A study of the theory and operation of a resonance fluorescence water vapour sensor for upper tropospheric humidity measurements

Abstract

AbstractIn‐situ methods for measuring upper tropospheric humidity are important for two reasons: (i) they can be used as accurate spot measurements with which to calibrate more extensive data from satellites and other sensors; (ii) they can provide high accuracy measurements from aircraft or balloon with which individual processes of transport, phase change or chemistry can be studied.In either case the accuracy of the in‐situ measurement is of paramount importance. This study compares the performance and accuracy of a resonance fluorescence type of sensor (the Fluorescence Water Vapour Sensor) with a standard frost‐point hygrometer.An intercomparison of these two hygrometers has confirmed a long‐standing difference between these two types of sensors (the FWVS overestimates the water vapour volume mixing ratio by 10–20%, depending on pressure). Testing the FWVS experimentally in the laboratory, along with a modelling study of the sensor has revealed that a significant source of error is due to contamination of the FWVS source emission, and the subsequent underestimation of the oxygen absorption cross‐section. Copyright © 2002 Royal Meteorological Society.