Found at a height of between 40 and 100 miles (64-161 km) above the Earth's surface, the mesosphere is the layer of our atmosphere that separates us from the cold, dark vacuum of space. Yet, according to NASA, it is little understood. The space agency plans to fix that with the world's first space-based LiDAR system designed to make sodium particles glow.
LiDAR is a system in which lasers are pulsed at a target and the light that gets reflected back can provide distance measurements. Amongst other applications, LiDAR has been used to measure forests from space, make for safer airplane takeoffs and landings, and it's increasingly finding a home in self-driving cars.
Because gases absorb light, the system can also be used to measure such things as carbon dioxide in the air by tuning the frequency of the laser to the absorption spectrum, something NASA has been developing with its Sounders program.
While sodium-sensing LiDAR has been used before on the ground on Earth, it's never been deployed in space, according to NASA. Doing so will provide valuable information about the mesosphere, including how weather closer to Earth's surface might effect it.
The plan is to have equipment circle the Earth and pulse yellow laser beams down upon the planet that would cause sodium particles in the mesosphere to glow. By tracking the particles, researchers could then figure out how much sodium was present, as well as determining its temperature and speed of movement. This would, in effect, help the researchers visualize what's happening in the mesosphere in much the same way dropping dye in a swirling bowl of water would make currents visible.
The team opted to tune their laser to specifically detect sodium, as it is easier to spot than other metals in the atmosphere such as iron and calcium. The device, which is currently under development, would send the laser pulses one to three km (about .6 to 1.9 mi) into the mesosphere over swaths that measure four to eight km wide (about 2.5 to 5 mi).
The next step is to show off a working version of the laser here on Earth, which would move it to a level-six technology-readiness level, a designation that means it is flight worthy.
"We've made significant progress on the laser," said laser expert Mike Krainak of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "If we win, we could be the first space-based sodium laser spectrometer for remote sensing."
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