Spacecraft Collects Lunar Observations After The Sun Has Set

The first set of lunar data collected from the Stratospheric Aerosol and Gas Experiment III (SAGE III), a NASA instrument that launched to the International Space Station in February 2017, is now available for public use.

The data is available through the Atmospheric Science Data Center and includes measurements of ozone and nitrogen trioxide. The initial release of SAGE III data in October 2017 focused only on solar data. From its perch on the space station, the SAGE III instrument is used to study profiles of aerosols and gases — ozone, for example, which is a gas found in the upper atmosphere that acts as Earth's sunscreen.

Since the SAGE III instrument collects lunar observations after the sun has set, it is able to record a picture of the atmosphere in the absence of sunlight. Nitrogen trioxide (NO3) virtually disappears from the atmosphere when the sun rises. SAGE III can measure its concentration at night using a technique called lunar occultation, which involves scanning the light from the Moon as it passes through Earth's atmosphere at the edge, or limb, of the planet.

"Essentially, the lunar occultation observations allow the instrument to measure the atmosphere at night in contrast to the solar occultations that occur in daylight," said SAGE III Project Scientist David Flittner. "The SAGE III lunar observations extend our measurements to locations and times not covered by the solar observations, augmenting the coverage."

This nighttime atmospheric gas, NO3, is produced by the combination of nitrogen dioxide (NO2) and ozone (O3). In the middle and upper stratosphere, the nighttime loss of NO3 is minimal and the gas acts as a simple indicator of elapsed time since the most recent sunset. The amount of NO3 observed varies strongly with temperature, meaning warmer temperatures typically result in more NO3.

While not included initially, later data releases will include solar occultation measurements of water vapor and lunar occultation measurements of nitrogen dioxide. Future data releases will follow a monthly release schedule.

(Source: NASA news release. Image from file)

FMI: www.nasa.gov