Professor Vilho Väisälä, who was Vaisala's founder and long-time managing director, undertook the planning and construction of a Finnish radiosonde in early 1931.

Professor Väisälä's fundamental idea was to use the variable capacitance principle for radiosonde sensors. The instument measures pressure, temperature and humidity in the upper atmosphere. The theory and principle of operation of the device had already taken shape by the end of the same year. The historic first flight of the Väisälä radiosonde took place on 30 December 1931. The sonde weighed 420g, its transmission signal was audible up to a height of 7 km. The radiosonde measured temperature only. This first Finnish radiosonde was later found and retrieved.

Development continues - first production model in 1935

After the first successful sounding, professor Väisälä continued with tests and radiosonde development. The new radiosonde was presented internationally to the meteorological community at the meeting of the Aerological Committee of the International Meteorological Organization held in the autumn of 1935. In the following year, the instrument was already considered to be suitable for routine meteorological use.

Being simple, reliable and moderately priced, the Väisälä radiosonde's structural features were considered excellent from the standpoint of usage and production. At that time only a very few types of radiosonde existed, all of which were heavier and considerably less advantageous than the Finnish instrument in terms of manufacturing and operating costs. The Vaisala radiosonde naturally aroused great attention. Before long, the Finnish radiosonde was adopted in all Scandinavian countries. Manufacturing was transferred to the premises of a factory established by Prof. Väisälä. Since 1936, Vaisala has been meeting the special needs of meteorological professionals.