ABSTRACT
Electromagnetic waves are potentially used in geodetic measurements like distance, directions, delay, etc. Depending on wavelength and purposes, the measurements of the parameters, like amplitude, phase, and angle of arrival, are of paramount interest. However, the effect of earth’s atmosphere offers a serious limitation to the accuracy and precision of geodetic measurements. Atmospheric water vapor is a limiting source of error (Resch, 1984) in determining the baselines by the technique of very long-baseline interferometry (VLBI). The use of a global positioning system (GPS) offers even more precision geodetic measurements (Bevis et al., 1992). On the other hand, it may be even more limited by the variable wet path delay component due to the very presence of water vapor. As early as 1976, a series of efforts began on the development of microwave remote sensing systems to determine the wet path delay for geodetic applications (Janssen, 1985). These efforts were culminated in 1982 with the asset of seven water vapor radiometers dedicated to the task of providing real-time path delay measurements at Goddard Space Flight Center (Resch, 1984).
