Atmospheric water plays a key role in climate. Water vapour is the most important greenhouse gas and its condensed forms exert a profound influence on both incoming solar and outgoing infrared radiation. Unfortunately, accurate, height-resolved global-scale measurements of atmospheric humidity are difficult to obtain. The change in concentration of five orders of magnitude form the ground to the stratosphere means there is no standard instrument that will measure everywhere. This has led to different measuring techniques, all with strengths and weaknesses. This book assesses all presently available techniques that are used in monitoring networks. Special weight is given to presenting the different technical concepts, the accuracy of different sensor types, addresses calibration issues and retrieval aspects.

Offering all aspects of humidity measurement and instrumentation, this work includes rudiments and theory, common applications, advantages and limitations of frequently-used sensors and techniques, and guidelines for installation, maintenance and calibration. The disk is intended for easy conversions of humidity parameters and units.

Abstract: "This report describes a new type of automatic frostpoint hygrometer for measurement of the atmospheric distribution of water vapor. The mass of the frost deposit on a cooled surface is detected directly by energy attenuation of alpha radiation. An automatic control maintains a constant amount of this frost by controlling the direction of current flow through a thermoelectric cooler. The instrumentation of this hygrometer is described in some detail, and balloon-flight tests of prototype units are presented."

General problems involved in sensing atmospheric water vapor in the tropopause and stratosphere are discussed. The specific problem of performing these measurements with a dew-point instrument on a large balloon and the results of a program which included the development of the alpha radiation hygrometer are presented. These results are considered in the light of laboratory investigations and theoretical considerations to determine the validity of the obtained profiles. (Author).

This report describes a new type of automatic frostpoint hygrometer for measurement of the atmospheric distribution of water vapor. The mass of the frost deposit on a cooled surface is detected directly by energy attenuation of alpha radiation. An automatic control maintains a constant amount of this frost by controlling the direction of current flow through a thermoelectric cooler. The instrumentation of this hygrometer is described in some detail, and balloon-flight tests of prototype units are presented. (Author).