NASA Developing Sodium Lidar To Help Examine Eartth’s Mesophere
October 30, 2013

NASA Looks To Unlock Mesosphere With Sodium

Peter Suciu for – Your Universe Online

Future trips to space will be looking closely at sodium. Not as in the salt that astronauts use to flavor their food and can be brought to space in small packets. NASA scientists are instead looking at the sodium – the sixth most abundant element in Earth’s crust – that exists in the mesosphere.

While sodium is already used as a coolant in nuclear power plants and can be used as a desiccant to remove humidity, it is also found in every cell in the human body – where it transmits nerve impulses and regulates blood pressure. Sodium can also be useful as a tracer for characterizing the region of the Earth’s atmosphere that is sensitive to the influences from both the atmospheric layers below and the sun above.

A team of scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland is looking to develop the world’s first spaceborne sodium lidar. This could be used to illustrate the complex relationship that exists between the chemistry and dynamics of the mesosphere, which is some 40-110 miles above the surface of our planet and is the region where the atmosphere meets the cold vacuum of space.

This region, which is comparably small to the rest of the atmosphere, is located directly above the stratosphere and below the thermosphere. Most meteors that enter the Earth’s atmosphere vaporize in the mesosphere and material from them lingers in this region. For this reason the mesosphere contains numerous elements, including granules of metals such as iron, magnesium, calcium and potassium. Sodium is also present and is the easiest to detect.

This creates a dust that makes up the so-called Zodiacal Dust Cloud that originates from the debris that is produced by asteroids and comets that are vaporized in the mesosphere.

“There is literally a layer of atomic sodium in the mesosphere,” said Principal Investigator Diego Janches, the leader of the lidar-development team, in a statement. “When you shoot yellow light into the region, the light bounces off the sodium particles, causing them to resonate, or glow. By detecting the glow-back, you can measure how much sodium is in the mesosphere, its temperature, and the speed at which it's moving.”

Because sodium is relatively abundant, it provides higher-resolution data that reveals more information about the small-scale dynamics that occur in the upper atmosphere. This allows the researchers to study the influence from the sun’s energy and helps differentiate its effect from that on humans.

While scientists have already used sodium lidars in ground-based measurements for nearly 40 years, there have not been efforts to gather data from a spaceborne instrument. Now the researchers are looking at how the spaceborne sodium lidar could change the global picture.

“We want to do this from space,” Janches added. “We want to map the entire mesosphere by the fluorescence of sodium.”

The team is now looking to Goddard R&D funding to advance this lidar technology with the aim of demonstrating it on the International Space Station, where instruments could also be used to study other planetary atmospheres.

This could also build on past research done by NASA’S Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) spacecraft. NASA has extended the mission several times since its 2001 launch, and this has provided scientists with the first long-term look at the mesosphere. The next logical step for the team is the spaceborne sodium lidar, which could illuminate a specific spot and gather data on that particular area only.

“Because of TIMED’s high inclination, it takes 60 days for the satellite to cover all longitudes at all local times. As a result, data from the satellite's SABER instrument (Sounding of the Atmosphere using Broadband Emission Radiometry) assume that the dynamics are constant during that time,” Janches said. “In addition, SABER is a scanning-type instrument. In other words, it looks at the horizon, gathering signals from all parts of the atmosphere.”

The technology would also benefit NASA in other ways.

“We have a lot of leverage from other missions we've done,” said Mike Krainak, a team member on the project and recognized expert in laser technologies.

Krainak added that NASA has already developed laser-related technologies for the Geoscience Laser Altimeter System on the NASA ICESat (Ice, Cloud, and land Elevation Satellite) mission and the Atmospheric Laboratory for Applications and Science, a space shuttle payload. That laser is a modified version of the lasers flown on NASA missions to Mercury and Mars.

“All of the laser components are the same,” Janches noted. “This work has put us 20 years ahead and saved us $30 million in development costs. We have a general idea of what's going on. We just want to get a bigger picture.”