Vaisala Oyj is a major provider of environmental measurement systems, such as weather instruments, dropsondes, hygrometers, barometers, and other devices. Prof. Vilho Väisälä made some of the first radiosondes in the 1930s and founded a company called Mittari Oy to sell them conmmercially. They were extremely popular, and continue to be so. The company started using its current name in 1955.
Vaisala is headquartered in Vantaa, Finland.
Like nearly every word in the Finnish language, "Vaisala" is pronounced with primary stress on the first syllable--VAI-sa-la.