Satellites Help Keep Communities Safe from Toxic Algal Blooms

Utah Lake had a secret.

In 2017, just days before the Fourth of July weekend, a harmful algal bloom was growing in the warm waters of one of Utah’s most popular summer holiday destinations. This hidden algal bloom had the potential to kill pets and make visitors ill—and nobody knew it was there. That is, until satellite imaging alerted officials to the dangers hidden beneath the water.

Satellite images can help warn decisionmakers of harmful algal blooms, saving communities all over the United States time, money, and trips to the hospital.

Resources for the Future (RFF) received a five-year, $3.5-million grant that funds RFF’s VALUABLES Consortium, a cooperative agreement between RFF and NASA that measures the benefits of satellite technology in communities. Through their work with VALUABLES, researchers have found cases in which satellites have helped people and communities make better decisions.

A very basic example would be like watching the weather report to decide whether you’ll take an umbrella to work the next day, explains Yusuke Kuwayama, an RFF fellow and director of the VALUABLES Consortium. Without that data, you might leave the house unprepared and get drenched while walking home. Or you might grab an umbrella and have to lug it around all day for no reason because it never rains, he adds.

With an aquatic public health hazard such as a harmful algal bloom, it’s the same idea of using informed predictions to make better decisions—but the stakes are higher.

Harmful algal blooms, or HABs, can occur in both fresh- and saltwater environments and cause problems worldwide by sickening humans, livestock, and pets; closing fisheries; and interrupting recreational water activities. Exposure to HABs can cause skin irritations, gastrointestinal issues, and even neurological problems in humans.

“Virtually every state has water bodies that have a problem with freshwater harmful algal blooms, and there are marine harmful algal blooms on every coast,” says Richard Stumpf, an oceanographer at the National Oceanic and Atmospheric Administration (NOAA).

Unfortunately, because the United States has so many bodies of water, monitoring all of its lakes, rivers, and streams for HABs through sample testing in a lab isn’t practical. In addition, sufficient monitoring in some areas requires repeated sampling in the same water body, which can be difficult or infeasible. And just because toxins don’t show up when people test the water doesn’t mean that toxins won’t appear one day, or even one hour, later. An initial lack of toxins during testing can create a false sense of security.

That’s where satellite technology can make a difference. “I’d love to send my monitoring team to all these lakes, but we have limited resources,” says Kate Fickas, an environmental scientist and program coordinator at the Utah Department of Environmental Quality. “Satellites help tell this significant story about how things are changing.”

Satellites Can Keep Us Safer, Healthier

Social scientists can look at a number of economic factors to calculate the financial impact of satellites. Of course, there’s an economic impact to avoiding health issues in humans and other animals, but there’s also a larger ripple effect that spreads throughout an entire community, says Sherry Larkin, the associate dean for research at the University of Florida and associate director at the Florida Agricultural Experiment Station.

Coastal residences, hotels, motels, and any activities that are based on clean, clear water are those most likely to experience an economic downturn. The fishing industry also takes a hit when HABs surprise fishers with unsafe fish, oysters, clams, and other seafood. In these cases, the early warnings that satellites make possible can help communities prepare for and recover from the economic impact of HABs.

Other problems can’t necessarily be quantified monetarily, but they still affect a community. For example, there’s an emotional toll on people, says Larkin. The stress of HABs impacts a person’s sense of place, their cultural identity, and their ability to access and experience a body of water. Furthermore, Larkin notes how upsetting it can be for visitors or locals to see dead fish and manatees or other affected marine life.

And, in an ironic twist, the toxin-producing organisms that populate freshwater HABs turn out to be a crucial part of our evolution as a human species. “We evolved from cyanobacteria. They’re the reason we have oxygen in the air,” Fickas says. “It just so happens they release toxins.”

Many US scientists rely on data from the satellites called Sentinel-3A and Sentinel-3B, which are owned by the European Union and were sent up in 2016 and 2018, respectively. “The data is free, and it’s collected routinely,” says Stumpf. “The best satellites for working with the algal blooms are the European ones, because they have the right set of bands and spatial resolutions,” which are critical for pinpointing outbreaks of HABs.

