Cloud-Aerosol Transport System (CATS) on the ISS

Sample data from the Cloud Physics Lidar -- a predecessor of CATS -- over the Western Atlantic is representative of airborne lidar data, showing cloud height and internal structure and boundary layer aerosol. 

Credit: NASA

Quick looks by a special CATS-eye attached to the International Space Station will help scientists catalog and track particles in Earth's atmosphere and act as a pathfinder for a new satellite planned for 2021.

Matthew McGill

"We're going to do operational Earth science that's new, looking at aerosols, pollution and clouds and real-time inputs to global climate models," said Matthew McGill, principal investigator for the Cloud-Aerosol Transport System (CATS) at NASA's Goddard Space Flight Center in Greenbelt, Md.

CATS will also help show NASA how to do low-cost, fast-turnaround payloads on station."

The approach is similar to low-cost Hitchhiker payloads—small studies that "hitched" a ride into orbit with larger investigations—that NASA flew on the space shuttle during 1984-2003.

"The International Space Station Program looked at our airborne Cloud Physics Lidar (CPL) instrument and its 15-year heritage flying near the edge of space [on the ER-2 aircraft] and asked, 'Can you put that in a box?'" McGill said.

"In other words, could we take this proven, autonomous aircraft instrument and transfer the design to be space station compatible, and CATS was born."

Weather satellites do a phenomenal job of monitoring clouds, air temperatures, moisture and other factors.

But measuring aerosols, whose role in weather and climate is a significant mystery, requires probing the air by using light in a manner similar to radar. This will be the job of the CATS investigation.

Aerosol means particles or droplets dissolved in air. The term is a century old, but humans have always been around them in the form of clouds, fog, smoke rising from a fire, exhaust from a car, spray from a sneeze, and even some emissions from plants.

Aerosols come in all shapes, sizes, populations, masses and other factors, making them a challenge for scientists trying to understand their impact on weather and climate.

"[Computer] models need to know if there is a layer of stuff in the atmosphere, its altitude—because that matters a lot—how thick that layer is, and what it is made of," McGill explained.

"The fundamental data from CATS will tell us if something is there, and then take ratios of different readings to tell us if it's ice, water or aerosols, and if it is an aerosol, is it dust, smoke or pollution."

This is a photo showing how payloads attach to the Exposed Facility of the Japanese Experiment Module on the International Space Station. 

The laser will always fire directly down from the space station into the atmosphere. 

Credit: NASA

Knowing what is where is important to understanding how energy is transported in the atmosphere. Particulates can absorb different quantities of sunlight or heat from surrounding air, and carry that energy to be released elsewhere.

Researchers also need to know how aerosol populations change during the day. Most Earth observing satellites are in polar orbits that cross the equator at the same local time.

That ensures an apples-to-apples comparison of data taken by multiple instruments across the years. But this also keeps them from observing the faster ebb and flow of some events in the atmosphere during the day or night. The space station's orbit will provide that coverage.