NASA’s new EMIT instrument has successfully demonstrated the ability to perform analysis aiding in detecting wastewater leaks on Earth from an orbital vantage point aboard the International Space Station.
The detections occurred in San Diego County, California, at the mouth of the Tijuana River, serving as proof of concept for the new environmental monitoring technique. The new ISS spectroscopic monitor can direct efforts and offer a means of filling in holes in direct sampling efforts.
Introducing ‘EMIT’
NASA’s Jet Propulsion Laboratory (JPL) developed EMIT, the Earth Surface Mineral Dust Source Investigation, which was launched in 2022. JPL has been advancing imaging spectroscopy technology since the 1980s. Today, the technique supports various terrestrial applications, including firefighting, agriculture, forest health, and atmospheric studies of distant exoplanets.
Although EMIT was originally designed to map mineral dust in arid regions, it can now analyze water pollution—an application its creators did not anticipate.
“The fact that EMIT’s findings over the coast are consistent with measurements in the field is compelling to water scientists,” said lead author Eva Scrivner, a doctoral student at the University of Connecticut. “It’s really exciting.”
Water Pollution
Located just south of Imperial Beach, the mouth of the Tijuana River is a major source of pollution, with millions of gallons of sewage, both treated and untreated, flowing into the river annually. The resulting contamination carries bacteria that pose health risks to humans and animals. The polluted water flows through densely populated areas and a national reserve on the U.S.-Mexico border. Reported health impacts include illness among U.S. Navy trainees, civilian beachgoers, and negative effects on marine ecosystems, fisheries, and wildlife.
While EMIT’s use in this context is novel, satellite instruments have previously been employed to monitor oceanic conditions. For example, color changes visible from space, such as green and red hues, can indicate the presence of phytoplankton or harmful algae blooms. However, detecting pollutants and bacteria has remained more challenging.
A New Pollution Monitoring Tool
EMIT’s spectroscopic analysis works by imaging sunlight reflected from Earth and separating it into hundreds of visible and infrared color bands. Each molecule has a distinct spectral fingerprint, allowing scientists to analyze imagery pixel by pixel and identify substances in the water. In this case, EMIT detected phycocyanin, a pigment commonly associated with harmful cyanobacteria. Ground-based instruments later confirmed the same spectral signature, validating the instrument’s effectiveness.
Public water quality information is based on localized sampling and direct testing. Researchers believe that EMIT could become an invaluable tool in guiding those efforts.
“From orbit, you are able to look down and see that a wastewater plume is extending into places you haven’t sampled,” said co-author Christine Lee, a scientist at JPL in Southern California. “It’s like a diagnostic at the doctor’s office that tells you, ‘Hey, let’s take a closer look at this.’”
Scrivner added that the findings “show a ‘smoking gun’ of sorts for wastewater in the Tijuana River plume.” She believes EMIT can improve monitoring efficiency in regions where on-site sampling is logistically difficult and prohibitively expensive, particularly in high-pollution zones.
The paper “Hyperspectral Characterization of Wastewater in the Tijuana River Estuary Using Laboratory, Field, and EMIT Satellite Spectroscopy” appeared on May 8, 2025, in Science Direct.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.