These satellites capture images of HABs by measuring the wavelengths of light, or “bands,” that bounce off the bacteria. Each species of bacteria contains a specific pigment such as chlorophyll a and phycocyanin. (Remember, chlorophyll is the stuff in plants that lets them make food through photosynthesis.) Together, these pigments absorb blue, red, and yellow light, so what bounces back to the satellite is a strong green light.

The satellites work like an advanced camera, Stumpf says. Instead of just measuring red, green, and blue, like your average digital camera, the satellites can detect many more wavelengths of light. Scientists can tell whether there’s bacteria in the water by looking at the light spectrum—which represents differences in wavelengths reflected and absorbed by the pigments— and searching for “wiggles.”

For example, if you looked at the spectrum of muddy water and plotted it on a graph, the results would be very flat because mud reflects all light pretty much equally. But if you plotted a graph with some chlorophyll a in it, the graph would suddenly take a big dip where chlorophyll a appears, which is the “wiggle.”

Scientists use that wiggle to determine the severity of a HAB. And in a lot of cases, using satellite data is far better than visiting a lake and taking samples of the water directly to search for harmful bacteria. Satellite imaging is so sensitive that it can detect an algal bloom before the bloom becomes visible to the naked eye. “Satellites can detect concentrations where you wouldn’t think there are blooms in the water,” Stumpf says.

While humans have to take breaks, satellites can function 24/7. The satellites Sentinel-3A and Sentinel3B are each able to cover the United States at least three days a week, providing six- and sometimes seven-day coverage, Stumpf adds. These passes happen as part of their individual 100-minute orbits.

Of course, while science is quickly adapting to realworld problems like HABs, algal bloom detection is still far from being perfectly efficient. Satellites have the difficult job of balancing coverage with resolution. If a lake is bigger than half a mile, satellites can fairly easily scan it for HABs, Keith says, but anything smaller is a challenge. Scientists stick to scanning bigger objects because it takes too long to scan every body of water. Right now, the satellites Sentinel3A and Sentinel-3B can scan an area as big as 15 FIFA soccer fields put together, but smaller ponds are difficult to track, because they require higher-spatial-resolution scanners. It’s like forgetting your glasses if you’re nearsighted and trying to look at something far away: satellites can see large objects, but the smaller ones are difficult to detect in detail.

“There are technological tradeoffs,” says Blake Schaeffer, a research scientist at EPA. Measuring larger lakes takes a few days, whereas trying to look at both large and small bodies of water could take up to a month. “The satellite can’t cover as much of the Earth,” Schaeffer adds. “People want to know what’s happening right now—they don’t want to wait.”

How Do Researchers Handle All That Data?

After satellites have taken their images, it’s up to scientists to look at the data and parse the relevant information. Fickas wrote extensive computer code to pull data for the entire state of Utah, showing where these harmful cyanobacteria are located, along with their severity by cell count.

“We can use views from space to protect the public as much as possible,” she says.

Scanning the United States for HABs is a large-scale collaborative effort among NASA, NOAA, and the United States Geological Survey. NASA has the capacity to run and store this imagery, which is a huge amount of data, measured at the scale of terabytes per day. (For reference, the entire text content of the Library of Congress takes up only 20 terabytes.) Stumpf says they’ve also used cloud computing for running lots of historical data, but the national effort is transferred over to NASA because of its larger processing capacity.

Luckily, state environmental protection and natural resources departments don’t need a supercomputer to process their data, because they’re focused on specific areas, rather than the entire country. In fact, Stumpf uses a 64-bit processor Linux machine, which requires only a few hours to process images. It takes about 20 minutes to process an area the size of the state of Florida, and it’s a system that can scale up easily with enough processing power. Stumpf usually runs a half-dozen or more at a time every day—tens of gigabytes per day for the equivalent of one to two states and hundreds of gigabytes per day, nationally. At the national scale, the data is equivalent to the amount of space taken up by 100 movies.

“Instead of having just one computer, you have 100 or 200 computers, and each one has maybe 16 processors, so you can simultaneously run lots of images,” Stumpf says. It’s possible to use multiple satellites, each with different types of scanners, but that’s a huge technological challenge, which is why researchers are sticking to their current methods—at least for now. Future plans, however, do include blending satellite data to create a more detailed picture of HABs.