Photo: NOAAA NASA instrument originally designed to study mineral dust is showing promise as a tool for tracking wastewater in coastal waters, according to new proof-of-concept results from San Diego County.
The Earth Surface Mineral Dust Source Investigation (EMIT), developed by NASA’s Jet Propulsion Laboratory and mounted on the International Space Station, has successfully detected signs of sewage in a large pollution plume at the mouth of the Tijuana River. The river, which regularly carries millions of gallons of treated and untreated wastewater through border communities into the Pacific Ocean, has long been a source of public health and environmental concern.
In the new study, researchers found that EMIT’s hyperspectral imaging capabilities were able to identify phycocyanin—a pigment produced by cyanobacteria—as a marker of wastewater. These findings matched results from spectroradiometer analysis of field samples taken near Imperial Beach. Cyanobacteria can be harmful to both humans and marine animals and often accompany sewage discharges.
The results signal a potential breakthrough in how agencies might monitor coastal water quality in high-contamination zones.
Traditional satellites track algal blooms using visible ocean color, but many other pollutants—including bacteria—are difficult to detect with conventional methods. EMIT, by contrast, parses light into hundreds of spectral bands, allowing scientists to identify molecular fingerprints from orbit.
“From orbit you are able to look down and see that a wastewater plume is extending into places you haven’t sampled,” said JPL scientist Christine Lee, a coauthor on the study. “It’s like a diagnostic at the doctor’s office that tells you, ‘Hey, let’s take a closer look at this.’”
Lead author Eva Scrivner, a doctoral researcher at the University of Connecticut who led the work while at San Diego State University, said EMIT helped reveal a “smoking gun” for wastewater in the Tijuana River plume. She added that the tool could be particularly useful in areas where on-the-ground sampling is costly or inconsistent.
Originally launched in July 2022 to map desert dust, EMIT’s sensitivity has since enabled new applications in agriculture, firefighting, and now coastal water monitoring. The study’s authors say the technology could soon complement field-based water quality efforts by helping target where and when sampling is needed most.
For utilities, regulators, and public health agencies grappling with cross-border pollution, the results offer a high-resolution view into where wastewater is moving and what it leaves behind.
