Temperature Error of the Vaisala RS90 Radiosonde

Abstract

The new F-Thermocap sensor used on the Vaisala RS90 radiosonde is a miniaturized capacitive sensor designed to decrease the solar radiation error and the time lag error that exists with the Thermocap sensor used on the RS80 radiosonde. The heating and response characteristics of the F-Thermocap sensor were evaluated by developing a heat balance model, RS90COR, that calculates the temperature of the sensor relative to the air temperature in various flight environments. The temperature of the F-Thermocap sensor was found to be essentially identical to that of the atmosphere in all nighttime environments. In daytime conditions solar heating of the sensor increases its temperature to slightly above that of the ambient air. The daytime error increases with altitude but remains less than 0.5°C to an altitude of 35 km. The time lag error of the miniaturized sensor is insignificant. The RS90COR modeling results were validated by using model-predicted errors to correct RS90 and RS80 temperature profiles from sondes flown on the same balloon. The corrected profiles agreed, except for a temperature bias of 0.1°?0.3°C that results from a calibration or electronics error in one or both of the sondes. A new source of temperature error in daytime flights of RS80, RS90, and VIZ radiosondes has been discovered that relates to the orientation of the sensor with respect to the impinging solar radiation. This orientation error is smallest in the RS90 sensor.