The Contribution of Ground-based Water Vapor Differential Absorption Lidar to Climate Research

.The role of water vapor in the global energy and water cycle is one of the most challenging issues in climate research. However, current observation techniques such as passive remote sensing systems and radiosonde networks suffer from substantial biases in their water vapor profiles. Therefore other reference measurement standards are needed to nail down the uncertainties of passive remote and in-situ sensors.

Water vapor differential absorption lidar (DIAL) is an active remote sensing technique which permits the measurement of water vapor profiles in the troposphere. As no calibration is required, the water vapor profiles have an error of typically <5%. With current DIAL systems, the time and the range resolutions are approximately 1-30min and 60-600m up to the middle troposphere respectively. Consequently, water vapor DIAL significantly exceeds the accuracy and resolution of other sensors so that our knowledge concerning the variability of the water vapor field is extended.

By means of intercomparisons with other sensors, the high accuracy of the water vapor DIAL measurements has been confirmed which meanwhile led to its acknowledgment as reference standard within the scope of the Global Water Vapour Project (GVaP), a subproject of the Global Water and Energy Cycle Experiment of the World Meteorological Organization.

This presentation demonstrates the accuracy and resolution of water vapor DIAL. It gives an overview on the ongoing efforts within GVaP to develop ground-based water vapor reference stations which will be equipped with advanced DIAL systems. Finally, the future potential of the DIAL technique is highlighted which for instance includes the investigation of 3-dimensional distributions of water vapor using rapid scanning systems