NASA readies first spaceborne sodium lidar instrument to study mesosphere

Scientist Diego Janches and laser experts Mike Krainak and Tony Yu, all of whom work at NASA's Goddard Space Flight Center in Greenbelt, Maryland, are leading a research-and-development effort to further advance sodium light detection and ranging (lidar), which the group plans to deploy on the International Space Station if it succeeds in proving its flightworthiness. This will be the world's first space-based or spaceborne sodium lidar to study Earth's poorly understood mesosphere.

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NASA's Center Innovation Fund and the Heliophysics Technology and Instrument Development for Science programs are now funding the instrument's maturation. However, the concept traces its heritage in part to NASA’s past investments in promising lidar instruments, called Sounders, originally created to measure carbon dioxide and methane in Earth's atmosphere.

From its berth on the orbiting outpost, the instrument would illuminate the complex relationship between the chemistry and dynamics of the mesosphere that lies 40-100 miles above Earth's surface--the region where Earth's atmosphere meets the vacuum of space.

"What we're doing is leveraging what we learned with the CO2 and Methane Sounders," Krainak said. Both instruments have demonstrated in multiple aircraft campaigns that they accurately measure greenhouse gases using lidar.

Sodium (Na)--the sixth most abundant element in Earth's crust--is a useful tracer for characterizing the mesosphere. Though this atmospheric layer contains other granules of metals, including iron, magnesium, calcium, and potassium (all produced by the evaporation of extraterrestrial dust when it encounters Earth’s atmosphere), sodium is easiest to detect. Literally, a layer of sodium exists in the mesosphere.

Because of its relative abundance, sodium provides higher-resolution data that can reveal more information about the small-scale dynamics occurring in the upper atmosphere. From this, scientists can learn more about how weather in the lower atmosphere influences the border between the atmosphere and space.

The group has begun developing its instrument, which is electronically tuned to the 589 nm range (yellow light). While in orbit, the lidar would rapidly pulse the light at the mesospheric layer, down 1 to 3 km over a swath measuring 4 to 8 km in width.

The light's interaction with sodium particles would cause them to glow or resonate. By detecting the glow-back, the lidar's onboard spectrometer would analyze the light to determine how much sodium resided in the mesosphere, its temperature, and the speed at which the particles were moving.

Scientists have used sodium lidars in ground-based measurements for at least four decades, but they never have gathered measurements from space. As a result, the data is limited in time and space and does not offer a global picture of the dynamics. With a specially designed spaceborne sodium lidar, however, scientists would be able to illuminate specific areas, revealing the small-scale dynamics that currently are the biggest unknown, Janches said.

"We've made significant progress on the laser," Krainak said. "If we win, we could be the first space-based sodium laser spectrometer for remote sensing."

SOURCE: NASA Goddard; https://www.nasa.gov/feature/goddard/2017/nasa-aims-to-create-first-ever-space-based-sodium-lidar-to-study-poorly-understood