Effects of the troposphere on the propagation time of microwave signals

Factors affecting the transit time of radio signals, which can be accurately measured, are reviewed. Variability in the density and composition of the atmosphere introduce variability into transit times, and this variability makes geodesy and radio astronomy using this parameter more difficult to carry out. Phenomena creating the difficulty include rotation of the earth, seasonal changes, weather cycles, weather systems, atmospheric turbulence, and the earth's gravitational field. These phenomena act on varying time scales, from several tenths of a second to 10 years. A knowledge of such effects will enable better earthquake prediction and theory.