though alone significant, the economic damages were compounded by another hazard that comes with wildfire: the smoke. According to the World Health Organization, wildfire smoke contains several hazardous air pollutants. These include fine air particles less than 2.5 µm in diameter (PM2.5), as well as nitrogen dioxide, ozone, aromatic hydrocarbons, and lead, all of which increase greenhouse gases in the atmosphere and damage human health.
Modern wildfire detection methods include the use of drones, planes, satellites, and, of course, fire lookouts. These methods are good, but they each have a downside. Drones have limited range and battery life, satellites may only pass over a location once every few hours leaving large gaps in coverage, planes are expensive to operate and maintain, and fire lookouts, while providing consistent area monitoring, cannot see past natural obstacles like hills or ridges.
At the University of Arizona Polarization Lab, part of the Wyant College of Optical Sciences, Clarissa M. DeLeon, Yukun Long, and lab Principal Investigator Meredith Kupinski are working on a solution to wildfire early warning. They hope that their imaging system, dubbed the ultraviolet linear stokes imaging polarimeter (ULTRASIP), might provide additional wildfire early-warning capabilities to first responders.
When DeLeon joined Kupinski’s lab in 2020, wildfires in North America were raging. Fires in California, Canada, Montana, and Arizona contributed to diminished air quality throughout much of the West, but eastern regions weren’t immune from the impact. The fires, for example, increased the presence of PM2.5 and other harmful pollutants. Air quality warnings were issued, and people were told to monitor the Air Quality Index (AQI) in case conditions should worsen.
On 16 September 2020, in Mammoth, California, near Yosemite National Park, an AQI of 587.9 was recorded, a level indicating extreme hazard to human health. Public health experts understood that people throughout the region were at risk of suffering from long-term exposure to smoke from the fires. A study from the Yale University School of Public Health, found that prolonged exposure to PM2.5 was associated with increased deaths from cardiovascular, endocrine, and digestive diseases.
Imaging System: ULTRASIP sensor at the University of Arizona. Photo credit: Clarissa M. DeLeon
DeLeon at the time was working on ultraviolet polarimetry for thin-cloud detection. She began to think that polarimetry might offer a new tool for wildfire science. Specifically, she and Kupinski pondered the possibilities of using ground-based polarimetry in an imaging system that would detect and pinpoint the location of wildfire smoke.
And now, “ULTRASIP is that ground-based instrument, designed to track the Babinet neutral point typically located 10-30 degrees above the sun, depending on observation wavelength, sun position, and atmospheric turbidity,” DeLeon says.
She explains that there are four polarization-neutral points in the sky, each at a specific distance from the sun. In addition to the Babinet, they are the Brewster, Arago, and Huygens neutral points—areas of the sky where the polarization effect is neutral, and aerosols can be most easily detected, such as those from wildfire smoke.
To investigate further how they might leverage neutral point phenomena, DeLeon and her team focused on the Babinet. Because it is located above the sun, the Babinet can be observed from dawn to dusk, making it ideal for tracking shifts in location as caused by specific types of particles from smoke or other aerosols. Using ULTRASIP’s sensors, they hope to establish a database of Babinet location displacements, information that might quickly identify aerosols in the atmosphere, including those emanating from wildfire smoke.
The team plans to field test ULTRASIP’s wildfire detection capabilities in the coming months. Their field deployments will allow for further data analysis and monitoring techniques to better understand the relationship between smoke and neutral point location. If their hypothesis bears true that polarimetry data can be used to detect wildfires via the particulate matter, those responsible for fighting fires and saving lives and property may have a new tool at their disposal.
“We can potentially detect the smoke without directly imaging it. Since the polarization signature of the sky is interconnected, even smoke outside of the field of view of the instrument could be detected through changes in the neutral-point position,” says DeLeon.
With a network of ULTRASIP instruments to supplement existing wildfire detection methods, DeLeon and her colleagues envision significantly enhanced wildfire detection, including wider area coverage and faster response times to new fires. Most importantly, their work with light might one day provide earlier wildfire warning that saves lives.
Jakab Terpstra is a digital marketing coordinator at SPIE.
