Field campaign LINEX 96/1 - Possibilities of water vapor observation in the free atmosphere

LINEX 96/1 was a field experiment to assess information content, accuracy, and availability for different remote sensing techniques measuring water va por. An important goal of LINEX 96/1 was the test of a new Differential Abs orption Lidar (DIAL) developed by the MPI fur Meteorologie Hamburg. Compari sons of DIAL with rawinsonde and tethersonde measurements showed an excelle nt accuracy of the DIAL method in the determination of water vapor with hig h vertical and temporal resolution. The operation of the microwave radiomet er WVR-1100 showed a high availability of water vapor and liquid water colu mn content measurements except during rain. Microwave radiometers are relia ble systems to measure the precipitable water vapor and liquid water conten t under unattended operational conditions with high accuracy and temporal r esolution. Measurements of the water vapor column content by groundbased GPS receivers proved highly reliable. Comparisons with corresponding values of the micro wave radiometer showed a bias less than 0.6 mm and a standard deviation les s than 0.9 mm. The main problem of an operational use of this new informati on is that the evaluated data are not available in real-time because, at pr esent, the data have to be postprocessed in a ground control center. During LINEX 96/1, possibilities for estimation of water vapor column conte nt from sun and star photometer measurements were also demonstrated. The co mparison of the precipitable water vapor content measurements oi sun and st ar photometers, microwave radiometer, and rawinsondes RS 80 showed a good a greement. Unfortunately, the use of optical methods like sun and star photo meters is restricted by cloudy conditions. The field campaign LINEX 96/1 was an important contribution to the COST Act ion 76 by investigation of the new possibilities measuring water vapor in t he free atmosphere with the objective of improvements of our knowledge abou t the 4-dimensional water vapor field.