Calibration of a radiosonde humidity sensor at low temperature and low pressure
Abstract
Relative humidity in upper air is frequently measured using radiosondes at an altitude of up to roughly 35 km. In this study, the calibration of a radiosonde humidity sensor was demonstrated using a humidity generator that can mimic the humidity, temperature, and pressure conditions in upper air. The calibration of the radiosonde humidity sensor was conducted in terms of relative humidity at a temperature range of -70 °C to 20 °C, and at a pressure range of 5 kPa to 101 kPa. Consequently, it was revealed that the radiosonde humidity sensor presents a significant temperature dependency in such a way that indicates lower humidity values than the reference values measured by the generator as temperature is lowered. The deviation from the reference humidity was measured at about 30%rh at -70 °C. However, the effect of low pressure (5 kPa) on the sensor measurement was less than 1%rh. The uncertainty budget on the calibration of the radiosonde humidity sensor, including factors due to humidity generation, correction of temperature effect, pressure effect, and sensor reproducibility, are presented. Consequently, the calibration uncertainty of the humidity sensor was 3.8%rh at the coverage factor k = 2. The calibration capability of the radiosonde humidity sensor demonstrated in this study will provide traceability to the International System of Units (SI) in the humidity measurement in upper air.
- Publication:
-
Metrologia
- Pub Date:
- October 2019
- DOI:
- 10.1088/1681-7575/ab336f
- Bibcode:
- 2019Metro..56e5008L
- Keywords:
-
- calibration;
- relative humidity;
- radiosonde;
- humidity sensor;
- uncertainty;
- low temperature;
- low pressure