IN JUNE 2020, A GIANT SAHARAN DUST STORM wafted across the Atlantic Ocean and invaded the southeastern U.S. and the Caribbean. For several days, this “Godzilla” of dust inflicted dangerous levels of air pollution on residents of the Florida Panhandle, Texas, Oklahoma and Puerto Rico.

To investigate how dust clouds affect human health, and to help prepare for future storms, public health researchers at the University of Puerto Rico Medical Sciences Campus have turned to an unlikely medical research tool: satellites.

Earth-observing satellites orbit the Earth at altitudes as high as 2,000 kilometers and record wide-ranging information about the planet’s atmosphere and conditions on land. In recent years, scientists have begun using data from these satellites to study respiratory diseases and forecast the spread of viruses. “Satellites are really opening up a whole new opportunity for exposure assessment,” says environmental health specialist Susan Anenberg at the George Washington University Milken Institute School of Public Health in Washington, D.C.

Traditionally researchers have depended on ground-based sensors to track air quality and environmental conditions. Yet even in the United States, such monitors are few and far between. “In D.C., we have just a handful of air pollution monitors for an entire city of several million people,” Anenberg says. “Satellite remote sensing offers the ability to view air quality all over the world from space. That can fill in the gaps between monitors on the ground and show what’s going on in many places that don’t have any monitors.”

In Puerto Rico, researchers used freely available satellite data from the National Aeronautics and Space Administration (NASA) to pinpoint when dust storms affected air quality on the island between 2015 and 2017. When the scientists checked the corresponding public health data, they found that the dust outbreaks were associated with increased mortality from respiratory conditions.

To help reduce the impact of future storms, the researchers used satellite technology to create an early warning system that can inform especially vulnerable people, such as those with asthma, that a dust storm is on its way. “The advantage of the satellite data is that it can show dust storms up to five days before they arrive,” says Pablo Méndez-Lázaro, associate professor at the University of Puerto Rico Medical Sciences Campus, who is leading that effort.

In September 2020, NASA announced that it awarded a project grant to Méndez-Lázaro to investigate how African dust storms might affect the severity of symptoms and mortality experienced by patients with COVID-19 in Puerto Rico, and the possible impact of environmental factors on the spread of the coronavirus. Researchers are now collecting information about the African dust particles in the air during the upcoming dust storm season, which they will compare to clinical data about respiratory disease and COVID-19 to determine whether virus symptoms may be exacerbated during African dust storm events. The researchers hope to have results by this summer.

Meanwhile, dust storms aren’t the only threat to human health that can be assessed from high in the sky. Although satellites’ remote sensing technology can’t directly detect human pathogens and disease, it can be used to identify combinations of environmental conditions—including temperature, rainfall, soil moisture and vegetation—that may help parasites, bacteria and viruses proliferate.

“Satellites bring information that we’re not getting from our human case surveillance,” says Mike Wimberly, a professor in the Department of Geography and Environmental Sustainability at the University of Oklahoma. Wimberly helped develop the Arbovirus Monitoring and Prediction (ArboMAP) system, which uses satellite data to produce weekly, county-level forecasts of West Nile virus risk in South Dakota—the U.S. state with the highest incidence of that virus.

West Nile virus remains a persistent public health hazard in many parts of the United States. Knowing where and when outbreaks might occur can help physicians and health care systems be prepared, Wimberly says. Normally surveillance involves trapping mosquitos in a particular region and testing them for the virus. But there’s no way to cover large areas using that approach. “Looking for the virus that way is like looking for a needle in a haystack, but you only get to poke some parts of the haystack,” Wimberly says.

But satellites can detect multiple environmental variables that affect the life cycle of a mosquito. That data, in turn, can help researchers know when large areas may have the right conditions for an onslaught of virus-carrying mosquitoes.

In experiments from 2016 through 2019 in South Dakota, ArboMAP, which combines on-the-ground mosquito surveillance and satellite data, was able to predict West Nile virus outbreaks one to two months before they were found on the ground. “We can pretty reliably tell by the end of June whether it’s going to be a low-incidence year like 2011 or whether there’ll be a big outbreak like in 2012,” Wimberly says. ArboMAP is also being implemented in Louisiana, Michigan and Oklahoma.

The value of satellite data to the medical community will only increase in the next couple of years, when NASA launches a new generation of instruments designed specifically for public health research. The forthcoming Multi-Angle Imager for Aerosols (MAIA) satellite-mounted instrument, for example, will be able to spot even tinier particles in the air, granting researchers an enhanced ability to study respiratory and cardiovascular health. “The new satellites are going to give us even more temporal and spatial resolution and advance our ability to address the public health problems that people are experiencing around the world,” Anenberg says.