"Snow White" is a chilled-mirror hygrometer for radiosonde application, and is a product of a Swiss company meteolabor AG. See also their Snow White page. Snow White may be used as the reference hygrometer for radiosonde humidity sensors, and as the hygrometer for upper tropospheric and lower stratospheric measurements.

The chilled-mirror method is directly based on the thermodynamics, and thus is regarded as the standard method for measuring water vapor concentrations. A small mirror (3 mm x 3 mm for the Snow White) exposed to the ambient air is cooled continuously so that it's temperature equals to the dew or frost point temperature. A lamp and phototransistor are used to monitor the thickness of the dew or frost layer on the mirror.

The advantage of the Snow White hygrometer is as follows: The meteolabor AG has nearly 20-year experience of developing chilled-mirror sensors for aircraft, laboratory, and surface measurements. The development of a sensor for radiosonde application began in 1996.

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