Standards Development

Scope

The document specifies testing procedures for determining calibration error for radiosonde humidity sensors sampled from a mass production batches based on varying the levels of relative humidity at atmospheric upper-air temperatures using a laboratory setup. Application of this document provides the following:

a) the technical requirements for a laboratory setup to evaluate the calibration errors of radiosonde humidity measurement;

b) a test procedure for evaluating calibration error of radiosonde humidity sensors for a temperature range of −70 °C to 35 °C and for a relative humidity of 1 %rh to 100 %rh. Note, this document, is based upon relative humidity defined by the percentage of water vapor pressure divided by saturation water vapor pressure over liquid water, not over ice, even at temperatures below 0 °C; hence, the maximum relative humidity is less than 100 %rh below 0 °C;

c) a method for evaluating the uncertainty for the measured radiosonde humidity calibration errors.

In this document, the requirements for a humidity generator, a test cell, a precision hygrometer, and a thermometer as essential laboratory setups are proposed in a). In b), the test procedure including the test preparation, the installation of radiosondes in the test cell, the operation of laboratory setups, and the comparison between the reference relative humidity and the radiosonde relative humidity are presented. In c), the method for evaluating uncertainties related to the reference relative humidity and the radiosonde humidity sensor is discussed.

NOTE 1 The water vapor pressure required for the reference relative humidity can be determined from frost or dew point temperature by either humidity generators or calibrated hygrometers as exemplified in Annex A. Frost/dew-point is the temperature at which air becomes saturated with water vapor and condensation occurs.

NOTE 2 Due to potential limitations in the number of test setups or laboratories available for conducting this test, peer-reviewed reports or papers published online or offline resulting from research activities conducted by academia or meteorological institutes can be utilized as a test report when following this test procedure.