Atmospheric Temperature and Humidity Measurements of Vaisala Radiosonde RS41

For meteorological and climatological observation needs, temperature and humidity are the key parameters received from an atmospheric sounding. Requirements for sounding data quality are high, and especially climate research has called for measurement performance that has not been fully met by operational radiosondes. Vaisala Radiosonde RS41 temperature and humidity measurements involve several new features, which upgrade sounding data quality, and thus, narrow the recognized performance gaps.

In RS41, both temperature and humidity sensors are designed and manufactured in-house, enabling optimization of sensor chip, sensor boom, and measurement electronics designs. This has resulted in features such as temperature measurement relying on highly linear and stable platinum resistor technology, and humidity measurement with negligible sensitivity to variations in prevailing solar radiation exposure. In addition to optimized sensing technologies, comprehensive sensor characterization (sensor models), and appropriate sensor calibration are also essential factors in producing trustworthy data. Reference instruments used for sensor modeling, as well as for individual calibration of RS41 units, are all traceable to international standards (SI units). Ground preparation of RS41 supports the goal of improved data quality, of which the new, desiccant-free zero humidity check is an illustrative example. In a sounding, the RS41 measurements are subjected to well-reasoned corrections: Time-lag and solar radiation corrections are applied for temperature, and time-lag correction is applied for humidity measurement. To verify the corrections, RS41 sounding results have been compared to reference instruments, such as a multi-sensor instrument for temperature, and a cryogenic frost-point hygrometer (CFH) for humidity.

The results of hundreds of test soundings and the comprehensive uncertainty analysis conducted for RS41 demonstrate that the new temperature and humidity measurements result in upgraded repeatability and measurement accuracy, benefiting all user groups of upper air data.