Montana State University (MSU) electrical engineering graduate students David Hoffman and Amin Nehrir have each received a $30,000 fellowship through NASA's Graduate Student Researchers Program, giving them the opportunity to work with some of NASA's top scientists in laser technology as interns at Langley Research Center in Hampton, Va., next year. At the university in Bozeman, Hoffman and Nehrir's work with lidar (light detection and ranging) involves sending a pulse of laser light into the sky and letting it bounce off the particles suspended in the air. By measuring the amount of light that bounces back, how that light is scattered and the time it takes to return, scientists can learn about the composition of the lower atmosphere. Hoffman built a two-color lidar to finish his master's thesis; now he is building an optical filter that will allow lidar systems to differentiate between those airborne particles and atmospheric molecules -- identifying and quantifying dust, pollen, pollution, etc. Nehrir is building a differential absorption lidar system that will detect the amount and distribution of water vapor in the atmosphere. Both students' work could one day help scientists study the climate and could help move MSU from the instrument-building phase into atmospheric research, said Kevin Repasky, an assistant professor in electrical and computer engineering who advises both students. "They're starting to build instruments that are up there with other instruments being built around the world," he said. NASA is particularly interested in the small, 2 x 4 x 4-ft lidar assemblies MSU is building. By comparison, some lidars are large enough to fill an entire 40-ft cargo container, Repasky said. Those instruments could be used to help understand how clouds form around different types of airborne particles, which affects the entire water cycle, from the types of clouds that form to the amount of precipitation expected from them.