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Proof-of-concept results from the mouth of the Tijuana River in San Diego County show how an instrument called EMIT could aid wastewater detection.<\/em> An instrument built at NASA\u2019s Jet Propulsion Laboratory \u00a0to map minerals on Earth is now revealing clues about water quality. A recent study found that EMIT (Earth Surface Mineral Dust Source Investigation) was able to identify signs of sewage in the water at a Southern California beach.<\/p>\n The authors of the study examined a large wastewater plume at the mouth of the Tijuana River, south of Imperial Beach near San Diego. Every year, millions of gallons of treated and untreated sewage enter the river, which carries pollutants through communities and a national reserve on the U.S.-Mexico border before emptying into the Pacific Ocean. Contaminated coastal waters have been known to impact human health \u2014 from beachgoers to U.S. Navy trainees \u2014 and harm marine ecosystems, fisheries, and wildlife.<\/p>\n For decades scientists have tracked water quality issues like harmful algal blooms using satellite instruments that analyze ocean color. Shades that range from vibrant red to bright green can reveal the presence of algae and phytoplankton. But other pollutants and harmful bacteria are more difficult to monitor because they\u2019re harder to distinguish with traditional satellite sensors.<\/p>\n That\u2019s where EMIT comes in. NASA\u2019s hyperspectral instrument orbits Earth aboard the International Space Station, observing sunlight reflecting off the planet below. Its advanced optical components split the visible and infrared wavelengths into hundreds of color bands. By analyzing each satellite scene pixel by pixel at finer spatial resolution, scientists can discern what molecules are present based on their unique spectral \u201cfingerprint.\u201d<\/p>\n Scientists compared EMIT\u2019s observations of the Tijuana River plume with water samples they tested on the ground. Both EMIT and the ground-based instruments detected a spectral fingerprint pointing to phycocyanin, a pigment in cyanobacteria, an organism that can sicken humans and animals that ingest or inhale it.<\/p>\n Many beachgoers are already familiar with online water-quality dashboards, which often rely on samples collected in the field, said Christine Lee, a scientist at JPL in Southern California and a coauthor of the study. She noted the potential for EMIT to complement these efforts.<\/p>\n \u201cFrom orbit you are able to look down and see that a wastewater plume is extending into places you haven\u2019t sampled,\u201d Lee said. \u201cIt\u2019s like a diagnostic at the doctor\u2019s office that tells you, \u2018Hey, let\u2019s take a closer look at this.\u2019\u201d<\/p>\n Lead author Eva Scrivner, a doctoral student at the University of Connecticut, said that the findings \u201cshow a \u2018smoking gun\u2019 of sorts for wastewater in the Tijuana River plume.\u201d Scrivner, who led the study while at San Diego State University, added that EMIT could be useful for filling data gaps around intensely polluted sites where traditional water sampling takes a lot of time and money.<\/p>\n The technology behind EMIT is called imaging spectroscopy, which was pioneered at JPL in the 1980s. Imaging spectrometers developed at JPL over the decades have been used to support areas ranging from agriculture to forest health and firefighting.<\/p>\n When EMIT was launched in July 2022, it was solely aimed at mapping minerals and dust in Earth\u2019s desert regions. That same sensitivity enabled it to spot the phycocyanin pigments off the California coast.<\/p>\n Scrivner hadn\u2019t anticipated that an instrument initially devoted to exploring land could reveal insights about water. \u201cThe fact that EMIT\u2019s findings over the coast are consistent with measurements in the field is compelling to water scientists,\u201d she said. \u201cIt\u2019s really exciting.\u201d<\/p>\n To learn more about EMIT, visit:<\/p>\n<\/p>\n Jane J. Lee \/ Andrew Wang Written by Sally Younger<\/p>\n 2025-078<\/p>\n<\/div>\n
Jet Propulsion Laboratory, Pasadena, Calif.
626-379-6874 \/ 818-354-0307
jane.j.lee@jpl.nasa.gov \/ andrew.wang@jpl.nasa.gov\u00a0<\/p>\n