New NASA satellite to unravel mysteries of clouds, aerosols

The same properties of light and optics that make the sky blue and cause rainbows can help scientists unlock the mysteries of certain cloud formation and the effects of tiny particles in our air.

NASA’s upcoming PACE mission will provide important insights into airborne particles of sea salt, smog, man-made pollutants and dust—collectively known as aerosols—by observing how they interact with light. With PACE data, scientists will provide better answers to key questions such as how aerosols affect cloud formation or how ice clouds and liquid clouds differ. Understanding the nature of airborne particles and clouds is critical to understanding how climate and air quality are changing.

Two instruments on NASA’s upcoming PACE mission will look at aerosols and clouds — the Plankton, Aerosol, Cloud, Ocean Ecosystem satellites A and C. After launching in early 2024, the PACE mission will scan the Earth and collect data on the chemical composition, movement and interaction of aerosols and clouds using two sophisticated polarimeters that measure light properties.

The properties of light visible to our eyes, such as color. Other properties that scientists call polarization are invisible to the human eye.

„Polarization is something we don’t intuitively see because our eyes don’t see it,” said Kirk Noblespies, the polarizer lead for the PACE mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. „If you look at the world with eyes that can see polarizers, like our sensors, you’ll see rainbows everywhere.”

The light leaving the Sun moves in different directions like a wave — it’s called unpolarized light, said Brian Cairns, PACE’s associate project scientist. When interacting with something like a cloud or aerosol particle, the light oscillates more in one direction than the other: this is now polarized light. This peculiarity of light behavior will help scientists learn more about the properties and interactions of aerosols and water droplets in the sky.

Polarimeters measure the angle at which light is polarized, which reveals the specific properties of what the light bounces off. With these instruments, scientists can piece together the size, composition, abundance, and other properties of particles in the atmosphere.

The two polarimeters on PACE—HARP2 and SPEXone—make an ideal pair because of the complementary differences in what they measure. HARP2, built at the University of Maryland in Baltimore County, will observe four wavelengths of light from 60 different angles. SPEXone, built at the Netherlands Space Research Organization (SRON) and Airbus Netherlands BV, uses five angles to peer down on a narrow swath, but sees light at hyperspectral resolution—the full range of colors in the rainbow. Together, the polarimeters will provide a picture of Earth’s atmosphere in unprecedented detail.

Scientists have been observing aerosols from space for decades, although the community has not had polarization data for a decade, noted Otto Hasekamp, ​​senior scientist at SRON. PACE will provide polar data from multiple nodes and due to technological advances in instruments, the data will be of better quality than ever before.

„It’s exciting to see the culmination of all the hard work on instrument models and prototypes,” said Jeroen Rytjens, instrument scientist at SRON, „and finally see it culminate in a real satellite.”

After PACE launches in early 2024, the satellite will scan the Earth every two days, collecting vast amounts of data on the chemical composition, movement and interaction of aerosols and clouds.

„We want to measure the properties of aerosols because aerosols affect climate,” Hasekamp said. They reflect light back into space and can also absorb it, which plays a role in how much of the Sun’s energy reaches the Earth’s surface. Aerosols affect cloud formation and properties, but the details of these relationships are not fully understood by scientists. The data that PACE collects will help clarify some of these unknowns.

The new polarimetry data will also provide real-time insights into air pollution. „PACE measurements will not only answer fundamental scientific questions, but also improve people’s quality of life,” said Marcela Loría-Salazar, assistant professor at the University of Oklahoma’s School of Meteorology and a PACE early adopter. The PACE Early Adopters Program promotes the integration of PACE data into practical applications of science.

Loria-Salazar is particularly interested in how aerosols change over time and with location, with an additional emphasis on the altitude of aerosols over the central United States. There, PACE will allow scientists to identify aerosols, while also understanding what air quality is.

Measurements from PACE’s polarimeters will also help improve our understanding of Earth’s climate. By adding PACE atmospheric data to the models, scientists can replace the estimates now used with data from current measurements to fill data gaps in those models.

„I hope to collect data that will reduce model uncertainty and help us make better predictions of what we expect our climate to look like in the coming decades and centuries,” Nobelspies said.