CALIBRATION AND PERFORMANCE OF AUTOMATIC COMPACT INSTRUMENTATION FOR THE MEASUREMENT OF RELATIVE-HUMIDITY FROM PASSENGER AIRCRAFT

Compact airborne humidity sensing devices using capacitive sensors are employed on board in-service aircraft to measure water vapor concentr ations in the troposphere up to 13 km altitude. The sensors are indivi dually calibrated before onboard installation, After every 500 flight hours, each sensor is calibrated in an environmental simulation chambe r under typical middle/upper tropospheric flight conditions. A Lyman-A lpha fluorescence hygrometer is used as reference instrument. Prefligh t and postflight calibration of each flown sensor agreed very well and showed good response. Typical overall uncertainties for the 1995 Meas urement of Ozone by AIRBUS In-Service Aircraft (MOZAIC) relative humid ity (RH) measurements are within +/-4% RH in the middle troposphere, i ncreasing to +/-7% RH between 9 and 13 km, In-flight comparison of the MOZAIC humidity device with other water vapor measuring techniques sh owed agreement within +/-(5-10)% RH and a time response of better than 10 s in the lower/middle troposphere, increasing to values of 1-3 min at 10-12 km altitude.