Submillimetre thermistors for balloon‐borne applications up to lower stratosphere: preliminary characterization with 0.02 K uncertainty

The French metrological laboratory LNE-CNAM, in the framework of a study commissioned by the Laboratory of Dynamic Meteorology LMD, has carried out a preliminary metrological characterization of a device based on submillimetre thermistors, to be used for atmospheric temperature and humidity measurements from the ground up to the lower stratosphere. The device is a measuring system intended to perform temperature measurements between 173 K (around -100 °C) and 233 K (around −40 °C). It is composed of a self-manufactured electronic device, in which submillimetre thermistors measure both air temperature and the temperature of a hygrometer sensor, in order to determine accurately water vapour concentration. Since the needed final measurement uncertainty is below 0.05 K, a comprehensive metrological characterization must be performed. One instrument prototype was supplied to the LNE-CNAM, to be characterized between 173 K and 273 K (around 0 °C). Measurements were carried out in the quasi-adiabatic calorimeter used by the LNE-CNAM to realize the national temperature standard below 84 K. The calorimeter was adapted to work at temperatures up to 273 K. At any setpoint between 173 K and 273 K, the stability of the temperature was within 5 mK for several hours. The thermistors were calibrated by comparison to a calibrated reference thermometer. Preliminary results showed that calibrations with an uncertainty of around 0.02 K are possible. Tests are going to be performed in situ by the LMD, and further characterizations will be carried out to assess the obtained uncertainties and check long-term reproducibility.