Accuracy of the Water Vapour Content Measurements in the Atmosphere Using Optical Methods

This paper describes the accuracy and the errors of water vapour content measurements in the atmosphere using optical methods, especially starphotometer. After the general explanations of the used expressions for the star-magnitude observations of the water vapour absorption in section 3 the absorption model for the water vapour band will be discussed. Sections 4 and 5 give an overview on the technique to determine the model parameters both from spectroscopic laboratory and radiosonde observation data. Finally, the sections 6 and 7 are dealing with the details of the errors; that means errors of observable magnitude, of instrumental extraterrestrial magnitude, of atmospheric extinction determination and of water vapour content determination by radiosonde humidity measurements. The main conclusion is: Because of the high precision of the results the optical methods for water vapour observation are suited to validate and calibrate alternative methods (GPS, LIDAR, MICROWAVE) which are making constant progress world-wide in these days.