Sounding Equipment

To provide data used for weather forecasts every day hundreds of radiosondes are launched worldwide. With a gas filling of a few cubic meters of hydrogen or helium they reach an altitude of more than 30 km within two hours. During the flight the data recorded is transmitted to the ground station from where the balloon is launched.

For our research equipment needed is compact enough so that the soundings can be performed by a mobile team anywhere in Switzerland where the payload weight is restricted to 2 kg by aviation regulations. Standard detectors used for water vapor are insufficient with respect to sensitivity and response time in the target region above approximately 7 km. Therefore dedicated frost point sensors are needed.

The SnowWhite sonde manufactured by meteolabor ag Wetzikon, operates according to this principle: Light reflected from a small mirror surface is dimmed by a thin ice cover. The mirror is heated or cooled by an electronic controller driving a Peltier element such that the light reflected stabilizes at an adequate intensity. In equilibrium with it environment this causes the mirror temperature to settle at the frost point level, from which the water vapor abundance is derived. A time response of better than one second - resulting in 5 m vertical resolution - is achieved. Prior to our balloon soundings we operated the SnowWhite sensor during the AquaVit water instrumentation intercomparison activity.

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