Weather balloons gather weather information in the stratosphere layer of the atmosphere.
http://www.learner.org/courses/essential/physicalsci/session7/
Links providing information on weather balloons.
http://www.youtube.com/watch?v=co7ikDXklkg&playnext=1&list=PL75D666F81C89C461&index=34
http://www.fema.gov/medialibrary/media_records/2321