Analysis of Temporal and Spatial Variations in Atmospheric Water Vapor Using Microwave Radiometry

Abstract: The amount of atmospheric water vapor is highly variable in both time and space. In this thesis some aspects of the variations in the atmospheric water vapor are treated. Short term variations of up to approximately a day in the radio propagation delay due to water vapor has an important role as one of the limiting factors in space geodesy and radio astronomical interferometry. Since the atmospheric water vapor is a greenhouse gas, its change over many years is of interest in climatology.

A microwave radiometer at the Onsala Space Observatory was used for data acquisition. Its data are used for characterizations of the variations in the amount of water vapor. The accuracy of the amount of water vapor determined using microwave radiometry is evaluated, as well as methods that utilize the knowledge of short-term atmospheric variability in order to improve the accuracy of the water vapor estimates.

The role of the water vapor in space geodetic techniques such as Very-Long-Baseline Interferometry (VLBI) and the Global Positioning System (GPS) is also discussed. In these techniques the radio wave propagation is used for precise positioning. It is shown that an increased statistical knowledge of the variations in the amount of water vapor can improve the estimation of the contribution of water vapor to the propagation path length. The result is better positioning, while at the same time the amount of water vapor can be derived from the geodetic data, which is of interest for the meteorological community.