Li enhances NASA instrument through algorithm adaptation

Sulphur dioxide (SO2) is a government-regulated gas that can diminish visibility and form acid rain and aerosols in the atmosphere. NASA, which uses the Aura satellite to measure atmospheric gases globally, keeps track of this pollutant using the Ozone Monitoring Instrument (OMI).

NASA recently selected ESSIC’s Dr. Can Li, an Assistant Research Scientist, to award its Exceptional Public Achievement Medal for his work in improving the instrument. Li uses OMI to measure the radiance of wavelengths, particularly ultraviolet rays. Using this data, he can determine the amount of SO2 in the atmosphere.

Originally from China, Li earned his undergraduate degree in chemistry and then switched his convetration to environmental science.

“Essentially, it’s chemistry. It’s just lab work,” said Li about his original career path. “I figured I wanted to do something with more practical applications.”

He completed his doctorate degree in the atmospheric and oceanic science department at the University of Maryland in 2008, subsequently joining ESSIC post-graduation.

Li has been working with the OMI group for satellite retrieval since 2012, monitoring SO2 levels and fluctuations around the world.

SO2 is caused by pollutants, such as power plants, and by volcanic eruptions. A government-regulated gas, it is reactive and can form acid rain or aerosols, according to Li.

In the case of volcanic eruptions, SO2 can be used to track ash, which is hazardous to aviation safety in that it can clog a plane’s engines.

“Particularly for the OMI group, I think what you do can actually have an impact on others,” Li said, citing that many groups are interested in using the data and buying similar instruments.

The new technique for data retrieval, called principal component analysis, was originally introduced by Dr. Joanna Joiner, the OMI team leader. She had used the technique to observe florescence in plants, and thought to apply it to atmospheric gases.

Li modified the details and adapted the technique to the OMI instrument within months, allowing scientists to detect much smaller point sources of pollution than before. Data from the Aura satellite, which was launched in 2004, is now more precise and clear, according to Joiner.

“Really, after ten years in space, to make such an improvement in a satellite product is very rare,” said Joiner.

The technique is also easily applicable to other instruments and gases. Li recently adapted it to Ozone Mapping and Profiler Suite, NASA’s instrument that measures the ozone using ultraviolet light, as well as to the gas formaldehyde.