NASA Technology May Help Spot Coastal Sewage from Space

On hot days, a refreshing swim seems perfect, but how do you know the water is clean enough? In the future, satellite images might help answer that question by detecting sewage in coastal areas, thanks to a surprising discovery about how wastewater interacts with light.

A team of researchers found that sewage-contaminated water absorbs specific wavelengths of orange light. This finding, published in Science of the Total Environment (June 15 issue), is now helping scientists identify sewage from space.

Traditionally, water quality is checked by testing a few locations for bacteria, which means many contaminated spots could go unnoticed. Space-based imagery, already used to track wildfires, algal blooms, and melting snow, could offer a broader view. However, spotting sewage has been tricky since bacteria themselves don’t reflect or absorb much visible light.

That’s where oceanographer Eva Scrivner’s research comes in. While at San Diego State University, Scrivner collected samples from a local wastewater treatment facility (yes, involving literal cups of sewage). She then used a tungsten bulb and a spectrometer to observe how the samples responded to light. The more bacteria the water had, the more orange light it absorbed.

The team then compared these results with satellite images taken by a NASA device called EMIT, which is installed on the International Space Station. These images of sewage flowing from the Tijuana River into Imperial Beach, California, showed the same orange-light drop-off, effectively creating a “color scale” for sewage levels.

Although EMIT can’t consistently view the same U.S. locations due to its orbit path, a future NASA mission called GLIMR will focus specifically on U.S. coasts and the Gulf of Mexico. It may also be able to detect this orange-light sewage signature.

Some scientists, like Brazil-based geospatial researcher Daniel Maciel, note that this method must be tested in other regions, especially since the orange-light change could also come from naturally occurring bacteria like cyanobacteria, which aren’t necessarily linked to pollution.

Still, this approach offers promise. Instead of guessing where to take water samples, scientists could use space-based snapshots to better identify contaminated areas. And for swimmers, that could mean safer decisions and fewer sick days after the beach.

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Source: Sofia Caetano Avritzer, ScienceNews