NASA plans a series high-altitude drone flights into a largely unexplored layer of our atmosphere.
The goal: Find out how changing atmospheric chemistry is affecting Earth's climate.
"Ultimately, we want to improve our mathematical models to predict climate change," said Eric Jensen, the principal investigator of the Airbone Tropical TRopopause EXperiment (ATTREX).
The tropopause is the boundary between the stratosphere, and the troposphere, where most weather takes place.
The probe's instruments, carried almost 20,000 metres up by an unmanned Golden Hawk drone, will measure atmospheric moisture and chemistry, radiation levels, meteorological conditions, and trace gas levels.
The first of six flights began January 16 and run until March 15.