Humidity measurements in the atmosphere are of essential importance, since water vapour, as the most important natural greenhouse gas, has a strong influence on the Earth's atmospheric radiation balance and, thus, decisively influences our climate. In addition, water is responsible for meteorological phenomena such as the formation of clouds and precipitation.
Hence, the atmospheric water content is an essential measurand in all climate models, but also when it comes to forecasting the weather; this measurand has to be determined with great accuracy if reliable predictions are to be made with regard to the weather and to the development of the climate.
However, measuring water vapour as far as into the upper atmosphere is not an easy task, which leads to air humidity measurements differing sometimes by more than 10 % when measured in different research projects, using alternative methods, even within the scope of demanding laboratory comparisons. Cloud-, precipitation- and also complex climate model computations should, however, be based on measurement data which is as accurate as possible to have sufficient significance.
In order to improve the quality of atmospheric water vapour measurements and to provide better comparability, PTB scientists have developed the traceable laser hygrometer SEALDH. SEALDH stands for "Selective Extractive Airborne Laser Diode Hygrometer" and works according to the principle of tunable diode laser absorption spectroscopy (TDLAS)....
Bombardier CRJ900 looking for clear skies, shot by Luis Argerich, Wikimedia Commons, under the Creative Commons Attribution 2.0 Generic license
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